VASIMR Ion Engine Could Cut Mars Trip To 39 Days

An anonymous reader writes "It would take about 39 days to reach Mars, compared to six months by conventional rocket power. 'This engine is in fact going to be tested on the International Space Station, launched about 2013,' astronaut Chris Hadfield said. The Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) system encompasses three linked magnetic cells. The 'Plasma Source' cell involves the main injection of neutral gas (typically hydrogen, or other light gases) to be turned into plasma and the ionization subsystem. The 'RF Booster' cell acts as an amplifier to further energize the plasma to the desired temperature using electromagnetic waves. The 'Magnetic Nozzle' cell converts the energy of the plasma into directed motion and ultimately useful thrust."

Comments

Billions and billions...

[GenP]

A few hundred Newtons here, a few hundred Newtons there, and pretty soon you're talking about some real delta-v!

Re:Billions and billions...

[ELProphet]

Let's run the math:

(Using classical mechanics, Google Calculator, and some rounding)
40 days, 60 million km to mars at closest approach.
Spend half the time accelerating, half the time decelerating.

For acceleration:
x = x0 + v0t + (at^2)/2
2 * 30 million km / (20 days) ^ 2 = 2e-2m/s^2

Let's use a Space Shuttle, 2,029,203 kg
The force of the engine is
F = ma = ((2 029 203 kg) * 2 * (30 million km)) / ((20 days)^2) = 40 774.5587 newtons
Work along a straight line is Force time distance
W = Fd = (40 774.5587 newtons) * 30 million kilometers = 1.22323676 × 10^15 joules
Power is work over time
P = W/t = 1.22323676 × ((10^15) joules)) / (20 days) = 0.707891644 gigawatts
Of course, we need to do this twice:
Ptotal = 2P = 2 * 0.707891644 gigawatts = 1.41578329 gigawatts

Which is surprisingly close to the power needed to propel a DeLorean through time...

Note that this is only the power needed to get the ship to Mars and then stop it; I have no idea the efficiency of their engine, life support, etc, but hey, the math works close enough for me.

I'm a little weak on my power generation math- anyone who knows something about solar panels and PV arrays want to take a shot at the power requirements?

No quite yet.

[Anonymous Coward]

No stated in this article.

But I'm pretty sure the engine discussed will need to be roughly 100x more powerful to make that 39 day trip a reality.

Re:No quite yet.

[doug]

No stated in this article.

But I'm pretty sure the engine discussed will need to be roughly 100x more powerful to make that 39 day trip a reality.

No, not really. Hauling the fuel for chemical rockets into orbit is expensive, so mostly they do hard burns to get the right speed and direction, then they coast most of the trip. VASIMR doesn't need the heavy fuel, as it is solar powered, so it provides constant thrust. Apparently days of constant acceleration makes a difference.

- doug

Re:No quite yet.

[TheRaven64]

VASIMR doesn't need the heavy fuel, as it is solar powered, so it provides constant thrust

Ummm, no. Or, rather, technically yes, but not really. In a chemical rocket, fuel and reaction mass are the same thing. The fuel burns, expands, and flies out of the back. With an ion engine, they are separate. The fuel is anything that can produce electricity (e.g. solar or nuclear plants) and the reaction mass is something that you've ionised. This still has mass, and still has to be carried with you until you throw it out of the back, irrespective of where the power comes from.

The important thing to remember is that all of these are reaction drives. They work according to the principle of conservation of momentum. When you throw some mass out of the back of your space ship, the space ship gains the same amount of momentum as the thing you throw out of the back. You can double the momentum that you gain from your engine by either doubling the speed of the ejected reaction mass, or by doubling the amount you throw out. With conventional rockets, the speed is limited by the rate of reaction, which is fairly fixed. With an ion drive, the speed is limited by the amount of power you put in.

You still need to carry the propellant, but if you can throw it out at ten times the speed then you need a tenth of the amount. If you need a tenth of the amount, then your space ship will mass a little over a tenth as much, and so the speed that it gains from this change in momentum will be almost ten times as much.

