Re: 72 kw - 3N Ion Engine

From: Richard Hofer (rhofer99_at_yahoo.com)
Date: 12/14/04 

To: sci-space-tech@moderators.isc.org
Date: 14 Dec 2004 06:03:29 -0800

As others have pointed out, the press release was written for a general
audience, so there are some confusing aspects of it. I worked on the
design of the NASA-457M at NASA GRC, so hopefully I can clarify a
couple of things.

First, the 72 kW/3 N operating point corresponded to:
650 V, 111 A, 71963 W (total power was 73201 W)
102.7 mg/s total xenon flow rate
2.95 N thrust
2930 s total specific impulse
58% total efficiency

The reference is:
Manzella, D. H., Jankovsky, R. S., and Hofer, R. R., "Laboratory model
50 kW Hall thruster," AIAA-2002-3676, 38th Joint Propulsion Conference,
Indianapolis, IN, July 7-10, 2002.
(You can download this paper at my website:
http://richard.hofer.com/research.html)

In the world of electric propulsion, if you want to talk performance
you need to define the following performance parameters:

Thrust-to-power ratio: T/P
Specific Impulse: Isp = T/mdot/g
Efficiency: h = T^2 / 2 / mdot / P

where,
T = thrust
P = total power input
Isp = specific impulse
mdot = total mass flow rate
g = acceleration of gravity = 9.81 m/s^2
h = total efficiency

There are lots of good books out there that go over this in more
detail, such as Sutton's "Rocket Propulsion Elements." In my
dissertation, I go over how the performance parameters for a Hall
thruster are defined in considerable detail (Chap. 4).

Since this paper, we've actually operated the 457M up to 100 kW. There
is another thruster, the NASA-400M which was also fabricated to study
high-power operation on Krypton propellant and we have recently been
awarded contracts to develop even high powered models.

Rich Hofer