VASIMR Plasma Thruster To Be Tested Aboard ISS

Toren Altair brings news that NASA and the Ad Astra Rocket Company finalized a Space Act Agreement earlier this week to test the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) on the International Space Station. The agreement hinges on a series of requirements for the thruster's performance and efficiency in ground-based tests. "The primary technical objective of the project is to operate the VASIMR VF-200 engine at power levels up to 200 kW. Engine operation will be restricted to pulses of up to 10 minutes at this power level. Energy for these high-power operations will be provided by a battery system trickle-charged by the ISS power system. These tests will mark the first time that a high-power, steady-state electric thruster will be used as part of a manned spacecraft." Reader clarkes1 points out related news of a runway trial for Virgin Galactic's WhiteKnightTwo, the mothership that is designed to carry SpaceShipTwo from the ground to 50,000 feet. A very brief video shows the oddly-shaped plane moving down a runway under its own power.

Comments

Nice acronym

[Concerned Onlooker]

Oy VASIMR...

Bugger that namby pamby stuff

[David Gerard]

Just give 'em gigantic pounding thrust, none o' this wussing about with plasma. OXYGEN AND KEROSENE. It was good enough for Wernher von Braun!

Re:Bugger that namby pamby stuff

[Titoxd]

Um... yeah, right.

If you want to do any deep-space maneuvers, you have to carry all that liquid propellant (be it LO2/LH2 or LO2/RP-1, for the rocketry equivalent of a gas guzzler (specific impulse of 200-500 s), instead of carrying a small amount of high-efficiency propellant with a specific impulse of up to 10000 s.

VASIMR and the like won't get you off the ground, because their thrust-to-weight ratio is less than one--meaning they can't beat the force of gravity here on Earth. But once in space, if you're going far, their performance characteristics mean that you can sometimes get to your destination faster and cheaper than you can with ordinary impulse-maneuvered chemical rockets.

Re:Bugger that namby pamby stuff

[sketerpot]

Real men are idiots. Wernher von Braun would be smart enough to know that a dude riding a cannonball would need to do a burn around the time he reaches apogee in order to move into a stable orbit. Your cannonball still needs to have rockets on it.

Re:white knight 2 looks too fragile

[Gothmolly]

And you're an aeronautical engineer, and thus qualified to make that determination? Oh wait...

Re:white knight 2 looks too fragile

[AikonMGB]

You must not fly at all then, since with any airplane, the only join between the hull and the sky are the wings.

Aikon-

""Runway Trial"

[HotNeedleOfInquiry]

Just to pick nits, the proper term is "high speed taxi test".

I know, but it's Saturday morning and I'm bored...

Re:white knight 2 looks too fragile

[Nyeerrmm]

Actually, on any airplane, the wing has to be able to support the full mass of the aircraft, albeit spread over the entire surface of the wing. If you think about it, it has to have the aerodynamic pressure be at least equal to the mass of the aircraft. And then all that load gets transferred to the spars, so on a normal single-wing aircraft, the central spar is carrying the entire aircraft mass, if its the type of design that carries through the middle of the aircraft.

Also, in order to strengthen it to support the weight of SpaceShipTwo, you can do it without any visible change, just make the spars in the wing heftier.

As far as having to make it look cool, of course they do... its supposed to appeal to people who want to spend $200k going to (suborbital) space. And given that the methods to check the structural soundness of such a set-up are well established, and that Rutan isn't an idiot, I'd imagine it can handle worst case scenario loads with a safety factor of 1.2 or 1.3, as is common for any aerospace application.

Re:white knight 2 looks too fragile

[ionix5891]

dont worry only the rich would get to ride on this, and if anything happens to them, well oh dear :)

Launch from altitude vs near equator

[ILikeRed]

I think I have heard that the US space program(s) launch near the equator (or as near as they can in the US) to get free energy from the spin of the Earth. I think it is great that Rutan's program uses an aircraft to additionally lift the rocket for the first 50,000 ft or so.

