VASIMIR

Well... interesting idea but it of course depends on what's in it for the spacefellowship and me

You can have your name up there as well if you like and the website written down each solar panel, think of all that publicity.

Hehe nice one to bad i can't edit the post date on this forum

But I can For EUR 25.000,00 to my Swiss bank account 0123-4567-8901-2345 and it's a done deal

Here's a recent interview with Dr. Franklin Chang-Diaz in which, among other things, he discusses the need for the development of small nuclear fission reactors for use in space. It's one of the better discussions of the VASIMR concept.


This cannot be emphasized enough. Power has always been a major (in many cases the major) bottleneck in space mission planning. Solar energy is cumbersome in earth orbit and useless in the outer solar system. RTGs are great, but they still don't provide nearly enough energy density for high bandwidth data transmission and other operations necessary for serious exploration. I firmly believe that the 2005 defunding of Project Prometheus was (one of) the largest long term setbacks to both manned and unmanned space exploration in recent years.

The VASIMR concept has the promise of solving the Propulsion problem of long distance space travel in the near to medium term. (Need to get to LEO first though.) It remains to be seen, however, when the Power problem will be solved. Hyperion maybe?

200kW is ridiculously small in the scale of rockets, by the way. Our very small 800lbf rocket flows 200kW through the chamber wall into the fuel before burning it. That's a very small portion of the total power output.

Notice that in none of the VASMIR stuff have they ever actually said that they produced useful thrust at a useful Isp, just that they've managed to dump 200kW into a plasma.

They have not yet talked about any actual thrust and ISP numbers, because it has not yet been tested as far as I know. The only numbers that are being "thrown" around are potential numbers. One of the mayor unknown factors is the question if the plasma gets detached from the engine at all.

See VASIMR - Current development, wikipedia (3rd paragraph)

Found some interesting stuff on Ad Astra's (new and waaaaay better than before) webpage:

Press release from the end of September 2009, when VX-200 actually reached the full 200 kW of its rated power: http://www.adastrarocket.com/Release_20 ... 9Final.pdf

And new "Executive summary" from 24th of January (2010): http://www.adastrarocket.com/EXECUTIVE% ... 240110.pdf

Some interesting Stuff there. But guess we still have to wait for quite some time before we see VASIMR going to the ISS...

Actually H2 is the BEST choice. I was also under the false assumption that heavier was better until recently. The lighter the ejected propellant, the faster it accelerates. Since the total energy is M*V*V the velocity is all important. 2(H2)+O2 (shuttle main engines) are the best you can get to with a chemical reaction - an ISP of ~450. VASIMR's ISP has the potential to be much better than that, but a nuclear motor is really the best option.

From http://en.wikipedia.org/wiki/Tripropellant_rocket:

I know wikipedia is not a very reliable source, but I've heard that tripropellant rockets can give higher ISP from other sources too.

johno

I just thought of something kinda off the wall. If a VASIMR engine is ejecting protons/hydrogen ions, won't the spacecraft become negatively charged due to this? And wouldn't a high powered electron gun, a beefed up version of those found in a CRT, give an incredible ISP due to the relatively tiny mass of electrons? It would also negate the problem of building up a negative charge on the spacecraft, which could be a big problem when docking.

I'm sure someone at Ad Astra has already thought of and fixed these issues though.

johno

I'm not sure exactly how VASIMR solves this problem, but I know most EP types have something called a "neutralizer" at the very end of the nozzle that gives electrons to the outgoing stream of particles. This is necessary for more reasons than just keeping the charge of the spacecraft neutral (actually not really all that required - moon dust generally carries a charge of up to 10V for example due to the solar wind). More importantly, it will keep the propellant actually travelling in a straight line and make its behavior more predictable, as well as guaranteeing the particles won't do undesired things like hit the solar panels or corrode any other component they happen to come across faster than they would otherwise.

You have to neutralize your exhaust if you want to go anywhere. A positively charged exhaust and a negatively charged vehicle will attract. The exhaust will just come flying back pulling the vehicle backwards. Some will escape sure, but it is an efficiency drain. I imagine that it would be best to get a very small net positive charge on your vehicle and maintain it.

Isn't the whole point to have a charged exhaust, and magnets force the exhaust out the back? If the exhaust isn't charged, how would VASIMIR work?

The exhaust is charged as it is accelerated within the engine and expelled from the rocket. After that though you need to inject electrons into the plasma to neutralize it.