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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.
Just to pick nits, the proper term is "high speed taxi test".
I know, but it's Saturday morning and I'm bored...
"Eve of Destruction", it's not just for old hippies anymore...
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.
As far as concepts go, you pretty much can't get more gigantic pounding thrust than Freeman's.
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.
IANARS (I Am Not A Rocket Scientist), but...
Launching from an airplane or from a mountaintop has almost nothing to do with getting out of our gravity well and a whole lot to do with getting out of our atmosphere.
Escape velocity from the earth's surface is 11.2km/s (i.e. if earth didn't have an atmosphere to slow things down via friction, you could shoot an object up at that speed and it would never fall back down). Escape velocity in low earth orbit is 10.9km/s, only a couple of percent less due to being farther out of the earth's gravity well, but tremendously easier to achieve because there's no air in the way to slow you down.
Launching from a moving plane, or via a powered launching system, can contribute to your velocity directly, but again the problem is the atmosphere. The fastest atmospheric vehicles we can make (military planes and such) only get up to around mach 3 (and they do that tens of kilometers up, in thinner air), which is about 1 km/s, whereas escape velocity is 11.2km/s and even to reach low orbit requires about 8km/s. Imparting a really significant fraction of a spaceship's final velocity before it leaves the atmosphere would require reengineering the ship to survive atmospheric friction at those velocities, which might cost you a lot of mass.
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
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.
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.
Sigh! So close, and yet so far away. E = .5*m * v^2 is what you meant.
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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.
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