I've looked, but not found the equations - what is the relative advantage of near equator (if any) vs height? Florida is close for the US, but how high would you have to be to make launching off a mountain in Colorado worthwhile? I realize the tallest mountain is only at ~29k feet (8.85km), but even that would have to be a boost out of the gravity well, wouldn't it?

What I really wonder, is why we don't have powered rails launching rockets off the top of mountains - seems like it would be worth the budget - but again, if anyone knows where to find the equations it would be much appreciated.

Re:Launch from altitude vs near equator

[Nyeerrmm]

You get some free energy from the spin, yes, but the main reason you try and launch from lower latitudes is that you want to have the option to get a near equatorial orbit inclination. Basically, you can't launch to an inclination lower than your latitude; if you think about it, launching due east (or west, but that would be going against the spin) would put you in an orbit thats the same inclination. If you aim a little north or south you end being inclined a little bit more... whether its north or south changes the position of the ascending node, but not the overall inclination. If you aim due north or south you get into a polar orbit. As far as the additional altitude... its such a miniscule amount that its not worth worrying about.

The reason you may want to have a low as inclination as possible is because if you're going to GEO or lunar or planetary missions, you want to be near zero inclination. In order to get there, you have to do an expensive plane change maneuver, which has a delta-v=sin(i)*V, so getting that inclination lower means big fuel savings.

As far as calculating the fuel savings, just consider the difference between the rotational speed of the point on the surface (sin(lat2)-sin(lat1))*r_earth*(2*pi/24 hrs) to get the additional velocity you get (and thus less delta-v you need to apply on orbit). Running that between the Russian Star City (45 degrees) and the cape (21 degrees) shows that we get ~150 m/s difference, which is nice but not game changing.

As far as sky launch or mountain launch, I learned a great little rule of thumb here a few weeks ago, the 666 rule. Launching from Mach 6 at 60000 feet (probably much higher than any reasonable air launch system), gives you only a 6% energy savings for orbital systems. So, it really doesn't give you a whole lot for the added complexity, which is why as far as i know theres only one air-launched system, an Orbital Sciences rocket that launches off an L1011. The reason why it works for Virgin/Scaled Composites is that it gives you probably 30% of the energy needed to reach the altitude, but not the orbital velocity.

As far as equations... the atmospheric drag models make launch hard to judge, but what is cleverly called the "Rocket Equation" is a really easy way to look at fuel usage with impulsive delta-vs... usually a more valuable quantity than energy since it directly applies to the amount of fuel needed and used.

Re:Launch from altitude vs near equator

[Deadstick]

As far as satellite launching is concerned, the height of the launch site is utterly trivial. In order to achieve a low earth orbit, you have to accelerate an object to about 23,000 feet per second; for a one-pound object, that will take over 8 million foot-pounds of energy. Lifting that same object from sea level to the top of Mt. Everest will take 29,029 foot-pounds.

The latitude of the launch site offers some tradeoffs. A site on the equator will give you a few hundred extra feet per second than one at 45 degrees latitude, not a real big advantage. However, a launch directly into orbit will always put you in an orbit whose inclination is at least the latitude of the launch site. Launch from Cape Canaveral, and you'll be in an orbit inclined at least 28 degrees from the equator. You can make it higher, but not lower. If you want to get an equatorial orbit -- which most communications birds need -- you have to launch into the inclined orbit first, fly to the equatorial plane, and then make a "plane change" maneuver which takes a substantial fraction of the energy it took to put you in orbit. From the equator, you can launch directly into any inclination, which is why the European Space Agency birds come out of French Guiana.

rj

Two scientists aboard the ISS

[RevWaldo]

- "Rochambeau for it?"
- "Two out of three?"
- "Deal."
- "OK. Rock-paper-scissors-Shoot! Rock. Rock-paper-scissors-Shoot! Paper. Rock-paper-scissors-Shoot! Rock."
- "I win!"
- "Yeah, you win... go ahead and say it.."
- "Helmsman! Engines to FULL IMPULSE POWER!"
- "Doofus." (pushes button)

Re:white knight 2 looks too fragile

[Cally]

You could just about persuade me to take a trip in the mothership, but I wouldn't go near the SS2 for all the tea in China - not until they've done, say, one percent of the number of test flights needed to certify a typical normal civil light aircraft, and not had any unfortunate incidents like the one that so nearly killed the pilot on the first SS1 launch. It blows my mind that people are willing to slap down hundreds of thousands of dollars for the chance to be torn to shreds by centrifugal force, incinerated by an engine failure, or even simply spiralling gently down with half the control surfaces missing for a nice leisurely twenty minutes before lithobraking.

