“Flying in Deep Space: The Galileo Mission to Jupiter, Part Two”

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4 Atlas vs. a Ford Galaxie:Ground Handling Incidents in the Cold War EraBy Joel W. Powell

11 Flying in Deep Space:The Galileo Mission to Jupiter (Part II)By David Clow

26 An Interview with Charles “Chuck” FriedlanderFormer Chief of the Astronaut Support Office, Cape KennedyBy Donald Pealer

39 Rethinking the Overview Effect By Jordan Bimm

48 Navigation, Guidance, and Control of a Saturn Rocket and Its PredecessorsBy Ed Durbin

ContentsVolume 21 • Number 1 2014

www.spacehistory101.com

BBooookk RReevviieewwss

62 AAnn AAccrree ooff GGllaassss:: AA HHiissttoorryy aanndd FFoorreeccaasstt ooff tthhee TTeelleessccooppeeBook by J. B. Zirker

Review by Gregory A. Good

63 EEyyeess iinn tthhee SSkkyy:: EEiisseennhhoowweerr,, tthhee CCIIAA,, aanndd CCoolldd WWaarr AAeerriiaall EEssppiioonnaaggeeBook by Dino Brugioni

Review by James David

64 PPsseeuuddoosscciieennccee WWaarrss:: IImmmmaannuueell VVeelliikkoovvsskkyy aanndd tthhee BBiirrtthh ooff tthhee MMooddeerrnn FFrriinnggeeBook by Michael D. Gordin

Review by Roger D. Launius

Cover ImageArtist’s view of Galileo flying past Jupiter’s volcanic moon Io. Theimage incorrectly shows the spacecraft’s high gain antenna in itsfully deployed position. Credit: NASA

While searching for high-resolution images to accompanythe article on “Primate Lives”, volume 20 #4, we came acrossthis undated, uncredited image.

Gordon Cooper

Normal Apollo crew rota-

tions from back-up crew to

prime flight crew was as fol-

lows—the back-up crew would

be named the prime crew of the

third mission down the line in

the Apollo flight program.

Based on this rotation, I should

have been selected as com-

mander of Apollo 13. However,

office “politics” in the Astronaut

Corps, the return to flight status

of Alan Shepard after the cor-

rection of an inner ear disorder,

and the view points of certain

NASA managers allowed for

the selection of Shepard ahead

of me for command of Apollo13. Shepard fell behind in train-

ing and was allowed to switch

to commander of Apollo 14,

moving Jim Lovell and his crew

up to Apollo 13. Of course, if I

had received command of

Apollo 13, it would have been

my “lost moon.” I would not

have been able to walk on the

moon because of the flaw in the

oxygen tank which caused the

explosion…If I had been select-

ed for command on Apollo 13,

there would not have been a

falling behind in training

because of my extensive work

experience during back-up on

Apollo 10. Shepard was very

fortunate to be pulled from

command of “13” and placed on

“14.” As it turned out, he was

the only one of us Mercury guys

to actually fly to and land on the

moon.

RR Auction, Lot 540,

21 November 2013

FROM THE ARCHIVES

FROM THE ARCHIVES

Q U E S T 21:1 201411


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Part I appears in the Volume 20 #4 issue

By David Clow

I had now decided beyond all

question that there existed in the heav-

ens three stars wandering about

Jupiter as do Venus and Mercury

about the sun, and this became plainer

than daylight from observations on

similar occasions which followed.

Nor were there just three such stars;

four wanderers complete their revolu-

tion about Jupiter.—Galileo Galilei1

This story of the Galileo mission to

Jupiter, begun in the previous issue of

Quest, should continue in the style of a

cliffhanger. James Van Allen himself had

referred to Galileo’s prelaunch history as

“The Perils of Pauline,”2 as years of polit-

ical delays, repeated revisions to the mis-

sion plan, fatal disasters, even an earth-

quake all seemed part of a sinister celestial

alignment to keep JPL’s Jupiter spacecraft

shackled in the surly bonds of Earth. It was

no easier for Galileo in space: it endured

blistering heat near Venus and two time-

consuming passes back to Earth; and as it

was finally on its way, years overdue, to

the destination it was built for, the antenna

that should have been the voice of the

machine could not open. Galileo was final-

ly about to fulfill its purpose, and all it

could do was whisper. Then—cue the

organ music—out of nowhere, a fiery

intruder coming faster than a speeding bul-

let! Could our plucky robot ranger catch a

comet and live to tell the tale?

Engineers rely on measurement to

achieve the immeasurable. No example is

more obvious than space exploration,

which applies the quantification of materi-

als, force, time, and speed to the pursuit of

something that is ultimately qualitative.

The most resonant arguments behind engi-

neering machines for space exploration

transcend engineering. They verge on

poetry—Bruce Murray said years before

Galileo, “I think space exploration is as

important as music, as art, as literature.” 3

James C. Fletcher was actually running

NASA when he defended the cost of the

Hubble Space Telescope in terms not typi-

cally used by federal employees petition-

ing Congress: “We're talking about the sal-

vation of the world.”4

There is no firm scale for enrichment

or wonder, but there has to be a point in the

“horse trading” between scientists and

engineers, and even in the deliberations

they make in their own minds, when they

weigh whether to push on past explicit

mission objectives into the territory of the

spirit. Measurably, logically, comet

Shoemaker-Levy 9 (S-L 9) was a distrac-

tion and even a threat to the Jupiter mis-

sion for which Galileo was built. It was

questionable in 1993 whether the machine

could achieve that original purpose, and

now here “the most spectacular astronom-

ical event ever to be witnessed in the heav-

ens during recorded history”5—all that

being a colossal maybe—elbowed its way

in and demanded that the spacecraft and its

team reach even further.

Engineering Judgment“Engineering judgment” is the collo-

quial term for handling this dilemma:

weighing the known and the unknown, the

calculated and the incalculable; a cost-ben-

efit analysis that sets off with rational

assessment and leads to places that old

maps marked Isola de dragoni. Some of it

is indeed “plainer than daylight,” but with

that clarity comes an irrational challenge,

even a requirement, to set off into the

unknown. It was the story of Galileo

Galilei’s life, discoveries, and hardship.

Bertolt Brecht articulated engineering

judgment for the Paduan astronomer in his

biographical play:

GALILEO: Jupiter’s moons will not

make milk any cheaper. But they have

never been seen before, and they are

there. From that the man in the street

draws the conclusion that there may

be many more things to see if only he

opens his eyes. You owe him that

confirmation.6

Maybe it is because scientists and

engineers identify with Galileo and his

struggle that they always call him by his

first name.

David Levy, one of comet

Shoemaker-Levy 9’s discoverers, summed

up Galileo’s story, the challenge facing the

spacecraft named after him, and the place

where the Galileo team at the Jet

Propulsion Laboratory found themselves

when a once-in-a-lifetime test happened in

their lifetimes: “Whether discovery

involves a concept, or an object, it usually

very much involves the discoverer’s gut.”7

With a year until the impact of

Shoemaker-Levy 9 into Jupiter, the

Galileo team was asking if it would be

involved, and if so, how. Project Scientist

Torrence Johnson’s memo of 9 July 1993

laid out the questions:

We have all been discussing the

possibilities presented by next year’s

encounter between comet

Shoemaker/Levy [sic] and Jupiter. For

Galileo, there are two issues—first,

understanding as well as possible

what happens to the Jupiter system as

a result of the event, second, identify-

ing what measurements (if any)

Galileo itself could make next July.

The first issue, I believe, will take care

of itself, as many of us are already

involved in planning ground-based

and Earth orbital campaigns to charac-

terize the event.

The second issue is more complex

and the purpose of this note is to solic-

it your thoughts and advice on this. As

you know, we have very limited

resources to apply to anything beyond

Q U E S T 21:1 201412


returning Ida data and preparing for

Jupiter. On the other hand, an event

such as the possibility of observing a

major commentary impact is a once-

in-a-generation type of opportunity

(at least!), and we should quickly

explore whether we have something

unique to contribute.

Any proposed Galileo activity

would have to meet a strict standard

of being unique or much, much better

than anything that can be done from

the home planet, keeping in mind

that by next July I anticipate that

most of the available telescope aper-

ture on or above Earth will be trained

on Jupiter. The two most obvious

things we might contribute are

unique types of measurements (e.g.,

spectral range) and unique

geometry.8

With its high-gain antenna jammed

and its data being squeezed back through

a tiny dish, with its components aging,

whether Galileo in its compromised state

could complete its primary mission was

in doubt, and priorities long-cherished

during the spacecraft’s Sisyphean journey

were now at risk. Senior Software

Engineer N. Talbot “Tal” Brady noted,

“The importance of returning the probe

data (50% of mission success) should be

stated here, if for nothing else than to con-

trast against the value of the comet data

which was unknown. Essentially, we

were risking a NASA rating of mission

failure against the comet data.”9 The S-

Band mission with the low-gain antenna

meant sacrifices of data, perhaps even of

entire objectives. “Planning for these sac-

rifices was difficult and time consuming;

time was already at a premium,” Brady

remembered. “NASA rated the return of

the atmospheric probe data as half the

success criteria of the mission. Dropping

a probe into Jupiter’s atmosphere didn't

happen every day either, and Galileo had

to collect and return that data.”10 There

were new software updates and sequences

to be written, tested and uploaded in

preparation for releasing the atmospheric

probe and capturing its data as it entered

Jupiter’s atmosphere, and for insertion of

the orbiter around the planet. Jupiter

loomed as though the Great Red Spot was

a predatory eye watching Galileo’s

approach. For the JPL team, taking on

more at this time had to have felt like ask-

ing too much. Before them was a chal-

lenging 18 months preparing for every-

thing their effort was originally designed

to achieve, so the obvious must have

occurred to the people working on this

mission: putting Shoemaker-Levy 9 on

Galileo’s shoulders really meant stacking

it on their own.

