DESIGN OF COLD GAS PROPULSION SYSTEM FOR A CUBESAT

Design of Cold Gas Propulsion System for a CubeSat

Surmit Bhui, Sumana Mukherjee, Sabina Mehra. Guide – Dr. Ugur Guven

Minor Project Report

on

DESIGN OF COLD GAS PROPULSION SYSTEM FOR A CUBESAT

Submitted by:

Surmit Bhui (R290211026)

Sumana Mukherjee (R290211025)

Sabina Mehra (R290211030)

B. Tech. Aerospace Engineering

Batch: 2011-15

Department of Aerospace Engineering

College of Engineering Studies (COES)

University of Petroleum & Energy Studies (UPES), Dehradun

May 2014



CERTIFICATE

I hereby certify that the work which is being presented in the project report entitled

“Design of Cold Gas Propulsion System for a Cubesat” in partial fulfilment of the

requirements for the satisfactory performance for Minor Project, third year, submitted in

the Department of Aerospace Engineering, University of Petroleum and Energy Studies,

Dehradun is an authentic record of my own work carried out during a period from July

2013 to December 2013.

Submitted By: Submitted To:

Surmit Bhui (R290211026)

Sumana Mukherjee (R290211025) Dr. Ugur Guven

Sabina Mehra (R290211030)

B.Tech. Aerospace Engineering

2011-2015

This is to certify that the above statement made by the candidate is correct to the best of

my knowledge.



ABSTRACT

Cubesats have become quite popular especially among university students as these

miniaturized satellites help them in carrying out space exploration feasibly. Till date,

cubesats have never flown in space with any well defined propulsion system. But in order

to increase mission capabilities like orbit raising and formation flying, or to perform

proximity operations, fine attitude control, drag make up and de–orbit without much

risks, it is important to use a propulsion system. Here in this report we have focused on

the use of cold gas thrusters in a cubesat.Cold gas thrusters consist of a pressurized tank

containing gaseous propellant, such as nitrogen, and a solenoid actuated valve system

leading to exit nozzles. Since the propellant is unheated and relies solely on the enthalpy

of the stored gas, the velocity at the nozzle exit is relatively low resulting in a low specific

impulse, typically around 60 sec, useful for small attitude adjustments and low ΔV

maneuvers. However, the power level, pressure, and weight required in the vessel are

though less, but still higher than the Cubesat Specifications provided by the CalPoly.

Rather than relying on high-pressure chambers, we propose the use of solid gas

cartridges, which upon ignition by lasers can be released into a chamber in the gaseous

form, from which nitrogen can be drawn for propulsive use. Moreover since only a

fraction of the propellant is used for propulsion use, it helps in reducing the tank size and

minimizes the risk of leakage and pressure limitations, with reduction in mass by around

20%. This way a suitable propulsion system for a cubesat can be developed which renders

increased performance with respect to mission capabilities without increasing the overall

mass of the satellite. The idea would also prove to be of much benefit for industries which

are planning future cubesat missions.



ACKNOWLEDGEMENTS

This project would not have been possible without the assistance from our mentor Dr.

Ugur Guven, Professor,UPES.

We wish to thank Mr. Linsu Sebastian, Mr. Pawan Kumar Nanduri and Mr. A.J. Arun

Jeya Prakash, Department of Aerospace Engineering, UPES for their constant support

and motivation for this project.

Also, we are indebted for the feedback and positive response from Mr. Vikrant Narang,

Student, International Space University, Dr. Megan Kane, NanoSatisfi, USA, Dr. Mart

Noorma, Head of Space Technology Department, Tartu Observatory and various

professionals and distinguished delegates from all over the world at 2013 International

Astronautical Congress, Beijing, China.



