Plasma Rocket Successful Full Power Test

Matt_dk writes "VASIMR is a new high-power plasma-based space propulsion technology, initially studied by NASA and now being developed privately by Ad Astra. A VASIMR engine could maneuver payloads in space far more efficiently and with much less propellant than today's chemical rockets. Ultimately, VASIMR engines could also greatly shorten robotic and human transit times for missions to Mars and beyond."

Comments

Plasma Rockets Suck.

[TheRealZero]

LCD rockets have sharper colors.

Re:Plasma Rockets Suck.

[oatesy]

true, but the plasma ones come in bigger models...

Re:Plasma Rockets Suck.

[coldmist]

Plasmas have deeper blacks, to really show that cosmos better.

Re:Plasma Rockets Suck.

[Tubal-Cain]

I first read that as "LSD rockets have sharper colors"

Re:Plasma Rockets Suck.

[MazzThePianoman]

No, Plasma does and it has a better viewing angle but you'll need to darken the area. Plus the don't burn out like they use to.

Re:Plasma Rockets Suck.

[Idbar]

It appears though that Plasma work better during daylight. So It all comes to if they are traveling at night.

Re:Plasma Rockets Suck.

[flitty]

Apparently, Keeping a website from being slashdotted IS HARDER than rocket science.

Re:Plasma Rockets Suck.

[YttriumOxide]

They do... they really do...

Re:Plasma Rockets Suck.

[Professr3]

That are guaranteed to fail within 9 years?

Re:Plasma Rockets Suck.

[Steve Baker]

I'm still waiting for OLED rockets.

Re:Plasma Rockets Suck.

[Woy]

Then you are blessed.

Re:Plasma Rockets Suck.

[Anonymous Coward]

Also true.

Re:Plasma Rockets Suck.

[Bazer]

Don't worry. The flashbacks subside after 30 years or a shock therapy after a manic depression episode (whichever comes first).

Re:Plasma Rockets Suck.

[oatesy]

but being that big who cares? its awesome and worth it :D

Re:Plasma Rockets Suck.

[Anonymous Coward]

Plasma Rockets? i thought plasma weapons were guns, not rockets! omg what will all the quake players do?

Re:Plasma Rockets Suck.

[dvh.tosomja]

Sorry but the original is only one

Re:Plasma Rockets Suck.

[glittalogik]

Mine's coloured in alternating stripes of Happy and D#. How about yours?

Re:Plasma Rockets Suck.

[YttriumOxide]

Mine tastes like blue and sounds like the smell of rose petals...

Although, in honesty, unless I take very large doses (greater than 400 micrograms), I find the only synaesthesia I get is seeing sounds. I love "watching" Halcyon and On and On towards the end of a good trip... There's some really nice wavy bits there and the colours in the vocal sounds are quite incredible.
With increased dosage, I've experienced almost every other kind of synaesthesia, but I'm not sure I've seen "happy" (although I may have tasted it...)

Re:Plasma Rockets Suck.

[Anonymous Coward]

I can only get the color Eb.

Re:Plasma Rockets Suck.

[Hordeking]

I don't know. Plasma has problems with burn-in.

Re:Plasma Rockets Suck.

[Anonymous Coward]

I thought LSD rockets had colors that tickle...

Re:Plasma Rockets Suck.

[Anonymous Coward]

I'm not sure I've seen "happy" (although I may have tasted it...)

That's what she said.

Re:Plasma Rockets Suck.

[Anonymous Coward]

I first read that as "LSD rockets have sharper colors"

You're hallucinating . . .

Re:Plasma Rockets Suck.

[KanSer]

Yes but LCD suffers from more interference and dithering. We do want our force fields to interfere with space, yes? At least the nasty pointy bits.

The interesting part (to me anyway)

[mcgrew]

The VASIMR engine works with plasma, a very hot gas at temperatures close to the interior of the Sun. Plasmas are electrically charged fluids that can be heated to extreme temperatures by radio waves and controlled and guided by strong magnetic fields. The magnetic field also insulates any nearby structure; so temperatures well beyond the melting point of materials can be achieved and the resulting plasma can be harnessed to produce propulsion. In rocket propulsion, the higher the temperature of the exhaust gases, the higher their velocity and hence the higher their fuel efficiency. Plasma rockets feature exhaust velocities far above those achievable by their chemical cousins, so their fuel consumption is extremely low and their fuel-related costs substantially reduced.

Re:The interesting part (to me anyway)

[bornwaysouth]

That is still technobabble. You still have to cart an energy source up, and it is usually stored chemically for big engines. I am guessing that by spitting out an atom (argon in this case) at some massive velocity, you do not need to cart as much mass about, which is where the real penalty comes from - accelerating fuel forward so you can spit it back later. But aspects of this argument seem really slippery. It is accepted wisdom, well established, and I assume true. But the science part of the article was really glossed over. OK, they know their audience, and science is to be presented as glossy bottom line stuff.

I'm no rocket scientist. Even metaphorically. Does anyone know why it really is more efficient? They are wanting to use a 200kwatt engine, so that is not going to be sourced using warm radioactive decay. As a once-chemist, I wouldn't choose argon as an energy source. That's a bit like carrying media consultants on a Mars mission, so you could keep throwing them back to Earth.

Re:The interesting part (to me anyway)

[Anonymous Coward]

The Argon is not an energy source, it is merely propellant. Argon is chosen due to ionization potential. There is no splitting of argon (that consumes energy rather than producing it)

Power would have to be carted up separately, and in the case of a plasma drive it would presumably be nuclear.

Re:The interesting part (to me anyway)

[mcgrew]

I thought it seemed fairly straightforward.

1. the hotter the flame, the more thrust you have and the more efficient the thrust. Your limit is when it's hot enough to melt the rocket's nozzle.

2. Since it's a plasma, you can control it with a magnetic field, to the point that its heat won't affect the rocket's nozzle.

More efficient=less fuel needed. In addition to keeping the heat away from the metal, being able to control it with a magnetic field means you don't have to have a moveable nozzle to steer the thing, making it possibly simpler than traditional designs.

Re:The interesting part (to me anyway)

[Smidge204]

As the AC mentioned, Argon is the propellant and not the fuel.

accelerating fuel forward so you can spit it back later.

I have no idea what that even means, or is even supposed to mean. I quote it only to highlight that the source of your skepticism seems based entirely on a gross misunderstanding of the technology involved.

All rockets work by ejecting mass at high velocities. Take Argon, strip the electrons from it (ionize) and then accelerate it through a electric field potential. The advantage here is you can (potentially) get much higher velocities - and therefore more momentum - using this method than using a chemical fuel. That more "umph" per kilogram of propellant (in traditional rockets, the fuel is the propellant as well).

The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious. But ion engines can potentially eject mass at much higher speeds.

The energy for both the ionization and field generation are what required the power source. Which could, for example, come from solar power. As long as the extra power/mass ratio of the whole system is better than traditional fuel systems, you're coming out a winner.
=Smidge=

Re:The interesting part (to me anyway)

[confused one]

Higher efficiency comes from higher exhaust velocities requiring less reaction mass (fuel) in order to provide the requisite propulsion

Re:The interesting part (to me anyway)

[Anonymous Coward]

There are only two things that matter in determining how much delta V you can get from a given rocket, Exhaust velocity and Propellant mass fraction.

The exhaust velocity is the mean velocity of the exhaust.

The propellant mass fraction is the fraction of vehicle launch mass that is propellant that will be slung out the back.

Now, in a conventional rocket, the propellants are typically accelerated by a simple thermodynamic gas generator (turbopumps and a chamber to burn the propellants to create high pressure hot gas) followed by a nozzle to convert the pressure and temperature into velocity. There are inherent limits in this process, not least that the heat source and reaction mass flow are inexorably coupled.

