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."
Re:Total power (Score:5, Informative)
For comparison, your car needs about 20 kW of power to maintain cruising speed on the interstate. 200 kW of power would be akin to running a 300 horsepower engine at its peak power output. With the way cars are designed, that doesn't happen much with the possible exception of expensive sports cars and pickups hauling a heavy load.
If we take the case of the sports car, we find that it's enough energy to slam you against your seat and hold you there while you do 0-60 in 3 seconds. (Hey look, ma! Artificial gravity!) In the case of a pickup pulling a heavy load, it's enough to accelerate reasonably while dragging a trailer full of spools of heavy steel cabling.
The difference between your car and the spaceship is that the spaceship will be powered by some sort of long-term fuel supply. e.g. A nuclear reactor. Which means that the spaceship will be able to continue accelerating for millions of miles while your car would have run out of gas after the first few hundred miles.
Since acceleration is cumulative, being able to continuously accelerate like that means that distances between planets become a lot smaller on one "tank of gas" as it were. Add more engines for greater thrust and redundancy, and you have a souped-up hot-rod of a ship that can take you interplanetary distances in record time.
Hmm... I'm sure someone is about to chide me for some horribly sloppy analogies, but look on the bright side. It's got cars in it! And hopefully it will make the energy budget a bit more understandable. ;-)
Re:Power to Power the VASMIR? (Score:3, Informative)
For 200 kW per engine, we're thinking nukes.
Re:Let's not get out of hand about Mars (Score:3, Informative)
You're partially correct. But only partially. While you generally need to wait for proper alignment to make your journey, the length of the journey is still dependent on how fast you go. Chemical rockets are so slow that we need to begin the orbital transfer ~260 days before the expected orbital intersection with Mars. With more acceleration, the ship could leave later and still make the rendezvous.
Ok, that's horribly simplified. But I simply don't have the time to look up and explain the myriad of orbital transfers [wikipedia.org] available. Suffice it to say, a little bit of extra speed won't help much at all. A lot of extra speed will open up many more options.
Or in other words, how fast you get somewhere depends on how much energy you want to waste to accomplish that goal.
Summary Wrong (Score:3, Informative)
Re:High Thrust, High Specific Impulse (Isp) (Score:3, Informative)
Your post says that VASIMR combines high-thrust with high-specific-impulse.
But the wikipedia article http://en.wikipedia.org/wiki/VASIMR_Engine [wikipedia.org] says instead that VASIMR operates in either high-thrust low-specific impulse mode, or in low-thrust high-specific-impulse mode.
Have I understood this correctly? Which is right?
Re:Let's not get out of hand about Mars (Score:5, Informative)
You're mixing about a zillion different orbits into one recollection.
If you've got enough fuel, just turn and burn man... simple. Of course that takes a heck of a lot of fuel, like your idea of 98% mass fraction of fuel.
A Hohmann TO is the simplest imaginable transfer to design and is pretty quick too. Draw an ellipse that touches both orbits...
http://en.wikipedia.org/wiki/Hohmann_transfer_orbit [wikipedia.org]
A Bi-elliptic is way slow, but if you're making a major/huge change to your orbital parameters it takes less fuel. Enter a giant orbit way the heck out there, then on the return pass enter your new orbit. Handy for inclination changes too.
http://en.wikipedia.org/wiki/Bi-elliptic_transfer [wikipedia.org]
And if you literally have decades of spare time there is the famous "ITN" which takes practically no fuel and takes practically forever, which works by wandering around the various eddies of the Lagrange points or something very vaguely like that.
http://en.wikipedia.org/wiki/Interplanetary_Transport_Network [wikipedia.org]
As for your claim of 98% mass fraction, check out the math on
http://www.iki.rssi.ru/mirrors/stern/stargaze/Smars2.htm [iki.rssi.ru]
"showing we need add just 2.966 km/s, a shade short of 3 km/s or 10% of the orbital velocity."
and then when you get there you need another 2.5 km/s to match mars orbit, although you can play various gravitational slingshot games to help that out...
Only if you're looking for exercise. (Score:3, Informative)
Biking for an hour at 25MPH costs 1181 kcal, according to this calendar [geocities.com] (others suggest it costs even more calories), which translates to 1373 watt-hours. (Your body isn't that efficient at converting fuel to energy.) So let's assume your 250W figure is correct, and your body is about 18% efficient in converting calories to power.
Biking for an hour at 65MPH (if you could) would burn 18669 calories -- remember, wind resistance goes up as the cube of speed. That works out to -- let's see -- 21712 watt-hours. Assuming the same 18% efficiency (and some active cooling for your legs, not to mention the rest of your body), you'd be putting out 3.95KW to sustain that speed.
When you look at it that way, spending five times the energy to move a car, with probably five or ten times the frontal surface area and more than ten times the passenger and cargo capacity, starts to sound like not such a bad deal.
Re:Yiddish (Score:1, Informative)
Yiddish isn't a creole. A creole is a language that has been created starting from a simple pidgin, then gradually become complex enough to use as a complete language on its own. Yiddish, in contrast, evolved from a language that was already complete. Yiddish has lots of loanwords from Hebrew and the Slavic languages. But in most respects it's Germanic and not a creole.
Still, I enjoyed your post.
Re:Let's not get out of hand about Mars (Score:3, Informative)
It's been a couple decades for me, too, though my masters class in space vehicle guidance and nav had the final as a mars shot (NASA Admin Griffin was the professor; yes he has always been hyped on mars!)
Anyway, while the sibling posts are correct, there are orders of magnitude between this technology and the reality of meaningfully shifting the duration of a Mars shot. There are certain "safe" transfer orbits which get the crew back to earth automatically (you can intercept mars, and if you miss injection your orbit will return you to earth orbit, tangent to earth's orbit, and at the same time that earth is in that location).
Even if you go with a non-safe orbit (non-tangential initial delta V) which doesn't intercept Mars at perihelion (Hohmann transfer of you leave earth tangential to the orbit), you've got to have some significant acceleration.
Now, this thing is going to need 200kW per engine to apply 5N worth of thrust. To get this into perspective, do you remember those old Estes engines you played with as a kid? The small ones produce about 5N of thrust. Now, strap one of those to a 200kW generator. The Topaz generator, flown by the Soviets produced 5kW of power and weighed over a ton. Now, that's the only thing I could find on google in 2 seconds, so we'll assume you can get an order of magnitude better performance today - strap that Estes C6 engine to a 5,000lb nuclear reactor. You're not exactly going to be racing the new Veyron in terms of acceleration. (okay, the Veyron won't do well in space...point taken).
If you do the math, I'm thinking you'll be getting 0.0001m/s/s acceleration if you count the generator/engine combo as 50% of the spaceship mass. In 9 months, you'll be traveling at 2.3km/s faster than when you left earth orbit, which was probably in the 6-7km/s range. At that point you can turn around and start decelerating to you reach Mars at a desirable rate.
None of which really matters (since the orbital durations may be highly suspect), except to say that you're not going to be getting any massive delta-V out of this thing on a short term basis.
Re:High Thrust, High Specific Impulse (Isp) (Score:3, Informative)