# Talk:Variable Specific Impulse Magnetoplasma Rocket

## UNITS discussion - m/s vs sec.

From the article: "Current VASIMR designs should be capable of producing specific impulses ranging from 10,000-300,000 m/s". Why is specific impulse expressed in m/s? Shouldn't it be in seconds? Maybe those numbers actually refer to the effective exhaust velocity, as listed here? --Grnch 23:23, 7 Jun 2005 (UTC)

It's good to see NASA using SI once in a while, as their own Inspector General told them to do, consistently. Seconds are SI units of time; seconds are not SI units of specific impulse. Specific impulse and effective exhaust velocity are not different things, even though they may be expressed with different numbers and different units in Fred Flintstone units.
Yes, when it is expressed in meters per second, it often is called effective exhaust velocity. When it is called specific impulse, the units are often stated in SI as the units of impulse (newton-seconds) divided by the units of mass (kilograms), or N·s/kg. But in the case of the SI units, the numbers for either are the same number: 1 N·s/kg = 1 m/s, so it doesn't matter if you reduce the N·s/kg to m/s because that is what they are in terms of base units. In other words, 300,000 m/s is 300,000 N·s/kg. But while 30,000 "seconds" is the same as 30,000 lbf·s/lb or 30,000 kgf·s/kg, you get different numbers if you express it as an exhaust velocity in terms of speed: it is 294,000 m/s or 965,000 ft/s. Two different numbers, but really measuring the same thing, calculated from the same values for the input variables.
Those "seconds" are really lbf·s/lb, or the equivalent kgf·s/kg. But there are no kilograms force in the modern metric system, so these are not the proper SI units. Of course, some people have made a post-hoc amendment to the formulas, gratuitously thowing in a metrological conversion factor which doesn't belong there because of the physics, to make the dimensional analysis work out for using "seconds" for specific impulse. Ends up being the same result as what actually happened originally, when the rocket scientists just used "pounds" to cancel out "pounds", never mind that in one case it is pounds-force and in the other case it is pounds-mass. ____

## When will it be practical?

How long until such a craft will be practical?

It's semipractical now. Unfortunately, it's severely limited by the power/weight ratio of energy sources... even nuclear power is inadequate, due to weight of the reactor and shielding. So, in practice it probably doesn't work better than conventional ion drives. What's really needed is lower ISP than ion drives, but VASIMR gives same/higher ISP. Wolfkeeper 00:34, 2005 Apr 22 (UTC)

According to the article: The radio waves and magnetic fields would be produced by electricity, which would almost certainly be produced by nuclear fission. Any conceivable chemical fuel used in a fuel cell or to activate a generator would be more efficiently used in a conventional rocket. Solar energy could be more efficiently used in a solar thermal rocket. However, wouldn't a nuclear thermal rocket also use nuclear energy more efficiently than VASIMIR? In any case, VASIMIR has a higher maximum specific impulse than solar thermal, so solar power should not be ruled out.