VASIMIR is essentially an ion drive variant which separates the reaction mass from the power source, and which allows the specific impulse to be varied (the number of NewtonSeconds of thrust per kg of fuel), this is useful as it allows for high thrust burns at relatively low specific impulse and low thrust burns at much better fuel economy to be mixed at will with the same motor.

The electrical power generator is an interesting problem, as most thermal generators on that scale would seem to need a vast amount of radiator to dump the waste heat from the condensers or equivalent. I suppose you could dump some of it into the fuel before it hits the injector, but that is going to be limited. Most likely the plan is to charge batteries with solar power, then discharge them rapidly to give a series of short burns.

I could see some sort of high temperature nuclear plant being flown, but as radiated power rises as the 4th power of absolute temperature, the radiators would have to run really hot to get good overall specific impulse from the complete propulsion assembly (Which means a relatively poor thermodynamic efficiency for the overall electrical plant), this might be a reasonable tradeoff.

Of course the political problems with launching a small reactor would be 'interesting'.

HTH.

Regards, Dan.

Re:The interesting part (to me anyway)

[Anonymous Coward]

This isn't a flame per se. The plasma isn't burning, it's being heated by an external energy source (the radio waves referenced above) and the resultant expansion drives it out the nozzle at very high velocities. Where this system is efficient is in its use of propellant. If you are using a rocket for transportation, you have to carry and then output some type of reaction mass. At higher exit velocities you need less mass to achieve the same increase in speed. However, the device to create the radio heating and its power source are also part of the picture. In space, you usually care about weight, so this system has to compete with others based on the sum of the small mass of plasma propellant and everything else that is required to heat it up and shoot it out the back of the rocket.

Re:The interesting part (to me anyway)

[Anonymous Coward]

He wrote spitting not spLitting? Ho hum. Anyway, ionisation is splitting an atom, kind of - splitting off electrons from the nucleus. Splitting the _nucleus_ is what people often mean when they say "split the atom" as in atomic bomb of course, but "atom" is a (now known to be terribly inaccurate since it means "indivisible") name for the nucleus PLUS surrounding electrons.

Re:The interesting part (to me anyway)

[Anonymous Coward]

I have no idea what that even means, or is even supposed to mean.

It means that in order to use the fuel, you have to carry the fuel with you. Seems obvious. The more fuel you need to carry, the more fuel you need to waste to move the fuel you're carrying. It's an exponential problem, and it's the reason rockets are mostly fuel with a tiny payload on top.

The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious.

Not quite so obvious. Newton's third law doesn't care how fast you're moving, the exhaust velocity is relative to the engine nozzle, and moving at the same speed as the exhaust velocity doesn't make the engine stop working. The real reason lower exhaust velocity limits the speed of the rocket is that in order to keep accelerating you need to add more fuel, which means you're adding more mass, and weighing down the rocket. You get rapidly diminishing returns if you try to get more speed by adding more fuel. That's why higher impulse engines are better. They get more thrust per pound of fuel, which means you use less fuel, and you waste less fuel pushing around other fuel.

Re:The interesting part (to me anyway)

[Anonymous Coward]

The advantage here is you can (potentially) get much higher velocities - and therefore more momentum - using this method than using a chemical fuel. That more "umph" per kilogram of propellant (in traditional rockets, the fuel is the propellant as well).

Here you reveal that you are also talking out your arse. The correct term for what you are describing is Isp (Specific impulse).

The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious. But ion engines can potentially eject mass at much higher speeds.

Talking out your arse again. Your hydrazine rocket could accelerate you well beyond your 'obvious' top speed. The velocity of the rocket exhaust is relative to the velocity of the rocket, and thus you can accelerate to some practical limits.

The first (and overwhelming) limit is how much fuel you can carry.

Where particle accelerators as rocket propulsion get interesting is that for a given mass of propellant, you get MUCH higher Isp. That means that with the same mass of propellant you can accelrate to far higher speeds, or to get to the same speeds you can carry far less total mass. Both have big benefits to space travel.

There are some times where you need brute, slow, and inefficient rockets. For example when you need very high thrust. (say, an insertion burn, or a rapid course correction during a flyby/encounter event)

Generally, these very high Isp rockets have really crappy thrust.

Re:The interesting part (to me anyway)

[Anonymous Coward]

>The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 >mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are >obvious. But ion engines can potentially eject mass at much higher speeds.

Hmm. Traveling at 1000mph relative to what? The aether?

Re:The interesting part (to me anyway)

[ShadeOfBlue]

The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious. But ion engines can potentially eject mass at much higher speeds.

Wrong. This completely fails the concept of relativity. The rocket expels mass at 1000 mph from its reference frame. It pushes on the exhaust, and hence the exhaust pushes back, causing the rocket to accelerate. The rocket does not care what reference frame (say, the surface of Earth) you choose to watch it from.

Re:The interesting part (to me anyway)

[Anonymous Coward]

> If your hydrazine rocket can expel mass at, say,
> 1000 mph (making numbers up here) then the top
> speed of your rocket is 1000mph for reasons I
> hope are obvious.

I'm no physicist, but anyone who's been through high school physics would know this statement is completely wrong. E

Re:The interesting part (to me anyway)

[Anonymous Coward]

If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious.

How does *that* work? The top speed of your rocket is only as fast as your propellant? In what frame of reference?

That's not obvious to me at all. A rocket is always stationary in its own frame of reference. Barring other influences, expelling some mass at *any* velocity will have an equal and opposite effect on the momentum of the remaining rocket/propellant mass.

"For reasons I hope are obvious" in deed.

Re:The interesting part (to me anyway)

[Migraineman]

Your top speed isn't limited to the exhaust velocity. Regardless of your current speed, energy is conserved if you tip mass overboard. For the force used to displace the exhaust, the reaction force is applied to your vehicle.

Ion, plasma, arc-jet, and the like are all about taking a small reaction mass (aka propellant) and ejecting it out the back at the highest speed possible. F=ma dictates that you can achieve a large force by tossing a large mass at a relatively low acceleration, or by tossing a small mass at a relatively high acceleration. With a big solar array or a nuclear reactor, you've got a whole lot of electricity with which to expel your relatively small amount of propellant out the back.

Re:The interesting part (to me anyway)

[opwierde]

The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious.

I'm not a rocket scientist but I do not believe that a rocket top speed is limited by nozzle velocity. Imagine going 1000mph and throwing an object in the direction you came from. Newtons law says you will get an equal and opposite reaction... you have just pushed the rocket and it will go faster due to conservation of energy. At least until you hit relativistic speeds...

Re:The interesting part (to me anyway)

[Tsar]

If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious. But ion engines can potentially eject mass at much higher speeds.

Actually, that turns out not to be the case. Neglecting outside forces, if two unequal masses are pushed apart, Newton's Third Law requires the smaller mass to move at a higher residual velocity. That's why most of a spacecraft's mass is fuel--to take advantage of that inequality.

Re:The interesting part (to me anyway)

[deander2]

it's not really the heat, but the velocity. you can have cold-as-ice propellant if you can throw it away from you fast enough.

of course, with chemical rockets, there is usually a relationship between heat and velocity, but that's not necessarily true for plasma engines.

Re:The interesting part (to me anyway)

[chrome]

For everyone who replied to you: http://xkcd.com/386/

Re:The interesting part (to me anyway)

[Jbcarpen]

I'm not a rocket scientist but I do not believe that a rocket top speed is limited by nozzle velocity. Imagine going 1000mph and throwing an object in the direction you came from. Newtons law says you will get an equal and opposite reaction... you have just pushed the rocket and it will go faster due to conservation of energy. At least until you hit relativistic speeds...

Relativistic speeds in whose reference frame? No matter how much you accelerate, or for how long, you will never perceive yourself as being anywhere close to the speed of light (it's still zipping past you at a relative speed of c). So, from your perspective you can maintain constant acceleration for as long as you have fuel, even if your spacecraft is 99.999% reaction mass at launch (that'd be an interesting trick now wouldn't it?)