In theory, you could use a small glass of water, accelerated to a significant fraction of the speed of light, as your propellant for an entire trip to Mars and back. In practice, there is a limit to the speed to which an ion thruster can accelerate the ions it's throwing out and so you still need quite a large amount of propellant.

Re:No quite yet.

[jollyreaper]

In theory, you could use a small glass of water, accelerated to a significant fraction of the speed of light, as your propellant for an entire trip to Mars and back. In practice, there is a limit to the speed to which an ion thruster can accelerate the ions it's throwing out and so you still need quite a large amount of propellant.

And also led to the scifi observation (niven or pournelle, I forget which) that any technology that makes for a decent spaceship engine also makes for a decent weapon.

Re:No quite yet.

[CopaceticOpus]

The VASIMR engine couples well with an idea I've been pondering. Imagine building a ship designed to latch onto a largish asteroid, and then use the asteroid's mass as the ejected reaction mass for acceleration.

The ship would need a powerful nuclear reactor, and robotics capable of slowly grinding the asteroid's mass to a fine powder. The engine would need to be able to accelerate this powder to an enormous speed, regardless of what the powder was made of.

Such a ship would be able to accelerate to amazing speeds, and could be a perfect deep space explorer. Imagine if we could do a close flyby on another solar system! The powerful nuclear reactor could be used to power advanced scientific instruments, and to beam a very strong signal back to earth.

I wonder how feasible this would be. I'd love to see an unmanned craft reach another solar system in my lifetime. To me, that would be more exciting than putting a man on Mars.

Re:No quite yet.

[Interoperable]

then you could just use it as a conventional nuclear rocket (i.e. superheated steam).

The VASMIR can accelerate a neutral gas to much, much higher velocities than a steam driven rocket would. This means significantly more impulse per unit mass so the fuel weight would be dramatically reduced. Sure the reactor is heavy but it still packs a much higher power density than combustibles so all in all a VASMIR can pull off an excellent power to weight ratio for an extended acceleration.

Re:No quite yet.

[GigsVT]

Imagine if we could do a close flyby on another solar system!

A close flyby at 0.5C might not be as exciting as you'd think.

Re:No quite yet.

[drinkmorejava]

Actually, conventional rockets are not limited by the rate of reaction. Momentum is limited by the density of the gas and the cross sectional area at the throat of the nozzle where the flow hits the sonic condition. You could speed up the reaction a million times and increase the pressure in the reaction chamber as much as you wanted, but the flow will absolutely not go any faster than Mach 1 at the throat, period. ...Just saying. And yes, I am a rocket scientist.

Re:No quite yet.

[EvilTwinSkippy]

Nuclear reactors don't have to be all that heavy. The Pioneer and Voyager spacecraft had plutonium power cells. You pretty much can scale nuclear power to whatever size and power you need. (We don't usually use small power plants simply because it's more cost effective to power devices other ways.)

Re:No quite yet.

[JerryLove]

There is no free lunch. VASIMR is not radically more efficient than a chemical rocket.

Yes. Yes it is. It's a very efficient Ion drive.

http://www.projectrho.com/rocket/rocket3c2.html

This particular VASIMR is an improvement because it can handle more power... more than solar panels could provide. It will require a nuclear powersource -- a fission plant, or a very very powerful RTG.

Solar panels can potentially provide the entire output of the sun in relevent wavelengths / the efficency of the solar panel... though to do that, it would need to encompass the sun.

I suspect the most likely power would be a nuclear battery (thermo-couples powered by the heat of radioactive decay), but there are many options.

But if you are willing to heft a fission plant into orbit, then you could just use it as a conventional nuclear rocket (i.e. superheated steam)

You don't get the same speed out of that reaction mass, so you don't have the same efficiency.

Re:No quite yet.

[Anonymous Coward]

The Kzinti lesson.

Re:No quite yet.

[TheKidWho]

Vasimr is capable of Specific Impulses of 5000+... Chemical Rockets have Specific Impulses of maybe 500 at most.

That's an order of magnitude difference.

Re:No quite yet.