I believe a nuclear thermal rocket's efficiency would be limited by the temperature its core elements could withstand; exotic ideas like gaseous cores aside, that's only a few thousand Kelvin compared to VASIMIR's 10 million K. I'm no expert, though, so if someone more authoritative comes along pay me no mind. Bryan 01:18, 31 May 2004 (UTC)
I'm no expert either, but the whole point of a VASIMR is that you can have outrageously hot exhaust gases (and let them cool when you're in a hurry). Of course, this guzzles power, so you need lots. It certainly is easier to build a high-power nuclear thermal rocket than a nuclear power plant producing the same power output that can be carried aboard a spacecraft. But on a long trip, you worry much more about reaction mass than consumption of nuclear fuel. So a fission-powered VASIMR seems reasonable.
No, probably not IMHO. There's a relationship between ISP and optimal mission delta-v- they should be comparable. VASIMR in high gear has an ISP of 100,000 m/s. I'm not aware of *any* mission that needs that. In low gear, it's more like 30,000 m/s, which is a better match for a Mars mission. Trouble is, lots of other drives have similar performance as low gear, at similar power consumptions.
If I understand correctly, what you mean by "optimal" here is "minimum total energy".
Correct, but the energy generator equipment comes out of the payload (as does the fuel of course). And energy efficiency is inversely proportional to exhaust velocity. The big problem with any really high ISP drive is its gross inefficiency- almost all of the power ends up in the high speed exhaust and very little ends up as kinetic energy of the vehicle (except where the vehicle ends up going similar speed to the exhaust, then the exhaust stops and the vehicle gets all the energy, actually the maths is even more bizarre than that...)
Well, gross energy inefficiency, which is balanced against high efficiency in reaction mass. If you have plenty of power, but limited mass, then this is a good tradeoff. --Andrew 18:54, Apr 22, 2005 (UTC)
This is not necessarily optimal for all mission plans - in particular, an energy-rich design (perhaps built with a large fission reactor - Kiwi-2A produced 4 GW) might use more energy than necessary in order to save on reaction mass.
You seem to be effectively assuming that the generator is lighter than the propellent. VASIMR's power requirements in high gear are so high that that assumption isn't valid- the power/weight ratio of current nuclear power isn't much better than solar.
Yes, I'm assuming that the generator is lighter than the propellant. For a long enough voyage, of course, this is almost certainly true, since the fuel requirements increase exponentially with delta-v, but I think your point is that maybe there aren't any long enough voyages to make this trade-off worth it.
Nevertheless, current nuclear systems are Radioisotope thermoelectric generators, which produce far less power than a critical nuclear reactor. --Andrew 18:54, Apr 22, 2005 (UTC)
If you're mass-limited and you have to carry your energy store with you, your optimal exhaust velocity (that is, for obtaining maximum delta-v from a fixed mass) is that where you eject a piece of depleted energy store at a veolcity where it carries off all the energy it contained as kinetic energy (in your frame).
Sure. But that's not VASIMR you're describing.
Think of it this way: suppose you get your energy from matter-antimatter annihilation, so there's plenty. You should then run your engines at huge Isps so you don't waste propellant (since energy is plentiful). On the other hand, if you're really energy-starved, lower Isps are a good idea.
Yes. Right now we don't have useful antimatter drive, and even if we did, it's unclear that VASIMR would be the best system to use it.
But maybe I don't understand what you mean by an optimal Isp. --Andrew 02:04, Apr 22, 2005 (UTC)
On the other hand, a VASIMR needs a certain minimum energy input to maintain its magnetic bottle and to heat its plasma. It is quite likely that the solar cells required would be enormous and unsuited to acceleration, defeating the purpose of the variable specific impulse.
In principle, the magnetic bottle doesn't need any energy to maintain it; superconducting coils should work.
Well, sort of. There's cryogenics, support and control circuitry, and so on. I mean, solar cells are really low-power when you're talking about megakelvin plasmas. --Andrew 02:04, Apr 22, 2005 (UTC)
As for chemical power, if you're using up the chemicals anyway, why not use them as reaction mass? And if you're doing that, then you have enough reaction mass to afford a low specific impulse.
That's correct. If you generate power by a chemical reaction, then sending the chemicals out the exhaust by using the energy liberated is a win. Wolfkeeper 00:34, 2005 Apr 22 (UTC)
All this suggests that that part of the article could use some clarification. --Andrew 05:54, 2 Jun 2004 (UTC)
If your propellant is hydrogen then surely the best source of power is a fuel cell. Of course you'll have to carry oxygen which will increase the weight of the rocket but there's two things that can mediate that. At launch time you can use atmospheric oxygen. For manned flights you'll want to carry oxygen to breath. The output of a fuel cell is water, which can be seperated back into hydrogen and oxygen at high efficiency using membranes and solar heating. Not only is the production of hydrogen and oxygen in this manner likely to be more efficient than powering the rocket using solar panels, it is also a lot less complicated (and therefore less prone to failure) and can be used like a battery to store solar energy when the rocket is not in use.
Keep in mind that for such an engine there are two things needed: energy and reaction mass. The difficult question is where to get the energy. If you get it chemically (from hydrogen and oxygen, say) what do you do with the reaction products? If you discard them, they might as well serve as reaction mass; this is most efficiently done in a straight chemical rocket - the high specific impulse requires more energy per unit reaction mass than can be obtained from chemical reactions. Perhaps more simply, you will need so much of the unreacted chemicals that you will lose the advantage of the low reaction mass requirements. In order to re-use the chemicals, you must obtain the energy to return them to their unreacted state from somewhere, so you're back to needing an energy source.
It may be appropriate to use a hydrogen-oxygen fuel-cell/electrolysis closed cycle as an energy storage system, or as part of a solar (or nuclear) energy collection system, but ultimately the energy needs to come from some other source. Moreover, the primary usage of such an engine would be for continuous low-level use, which requires a long-term energy input; a storage system won't help with this. Of course, a VASIMR has another mode, a high-thrust mode, and in this case it might be appropriate to use some sort of stored energy, but it will be difficult to store enough to be useful in a reasonable amount of chemicals.
High specific impulse engines are designed to take advantage of plentiful energy and scarce reaction mass. Almost any system based on chemical energy will require far too much mass to carry enough energy - chemical energy is not really dense enough to carry around. Nuclear energy can be obtained from much less material, and solar energy can (sometimes) be obtained from the environment. --Andrew 05:19, 11 Jul 2004 (UTC)
As for when a VASIMR-propelled craft will be practical, the technology exists today, more or less; NASA has run prototypes. But they're big, complicated, and fragile. I believe that they're also poorly suited to launch applications, at least as used now; the power consumption at launch is huge, and if you're not getting it from the reaction mass, you have to have some huge power plant aboard. So if they're no use for launch, then they're mainly suited to long space-to-space voyages. And since they're big, they're suited to big vehicles. The market for large, complex space-to-space vehicles suited for long voyages is, so far, pretty small. --Andrew 05:54, 2 Jun 2004 (UTC)
The bottom line to me is that only the very lowest gears for VASIMR is that much use, the high gear might get you a small speed boost when you're more or less coasting, but the 1000 seconds end determines whether it's useful or not. In fact, I've a horrible feeling that VASIMR is inefficient for some reason at 1000 seconds, which is why they're not talking about it. If so, then a system using Hall effect thrusters might in fact be better- and there's no reason at all why Hall effect thrusters can't use VASIMR's power supply.
But none of the papers are emphasising this point; they talk about the high end. Rockets are like drag racers- they need to accelerate. VASIMR is like advertising a drag racer's fuel efficiency at high speed. Who cares?
Still, VASIMR is an ongoing research project, and it's been ongoing for 30 years. That's worrying in and of itself. Wolfkeeper 14:50, 2005 Apr 22 (UTC)

#### earth launch characteristics?

One idiots questions. Bear in mind this is massively speculative. But answers would be greatly appreciated. This is definately discussion.

VASIMR seems to have two ionization systems. First, hydrogen is ionized through radiowaves and magnetically threaded into the core. Second, magnetic containment and further radio bombardment serve to raise core temperature and presumably ionization state to far-exceeding-astronomical levels. (see Saha ionization equation). Essentially fancy ways of dumping lots of energy into a exceedingly ionized plasma core.

How would VASIMR handle earth launch characteristics?

