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Astra Test Flight (The craziest launch you'll see this year!)
NASA TV via YouTube ^ | 29 Aug 21 | NASASpaceflight

Posted on 08/29/2021 5:07:43 AM PDT by Politically Correct

Skip ahead to 1:33:00 for all the excitement and then (wait for it) continue to watch for the unexpected finish.


TOPICS: Miscellaneous; Science; Weird Stuff
KEYWORDS: failure; rocket; weird
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To: Politically Correct
The reason rockets like this don't have fins to stabilize them is that they've eliminated the need for the aerodynamic stability provided by fins with mechanical stability provided by rocket nozzles that "gimbal," which is an articulation that in concept works the same as fighter jets that use "vectored thrust" to enhance maneuverability.

The gimballing exhaust nozzles control the stability of the rocket the same way that a circus clown balances a broom on his chin. If the rocket starts to tip over to the right, the nozzles direct exhaust to the left and essentially push the bottom of the rocket back underneath the nose.

FF to 1:20 to see gimballing of STS man engines at lift-off:
https://www.youtube.com/watch?v=OnoNITE-CLc
The engines are lit at this point but the flame from the liquid fuel main engines, which is different from the flames from the solid fuel boosters, is invisible from this perspective.

So this gimballing is a reactive system that forever is chasing to keep the rocket's butt directly underneath its nose. And depending on the amplitude of the excursions that are possible before the gimballing reacts and arrests the wandering can be substantial. Apollo 8 astronaut Bill Anders remarked that the Saturn V shook violently enough that he felt "like being a rat in the jaws of a giant terrier." But that was a far less refined system and Anders' seat was close to 350 feet above the exhaust nozzles, so the shaking had quite a long moment arm.

The US started experimenting with gimballing exhausts in 1948 because using fins for stability had a number of drawbacks, including increased structural complexity and weight and the fact that fins impart stability by creating drag. And if you aspire to shoot a rocket 17,500 mph (or faster), reducing induced drag is usually a simpler and less costly proposition than increasing thrust. So gimballed thrust won out over fin stabilization.

What happened in this case appeared to be that the instant it left ground the entire rocket began to fall over toward the failed engine. But before anything catastrophic could happen, the gimballing began pushing the bottom of the rocket in the same direction as it was falling over to "catch up" with the nose. And that's why it appeared to be sliding to one side on lift-off; because the imbalance of thrust was displacing the nose to one side by some small amount and the gimballing of the operating exhaust nozzles was redirecting thrust so effectively that the displacement off vertical was essentially imperceptible.

Minus one engine this thing probably never was going to get to orbit (not to mention the operating engines had their nozzles cocked at a less that optimum angle), at which point the primary objective should have been minimizing risk to human life, which it managed to accomplish. The gimballing compensated for the thrust imbalance and gave them control over the vehicle such that they could direct it to a crash site where risk to humans or habitations was negligible.

So it might have been a failed launch but it wasn't a complete failure because they just conducted a true-to-life worst-case scenario test of the effectiveness of their stability control system, and it worked a treat. If it had been less effective that video probably would have had a much more entertaining (Hindenberg-like) finish.

21 posted on 08/29/2021 9:42:51 AM PDT by Paal Gulli
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To: Paal Gulli
Great review and explanation. Props to the engineers and programmers for providing an amazing launch after what would previously have been a tremendous and demoralizing launchpad explosion.

They did indeed get a lot of operational info from this launch.

22 posted on 08/29/2021 10:50:28 AM PDT by corkoman
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To: Politically Correct

They need to play around with Kerbal Space Program (KSP) a little more...


23 posted on 08/29/2021 1:23:13 PM PDT by Bikkuri
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To: GranTorino
I noticed the Mohawk on one of the flight controllers.

The one on the right appeared to have googly eyes on the back of his twin monitors.

24 posted on 08/29/2021 4:23:02 PM PDT by Albion Wilde ("Let us not talk falsely now, the hour is getting late." —Bob Dylan)
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