Target of Opportunity“When [S-L 9] was discovered [in

March 1993] it was [different from] just a

regular comet,” remembered JPL plane-

tary astronomer Dr. Paul W. Chodas. “By

then, it was clearly broken into pieces. It

was Brian Marsden [of the International

Astronomical Union] in Cambridge,

Massachusetts, who put two and two

together and said it must have been bro-

ken up by passing within the [Jovian]

Roche limit [i.e., the threshold at which a

body’s gravitation is strong enough to

overwhelm the internal gravitation of an

approaching body].” To that unusual

occurrence, the astronomers shortly

added some extraordinary news:

Marsden’s momentous InternationalAstronomical Union Circular 5800 of 18

May 1993, said, “This particular compu-

tation indicates that the comet's minimum

distance Delta_J from the center of

Jupiter was 0.0008 AU [i.e., within the

Roche limit] on 1992 July 8.8 UT and that

Delta_J will be only 0.0003 AU (Jupiter's

radius being 0.0005 AU) on 1994 July

25.4”11. That meant that that Comet S-L

9’s closest approach would be inside the

planet’s radius. On the next pass,

Shoemaker-Levy 9 was going to hit

Jupiter, creating an opportunity unprece-

dented in scientific history. “That’s how it

was announced,” Chodas smiled as he

read Marsden’s understatement.

Because the comet was not one

object but many objects, flying in forma-

tion but each on its individual path,

“There really wasn’t any distinct place

[within the S-L 9 chain] to measure, so it

was very difficult to track with preci-

sion,” Chodas said. The global astronom-

ical community scrambled to calculate

exactly where and when the impacts

would happen.

It was a process of continually

updating the data, getting better and

better orbit solutions and better and

better predictions. That involved

answering questions like, when did

[S-L 9] break up, and what would be

the time of impact (which depends on

how big Jupiter is), and at what alti-

tude it would disintegrate. It was at

least a week or two before I got

Figure 1. Dr. Paul Chodas’s drawing of the S-L 9 trajectory, 1 July 1993. Courtesy: Paul W. Chodas, PhD.

around to figuring out where the

impact on Jupiter would be. It looked

like it would be on the night side.

This all was done with a relatively

poor orbit solution. We computed the

orbit from angular measurements of

its position, right ascension and decli-

nation in the sky, and those are angles

with the precision of something like

one arc-second, but the distance is

something like five astronomical

units, and that corresponds to a fairly

large uncertainty. That meant there

was large uncertainty in the orbit, and

we’d only observed it for a brief time.

Over the next week or two the impact

probability went to 100% and the

interest worldwide was increasing

dramatically in the astronomical com-

munity, with the collision still more

than a year away.12

It was then, with global attention

rising and Galileo out there, that Johnson

laid things out for his colleagues: “an

event such as the possibility of observing

a major commentary impact is a once-in-

a-generation type of opportunity (at

least!), and we should quickly explore

whether we have something unique to

contribute.”13

So why do it? What were the possi-

ble scientific payoffs offered by S-L 9?

David Levy reaffirmed the obvious

one, a variant on that compelled Galileo

himself: “in all of history no one had ever

confirmed seeing an impact on another

planet.”14 That was enough to galvanize

both professional skywatchers and enthu-

siasts. To that add that S-L 9 was already a

rarity in its “string of pearls” state. Also,

the fragments smashed into the planet, the

dynamics of the collisions, their magni-

tudes, the depth of the penetrations, the

sizes of the possible detonations, and the

seismic effects might reveal much about

both the comet and the planet.

Spectroscopic data and impact data could

indicate just what this particular comet

was made of: ice, rock, CO2. The explo-

sions and the effects they produced could

say much about the chemistry of both this

comet and what lay beneath Jupiter’s visi-

ble atmosphere, as well as about Jupiter’s

magnetic field.

In the best case, the impacts would

happen close enough to the visible side of

Jupiter, and would be big enough, so that

the post-impact plumes might be seen.

Perhaps even some remnants of the fire-

balls drilling in and their trails could be

visible, which would reveal clues on the

fragment sizes and masses. Most might

penetrate 100-150 km into the cloud layer,

and the bigger ones might drill even deep-

er. The 30,000 Kelvin fireballs would

dwarf any man-made nuclear explosion

and bloom above the clouds by as much as

1,000 km, mushrooming and rippling out,

changing colors as the heat dissipated.15

The opposite shock could push downward

and cause a quake inside the clouds, mak-

ing their composition legible as never

before, sending waves outward through

them that might travel for hours, even

days. The comet trails might have their

own effects, such as interfering with

Jupiter’s powerful radio emissions, and

they might even make a dust ring—the

second one—around the planet. The mag-

netic field of the planet might be changed.

Even out of sight, each impact could pro-

duce a brief instant of brightening on the

inner moons, and scars in the Jovian

clouds. Jupiter whirls so rapidly that the

impact spots might turn into view just

minutes after each impact,16 perhaps with

lingering fireballs, gas plumes, and debris

heaved up and falling back down.

“Might,” “perhaps,” “could” opin-

ions were not unanimous, by any means,

on the possible effects of S-L 9’s demise,

but with the fragments hitting at 130,000

mph (60 km/s), Levy anticipated colossal

blasts.17 At impact, Jupiter would be

nearly half a billion miles from the

Earth.18 One did not wish to get any clos-

er, not in person anyway. As fate would

have it, after all the prelaunch re-plans and

delays, and after the long VEEGA [Venus

Earth Earth Gravity Assist] trajectory,

Galileo was in the right place at the right

time.

“I was hoping they’d do it,” Paul

Chodas said. “Feelings were mixed. But

the uniqueness of the opportunity out-

weighed [the concerns].” While the dis-

cussion among his colleagues at JPL pro-

ceeded on what might happen on Jupiter

and what to do about it, Chodas and the

astronomers focused on delivering ever-

closer estimates of the timing of the

impacts. If Galileo was going to partici-

pate in any observations, timing was criti-

cal. Programming sequences had to be

created and tested at JPL to position and

operate the spacecraft’s instruments pre-

cisely; the impact sites and timing were

essential to know, and soon. Galileo could

not just open its shutter and squeeze off

photos. JPL’s astronomers had to refine

and refine their data to know where and

when to aim.

“I was worried that I’d have to pre-

dict the impact times months ahead of

time, and it was not easy to do this,” said

Chodas.

It was difficult especially because

of the first eight months or so [after

the discovery] no one was recording

the positions of the individual frag-

ments, only the center of the train.

Some of that data was being recorded

later from the ground and from the

Hubble, but their data recorded rela-

tive positions. Usually when you

determine the position of a comet you

have the images of background stars

whose positions are known, and you

can determine the position of the

nucleus by using those fixed refer-

ences. Not so with this one. The

Hubble, because of its narrow field of

view, doesn’t typically give you cata-

loged stars in the field, so we had to

work with relative positions. I collab-

orated with other scientists on deter-

mining the orbit of the center of the

train, really kind of an arbitrary point,

and we used a mathematical model of

the [comet’s] fragmentation in 1992.

We assumed that the breakup of the

comet happened at a particular

time—not necessarily right at peri-

jove by the way—and then looked at

what the separation of the fragments

would be, and then tried to match the

Hubble images, of which we had a

few. That way we could get the rela-

tive times of all the impacts.19

The K-T EventThe thrill of a global catastrophe on

someone else’s globe made great press.

The fact is, it has happened on our own

planet, which gave S-L 9 a measure of

personal immediacy.

“We’re talking about a million

megatons of kinetic energy,” was how

Eugene Shoemaker described it to CNN.

Q U E S T 21:1 201413


“We're talking about the kind of event that

is associated with mass extinction of

species on Earth; really and truly a global

catastrophe. It might not take out the

human race but it would certainly be very

bad times.”20 Shoemaker knew what he

was talking about. It was he who proved

that Meteor Crater in Arizona was an

impact crater, and big as it is, it is a com-

parative divot. He estimated that really

sizable objects in the range of 10 km hit

the Earth every hundred million years,

with smaller ones of a kilometer or so

every 100,000 years, plus a steady shower

of the rocks we see as shooting stars every

night.

Comet S-L 9 was an ideal opportu-

nity to be a spectator to something remi-

niscent of the Cretaceous-Tertiary Mass

Extinction, the “K-T event,” now general-

ly accepted as proven, wherein the 180-

km diameter crater “Chicxulub” in the

Yucatan/Gulf of Mexico was created by a

species-killing impact 65 million years

ago.21 The outcomes of that included

shockwaves, global dust, and acid rains.22

Smaller impacts on Earth are indicated by

craters still being detected, such as the one

now known to underlie Decorah, Iowa,

where an asteroid “as big as a city block”

struck about 470 million years ago and

dug a crater almost four miles wide.23

The Decorah crater also lines up with the

Rock Elm crater in Wisconsin and the

Ames crater in Oklahoma—could they

have been created by a multiple impact?