Re:The interesting part (to me anyway)

[Anonymous Coward]

Political problems, bah! The Chinese will do this first, launching a nuclear version that is. They will simply do it and dare the world to do anything about it! Domestic protest, if it occurs in China, will simply be harvested and skinned for their collagen so western women can have skin with the 'high pro glow'. Foreign protest can simply be dealt with by secretly threatening the protester hosting nations with trade repercussions against their bloodsucking co-conspirator industrialists. Look what happens when Canadians protest! See how fast they get absolutely hosed with pepper spray if they dare to breath a word of complaint against Chinese actions...or corporate monopolist actions as well.
    Actually I say more power to the Chinese. They have the will to be winners in the world survival game. We in the west have lost our will, and survival will go to those able to achieve the triumph of the will, as then they will prove themselves fit to rule. We have proved ourselves unfit as we are weak and internally conflicted, lacking the guts to survive.
    This technology seems to have great potential if is can be scaled up to earth surface main propulsion like a future space shuttle. A real shuttle that is single stage to standard orbit or planetary escape from earth sized planets would be very desirable for us as a species to have, and would give us true access to space. It will just take real men and woman to built it, not weaklings and wussies only fit to become fawning servants....as long as they can learn enough Chinese to obey simple commands, and stay out of the way of their rightful masters.

Re:The interesting part (to me anyway)

[Anonymous Coward]

Not having RTFA yet, I wouldn't be surprised if this is plasma drive is based on some variation of a nearly century-old technology...thermionic emission

So...why do I have this image of a Thyratron, (minus the glass package) as the best way I can visualize how this plasma drive could work?

Re:The interesting part (to me anyway)

[Teancum]

Keep in mind that unless you are doing something like a Bussard ram scoop that is collecting material enroute, the only thing you have to be able toss out the back of your vehicle is reaction mass you have brought with you.

So your top "speed" is limited to exhaust velocity. All of these more exotic propellant systems are about increasing the efficiency of throwing the mass to increase the velocity of the vehicle.

The problem with these propulsion systems is that none of them are strong enough to be able to push against the 9.8 m/s^2 acceleration that we have on the ground here on Earth, so they are only useful once you get into space. They are highly efficient but overall only give relatively low amounts of acceleration.

Their advantage is that they can be operated for long periods of time... days, weeks, months, or even years potentially. Over time, even a modest acceleration adds up to a huge velocity change and can be significant in terms of travel to distant places like the outer planets of the solar system or even Mars. You can even take trajectories other than a modified Hohmann transfer orbit in this case between planets.

If you toss out a huge amount of mass at low velocities, your reaction mass is gone. Tossing that mass out at a significant fraction of the speed of light... well, you don't have to be using all that much reaction mass in order to be getting some real benefit in terms of changes in velocity.

BTW, I just don't see huge efficiencies with solar arrays being used to generate the electricity needed to run these exotic motors. The mass of the panels themselves quickly start to become a major issue as you scale up the thrust to make them useful, not to mention that travel beyond the Earth (aka to Mars or the outer solar system) results in significantly reduced amounts of solar energy that would even hit the solar panels.

For satellite station keeping (rather than using hydrazine or other chemical thrusters) this is an option as you need the power anyway for vehicle operations and can temporarily shut down some high energy consumption activities in exchange for maneuvering the vehicle. Typically the on-board fuel is one of the things that limits the lifetime of satellites... particularly things like spy satellites who want to use thrusters to vary their orbital characteristics and make it much more unpredictable about where they might be in the sky at any given moment. Geosync satellites could also take advantage of this as a huge expense is simply getting the satellite from low-earth orbit to a higher altitude, but it doesn't have to be done immediately and can take several months if necessary... or to correct for drift from their position once they get to the correct altitude.

Re:The interesting part (to me anyway)

[Hal_Porter]

Political problems, bah! The Chinese will do this first, launching a nuclear version that is. They will simply do it and dare the world to do anything about it! Domestic protest, if it occurs in China, will simply be harvested and skinned for their collagen so western women can have skin with the 'high pro glow'. Foreign protest can simply be dealt with by secretly threatening the protester hosting nations with trade repercussions against their bloodsucking co-conspirator industrialists. Look what happens when Canadians protest! See how fast they get absolutely hosed with pepper spray if they dare to breath a word of complaint against Chinese actions...or corporate monopolist actions as well.

    Actually I say more power to the Chinese. They have the will to be winners in the world survival game. We in the west have lost our will, and survival will go to those able to achieve the triumph of the will, as then they will prove themselves fit to rule. We have proved ourselves unfit as we are weak and internally conflicted, lacking the guts to survive.

You remind me of D S Savage

http://antichomsky.blogspot.com/2004/07/orwell-vs-proto-chomskyites.html

he said
The pacifists' "championing" of Hitler referred to by Orwell is simply a recognition by us that Hitler and Germany contain a real historical dynamic, whereas we do not. Whereas the rest of the nation is content with calling down obloquy on Hitler's head, we regard this as superficial. Hitler requires, not condemnation, but understanding. This does not mean that we like, or defend him. Persoanlly, I do not care for Hitler. He is, however, "realler" than Chamberlain, Churchill, Cripps, etc, in that he is the vehicle of raw historical forces, whereas they are stuffed dummies...living in unreality. We do not desire a German "victory"...but there would be a profound justice, I feel, however terrible, in a German victory.

Being like him is a very bad thing. George Orwell wrote acidly that "pacifism is objectively pro Fascist".

Re:The interesting part (to me anyway)

[WebmasterNeal]

what the heck did you just say?

Re:The interesting part (to me anyway)

[savuporo]

"The mass of the panels themselves quickly start to become a major issue as you scale up the thrust to make them useful,"

Thin film cells. They havent been flown in space yet apart from FTSCE/MISSE-5 tests, but you can get pretty good power to weight ratios with them, IIRC around 2KW/kg has been achievable.

Re:The interesting part (to me anyway)

[Retric]

It's not that hard to understand with Chemical Rockets your reaction mass and your energy are the same thing. With Plasma Rocket's the reaction mass is faster but it does not provide any energy.

The reason why this is a good thing is over time a solar cell can provide a lot of energy per unit weight. Using systems like this you can dramatically alter the orbit of satellites without taking ridiculous amounts of fuel into orbit. Or for long range probes you can use nuclear energy and high velocity reaction mass to reach vary high speeds without using a lot of fuel.

Think of it like using a sailing ship vs fossil fuel boat. With fossil fuel you can cross the ocean in a few days... But once your boat runs out of fuel it's dead in the water so over time the sail boat can travel further.

Re:The interesting part (to me anyway)

[ultranova]

Your top speed isn't limited to the exhaust velocity. Regardless of your current speed, energy is conserved if you tip mass overboard. For the force used to displace the exhaust, the reaction force is applied to your vehicle.

Actually, the relevant thing here is the conservation of momentum. Assuming that you are ejecting mass straight back - a reasonable assumption, since that's the most efficient way - vm=VM, V=vm/M, where V=velocity (actually delta-v) of rocket, M the mass of same, and v and m the same for the propellant.

The problem is that, in order to double the delta-v you get from the same amount of propellant, you need to throw it twice as fast; but doing so requires four times as much energy (not taking relativity into account). In other words, the more reaction mass efficient a rocket is, the less energy efficient it is, and vice versus. That's why all high-impulse rockets are necessarily low-thrust, unless equipped with a fantastically powerful energy source. Even a nuclear plant would be hard pressed to supply all the power a truly efficient thruster needs to rise from Earth's surface.

At this point, I think that the future of space travel depends on finding some better carrier for momentum than ordinary matter, or by building an actual space cruiser with lots of room to spare and associated recreational areas - a de facto mobile village in space, or a generation ship. Otherwise, the sheer monotony of interplanetary travel will drive most attempters insane.

