VASIMR VX-200 engine successfully tested

[dragon]

Surprised that didn't see anyone posted this yet. Not sure how news trusty the site is though. Great start

Using traditional chemical rockets, a trip to Mars – at quickest — lasts 6 months. But a new rocket tested successfully last week could potentially cut down travel time to the Red Planet to just 39 days. The Ad Astra Rocket Company tested a plasma rocket called the VASIMR VX-200 engine, which ran at 201 kilowatts in a vacuum chamber, passing the 200-kilowatt mark for the first time. "It's the most powerful plasma rocket in the world right now," says Franklin Chang-Diaz, former NASA astronaut and CEO of Ad Astra. The company has also signed an agreement with NASA to test a 200-kilowatt VASIMR engine on the International Space Station in 2013.

The tests on the ISS would provide periodic boosts to the space station, which gradually drops in altitude due to atmospheric drag. ISS boosts are currently provided by spacecraft with conventional thrusters, which consume about 7.5 tons of propellant per year. By cutting this amount down to 0.3 tons, Chang-Diaz estimates that VASIMR could save NASA millions of dollars per year.

The test last week was the first time that a small-scale prototype of the company's VASIMR (Variable Specific Impulse Magnetoplasma Rocket) rocket engine has been demonstrated at full power.

Plasma, or ion engines uses radio waves to heat gases such as hydrogen, argon, and neon, creating hot plasma. Magnetic fields force the charged plasma out the back of the engine, producing thrust in the opposite direction.

They provide much less thrust at a given moment than do chemical rockets, which means they can't break free of the Earth's gravity on their own. Plus, ion engines only work in a vacuum. But once in space, they can give a continuous push for years, like wind pushing a sailboat, accelerating gradually until the vehicle is moving faster than chemical rockets. They only produce a pound of thrust, but in space that's enough to move 2 tons of cargo.

Due to the high velocity that is possible, less fuel is required than in conventional engines.

Currently, the Dawn spacecraft, on its way to the asteroids Ceres and Vesta, uses ion propulsion, which will enable it to orbit Vesta, then leave and head to Ceres. This isn't possible with conventional rockets. Additionally, in space ion engines have a velocity ten times that of chemical rockets.
Specfic impulse and thrust graph. Credit: NASA

Specfic impulse and thrust graph. Credit: NASA


Rocket thrust is measured in Newtons (1 Newton is about 1/4 pound). Specific impulse is a way to describe the efficiency of rocket engines, and is measured in time (seconds). It represents the impulse (change in momentum) per unit of propellant. The higher the specific impulse, the less propellant is needed to gain a given amount of momentum.

Dawn's engines have a specific impulse of 3100 seconds and a thrust of 90 mNewtons. A chemical rocket on a spacecraft might have a thrust of up to 500 Newtons, and a specific impulse of less than 1000 seconds.

The VASIMR has 4 Newtons of thrust (0.9 pounds) with a specific impulse of about 6,000 seconds.

The VASIMR has two additional important features that distinguish it from other plasma propulsion systems. It has the ability to vary the exhaust parameters (thrust and specific impulse) in order to optimally match mission requirements. This results in the lowest trip time with the highest payload for a given fuel load.

In addition, VASIMR has no physical electrodes in contact with the plasma, prolonging the engine's lifetime and enabling a higher power density than in other designs.

To make a trip to Mars in 39 days, a 10- to 20-megawatt VASIMR engine ion engine would need to be coupled with nuclear power to dramatically shorten human transit times between planets. The shorter the trip, the less time astronauts would be exposed to space radiation, and a microgravity environment, both of which are significant hurdles for Mars missions.
VASIMR. Credit: Ad Astra

VASIMR. Credit: Ad Astra

The engine would work by firing continuously during the first half of the flight to accelerate, then turning to deaccelerate the spacecraft for the second half. In addition, VASIMR could permit an abort to Earth if problems developed during the early phases of the mission, a capability not available to conventional engines.

VASIMR could also be adapted to handle the high payloads of robotic missions, and propel cargo missions with a very large payload mass fraction. Trip times and payload mass are major limitations of conventional and nuclear thermal rockets because of their inherently low specific impulse.

Chang-Diaz has been working on the development of the VASIMR concept since 1979, before founding Ad Astra in 2005 to further develop the project.

link

[Ford Prefect]

Hey, wow, VASIMR in action! Though I heard of VASIMR years ago, I'd never actually heard of serious testing involved with it. Hopefully when 2013 comes around Ad Astra are still rolling well enough that they really can test their 200KW drive at the ISS. It would be a shame to see such a project fall by the wayside, though doing a little research now it seems they've been at it for years.

[Sky Captain]

Here is a short video of VASIMR test firing.

[ThomasP]

Next Big Future had a post on this recently, talking about the potential of this VASIMR rocket attached to a small-scale megawatt-range nuclear reactor around 2020 or so. I forget whether that was a proposal that this team was making, or whether he was just crunching numbers in the post, but it made for some interesting figures in either case.

It's still no magic torch-drive, but who can complain? It's got potential to realistically open up most of the solar system for us.

