Efficiency of VASIMR and ion thrusters.

Does anyone know the expected efficiency for the VASIMR for various ve, in
terms of conversion of electric power to thrust? Also for the currently used
ion drives and future proposals? Also, how much do they mass for various
power handling capabilities? Any figures for MTBF.

--Roger

"Roger Stokes" writes:

Does anyone know the expected efficiency for the VASIMR for various ve, in
terms of conversion of electric power to thrust?

Expected by whom?

For figures claimed by the proponents, an IEPC (Inernational Electric
Propulsion Conference) paper this year specified a 24 kW VASIMR with
51% efficiency at 10,000 seconds Isp.

This being a viewgraph rocket, the range of expectation regarding its
actual efficiency run from 0% to 51%.


Also for the currently used ion drives and future proposals?

The NSTAR ion thruster used on DS1 demonstrated an efficiency of 61%,
at 2.3 kW power and 3120 seconds Isp.

There are again viewgraph thrusters with predicted efficiencies which
are all over the board, and Boeing's operational XIPS series whose
exact performance is I believe proprietary.


Also, how much do they mass for various power handling capabilities?

The proposed 24 kW VASIMR massed 84 kilograms; I don't know if that
was just the bare thruster or also included the power processing unit
and propellant management system. Those usually outweigh the thruster
itself, and an honest assessment must include them, but some people
get sloppy and/or deceptive, and you can't take it for granted that
a published "thruster mass" includes a complete propulsion system.

The NSTAR ion engine, a 2.3 kW system, massed 8.3 kilograms for the
thruster. I have figures of 15 kg for the PPU and 20.2 kg for the
PMS, but I am less certain of the accuracy of those values.


Any figures for MTBF.

The NSTAR ion engine had a design life of 12,000+ hours. VASIMR,
is not yet sufficiently real for engineers to talk meaningfully
about design life, MTBF, or such things.


--
*John Schilling * "Anything worth doing, *
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If quantum nucleonics ever turns nuclear isomers into a viable power
source, perhaps the nuclear isomers could be used to power a VASIMR
engine.

Under X-ray stimulation, the isomers would release their internal
energy as gamma rays which might then be used to power the helicon and
ICRH wave antennae for the ionization and heating of the propellant
stream.

This might then serve as a powerful and compact energy source, for
SSTO vehicles.

(sanman) writes:

If quantum nucleonics ever turns nuclear isomers into a viable power
source, perhaps the nuclear isomers could be used to power a VASIMR
engine.

Under X-ray stimulation, the isomers would release their internal
energy as gamma rays which might then be used to power the helicon and
ICRH wave antennae for the ionization and heating of the propellant
stream.

As we keep telling you, the original that claim the second paragraph
of your wishful thinking is based on has been =VERY= solidly debunked !
There is no =CONFIRMED= evidence that puny little dental X-rays at
mere keV energies can "stimulate" nuclei to emit gamma-rays with
energies that are THREE ORDERS OF MAGNITUDE HIGHER, and the very idea
that they could was just plain physically nuts to begin with !!!

Moreover, as we AGAIN keep telling you, even if the claim =WASN'T= false,
high-energy gamma rays really =SUCK= as an energy source !!! There is
=NO= physically plausible mechanism for "directly converting" gamma rays
into electricity. Nor can gamma rays be directly used to power a rocket,
because they are simply FAR TOO PENETRATING, and are =NOT= absorbed well
by any reasonably thickness of gas or most liquids, leading to a very low
=EFFECTIVE= power density (you have to take into account the thickness
and mass of the absorbing blanket in the power-density calculation). Hence,
trying to use gamma rays to power a heat-engine or rocket is simply =NUTS= !!!

Please note that the physics of the Universe we actually live in differ
quite significantly from those in "The Mighty Marvel Universe(tm)," where
Dr. Bruce David Banner can build powerful "gamma reactors" and "gamma bombs."
Over here, in the Universe we _actually_ live in, IIRC we haven't even had
a confirmed observation of a gamma-ray laser yet, despite several _DECADES_
of research that has gone into trying to build one !!!


This might then serve as a powerful and compact energy source, for
SSTO vehicles.

And if pigs had wings, they could fly, maybe ???


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

"Roger Stokes" wrote in message .. .
Does anyone know the expected efficiency for the VASIMR for various ve, in
terms of conversion of electric power to thrust?

Low. The ISP starts at 30,000m/s and goes up to 300,000 m/s. This is
much, much higher than the likely mission delta-v to Mars of about
6,800m/s. From the point of view of getting the minimum energy usage,
for a fixed ISP, the optimum ISP is about 2/3 the mission delta-v, and
for the same power, thrust is inversely proportional to ISP. Of course
VASIMR trumpets the variable ISP aspect, but it starts somewhat too
high and goes up from there. The upshot is that VASIMR needs lots, and
lots and lots of energy. And energy production in space is difficult.

Now the proponents of this drive claim that the energy source to make
it work is quite possible. Trouble is, if that is true, then the
other, lower ISP drives gain even more from using that same power
source. Of course the other drives need more fuel, but all electric
propulsions all use relatively little fuel anyway, so the extra costs
of fuel are not so very large.

Also for the currently used ion drives and future proposals?

Hall effect thrusters look fairly good. The main problem is to keep
the ISP down nearer to the mission delta-v, whilst using cheap fuel
and not wasting too much energy as heat. Hall Effect thrusters
allegedly can run on 95% oxygen, have relatively low ISP, and are
about 50% efficient in terms of wasted energy. Whether they can hit
these figures simultaneously is another question however.

Also, how much do they mass for various
power handling capabilities? Any figures for MTBF.

Hall effect thrusters have lifetimes in the 10s of thousands of hours
and atleast as good MTBF.

--Roger

John Schilling wrote:
"Roger Stokes" writes:
snip

Also, how much do they mass for various power handling capabilities?

The proposed 24 kW VASIMR massed 84 kilograms; I don't know if that
was just the bare thruster or also included the power processing unit
and propellant management system. Those usually outweigh the thruster
itself, and an honest assessment must include them, but some people
get sloppy and/or deceptive, and you can't take it for granted that
a published "thruster mass" includes a complete propulsion system.

The NSTAR ion engine, a 2.3 kW system, massed 8.3 kilograms for the
thruster. I have figures of 15 kg for the PPU and 20.2 kg for the
PMS, but I am less certain of the accuracy of those values.

Though power supply technology is improving quite rapidly, being driven
hard by the need for lighter laptops etc, so the age of the PPU mass estimate
may be needed too.


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http://inquisitor.i.am/ | | Ian Stirling.
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Just what I choose it to mean - neither more nor less." -- Lewis Carrol