“Catenae,” a linked chain of like-sized

craters apparently made by a series of fast,

violent impacts, have been detected on

other planets. Davy Catena, east of

Ptolemaeus and Alphonsus (and danger-

ously close to home) on the Earth’s Moon,

looks like a tommy-gunned wall. Similar

formations were observed on Callisto by

Voyager 1. In 1997 Galileo would detect

one on Ganymede.24 Perhaps other

“string of pearls” phenomena, such as S-L

9, created them.

The Earth’s dynamic surface may

have erased most such formations. but

Decorah, if confirmed, is the 184th one

found so far. And as the 15 February 2013

Chelyabinsk impact showed, lesser

impacts could be local catastrophes. This

one, thought to be from an object 55 feet

wide, injured an estimated 1,200 peo-

ple.25

CaveatsWeighing the pros and cons of

Galileo’s participation did not mean

weighing scientific possibilities against

engineering realities as opposing positions

in principle; the engineers played for the

same team as the scientists, after all, and

wanted the same successes. What had to

be asked was whether the engineering

realities could in fact deliver on the scien-

tific possibilities, even with the engineers’

total support for the science. Everyone

had to soberly weigh the cons, first about

the machine itself:

� With the high gain antenna off the

table, Galileo would be able to transmit

back only a fraction of the data it cap-

tured in even the best case.

� The tape recorder, intended as a

backup, was now thrust into the role of

primary data storage, and there was no

backup for it. It was absolutely needed

for the actual Jupiter mission and it had

to be ready.

� The Deep Space Network would

have inherent limits of time and line-of-

sight to receive anything that was sent,

and there were always other spacecraft

and interests who needed to use it.

� The times of impact would be uncer-

tain and Galileo’s programming

sequences for the observation would

need to have been transmitted weeks

ahead.26

At the Jet Propulsion Laboratory,

reservations about using Galileo for S-L 9

were expressed in discussions that were

characterized tactfully by insiders: “The

science team had to work long and hard to

prioritize science goals, develop new sci-

ence plans, and, in some cases, plan

updates to onboard software in the instru-

ments to increase data efficiency,” they

said. “Clear, frank, and frequent commu-

nication between the science team and the

development team was required to bal-

ance science desires with the capabilities

of the system.”27 Meaning: clearly long

hours and late nights, frank arguments

about contending research interests, and

the frequent evaluation of personal goals

and even careers weighed against what

was known and measurable about the

hardware, and about the emerging scenar-

ios, best case and worst-case, of

Shoemaker-Levy 9’s impact. One could

have heard Brecht’s Galileo in the meet-

ings responding to every doubt and ques-

tion with the trump card: Nothing like S-L9 has even been seen before, and it isthere. The point Torrence Johnson and

David Levy were suggesting was not sim-

ply that S-L 9 was a first. The point was

that because S-L 9 was a first, and possi-

bly a thing never to be seen again, it was

the duty of the scientific community to

take the target.

From that the man in the street

draws the conclusion that there may be

many more things to see if only he

opens his eyes. You owe him that con-

firmation, regardless of the risk.

Q U E S T 21:1 201414


Figure 2. Davy Catena. Credit: NASA

Q U E S T 21:1 201415


Engineering judgment, crystallized.

Claudia Alexander was a newly-

minted PhD from Michigan on her first

JPL assignment when S-L 9 invited itself

to Galileo’s party. She recalled,

I remember the meeting where we

were all told, ‘we’re not going to do

this S-L 9 thing because we’re going

to focus on getting ready for Jupiter.’

And I remember being a junior mem-

ber of the team saying, ‘Uh, you

know, I hate to disagree with the proj-

ect manager, but this is a one-time

opportunity and we don’t know what

the benefits will be; it seems that we

can take a little time to do what can be

done to gather data from this.’ I

remember my own nervousness, this

being my first time engaging the PM.

Fortunately for me, Torrence Johnson

stepped up, and he articulated the sci-

entists’ point of view. The PM con-

ceded after a day or so, provided that

we all continue doing the readiness

exercises for orbital entry. We had to

absorb the extra workload.28

Robert Gounley, then systems lead

on Galileo’s Orbiter Engineering Team,

remembered it likewise: “On the engi-

neering side I saw the same thing—we

were getting beaten about the head and

shoulders to get ready for probe release,

get ready for orbital deflection maneuver,

get ready for Jupiter orbital insertion—

and oh by the way, two or three of you can

work on this cometary stuff.” Gounley

called the S-L 9 decision “a classic case of

tension between engineers and the scien-

tists—engineers have to be the realists

and recognize the limitations of the

machines. But in this case the engineers

were just as excited as the scientists to try

figuring out how to do this, and in fact

they were looking at the hardware and

seeing more limitations than the Project

Manager even knew about.”29

Management surely understood all

the engineering arguments against using

Galileo. Tal Brady recalled, “Whether it

supported S-L 9 data capture or not, the

spacecraft computer systems had to be

reprogrammed to allow atmospheric

probe data collection and Jupiter orbit

insertion in the absence of a functional

high gain antenna. The uploading of these

new programs was scheduled to start in

January 1995, with no postponements

allowed. Some of the people and equip-

ment involved in developing these new

programs would be needed to support S-L

9 software sequences and updates. There

would be schedule impacts.”30

“There were some late nights about

[that decision],” Mission Design Manager

Robert Mitchell agreed.

Here we were being given an

opportunity that might have been

unique in history, and we might not

have been able to use it. Galileo was

the only observatory that was going

to be actually seeing [the impact of S-

L 9] happen—and there was specula-

tion you wouldn’t see anything. And

there were two complications with

the spacecraft. One was being able to

get the sequences built and verified

that would support those observa-

tions, and to know they were safe and

effective. At this point we were still

developing the new software that

would be used to operate the low gain

antenna. We hadn’t even fully devel-

oped the processes we were going to

use to develop the Jovian orbit inser-

tion sequences. This was a year-and-

a-half away from the time when we

thought we’d be doing that. It goes by

awfully quick for something as com-

plex as this. The other complication

was, we were very concerned about

the tape recorder. It’s a mechanical

device. We had only one, and we

were concerned to use it as little as

practicable. So when the request

came along to do Shoemaker-Levy 9,

one of the first issues was, well, that

means you have to use the tape

recorder. Start it. Run it. Activate the

tape. We weighed the desire to be

very conservative about using it ver-

sus the nature of the opportunity and

we decided to use it.31

The leadership saw how problem-

atic it would be to execute even the

planned Jovian mission,” Alexander

said. “Part of the genius of JPL, in my

opinion, is learning the right balance

between prudence and daring, risk and

conservatism. Too daring, too risky,

and you have a mission that goes

belly-up and you’re the one explain-

ing it to a hostile interviewer on

Nightline. So it's possible for someone

in that position to think, ‘Oh no, I have

Galileo with this antenna problem and

the tape recorder question and now

here’s a comet—strike three.’32

Eyes on TargetThe comet had been out of sight for

months, too close to the Sun to observe,

and it would stay hidden until later that

winter. It came back into view with flair

on 9 December. Its fragments had spread

into an elongated train “with their tails

dancing in line like the Rockettes,”33 as

David Levy said. Now the calculations

for its trajectory could be resumed and

refined. That was good news, sort of. That

the impacts would happen on the night

side was still the best determination. They

would be close enough to the morning ter-

minator and the visible portion of the

planet to make the results visible within

10 minutes; so while the characters were

all in costume and the drama was build-

ing, the audience still might not get to see

the dénouement. The American Astronomical

Society’s Division for Planetary Sciences,

an AAS sub-group for solar system

research, held its 25th annual meeting in

Boulder, Colorado, October 1993. It was

Eugene Shoemaker’s retirement party

from the U.S. Geological Survey (not that

he was putting his feet up anytime soon)

so perhaps there was a sentimental edge

to the excitement as his keynote address

shared the best current expectations for

his discovery. “There was a special ses-

sion for S-L 9 at Boulder,” Paul Chodas

recalls, “and it was packed. Shoemaker

was the session chair. David Levy was

there. I had been working with Zdenek

Sekanina of JPL, who is an expert on

cometary fragmentation, and I presented

the results of our analysis on the impact

times and locations of the fragments.

(Sekanina was also the one who intro-

duced letter names for the fragments, not

the numbers David Jewitt of UCLA had

been using.) This was still early, and there

was very little orbital data available on

the individual fragments; I think this was

the first analysis of how the impact times

and locations were spread. Carl Sagan

asked, ‘Are you sure it’s going to be on

the back side, on the side facing away

from the Earth?’ At that point we were

Q U E S T 21:1 201416


very sure about it. As it turned out, the

orbit predictions shifted more than I

expected as we got closer to the impact—

the predicted locations were heading for

the limb, but they never made it there.

The impact positions were always on the

far side.”34

“Never in the history of astronomy

had this much telescope time been allo-

cated for a single event,”35 Levy said

later, but quantity did not equal quality.

[Tele]scopes on Earth were limited by

their unevenly distributed locations

around the spinning planet; by the time of

day for line of sight; and by the weather,

giving each of them one-in-three odds of

seeing Jupiter at the right time.36

There were eyes in the sky:

� The Ulysses solar probe, launched in

1990, was on a course to fly under the

south pole of the Sun in September

1994. Its trajectory would put it 375

million km south of Jupiter in July.

Onboard were radio receivers sensitive

enough to gather data on both the col-

lisions of the comet fragments with

Jupiter, and on the how they affected

the Jovian magnetosphere. It might

have been able to detect thermal/cool-

ing radiation from the impacts, if

indeed they were detectable, and rose

high enough above the atmosphere.

Ulysses would have a line of sight at

the impact points, but it carried no

camera.37

� Voyager 2 was about 6.4 billion

miles away. It could look back at

Jupiter, but from its position, the

largest planet in the Solar System was

just a dot. Voyager’s camera had been

shut down for years, and even if budg-

et money could be found, anyone from

JPL who might have known how to

revive it was retired. Voyager’s ultravi-

olet spectrometer was still active and

could possibly have been of value, and

its planetary radio astronomy (PRA)

experiment would look for radio emis-

sions.38

� Clementine was a new lunar/asteroid

probe with good imaging capabilities,

but being in the Earth-Moon system, it

would be little closer than telescopes

on terra firma.39

� The Hubble Space Telescope had

already served as a key observatory,

even before the December 1993 STS-

91 mission that rectified its imaging

problems. However, like Clementine, it

was close to home; and it was orbiting

the Earth every 95 minutes, so while

this would be its priority, its capacity to

acquire and hold Jupiter as a target was

limited. It also required time for

uplinking and downlinking, calibrat-

ing, managing its antennas, and data

transmission.39

At the time of the impacts Galileowould be just 150 million miles from

Jupiter, with a line of sight and a camera

comparable to the best ones shooting

from Earth. It could take light readings

with its ultraviolet spectrometer, near-

infrared mapping spectrometer, and pho-

topolarimeter. Its plasma-wave sensors

and dust detector could pick up radio

emissions and detect effects from the

impacts in Jupiter’s dust.40 The operators

would need to ration themselves on how

much to collect, and to time their efforts

as closely as possible; but that said, there

was still no other option as good as

Galileo.41

K=½mv2: Fireworks and FizzlesAs the comet fragments moved,

they provided better and better data on

what they had been prior to the breakup.

JPL’s Donald Yeomans and Paul Chodas

postulated that the progenitor of the S-L 9

fragments had held itself together for as

long as 1.4 hours after its closest

approach, so it must have been a big one,

around 9 km in diameter, resulting in

fragments as large as 4 km.42 Knowing

the size helped in estimating the masses

of the fragments and thus in estimating

the energy they would release on impact.

The formula is K=½mv2: kinetic energy

is one-half mass times velocity squared.

A 1-km fragment of ice impacting at 60

km/sec meant 1,028 ergs of kinetic ener-

gy, equal to 200,000 megatons of dyna-

mite. Bigger fragments naturally meant

bigger blasts.43

By then, it was not just the science

community, but the press at large paying

attention as well. A lurid depiction of a

Figure 3. The “String of Pearls” of Shoemaker-Levy heading for Jupiter, as seen from the Hubble Space Telescope on 17 May 1994. Courtesy: NASA, ESA, and H. Weaver and E. Smith (STScI).

disaster-movie blast made the cover of

TIME, 7 May 1994. “Jupiter’s Inferno” it

titled the story, asking darkly, “Could it

happen here on Earth? Yes…”44 (Cue

the organ music.) Press hyperbole and

astronomers’ optimism aside, not all the

predictions said that S-L 9 would produce

giant blasts. Even TIME’s story conceded

that the comet might not actually end the

known universe.45 At the Laboratory, a

note of sobriety was offered by Research

Scientist Dr. Paul Weissman of JPL’s

Earth and Space Sciences Division, who,

shortly before the impact, placed a bet in

Nature that the show would be a letdown:

As the clumps approach Jupiter

for their final plunge into the atmos-

phere at 60 km sec-1, Jupiter's gravi-

ty will again pull them apart. Rather

than hitting as a single solid body,

they will likely come in as an elon-

gated shotgun blast of smaller pellets.

Because of Jupiter's rapid rotation,

the impact sites will be spread in lon-

gitude, like machine gun bullets lac-

ing into a moving target. Each snow-

ball will individually ablate and burn

up like a meteor in Jupiter's upper

atmosphere. Lacking the momentum

and the structural integrity of a single

solid body, they will likely not pene-

trate deeper into the atmosphere

where they might explode with multi-

thousands of megatons of

energy…the giant impacts will pro-

duce a spectacular meteor shower of

bright bolides, but not the massive

fireball explosions that have been

predicted by some researchers. The

impacts will be a cosmic

fizzle…closer to about 30 megatons

each, but still far less than the

100,000 megaton explosions that

some have predicted.46

Harold Weaver of the Space Telescope

Science Institute said flatly: “Nobody can

predict it won’t be a dud.”47

The Stage Is SetBy April, plans for when and where

to direct Galileo’s attention were largely

set, based on the best estimations for the

impact timing.48

David Levy came to JPL on 17

May 1994. “This is a marvelous opportu-

nity to increase public awareness of what

we [astronomers] do,” he told the team.

“For the first time in the history of the tel-

escope, we are witnessing the impact of a

comet on a planet. I still can't believe

how fortunate we are to have this won-

derful spacecraft available to us. It is so

rare in science to have everything work-

ing together. This is truly an event of the

first magnitude.”49 Levy was preaching

to a choir who had been making an effort

of the first magnitude. It had been a win-

ter of exceptional pressure in the days of

people who shared his enthusiasm. In

effect, S-L 9 had created a new mission

without adding a new budget or new

months on the calendar, so the shortfalls

of money and time were compensated for

by sheer will from the members of the

team. “I was more than full time on

Galileo and going overboard,” Claudia

Alexander recalled.

It was exhilarating and stressful at

once. There was no way to mitigate

the workload and no way to know if it

would be successful. You learn to live

with the disappointments but I hadn’t

yet. I was constantly overreaching

myself. The worst part of it for me

was I was formally half time so I

couldn’t put in for overtime. I was

doing 45 hours a week on Galileo but

only 20 on the schedule, and working

on another supposedly ‘half-time’

project, so this amounted to a period

of 90 hour weeks. We were really

killing ourselves to pull this mission

off, and sometimes I felt that our

management was looking the other

way. It’s like the film industry—peo-

ple will do anything to be in a movie

and you can take advantage. We knew

the stakes were high and we knew we

needed the mission to live up to the

investment in a time when govern-

ment was skeptical. In that time, in

that environment, as a young person I

wanted to help show that with this lit-

tle robot, we could get out to Jupiter

and that it could change our lives.50

Torrence Johnson told the April

meeting of the American Geophysical

Union in Baltimore, “Galileo’s imaging

system and its near-infrared mapping

spectrometer will divide up most of the

opportunities,” Johnson said, “while the

photopolarimeter observes several other

events.” He explained that Galileo’s

ultraviolet spectrometer, plasma-wave

sensors and dust detector would also be

mobilized, and that the camera would

capture time-lapse sequences with and

without color filters, slow scans and

long, sweeping scans.

“We’re hoping that one or more of

our observational schemes will succeed

in recording observations of the impact

events themselves with their immediate

consequences, possibly including large

hot fireballs produced by the explosion of

comet fragments as they are stopped by

Jupiter’s atmosphere,” Johnson said,51

which reinforced all the “coulds” and

“maybes.” The motto for the whole

Shoemaker-Levy 9 adventure was:

“We’re hoping.”

During the ImpactsPerhaps it was the cosmos finally

giving JPL and Galileo a break that

Saturday, 16 July, when the impacts

began, was the first day of the 1994 Jet

Propulsion Laboratory Open House. As

always for this annual event, the campus

was thronged with visitors. Meanwhile,

millions of eyes around the world looked

up. It was just before one in the after-

noon, Pacific time, that the first fragment

Q U E S T 21:1 201417


Figure 4. TIME magazine’s coverage. Credit: Time-Life

Q U E S T 21:1 201418


hit Jupiter.

Robert Gounley was handling visitor questions next to the

full-scale model of Galileo in the exhibit area of Theodore von

Kármán Auditorium when he heard a commotion in the lobby. He

walked out to find Paul Chodas holding a printout with the first

report. Chodas told Gounley, “We can see it!”52

“I had delivered the final update on impact times earlier

that morning,” Chodas said, “and thereafter there was nothing to

do but watch the emails for reports. After the first fragment hit

there came a report from the Canary Islands that a dramatic

impact had been seen brightening in the infrared. It was just a

couple of sentences. I printed that out and ran around talking with

anyone I could find. Everyone was just ecstatic—we were actu-

ally seeing the impacts, and the spacecraft would get good

data.”53

The Shoemakers and David Levy were in Baltimore at the

Space Telescope Science Institute. Reports came of a tenfold

increase in radio emissions from Jupiter; and from Spain came

word that something had actually been seen. Shoemaker got con-

firmation during the late afternoon press conference when a col-

league whispered in his ear the latest from Calar Alto observato-

ry in Spain. Shoemaker exclaimed, “You mean they saw a

plume?!” That was, as Levy called it, “just the overture.”54

The markings on the planet were so pronounced they could

be seen with a backyard telescope. With a large instrument the

scars showed that the fireworks had indeed lived up to the hyper-

bole.

