Author Topic: Power Supply for VASIMR  (Read 30430 times)

Offline TyMoore

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Re: Power Supply for VASIMR
« Reply #80 on: 05/13/2008 12:20 PM »
Given constant jet power, when utilizing a heavier molecular weight propellant stream, then all other things being equal, the speed of the ejected jet ought to be roughly proportional to 1/sqrt(m.w.) when compared hydrogen...

One of the greatest utilities of VASIMR is its inherent ability to be able to process different propellant streams--this allows us to contemplate the possibility of utilizing a less efficient but more plentiful and denser cryogen: oxygen.

I've actually written to Dr. Franklin Chang-Diaz (the inventor of the VASIMR concept) proposing this mode. According to him, the biggest hurdle in using oxygen as reaction mass is that singly ionized oxygen is probably one of the most chemically reactive species in the universe--as such, erosion of internal engine components from bombardment and sputtering of oxygen ions and neutral atomic oxygen will be a huge hurdle.

As far as performance metrics are concerned--that is a wide open field. There are multitudes of different ways to achieve the same thing. Each mission is different, and so a specific analysis needs to be made for a given mission and each engine operating mode would have to be explored--a complex undertaking to say the least.

However, in general, it is better to increase the Isp so that total mission delta-V is maximized for the available propellant. This can be achieved by dumping more energy into the exhaust stream. In the VASIMR concept this is done by dumping more power into the RF (radio frequency) ion-cyclotron resonance heater helicon antenna and thinning out (leaning) the plasma...though your Isp will increase, your thrust will decrease. And this begins a whole new level of optimization because long integration times at low thrust are slightly less propellant efficient than high thrust low integration times. It has to do with how much propellant is used to accelerate propellant still onboard--generally you want to reduce that as much as possible...

And again, this becomes a mission specific optimization--because at what point are the mission parameters satisfied (mission success: payload delivered) for a reasonable propellant expenditure. When is it good enough?

Offline lewis886

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Re: Power Supply for VASIMR
« Reply #81 on: 07/22/2008 12:05 AM »
did they ever do their test?  i have seen all kinds of things mentioning that they had a test planned for this year (early 2008, then changed to Q2 2008.)  just wondering if it's actually happened yet, or if we're still waiting on it.

Offline lewis886

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Re: Power Supply for VASIMR
« Reply #82 on: 08/06/2008 08:28 PM »
could a high power laser be a possible power supply?  or maybe be used in conjunction with other power supplies?  just wondering... because it seems that the power requirements are pretty steep... and combing VASIMR with Beamed Energy might be an interesting marriage....   then again i don't know if there's even a good efficient way to transform the beam into usable electrical energy.... dunno....
just a thought....

Offline iamlucky13

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Re: Power Supply for VASIMR
« Reply #83 on: 08/06/2008 11:06 PM »
Interesting development on the Vasimir front:

http://www.flightglobal.com/articles/2008/08/05/226329/nasa-to-test-plasma-engine-on-space-station.html

Hopefully this leads down the road to practical applications of the vasimir design. I've always thought the ISS ought to be a pretty good testbed for ion propulsion technology.

As nothing is mentioned about reboost, I'm assuming the prototype will be too small to make a meaningful dent in the ISS's delta-V needs.

Offline A_M_Swallow

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Re: Power Supply for VASIMR
« Reply #84 on: 08/07/2008 02:03 AM »

As nothing is mentioned about reboost, I'm assuming the prototype will be too small to make a meaningful dent in the ISS's delta-V needs.

The VF-200 can reboost the ISS but the burn would take several months.  The ISS would probably need extra solar panels to supply the 200kW of power.
http://www.adastrarocket.com/Plans.html

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