TABLE OF CONTENTS

1. Introduction……………………………………………………………………...09

2. 2.1Aim…………………………………………………………………………...11

2.2Objective……………………………………………………………………...11

3. Methodology

3.1 Semi-Conductor Laser……………………………………………………….12

3.2 Solid Nitrogen – The Propellant……………………………………………..14

3.2.1 Gas Properties ……………………………………………………….15

3.3 Hose………………………………………………………………………….16

3.4 Suction Chamber

3.4.1Solenoid Valves………………………………………………………...17

3.4.2 Actuator………………………………………………………………..18

3.4.3 Nozzle………………………………………………………………….19

3.5 CAD Model………………………………………………………………….20

3.6 Calculations……………...…………………………………………………..21

4. Literature Review

4.1 Pulsed Plasma Thrusters……………………………………………………..24

4.2 Resistojet……………………………………………………………………..25

4.3 Cold gas Propulsion………………………………………………………….26

4.4 Research done by TNO………………………………………………………27

4.4.1 Cool Gas Generators………………………………………………...27

4.5 Modifications in the system…………………………………………………27

5. Results and Discussions………………………………………………………….29

6. Future work………………………………………………………………………31

7. References………………………………………………………………………..32



LIST OF FIGURES

1. Fig 4.1 – Physical Origin of gain in a Semiconductor (Page 14)

2. Fig 4.2 – Semiconductor Diode Laser ( Page 14)

3. Fig 4.3 – Solid Nitrogen (Page 15)

4. Fig 4.4 – Rubber Hose Pipe (Page 17)

5. Fig 4.5 – Electric Actuator (Page 18)

6. Fig 4.6 – CAD Model ( Page 20)

7. Fig 5.1 – Pulsed Plasma Thruster (Page 24)

8. Fig 5.2 – Resistojet (Page 24)

9. Fig 5.3 – Cool Gas Generator (Page 26)



ABBREVIATIONS USED

1. Ft. = Feet

2. Fig. - Figure

3. Sec. = Second

4. m = meter

5. m1 = Initial Mass of Propellant

6. m2 = Final Mass of Propellant

7. Isp = Specific Impulse

8. W.R = Weight Ratio

9. LEO = Low Earth Orbit

10. ∆V = Delta-Velocity ( change in velocity )



TIMELINE

Month (Year) Progress (Completed/Projected)

August (2013) Review of Literature

September (2013) Presentation of Design at IAC 2013

November (2013) First Minor Project Presentation

December (2013) Calculations; Second Minor Project

Presentation

January (2014) Procurement of Material for model

Building

February (2014) Beginning of model Building process

April & May(2014) Completion of model Building and its

testing.



CHAPTER 1:

INTRODUCTION

The concept of cubesat was born in 1999, with professors at California Polytechnic State

University and Standford University outlining the set of specifications for a simple pico-

satellite, naming it the 'CubeSat' in the form of a cube with predefined specifications.

However, after more than a decade of cubesat being in practice, no cubesat has flown

with a propulsion system in space.

Photo Courtesy: NASA

Fig. 1.1 A Cubesat

Propulsion capability is of prime importance for tasks like orbit change and raising ,

formation flying , proximity operations , fine altitude control , or drag make up and de

orbit. Few of the above mentioned tasks could be performed singly without a propulsion

system but their application is limited.We thereby emphasis on the design of a Cold Gas

Propulsion System for a cubesat, adhering to the specifications of the Cubesat platform.

The cubesat model has no specific restrictions but there are a few general requirements

for building a cubesat.



These requirements have been defined by Professors at the Stanford University and

California Polytechnic University and are as follows:

1. The vessel should have a maximum pressure of 1.2 ATM and a factor of safety

not less than 4.

2. Limitations on the pressure at which propellant can be stored also limit the

specific impulse (Isp) and thrust capabilities as the thrust level relies heavily on

the storage of pressure

3. Also , pyrotechnics of any kind are not allowed on board a CubeSat as they are

used as igniters for a chemical propulsion system

4. Further restrictions in use of hazardous materials imply the limit on allowable

propellant type.

Photo Courtesy : Tartu Space Observatory

Fig.1.2 Estcube-1 – First Estonian Cubesat to be launched into space



CHAPTER 2:

2.1 AIM:-

To design and test an original Cold Gas Propulsion System for a cubesat.