[ZombieWomble]

There's a bit of a confusion of terms here - nuclear reactors do have some degree of a size restriction, but neither the Pioneer or Voyager programs used nuclear reactors as their power source. They both used radiothermal generators (RTGs) - that is, they derived their power from the heat generated by the decay of a nuclear isotope, rather than a fission reaction.

This latter kind of generator is pretty much infinitely scalable, as you say, but aren't so efficient for big power demands - most of the RTGs in the probes you mention provide a few hundred watts, even when new.

For these thrusters, you're talking about burns of 10 MJ or more, which would require a vastly bigger RTG (or, more likely, a true reactor as the scaling would make it the more efficient choice) to get a reasonable pulse rate out of it.

Re:No quite yet.

[qc_dk]

VASIMR is not radically more efficient than a chemical rocket

Yes it is. The efficiency of a rocket is tied to the velocity of the propellant. VASIMR has a much higher velocity(~ speed of light /- 10%) than chemical(liquid propelant ~4,400 m/s) rockets. On the other hand VASIMR has very litte thrust. That means it is only useful in situation where there are no forces working against you i.e. already in orbit and no atmosphere.

Re:No quite yet.

[TheRaven64]

As someone else already pointed out to the last person to make that comment: Kinetic energy and momentum are not the same. Momentum is always conserved, even in the presence of special relativistic effects[1]. Kinetic energy is not. The total energy in a closed system is constant, but in a rocket a lot of it will be lost as heat, which adds nothing to the thrust.

This is actually partially the reason why ion drives are difficult to build and lower-velocity rockets are easier. The energy required scales with the square of the velocity, but the momentum scales linearly. If you double the mass of your propellant, you double the momentum and double the imparted momentum (and therefore the acceleration). If you double the velocity then you increase the power needed by a factor of four. You quickly run out of chemical energy if you try to scale this up with chemical rockets. The advantage that ion drives have is that the energy comes from outside, so the velocity is only limited by the amount of energy you are willing (and able) to pump into it. And the amount it can take before melting, of course.

If you've got a nuclear reactor then you can pump a huge amount of energy into your electromagnets and accelerate the ions to a very high speed, but (assuming no losses) you need to increase the energy you put in by a factor of four to double the acceleration.

Faster, less-massive, particles are still generally better because you have to carry fewer of them. This has a knock-on effect, because you don't have to accelerate the ones you aren't carrying, so the imparted momentum goes a lot further.

[1] You can actually derive special relativity from the principle of conservation of momentum. I had to at school; it's quite an elegant bit of mathematics, and only takes about one page. General relativity is a lot more complex and hurts my brain

Re:No quite yet.

[mmontour]

There's a bit of a confusion of terms here - nuclear reactors do have some degree of a size restriction, but neither the Pioneer or Voyager programs used nuclear reactors as their power source.

The Soviet Cosmos satellites used true nuclear reactors.

Re:No quite yet.

[cheesybagel]

Nuclear reactors for electric propulsion in near Earth space are not nearly as useful as claimed... You need to dissipate a lot of thermal energy from the reactor using radiative dissipation. The dissipation panels end up being so large and heavy you were probably better off using the solar panels in the first place.

Once you get away from Mars though, they start to make sense.

Re:No quite yet.

[Nefarious Wheel]

yes but if we use all the comets, where will we get the ice without bugs in it to cool the oceans to combat global warming?

I think we Oort to have enough.

Sound

[whisper_jeff]

But does this process create feedback over communications systems to create cool sound effects as the ship whooshes by?

Sorry. Star Wars geek moment...

Re:Sound

[isaac]

But does this process create feedback over communications systems to create cool sound effects as the ship whooshes by?

Quite possibly, actually; at the very least, there might be enough radio emissions at audible frequencies as the plasma dissipates in the presence of a magnetic field (i.e. planetary orbit) to induce something audible in a speaker wire or analog amplifier. It's been speculated that such a mechanism is responsible for the phenomena of hissing, whooshing, or popping sounds heard simultaneously with the appearance of meteorites passing through the atmosphere (as opposed to delayed like a sonic boom.)

-Isaac

Re:Sound

[MobileTatsu-NJG]

My thoughts on why one hears other spaceships around in sci-fi movies is that their propulsion pushes directly off of space time which creates waves which one can hear when they hit the side of the spaceship.

