State of the art Ion Engines

What's the current state of the art in ion engines? How well
do they do, and when one adds solar panels (or some other energy source)
and such to the mix, what's the thrust/weight ratio?


Ion engines are the current winner in the very-low-acceleration game, right?


-Much Thanks

"Charles Talleyrand" wrote in message ...
What's the current state of the art in ion engines? How well
do they do, and when one adds solar panels (or some other energy source)
and such to the mix, what's the thrust/weight ratio?

Low.

I think I've found "60kg per Newton of thrust" for Hall thrusters, but
that's not counting solar panels.

Ion engines are the current winner in the very-low-acceleration game, right?

Ion engines are "winners" in the sense of having more high profile
flight experience. The other electric engines used (typically for
station keeping) have less exciting missions.

Flip through the electric engines section of:

http://www.islandone.org/APC/

There's a surprising number of low acceleration engines that have been
flown. Arcjets, resistojets, hall thrusters, ion engines, etc. I'm
partial to Magnetoplasmadynamic (MPD) thrusters, personally, because
some forms of them can operate directly off solar cell power feeds and
they have high efficiencies. Plus, the pictures are kewl.

Mike Miller, Materials Engineer

http://www.islandone.org/APC/Electric/00.html

In article ,
Charles Talleyrand wrote:
What's the current state of the art in ion engines? How well
do they do, and when one adds solar panels (or some other energy source)
and such to the mix, what's the thrust/weight ratio?

Pretty poor. :-) It's difficult to find useful numbers, because there
are so many variables. The power-conditioning electronics behind the
engine often considerably outweigh the engine itself, and then there
are the solar arrays...

Deep Space 1's engine hardware (including electronics) was 48 kg, giving
92 mN of thrust and 30 km/s exhaust velocity, using 3 mg/s of xenon, at
full power (2.5 kW, which the spacecraft in fact couldn't quite deliver).
You can probably do better than that -- it was a conservative design.

Solar-array masses depend on how optimistic you are (and how careful you
are about accounting for *all* support hardware etc. -- inflated numbers
counting only part of the hardware are common). For the entire system,
40 W/kg is routine, 100 W/kg is aggressive and experimental, and really
optimistic people think several hundred W/kg could be had with determined
use of new technologies.

Ion engines are the current winner in the very-low-acceleration game, right?

Depends on what you mean by "winner". :-) They're the obvious choice right
now if you have lots of power, don't need much thrust, and absolutely need
high Isp (i.e., minimum propellant consumption). They lose badly if you
have limited power or need significant acceleration.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

"Charles Talleyrand" writes:

What's the current state of the art in ion engines? How well
do they do, and when one adds solar panels (or some other energy source)
and such to the mix, what's the thrust/weight ratio?

The current state of the art in ion thrusters is probably the
Boeing XIPS-25, as used on the 702 series comsats. But that's
a proprietary system, and so hard data is scarce.

The NSTAR ion thruster used on the NASA DS-1 spacecraft, is still
fairly good, and there's plenty of data on that. Nominally uses
2.3 kW of electric power to produce 92 mN of thrust at a specific
impulse of 3,120 seconds, though you can tweak all of those values
as circumstances demand.

Weight of the bare thruster I have as 8.3 kg, giving a thrust/weight
ratio of 1/885. But wait(weight?), there's more. The thruster doesn't
just plug into a wall outlet and a Xenon bottle. It needs a power
processing unit which masses 15 kg and a propellant management assembly
that masses 20.2 kg, so the thrust/weight ratio of the complete system
is 1/4,640.

Assuming your solar arrays and associated hardware have a specific
power of 40 W/kg, which again is pretty much state-of-the-art, you
need another 57.5 kg of solar to get that 2.3 kW, which brings the
total mass to 101.0 kg and the overall T/W ratio to 1/10,770.


This illustrates something that often gets overlooked in cursory
analysis of advanced propulsion systems. The mass (and cost, complexity,
etc) of the thruster is usually small compared to that of the PPU and
other necessary support systems, and the mass of the propulsion system
as a whole is usually small compared to the mass of the power system.

People look at, wax enthusiastic about, and try to improve the performance
of bare thrusters, because Ion Drives! are cool and sexy and all that, but
what matters is the systems engineering that goes into boring old switching
power supplies and gas flow controllers and whatnot.