[Tolya]

It needs a menacing, ISD like sound. Too bad the test was done in vacuum.

As a side note, Im curious: did they fire it up in vacuum to simulate interplanetary environment or is there some reason for this type of propulsion not working in atmosphere?

[Starglider]

As a side note, Im curious: did they fire it up in vacuum to simulate interplanetary environment or is there some reason for this type of propulsion not working in atmosphere?

I'm fairly sure it wouldn't work in an atmosphere, for pretty much the same reason that an open-air magnetic confinement fusion reactor wouldn't work. The plasma consists of a very small mass of ions at very high temperature. If you allowed air in the plasma would lose all of its heat to the (several orders of magnitude more dense) air very quickly, and the engine would quench. You wouldn't want to operate this engine in an atmosphere anyway, since even in 'low gear' mode it has a very poor thrust-to-weight ratio, compared to chemical or nuclear thermal - certainly not enough for surface launch.

[Coyote]

The only fly in this ointment will be the usual anti-nuclear hysteric brigade screeching about "nuuuukes in spaaaaaace!"

Otherwise, this fucking rocks. Mars in just over a month? Good for astronauts, to be sure. I bet a fast-transit ship equipped with this sort of engine could be useful for a robotic or teleoperated probe even further out. If it takes 39 days to reach Mars, it would be, what, about 4 months to the moons of Jupiter? (Wild guess).

Although I wish they had provided hard numbers for what constituted "higher payloads". Sure, it'll be more than what we have now, but by how much, exactly?

[phongn]

The only fly in this ointment will be the usual anti-nuclear hysteric brigade screeching about "nuuuukes in spaaaaaace!"

It doesn't have to be nuclear powered though that's the best energy source to drive it.

Otherwise, this fucking rocks. Mars in just over a month? Good for astronauts, to be sure. I bet a fast-transit ship equipped with this sort of engine could be useful for a robotic or teleoperated probe even further out. If it takes 39 days to reach Mars, it would be, what, about 4 months to the moons of Jupiter? (Wild guess).

Not sure how they're arriving at those numbers - though you can experiment with various parameters here (Java required). I think they were testing at ~60kps or so but their charts show them going to > 300 kps.

Although I wish they had provided hard numbers for what constituted "higher payloads". Sure, it'll be more than what we have now, but by how much, exactly?

Well, a liquid-chemical rocket will require a fuel fraction of ~71.1% (ve ~= 4.5 kps) whereas a plasma rocket sustaining ve ~= 300 kps would drop that fuel fraction to 1.8%. All this assumes using a minimum-energy Hohman transfer orbit; going faster requires more fuel.

[Starglider]

Well, a liquid-chemical rocket will require a fuel fraction of ~71.1% (ve ~= 4.5 kps) whereas a plasma rocket sustaining ve ~= 300 kps would drop that fuel fraction to 1.8%. All this assumes using a minimum-energy Hohman transfer orbit; going faster requires more fuel.

Although with an engine this power hungry you have to consider the added mass of the power generator (i.e. a small nuclear reactor and associated plant), which will take back some of the mass saved by the greatly improved specific impulse - unless you needed that generation capacity anyway for the spacecraft's main mission.

[phongn]

Although with an engine this power hungry you have to consider the added mass of the power generator (i.e. a small nuclear reactor and associated plant), which will take back some of the mass saved by the greatly improved specific impulse - unless you needed that generation capacity anyway for the spacecraft's main mission.

Quite so, and there's still the issue of getting stuff up off the ground (enormous amounts of fuel required since you must have high-thrust engines).

[fnord]

Pretty sweet, especially when using a small, liquid-fuelled, gen-4 reactor, such as MSR/LFTR. After all, one of the byproducts of nuclear fission-based power production is xenon, which appears to be commonly used as reaction mass in ion drives.

After all, time does compost the fission products for us - Xe-133 has the longest half life, at 5 days, decaying to stability inside 50 days. Give it a few days to cool, then pitch the extracted xenon out the engine - we're making, to excuse the loose use of the word, some of our reaction mass as we go. I am not too sure about the Xe production per MWh, though - I think it will only be a small top-up.

[Starglider]

Pretty sweet, especially when using a small, liquid-fuelled, gen-4 reactor, such as MSR/LFTR. After all, one of the byproducts of nuclear fission-based power production is xenon, which appears to be commonly used as reaction mass in ion drives.

High atomic weight elements are better for thrust (and reducing fuel tankage mass), low atomic weight elements are better for ISP. In theory VASIMR will work with pretty much any reaction mass - xenon wouldn't be a good fuel choice for a long range mission, but if you're getting it for free from the reactor then no reason not to use it I suppose. Unless the mass/complexity cost of extracting it from the reactor cooling system is prohibitive.

[fnord]

Sparging gaseous fission products was done with helium bubbles, in the 1968 MSR prototype. So that shouldn't be too difficult mass/complexity wise.

It also means a massive component of the vessel (the fuel load) can at least partly double up as reaction mass.

[Alerik the Fortunate]

If reactor mass is an issue, wouldn't beamed power from a stationary power source be an alternative, such as a focused microwave beam from a solar power satellite?