Ah. That explains the John Williams score we hear in space, too.

Re:Sound

[mlush]

I've always assumed the whoosh was synthesized by the ships systems as a audio representation of the local battlespace

Re:Sound

[tsm_sf]

If they don't have an audio representation for silent space battles, someone always ends up piping 'Blue Danube Waltz' over the ship's PA.

Re:Tag as SLASHVERTISEMENT

[Anonymous Coward]

Yeah, I was totally going to go for one of those conventional rockets for my trip to Mars, but now I'm seriously considering a VASIMR Ion Engine.

Re:Tag as SLASHVERTISEMENT

[dkleinsc]

Yeah, coverage like this really makes we want to go out and buy one for my own space ship.

Seriously, I think this might be getting coverage because this is potentially technology that could make a manned mission to MARS much more feasible and safer. Of course, getting back might still be challenging, but I for one would take the honor of being the first man on Mars away from Philip Fry if I could.

Re:I'm dizzy.

[ageoffri]

39 * 2 = 78 days for round trip to Mars in the article which is less then 3 months. The 39 days is one way just to get there.

Please, please, PLEASE...

[Kirin Fenrir]

Let the common name be "impulse engines".

Re:Please, please, PLEASE...

[John Hasler]

All rockets are "impulse engines".

Needs serious power input for fast travel

[Anonymous Coward]

Mind you to obtain this 39 day route, you're not going to be doing it by feeding the VASIMR's klystrons off solar cells stuck to the outside of the ship. That's more of a one year sort of trip.

If you want the 39 days, you're going to need to pump the voltage in with a classic onboard nuclear reactor. Not to worry though, both the US and Russians made and tested (The Russians flew) several dozen types of space borne fission reactors in the 60s-80s so this is no great leap. Other than perhaps getting the eco-hippies to shut up about lofting lots of highly enriched nuclear fuel.

Comment removed

[account_deleted]

Comment removed based on user account deletion

Re:I'm dizzy.

[click2005]

You could have travelled those 800 miles in 4 hours with a VASMIR Ion Drive.

Actually...

[denzacar]

It already is.

Re:Can it be used for ISStation keeping?

[Anonymous Coward]

LOL, if it can push a rather large ship out of Earth's orbit, it can keep the ISS in orbit. The one that is being sent up is rather on the small side though. There was mention in one of the articles about it recently that it could be used for station keeping however.

Bear in mind that it requires a power source for all the energy expended in heating and controlling that plasma, shich in this instance would have to come frrom the station's solar panels. That kind of energy draw was never considered in the original design.

made in Webster, TX

[boristdog]

Hooray! Now maybe Webster, TX will be know for something other than being a speed trap between NASA and I-45.

Re:Tag as SLASHVERTISEMENT

[wisty]

And in 12 months time, Richard Branson will probably have one.

Re:I'm dizzy.

[DoofusOfDeath]

In three paragraphs we go from 89 days to 39 days.

It's called acceleration. Duh...

Re:CANADA ROCKS!!!! Woooh

[thrillseeker]

Oh good point ... so is it 39 days or, ahem, 39 Canadian days ...

Old news

[davidwr]

If I'd left when I first heard this, I'd be about 1/3 way there, time-wise.

Re:"A new NASA rocket engine"

[sh00z]

Also, correct me if I'm wrong, but ain't VASIMIR developed private company, not by NASA? Sure, NASA is working together with Ad Astra Rocket Company, but does NASA really deserve all the fame?

This started as a NASA project, at the Advanced Space Propulsion Laboratory at the Johnson Space Center.

Dr Franklin R. Chang Diaz (the other former astronaut involved, and not mantioned in this Canada-centric article) took the project to private industry in 2005

Bathroom stops

[NoYob]

Trip times may vary as folks stop for bathrooms, coffee, and whatnot along the way. So that's where they're getting the 50 day difference.

Re:Can this be the primary engine of a space shutt

[geckipede]

The vasimr can operate in a high thrust mode. It's got an operating method that acts a bit like an afterburner, if you're willing to lower your efficiency.