“I was at Mount Palomar for a night during the impacts,”

Chodas remembered.

I’d never been there. I went out to the 60-inch telescope

with a tour group, where they were showing Jupiter to any-

one who wanted to look. I lined up with the crowd and

looked and there on Jupiter were these dramatic spots—here

was a planet that had suddenly changed due to the impact

events, and anyone could see it with their own eyes from the

Earth! It brought this understanding to the public—anyone

with a small telescope could go out and see the effects.

People who were new to astronomy were impressed, but

people who had seen it before—they were overwhelmed.55

Shoemaker-Levy 9 had its most important effects not on

Jupiter but here, creating a case study in accelerated global scien-

tific collaboration. It was not limited to the experts. Public inter-

est soared in the international media. More than 1.6 million view-

ers accessed the JPL website, a record at the time. Many observa-

tories during the 16th through the 22nd hosted school classes and

shared the discoveries with children as they happened.56 “It’s not

often you have the opportunity to witness such a dramatic celes-

tial events,” Chodas said. “You go through an incredible amount

of calculations; you hope all the math is right, and it was. The

personal satisfaction, the risk taking, the commitment are all

something that school kids learn from. Math is a dry subject for

most people and the connection to the real world and how math

can describe it—that’s a connection that can inspire a lot of

kids.”57

The question now was, what had Galileo made of it, and

what could it send back to Earth?

The Data ReturnJPL had doubled its effort to make the S-L 9 observations.

Now the Lab redoubled it to pluck the data off the tape recorder

and send it at crawling speed via the low-gain antenna, starting in

Figure 5. Impact scars from Comet Shoemaker-Levy 9 appear as darkspots on the surface.

Credit: Hubble Space Telescope Comet Team and NASA

Figure 6. A “jail-bar” image of S-L 9 Fragment K striking Jupiter.

Credit: JPL/Caltech58

Q U E S T 21:1 201419


August. Whole images wasted precious space and time. JPL took

only what it absolutely needed to reconstruct the impacts.

“Jail-bar” images told them the minimum, but that was

enough. They could extrapolate the missing imagery of each

impact as the weeks passed, while drawing back the data from the

ultraviolet spectrometer, the infrared mapping spectrometer and

the photopolarimeter and the rest of the onboard instruments. The

data was posted on the Web as it came in: light-intensity readings

from the impacts of three fragments. Images of six impacts and

infrared readings of four. Galileo was about 400 million miles

from Earth—36 light-minutes to ask a question, 36 to answer,

with the 7 December orbit insertion date looming.59 The urgent

need was to get everything back and clear the slate for repro-

gramming Galileo on the fly for the Jovian mission.60 As the

data trucked in every hope for the Shoemaker-Levy 9 mission

was vindicated. The imagery from one S-L 9 fragment showed a

fireball five miles across and 14,000 degrees F, hotter than the

surface of the Sun. The impact scar measured “hundreds of miles

across.”61 Scientific convocations all that winter made a feast of

the findings.62 JPL’s own project newsletter, The GalileoMessenger, after years of bearing mixed news, could at last exult.

We can see it.63

Readying for JupiterIt would take until January 1995 for the rest of the S-L 9

data to come home. Meanwhile, there were no moments to rest on

the laurels at JPL. What followed was the reprogramming of the

spacecraft to ready Galileo for Jupiter, the first attempt ever to do

so literally on the fly. Tal Brady called those weeks a “Death

March.” “You have a time limit,” Brady said. “When you reach

it, whether you succeed or fail, what you’re still doing is dead and

won't be implemented. So you work to that limit—whatever it

takes.” Said JPL Principal Software Engineer Dan Erickson,

“Even the tools we were using to develop the software were

decaying. The lab for testing flight software for Galileo went

away before the end of the mission. The test bed was bread-

boards, wire wrapped boards that replicated the hardware. The

paradox of this miraculous technology is that it’s in the forefront

in space, but generations behind at home.”

“Our schedule was dictated by the orbital geometry of the

spacecraft,” Brady said.

The timing and operations of the spacecraft were subject

to the dynamics of gravity and mass as Galileo moved in the

Jovian system, and people’s schedules came from that.

Galileo was a quarter of a billion miles away, on a fixed

timeline, and we had to have the software written, tested,

approved, sent, loaded, ready, and working when the time to

use it arrived. If you have one test bed and twelve people

testing, it’s a bottleneck. Many times we ran two or three

shifts covering all 24 hours. Some tests took hours to run. I

was the team lead, so at times I set up a cot and lived in my

office so I could provide support to all the shifts and also run

my tests. We became a public line item in the NASA budget

for a while, meaning every day a report was made to NASA

HQ in Washington, and NASA had to report to Congress, so

there was a meeting held every morning and the software

development test lead and the software test team had to bring

their charts and updates. For a long period that was my job.

I’d come in and give the report. I found out there was a pool

being kept, indexed to how tired I was. People were keeping

track of the number of times I’d swear in my report: The Tal

Scatology Count.65

The uplink of Galileo’s new operating system ran from 30

January into March. It would help to control the spacecraft for

deployment of the atmospheric probe, a long-awaited flyby of the

Galilean moon Io, and to control Jupiter Orbital Insertion (JOI).

It also provided a secondary probe data storage mechanism in

spare spacecraft memory as a backup to the reel-to-reel tape

recorder’s miniscule 900 megabits.66,67 As Brady remembered,

“Originally the high rate downlink was the primary capture

mechanism for the probe data (which was mission critical) and

the recorder the secondary or backup. With no high rate down-

link, the recorder became the primary and we were required to

provide a secondary method using spacecraft memory to store

‘edited and compressed’ probe data.”68

Which is precisely where Galileo’s next problem hap-

pened, and it nearly ended the mission.

The Tape Recorder ProblemThere was a moment of celebration on 11 October, 1995.

Galileo’s NASA/Ames atmospheric probe had been released as

planned from the orbiter in July 1995, a year after the S-L 9

drama. Since then the package had plummeted toward the planet

on its kamikaze mission. With the probe on course, a 7 December

orbital insertion pending, Galileo’s69 controllers imaged Jupiter

from a distance of 22 million miles, managing to capture the

whole planet in its striped splendor, and the entry point for the

probe as well. The images were stored on the tape recorder for

playback. From Earth, the machine was ordered to rewind. It

should have taken 26 seconds. Instead, the reels spun for hours

and the rewind never finished.70

One more cue for the cliffhanger organ music: this “Peril of

Pauline” could have killed the mission right there. The tape

Figure 7: The Galileo Messenger’s front-page obituary for

Shoemaker-Levy 9. Credit: NASA/JPL64

Q U E S T 21:1 201420


recorder was specially built, naturally, but the design was not sig-

nificantly different from reel-to-reel machines on Earth that by

this time were long since obsolete. Galileo’s tape recorder had

rollers, tape heads, capstans, gears, springs, shafts, 21 pairs of

ball bearings mounted in housings and lubricated with filtered

Exxon ANDOK C applied through a syringe—moving parts

inside moving parts. The tape was AMPEX 799 one-quarter inch

made of polyethylene terephthalate base—Mylar, in other words.

It was available off-the-shelf.71 In 1995, the rattiest recording

studio in Hollywood probably had better hardware.

An awful dread hit the Galileo team: the tape might be bro-

ken. Robert Mitchell remembered,

The concern was that we had weakened the tape by hav-

ing it spinning like that. After we verified that it wasn’t bro-

ken, we wound up changing the software, rewinding the tape

past the point we expected to have been weakened, and then

winding the tape several times over that damaged spot. We

programmed it such that we couldn’t ever go back over that

damaged spot. So we actually did capture that image of the

planet but we couldn’t ever get it downloaded from the tape

recorder back to Earth—it was on the tape in the damaged

section.72

This required one more exercise in engineering judgment,

and this one was especially painful.

The fabulous moon Io was situated for a flyby pass, the first

one Galileo would actually do in the Jovian system. It was a long-

awaited interest of researchers at JPL and around the world.

However, with the prime mission on the line and orbital insertion

just weeks away, Io observations had to be sacrificed. The tape

recorder was just too fragile to risk. It was a grim echo of the

argument that had been made many years before in opposition to

the whole mission, a mindset that JPL had striven relentlessly to

overcome: “Jupiter will be there five or ten or fifteen years from

now when this project can be reinstated,” Congressman Edward

Boland had said in trying to stop Galileo in 1977.”73 Now JPL

had to say it: Io will be there. This time we have to leave it on the

table.