2.2 OBJECTIVE:-

The main objective of the idea to design a Cold Gas Propulsion System is for the

full utilization of the CubeSat Platform innovatively and efficiently.

Various Operations like Orbital Change, Proximity Operations, fine Attitude

Control and de-orbit can be achieved with a Cubesat with propulsion capabilities.



Chapter 3:

METHODOLOGY

For building the original system, 3D prototyping is used. The thruster is manufactured in

a couple of weeks using the stereolithography (SLA) process. The entire thruster,

including the main tank, all secondary tanks, internal piping, and converging-diverging

nozzle, is encased in one block of plastic. By the stereolithography process, parts can be

printed in layers with a thickness of as little as 0.1 mm . With such capability, extremely

precise features can be built into the design such as a converging-diverging thruster

nozzle. But since the use of such expensive rapid prototyping process is beyond the scope

of our minor project , we intend to build the prototype using the prototyping processes

available at hand , i.e. at the CAM labs at the University.

A serious risk involved in using plastic for the components is that Laser can burn the

plastic material since the latter would absorb energy from the semiconductor laser.

Therefore, fiber composites might be used for the actual cold gas propulsion system since

it is non-corrosive as well as lightweight. But just for the purpose of building the

prototype, plastic could be used.

3.1Semi Conductor Laser :

One of the major advantages of using semiconductor laser is that they are comparatively

cheap and compact in size.They consist of complex multi-layer structures requiring

nanometer scale accuracy and an elaborate design.

A semiconductor laser is a solid-state device that consists of two outer semiconductor

layers separated by a middle layer and generates laser radiation when charge carriers of

opposite polarity, one each from the top and bottom layers, meet in the middle layer.

Semiconductor lasers are lasers based on semiconductor gain media, where optical gain is

usually achieved by stimulated emission at an interband transition under conditions of a

high carrier density in the conduction band.

The physical origin of gain in a semiconductor (for the usual case of an interband

transition) is illustrated in Figure 1. Without pumping, most of the electrons are in the

valence band. A pump beam with a photon energy slightly above the bandgap energy can



excite electrons into a higher state in the conduction band, from where they quickly decay

to states near the bottom of the conduction band. At the same time, the holes generated in

the valence band move to the top of the valence band. Electrons in the conduction band

can then recombine with these holes, emitting photons with an energy near the bandgap

energy. This process can also be stimulated by incoming photons with suitable energy. A

quantitative description can be based on the Fermi–Dirac distributions for electrons in

both bands.

Most semiconductor lasers are laser diodes, which are pumped with an electrical current

in a region where an n-doped and a p-doped semiconductor material meet. However,

there are also optically pumped semiconductor lasers, where carriers are generated by

absorbed pump light, and quantum cascade lasers, where intraband transitions are

utilized.

Common materials for semiconductor lasers (and for other optoelectronic devices) are

GaAs (gallium arsenide)

AlGaAs (aluminum gallium arsenide)

GaP (gallium phosphide)

InGaP (indium gallium phosphide)

GaN (gallium nitride)

InGaAs (indium gallium arsenide)

GaInNAs (indium gallium arsenide nitride)

InP (indium phosphide)

GaInP (gallium indium phosphide)

Fig.3.1 Physical origin of gain in a semiconductor.



Fig.3.2 Semiconductor Diode Laser

According to studies, the amount of power required for decomposing solid nitrogen

propellant is around 2.5 W which is available from any of the semiconductor lasers and

can be susscessfully used in the prototype.

3.2 Solid Nitrogen - The Propellant

Nitrogen is mainly found in the atmosphere, where it accounts for 78 % by volume of the

air we breath. But nitrogen is also found:

- in the Earth's crust, to a limited extent (in the form of nitrates, etc.),

- in organic form (in the living or dead plants and organisms which form humus)

- and in mineral form (ammonia), and thus contributes to soil fertility. In gaseous form,

nitrogen is a neutral and colorless gas. It is inerting and does not sustain life.

Liquid nitrogen can easily be converted to a solid by placing it in a vacuum chamber

pumped by a rotary vacuum pump. Liquid nitrogen freezes at 63 K (−210 °C; −346 °F).