It can't manage a positive thrust to weight ratio in any mode, and in any case can only operate in a vacuum, so it would end up being launched from ground on top of a chemical rocket. In theory once in space you shouldn't need other types of engine.

Re:Tag as SLASHVERTISEMENT

[Anonymous Coward]

For 10 years now, I'm commuting to work with my old Ford Pinto.
Until I read the ad in the news paper and decided it was time for a change.
Now I'm owning on of the modern cars with a VASIMR Ion Engine and have cut my commuting time down by 105 percent. And with the money saved I'm buying a new house, yacht, motorbike and wife.
And when my boss saw my new VASIMR ion engine has gave me a raise and promoted me !

Thanks VASIMR ion engine cooperation, your incredible product saved the day and changed my life for the better !

Re:Can this be the primary engine of a space shutt

[Guysmiley777]

These types of ion engines are only useful once you're in orbit, they're of no use in a deep gravity well or in an atmosphere. They are useful for things such as station keeping thrusters in satellites where you don't want to have to carry a lot of fuel with you.

Sure, they'd be nice for a Mars mission as well, the problem is that they require external power. Not a big deal when you're talking about a couple hundred watts of electric power for less than a Newton of thrust. When you're talking about hundreds of kilowatts it gets a lot more impractical.

Re:CANADA ROCKS!!!! Woooh

[Anonymous Coward]

Bad premise. Since the Bush administration, most of us don't have any national pride.

True, but then Canada isn't a real country either! (ducks!)

Not in space

[NoYob]

Other than perhaps getting the eco-hippies to shut up about lofting lots of highly enriched nuclear fuel.

From what I gathered from Googling, the only thing the "eco-hippies" have a problem with is when those nuclear reactors fall back to Earth - or when they're sunk during a nuclear submarine or ship accident.

I don't think anyone will have any problem launching a nuclear reactor into space other than the astronauts who are on board with it. And considering the long track record of such things, I don't think they will have a problem either.

Re:Not in space

[CrimsonAvenger]

From what I gathered from Googling, the only thing the "eco-hippies" have a problem with is when those nuclear reactors fall back to Earth - or when they're sunk during a nuclear submarine or ship accident.

Nah, when the subject of launching one into space came up decades ago, they opposed it completely, on the grounds that it might fall back to Earth.

I should also note that the reactor vessel of a ship's nuclear reactor isn't going to corrode to the point of allowing the contents out in less than many centuries.

I don't think anyone will have any problem launching a nuclear reactor into space other than the astronauts who are on board with it. And considering the long track record of such things, I don't think they will have a problem either.

Considering the way the word "nuclear" causes panic in the minds of many Greens, I'd guess you'd have a lot more problems than that if you tried to launch one.

Re:I'm dizzy.

[gEvil (beta)]

He's clearly taking the Interplanetary Date Line into account in his calculations.

Re:Primary power source?

[confused one]

They usually discuss using it with solar arrays for near Earth use and with nuclear reactors on the order of 10-100MW for Mars and outer solar system.

Re:CANADA ROCKS!!!! Woooh

[Anonymous Coward]

About as many as don't have heath care coverage.

4 out of 5 astronauts surveyed

[bl8n8r]

preferred 39 days of abstinence to 6 months!

Re:Tag as SLASHVERTISEMENT

[slack_justyb]

I have to agree with the grandparent. VASMIR is old news as far as cutting edge technology. Really, why not put out an article about how awesome Blu-Ray is (rolls eyes)? So let's look pass the whole VASMIR thing and start looking at the applications themselves, "to be used on ISS in 2013" strikes me as the most useful piece of information in the summary. VASMIR technology is getting better and better every day, but so is diesel and bio-diesel technology.

At some point, continuing to beat the gong on something starts to make it look like those "Wow" commercials from the Windows Vista days, or all those promises of action during the campaigning days here in the United States.

Re:CANADA ROCKS!!!! Woooh

[Bob-taro]

Oh good point ... so is it 39 days or, ahem, 39 Canadian days ...

That's 39 Metric days. To convert to American days, you double it and add 30.

Re:I'm dizzy.

