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