Under normal atmospheric pressure, nitrogen can exist as a liquid between the

temperatures of 63 K and 77.2 K(-346°F and -320.44°F). Below 63 K, nitrogen freezes

and becomes a solid. Above 77.2 K, nitrogen boils and becomes a gas.

It has been experimentally proved that solid nitrogen can be produced and stored at a

pressure of .124 atmosphere or 94.24 torr which needs to be maintained within the

chamber where the propellant is to be kept. the solid nitrogen would be wound around a

rod and would be rotated at a low rpm to allow the decomposition of the solid propellant

by the impingement of semiconductor laser onto it. The solid nitrogen will slowly get

decomposed into gaseous nitrogen which would pass through the hose pipe to the suction

chamber.



Fig.4,3 Solid Nitrogen

3.2.1 Gas Properties

Molecular Weight

Molecular weight : 28.013 g/mol

Solid phase

Melting point : -210 °C

Latent heat of fusion (1,013 bar, at melting point) : 25.702 kJ/kg

Liquid phase

Liquid density (1.013 bar at boiling point) : 806.11 kg/m3

Liquid/gas equivalent (1.013 bar and 15 °C (59 °F)) : 680.4 vol/vol

Boiling point (1.013 bar) : -195.8 °C

Latent heat of vaporization (1.013 bar at boiling point) : 199.18 kJ/kg

The isolated nitrogen molecule N2 has dimensions, defined by the surface enclosing 95%

of the electron density, of about 3.39 Å diameter 4.34Å in length. Spectroscopic studies



of the vibrational (stretch) modes of the molecule indicate that in the condensed states the

molecule is slightly distorted by interactions with neighbouring molecules.

Nitrogen exists as two stable isotopes - 99.63% is 14N with nuclear spin 1 and 0.37% is

15N with spin 1/2. With such a small fraction of 15N2 the properties of solid, natural N2

and solid pure 14N2 are virtually indistinguishable.

3.3 HOSE

A hose is a flexible hollow tube designed to carry fluids from one location to another.

Hoses are also sometimes called pipes (the word pipe usually refers to a rigid tube,

whereas a hose is usually a flexible one), or more generally tubing. The shape of a hose is

usually cylindrical (having a circular cross section). Hoses are made from one or a

combination of many different materials. Applications mostly use nylon, polyurethane,

polyethylene, PVC, or synthetic or natural rubbers, based on the environment and

pressure rating needed. In recent years, hoses can also be manufactured from special

grades of polyethylene (LDPE and especially LLDPE). Other hose materials include

PTFE (Teflon), stainless steel and other metals.

To achieve a better pressure resistance hoses can be reinforced with fibers or steel cord.

Commonly used reinforcement methods are braiding, spiralling, knitting and wrapping of

fabric plies. The reinfocement increases the pressure resistance but also the stiffness. To

obtain flexibility corrugations or bellows are used. Usually circumferential or helical

reinforcement rings are applied to maintain these corrugated or bellowed structures under

internal pressure.

Fig.4.4 Rubber hose pipe

The hose will direct the gaseous nitrogen from the upper chamber to the lower suction

chamber.



3.4 Suction Chamber

The suction chamber is placed downstream of the hose pipe where the gaseous nitrogen

will enter and will be finally used for propulsion. The pressure within the suction

chamber would be lower than that in the upper chamber so that the gas can flow through

the hose due to the pressure difference in the two chambers. The suction chamber will

consist of solenoid valves, actuators and end with the nozzle.

3.4.1 Solenoid valves

A solenoid valve is an electromechanical device used for controlling liquid or gas flow.

The solenid valve is controlled by electrical current, which is run through a coil. When

the coil is energized, a magnetic field is created, causing a plunger inside the coil to

move. Depending on the design of the valve, the plunger will either open solenoid valve

pictureor close the valve. When electrical current is removed from the coil, the valve will

return to its de-energized state.In direct-acting solenoid valves, the plunger directly opens

and closes an orifice inside the valve. In pilot-operated valves (also called the servo-type),

the plunger opens and closes a pilot orifice. The inletline pressure, which is led through

the pilot orifice, opens and closes the valve seal.The most common solenoid valve has

two ports: an inlet port and an outlet port. Advanced desigs may have three or more ports.