[Aceticon]

I think they mean 39 work-days, 89 days in total.

Obviously the engine will not work on weekends, so that's 2 days out of 7, roughly 24 in total.

Then there are religious holidays for the astronauts, not to mention national holidays for each nationality represented in the team. I reckon that's about 3 days a month, or roughly 9 days in total.

Then there's mandatory vacation time, about 25 days a year or roughly 8 days for the trip.

Assuming everybody is working really hard, coffee, cigarette and bathroom breaks will probably only add up to 3 days in total.

Of the remaining 45 days, one is preparation before the trip, one to really get going and one is basically wasted on the whole "arrival, get the luggage out and unpack it". Same thing on the Mars side. That's another 6 days.

This is the reason for the difference.

Re:Tag as SLASHVERTISEMENT

[lordfoul]

Pass..I hear it won't run Hulu in full Screen..

Re:Tag as SLASHVERTISEMENT

[operagost]

Why buy a new car, when you can just make your "pinto" bigger with C1AL15!

Newsflash

[Dunbal]

Engine that hasn't really been invented yet might rhubarb rhubarb rhubarb rhubarb....

      Of course as a nationalized Costa Rican citizen, perhaps I should celebrate the fact that Franklin Chang Diaz is the creator of this engine, however let's wait and see until it has actually been tested before we make specific claims, yes?

Re:I'm dizzy.

[TheRaven64]

Depends on how much he weighs. The drive provides a force of 0.5N. A typical car plus passengers masses around 1000kg. F=ma, so, 0.5 / 1000 gives him an acceleration of 0.0005 m/s/s (ignoring friction and air resistance). 800 miles is a little under 1,300 km, or 1,300,000m. Assuming a stationary start, and accelerating for the whole time, we get sqrt(2s/a), which is around 51,000 seconds, or around 14 hours. Of course, after that time he'd be going quite quickly, so he'd probably want to be slowing down for the second half of the journey which increases the total travel time to about 20 hours.

Ion drives are not (yet) fast. They provide a much lower acceleration than conventional rockets, which is why no one is talking about using them to get to orbit. They use a lot less propellant to produce this thrust than an equivalent chemical rocket though, which means that they can provide this thrust for longer. After 14 hours, the car would be going at 25m/s. Not particularly fast; a chemical rocket can get to that speed in a couple of seconds. After a week it would be going at over 300m/s, which is a lot more respectable.

Your distance from earth to mars looks sensible, and makes the average speed 16.3km/s. Assuming linear acceleration and deceleration (which is incredibly wrong when we're talking orbital mechanics, because this would be a transfer orbit so you'd actually be accelerating for most of it), that would mean that the top speed would be 32.6km/s and you'd spend half of the time accelerating to this speed and half slowing down from it. That gives a delta v of just under 0.02m/s/s, which means that either they have more than one ion engine on the craft, or they are using something that weighs a lot less than a car. At that acceleration it would take just over 3 hours to travel 800 miles, which is close to what the grandparent said. I'm not sure where you get your 1.7km/s/s from, but I I think you dropped a 'k' somewhere in your calculations.

Re:Tag as SLASHVERTISEMENT

[bds1986]

If something goes wrong on the surface, help is 39 days away, instead of 6 months.

no big loss

[juan2074]

If we launch from Cape Canaveral, we only risk contaminating Central Florida.

Re:Tag as SLASHVERTISEMENT

[pixelpusher220]

I believe the 'safer' idea is that instead of a 2 year round trip, we might be talking a few months. Lots easier to get help when it's only 45 days away rather than 6-12 months.

And yes, 'easy' in this case is still ridiculously hard...but still it's a good bit better than 2 years.

Light speed probes

[GodfatherofSoul]

I'd like to see a test probe fly just as fast as we can get it to go. I'm sure it'll be pulverized by dust motes if you can get it moving fast enough, but it would be cool to see something we've created jetting about a some considerable fraction of light speed. Maybe you can get to another star system in a human lifetime?

Re:Light speed probes

[nitehawk214]

Yes, as you get get going faster, your effective mass goes up. This means to get to relativistic speeds you must apply thrust exponentially. Another problem is an engine of this type will eventually spit out all of its plasma and will run out of "fuel", so to speak.