Re:The interesting part (to me anyway)

[holmstar]

So your top "speed" is limited to exhaust velocity.

No, you get an F in high school physics.

Lets take a very simple example... Lets say you have a spacecraft that is mostly reaction mass. Within your own frame of reference you are at rest. Now you push 50% of your spacecraft away at 10mph. This gives your craft a velocity of 5mph and the portion that you pushed away 5mph in the opposite direction (relative to your original frame of reference). Now you push away 50% of what is left, again at 10mph. This gives your ship a 5mph boost. Repeat one more time and your space ship has a velocity of 15mph.

Clearly, top speed is NOT limited to exhaust velocity.

Re:The interesting part (to me anyway)

[savuporo]

Er, scratch that. Mars Phoenix flew with ATK UltraFlex array, with Boeing Spectrolab cells
http://www.pv-tech.org/chip_shots/_a/no_juice_no_glory_inside_the_solar_arrays_powering_the_phoenix_mars_lander/

105W/Kg

Similar array is scheduled to fly on ST8
http://nmp.nasa.gov/st8/
Shooting for 175W/Kg

Re:The interesting part (to me anyway)

[w0mprat]

My understanding was that chemical combustion doesn't really occur in a plasma, which is a better way to understand why it is not considered a flame. Ionized atoms are stripped of their electrons to some extent so this means chemistry doesn't really happen. Even higher temperatures plasma becomes practically a soup of subatomic particles. If that's the right way to put it in a nutshell...

Re:The interesting part (to me anyway)

[Anonymous Coward]

No, no, this sucker's electrical! But I need a nuclear reaction to generate the 1.21 gigawatts of electricity

Constant Boost?

[Fished]

I couldn't find an answer in the article, or on the Wikipedia page... are the "reduced reaction mass" requirements for this engine such that constant boost becomes a possibility for longish missions? If so, then this effectively puts the Solar System within reach.

Re:Constant Boost?

[nih]

If so, then this effectively puts the Solar System within reach

I just left work to get another part of the solar system 'home' without this so called 'Plasma Rocket'

Re:Constant Boost?

[Kjella]

In theory, we could always do that, in practise I don't think we'll ever do that. Getting anywhere really fast burns a ton of extra energy, plasma drive or not. Most of the really long-distance missions haven't accelerated to that speed, they've done a slingshot trip around jupiter or something like that. Even on a Mars mission we're really just waiting for Mars to be in the right position to leap orbit and minimize the rocket use, not plotting a course or going from full impulse to full stop in seconds like you see on Star Trek. It would still cut a lot of costs but the cheapest route is still the slow one.

Re:Constant Boost?

[jollyreaper]

Typically these rockets are more efficient than their chemical cousins. For a given reactant mass, rockets will give you more thrust (can't get into orbit with anything but rockets at this point) but the plasma and ion engines are more efficient, low-thrust but higher change in velocity (delta-v.)

As it was described, a mars mission using an ion engine would not leave the space station with a dramatic blast of flame. The captain would say "turn the engine on," go, get coffee, watch a movie, look out the window and still be able to wave back to people at the station. Tune back in three weeks later and he'll be moving at a clip that would make chemical rockets weep in jealousy.

Re:Constant Boost?

[digitalsolo]

{STAR TREK FANBOY}

You can't go full impulse to full stop in seconds without inertial damping anyway. Duh.

{/STAR TREK FANBOY}

Re:Constant Boost?

[Joe Snipe]

Sounds like the smart move would be to combine the systems to get the best of both worlds (some sort of chemical/plasma/ion transmission system)

Re:Constant Boost?

[doug]

If it launched from a station in orbit, it will need to accelerate from 5mps to 7mps to break orbit. Does this slow acceleration imply that VASIMR power ships will have to circle the earth a few times to build up speed?

Re:Constant Boost?

[Anonymous Coward]

Ahh, but you're forgetting about the Stargate Atlantis episode 405, when Sheppard stops the ship with interial dampening turned off, and sends everyone on the bridge flying.

Re:Constant Boost?

[Anonymous Coward]

in practice I don't think we'll ever do that.

You greatly underestimate mans desire to kill each other. You get two nations in space, and the military hardware will be capable of all kinds of things.

Re:Constant Boost?

[Frnknstn]

Regarding your sig:
'Can someone explain to me why the () go inside the period, but the "" go outside the period?'

They don't. Correct (but old-fashioned) English usage has them both have the . inside the () or "". Modern usage, especially among science type, is to have the . outside any parenthesis, to keep the base sentence internally consistent (and other logical reasons).

Your perception stems from the way science types use () more often than "", and older English teachers use "" more often than ().

Re:Constant Boost?

[Joe Snipe]

Regarding your sig:
'Can someone explain to me why the () go inside the period, but the "" go outside the period?'

you just did it there. Why is the ? inside the quotes? Because it's part of my question? Should'nt it then be

you asked 'Can someone explain to me why the () go inside the period, but the "" go outside the period?'.

See what I mean? I'm not trying to be trite, I am honestly confused. If I quote the word time and say I need more "time", why is that incorrect?

Re:Constant Boost?

[ceoyoyo]

Certainly. You'd probably want to use one of these things at pretty much constant boost.

Now, that doesn't mean 1 G.

Re:Constant Boost?

[ceoyoyo]

You're assuming (as most likely the grandparent did) that constant boost means HIGH constant boost (like 1 G).

We've launched a few ion engine powered ships that employ more or less constant boost. The acceleration is very small, but it adds up over time.

Getting somewhere really fast takes extra propellant, but you have to burn a certain amount to get there at all. Constant boost just means you burn it slowly, as you go, rather than burning it all in a few seconds or minutes and then coasting the rest of the way. In general, constant boost is MORE efficient because you can use some of the very high ISP but very low thrust methods like plasma or ion engines.

Re:Constant Boost?

[Frnknstn]

In the case you mention, the ? belongs to your quote; thus, I include it in the ''. The following example illustrates the other case:

What did you mean when you said 'that idea is poison'?

In the preceding sentence, the ? is outside the '' because the question belongs to the speakers words, not to the quote he is using.

In all honesty, the real reason in this case was I was too lazy to type out the <blockquote> </blockquote> tags, instead I just used the ' '.

Re:Constant Boost?

[marco.antonio.costa]

Yeah. Check out this conceptual video they put up for a possible Mars mission with 3 VASIMR engines.

Re:Constant Boost?

[Joe Snipe]

Thank you very much for helping me understand this. I really appreciate it.

Re:Constant Boost?

[recharged95]

Not being a rocket scientist here, I thought ejection velocity was a positive benefit of plasma rockets. Since you can get high ejection velocities, you can require less mass to achieve the same final velocity. Hence, mass is not as critical compared to tradition rockets. This is great for long term missions as we have plenty of time to get upto speed (and down to speed). But for maneuvering, I think chemical ejection would be more appropriate since less time is needed to make a maneuver.

Or for that matter, solar sails would have offered higher ejection velocities for long term missions and are more efficient. I'm surprised only the planetary society has stepped up to the plate on that technology.

Re:Constant Boost?

[mdielmann]

Sounds like a small-ish booster stage to break orbit, and keep going with the VASIMR would be a useful idea, so far as absolute time goes. I doubt it would be worth the extra effort, though.

Re:Constant Boost?

[DerekLyons]

Typically these rockets are more efficient than their chemical cousins.

They are more efficient on paper, but in real world engineering, not so much.
 

For a given reactant mass, rockets will give you more thrust (can't get into orbit with anything but rockets at this point) but the plasma and ion engines are more efficient, low-thrust but higher change in velocity (delta-v.)

But much of the theoretical performance gain is eaten up by the need to provide a source of power - and for any significant payload, that power source dominates the mass budget and eats up almost all of the theoretical advantage. You do end up going faster, but you do so with much smaller payload.