Some designs utilize a manifold-type design.Solenoid valves make automation of fluid

and gas control possible. Modern solenoid valves offer fast operation, high reliability,

long service life, and compact design.

3.4.2 Actuator

An actuator is a type of motor for moving or controlling a mechanism or system. It is

operated by a source of energy, typically electric current, hydraulic fluid pressure, or

pneumatic pressure, and converts that energy into motion. An actuator is the mechanism

by which a control system acts upon an environment. The control system can be simple (a

fixed mechanical or electronic system), software-based (e.g. a printer driver, robot control

system), or a human or other agent.

A hydraulic actuator consists of a cylinder or fluid motor that uses hydraulic power to

facilitate mechanical operation. The mechanical motion gives an output in terms of linear,

rotary or oscillatory motion. Because liquid cannot be compressed, a hydraulic actuator

can exert considerable force, but is limited in acceleration and speed.

A pneumatic actuator converts energy formed by compressed air at high pressure into

either linear or rotary motion. Pneumatic energy is desirable for main engine controls

because it can quickly respond in starting and stopping as the power source does not need

to be stored in reserve for operation.

An electric actuator is powered by motor that converts electrical energy to mechanical

torque. The electrical energy is used to actuate equipment such as multi-turn valves. It is

one of the cleanest and most readily available forms of actuator because it does not

involve oil.



A mechanical actuator functions by converting rotary motion into linear motion to

execute movement. It involves gears, rails, pulleys, chains and other devices to operate.

For the proposed cold gas system , an electric actuator would be used.

Fig.4.6 Electric actuator

3.4.3 Nozzle

A nozzle is a device designed to control the direction or characteristics of a fluid flow

(especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe.

A nozzle is often a pipe or tube of varying cross sectional area, and it can be used to

direct or modify the flow of a fluid (liquid or gas). Nozzles are frequently used to control

the rate of flow, speed, direction, mass, shape, and/or the pressure of the stream that

emerges from them.

The most common form of nozzle is the de Laval nozzle with a converging portion

followed by a diverging portion.



Fig.3.4.3 de Laval nozzle geometry[8]

The nozzle could basically be used for expelling the nitrogen gas from the suction

chamber in order to generate thrust for propulsion.

In case of microsatellite propulsion, where the main purpose is not to generate high thrust,

conventional conical convergent-divergent nozzles are used. The length is kept minimum

so as to avoid boundary layer separations. In these kind of nozzles , the effect of half

angle which is usually 15 to 20 degrees in case of De Laval Nozzles, is much less so

precision in terms of angular shape is not required.



3.5 CAD Model :

The design given below is the CAD Model, made on CATIA V5 of the Cold Gas

Propulsion System, as proposed by us in the preceding section.

Fig. 4.6 CAD Model



3.6 Calculations :

For any propulsion system to be onboard a space vehicle, a few specific performance

parameters must be considered like :

1. Specific Impulse (Isp) - Itis a way to describe the efficiency

of rocket and jet engines. It represents the force with respect to the amount

of propellant used per unit time. If the "amount" of propellant is given in

terms of mass (such as in kilograms), then specific impulse has units

of velocity. If it is given in terms of weight (such as in kiloponds or newtons),

then specific impulse has units of time.

2. Delta V (∆V) - In astrodynamics a Δv or delta-v is a scalar which takes units

of speed. It is a measure of the amount of "effort" that is needed to change

from one trajectory to another by making an orbital maneuver. Delta-v is

produced by the use of propellant by reaction engines to produce a thrust that

accelerates the vehicle.

3. Mass Of Propellant (m) - The mass of the propellant is a very important

factor in determining the performance capabilities of a space bound vehicle.

The initial mass is designated as m1 and final mass as m2.

4. Weight Ratio (W.R) - The ratio of initial and final mass is referred to as the

weight ratio.