Claudia Alexander remembered:

Jupiter had been observed since the 1950s behaving like

a pulsar, with powerful radio signals emanating from the

vicinity of Io! That’s a massive radiation environment and it’s

deadly for electronics. The J-Zero pass was the only one

where we could get data on Io—and we could not do the pho-

tography. The scientists were up in arms—the only place in

the solar system with active volcanism, the only pass we have

and we’re not going to take it? We thought it would be taxing

the spacecraft too much to pass through that radiation to enter

orbit and to collect data at Io. This really provoked serious

feelings, and no wonder—15 years of planning, a once in a

lifetime chance, and—gone. You feel your whole career there

being changed, threatened by factors you can’t control, the

fulfillment of all that effort and training and sacrifice and it’s

lost. The grief you feel when you lose that kind of scientific

opportunity is like what you feel when you lose a space-

craft—you realize how much of your life has been invested

in this experience and through some accident it’s gone in a

puff of smoke, or because of a tape recorder. As all this was

happening planetary science was under threat; the Hubbledidn’t function as it should have, Galileo’s antenna fails; and

now we lose Io. It was hard.74

Jupiter at Last

Lack of time prevents my going further into these matters;kind Reader, expect more on these subjects shortly. F I N I S75

Galileo’s atmospheric probe was released as planned from

the orbiter in July 1995, a year after the S-L 9 drama. The pack-

age plummeted toward the planet on its kamikaze mission. On 7

December, the orbiter braked to enter Jupiter orbit; the probe sent

back its findings; and everything that the planners, scientists,

engineers, and supporters had hoped for, for so many years, start-

ed coming true.

“The probe, a key experiment, should get more than a pass-

ing mention,” noted Claudia Alexander.

So much time and energy went into that experiment,

years of expectations and anticipation. It also seemed a ‘fiz-

zle’ at first, but decades later those data set the stage for the

JUNO mission, for example, by calling into question where

the planet formed, just how evolved it may be, and for such

paradigms as the Nice model of solar system origins (as con-

troversial as that model is). Data from an actual probe into a

giant planet’s atmosphere caused us to completely re-exam-

ine so many (now passé) notions.76

Figure 8. The Galileo orbiter receives telemetry from the Jupiter atmos-pheric probe. Credit: NASA/JPL

Q U E S T 21:1 201421


ConclusionIt seems fitting that an article on

Galileo should have to leave material out

due to space limitations. Plenty of good

books and articles detail the results of the

mission until its ultimate demise in 2003,

when, after two mission extensions

(including the delayed Io flyby in 1999),

the spacecraft was deliberately crashed

into Jupiter to prevent any possible for-

ward contamination of a Jovian moon. It

had long since outlived its expected life,

but then, holding Galileo to expectations

had long since proven unwise, as was

proven when it revisited Io. That first

missed opportunity was redeemed when it

braved Io’s brutal radiation environment

and collected data thought lost.77

The most important aspect of

Galileo’s story, and indeed, of the stories

of all deep space exploration today, is

such a simple one that it gets passed over

in discussions of supposedly “unmanned”

spaceflight: they are not “unmanned.” It is

the key lesson: every success, every

obstacle overcome, every discovery

Galileo made happened because people at

the Jet Propulsion Laboratory invested

themselves, many at a cost of decades of

their lives, to make it so. Dan Erickson

explained:

It happens in every mission, but

Galileo exemplified the fact—things

happened, you had to react. The

delayed launch; the [high gain anten-

na] failure; the launch vehicle ques-

tion, VEEGA, the tape recorder got

sticky; you started getting electronic

effects from the wear and tear in the

spin bearings and from radiation; and

we’re starting with a very limited set

of resources…we had a body of peo-

ple who understood how to do some-

thing together with people who

understood the spacecraft and what it

could do. And yeah, there were a lot

of hours, a lot of emotional ups and

downs. But this is the kind of people

we are, people who are attracted to

these first of a kind, one of a kind

projects. We love to solve problems.

That’s how we value ourselves.78

Robert Mitchell reflected beside the

Galileo model at von Kármán

Auditorium. “In my first fifteen years

here at JPL I worked on four different

projects to Venus and Mars,” he said. “In

the thirty-two years from then on, with a

five-year hiatus, I worked on two, Galileoand Cassini. The outer-planet projects are

quite different from inner planet proj-

ects.”79

Claudia Alexander, whose career

began with the mission, was the fourth

and final project manager for Galileo. On

28 February 2003, her 15th year with it,

her team pulled a last harvest back from

the ancient tape recorder, and uplinked a

final sequence directing Galileo to coast

for seven months and then send back one

last sampling of measurements. Finally, to

protect the Jovian system against any pos-

sible contamination, Galileo was to fly

into Jupiter’s lethal atmosphere on 21

September.80 Alexander said,

By that time we were all pretty

attached to the spacecraft, the way

you get with an old car. You know its

moods. We’d invested a huge amount

of intellectual energy to get it through

its primary mission, through S-L 9,

and through the extensions, and we

realized how much it was giving

back. We’d fried it repeatedly in the

Jovian radiation belt. We were think-

ing, it can’t survive this time, but

we’d get beep beep beep and it was

reporting back. You felt you had

almost a living thing that was palpa-

bly returning all the love we’d lav-

ished on it. Some of my colleagues

were very emotional about saying

goodbye. The public would send us

letters saying no. But I’d seen the pic-

tures from Cassini and I realized that

the technology’s time had passed on

Galileo. We all came back with great

deal of nostalgia and even sadness for

an old friend, but the technology gal-

lops along. We knew that hanging on

would serve neither humankind, nor

the Galileo staff.81

The engineering judgment that

comes to bear on such enterprises is much

like the questions that weighed on Galileo

himself. Having sought to know about

movement in the heavens, he asked him-

self, what must I do to learn? Knowing

what he knew about the price of learning

on Earth, he had to ask as well, what will

this commitment require of me?

The Papal Condemnation of Galileo

Galilei was handed down on 22 June

1633.

We say, pronounce, sentence, and

declare that you, the said Galileo, by

reason of the matters adduced in trial,

and by you confessed as above, have

rendered yourself in the judgment of

this Holy Office vehemently suspect-

ed of heresy, namely, of having

believed and held the doctrine—

which is false and contrary to the

sacred and divine Scriptures—that

the Sun is the center of the world and

does not move from east to west and

that the Earth moves and is not the

center of the world; and that an opin-

ion may be held and defended as

probable after it has been declared

and defined to be contrary to the Holy

Scripture; and that consequently you

have incurred all the censures and

penalties imposed and promulgated

in the sacred canons and other consti-

tutions, general and particular,

against such delinquents.82

He spent the rest of his life paying

for discovery—not just for the results, but

for insisting that he owed the future and

himself the very idea of discovery and the

embrace of its hazards. Galileo recanted

his outcomes to avoid torture, but he did

some of his best scientific work while

under house arrest, and he never

expressed regret that he had once looked

through a telescope and seen that there

existed in the heavens three stars wander-

ing about Jupiter. What was plainer than

daylight could not fall into shadow again.

Things have changed, of course, but it

remains true that breakthroughs in deep

space are earned in real time at a price,

not just programmed to happen. That this

spacecraft was named after Galileo

acknowledged more than his success. It

recognized what it took.

Tal Brady tells an emblematic story.

“My favorite public interaction happened

at a JPL Open House,” he said.

I was standing beside the model

of Galileo explaining the spacecraft

and the mission to a couple of visi-

tors, an elderly lady and her daughter.

Q U E S T 21:1 201422


They listened earnestly as I told them about the instruments,

but they looked confused. Finally the mother whispered

something to the daughter, who told me, “My mother says it’s

a very interesting machine, but where do the people sit?”

AcknowledgmentsThe author sincerely thanks John Casani, PhD; Robert T.

Mitchell, PhD; Paul M. Chodas, PhD; Claudia J. Alexander, PhD;

Dan Erickson; Z. Nagin Cox; Anita M. Sohus; and Jia-Rui Cook

of the Jet Propulsion Laboratory for their invaluable time and

assistance; and the NASA/JPL Education Office for its superb

online resources; Captain Mike McCulley, U.S.N. (Ret.); Ellen

Baker, MD; and Shannon Lucid, PhD, of STS-34; who provided

their recollections of taking Galileo to space; and Patrick

Wiggins of the NASA/JPL Solar System Ambassador program.

N. Talbot Brady of JPL provided especially valuable assistance in

reviewing both manuscripts for this two-part article, which is

gratefully acknowledged.

Robert Gounley, who spent 13 years with Galileo in his (to date)

30-plus years of near-Earth and deep space exploration, was the

both inspiration and indispensable mentor for this article. I am

honored to have helped Bob and his colleagues share their stories.

About the AuthorDavid Clow is a Los Angeles-based writer. He can be reached at

[email protected].

* * *

Comets and Mirrors: Afterword by Robert Gounley

“Uh, guys? GUYS! I see it!” our fellow stargazer Diane

Rhodes shouted.

Dr. John Callas and I looked skeptically at one another.

That July night in 1994 we were perched beside a mountain

road overlooking Los Angeles with our portable telescope point-

ed at Jupiter. Yesterday, the Galileo orbiter began (so we’d

hoped) viewing the fireballs created as each fragment of Comet

Shoemaker-Levy 9 [SL-9] bombarded the planet where no one

else could see them. The spacecraft may have collected dozens of

stunning images or none at all—it would be weeks before we

knew. Meanwhile, we strained to see any of the dark lesions that

professional astronomers, with far larger scopes, were seeing

whenever a predicted impact site on the planet came into view.

No joy. For tens of minutes, Callas and I squinted at a cor-

ner of Jupiter’s disc. By now, its rotation should have brought

some impact blemishes, each as big as the Earth, into daylight.

We saw nothing. Convinced our telescope was too small, we’d

begun to pack up.

