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miércoles, 4 de noviembre de 2009

Aerial View of Ares 1-X Launch

We're pleased to share with you today some really unique video coverage from last week's Ares I-X launch. A Cessna Skymaster aircraft, flying at 12,000 feet in the vicinity of booster splashdown and equipped with a gyro-stabilized camera, captured this high-definition video. This footage gives us some extremely valuable engineering data, as well as spectacular footage of the recovery sequence in rarely seen detail.

First a few words to preview what you will see after booster burnout, as some of the events happen quickly. First you'll see the thrust plume diminish followed by a brief flash, which is the firing of the booster deceleration motor, then a smaller flash on the side of the booster, which is the tumble motor firing. Then after a couple minutes of descent, you will see the drogue chute deploy to stabilize the booster tail-down. Then, the forward skirt assembly is jettisoned and the drogue pulls it up and away from the booster. The three main parachutes follow immediately, and you will be able to see how one deflates and a second remains only partially inflated. Right before water impact, if you look closely at the nozzle, you will see the jettison of the nozzle extension and then booster splashdown. Finally, you will see the drogue lowering the forward skirt assembly in a second splashdown event just to the left of the booster.

The first stage flew very precisely and smoothly through ascent. Our primary interests on ascent included vehicle control margins, roll stability and also an assessment of thrust oscillation. We saw very positive results with respect to controllability. The roll control system only fired three times during all of ascent, while our preflight analysis predicted as many as 20 firings of the RoCS system. So, this is an excellent outcome. Also, we saw minimal vibration due to thrust oscillation, both in the data and from onboard cameras. The pressure oscillations from the Ares I-X booster were well within historical levels seen on shuttle flights.

As the booster burns out, you see here a flash during the firing of the booster deceleration motor, then, you see here the firing of the booster tumble motor. The booster begins to rotate and separate from the upper stage. You notice also that the upper stage begins to rotate. This was expected, as the upper stage did not have a control system. In fact, the separation event for Ares I-X was more challenging than Ares I design conditions. Because we only had four segments of propellant, we burned out at lower altitude and higher dynamic pressures -- 90 pounds per square foot for Ares I-X, as compared to only 10 pounds per square foot for Ares I. So, this resulted in a stress case separation and was very successful.

One thing to watch here during the descent of the booster is the trailing smoke from the nozzle. This helps us see the flight path of the descent, which initially is horizontal to the Earth, and later as the vehicle slows will become more vertical. Early on in our engineering assessments for Ares I-X we were concerned we might have a nose-first re-entry of the booster because of the forward-end weight of the fifth segment simulator. About a year ago, we had calculated up to 20 percent probability of nose-first re-entry, which would have likely resulted in burn-up of the parachute assembly and loss of the booster. After several refinements to our weight and balance of the booster, we got our predictions down to only a 3 percent probability of nose-first re-entry, which proved to be valid on our I-X flight test, as the vehicle stabilized nozzle-down for most of the descent. Several oscillations can be seen in the booster orientation, and as speed decreases, the flight path becomes nearly vertical as seen by the trailing smoke plume.

It is interesting to note that during the vertical descent there is a slow oscillation and the booster is actually at about 110-degree angle of attack to the flight path as the drogue chute deploys. This results in several dramatic oscillations under the drogue, but it performs beautifully and the booster stabilizes nicely after about four oscillations.

Watch closely at the top of the booster here as the forward skirt extension is jettisoned and pulled away by the drogue. This entrains the risers of the three main parachutes for their initial inflation to the "reefed," or partially inflated, position. All three chutes make it to this first inflation position but the chute on the left quickly deflates and fails, trailing a streamer, which appears to strike the chute in the middle, perhaps damaging it as well.

So, just prior to water entry we essentially have 1 1/2 chutes suspending the booster. Also, at this point you can see the nozzle extension pyrotechnically severed at the bottom of the booster, just before water entry. The booster hits at a higher velocity than planned, which causes a hard slapdown and buckling of the aft segment motor case. This has also been experienced in the shuttle program. A total of 11 chute deployment failures have occurred in the life of the shuttle program, most recently on STS-128. So, we have abundant data here to resolve this for future missions. Ares I-X was also a parachute stress test, as the booster was nearly 40,000 pounds heavier than an Ares five segment booster due to the hardware in the fifth segment simulator. The parachutes were a world-record-setting 150-foot diameter, and were tested at total payload weight for the first time during Ares I-X.

Now that the booster is down in the water, watch for the drogue and forward skirt extension to enter into the image just to the left of the booster. All of these sequences worked exactly as designed. Today, the booster is on dock at Cape Canaveral and is undergoing teardown inspections. In the next few days, we will be able to recover the data recorders and begin the detailed data analysis of the entire flight.

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