Post on 31-Mar-2015
Nanoparticle Electric Propulsion for Space Exploration
Phys 483Monday, March 31 2008
Team 1: Perry Young,
Kiyoshi Masui,
Mark Hoidas,
Andrew Harris
Deep Space 1 Launched in October 1998
Meant to test 12 new technologies that were too risky for previous missions
Among those technologies was an ion thruster, a type of electric propulsion Represented a departure from conventional chemical propellants
Deep Space 1 completed successfully completed an extended mission and was retired at the start of 2002
The ion thrusters provide a high fuel efficiency, reducing the propellant load, and a low thrust, which is compensated for through long acceleration times.
Recently it has been proposed that this system could be improved upon by using conductive nanoparticles in place of the xenon ions, which would increase the level of control that can be gained over the induced charge. This is termed a nanoparticle field extraction thruster or nanoFET
Background
Propellant is a major component of mass transported in space travel
Solar electrical energy is available in the solar system
Mass efficiency can be increased by electrically accelerating propellant to high energy
More momentum gained per unit mass of propellant
Theory and Definitions
Propulsion systems often quote specific impulse Isp (in s/g), momentum gained per unit mass of propellant
Isp describes how effectively an engine consumes mass Another measure of an engine is thrust to power ratio
which describes how effectively an engine consumes energy
There is a trade off between these two quantities, classically:
p
m
p
mp
E
p
P
Fm
pI sp
222
Ion Engines
Comparable in concept to nanoparticle electric propulsion Ion engines have already been tested in space flight Provide low trust but excellent propellant efficiency
Apparatus
Cylindrical nanoparticles transported through a thin layer of liquid, which is either dielectric or conductive
Particles charged and field-focusing extracts them from liquid
Charges particles accelerated through the a potential and expelled from thruster
Dielectric Liquid Configuration
Particles charged by contact with a conducting plate
Particles with sufficient charge travel from the plate to liquid surface through the potential V0
Main loss due to viscous drag and charge loss traveling from the plate to the liquid-vacuum interface
Conductive Liquid Configuration
Particles only become charged at liquid surface due to vacuum potential
Passive transport to surface through thermal motion or convective mixing
No charge losses due to liquid
Apparatus
Stacked gate design Ability to provide large acceleration potentials
without exceed individual gate breakdown threshold
Decoupling of acceleration potential from potential applied to liquid in dielectric configuration
The specific charge on a nanoparticle in a dielectric liquid is a function of the applied field, the fluid properties and especially the particle geometry
This geometry can be controlled
The relationship between specific charge and specific impulse therefore implies that the Isp can be controlled by the particle geometry
By using several sets of nanoparticles a very wide range of Isp conditions can be obtained.
Efficiency
Carbon Nanotube particles
1:5 nm diameter|100 nm length
2:1 nm diameter| 10 nm length
3:1 nm diameter | 3.5 nm length
Potential: 800 V – 10 kV
Simulation with three different sizes of carbon nanotubes in silicone oil
Combined, they span the Isp range of all other electrical propulsion technologies.
Cost
Summary
-reduce propellant load
-flexibility (allowing Isp optimization)
-engine design and mission planning are decoupled
-compact low mass due to MEMS technology
-lower maintenance then ion engines (Xenon surface erosion)
-avoid complications due to ion optics
Nanoness-control of the specific charge with respect to the particle geometry is specific to nanoparticles
-replacing microscopic atoms with nanoparticles which can be electrostatically charged