Re:Constant Boost?

[DMUTPeregrine]

"They don't. Correct (but old-fashioned) English usage has them both have the . inside the () or "". Modern usage, especially among science type, is to have the . outside any parenthesis, to keep the base sentence internally consistent (and other logical reasons)."

Wrong. Old fashioned English usage is to place only those elements in the quotes which were actually quoted. Same goes for parentheses. See my quote of your statement above. Modern usage came from typography, and involves placing punctuation inside quotation marks and parentheses. This usage is being supplanted by the older usage for the reasons you stated.

Re:Constant Boost?

[Frnknstn]

I was not aware of the typographical link. Given that movable type has been around in Europe since at least the 15th century, I don't think I was wrong to call that standard 'old-fashioned'.

Re:Constant Boost?

[digitalsolo]

First off, it's damping, not dampening, unless you want to make something wet.

Secondly, full impulse is technically an acceleration rate, not a speed, but say impulse hits a maximum speed of 1/4 c (~167,000,000 mph), going from that to 0 in seconds without inertial damping wouldn't throw you across the bridge, it would turn you into goo, as well as obliterating the ship. I reckon that's enough pretend science though. Back to the basement I go...

Re:Constant Boost?

[weber]

"Ever" is a long time. Sometimes you don't want to go for the cheapest. It all depends on the cost of the energy versus the time spend traveling. If energy was cheap enough (and the engines capable of a large constant acceleration), we'd accelerate with 1g half the way to the destination, and almost half way there turn the ship around and decelerate at 1 g.

The distances (to other planets or evene stars) we talk (or dream) about here means spending a large fraction of your life traveling. I'd even say that during "night time" on the ship, one could sleep submerged in water or similar and the ship would accelerate even more.

Fusion adaptation?

[Ironsides]

The VASIMR engine works with plasma, a very hot gas at temperatures close to the interior of the Sun. Plasmas are electrically charged fluids that can be heated to extreme temperatures by radio waves and controlled and guided by strong magnetic fields. The magnetic field also insulates any nearby structure; so temperatures well beyond the melting point of materials can be achieved and the resulting plasma can be harnessed to produce propulsion.

Anyone know if this could be used in fusion reactor containment?

Re:Fusion adaptation?

[Anonymous Coward]

Well that's how fusion reactors work.

Re:Fusion adaptation?

[moderatorrater]

That's what they do. The problem is that when you're doing a fusion reactor, you need to have positive energy yields. With a plasma engine, you just need to be able to propel yourself. So in the short term, I doubt anything will come of this.

However, in the long term, this could be key to getting workable fusion reactors. If the technology for a plasma engine becomes widespread with several independent firms working on it, it's entirely possible that a big breakthrough for fusion reactors will come from research into these engines. If nothing else, this should lead to greater efficiency in the containment fields.

Re:Fusion adaptation?

[idontgno]

Yup, as planned for ITER.

Thanks, Andrei

Re:Fusion adaptation?

[X0563511]

Even indirect help. Those higher efficiency containment fields would end up making fusion research cheaper to perform, correct?

Re:Fusion adaptation?

[Anonymous Coward]

Yes, but I suspect this project is already relying on research done by the fusion teams, rather than the fusion teams relying on VASIMR research. The plasma containment and heating work for fusion has been going on for decades. Who know, maybe Ad Astra will come up with something novel, but I think novel ideas are much more likely to come from the ITER project, with it's grossly more substantial financial resources and brain pool than from VASIMR. That said, the geometries are different, so there are limits to the cross-applicability of specific technologies.

Now we just need a good hull...

[Cyclopedian]

Preferbly General Products #2 with a statis field.

Re:Now we just need a good hull...

[Qzukk]

a statis field.

While I applaud finding a use for the whole lot of them, I'm not sure just what kind of protection you'd get from strapping a bunch of Big Government democrats and republicans to your hull... oh wait, you meant stasis not statist ;)

Re:Now we just need a good hull...

[Coraon]

Don't forget to add a few on the front of the ship as well, less you forget the The Kzinti Lesson: http://www.projectrho.com/rocket/rocket3x.html

Re:Now we just need a good hull...

[R2.0]

"I'm not sure just what kind of protection you'd get from strapping a bunch of Big Government democrats and republicans to your hull..."

Well, they aren't that great at meteor or radiation protection, but they are cheap, there's a lot of them, and no one will really miss them.

And the drumming of their feet on the hull as they suffocate is very relaxing.

Re:Now we just need a good hull...

[treeves]

I'm sure a field of statice would be very pretty, but not much good as a spacecraft hull.

I need to know...

[Anonymous Coward]

...whether this technology is more like Windows or Linux before I can form an opinion.

Unless there's an RIAA angle, of course.

Re:I need to know...

[Anonymous Coward]

I, for one, welcome a beowulf cluster of car analogy overlords who should get off my lawn.

Franklin Chang-Diaz

[Anonymous Coward]

VASIMIR is the brainchild of the genius astronaut Franklin Chang-Diaz who also happens to look like Mr. Sulu. He allegedly figured the idea out during one mission where he had to change the polarity of the main deflector of the Space Shuttle to get away from some nasty aliens.

Re:Franklin Chang-Diaz

[Anonymous Coward]

Really, I think Chang-Diaz looks more like Chekov, which makes sense because VASIMR is an example of a "nuclear wessel."

But where does the energy come from?

[Kristian T.]

This is all fine with regards to the rocket equation, but that's just about conservation of momentum. You still have to provide it with energy, and 2*H2+O2 -> 2*H2O happens to be as good as you can get in terms of energy/mass ratio. As I see it, this plasma rocket is not really useful without a nuclear power source of some kind.

Re:But where does the energy come from?

[bornyesterday]

no fusion is involved here. they ionize hydrogen gas and turn it into a plasma and then heat it even further by applying radio waves (i.e. they basically put it in the microwave) and then they let the plasma out through a ring of magnets which focus and accelerate the exhaust. there isn't much in the way of specific data regarding this, but i don't think that the amount of energy needed to create radio waves or to ionize the hydrogen gas is really that great. the majority of the acceleration force is inherent in the energy of the particles since they are at over 100 million degrees F and that force is then amplified by magnets which themselves likely require little to no electrical power

Re:But where does the energy come from?

[mshannon78660]

As I see it, this plasma rocket is not really useful without a nuclear power source of some kind.

I think they've already solved that one.

SNAP

RTG

Nuclear Reactors for Space

Re:But where does the energy come from?

[bornyesterday]

correcting myself, they are ionizing argon, not hydrogen

Re:But where does the energy come from?

[rrohbeck]

Only nuclear reactors. RTGs deliver too little power. A Polywell would be nice if it woks.

Re:But where does the energy come from?

[edrobinson]

DiLithium crystals should suffice as a fuel.

Re:But where does the energy come from?

[ceoyoyo]

ALL of the acceleration energy comes from heating (via the radio waves) and accelerating (via the magnets). It takes a considerable amount of energy. Slightly more than you get in the kinetic energy of your spacecraft, actually.

Re:But where does the energy come from?

[vlm]

As I see it, this plasma rocket is not really useful without a nuclear power source of some kind.

Solar would work quite well, especially on a trip to the inner solar system (mercury / venus)

I think it would be wiser to head inbound for manned missions... easier to keep warm and vastly higher solar output levels.

Re:But where does the energy come from?

[TheCrazyMonkey]

and 2*H2+O2 -> 2*H2O happens to be as good as you can get in terms of energy/mass ratio.

Not true, as has already been mentioned multiple times. Nuclear power would be the an obvious choice of energy source for these types of engines. I'm too lazy to look up the numbers, but direct mass to energy conversion can definitely beat burning hydrogen. E=Mc^2 is your friend.

Re:But where does the energy come from?