It wouldn't. You can't strike the plasma at earth atmosphere pressures. At very high altitude, it's theoretically possible though. But, the thrust/weight ratio of VASIMR, with or without the power source is *very* much less than 1, so it wouldn't do much good.Wolfkeeper 00:34, 2005 Apr 22 (UTC)
Some comments to this effect are now in the article. --Andrew 02:04, Apr 22, 2005 (UTC)
How does earth's atmosphere come into play for starting the plasma? the plasma is extremely dense, I cant see earth as being any way signficantly different from the relative zero pressure of space.
The main reason I think VASIMR is interesting for launch is because it partly escapes the conventional aeronautical limitations of being bounded by reaction mass. There's two (correlated) adjustable limitations; the amount of energy you can dump into your system at any given time and how many ions you are generating. VASIMR isnt designed to generate enough nearly enough ions for high thrust and it doesnt pour nearly enough energy into the system in the first place to support all those ions, but these are just current limitations. VASIMR is really three systems in one; a plasma generator, a plasma exciter, and a magnetic nozzle system. With a scaled ion/plasma generation systems and much higher energy output (when the exciter becomes a full fledged fusion reactor), it doesnt seem entirely implausible for a launch system; one that can be scaled very well. Particularly when you can ignite the (extremely costly fusion reaction planetside.

Would there still be a "completely" ionized plasma core, or would the core start shifting towards more merely-astronomical temperatures & ionizations (or even, gasp, cold plasma states)? In launch conditions, the core trades off ion speed & presumably/consequentially temperature for sheer ion quantity, but then how do ions get made? This is probably cyclical, but isnt a very hot plasma core instrumental to rapidly exciting more plasma?

Bear with me; you want to be able to (more or less) dump equal amounts of energy into the primary plasma core whether you're lifting off or interplanetary. Earth-bound launch is mainly special because it requires a huge number of already-excited ions coming into the system. Do you have to generate these ions as you're ejecting them, or does it make any sense to have a secondary ion/plasma containment-or-generation system? Containment makes sense in terms of building up plasma pre-launch, but we're not aiming for high-velocity, just lots of ions. What is the efficiency of radio-wave ion generation compare to, say Pulsed inductive thruster or other ion generation systems? Pulsed inductive thruster is interesting because it seems like you could scale it three dimensionally + with relatively little weight. How different would the plasma flow be for earth launch? Lower energy makes me think the containment would be easier, but how adaptable are the magnetic containment systems? Again, massive speculation, but wouldnt velocities be far different?

I'd like to know a lot more about the radio-excitiation. jt60's rf excitation is the only source of information i've found so far, and is somewhat disturbing. the ion generation / general heating system runs just shy of 110mhz at only 10 MW... and it looks massive. I've found little discussion on the topic at large, even with Plasma source. I'm presuming Electron cyclotron resonance heating is the general topic, found from Talk:Fusion_power.

Can we get details on the magnetic nozzle? Surely such a system must consume just-as-many gobs of power.

If you did promote fusion inside a plasma core, how would you keep random elements from forming and ionizing into deadly ions? The neutron issues would be horrendous. Is there any way to prevent fusion from occuring in ultra-high-temperature cores? Would there be any way to share plasma or to pre-excite ions by leaching off the fusion core (again without launching ions of every sort into space?) Someone please shoot me down on this next one; but what about hybridizing fusion+vasimr into a single system?

Um. VASIMR started out as that, and was watered down because nobody knows how to do fusion, never mind being able to turn it into a vehicle thruster.Wolfkeeper 00:34, 2005 Apr 22 (UTC)
It seems beneficial because you could avoid many of the difficult power-recovery steps associated with fusion. Instead of running some nuclear power source to generate RF to bombard ions, you "just" maintain fusion while dumping in more plasma and ejecting some out the back. The fusion sustains the excitement process rather than having to RF excite your ions. A couple ionic cyclotrons (VASIMR sans nozzles) feeding a plasma reactor with a magnetic nozzle out the back of the plasma reactor. But yes, way beyond current science.

A 3he fusion/vasimr hybrid would be the system to end all systems, but i have no idea if its in any way feasible.

Now you're dreaming in technicolour. The ignition temperature/pressure is *way* higher for 3he fusion than conventional fusion.Wolfkeeper 00:34, 2005 Apr 22 (UTC)
Above and beyond this, there are concerns with bremsstrahlung losses that may make any of the aneutronic reactions infeasible without truly gargantuan (kilometers of plasma) reactors. See Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium thesis of Dr. Todd Rider at MIT. --Andrew 02:04, Apr 22, 2005 (UTC)
Wow, fantastic paper. I think i'm going to go home and cry now. I always assumed fusion was just a ignition/containment problem. I'm amazed the impossibility of useful aneutronic fusions remains unknown.

Between varying containment needs and reactant maintenence, i have no idea if fusion + VASIMR is in any way possible. VASIMR seems so similar to fusion its hard to image the two reactors couldnt be muxed somehow.

How is the core thermally contained? I'm presuming magnetic containment is the first line of thermal containment, I cant imagine how else you'd hold 10m K. the goal is to keep as much heat in one place, how do is this accomplished? this is especially important in space where you really have no choice but to carry your heat with you or toss it out the back.

Yes, cooling is known to be a problem :-) Wolfkeeper 00:34, 2005 Apr 22 (UTC)

--User:Myren 4:30, 21 April 2005 (ECT)

## Extra detail

The article statse "The ions spiral around the magnetic field lines with a certain natural frequency; by bombarding them with radio waves of the same frequency, the system heats the ions to 10 megakelvins."

The article should either go into detail on how the ions are heated to such a high temperature, or should link to an article that explains in more detail.

## Thrust figures

Anyone have some thrust figures? ··gracefool 00:51, 18 May 2007 (UTC)

From an early experimental model i.e. a production VASIMR will be better.
Ref AIAA 2004-0149
The VASIMR Engine - Project Status and Recent Accomplishments
Page 3. "The standard 3kW helicon discharge produces about 6-7 mN of force on a target placed a few centimeters away from the magnetic throat. The neutral propellant input rate (about 3x10-7 Kg/sec) leads to an Isp estimate of about 2000 sec."
In the same document Figure 3 shows that a 1 MW VASIMR with an estimated mass of 1.2 metric tons may be able to produce between 10 N and 15 N, depending on the Isp selected when the fuel is He.

Andrew Swallow 01:54, 21 June 2007 (UTC)

For any given amount of power, the maximum thrust that can be generated is defined by ${\displaystyle T=2*P/V_{e}}$, where P is power, T is the thrust, and ${\displaystyle V_{e}}$ is the exhaust velocity. ${\displaystyle V_{e}}$ can be calculated from the specific impulse, ${\displaystyle I_{s}}$, where ${\displaystyle V_{e}=I_{s}*g}$

Assuming 100% efficiency VF-200 has the following thrust limits:

at 1000 isp -> 2 * 200 kW / (1000 s * 9,81 ${\displaystyle m/s^{2}}$ ) = 40,77 N

at 30.000 isp -> 2 * 200 kW / (30000 s * 9,81) = 1,36N

and fantasizing for a moment that one would be allowed to fly regular, full sized nuclear reactor into space than VF-1000000 engine would be possible

giving us at 5.000 isp throttle = 40774 N thrust e.g. 2 * 1000 MW / (5000 s * 9,81) = 40,8kN

So I belive the key to VASIMR's success (over other ion engines) is efficiency of power utilization - mass etc. seems to be only secondary consideration.

I wonder if anybody has up-to-date figures on power efficiency? And perhaps it would be beneficial to add efficiency comparison (vs. other ion drives) to the main article.

83.24.75.84 (talk) 20:48, 7 January 2008 (UTC)

According to Ad Astra's website the VX-200 uses 200 kW input power to produce approximately 1 lbf of thrust at an Isp of 5000 s when Argon is the propellant. [2]
Andrew Swallow (talk) 16:19, 24 April 2010 (UTC)

#### moon launch possible?

A VASIMR spaceship may not be able to take off from the Earth but Moon may be different.

Using the above thrust of 40.8 kN and the lunar gravity of 1.622 m/s/s

F = m a or m = F/a m = 40,800 / 1.622 = 25,154 kg = 25 tons.

So a spaceship weighing about 20 metric tons including propellant could be lifted from the moon's surface using a VF-1000000 VASIMR engine. On the Moon solar electric power is possible. Andrew Swallow (talk) 21:39, 16 February 2008 (UTC),

It might be tricky to get 1GWe and VX-1000000 in 20t though.

## Phobos Base launch and landings

Phobos is a moon of Mars. Phobos has a tiny gravity field so only a small thrust is needed for launches and landings. A suggestion has been made that electric propulsion Earth-Mars transfer vehicles carrying cargo land at a base on Phobos. The cargo can be building material for the base, return propellant for Earth-Mars manned spacecraft, supplies for the underground base and supplies for astronauts on Mars. Mars supplies would be sent to the planet by moving them to a chemical propulsion Mars lander. An example 1MW, 60% efficient VASIMR 100 tonne OTV vehicle may be able to get to Phobos if it has extra large solar panels.

Due to its odd shape Phobos's equatorial surface gravity varies between 0.0084–0.0019 m/s² and has an escape velocity of 11.3 m/s (40 km/h, 25.3 mph).

The gravity is applying a force on the OTV of up to F = m a = 100,000 * 0.0084 = 840 Newtons (N)

Using an Isp of 1000 thrust T = 2 * P * e / (Isp * g) = 2 * 1,000,000 * 0.60 / (1000 * 9.81) = 122 N

To hover on Phobos the OTV needs an Isp = 2 * P * e / (T * g) = 2 * 1,000,000 * 0.60 / (840 * 9.81) = 145.6

If launch requires more thrust than the VASIMR in the Orbital Transfer Vehicle (OTV) can generate a RCS able to supply the thrust for 3 - 4 km can be specified. Equipping the base's hanger with a robot arm should permit ground parking of the vehicle. Andrew Swallow (talk) 10:48, 28 October 2009 (UTC)

## Sharing Power and Cooling with the Space Elevator

The proposed lifters for the Space Elevator will be carrying photovoltaic panels that supply about 3 MW to 4 MW of electrical power and similar sized cooling panels. Switching this solar power from the wheel motors to a VASIMR would not be difficult.

Space Elevators are good at raising payloads from planetary surfaces to Geostationary Orbit (GEO) and above. They can also be used for landings providing the spaceship docks at GEO point. From higher up the ribbon cargoes can be thrown towards the Moon or Mars but it is a slow trip and there is little control over where the cargoes lands. A VASIMR thruster able to produce at least 100 Newtons of force is able to supply the velocity and accuracy needed.

VASIMR plus Space Elevator would provide a low cost solar electric space transportation system that starts on the Earth's surface. An annual check to see if the Space Elevator is being built may be worth while.

Andrew Swallow 04:27, 15 June 2007 (UTC)

## Bismuth as propellant

Hall effect thrusters are increasing their efficiencies by using the metal bismuth as a propellant. Will the same trick work with a VASIMR?

Andrew Swallow (talk) 02:13, 10 December 2007 (UTC)

## Unique Selling Proposition of VASIMR OTV

A Unique Selling Proposition (usp) is basically what your product can do but your competitor's product cannot do.

"An OTV (space tug) powered by a single VF-200 engine would be capable of transporting about 7 metric tons of cargo from Low Earth Orbit (LEO) to Low Lunar Orbit (LLO) with about a six month long transit time. {snip}"

The Delta IV heavy can launch 6,275 kg to geosynchronous orbit (GEO), so the payload figures are too close to make a unique selling point. However a small tug that can lift 8 or 12 tonnes to GEO or LLO does have a use. The small OTV will not have a rival until the project Constellation's Earth Departure Stage (EDS) is built. Even then the small OTV and say Falcon 9 is likely to be cheaper than the EDS + Ares V. The 9 months or 1 year trip time will be a disadvantage but if that is the only way of launching a 10 tonne GEO satellite then the customer will have to do it that way.

Larger satellites and lunar landers can use a EELV or J-120 and the big OTV. Andrew Swallow (talk) 01:33, 18 March 2009 (UTC)

There is talk about building a spacestation at Earth Moon Lagrangian point L1 or L2 within the next decade. Chemical propulsion will probably be used to move people and food to the spacestation, however a VASIMR OTV may be used for moving large items like lunar rovers and propellant for a co-located propellant depot. Such a spacestation would be a good place to park a returning Mars Transfer Vehicle.

Andrew Swallow (talk) 02:34, 24 January 2010 (UTC)

## Article cleanup

I have cleaned up the article and removed the __cleanup__ tag. Please respond it you think that this was in error. Kind regards SimonHarvey (talk) 04:51, 18 January 2008 (UTC)

I have added a reference to a document about the proposed Orbital Transfer Vehicle. The format needs correcting. Andrew Swallow (talk) 02:24, 19 August 2009 (UTC)

## The Devil is in the Heat !? - 2008 development issues

The recent press release [3] glowing over 2007 AdAstra achievements also seems to highlight in_between_the_lines two (possibly related?) issues that appear to be stumbling blocks:

- delays with superconducting magnets: "in order to give Scientific Magnetics of Culham, UK. the needed time to complete its certification of the superconducting subsystem."

- problems with heat generated as a by-product of plasma creation and speed-up: "addressing the challenging thermal management aspects of the VASIMR™ engine" & "generated new patents in the efficient production of high speed plasma jets and associated thermal management technologies. These are necessary in order to achieve the overall performance of which these engines are capable."

=> I guess 70% efficiency also means that 1/3 of that (relatively) enormous power ends up to be waste heat! 70kW+ of heat generation sounds like a serious problem! (for VX-200) Anybody has knowledge in the area of heat management? How can they cope with this?

Is it going to add a lot of weight to the engine?

=> has anybody seen these patents they talk about? Perhaps some interesting info there...

83.7.204.254 (talk) 17:09, 9 March 2008 (UTC)

Looking through Nautel website http://www.nautel.com/Resources is appears that their analog AM transmitters (solid state) have 84% efficiency. Since the RF transmitter for VASIMR has much simpler job (after all it can do away with all music modulation...) than perhaps their claimed 90% efficiency for ion generation is credible. 83.7.204.254 (talk) 17:09, 9 March 2008 (UTC)

Recycle the 80 kW of waste heat. Run the cooling pipes going to the radiators through a Stirling engine converter or Brayton cycle engine and use the electricity generated to power the avionics. Andrew Swallow (talk) 05:25, 25 February 2009 (UTC)

## Comparison to ion thruster

It would be helpful if a sentence or so could be added to show how this technology is different from ion thrusters. As far as I can tell, the difference is that this adds more energy to the atoms, but it'd be good to make it explicit. A comparison of specific impulse outputs would also be helpful. ·:· Will Beback ·:· 21:59, 8 August 2008 (UTC)

As far as I know, the "Variable Specific Impulse" part of VASIMR is hardly unique. Most electric thrusters (e.g. Ion, Hall) can have variable specific impulse - just vary the grid voltage. This information is straight from Professor Keith Goodfellow at USC.

## new article

This article could also be helpful for getting information: http://dsc.discovery.com/news/2008/08/07/plasma-rocket.html --62.214.214.39 (talk) 10:46, 9 August 2008 (UTC)

Very nice article, thanks for the heads up. I'll put it on my to-do list. Huntster (t@c) 15:49, 9 August 2008 (UTC)

## future optimum trust level & specific power -> trust to weight ratio

I wonder if anybody has some inside why Ad Astra chose 200kW as design baseline. I have found references to specific power being 1,5 kg/kWh -e.g. VF-200 having mass of 300kg

Given the trust of 5 - 8 N - that gives ratio of max. 0.0026 x . But if, for instance, VF-1200 improves specific power to 0,625 kg/kWh or by factor of 2,5, than trust to weight ratio (while still no competition for chemical rockets) would improve to 0.0065 x

And what is the theoretical limit on specific power? is the limiting factor the ICRF magnet or helicon?

A new section in the article about future developments of the engine and possibilities of improvement should include discussion about this. Awatral (talk) 12:10, 26 March 2009 (UTC)

I imagine this is a situation of "start small and build from there". When developments occur, I'm sure such a section will be added. Huntster (t@c) 03:38, 27 March 2009 (UTC)
The 200kW design baseline was chosen as that's the power necessary to move the ISS. I read it on Slashdot. --198.49.180.40 (talk) 00:42, 6 October 2009 (UTC)

## Another new article -- in IEEE Spectrum

There is a substantial new article about VASIMR, Chang Diaz, Ad Astra, etc. in the June 2009 issue of IEEE Spectrum, a general interest technical magazine for Electrical Engineers. Here is the link: http://www.spectrum.ieee.org/aerospace/space-flight/rockets-for-the-red-planet/0 N2e (talk) 19:25, 4 June 2009 (UTC)

## Why VAriable? What's the point? Isn't that inefficient?

When/why would you want to vary the specific impulse? If what you want is a variable amount of output (work), when/why would you you accomplish it by varying specific impulse rather than by simply varying the time it's being operated? It seems to me that operating this engine at anything less than its maximum specific impulse is a waste of reaction mass (fuel). Isn't that an extremely precious commodity, for the applications described? --ZZZZ —Preceding unsigned comment added by 198.49.180.40 (talk) 00:40, 6 October 2009 (UTC)

Not sure. It may be that some applications, such as deep space probes, would benefit from very strong thrusts at times, and longer, lower powered thrusts at other times. Good question, though. Huntster (t @ c) 04:34, 6 October 2009 (UTC)
It is a compromize between reaction mass and energy use.

For a given mass flow the force are proportional to the exthaust speed but the power consumption increases with the square of the speed.

In order to increase the force without exceding the maximum electrical power avilable the massflow must be increased and the exthaust speed must be decreased.82.209.155.237 (talk) 11:03, 12 October 2009 (UTC)

I think I see what you mean: in an application where (electric, therefore kinetic) energy is the limited resource (let's say, "not renewable"), and reaction mass is in comparison not limited, you could find an optimal tradeoff between first-stage power consumption (the electrical work which operates the engine) and second-stage power output (engine work). Originally, I was thinking of an application where the reaction mass itself is the more limited resource ("not renewable"), and electric (therefore kinetic) energy is in comparison not limited (maybe because it's either somehow "renewable" or a much-lower-mass component of the vehicle than the initial load of propellant itself).

In such an application, in order to get the maximum possible work out of the engine, you'd want every particle of propellant to be emitted at the highest possible speed. So the way to get variable work output would not be to vary the specific impulse, but to vary either the duration of the operating periods or the massflow.

Thank you for pointing out that the specific impulse of reaction mass (exhaust) is a function of the (electric) power consumed by the magnetoplasma accelerator stage of the rocket. This suggests that keeping massflow low while keeping specific impulse high is a means of remaining within the sustainable constant-operating power capacity of the electric parts of the rocket, while exhausting propellant in the most efficient manner possible at the same time ("efficiency" in this case referring to conservation of finite quantity of rocket propellant while still getting useful amounts of work). --71.198.34.87 (talk) 00:20, 24 November 2009 (UTC)

I had the pleasure with speaking with the man himself when he visited my university. The basic idea is like that of a car and its transmission. Actually most multi-stage rockets use this technique by using different engines at the various stages, as does the Space Shuttle; the SRBs give a massive amount of thrust while the the SMEs have a much better specific impulse. Of course, on a spacecraft we usually only have that one set of engines, but the VaSIMR solves that problem —Preceding unsigned comment added by 173.2.224.226 (talk) 05:20, 4 December 2009 (UTC)

## specification

Maybe I miss something, but do current VASIMR designs allow something like 1g acceleration for 100000t mass? (or is there a formula to calculate this from the thrust values in the article) Alinor (talk) 15:52, 6 November 2009 (UTC)

The VASIMR are no where near that powerful. Your right arm has about the same thrust/force as the current VASIMR.

The good old formulas F = m a and E = 0.5 * m v2 apply. The mass is in kg and 1 metric ton is 1000 kg

Using the figures from the Thrust section above. a = F / m = 40 N / 1,000,000,000 = 0.000 0000 4 m/s2 = 4.08E-9 g

Andrew Swallow (talk) 01:47, 7 November 2009 (UTC)

Thanks! So, it seems a 1kN constant-acceleration engine could propel 100t (not 100000t) at 1g. Now I wonder how much would such engine weight and what will be its fuel consumption (kg/s)? Alinor (talk) 19:29, 7 November 2009 (UTC)
No. You have the decimal place wrong, 1kN would propel 100t at 0.001g.
It is not accidental that the SI units are N, kg and m/s2
Turning it around F = m a; m = F / a
a = g = 9.81 m/s2
m = 1000 N / 9.81 m/s2 = 102 kg or 0.102 metric tons
Andrew Swallow (talk) 02:34, 8 November 2009 (UTC)

## Charge balance

I'm not a plasma physicist, but in reading this article and other articles about ion propulsion, I have the following question about VASIMR: What happens to the electrons? In other ion thrusters, it seems that electrons are injected into the thrust separately, to prevent the build-up of charge on the vehicle. This doesn't seem to be the case with VASIMR.

It seems to me that the electrons would be free in the cold plasma, and would still be in the hot plasma, they just wouldn't be heated by ICH. What doesn't make sense to me is how or if they will be accelerated by the magnetic nozzle. If they are precessing in the opposite direction from the positive ions, would they not be accelerated in the opposite direction (i.e. into the vehicle)? --Dbuijs (talk) 15:35, 23 December 2009 (UTC)Dbuijs

A: Actually this is non-issue for ELECTRODELESS PLASMA engine - you can view plasma as "mixture" of ions and electrons, in VASIMR they are both (and indiscriminately e.g. in proportional amounts) ejected from the magnetic "nozzle" so there is no build up of electrical charge and no "left-over" electrons to be ejected.

However there is an (potential) issue with plasma detachment from magnetic lines of the nozzle .... but that is an entirely different topic.

I guess it would be worth expanding / clarifying that information in the main article. Awatral (talk) —Preceding undated comment added 22:12, 15 February 2010 (UTC).

## 2011 target date for testing in space on the ISS

This interview was just released and mentions, among other things, the Ad Astra goal of testing the VASIMR technology, in space, by early 2011, on the International Space Station, and the theoretical potential of a 39-day trip to Mars using this technology, per Franklin Chang-Diaz, who is clearly an authorized spokesman for Ad Astra. This is the early half of the "2011-2012" statement now in the article. The link is from a space news blog, but I suspect the vid could also be located at Ad Astra, if a more acceptable source is desired. N2e (talk) 19:45, 27 February 2010 (UTC)

Jeez, is that what's responsible for the hundred-fold increase in traffic? Was it on national tv, or something? 91.84.208.36 (talk) 15:50, 2 March 2010 (UTC)
NASA performing an official study on using Ad Astra's VASIMR as the engine on a lunar tug [url]http://www.parabolicarc.com/2010/01/25/nasa-studying-ad-astras-vasimr-engine-lunar-tug[/url] may have also triggered some of the extra traffic. Andrew Swallow (talk) 01:12, 4 March 2010 (UTC)
That's a very nice uptick in visitors. The term "VASIMR" has found it's way into 371 new stories in the past week, according to Google News, with a sizeable number of those being non-English. Huntster (t @ c) 05:10, 4 March 2010 (UTC)
May 4, 2010 article from Discovery Channel at MSNBC. Thrust per mass compared to ion engines would be useful in this article. Edison (talk) 22:16, 4 May 2010 (UTC)
The MSNBC article mentioned a possible 2017 trip to an asteroid. That is interesting. The power drops off the further the asteroid is from the sun. I wonder how close the design is to being a general purpose tug? Andrew Swallow (talk) 04:47, 5 May 2010 (UTC)
(outdent) The June 2010 Aviation Week article I mention below says 2014 for testing on the ISS. N2e (talk) 11:43, 17 June 2010 (UTC)

## Tense of the article

Think I fixed the dreaded "present tense-ness" of the article. I wish people wouldn't write that way! :) But someone might check my work. Nice article. Mydogtrouble (talk) 20:55, 27 February 2010 (UTC)

Good work! I'm hoping to improve this article significantly. This deserves to be a WP:Good article, but it's a long way off yet. Anxietycello (talk) 17:11, 1 March 2010 (UTC)

"It can also be seen as an electrodeless version of an arcjet, able to reach higher propellant temperature by limiting the heat flux from the plasma to the structure. Neither type of engine has any electrodes. The main advantage of such designs is elimination of problems with electrode erosion."

The above text appears to contradict itself. Perhaps its meaning could be clarified by better wording? Anxietycello (talk) 17:08, 1 March 2010 (UTC)

## June 2010 Aviation Week article

A new article, full of technical detail on improvements in the latest testing phase over the past six months, was published in Aviation Week on June 16th. I've added a link to the Additional resources part of the VASIMIR WP article, but have not had time to cull substantial new info from the source to improve the article. Have at it. N2e (talk) 11:41, 17 June 2010 (UTC)

## July 2010: overview and update by Chang-Diaz at NewSpace 2010 conference

There is a fairly information-rich overview and update on current plans, given by Chang-Diaz at the NewSpace 2010 conference, in a panel discussion held on July 25th. Chang-Diaz' opening remarks and good summary is in the first ten minutes of the video. Here is a (slight variation of a) citation I used to support a totally unsourced claim in another Wikipedia article. Cheers, N2e (talk) 20:49, 30 July 2010 (UTC)

Approaching Warp Speed: Advanced Space Propulsion, NewSpace 2010 conference panel discussion, 2010-07-25, VASIMIR segment, Franklin Chang-Diaz, Ad Astra Rocket Company, Spacevidcast video, at time 2:30-10:00, accessed 2010-07-30.

And if you like citation templates, try the following. Huntster (t @ c) 03:42, 31 July 2010 (UTC)

Template:Cite video

## Interwiki

The citation from Help:Interlanguage links#Bots and links to and from a section:

“The activity of the bots also requires that interlanguage links are only put from an article to an article covering the same subject, not more and not less. It is technically possible to make an interlanguage link from an article to a section of an article, just like any link to a section. The bots can handle this. They will not try to link back from a section to the article that links to it. Maintaining such a link by hand, however, is complicated, so linking to a section is still not recommended.

The german article has interwiki to plasma propulsion engine. Русские идут! (talk) 16:52, 8 November 2010 (UTC)

Yes, but the German article has a section on VASIMR, which is what the interwiki links to. Your quote above specifically allows for it. It just means that the German article won't automatically be linked back to this one. Huntster (t @ c) 21:29, 8 November 2010 (UTC)
Doesn't it should be avoided? Русские идут! (talk) 22:31, 8 November 2010 (UTC)
No, it says that bots can detect and handle interwikis with section links; they simply will not link back to the local article from the other language article (since that article as a whole isn't about our local topic). Huntster (t @ c) 03:14, 9 November 2010 (UTC)
could this be achieved by using a new redirect page on the de.wiki, linking to the sub-section? Just an idea. regards, Lynbarn (talk) 12:25, 9 November 2010 (UTC)

## Waste heat management

Does anyone have a citation for the claim: "Another issue was waste heat management (60% efficiency means about 80 kW of unnecessary heat) critical to allowing for continuous operation of VASIMR engine."? Has anyone done research on what would be required to dissapate into space 80 kW of heat? How big would such a system be? How much would it weigh? What fraction of the ISS total waste heat dissipation budget is this? Cheers. N2e (talk) 20:18, 9 December 2010 (UTC)

That one is conservation of energy and basic maths. 200kW * (100% - 60%) / 100% = 80 kW
The size of space radiators depends on the fourth power of the temperature. Andrew Swallow (talk) 05:49, 10 December 2010 (UTC)
Yup - it seems that too little R&D attention is paid to space radiators. I believe that ISS is using radiators build by LOCKHEED MARTIN utilizing liquid ammonia. This is hardly state of the art hence it requires huge surface area to radiate. The capacity of the system has to account for ALL of electrical energy generated by ISS solar panels plus give or take 6x 100W (human body heat) - one way or the other that electricity ends us as waste heat. So actually with VASIMR operating the demand for heat rejection WILL BE LOWER so it improves ISS cooling budget by 120kW during the 15 minutes bursts that VASIMR will operate. Awatral (talk) 13:23, 4 January 2011 (UTC)
I am curious - can anybody point me to some worth while research regarding high temperature radiators? Awatral (talk) 13:23, 4 January 2011 (UTC)

## Fuzzy specific impulse specification(s)

As I read the article today (25 Jan 2011), I cannot find the article making an explicit claim of the maximum specific impulse, either for any particular AdAstra prototype, nor for the theoretical limits thought to be associated with VASIMR technology. Am I just missing it? Or is this an oversight?