Back then, John and I had, between us, 22 years experience

in deep-space projects with NASA’s Jet Propulsion Laboratory as

scientist and engineer, respectively. (Today it’s over 50 years.) He

was working on a succession of Martian exploration missions, on

which he remains today as project manager for the Mars

Exploration Rover [MER] project. I was a deputy chief on

Galileo’s Orbiter Engineering Team; ahead was twenty (and

counting) more years with missions such as Deep Space 1, MER,

Dawn, and GRAIL. To all this, on that July evening, you could

add three advanced degrees and 20/20 vision (with correction).

So, after first glancing in the direction of Jupiter, the scientist and

the engineer smiled and politely explained that our friend Diane

must be mistaken. We’d seen nothing.

Diane replied, “No, not where you’d been looking. Look on

the opposite side!”

John and I, novices at backyard astronomy, had failed to

consider a basic principle: our loaned telescope, a small reflector,

inverts the image. We’d been looking at the wrong spot on

Jupiter’s disk. We jumped to see what we’d been missing.

There they were—gigantic spots on a gigantic world. From

a half-billion miles away, we were seeing Jupiter continue its four

billion years of growth.

That opportunity had driven the Galileo project, already

burdened with a weak communications link and preparations for

Jupiter arrival, through a hard slog to capture impact images as

they happened. Over the years, Galileo required countless late

nights and weekends to sort out the design and operational chal-

lenges for its expected mission. Readying the spacecraft for this

surprise task took even more. Now we waited anxiously to see

whether our hard work and out tenacious spacecraft could pro-

vide the images millions hoped to see—the actual impacts of

comet SL 9 on the planet's atmosphere. As we found, it could.

The following year, I’d keep two anxious vigils monitoring

real-time data from the Galileo orbiter, one to watch it release its

atmospheric probe and another to fire its main rocket engine in

flight for the first time. Would they work? They did.

Q U E S T 21:1 201423


Systems engineers are generalists,

making sure all parts of a project, hard-

ware, software, and operations, work

together as intended. It was my role on

Galileo and other deep space missions

that visited Mars, a comet, and both Near-

Earth and Main–Belt asteroids.

Their successes bring me great joy.

Best of all, these missions let me to work

with many of the finest engineers and sci-

entists in the world. Our workplace is

NASA’s Jet Propulsion Laboratory.

We stumble at times but, over and

over, we get up again to continue the

adventure. The Galileo mission exempli-

fies that spirit.

I’m proud to have played a part.

* * *

Robert Gounley was deputy chief of

Galileo’s Orbiter Engineering Team at

NASA's Jet Propulsion Laboratory.

Notes1. Galileo Galilei, The Starry Messenger.The History Guide, Lectures on Early ModernEuropean History. http://www.historyguide.org/earlymod/starry.html. Accessed 13January 2013.

2. J. W. Layland, TelecommunicationsScience and Engineering Division; L. L.Rauch, TMO Technology Office andCalifornia Institute of Technology. “TheEvolution of Technology in the Deep SpaceNetwork: A History of the Advanced SystemsProgram.” TDA Progress Report 42-130 15August 1997. http://deepspace.jpl.nasa.g ov / te c h n o l o g y / 9 5 _ 2 0 / 9 5 - 2 0 . p d f .Accessed 13 January 2013.

3. Bruce Murray, et al., Mars and the Mindof Man. New York: Harper & Row, Publishers.1973, 17.

4. Hampton Roads Daily Press, “WishfulThinking, Cost Cutting Plagued Hubble FromInfancy”. 29 July 1990. http://articles.daily-p r e s s . c o m / 1 9 9 0 - 0 7 - 2 9 / n e w s/9007290113_1_hubble-telescope-space-telescope-science-institute-beggs. Accessed15 February 2013.

5. Richard A. Kerr, “Jupiter BombardmentNow Certain, but How Big a Show?” Science,Vol. 261, 30 July 1993, 17.

6. Bertolt Brecht, Plays, Volume 1. “The Lifeof Galileo.” London: Methuen & Co. Ltd.1960, 266.

7. David H. Levy, Impact Jupiter. The Crashof Comet Shoemaker-Levy 9. New York andLondon. Plenum Press. 1995, 31.

8. Torrence V. Johnson. Jet PropulsionLaboratory. INTEROFFICE MEMORANDUM.TVJ:93-021. 9 July 1993.

9. Correspondence from N. Talbot Brady,26 April 2013.

10. Correspondence from N. Talbot Brady,26 April 2013.

11. Central Bureau for AstronomicalTelegrams, INTERNATIONAL ASTRONOMICALUNION. Smithsonian AstrophysicalObservatory, Cambridge, MA 02138, U.S.A.Circular No. 5800. “PERIODIC COMET SHOE-MAKER-LEVY 9 (1993e)” http://www.cbat.eps.harvard.edu/iauc/05700/05800.html.Accessed 21 January 2013.

12. Interview by the author with Paul W.Chodas, Ph.D. Jet Propulsion Laboratory,Pasadena CA. 18 January 2013.

13. Torrence V. Johnson. Jet PropulsionLaboratory. INTEROFFICE MEMORANDUM.TVJ:93-021. 9 July 1993.

14. David H. Levy, Impact Jupiter. The Crashof Comet Shoemaker-Levy 9. New York andLondon. Plenum Press. 1995, ix.

15. Frequently Asked Questions about theCollision of Comet Shoemaker-Levy 9 withJupiter. Pre-Impact Questions and Answers.Last Updated on 12 July 1994. Dan Bruton,Ph.D., Professor Department of Physics &Astronomy, Stephen F. Austin StateUniversity Nacogdoches, TX. http://www.physics.sfasu.edu/astro/sl9/cometfaq.html#Q1.4. Accessed 13 January 2013.

16. Ray L. Newburn, Jr., Periodic CometShoemaker-Levy 9 Collides with Jupiter:Background Material for Science Teachers.Pasadena, CA: Jet Propulsion Laboratory.1994, 11.


18. Frequently Asked Questions about theCollision of Comet Shoemaker-Levy 9 withJupiter. Pre-Impact Questions and Answers.Last Updated on 12 July 1994. Dan Bruton,Ph.D., Professor Department of Physics &

Astronomy, Stephen F. Austin StateUniversity Nacogdoches, TX. http://www.physics.sfasu.edu/astro/sl9/cometfaq.html#Q1.4. Accessed 13 January 2013.



21. Comet Shoemaker-Levy Collision withJupiter, “K-T Event.” http://www2.jpl.nasa.gov/sl9/back3.html. Accessed 21 January2013.

22. Comet Shoemaker-Levy Collision withJupiter, “K-T Event.” http://www2.jpl.nasa.gov/sl9/back3.html. Accessed 21 January2013.

23. Brian Vastag, “Crater found in Iowapoints to asteroid break-up 470 million yearsago.” The Washington Post. http://www.washingtonpost.com/national/health-science/crater-found-in-iowa-points-to-aster-o i d - b r e a k - u p - 47 0 - m i l l i o n - y e a r s -ago/2013/02/18/545131f8-76d5-11e2-aa12-e6cf1d31106b_story.html. Accessed18 February 2013.

24. Astronomy Picture of the Day, 15December 2001. http://apod.nasa.gov/apod/ap011215.html. Accessed 16February 2013.

25. Ellen Barry and Andrew E. Kramer,“Shock Wave of Fireball Meteor RattlesSiberia, Injuring 1,000.” The New YorkTimes. http://www.nytimes.com/2013/02/16/world/europe/meteorite-fragments-are-said-to-rain-down-on-siberia.html?hpw.Accessed 15 February 2013.


27. Erik N. Nilsen and P.A. “Trisha” Jansma.“Galileo's Rocky Road to Jupiter”. ASKMagazine: NASA Academy ofProgram/Project and EngineeringLeadership. Issue 42, Spring 2011.

Q U E S T 21:1 201424


http://www.nasa.gov/offices/oce/appel/ask/issues/42/42s_galileo_rocky_road_jupiter.html. Accessed 30 January 2013.

28. Interview by the author with Claudia J.Alexander, Ph.D. Jet Propulsion Laboratory,Pasadena CA. 18 January 2013.

29. Interview by the author with RobertGounley. Jet Propulsion Laboratory,Pasadena CA. 18 January 2013.

30. Correspondence with N. Talbot Brady,27 April 2013.

31. Interview by the author with Robert T.Mitchell. Jet Propulsion Laboratory,Pasadena CA. 18 January 2013.


33. David H. Levy, Impact Jupiter. The Crashof Comet Shoemaker-Levy 9. New York andLondon. Plenum Press, 1995, 121.





38. Ray L. Newburn, Jr., Periodic CometShoemaker-Levy 9 Collides with Jupiter:Background Material for Science Teachers.Pasadena, CA: Jet Propulsion Laboratory.1994, 19-20.

39. Rob Landis. "Comet P/Shoemaker-Levy's Collision with Jupiter: Covering HST'sPlanned Observations from YourPlanetarium". International PlanetariumSociety Conference Astronaut MemorialPlanetarium & Observatory Cocoa, Florida10-16 July 1994. http://www2.jpl.nasa.gov/sl9/hst1.html. Accessed 13 January 2013.