[Anonymous Coward]

Just a couple of minor nitpiks. Hope you don't mind.
1) The article clearly states they use argon, not hydrogen.
2) Radio waves and microwaves are very different so I don't know how you figure "they basically put it in the microwave."
3) Microwaves do not excite hydrogen molecules or atoms of argon so the microwave comment is even sillier than previously stated. Microwaves only excite molecules with a dipole moment. Atoms and symmetric molecules (H2) do not have dipole moments.

Re:But where does the energy come from?

[zolaar]

I'm resisting my nerd-urge to nerd-correct you.

Oh, boy.

Oh boy, oh boy. Wow. This is hard. The doctors said it'd be hard, but I didn't th--...

[deep breaths]

My family would be so proud of me right now.

Re:But where does the energy come from?

[hicksw]

We need to build a launch laser (see "Fourth Profession" by Larry Niven).

Specific Impulse?

[necro81]

The article didn't mention is, so I'll ask the crowd: does anyone know what the specific impulse of this device would be when completed?

Re:Specific Impulse?

[Anonymous Coward]

Ad Astra hasn't put up a whole lot of detailed information on their website (I assume they're busy doing engineering and test work...PR can come later), but wikipedia gives an unsourced number of 3000 to 30,000 seconds, presumably depending on the settings of the engine since one of the touted advantages of VASIMR is the ability to switch between "high" thrust or high efficiency settings for the same size power supply. 3000 seconds is on par with existing ion engines, and slightly below other under development models like HiPEP, while 30,000 is quite significantly better.

It should be pointed out that VASIMR takes a lot of power to realize its full potential. The model in development is rated at 200 kW, which is about the same as the entire ~150,000 pound ISS solar array system. To justify using the VASIMR, you either need a lighter weight power supply (which should be possible even with solar because the ISS truss structure is more than just the solar arrays), or to be going for a lot of delta-V (over 150,000 pounds of fuel worth).

Efficiency is an area where ion rockets excel, but power is where chemical rockets excel. The first stage of the Saturn V actually burned propellent at a rate of about 190,000 MW, which is equivalent to nearly 200 commercial nuclear power plants. However, converting all that power to electricity so it can be effectively used in an ion thruster would be horribly impractical.

Re:Specific Impulse?

[marco.antonio.costa]

Efficiency is an area where ion rockets excel, but power is where chemical rockets excel. The first stage of the Saturn V actually burned propellent at a rate of about 190,000 MW, which is equivalent to nearly 200 commercial nuclear power plants. However, converting all that power to electricity so it can be effectively used in an ion thruster would be horribly impractical.

Of course, but since the VASIMR is so much more efficient, you would only need a fraction of that power to have a really, really fast space-only drive.

If a 190 GW-rated VASIMR engine could be built and the power plant for it ( antimatter? dilithium crystals? ) was available, then I think .999c would seem like first gear. :-P

Finally repulsor propulsion!

[Drakkenmensch]

So when can I put in an order for my very own Ironman suit?

Something Interesting

[Anonymous Coward]

The Ad Astra Rocket Company is located in Guanacaste, Costa Rica. Maybe we visit the facility and later visit the beaches... Costa Pura Vida!!!

Re:Something Interesting

[alexj33]

"Ad Astra"... Hmmmm... Read the short story from the 1930s called "Proxima Centauri" by Murray Leinster. The earth ship was called the "Adastra." Coincidence?

In the story, the thrust rockets took the Adastra to a place they wish they hadn't gone. (Insert blood-curdling screams of carnivorous alien plant men here.)

Re:Something Interesting

[Elder Lazarus]

Coincidence? Likley not, IIRC "ad astra" is latin for "to the stars"

Re:Something Interesting

[32771]

Funny how you guys have forgotten the work and effort which goes into this or how the saying goes,

"Per aspera ad astra"

Re:Something Interesting

[adamofgreyskull]

"Per Ardua ad Astra" is the motto of the RAF, and "Per Aspera ad Astra" is the motto of NASA, which has a similar translation: "Through hardwork/hardship to the stars".

The "Ad Astra" part meaning "to the stars", so it's not all that coincidental.

The risk

[Overkill Nbuta]

Does anyone know the risk of explosion of a rocket based on this technology compared to a typical fuel rocket? Does the need for less fuel result in a safer rocket?

Re:The risk

[bornyesterday]

no way of judging at this point because they only have a partial engine built. it isn't going to be used for escaping the earth's gravity well though. it'll be launched using a standard lift system and then engaged once in space.

Re:The risk

[azemute]

VASIMR is not a conventional rocket and instead uses ionized argon gas as a propellant. Argon gas is inert and thus unreactive; meaning that there's really no serious explosion danger compared to a conventional rocket powered vessel.

Mind you, much like ion drives, it can only be used in a vacuum, making it totally useless for load-lifting object *into* space and really only useful for moving them around while up there. Ion drives have classically been used as station keeping drives on space stations and in deep space probes.

Re:The risk

[Roger W Moore]

They are using Argon which is a noble gas so, other than the pressure they keep it at, there is no chance of an explosion. In fact if there was a fire and the gas was released it would probably put out the fire.

Wamprats

[Wiarumas]

Now if we can only find a pilot that can maneuver down a trench and target a thermal exhaust port 2 meters wide...

Re:Wamprats

[Anonymous Coward]

That's impossible - even for a computer.

Are there useful numbers on this?

[Animats]

OK, this is a classic plasma rocket - ionize an inert gas (here argon) and push it out with an electric field (not done in this test). So what are the numbers? How much argon are they using per unit thrust? How much electric power does this take. Is 200KW the input, or the output?

You still have to carry reaction mass; that's the argon. So you can't just keep boosting as long as you have power.

It's not a bad idea, but it's not clear how good the implementation is.

Re:Are there useful numbers on this?

[bornyesterday]

check out http://www.adastrarocket.com/Jared_IEPC07.pdf

it's a paper that the researchers published last year describing what they had done with the previous version of the engine and what they planned on doing with this version

Wiki says 3k to 30k seconds

[StefanJ]

The same incorporates "variable specific impulse" so you have to use a range.

3,000 seconds is comparable to a ion motor.

30,000 seconds is better than the predicted Isp of the Orion nuke-bomb drive.

The Numbers

[StefanJ]

The Wikipedia entry says it can be tuned for an Isp of 3,000k seconds to 30,000k seconds.

A liquid fueled chemical rocket has an Isp of about 500 seconds. A really good fission thermal rocket, maybe 1000 seconds. The Deep Space 1 ion rocket could do 3.1k seconds.

How to turn this into usable numbers:

Find the exhaust velocity. Vex. Multiply the Isp by "g". So, your chemical rocket has an exhaust velocity of about 5 kps, and your VASIMIR 30 kps.

The figure out the velocity change you want. Vd.

Then:

M(o)/(M(o)+M(f)) = e^(Vd/Vex)

M(o) = Mass of spaceship without reaction mass
M(f) = Mass of reaction mass
e = natural log number, about 2.178

A Hohmann orbit trip to Mars orbit from Earth orbit without need for aerobreaking of the like might require 20 kps. Hohmann orbit to Mercury, 40 kps.

Drawback to ion drives and VASIMIR is a really, really low thrust. You might be better off with lower efficiency but higher thrust or you'll lose the fuel (uh, reaction mass) savings in consumables, and/or risks to your crew from flares.

Re:The Numbers

[ahabig]

e=~2.71828

Re:The Numbers

[ceoyoyo]

Your VASIMR ISP figures are out by 1000. It's 3000 to 30000 seconds, or 3 to 30 k seconds, NOT 3000 to 30000 k seconds.

Generally, if you're going a decent distance, you SAVE time with a high ISP engine, even if it is low thrust. "Decent distance" depends on the specifics, but for most of these engines Mars is far enough away, the moon, probably not.