Ion engines are the current winner in the very-low-acceleration game, right?

Oh, there are propulsion sytems that offer much lower acceleration than
that :-)

I know what you mean, though, and it's not clear that Ion engines are
the winner in that regime. Their main competition is a sort of plasma
thruster called the Hall Effect Thruster or Stationary Plasma Thruster,
depending on who you talk to. Somewhat less specific impulse, but
correspondingly more thrust.

State of the art there is the Fakel SPT-140. 4.5 kW of power gives
290 mN of thrust at a specific impulse of 1770 seconds, again all
tweakable to mission demands. Bare thruster mass 6.8 kg, PPU mass
13.7 kg, propellant management I don't have good numbers for but
previous Fakel SPTs all used a 3.9 kg PMA.

So, propulsion system T/W is 1/825. Add in the 112.5 kg solar
arrays needed for that 4.5 kW, and your T/W drops to 1/4630.
More than twice the value for the NSTAR ion thruster, at slightly
more than half the specific impulse.


Most of the missions I look at, the SPT-140 is the winner. But
sometimes pure Isp is what is needed, even if your thrust drops
off the bottom of the scale, and there are applications for ion
thrusters as well.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *

"Charles Talleyrand" writes:

What's the current state of the art in ion engines? How well
do they do, and when one adds solar panels (or some other energy source)
and such to the mix, what's the thrust/weight ratio?

The current state of the art in ion thrusters is probably the
Boeing XIPS-25, as used on the 702 series comsats. But that's
a proprietary system, and so hard data is scarce.

The NSTAR ion thruster used on the NASA DS-1 spacecraft, is still
fairly good, and there's plenty of data on that. Nominally uses
2.3 kW of electric power to produce 92 mN of thrust at a specific
impulse of 3,120 seconds, though you can tweak all of those values
as circumstances demand.

Weight of the bare thruster I have as 8.3 kg, giving a thrust/weight
ratio of 1/885. But wait(weight?), there's more. The thruster doesn't
just plug into a wall outlet and a Xenon bottle. It needs a power
processing unit which masses 15 kg and a propellant management assembly
that masses 20.2 kg, so the thrust/weight ratio of the complete system
is 1/4,640.

Assuming your solar arrays and associated hardware have a specific
power of 40 W/kg, which again is pretty much state-of-the-art, you
need another 57.5 kg of solar to get that 2.3 kW, which brings the
total mass to 101.0 kg and the overall T/W ratio to 1/10,770.


This illustrates something that often gets overlooked in cursory
analysis of advanced propulsion systems. The mass (and cost, complexity,
etc) of the thruster is usually small compared to that of the PPU and
other necessary support systems, and the mass of the propulsion system
as a whole is usually small compared to the mass of the power system.

People look at, wax enthusiastic about, and try to improve the performance
of bare thrusters, because Ion Drives! are cool and sexy and all that, but
what matters is the systems engineering that goes into boring old switching
power supplies and gas flow controllers and whatnot.


Ion engines are the current winner in the very-low-acceleration game, right?

Oh, there are propulsion sytems that offer much lower acceleration than
that :-)

I know what you mean, though, and it's not clear that Ion engines are
the winner in that regime. Their main competition is a sort of plasma
thruster called the Hall Effect Thruster or Stationary Plasma Thruster,
depending on who you talk to. Somewhat less specific impulse, but
correspondingly more thrust.

State of the art there is the Fakel SPT-140. 4.5 kW of power gives
290 mN of thrust at a specific impulse of 1770 seconds, again all
tweakable to mission demands. Bare thruster mass 6.8 kg, PPU mass
13.7 kg, propellant management I don't have good numbers for but
previous Fakel SPTs all used a 3.9 kg PMA.

So, propulsion system T/W is 1/825. Add in the 112.5 kg solar
arrays needed for that 4.5 kW, and your T/W drops to 1/4630.
More than twice the value for the NSTAR ion thruster, at slightly
more than half the specific impulse.


Most of the missions I look at, the SPT-140 is the winner. But
sometimes pure Isp is what is needed, even if your thrust drops
off the bottom of the scale, and there are applications for ion
thrusters as well.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *