NASA apparently plans its first Ares flight test a year from today.
The April 2009 flight will be the first of four test fights for the rocket's first stage, derived from the current space shuttle's solid-rocket boosters. In particular, NASA hopes the flight will validate measures it is now undertaking to quell an anticipated vibration issue in the booster system, which could pose problems down the line for the survivability of later variants of the rocket.
The flight will also demonstrate the abilities of the first-stage flight control systems to keep the "single stick" rocket on course, without the benefit of control fin surfaces.
For the first test flight, NASA will use a four-segment booster, topped with an empty fifth segment. Replicas of an Ares 1 second stage, Orion space capsule and launch abort system rocket will ride up top. The dummy segments will feature correct exterior detailing for aerodynamics testing, and will weigh about the same as their real-life counterparts.
"It's made to look a lot like the Ares 1 vehicle, but it's a very different animal," said NASA lead ground operations engineer Tassos Abadiotakis. "We're also going to get some aerodynamics data, some thermal data -- just the basic rocketry laws to make sure what we're proposing to go fly for Ares 1 actually is going to perform as advertised."
OK, so, if it's "a very different animal," how is it going to validate the real animal? I thought that the concern with the vibration was the fact that they've never flown a five-segment booster, and don't know what its resonant modes will be. I don't see how flying an four-segment booster with an empty casing on top resolves those concerns in any way. Why can't they fly a five-segment booster? Presumably because it won't be far enough along in development to allow a test flight a year from now.
And will the upper stage be just a dummy mass, or will it be active? I thought that the Ares was supposed to get roll control from the upper stage, since it has no way of doing it with the booster (as the article points out, it has no fins, and even if it did, they'd be useless once it left the atmosphere). The first stage can control pitch and yaw through gimbaling, but absent some kind of control jets on the circumference, there's no way for it to control roll on its own.
So, just what is it that this test is supposed to accomplish? Other, of course, than getting something on the pad and flying it to maintain program momentum at a time that a new administration is coming in and considering what to do with it?
[Update on Thursday morning]
I've gotten more than one private email from program insiders that this is a political stunt, not a useful engineering test.
They're probably not flying a full 5-segment booster design because the propellant grain design will be different and hasn't been ground tested yet. As the article says, they're trying to get data on flight control and vibration. As long as the mass and structure are approximately right, they'll get some decent data to validate their models. I've been doing some work recently with shock & vibration testing, and suffice it to say that it isn't exactly as precise a science as experimental fluid mechanics (and that's saying something when you're investigating 2-phase and turbulent flow phenomena.)
Thrust oscillation has been around since early Shuttle days. See, e.g., AIAA 79-1138, "Thrust Oscillations of the Space Shuttle Solid Rocket Booster Motor During Static Tests," presented at the 15th JPC. The frequency will be a little lower for Ares I since the SRB will have five segments, not four. The issue is the structural response of the vehicle, which as of today is still significant. But NASA is working it, and intends to flight-test some fixes.
Last I heard the RoCS for I-X will be different hardware from Ares I, but still mounted on the interstage. From my standpoint I wish the staging system were closer to the Ares I baseline, but they don't pay me to make those decisions....
The test is an evolutionary development test and will not validate the entire Ares I. Get over it!
BBB
"The flight will also demonstrate the abilities of the first-stage flight control systems to keep the "single stick" rocket on course, without the benefit of control fin surfaces."
Since when have rockets with active navigation had need of control fins? I'd think that among the lesser uncertainties of this new design.
Since when have rockets with active navigation had need of control fins?
Without knowing what the phrase "active navigation" means, I have no idea how to answer that question. The issue is, how do you do roll control with a vehicle that has a single solid motor for an upper stage, with no control mechanism other than gimbal?
>>The issue is, how do you do roll control with a vehicle that has a single solid motor for an upper stage, with no control mechanism other than gimbal?
Er, you meant 'first stage'....
BBB
Er, you meant 'first stage'...
Yes, that is what I meant.
The 'lone thruster' first stage isn't as unprecedented as I originally thought. The MX (aka Peacekeeper) missile also has a solo nozzle at the 'hot end', where the Minuteman missiles had a solo thrust chamber but four steerable nozzles. Stability hasn't been a problem with operational flights for MX. The scaling is still a bit off (MX is smaller), but the difference in 'aspect ratio' (not the right term, but it's what I thought of for now) comparing length and diameter is going to be much different on the Ares.
I guess this test would be a stepping stone approach, but still have trouble believing it's too much more than a publicity stunt.
The whole purpose is to maintain "momentum." The 5th segment is a dummy, the US is a dummy, the CEV and LAS are dummies. There is really nothing in this test that can be transferred to the real vehicle (the 1st stage acceleration profile is wrong)
They still verify the clearances on the pad. Even if we assume that exhaust goes where it should, they'll check if the rotating service structure closes around the vehicle at least.
Does NASA have a backup rocket for this mission?
If it's a real test "to make sure what we're proposing to go fly for Ares 1 actually is going to perform as advertised," they ought to have one. Otherwise, a failure would set the program back many months, perhaps years, while they build a replacement.
If it's a PR exercise, no backup is necessary.
Roll control for Ares I first-stage flight is mounted on the interstage ring between first and second stages. For the first demo flight scheduled for next year, it'll be a temporary ad-hoc design using surplus ICBM upper stage hypergol motors, last I heard.
Prototyping is a multi-step process that involves incremental additions to components or processes that are proven and known to work.
The only data NASA has right now about the flight characteristics of a lone SRB in powered flight are from watching footage of the Challenger disaster.
"George Skinner wrote:
They're probably not flying a full 5-segment booster design because the propellant grain design will be different and hasn't been ground tested yet.
April 16, 2008 2:26 PM"
Actually, I thought they did ground test a 5 segment SRB some time ago.
http://www.youtube.com/watch?v=BSPXSjQ5b-U