Considering Low Earth Orbit (L.E.O) at an altitude of 200 km, the value of acceleration

due to gravity (g) can be calculated as :

( )

(

)

(1)

Where, g(h)= Acceleration due to gravity at point h=200 km

R = Radius of Earth = 6371 km

g = 9.822 m/sec2

Therefore, g(h) = 9.22 m/sec2



Even though the value of g in LEO is appreciably high, yet the condition of microgravity

exists in the region. The reason being the value of g is cancelled and compensated by the

centripetal acceleration provided by the orbital motion of the satellite.

The approximate velocity of a satellite in the orbit is 25,580 ft/sec. The expression for

centripetal acceleration is given by:

Substituting the values in the expression;

a = 8.95 m/sec

2

Hence, the net amount of acceleration in the orbital region = 0.38 m/sec

2 , a very low

amount to experience the effect of weight.

For the given Cold Gas Propulsion System, the value of exhaust velocity (Ve) from the

nozzle is very low. It is related to Isp as follows :

( )

For the given system, Isp = 60 sec.

Hence, Ve = 22.8 m/sec

Now, ∆V is related to the other parameters as :

(

)

The initial mass of the cartridge would be 300 gm. If 10% of the propellant is used in the

process, the value of ∆V would be :

∆V= 2.40 m/sec.



Since the value of ∆V is very low, more number of cartridges are required which are

joined together to the suction chamber. Using four such cartridges containing the

propellant and using up 10% of the propellant;

∆V= 4x2.40 = 9.60 m/sec.

Hence, at operations where more propellant is required the other cartridges can be used to

provide additional value of ∆V and accomplish the maneuver.



CHAPTER 4:

LITERATURE REVIEW

CubeSats are often not placed in ideal orbits for their scientific payload simply because

they are transported to their orbit as “stowaways” on a launch vehicle designed to

transport a larger space vehicle whose orbital considerations take precedence. The

ability to maneuver from these non-ideal orbits would greatly extend the capabilities of

CubeSats. There have been various methods devised andformulated to be used on a

Cubesat. Some of them are :

4.1 Pulsed Plasma Thruster

A Pulsed Plasma Thruster (PPT), also known as a plasma jet engine, is a form of electric

spacecraft propulsion. PPTs are generally considered the simplest form of electric

spacecraft propulsion and were the first form of electric propulsion to be flown in space,

having flown on two Soviet probes (Zond 2 and Zond 3) starting in 1964. PPTs are

generally flown on spacecraft with a surplus of electricity from abundantly available solar

energy.

Most PPTs use a solid material (normally PTFE, more commonly known as Teflon) for

propellant, although a minority use liquid or gaseous propellants. The first stage in PPT

operation involves an arc of electricity passing through the fuel, causing ablation and

sublimation of the fuel. The heat generated by this arc causes the resultant gas to turn into

plasma, thereby creating a charged gas cloud. Due to the force of the ablation, the plasma

is propelled at low speed between two charged plates (an anode and cathode). Since the

plasma is charged, the fuel effectively completes the circuit between the two plates,

allowing a current to flow through the plasma. This flow of electrons generates a strong

electromagnetic field which then exerts a Lorentz force on the plasma, accelerating the

plasma out of the PPT exhaust at high velocity. The pulsing occurs due to the time needed

to recharge the plates following each burst of fuel, and the time between each arc. The

frequency of pulsing is normally very high and so it generates an almost continuous and

smooth thrust. While the thrust is very low, a PPT can operate continuously for extended

periods of time, yielding a large final acceleration.

The energy used in each pulse is stored in a capacitor.By varying the time between each

capacitor discharge, the thrust and power draw of the PPT can be varied allowing

versatile use of the system.