Still, since you can run a plasma or ion engine from an external power source (the sun), you do get a massive jump in specific impulse.

Re:Tag as SLASHVERTISEMENT

[avandesande]

The logical thing to do would be to get the return vehicle in orbit around mars, ready to go before an astronaut leaves earth. This would be make reduce the number of errors that would put an astronaut into a life threatening situation (return failure).

A relatively small rocket could be used to get the astronaut off of Mars' surface. It won't take much with its lower gravity and thin atmosphere. We could even test all these scenarios remotely.

How did you get modded up?

[WindBourne]

First, it is easy to send up lots of uranium into space. It can be sent in capsules that can take any issue (heat, water, etc). BUT, the simple fact is, that the moon has been found to contain Uranium. And it appears to be a LOT. It should be possible to mine it and send it various places. While I was actually a fan of Mars first, now I back the moon due to the water and uranium. Combine that with an electric launcher and it should be possible to send missions at extremely fast rates through the solar system.

Re:I'm dizzy.

[CrimsonAvenger]

Depends on how much he weighs. The drive provides a force of 0.5N. A typical car plus passengers masses around 1000kg. F=ma, so, 0.5 / 1000 gives him an acceleration of 0.0005 m/s/s (ignoring friction and air resistance). 800 miles is a little under 1,300 km, or 1,300,000m. Assuming a stationary start, and accelerating for the whole time, we get sqrt(2s/a), which is around 51,000 seconds, or around 14 hours. Of course, after that time he'd be going quite quickly, so he'd probably want to be slowing down for the second half of the journey which increases the total travel time to about 20 hours.

"quite quickly"? He'd be going (using your approximations) about 25.5 m/s. Which is only about 92 km/hour (57 miles per hour for those who don't do metric). He should be able to stop just fine with normal brakes in just a hundred feet or so.

Re:You were up-modded by people who don't read

[andrikos]

Spend more time reading, and less time posting, please.

You must be new here, right?

Don't let this one fade into obscurity

[prisoner-of-enigma]

I for one am tired of hearing about all these wonderful propulsion ideas that inevitably fade into the background. What is it going to take to get one of these damned things built and tested?

Yes, I know the trite answer is "money," but that's merely a means. What we lack is desire. I have a funny feeling that all the billions we've wasted on the ISS and keeping the nigh-useless Shuttle flying these past decades could've easily funded an unmanned test vehicle that could've used VASIMIR to fly to Mars and back as a technology demonstrator.

Let's quit talking about what this technology "could" do and actual do it for a change. If it's feasible then we should be screaming at our Congress-critters to get behind it.

Oy...

[xx01dk]

VASIMR.





...what.

Re:I'm dizzy.

[TheRaven64]

Yup, I wrote that before calculating exactly how fast. Of course, in a hypothetical world where friction is low enough that you could use a 0.5N ion engine on the ground, your brakes probably wouldn't work so well...

Re:Can it be used for ISStation keeping?

[TheRaven64]

You mean, the thing I described in the sentence immediately following the one you quoted?

Re:CANADA ROCKS!!!! Woooh

[jafac]

I dunno.

If Freud were alive today, he'd have a field-day comparing launch vehicles (size, reliability, national ego, etc.) to penises. I reckon especially with the new flesh-colored Ares upper-stage.

I know I do.

Re:Tag as SLASHVERTISEMENT

[Creepy]

Actually, I've found the latest VASIMR progress quite interesting, but that article seemed more intent on promoting Canada than feeding news. Heck, the ISS mission has been known since 2007.

A google search was also able to come up with an article with a lot more meat. This explains that the project is working towards 200MW ion rockets (MUCH more powerful than the earlier .3kW), would be powered by a cheap nuke drive instead of solar panels, and they believe it's doable by 2020. Similar info is in PopSci this month.

Now if they could just get that dense plasma fusion device (see Slashdot yesterday) to power the craft instead of fission, that would be cool... yeah, I know I'm pipe dreaming again, but I can't help it.