40. JPL Fact Sheet, Galileo. [undated]http://www2.jpl.nasa.gov/sl9/gll8.html.Accessed 21 January 2013.

41. JPL Fact Sheet, Galileo. [undated]http://www2.jpl.nasa.gov/sl9/gll8.html.Accessed 30 January 2013.



44. TIME Magazine, Covers, Comet HitsJupiter, 23 May 1994. http://www.time.com/time/covers/0,16641,19940523,00.html


46. Paul Weissman, “The Big Fizzle isComing.” Nature, News and Views, 14 July1994. http://www2.jpl.nasa.gov/sl9/news9.html. Accessed 12 January 2013.

47. Richard A. Kerr, “Jupiter BombardmentNow Certain, but How Big a Show?”,Science, Vol. 261, 30 July 1993, 17.

48. Clark R. Chapman, “Preview of Galileo'sTentative SL-9 Observing Plans.” 6 April1994. http://www2.jpl.nasa.gov/sl9/gll1.html. Accessed 21 January 2013.

49. Jet Propulsion Laboratory, The GalileoMessenger, Issue 34, June 1994. CourtesyAnita Sohus, Jet Propulsion Laboratory.Accessed 25 January 2013, 5.


51. “Galileo Set to Observe CometShoemaker-Levy, Galileo set to observe 16of 21 `pearls' in Shoemaker-Levy-9 string.”JPL Universe, 3 June 1994. http://www2.jpl.nasa.gov/sl9/gll5.html. Accessed21 January 2013.

52. Interview by the author with RobertGounley, Jet Propulsion Laboratory,Pasadena CA. 18 January 2013.


54. David H. Levy, Impact Jupiter. The Crash

of Comet Shoemaker-Levy 9. New York andLondon. Plenum Press. 1995, 151.

55. Interview by the author with Paul W.Chodas, Ph.D. Jet Propulsion Laboratory,Pasadena CA. 18 January 2013


57. Interview by the author with Paul W.Chodas, Ph.D. Jet Propulsion Laboratory,Pasadena CA. 18 January 2013

58. “Galileo Jail-Bar Image of Fragment KImpact” http://www2.jpl.nasa.gov/sl9/image236.html. Accessed 20 February2013.

59. Public Information Office, Jet PropulsionLaboratory, California Institute ofTechnology, National Aeronautics and SpaceAdministration, Pasadena, California 91109.Galileo Mission Status Report, 1 August1994. http://www2.jpl.nasa.gov/sl9/gll12.html. Accessed 21 January 2013.

60. Public Information Office, Jet PropulsionLaboratory, California Institute ofTechnology, National Aeronautics and SpaceAdministration, Pasadena, California 91109.Galileo Mission Status Report. 1 September1994. http://www2.jpl.nasa.gov/sl9/gll14.html. Accessed 21 January 2013.

61. Public Information Office, Jet PropulsionLaboratory, California Institute ofTechnology, National Aeronautics and SpaceAdministration, Pasadena, California 91109.“Galileo Comet SL9 Observations.” 31October 1994. http://www2.jpl.nasa.gov/sl9/gll22.html. Accessed 21 January 2013.

62. Public Information Office, Jet PropulsionLaboratory, California Institute ofTechnology, National Aeronautics and SpaceAdministration, Pasadena, California 91109.Galileo Mission Status Report. 1 November1994. http://www2.jpl.nasa.gov/sl9/gll23.html. Accessed 21 January 2013.

63. Dr. Claudia Alexander notes here,“Beyond the fact that we ‘saw’ it, the pointshould be made that decades later, scien-tists are finding that data set constitutes asingular insight into the behavior to be stud-ied for a new class of solar impacts, those ofsun-grazing comets; which, with techniquescontemporary to 2013, represent a uniquesampling opportunity for solar chromospher-

Q U E S T 21:1 201425


ic ablation effects. Now that we have tech-niques to observe comets impacting the Sun,the Galileo data set from SL-9 gives us criticalbackground data needed to design experi-ments to mine the Solar opportunities, andthose papers (Brown et al., “Mass Loss,Destruction & Detection of Sun-grazing & -impacting Cometary Nuclei”, Astro &Astrophys [2011]; Carlson et al, “Galileo IRObservations of comet Shoemaker-Levy 9Impact Fireball”, Geophys Res Lett [1997])are now studied with great appreciation.”Comment on 26 February 2013.

64. Jet Propulsion Laboratory. The GalileoMessenger. Issue 35. December 1994.Courtesy Anita Sohus, Jet PropulsionLaboratory, 1.

65. Dan Erickson, principal software engi-neer, Jet Propulsion Laboratory; N. TalbotBrady, retired senior software engineer, JetPropulsion Laboratory. Interview by theauthor 26 January 2013.

66. Jean H. Aichele, Editor, Galileo: The TourGuide (And a Summary of the Mission toDate). Pasadena: Jet Propulsion Laboratory.JPL D-13554. June 1996, 27.

67. Public Informtion Office, Jet PropulsionLaboratory, California Institute of Technology,National Aeronautics and SpaceAdministration, Pasadena, California 91109.Galileo Mission Status Report. February 1,1995. http://www2.jpl.nasa.gov/sl9/gll27.html. Accessed 21 January 2013.

68. Correspondence with N. Talbot Brady, 26April 2003.

69. Douglas Isbell, [NASA] Headquarters,Washington, DC; Franklin O'Donnell, JetPropulsion Laboratory, Pasadena, CA;RELEASE: 95-182. “Galileo SpacecraftAnomaly Being Investigated.” 12 October1995. http://nssdc.gsfc.nasa.gov/planetary/text/gal_tape.txt. Accessed 30 January 2013.

70. Michael R. Johnson and Greg C. Levanas,California Institute of Technology, JetPropulsion Laboratory. Pasadena, California.“The Galileo Tape Recorder Rewind OperationAnomaly.” 31st Aerospace MechanismsSymposium held at NASA Marshall SpaceFlight Center, 14-16 May 1997. BEACONeSpace at Jet Propulsion Laboratory.http://trs-new.jpl.nasa.gov/dspace/handle/2014/21779. Accessed 23 January 2013.

71. Michael R. Johnson and Greg C. Levanas,California Institute of Technology, Jet

Propulsion Laboratory. Pasadena, California.“The Galileo Tape Recorder Rewind Anomaly.”31st Aerospace Mechanisms Symposiumheld at NASA Marshall Space Flight Center,14-16 May 1997. BEACON eSpace at JetPropulsion Laboratory. http://trs-new.jpl.nasa.gov/dspace/handle/2014/21779. Accessed23 January 2013.

72. Interview by the author with Robert T.Mitchell. Jet Propulsion Laboratory, PasadenaCA. 18 January 2013. Tal Brady added, “Weactually developed a flight software patch tomove the tape to and play back this image atthe end of the mission, but the success of theextended mission meant that we ran so longthat we ran out of time and money to do thatone last thing.” (Correspondence with N.Talbot Brady, 26 April 2013).

73. Bruce Murray. Journey Into Space, NewYork: W.W. Norton & Company. 1989, 191.


75. Galileo Galilei, The Starry Messenger, TheHistory Guide, Lectures on Early ModernEuropean History. http://www.historyguide.org/earlymod/starry.html. Accessed 13January 2013.

76. Comment by Claudia J. Alexander, Ph.D.,26 February 2013.

77. Correspondence from N. Talbot Brady, 26April 2013.

78. Dan Erickson, principal software engi-neer, Jet Propulsion Laboratory; N. TalbotBrady, Retired Senior Software Engineer, JetPropulsion Laboratory. Interview by theauthor, 26 January 2013.

79. Interview by the author with Robert T.Mitchell. Jet Propulsion Laboratory, PasadenaCA, 18 January 2013

80. Space Today, “The Eight-Year Tour ClosedSpectacularly”. http://www.spacetoday.org/So lSys/Jup i te r/Ga l i leoMiss ion .h tml .Accessed 21 February 2013.


82. “Papal Condemnation (Sentence) ofGalileo (22 June 1633).” http://law2.umkc.edu/faculty/projects/ftrials/galileo/condem-nation.html. Accessed 14 February 2013.

83. Dan Erickson, principal software engi-

neer, Jet Propulsion Laboratory; N. TalbotBrady, retired senior software engineer, JetPropulsion Laboratory, Interview by theauthor 26 January 2013.

* * *

Wally Schirra

“Mostly it’s lousy out there. It’sa hostile environment, and it’s tryingto kill you. The outside temperaturegoes from a minus 450 degrees to aplus 300 degrees. You sit in a flyingThermos bottle.”

Associated Press, 1981.

* * *

His goal was to be “a hot shot testpilot, not just a scarf and goggles type,but one who could use his engineer-ing confidence to work on systemsand make the best airplane, ever.”

The Real Space Cowboys [ApogeeBooks, 2005], written with Ed Buckbee

* * *“I didn’t really volunteer for ProjectMercury,” he said, but he became acandidate after being ordered toWashington to hear a presentation.“We were listening to a pair of engi-neers and a psychologist describingthe feeling when you’re on top of arocket in a capsule and going aroundthe world,” he remembered. “I wasimmediately looking for the door, andthey said, ‘Not to worry, we’ll send achimpanzee first!’ There’s no way atest pilot would volunteer for some-thing like that.”

New York Times, Obituary[4 May 2007]

Gordon Cooper

Visiting the factory where the boosterrocket for his mission was being built,he attached a NASA seal to its side,drew an arrow pointing up and wrote,“Launch This Way!”

New York Times [5 October 2004]

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“Flying in Deep Space: The Galileo Mission to Jupiter, Part Two”

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