Figure 4.1 Pulsed Plasma Thruster

4.2 Resistojets

A resistojet is a method of spacecraft propulsion (electric propulsion) that provides thrust

by heating a (typically non-reactive) fluid. Heating is usually achieved by sending

electricity through a resistor consisting of a hot incandescent filament, with the expanded

gas expelled through a conventional nozzle.[1]

Resistojets have been flown in space since 1965 on board military Vela satellites,

however they became used in commercial applications in 1980 with launch of first

satellites in the INTELSAT-V program. Nowadays resistojet propulsion is used for orbit

insertion, attitude control, and deorbit of LEO satellites, including satellites in the Iridium

satellite constellation[1] and do well in situations where energy is much more plentiful

than mass, and where propulsion efficiency needs to be reasonably high but low thrust is

acceptable.

Fig. 4.2 Resistojet



4.3 Cold Gas propulsion

A cold gas thruster is a rocket engine/thruster that uses a (typically inert) gas as the

reaction mass.

A cold gas thruster usually consists of simply a pressurized tank containing gas, a valve to

control its release and a nozzle, and plumbing connecting them. A very simple example

would be the use of a handheld CO2 or nitrogen gas fire extinguisher while sitting down

in a rolling office chair; motion is achieved by pointing the nozzle in the direction

opposite of the desired movement and activating the extinguisher.

Because the gas is usually unheated, speed at the throat is low and very low performance

is achieved; in a vacuum with nitrogen gas a specific impulse of 68 seconds can be

achieved.

Cold gas thrusters are mostly useful for vernier engines, and are employed chiefly for

simplicity and reliability.

4.4 Research done by TNO

Based on its experience in ignition systems and rocket motors for space applications,

TNO has expanded its gas generating capabilities into four different areas of expertise

Small Propulsion

Based on the igniter experience TNO is developing innovative thrusters for attitude

control of launchers. Another research area is micro propulsion. TNO is developing some

of the smallest fully functional propulsion systems in the world based on hydrogen

peroxide or nitrogen gas using micro technology to miniaturise and integrate propulsion

components. Together with companies and universities it is advancing the technology

level in this field in Europe.

4.4.1 Cool Gas Generators:

This unique technology produces a pure cool gas from a solid (propellant) charge without

the need for external coolers. The technology is available for nitrogen and oxygen while

carbon dioxide and hydrogen cool gas generators are in development. Cool Gas

Generators are a very efficient, safe and rugged way to store gasses as they do not have

moving parts, are not pressurised and have no leakage during storage. Applications

of this technology are vast: from propulsion and inflatable structures in space to life rafts,

medical oxygen delivery and fire extinguishers on Earth. TNO is working with a number

of partners to develop products using the Cool Gas Generator technology, for example

Bradford Engineering for Space Applications and APP for Aeronautical Applications. In

all these fields TNO combines a strong theoretical background and

capabilities with the possibility to build,test and develop systems and products usually

together with its research and industrial partners.



Fig. 4.3 Cool gas generator designed by TNO (Photo Courtesy : TNO, Netherlands)

Currently TNO and senior researchers at Delft University are striving to build a fast acting

mechanical valve for the cold gas propulsion system.

Fig. 4.4 Schematic Diagram of a Cold Gas Propulsion System

4.5 Modifications in the system:

Due to the unavailability of certain components and difficulty in solidifying nitrogen gas,

several alternatives were adopted to make the proposed system work.

Firstly, instead of using nitrogen gas , Tetrafluoroethane was used as a propellant in the

gaseous form, the properties of which are as follows:

Molecular weight : 102.03 g/mol

Solid phase

Melting point (1.013 bar) : -101 °C

Liquid phase

Liquid density (1.013 bar and 25 °C (77 °F)) : 1206 kg/m3

Boiling point (1.013 bar) : -26.55 °C

Latent heat of vaporization (1.013 bar at boiling point) : 215.9 kJ/kg

Vapor pressure (at 20 °C or 68 °F) : 5.7 bar






Critical temperature : 100.95 °C

Critical pressure : 40.6 bar

Critical density : 512 kg/m3

Triple point

Triple point temperature : -103.3 °C

Gaseous phase

Gas density (1.013 bar at boiling point) : 5.28 kg/m3

Gas density (1.013 bar and 15 °C (59 °F)) : 4.25 kg/m3

Compressibility Factor (Z) (1.013 bar and 15 °C (59 °F)) : 1

Specific gravity : 3.25

Specific volume (1.013 bar and 15 °C (59 °F)) : 0.235 m3/kg

Heat capacity at constant pressure (Cp) (1.013 bar and 25 °C (77 °F)) : 0.08754

kJ/(mol.K)

