More on the “flight test” of Ares 1-X, which seems to be mostly for show. Though if it’s as risky as indicated here, it may be a more spectacular performance than they count on.
Unfortunately, the same folks who think a flight dynamics test of a four segment SRB with a different propellant, old-style grain design, and inert (that is to say, non-sloshing and stiff) upper pieces is a good idea also thought they could grab a bunch of used equipment (Atlas avionics software, Peacekeeper hardware, etc.), chewing gum, and duct tape (perhaps FEMA is helping the minions) and use it to demonstrate how something “like” ARES-1X might get off the ground after “the gap” has widened to its furthest extent.
And, like all of the shortcuts the Emperor’s minions have taken to date, this approach, too, is soon to come back and bite them. The list of critical components going into ARES-1X that are either beyond shelf life or being put to work in an environment for which they were not intended is astounding. And the risks that are being accepted, because of schedule and budget pressures, are equally marvelous.
Hey, it’s OK. That’s what waivers are for.
The sniping at the Ares 1-X test is getting really pathetic. It’s a flight dynamics test. Key questions: how does a single SRB-based design fly, and what sort of vibration does it produce in the payload? The use of different avionics is irrelevant – look at the number of technology demonstrators that’ve used off the shelf systems to make a functional system to validate other aspects of the design. Other design features are also less representative of the intended final design – so what? You think that engineers haven’t figured out how to simulate the dynamic mass of a payload yet in rocket testing? That having exactly the right grain design in the propellant is more critical than characterizing the shock & vibration environment in the spacecraft? Ares 1 may be a ridiculously non-optimal design, but a test like this is exactly what’s necessary to define the problem better instead of having a war of models and opinion.s
Key questions: how does a single SRB-based design fly, and what sort of vibration does it produce in the payload?
And they aren’t going to learn anything about the actual launch vehicle with this test, because it uses a four-segment solid, whereas the current plan for the vehicle is five-segment. That’s going to make a huge difference in both frequency and magnitude of the vibrations.
5 segments will change the natural frequency and possibly the excitation modes for the booster, but I think what they’re really after is the interaction between the excitation produced by the combustion of the solid fuel and the response of the booster structure. It’s difficult to model the combustion instability of the burning solid fuel because it’s a turbulent reacting flow, and it’s difficult to measure the excitation in a static test or even on the shuttle because the booster is constrained. The flight test is going to provide some data on how the combustion excitation forces the structural response in flight. Characterizing the forcing function should help improve confidence in the model. At that point, they could find out that the vibration problem isn’t as bad as they’d feared, or they could find that they’re totally and hopelessly screwed. If flying a kludged booster helps, why not? If they’re foolish enough to ignore or downplay adverse test results, well, too bad.
“And they aren’t going to learn anything about the actual launch vehicle with this test, because it uses a four-segment solid, whereas the current plan for the vehicle is five-segment. That’s going to make a huge difference in both frequency and magnitude of the vibrations.”
Exactly. The test vehicle won’t prove all that much because it’s not going to come close to behaving like the proposed final product since there are so many differences in the designs. It won’t be a valid “flight dynamics test” for that very reason. A valid flight dynamics test would consist of flying a launch vehicle with design parameters as closely matching to the flight vehicle as possible at this stage. Four segment motor vs. five? No match. Inert second stage? No match. STS vs. Ares-grained motor castings? No match. Not much will be learned about the dynamic flight characteristics of the Ares launch vehicle by this flight.
I’m not saying that the test is worthless, but I don’t think it’s worth the cost. How much more would it cost to fly with an actual lower stage, and how much delay? As you say, they may get the data they need, but they also may not.
At that point, they could find out that the vibration problem isn’t as bad as they’d feared, or they could find that they’re totally and hopelessly screwed.
And where would the smart money be on those two alternatives?
What bothers me is that they don’t even seem to consider the possibility of the latter. They just assume that they will solve it, somehow, though that’s in defiance of any realistic knowledge of the history of engineering.
The primary problem that this author has with the Ares-1X test is that by not using the 5th segment, you are missing the majority of the issues with the booster. The 5th segment would increase the energy of the system by 20%, a non trivial number. Also, by not having an upper stage simulator with similar frequency response modes, there is no test of the couplings between the stages. This renders any coupled modes analysis practically moot for the real vehicle.
There is also no test of the funky reverse thruster motors on this flight, and while this was a late addition, it would be very useful to test.
Finally, NASA’s own documents indicate that the 1-X test will not help them with the Thrust Oscillation problem and that they will not have any data on that until the Ares 1-Y test in 2012-2013, safely beyond the end of the Shuttle program so when the entire concept falls apart, there will be no STS to fall back on.
Watch the 1-X test slip as far as possible to the right so that any failure will not be an excuse to kill the stick.
Also, burnout is probably where these thrust vibration problems will be their worst. And to really test that requires a active five segment engine not a four segment engine with an inert fifth segment. Still bending metal is good in principle. It would be nice if there was more in common here with the actual Ares I.