On the other hand, conneisseurs of huge explosions are eagerly awaiting the first test flight of Falcon-9, which as the name suggests bundles nine of the Falcon S1 engines that put their test mass into orbit a few months back. Unlike F1 which have been at Kwajelien Atoll in a US army test range, F9 launches from the Cape. There's no keeping spectators and TV crews away from that baby, no sir!

NUCLEAR ISOMERS

[sanman2]

Since energetics is the key trumping factor for overcoming the earth's gravity well, we need more energetic power sources than mere chemical fuels. I've read that there have been some recent new successes announced in the past few months in nuclear isomer research. As we know, nuclear isomers are atomic nuclei whose protons and neutrons have absorbed extra energy to keep them at a higher energy state, analogous to the idea of electrons absorbing energy and being promoted to a higher energy state. But the far heavier mass of the protons and neutrons means they absorb way the hell more energy. This is the kind of energy we need to power space travel.

Re:NUCLEAR ISOMERS

[GreenTom]

IMHO (and I am not a rocket scientist), this misses on two fronts: the difficult thing with rocket propulsion is reaction mass, not energy, and nuclear energy states are more energetic than electron states because of the higher binding energies of the strong (or is it weak?) force compared with electromagnetic forces, not because of the greater masses of protons and neutrons.

Re:NUCLEAR ISOMERS

[techno-vampire]

E = m * v^2

Sigh! So close, and yet so far away. E = .5*m * v^2 is what you meant.

Re:Yes, but...

[Titoxd]

Indeed, the power supply problem does exist, and is actually the limiting factor in the performance of ion thruster engines and electric propulsion in general. That limitation actually causes very high specific impulses to be undesirable as the power supply weight savings exceeds the mass savings in propellant. The ideal specific impulse then becomes an optimization problem.

That said, my point is that there are particular applications for which electric propulsion is better than conventional methods (long-distance robotic missions, to pick one), and there are other applications in which chemical propulsion is better than electric propulsion (such as moving a satellite from low-Earth orbit to geostationary orbit... we don't want to wait months for that to occur!) Kind of like in anything involving engineering, you have trade-offs that you have to consider for a particular mission. But assuming that big liquid propulsion rockets are the solution to all the problems is rather lame.

doing the obvious on the ISS

[heroine]

After 8 years of crews testing obscure basic science, they finally have the first tentative approval for the most obvious experiments some time in the future. Incredible.

Re:white knight 2 looks too fragile

[Teancum]

Had SS1 gone into the additional mission phase as was originally anticipated, I'm quite certain this issue would have been resolved.... and it certainly is being accounted for in the SS2.

Since SS1 went to the Smithsonian, there was no reason to keep tinkering with the launch regime, and it was sufficient to note that it was an issue. The SS2 test flights will certainly be interesting in this regard, but the larger mass may help it keep a slightly more stable flight profile as well.

It was a good point you made here, however, that the flights weren't without incident and could have ended catastrophically. I certainly wouldn't want to be on the first flight of SS2 without having substantial experience as a professional test pilot, of which Mike Melville certainly is one of those. It also doesn't hurt that the White Knight & SS1 share the same flight controls (as does the WK2 & SS2), so there was some built-in real-world flight experience that Mr. Melville could fall back on instead of purely simulator experience.

