January 05, 2011

IEC thrusters for satellite maneuvering - actual experiments

Space Probe Application of IEC Thrusters

A novel plasma jet thruster, based on Inertial Electrostatic Confinement (IEC) technology, is under development for an ultra maneuverable - space thruster for satellite and small probe thrust operations. The IEC Jet design potential offers unique capability to cover a wide range of powers (few Watts to Kilowatts) with good efficiency while providing a plasma jet that can start with a large diameter but be narrowed directionally to focus on targets.

This is part of several lab experiments that are in progress related to a larger nuclear fusion space propulsion effort. They have lab work for the jet thrusting and there has been other lab work for other parts. Various grants funded different work over the last few decades. i put up a post on some lab work related to a satellite maneuvering thruster competitor using this tech and what they have not revealed the details of is a new system which will get ten times the thrust of Hall Thrusters. So Richard Dell Jr and George Miley are saying that they will within a few years (3-5 year ?) get to about (my guess) 2-3 Newtons with my guess of 1000-3000 ISP. I would guess that there is new lab work that provides justification for this case but not until the later this year or next year for the "breakthrough in small nuclear fusion" to firm up.

Space thrusters for orbit insertion and station keeping have been using hydrazine propellant more recently for large GEO satellites, Arc Jet Thrusters which electrostatically enhance the hydrazine propellant. High Power Hall Current Thrusters electrostatically accelerating Xe ions have been developed by NASA with at discharge power levels ranging from 6.4 kilowatts to 72.5 kilowatts. The device produced thrust ranging from 0.3 newtons to 2.5 newtons and specific impulses up to 4500 sec at 1 kV. More recently AeroJet together with Lockheed Martin Space Systems Company has qualified 4.5 kW Hall Thruster Propulsion System (HTPS) which will be used on military communication satellites and has demonstrated 244 mN of thrust with specific impulse of 1981 s at 400 V acceleration. The total thruster mass including power processor unit is 25.85 kg and life testing has demonstrated in excess of 4500 hrs of operation.

The IEC device is basically a spherical plasma diode. It has a ground potential on an outer sphere, and a negative potential on a transparent inner spherical grid. Ions are generated in a discharge region between the vacuum chamber wall and the grid. Adding electron emitters at the boundary and additional electrical grids near the grounded outer sphere can increase and control the efficiency and better localize the generation rate of ions in the device and is proposed later for the thruster design. That configuration also allows the device to operate at much lower gas pressures.

To obtain thrust from an IEC device, a valley or trough must be created in the electrostatic potential, and a hole must be physically cut into the ground sphere. This allows high-speed ions to escape in the form of a plasma jet, as described in the preceding section. Ions are generated near the ground potential with the aid of electron emitters and additional grids. A central spherical electrical grid accelerates ions to the core region. A cylindrical "channel" grid with the same electrostatic potential as the central spherical grid creates a passage through which ions can escape to the outside. Thus this trough in the electrostatic potential profile across the centerline (thrust axis) of the IEC thruster is a unique feature compared to the linear profile for a planar device.

Pulsed operation requires state-of-the-art pulsed power technology to achieve high peak currents, thus taking advantage of the strong scaling with current. Scaling the data from the prior study, the 100-kWe IEC power plant is estimated to weigh about 100 kg, exclusive of cooling radiators. This result is very encouraging for use with future 100 kW commercial space power applications discussed earlier

The attractive characteristics of the electrically driven device, namely light weight, low maintenance, low fuel leakage and extreme maneuverability make it a near-term competitor with other devices such as Hall thrusters for future commercial thruster applications in the multi-kW range.

IEC Ion Thruster

Present experimental studies use an existing spherical IEC chamber of ~30-cm with a 1-cm diameter port on one side of it for beam extraction (this unit is somewhat larger than needed for micro-satellites). An 8-cm diameter spherical electrical tungsten or tantalum wire grid, having a geometric transparency of ~90%, will be mounted inside the chamber.

Specific Impulse (s ) 3000
Thrust (mN) 34
Jet Power (W) 500
Net accelerating Potential (V) 600
Beam Current (mA) 832
Power Loss to Grid (W) ≤50
Power Loss to Bresstrahlung Radiation (W) < 1 Power loss to Ionization of Propellant (W) 200-250 Input Power (W) 750-800 Thruster Efficiency (%) 62-68 If you liked this article, please give it a quick review on ycombinator or StumbleUpon. Thanks
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