Re:The Numbers

[Fzz]

M(o)/(M(o)+M(f)) = e^(Vd/Vex)

M(o) = Mass of spaceship without reaction mass
M(f) = Mass of reaction mass
e = natural log number, about 2.178

Are you sure you got the mass ratio the right way up?
M(o)/(M(o)+M(f)) is fractional, but e^(Vd/Vex) is greater than one for positive Vd, Vex, so this can't work.

Re:The Numbers

[DMUTPeregrine]

Actually ~2.718281828 It's one of the easier numbers to remember, due to the repetition of the "1828" sequence.

SCO

[mfh]

Unless there's an RIAA angle, of course.

Those poor scientists. My sister's boyfriend's little brother's babysitter's mother's uncle's mechanic said that he has a friend who was fired from the project because he accidentally showed some of the source code to Darl McBride of the SCO Group. Was that enough punishment? You decide.

Old news...

[Meumeu]

VASIMR is a new high-power plasma-based space propulsion technology

Yeah, if by new, you mean 30 years old...

rob

[robcauss]

So, I am new here and I have a question, according to the caption under the photo on the site referenced, the unit is UNDERGOING vacuum testing. How long will it be before that guy in the picture implodes? Is this just me?

Re:Are there useful numbers on this?

[Anonymous Coward]

All those specifics are no longer important now that we realize it is possible to synthesize excited bromide in an argon matrix.

Arrrrrgon?

[mfnickster]

Q: What's a pirate's favorite rocket propellant?
A: Arrrrgon!

Q: What's a pirate's favorite sock pattern?
A: Arrrrgyle!

Q: What's a pirate's favorite rating system?
A: Arrrrbitron!

Q: What's a pirate's favorite Dudley Moore movie?
A: Surprisingly, it's 'Micki and Maude'

Re:Are there useful numbers on this?

[confused one]

VASIMIR is not ionize a gas and push it out with an electric field. It's ionize a gas, then pump MUCH MUCH MORE energy in using non-contact RF coupling. The push is against a solenoidal magnetic field.

Re:Boring

[Anonymous Coward]

Go back to 4chan, dumbass.

Physics doesn't work like you seem to think

[MarkusQ]

accelerating fuel forward so you can spit it back later.

I have no idea what that even means, or is even supposed to mean. I quote it only to highlight that the source of your skepticism seems based entirely on a gross misunderstanding of the technology involved.

I'm not the person to whom you were responding but I suspect the misunderstanding is on your end, not his. The meaning of the phrase is quite clear; in a system with sustained thrust the fuel (and reaction mass) used in a later portion of the trip has to be accelerated (along with the rest of the ship) for the whole proceeding portion of the trip. This means that, early in a long trip, the majority of the fuel/reaction mass you use accelerating the remainder, and only a small fraction is accelerating the payload. That's why large rocket use stages.

The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious.

The "reasons" may be obvious to you, but they aren't valid. The actual relationship between final speed (from a standing start in some reference frame) and the exhaust velocity has as a factor the natural log of the starting mass over the payload mass. So (to use your made up numbers) if you started with a ship that was 90% hydrazine (by mass) your final velocity would be 1000*ln(100/10) mph or about 2300 mph, over twice your exhaust velocity. If the ship was 99% fuel, the final velocity would be 4600 mph, and so on.

--MarkusQ

Re:Physics doesn't work like you seem to think

[jacksdl]

Thanks for clearing this up. It certainly wasn't "obvious" to me that a rockets maximum velocity was limited by its propellant velocity.

Velocity is not limited by propellant speed...

[Zader]

The other advantage is maximum top speed. If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious. But ion engines can potentially eject mass at much higher speeds.

The expelled mass and velocity defines the energy, which in turn you derive the important part -- the force vector and acceleration, not velocity. Velocity is the acceleration over time and is only limited by the acceleration and how long you accelerate. So yeah, your top speed is greater given the efficiency assuming higher velocity propellant over the same period of time, or acceleration over a longer time period. Not as you described. Even that explanation is overly simplified since your hypothetical rocket ship mass will also change over time at different rates due to the propellant burn rate differences, but the general idea is sound.

The much shorter version is that you can achieve any speed short of the speed of light with acceleration over a long enough period of time; it's not at all limited to the particle velocity of the propellant. (Speaking theoretically of course and completely ignoring all kinds of practical details.)

Is this really such a big deal?

[omuls are tasty]

From what I gather, they only tested the first stage of the engine, 30kW out of total 200. And they already have working models for a total of 100kW. I realize that it's probably not trivial to double the power, but is this really such a big deal?

And is there any news on the energy efficiency? The Wikipedia page suggests that the efficiency of the previous prototype was 72%, compared to 80% for working classical ion propulsion engines?

Re:Are there useful numbers on this?

[X0563511]

Why is this funny? Informative I would think.

top speed is HUH?!

[Rick Bentley]

If your hydrazine rocket can expel mass at, say, 1000 mph (making numbers up here) then the top speed of your rocket is 1000mph for reasons I hope are obvious

Not true. If I'm expelling gas at ANY speed, then I'm generating thrust. Thrust means acceleration. If I can keep the acceleration going indefinitely then I can accelerate to any speed (short of c).

Re:top speed is HUH?!

[Rick Bentley]

In fact, the equation for top speed is:

top speed = v * ln(M/m) + v0

where:
v = exhaust gas speed
M = starting mass of rocket + fuel
m = ending/empty mass of rocket
v0 = initial velocity

so the exhaust gas might be only 1000mph but you can go pretty much up to the speed of light if you can get ending mass to 0...

Re:top speed is HUH?!

[Growlor]

One thing I've always wondered about ion engines is Can we take advantage of relativistic mass to give us greater thrust? For example, can we say use tiny rest masses (like say hydrogen nuclei) accelerated to a ridiculous fraciton of the speed of light to give us equivalent (or great thrust) than a chemical rocket?

Re:top speed is HUH?!

[ShadeOfBlue]

Sort of. The additional relativistic mass does indeed contribute to the particle's momentum so that an electron at 0.9999 c could exert as much thrust as an argon atom at 0.5 c (0.9999 being an arbitrary number of nines).

However, good ol' E = mc^2 doesn't let us get away that easily. It turns out that all the energy needed to accelerate the electron to speeds high enough to pick up the additional rest mass adds mass no matter what form the energy is stored in. That is, if it takes 1.21 gigawatt-hours of energy to accelerate an electron so that it weighs 1 lb, then when I charge my battery up with 1.21 gigawatt-hours the battery will be at least 1 lb heavier, just due to the energy stored in it.

So, you're not really getting extra mass, you're just keeping less of the mass as rest mass and more as energy-mass.

I think for the same accelerating voltage, using heavier particles is more efficient, but it's too late for me to be particularly rigorous (extreme example -> photon is all relativistic mass but provides very little thrust per unit energy). And of course, that's not even considering the technical difficulties in building an accelerator that can push a lot of particles close to 1 c in a spaceship.

Re:top speed is HUH?!

[Teancum]

Not true. If I'm expelling gas at ANY speed, then I'm generating thrust. Thrust means acceleration. If I can keep the acceleration going indefinitely then I can accelerate to any speed (short of c).

But you run out of mass more quickly if you throw it away more slowly. You can't keep accelerating indefinitely as eventually you run out of mass to throw away (or having to decide if you want to throw out something in the "payload" instead).

The top speed isn't quite limited to the velocity of the exhaust as there are a number of factors that go into it, and most propulsion systems tend to have a constant force they can apply to ever decreasing mass. That is why toward the end of most conventional rocket burns you have the greatest acceleration... often deliberately cut short to avoid damaging the payload even if there might be fuel left over. It is also why some rockets spend an embarassingly large amount of fuel just trying to clear the launch tower, yet are still considered efficient engines.

