Successful Test of Superconducting Plasma Rocket Engine 168
xp65 writes to mention that Ad Astra has successfully tested their VX-200 plasma engine at full power in superconducting conditions, the first time such an engine has been tested at those power levels. "The VX-200 engine is the first flight-like prototype of the VASIMR® propulsion system, a new high-power plasma-based rocket, initially studied by NASA and now being developed privately by Ad Astra. VASIMR® engines could enable space operations far more efficiently than today's chemical rockets and ultimately they could also greatly speed up robotic and human transit times for missions to Mars and beyond."
High Thrust, High Specific Impulse (Isp) (Score:5, Interesting)
For those of you who are unclear on why the VASMIR system is so cool, allow me to give you a brief bit of background. Practically every propulsion method developed to date falls into one of two categories:
1. High thrust, low efficiency
2. Low thrust, high efficiency
Generally how it works is that the more power you get out of engines, the less energy you extract from the fuel. This is the case of chemical fuels like Liquid Hydrogen/Oxygen or Kerosine. These fuels provide the massive amounts of thrust necessary to get off the ground, but they burn through their fuel very quickly. Interestingly, LHOx is more efficient than Kerosine, but it's also harder to get as much raw thrust out of it. That's one of the reasons why Kerosine was the heavy lifter during the space race with the LHOx engines reserved for in-space stages.
On the other side of the coin, you have engines like Ion propulsion. These engines are able to inject incredible amounts of energy into tiny amounts of fuel, thus making them extremely fuel efficient. The only problem is that the amount of thrust is very low. Most of the ion engines that have operated to date produce thrust that matches the weight of a sheet of paper. Definitely not enough for liftoff, but perfect for extended missions in space where constant low thrust provides more velocity over time than the chemical engines which fire once, then coast the rest of the way.
The problem with both types of engines is that neither one gets spacecraft to their destination all that fast. Chemical rockets have the thrust to do it, but you couldn't feasibly build a chemical rocket with enough fuel to get you to another planet in a reasonable amount of time. A nuclear pulse propulsion craft could feasibly get fairly close, but it would just have more power in the intial thrust rather than providing a constant, high power thrust. (Obviously these have been discounted over the difficulties of building a large enough craft without using a nuclear ground launch. Nuclear ground launches are a no-no under current test-ban treaties.)
This is where VASMIR comes in. These engines are incredibly efficient. The specific impulse (measurement of efficiency) is between 3,000-30,000 seconds depending on the configuration and current thrust levels of the engine. This compares favorably with the ~450 seconds of shuttle engines and 3,000-10,000 seconds of Ion thrusters. Meanwhile, the thrust of Ion engines ranges from 90-3,000 mN while the thrust of VASMIR is expected to be ~5000 mN of thrust when tested at 200 kW of power.
What this means is that we may be able to build spacecraft where a trip from LEO to the moon is a daily affair and a trip from LEO to Mars takes only a few months (or less!) vs. the current flight time of nearly a year. The better these engines get (and the more we can put on a craft), the faster those flight times will get!
Let's not get out of hand about Mars (Score:5, Interesting)
Now don't quote me on this b/c it's been a while since I took orbital mechanics... but I seem to remember the "optimal" window for an Earth-to-Mars transfer opening up once every 2.5 years, it would take 8 months to travel there, 90-98% of your ship's mass would have to be fuel, and then you'd have to wait 1.5 more years for the "optimal" Mars-to-Earth orbital transfer window. In other words, doing a round-trip flight to Mars is no trivial matter.
Even with a more efficient fuel, perhaps you can stretch those windows, but you're not going to find an astronaut who is willing to leave now for a 1.5-year-commute to Mars, instead of waiting a year and doing an 8-month-commute. Even if those times are shrunk by a factor of 2 with a more efficient fuel, it's always going to be a huge operation.
Re:High Thrust, High Specific Impulse (Isp) (Score:3, Interesting)
Gas Core Nuclear Thermal Rockets are still science fiction. No one has yet built the necessary components, and there is a great deal of argument over whether or not "nuclear light bulbs" are even possible.
I'd love to see a 3,000 - 5,000 second NTR engine as well, but it would still be better suited for liftoff. For interplanetary travel, you simply can't beat the efficiency numbers of VASMIR. They start at the theoretical limits of NTRs!
I don't have the reference in front of me, but I seem to recall that solid core NTRs were brought as high as 1200 seconds. On paper, anyway. No one has built them since the 80's timberwind project.
Re:High Thrust, High Specific Impulse (Isp) (Score:4, Interesting)
" ... but you couldn't feasibly build a chemical rocket with enough fuel ... "
In fact, you can't do it all. There is a theoretical maximum amount of chemical energy/mass
you can achieve. Even when you are able to use this energy at 100% efficiency, the amount of energy required
to move the fuel itself reaches a point at which its payload can go no faster.
Re:High Thrust, High Specific Impulse (Isp) (Score:4, Interesting)
THIS is why we need to go to the Moon and Mars and beyond... it is only through pushing through the boundaries to the unknown that we advance as a species.
A good way to explain it to the technophobes is this with the Turner Thesis [wikipedia.org], which stated that what made America exceptional was its frontier. And in a lot ways, Turner was right. Continental expansionism (the so-called Manifest Destiny [wikipedia.org]) was the impetus for much technological innovation in North America, including the telegraph, the steam locomotive, etc.
Yiddish (Score:4, Interesting)
In Yiddish (the Jewish-German creole of Eastern Europe), VASIMR means "woe is me".
I know, probably o/t.
Re:High Thrust, High Specific Impulse (Isp) (Score:5, Interesting)
Both are, to some extent. You (and Wikipedia) are correct in that VASIMR engines can change between high-power and high-efficiency (think of it like changing gears in your car; you're much more fuel-efficient cruising in top gear, but can accelerate much harder in low gear). Indeed, that's a fundamental characteristic of the engine, and explains the first two letters of the acronym (VAriable Specific Impulse Magnetoplasma Rocket). However, the OP is also correct in that VASIMIR engines are extremely efficient in general. Part of this is due to their variability - as with a car, the efficient way to use a rocket is to increase its specific impulse (gear ratio/fuel efficiency) as its speed increases (currently no other rocket engine that I know of can do this). On the other hand, look at the high-end of that specific impulse - it's several times what our best Ion drives produce, while also putting out substantially more thrust. Theoretically, VASIMR engines are strictly superior (in terms of thrust and SIP, at least) to ion engines.
Of course, even at maximum thrust, current VASIMR drive designs produce *maybe* enough thrust to lift about .5 kilos (call it 1 lb) into space from the surface. Since the engine itself masses far more than that, you'll still need something with really high thrust to get it into space in the first place. Based on that, chemical engines will probably be around for a while, unless we can whip up a space elevator while we're at it. Theoretically you could run more power through a VASIMR and get more thrust, but I suspect the practical limit on doing so is far less than would be required for liftoff (if you could even get it to operate in an atmosphere). Even without that, though, it would be an incredible boon to intrasystem travel, or for station-keeping engines on satellites.