Re:white knight 2 looks too fragile

[Napoleon The Pig]

Actually all the military stuff is governed by MIL-HDBK-516. They don't explicitly specify a SF when they release the RFP. The whole process is extremely tailorable to the specific aircraft being designed, meaning there are no hard requirements just vague criteria like "Verify that the airframe is designed such that ultimate loads are obtained by multiplication of limit loads by the appropriate factors of uncertainty. Also verify that the ultimate loads are used in the design of elements of the airframe subject to a deterministic design approach." (MIL-HDBK-516B, 5.1.5)

That criteria is used as the starting point for negotiations between the aircraft designers and the airworthiness certification offices. Not all criteria listed in 516 are applicable to all aircraft so the first task is to go through the document and determine what is applicable and what isn't. If a criteria is found to be applicable you can't modify it in any way, but you can enact a standard to fulfill that criteria. These standards are the primary source of negotiation between the certification offices and the designers. For example, a typical standard for criteria 5.3.3 (Stresses and strains in airframe structural members are properly controlled...) would be something like a SF of 1.33 for cast parts, 1.15 for fitted parts (if not demonstrated by static test), and 2.0 for bearings for elements with relative motion. However if an aircraft manufacturer comes back with a new process for casting a part that reduces foundry quality control problems and can prove through testing that they have a more accurate construction method thus reducing the need for a factor of safety, then they'll most likely get a reduction on that standard.

Anyway, long story short:

None of the military requirements are set in stone. The standards are negotiated with military technical area experts (TAE). From that the designers submit an Engineering/Data Requirement Agreement Plan (EDRAP) and use that document to outline all the analysis testing and evaluation needed to be done. Since the testing and evaluation is a huge cost driver for the developer they want to reduce the number of tests performed on the system. Each test creates an artifact that is submitted with the agreed upon EDRAP as well as other documents (system safety outline, FMEA, etc) which are then sent back to the certifying authority who then determine whether or not all the requirements were met. If they have been, then a flight clearance is released for that design.

And that, in a nutshell, is the military airworthiness certification process.

Re:white knight 2 looks too fragile

[LenE]

Mike has had his share of scary moments in experimental planes, but this famous episode ranks way down the list, and was certainly not a near-death experience. It was not an uncontrolled nor uncommanded spin, and he regained roll stability well before entering the atmosphere by using the RCS system, which was implemented on the vehicle for just such occasions.

This flight was a test flight. It lead to changes in the flight profile that eliminated the aggravated roll condition. All of the following flights were successful at avoiding the excessive roll. Lessons were learned and applied.

Both Mike and Brian Binnie experienced what would best be described as massive sensory overload from the whole launch experience. No amount of simulator flying could have prepared them, and the test program was far too short to give them enough familiarity to overcome the overload. In this condition, it was hard enough for them to remember their own names while the rocket was firing, let alone keep the flight controls doing what they were supposed to do.

My sarcastic comments about Mike being in one piece were aimed at the hyperbole statement about him being "almost killed" on the first flight. While it made a stunning piece of video with the earth spinning around the windows, he was not in any danger at the time. He told me that since he was basically in microgravity at the time, he could close his eyes and not tell that he was spinning at all. He focused on doing his job and using the RCS system to arrest the roll.

A roll and a spin are two different things. In the case of a plane spinning in thick atmosphere, many times this is an unrecoverable condition. At the very least, it takes non-intuitive action to break out of the spin. Also the chance of structural failure caused by aerodynamic forces tends to make spins very deadly, hence the sense of danger for commonly understood spins. When you take the atmosphere away and configure the vehicle to counter exo-atmospheric orientation problems with the feather and an RCS system, the problem is greatly minimized. So while stunning and hair-raising for all of the arm-chair pilots to watch, the situation on that SS1 flight was not serious beyond the fact that such flights and conditions had not been experienced before.

-- Len

Re:white knight 2 looks too fragile

[WindBourne]

Well, Actually, I MIGHT consider going on something designed by Scaled. They have some of the best engineers in the business and have a LONG reputation for safety. The current stuff is NOT all that different from their previous work (SS2 is a derivative of SS1 and WK2 is not that difficult; LOTS of other work out there). All in all, I would consider being one of the originals.

Re:white knight 2 looks too fragile

[dragonbutt]

I'd have thought falling would have been the opposite of zero g :D

Thats just the abrupt stop at the bottom