If somehow you can throw out the reaction mass at something close to the speed of light, you can keep accelerating for a long period of time... which is what these alternative engines are trying to accomplish by increasing the exhaust velocity to nearly insane levels.

Re:top speed is HUH?!

[holmstar]

The top speed isn't quite limited to the velocity of the exhaust

No no no. Top speed is not limited to the exhaust velocity in any way.

most propulsion systems tend to have a constant force they can apply to ever decreasing mass

exactly... so answer me this:

You have a spacecraft that has a mass of 100kg, of which 90kg is reaction mass. Its engine can produce a force of 100 newtons and consumes 0.1kg of reaction mass per second. If the spacecraft begins at rest and fires its engine until all reaction mass is used, what is its final velocity?

You can find an answer to that question with no additional information... notice how exhaust velocity is nowhere to be found?

Re:top speed is HUH?!

[Teancum]

OK, you want me to answer this question? Sounds like a classical college physics problem.

You already gave away the answer here, but hidden in the variables.

F = m * v^2

v = sqrt(F/m) = sqrt (100/0.1)

QED, v = ~ 32 m/s

That, BTW, is the minimum exhaust velocity, treating the exhaust as purely linear stream and not accounting for variables like gaseous expansion or other factors. Any more questions? Not college but high school physics here BTW. Calculating the final velocity of the spacecraft does require a bit of calculus, but even that isn't a tricky problem.

So therefore the final velocity of the spacecraft is dependent upon the exhaust velocity of the components thrown out of the back of the vehicle.

The final velocity BTW? About 2300 m/s. The only reason spacecraft don't get going that fast on the earth is that they are also fighting a constant negative 9.8 m/s^2 acceleration. I could show the math here, but /. isn't necessarily the best forum for such types of discussions.

I'll leave it to you, if you care, to derive the actual relationship between treating the exhaust velocity as a variable and the final vehicle velocity, but keep in mind that varying the exhaust velocity will vary the force of the engine, and that is a direct relationship 1:1 with the final velocity. Aka double the exhaust velocity and you double the final spacecraft velocity.

The reason this doesn't go to infinity is because there is a fixed minimum mass to the vehicle (aka a "payload") that limits the problem instead of going with superlatives of an infinitely small spacecraft.

Lowest possible Orbit?

[32771]

So, does anyone know what the lowest possible orbit is one can use that thing from?

One reason ion engines cannot be used from ground to orbit is that they need a vacuum to operate, the other one is that the trust is too low to get into orbit.

With Vasimir however one can get higher trust than with typical ion engines. Could it be possible that suborbital trajectories might be enough?

To get a usable orbit one needs an engine which raises the perigee from the ground to a point outside the atmosphere (I even tried this in Orbiter once), could it do that too?
 

Re:Lowest possible Orbit?

[32771]

While I don't have an answer to my question, let me mention that I somehow had the dream of ion engines being the best thing since sliced bread since they have such a high exhaust velocity (v_e).

Since v_e affects the delta v linearly as opposed to logarithmically like the mass fraction this is just such a nice knob to play with.

Unfortunately the power plant weight of the ion engine is something we are stuck with forever, so there is no nice mass ratio involved with ion engines.

The other thing is that according to a Wiki article

http://en.wikipedia.org/wiki/Spacecraft_propulsion

the propulsion efficiency behaves as follows:

"if the exhaust velocity can be made to vary so that at each instant it is equal and opposite to the vehicle velocity then the absolute minimum energy usage is achieved. When this is achieved, the exhaust stops in space ^ and has no kinetic energy; and the propulsive efficiency is 100%- all the energy ends up in the vehicle"

So there is little point in using it early in the mission if you want to be efficient.

This quote also motivates the existence of VASIMIR though - you can adjust the exhaust velocity to the current spacecraft speed.

I can't offer any quantitative analysis but I don't expect my previous question to be particularly useful or applicable to any realistic mission.

Is a fine fusion reactor only 9.3e7 miles away

[Ungrounded Lightning]

As I see it, this plasma rocket is not really useful without a nuclear power source of some kind.

There's a fine, time-proven, continuous fusion reactor about 93 megamiles away from Earth, complete with a power beam system sending plenty of power out this way. They call it "the sun".

At this distance it provides over a kilowatt per square yard of receiver surface area. In orbit (or at feather-light acceleration) the collection structures can be very low mass. So even something with pretty low efficiency and derated by being at a mars or jupiter orbital distance will be more than adequate to keep the craft powered. Using such "beamed power" also means you don't have to carry fuel at all - just the reaction mass.

The question will be whether it's a better tradeoff to carry a nuclear reactor, a solar collection system, or a lightsail. (The ion engine gives you more controllability than a lightsail so solutions involving it might be better even if more massive and/or less powerful.)

Re:Are there useful numbers on this?

[marco.antonio.costa]

Clicko probably. :P

D'oh!

[StefanJ]

See what happens when you post with a low-grade fever?

I managed to post the Isp without the extraneous "k"s down the page a bit.

What about the sharks?

[SnarfQuest]

This isn't going to become a useful technology, like lasers, until you can mount it on a shark!

Old News

[goldinthemtharhills]

My grandmother used to talk about this technology all the time: "Oy! Vasimir!"

Grammar nazi

[Anonymous Coward]

If the grammar nazis can have their day, so can I.

The natural log number is 2.718, not 2.178 as you posted.

warp speed, mr. scotty!

[noanoxan]

so, where's my anti-matter reaction chamber?

slackers.

Ion drive powered tug?

[strack]

How about using one of these as a sort of space tug, where it docks with satellites inserted into low earth orbit, receives a amount of fuel from the satellites to top up its tank, say through the docking interface, and then over the course of weeks or months, raise it to a higher orbit, like, say, geostationary orbit. power could probably be beamed from a solar array in orbit to the ion engines. No atmosphere to get in the way. No need for the satellite (or cargo) to carry a large amount of fuel, or significant propulsion system. Even with the extra fuel for the tug to get back down to low earth orbit to pick up the next satellite, at a isp of 30,000, it would be more efficient than using extra boosters.

Re:Obama wants to cut NASA funding! Read this!

[Anonymous Coward]

Best first post I've read in a while!

Re:Fusion? Steam driven IEC hybrid or POPS polywel

[Ginsu2000]

Maybe it will can draw from Bussards IEC fusion with POPS... I don't necessarily trust large fusion projects that go on for decades with substantial financial resources, adding to the brain pool and not really going anywhere... especially where military grade lasers are concerned! See the late Dr Bussard's 'Google address' for his view on the larger fusion initiatives (versus the POPS Polywell). Keep it simple, the sun is a pretty good model... Or maybe the team at General Fusion and their lithium/steam/IEC hybrid will also have a shot. A steam driven fusion ion drive... now that would be a hoot :)

Missing some vital data here

[WindShadow]

You really need to know the thrust developed here before you can tell if this means anything, or at least anything which is going to change the paradigm for space travel.

The important thing may be the exit velocity, the thrust per unit weight of propellant goes up with velocity, but the energy needed goes up with square of velocity. So fast exhaust saves fuel but takes more energy.

I look forward to more detail on this.

VASIMR videos on Youtube

[plasmaben]

Dear Slashdot readers, Here are a few videos of VASIMR that we have taken in the Ad Astra lab: Kind Regards, Ben

VASIMR videos on Youtube

[plasmaben]

Dear Slashdot readers, Here are a few videos of VASIMR that we have taken in the Ad Astra lab:
http://www.youtube.com/watch?v=E_FGqb0cr1k
http://www.youtube.com/watch?v=KVsgSjm_vXg
http://www.youtube.com/watch?v=ZXofYP_VfUg
http://www.youtube.com/watch?v=yvg-Dsh9s2I
Kind Regards, Ben

KDE

[bentob0x]

Building rockets as an alternative business seems to be a new trend in the software industry, after Carmack, now the KDE team ...