I searched for all the instances of "specific impulse" as well as "ISP". I find a couple of mentions of optimum (throttled-back? on the low end of the "variable range"? in the middle of the "variable range"?—it is not clear) Isp of 3000 to 5000 s. I can also find mention of some numbers here on the Talk page. But I think the article itself ought to have some explicit (and well sourced) claims about something so important. And a cited claim for the useful operating range of ISP and the minimum ISP of the "variable" design would also be quite useful to our readers. N2e (talk) 17:28, 25 January 2011 (UTC)

The slides presented by Ad Astra in mid-January at the FISO colloquiam (see citation below, in next section, pp 10) show that the design point for good efficiency on the VX-200 is 50 km/s exhaust velocity, or an Isp of 5000 s. This is for a thruster efficiency of 70% (which Ad Astra is explicit now that this is achievable) yielding an overall system efficiency (DC electricity to thruster power) of 60% (since the DC to RF power conversion efficiency exceeds 95%). N2e (talk) 04:32, 31 January 2011 (UTC)
I have updated the article, per the source mentioned above. It does not appear that Ad Astra's design orientation is to achieve the "maximum" Isp, as there would likely be tradeoffs in engine life, propellant usage, etc. They seem to be going for "optimum." With these updates, at least for me, the fuzzy Isp problem in the article has been eliminated. Others feel free improve further as you wish. N2e (talk) 04:21, 2 February 2011 (UTC)

## AdAstra presentation at 19 Jan 2011 FISO colloquiam

Ad Astra Director of Development Tim Glover presented to the (industry/academic/NASA) Future in Space Operations (FISO) Colloquium on 19 Jan 2011. I found the presentation extremely informative on the development and testing of the current VX-200, with a number of good images and charts, and specifics on use of such a device on a future Mars mission. The slides are available online at the URL given here: ```<ref name=fiso20110119> [http://spirit.as.utexas.edu/~fiso/telecon/Glover_1-19-11/Glover_1-19-11.pdf VASIMR VX-200 Performance and Near-term SEP Capability for Unmanned Mars Flight], Tim Glover, Future in Space Operations (FISO) Colloquium, 2011-01-19, accessed 2011-01-31.</ref>``` Cheers. N2e (talk) 04:17, 31 January 2011 (UTC)

## Vacuum

I am puzzled by the text, "VASIMR is not suitable to launch payloads from the surface of the Earth due to its low thrust to weight ratio and its need of a vacuum to operate." I have not seen arguments as to why vacuum is required. If-only I had sufficient electrical power, could I not strap one of these onto a vehicle? Could I not propel a scramjet this way? -- 99.233.186.4 (talk) 23:17, 3 February 2011 (UTC)

A rocket needs a thrust to weight ratio of greater than 1 to make it off the ground. (Weight on Earth's surface.) Otherwise, the weight, the force of gravity, is greater than the thrust, and the rocket would be falling. Since electric engines have thrust-to-weight ratios in the .01 to .1 range, they are not suitable on the Earth or any body with significant gravity, air or no air. Add in atmospheric drag, and your thrust requirement for launch increases further. — Preceding unsigned comment added by 128.125.139.43 (talk) 07:50, 21 September 2012 (UTC)

The design of the VASIMR (and all ion thrust engines) requires it to be operated in a vaccuum. If it were not operated in a vaccuum, air would affect the ability of the engine to do work using the ion fuel. The energy would be dispersed inside the engine, which would inevitably destroy itself. NotAsleepPhysorg (talk) 17:22, 18 November 2011 (UTC)

## 0.5 N thrust?!

The first VASIMR engine model VX-50 proved to be capable of 0.5 newtons (0.1 lbf) thrust.

How would this thing ever move then? The gravity of earth is 9.81N, obviously much higher than this. It won't even get off the ground. — Preceding unsigned comment added by 202.156.11.10 (talk) 16:29, 9 August 2011 (UTC)

A conventional rocket is used to lift the VASIMR to space. Once the spacecraft is in orbit gravity becomes much simpler to deal with.
Air reduces the usable thrust from rockets because it has to be pushed out of the way. Consequently rockets produce more thrust in a vacuum.

Andrew Swallow (talk) 00:16, 10 August 2011 (UTC)

## Name controversy

Is there a specific reason why name VASIMR gets spelled as VASIMIR? (apart from the Russian pronunciation likeness) 1 time in the article (in the criticism section), 5 times in this discussion, and also here: Exoplanet Atlas (although they've managed to mess the Celsius scale too) — Preceding unsigned comment added by 118.160.199.71 (talk) 05:51, 9 December 2011 (UTC)

I've not heard a particular reason, but almost certainly because the "MR" part is typically pronounced as "MEER" or "MUR". Nothing to worry about...just fix it in the article if/when you find an instance. Huntster (t @ c) 09:35, 9 December 2011 (UTC)

## 2012 news

Does anybody have some source of news regarding Ad Astra? - They have been awfully quiet for over half a year now. Do they continue to work on VF-200 or are there financial problems hindering VASIMR development? — Preceding unsigned comment added by 62.121.115.9 (talk) 10:29, 15 February 2012 (UTC)

## Criticisms of VASIMR section should be removed

The are three sentences in the section 1) "... VASMIR is less efficient than other electric based thrusters which are now operational." - is not correct. System efficiency of VASIMR (as measured in VX-200) is more than 60% (http://www.adastrarocket.com/Ben_IEPC11-156.pdf) which is more or about the same as other electric thrusters. 2) "Zubrin also believes that electric propulsion is not necessary to get to Mars and therefore budgets should not be assigned to develop it." and 3) "His second point of criticism concentrates on lack of suitable power source." - are related to Electric Propulsion in general and can be transfered to the corresponding page.

Note: the above comment has no date, and is not signed. Don't see any replies to it as of Dec 2013.
For interest, here is an essay published in SpaceNews that is critical of VASIMR: SpaceNews, July 2011. I am currently agnostic on the claims, but think they ought to be able to be seen and read by other editors as well. N2e (talk) 17:28, 30 December 2013 (UTC)
While both sides should be presented, it really does seem to be a case of Zubrin screaming out in every venue he can get into, which seems to be rather UNDUE. I mean, the criticism section was renamed to specifically name Zubrin because he's the only real voice out there! I'm not sure what should be done, but I'm not comfortable with the status quo. Huntster (t @ c) 00:50, 31 December 2013 (UTC)