[Simon_Jester]

Only if it's cost-effective in terms of mass. For one, I'm not sure 200 kW worth of solar cells is lighter than 200 kW worth of power plant (it might be, I'm not ruling it out, I just don't know).

For another, that means you have to launch the power satellite and beaming equipment into orbit along with the interplanetary spacecraft, which means more fuel-expensive launches from heavy lift boosters to get the overall assembly into space.

[Starglider]

Only if it's cost-effective in terms of mass. For one, I'm not sure 200 kW worth of solar cells is lighter than 200 kW worth of power plant (it might be, I'm not ruling it out, I just don't know).

Huge solar arrays also have the issue of being vulnerable to micrometeorite deterioration over long journeys; much moreso than the radiators of a nuclear plant, particularly since you can use droplet radiators but there's no such thing as a droplet mirror. Microwave collectors less so, since they're made of wire mesh, but at that wavelength beam diffraction may rule out use as an effective power source for probes.

[Sky Captain]

How well state of the art solar systems compare to state of the art nuclear systems regarding power to mass ratio?
Nuclear plant is heavy, it requires power conversion machinery (probably gas turbine of some sort) to produce electricity to run VASIMR and radiation shielding. On the other side solar panels can be made of thin film supported by lightweight frame and also solar cells are solid state there is no mechanical parts prone to breakdown. As I understand VASIMR engine itself also don`t have moving parts so there is a possibility to make a system that is very reliable and could operate for years without maintenance. Of course if you want to go farther than Mars orbit or asteorid belt at most nuclear is an only option in near future if you want reasonable transit time. But for operation in inner solar system say Earth - Mars ferry what would be better - nuclear or solar?

[Starglider]

Nuclear plant is heavy, it requires power conversion machinery (probably gas turbine of some sort) to produce electricity to run VASIMR and radiation shielding.

The only nuclear reactors flown in space to date used solid state thermionic conversion, peaking at somewhere between 5 and 10% efficiency (though liquid coolant was required). The lower thermodynamic efficiency vs turbomachinery is almost certainly worth the benefits of simplicity and higher reliability in a small unmanned probe, probably not for a large manned ship. Radiation shielding should only consist of a shadow shield between the reactor and the payload section, which doesn't have to be that big if the ship is elongated.

[fnord]

I'd be inclined myself to go with SOTA fission over SOTA solar.

As mentioned above,
1 - no solar panels to get eroded by the interplanetary medium, micrometeors, etc
2 - laugh at getting shadowed by passing planet/moon/bloody volvo driver. The mass you would have to otherwise dedicate to energy storage can be used for other, more productive things (like carrying more grub)
3 - no solar panel mountings to impose acceleration limits (admittedly, not a near-term concern)
4 - can run hot enough to not require a heat pump to feed your radiators with waste heat (thinking LFTR at 1000 K)
5 - can "manufacture" some rx mass en route (fission product scrubbing from a liquid fuelled reactor)
6 - compact - I'm talking 2.2 GWth core in 15 cubic metres compact

As a further benefit of the LFTR: I put it to you, a neutron absorbed in a breeding blanket, transmuting Th232 into Th233 then U233, will find it difficult to be radiated beyond said blanket. A 90%+ attenuation in neutron radiation means the shadow shield can be made less massive to give the same core-to-crew attenuation.

[Sky Captain]

After doing some little googling I found out something like this would be optimal

For unmanned probes solar power makes sense up to an asteorid belt (perhaps stretchable to Jupiter if you are willing to accept significantly reduced performance) An increase of transit time could be worth the reduced cost/complexity of not having a nuclear reactor.

For probes operating farther out than Jupiter nuclear reactor or RTG is only option. Some sort of thermionic conversion likely will be used to make the whole system as reliable as possible.

For manned craft some advanced high temperature high power to mass nuclear reactor with gas turbine based electrical generator for maximum thermal efficiency would be optimal. Major drawback is such system will be expensive. If operating between Earth and Mars it would be possible to go with solar power if lightweight high efficiency solar panels are developed however transit time would longer, but still better than with chemical propulsion.

[fnord]

So what would the relative costs be for a 20 MW high temp nuclear plant (such as MSR) hooked up to a (supercritical CO2?) gas turbine genset vs 20 MW of solar (at Mars orbit) + power conversion and storage?

Higher thermal efficiencies directly imply less waste heat to dump via radiators, ceteris paribus. Also,. SCO2 turbines are comparatively small (Dostal et al claim ~ 1m in length and diameter for a 500 MWe unit - probably wouldn't gain much further size drops as power output declines, though.). You would probably have to use a heat pump to upgrade the heat rejection temperature to allow you to shrink your radiators somewhat, putting a bit of a kibosh on 4 in my previous post.

V. Dostal, M. J. Driscoll, P. Hejzlar, and N. E. Todreas, “A Supercritical CO2 Gas Turbine Power Cycle for Next-Generation Nuclear Reactors,” ICONE 10-22192, Proceedings of ICONE 10, Tenth International Conference on Nuclear Engineering, Arlington, April 14-18, 2002.