Slight Problem

[maroberts]

Gravity wells. As has been mentioned before, ION engines are great for long distance travel. The only problem is getting down and up from Mars or any other planet you decide to visit, where you're back to needing a big rocket for the high thrust needed. So you can get your astronauts in orbit round Mars, but the problem is how to get them down and up from the surface?

Canadian Space Agency

[stoob0]

Do all Canadian astronauts launch with mittens close at hand? Does the other pocket visible in the picture contain pucks?

Re:I'm dizzy.

[gnieboer]

Another main reason for the length of time involved is the orbital dynamics of the positions of the two planets. There is a astro concept called a Hohmann Transfer (http://en.wikipedia.org/wiki/Hohmann_transfer_orbit), which is a specific impulse efficient way of moving from one orbit to another. But it takes time, and requires waiting until the bodies are in the right position before we do it.

So you end up having to hang around on Mars for several months.

Going just a -little- bit faster doesn't gain anything because then you just have to wait longer for the planets to align.

Since this proposes something vastly quicker, the comment in the article about being able to do it in one planetary pass is what makes the 89 days possible. Requires tons more delta-V to do an orbital transfer this way, but the amount we'd save on human sustainment would more than make up for it.

Of course, not sure yet about hauling the nuke reactor into space...

Re:"A new NASA rocket engine"

[Zvezdanaut]

Actually, this was started as a private project. Dr. Chang Díaz has been working on some form of concept/design since his graduate school days at MIT in the late 70s. See the Ad Astra site. "Dr. Chang Díaz invented the VASIMR® concept and has been working on its development since 1979, starting at The Charles Stark Draper Laboratory in Cambridge Massachusetts and continuing at the MIT Plasma Fusion Center before moving the project to the Johnson Space Center in 1994. In the development of the VASIMR® engine, Ad Astra Rocket Company was teamed with NASA JSC, Oak Ridge National Laboratory, University of Texas at Austin, University of Houston and other various government space and research centers, industrial companies and academia including foreign universities." Ad Astra subsequently went private again on January 14th, 2005.

Reaction mass vs. Reactor Mass

[James McP]

The features of nuclear steam and VASIMR are pretty much a list of opposite pros and cons. E.g.:

nuclear steam doesn't waste any mass with electrical generating components so it is lighter overall than VASIMR.

Contrast this with VASIMR which can run on solar arrays and can share its electrical power source with other components.

Nuclear steam has a lower exhaust velocity so the overall power source requirement is lower.

Vasimir's higher velocity mean the specific impulse of reaction mass is 5x greater than nuclear steam, reducing carried mass and power generating needs. This has significant impact when duration of thrust is very large.

These attributes define the design envelopes.

If you need occassional thrust without a lot of mass and already have an electrical power source, VASIMR is good (e.g. orbital correction for satellites and space stations).

If you want to move a payload under continous thrust for days on end, a nuclear rocket is a good choice.

If you have a payload that has a fairly beefy electrical power source that you want to move under continous thrust for weeks on end, VASIMR is worth considering but may or may not be the best choice.

If you want to move a payload under continous thrust for a many months, go with VASIMR.

E.g. a russian ERTA generator can produce 150kW for 1.5 years while weighing 7500kg. A 150kW VASIMR drive would weigh 225kg and produce 4N. Fuel for 1.5 years is 9300kg. Total starting mass for 1.5years of 4N thrust is 17,025kg.

The SNTP nuclear rocket weighs ~13kg/N so 50kg of motor. Generously assuming the nuclear fuel would last 1.5 years, it still needs 49,000kg of reaction mass. Total starting mass for 1.5 years of 4N thrust is 49,050kg.

Assuming I've done the math right (which is not guaranteed since it involves partial fraction calculus) under that whopping 4N of thrust the VASIMR rocket will crank up to yawn-inspiring 0.004 m/s while the nuclear rocket will do a pokey 0.0012 m/s. Distance wise, the Vasimir will traverse 10.8 km vs. the nuclear rocket has only covered 3.8km.

While utterly theoretical, it does show that for ultra long burns, the reactor overhead of VASIMR is outweighed by the reaction mass increase of a nuclear rocket.