In-Space Propulsion Systems

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In-Space Propulsion Systems Low
Thrust Micropropulsion Michael M. Micci The
Pennsylvania State University Presented at
the NASA Technology Roadmaps Propulsion and
Power Workshop National Research
Council California Institute of
Technology Pasadena, CA March 22, 2011
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My background
Micropropulsion for Small Spacecraft, edited by
M. M. Micci and A. D. Ketsdever, Progress in
Astronautics and Aeronautics, Vol. 187, AIAA,
2000. 30 years on the faculty of The
Pennsylvania State University. Experimental
experience with Solid and liquid propellant
rockets Microwave and RF plasma electrothermal
thrusters Miniature RF and microwave ionization
ion thrusters Year sabbatical in electrospray
lab at University of London, QM.
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Micropropulsion 2.2.1.4

• By definition Low Thrust
• But also
• Low electrical power
• Low mass
• Low volume
• Precise thrust and impulse bits
• Low cost

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Micropropulsion

• Propulsion for microsats, nanosats, and CubeSats.
• But theyre not just for small spacecraft
  anymore.
• Useful anytime low thrust or impulse bits are
  required.
• Drag make-up (GRACE)
• Formation flying (LISA)
• Asteroid and planetoid orbits
• Close proximity (Inspector) missions
• Precise positioning missions (JWST occulter)
• Franklin and Edison microspacecraft missions

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Micropropulsion

• You cant just scale down a current thruster and
  expect the same
• performance.
• Physical processes detrimentally affecting
  micropropulsion
• Large surface to area ratios.
• Higher heat losses than larger scale devices.
• Small flow passages.
• High viscous losses, both in nozzles and flow
  passages.
• Subject to flow blockage due to contamination
  and bubbles.
• Smaller volumes for charged particle
  containment.
• Lower charged particle residence times.
• Higher magnetic fields required for charged
  particle confinement.
• Small thrust and propellant mass flow levels.
• Difficulty making accurate thrust and flow rate
  measurements.

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Micropropulsion
Eight technologies listed in NASA
Roadmap Chemical 2.1.7.1 Solids 2.1.7.2 Cold
Gas/Warm Gas 2.1.7.3 Hydrazine or H2O2
Monopropellant Electric 2.2.1.4.1 Microresistoje
ts 2.2.1.4.2 Microcavity Discharge 2.2.1.4.3 Mic
ropulse Plasma 2.2.1.4.4 Miniature
Ion/Hall 2.2.1.4.5 MEMS Electrospray
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Solids 2.1.7.1
Advantages High TRL level (gt6). Simplicity. No
need for liquid or gas storage and
management. Disadvantage No controllability. Co
mment No discussion of digital microthrusters,
which have been investigated and would provide
controllability and scalability.
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Cold Gas/Warm Gas 2.1.7.2
Advantage High TRL level (gt6) due to
simplicity. Disadvantages Low performance (Isp)
compared to other devices. Leakage from small
valves. Need to contain high pressures if high
performance is desired. Comment Do we really
want to invest more in this due to
low performance?
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Hydrazine or H2O2 Monopropellant 2.1.7.3
Advantages High chemical performance (Isp) and
controllability. Disadvantages Lower TRL levels
for smaller thrusters. High heat losses for
smaller thrusters. Comment No discussion of low
toxicity (HAN-based) monopropellants which would
simplify handling while improving performance.
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Microresistojets 2.2.1.4.1
Advantages High TRL level due to large scale
heritage. Simplicity. Disadvantage Low
performance (Isp) compared to other
devices. Comments Do we really want to invest
in this due to low performance? No discussion
of Free Molecular Micro-Resistojet (FMMR)
developed by AFRL and Air Force Academy.
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Microcavity Discharge 2.2.1.4.2
Advantages Higher performance than
resistojets. Scalable to very small dimensions
(MEMS based) as well as to large scale to obtain
high thrust. Disadvantages Low TRL
levels. High heat losses and electrode
erosion. Comment No discussion in Roadmap of RF
or microwave discharges, both of which are under
development and show the potential for increased
performance and longer lifetimes due to
electrode-less operation.
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Micropulse Plasma 2.2.1.4.3
Advantages Easy to miniaturize. Can use solid
propellants. Disadvantages Pulsed operation
effect on power system design (capacitors and
switches). Low overall system efficiencies. Elec
trode erosion due to pulsed operation. Comment N
o discussion of Micro Pulsed Plasma
Thruster developed to a high TRL level by AFRL.
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Miniature Ion/Hall 2.2.1.4.4
Advantages Potential for high performance (Isp
and efficiency). Uses inert propellants
(xenon). Disadvantages Lower charged particle
residence times. Need to increase magnetic field
strengths to maintain charged particle
confinement. Need small electron sources (hollow
cathodes). Comment No discussion of miniature
(1 cm) low power (10 W) ion thrusters using RF
and microwave ionization developed at Penn State
and in Japan.
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MEMS Electrospray 2.2.1.4.5
Advantages High TRL level (7), scheduled for
LISA Pathfinder. High performance (Isp and
efficiency). Can take advantage of MEMS
technology. Scalable to high thrust. Disadvantag
es Propellant distribution to large numbers of
emitters. Flow blockage due to contaminants and
bubbles. Electrochemical degradation of
emitters. Comment Shows great promise if above
problems can be solved.
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Micropropulsion Other thoughts

• Micropropulsion is a relatively young technology
  but is
• poised to make a large impact on NASA current,
  planned
• and unforeseen missions near the tipping
  point.
• Micropropulsion advances technology that has
  application
• outside of aerospace, for example electrosprays
  and
• miniature plasma sources in the biomedical and
  electronic
• fabrication areas.
• Micropropulsion, through its small size, allows
  substantial
• small business, academic and student
  participation.

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Micropropulsion Summary of Roadmap comments

• Many potential high-performing concepts will
  require
• an investment to increase TRL levels but are
  worth it
• and are near term.
• Too many non-NASA concepts are not discussed in
• the Roadmap (Not invented here?).
• Too much emphasis on low performing technologies.