Miscellaneous

Solubility in water (1.013 bar and 25 °C (77 °F)) : 0.21 vol/vol

In addition to that, use of solenoid valves were avoided due to its unavailability. The

Freon gas (also known as tetrafluoroethane) was passed through a pipe from the gas

cylinder into the suction chamber and was allowed to pass through the nozzle. The exit

velocity of the gas coming out of the nozzle was measured and the specific impulse was

calculated.

Fig.5.5 Model without the solenoid valves and solid propellant



CHAPTER 5:

RESULTS AND DISCUSSIONS

The exit velocity of the gas was calculated using pitot tube fitted at the nozzle end.

The difference in pressure in the manometer gave the velocity :

V=(2(p0-p)/density of air)^1/2.

The exit velocity was found out to be

The exit velocity in turn gives specific impulse, Isp= V/g

The specific impulse was found to be

which is close enough to that required in a cubesat.



Chapter 6:

FUTURE WORK

We look forward to carry this research on this cold gas propulsion system for Cubesats

and nanosatellites in order to make orbital maneuvers, formation flying, etc. and most

importantly de-orbiting possible to deal with problems of space debris. The model

presented as a part of this project is only to check the feasibility of the system. We have

been lucky enough to receive an internship opportunity at the Tartu Space Observatory,

Estonia where we would be working on a flight model of this system under Dr. Mart

Noorma. As interns at the observatory and as part of the Estonian student satellite

program, our prime focus would be on the feasibility of the system which would fly

onboard a Cubesat named Estcube-2. This would present the right set of circumstances to

get hands-on experience on the industry model of this propulsion system. We hope to

exploit this opportunity to learn the intricacies and complexities of a flight model in order

to develop our system.



CHAPTER 7:

CONCLUSION

With major space actors and organizations realizing the huge potential for manufacturing

Cubesats, the use of a propulsion system is inevitable, and with the weight constraint

upto approximately 4kg, the cold gas propulsion system provides the most viable

option to be used on a 3U Cubesat, without compromising on the structural integrity and

performance capabilities of the microsatellite. The study has emphasized the practicality

and the usability of such a system. To the best of the knowledge of our team, the use of

lasers for initiating the system and the internal design of the system has not been

implemented in any system



CHAPTER 8:

REFERENCES

[1]Cote, K., Gabriel, J., Patel, B., Ridley, N., Taillafer, Z., & Tetreault, S.

(n.d.).Mechanical,Power and Propulsion subsystem Design for A Cubesat. Worcester

Polytechnic Institute.

[2]Cubesat Design Specification Rev. 12. (n.d.). Calpoly SLO: California Polytechnic

State University.

[3]Mueller, J., Hofer, R., & Ziemer, J. (n.d.). Survey of Propulsion Technologies

Applicable To Cubesats. Pasadena, CA: Jet Propulsion Laboratory, California Institute Of

Technology.

[4]Nothnagel, S. L. (2009). Development of A Cold Gas Propulsion System for the

TALARIS Hopper. University of Southern California.

[5]Sanders, B., Schuurbiers, C., Vliet, L. v., & Nardini, F. T. (2010). ResultsOf

Qualification and Flight Tests of Cool Gas Generators. Space Propulsion Conference.

San Sebastian,Spain.

[6]Zaken, K. (n.d.). Innovative Plug and Play Micropropulsion Systems. Retrieved

August 30, 2013, from www.tno.nl: http://www.tno.nl/gasgenerators.

[7] http://eprints.eemcs.utwente.nl/14567/01/PMME_45.pdf

http://www.tno.nl/

http://www.tno.nl/gasgenerators

http://eprints.eemcs.utwente.nl/14567/01/PMME_45.pdf

DESIGN OF COLD GAS PROPULSION SYSTEM FOR A CUBESAT

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