Space X dumps a booster

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bernomatic
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#1 Space X dumps a booster

Post by bernomatic »

from Space X page
On Wednesday, December 5, 2018, SpaceX launched its sixteenth Commercial Resupply Services mission (CRS-16) to the International Space Station. Liftoff occurred at 1:16 p.m. EST, or 18:16 UTC, from Space Launch Complex 40 (SLC-40) at Cape Canaveral Air Force Station, Florida.
Now when stage 1 was supposed to be coming in for a landing, the video for the first stage cut off, while the upper stage videos continued. Could it have been they didn't want the general public to see a spectacular failure and thus were the feed was cut off? The official word was that there was a problem (like the booster not coming in where it was supposed to land?) Now to be fair, 1) Space X has shown us the failures in the past in real time 2) This wasn't a complete and total failure, as the booster came in and as subsequent footage shows, made a controlled landing on the water before falling over and venting any explosive materials thus no tragic loss of material.
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#2 Re: Space X dumps a booster

Post by luke strawwalker »

It came to light in the subsequent "tweets" by Elon Musk that the grid-fin control hydraulic pump "stalled" (locked up, seized, or the drive mechanism quit?) and thus the grid fins lost their control authority, when partially "hard over" during the atmospheric entry portion of the flight. I was watching the launch coverage on youtube live, and the feed was still running after the reentry burn of the first stage, which brakes its speed shortly before it reenters the lower "sensible atmosphere" above CCAFS and LZ-1, so it doesn't heat up excessively or slam back down into the denser atmosphere at too high a speed... The grid fins are deployed BEFORE this "reentry burn" to slow the stage, but since it's above most of Earth's atmosphere at that point (as 90% of Earth's atmosphere is within 20 miles of the surface), they actually do very little to nothing at that point in flight. As the reentry burn is completed, the stage is low enough that the air is thick enough to start having an effect, and the grid fins start steering the vehicle down toward the Landing Zone 1 landing pad at Cape Canaveral. The stage then continues to fall ballistically, with air drag preventing it from accelerating beyond terminal velocity (basically a couple hundred MPH). The hydraulic pump failure led to a control failure of the grid fins, while they had been attempting to correct the tracjectory, and so they ended up partway "hard over" when the pump quit, with no way to "neutralize" them or "return them on center" control-wise... so the grid fins, partially "hard over" induced a spin into the vehicle as it continued to fall, which quickly built as there was no way to neutralize it (as the air jet thrusters become less effective and run out of fuel, and the forces are building as the air gets thicker that the fins are moving through. The stage started rotating uncontrollably and even developed a partial "flat spin" (multi-axis spin, ie "pitch-roll coupling" as described in G.Harry Stine's "Handbook of Model Rocketry" which leads to basically a spiralling flight path that eventually takes the vehicle "horizontal" to the flight path, essentially "pancaking in" so to speak). As soon as it became apparent that the vehicle was deviating from "normal behavior", within a few seconds the feed from the booster camera was cut.

It was subsequently explained in "tweets" from Elon Musk and by a SpaceX spokesman in a post-launch press conference put on by NASA, that "the video will be released, good or bad" and that the stage hydraulic pump controlling the grid fins had failed, but the stage had made a controlled descent ANYWAY and managed to land softly about 2 miles offshore from CCAFS, and continued to transmit telemetry and some video from the landed stage, floating in the water, and that SpaceX had dispatched a ship to recover the stage from the ocean. The stage is actually targeted for an "impact point" slightly offshore during the boost-back burn and reentry burn, in case something goes wrong, so the stage can safely crash "out to sea" and not splatter itself all over the pad or, if the trajectory is wrong, not overshoot and hit something else at CCAFS (like SLC-40 or any of the other facilities), or worse yet, overshoot CCAFS entirely and pancake in somewhere in the middle of Cocoa Beach or something... As the vehicle progresses towards touchdown, each step of the way, the "impact point" is moved closer to the final landing spot... ie the impact point is targeted offshore during the reentry burn, so if the stage fails completely after that point, it will still crash out to sea, offshore. The impact point is moved closer to shore after the reentry burn, and the grid fins steer the stage toward land at CCAFS after the reentry burn, but the final "translation" to the landing pad at LZ-1 is ONLY made after the final landing burn is started and the vehicle is in a controlled landing mode with everything working properly, so that it actually targets the landing pad, flies down to it, deploys the landing legs and touches down. Since the grid fin hydraulics malfunctioned, the impact point was actually steered out to sea, so that the vehicle, if control or authority over the flight were lost, would crash safely offshore and not threaten or damage any of the facilities at CCAFS. The booster landing system then continued with the descent, and actually ignited the single rocket engine on-time and in the proper manner for its landing, just that the aiming point had been overridden from the LZ-1 landing pad to the offshore impact point. There is footage from an amateur photographer on YouTube of the landing, as the landing burn proceeded and the stage fought valiantly for control, to override the rotation induced by the grid fins, which FINALLY it was able to do as the velocity decreased and the grid fins become less and less effective at inducing rotational forces into the vehicle (same reason some of our model rockets will "tail-slide" if launched straight up in still air-- as they reach apogee, they slow, the fins are less and less effective with less air moving over them, until the rocket stops, and starts to fall backwards... air flow over the fins is reversed and builds up as speed increases, for a few moments until the force is sufficient to "flip" the rocket over nose-down, hopefully just as the ejection charge fires in our case, before velocity builds up TOO much!) Anyway, with the rocket thrust of the wildy-gyrating gimballing Merlin rocket engine trying to control the rocket and bring it to a near-hover at touchdown, the engine actually gained control of the stage, and rotation slowed greatly as the terminal descent was taking place, and virtually stopped completely once the landing legs deployed, which the spokesman attributed to the "spinning skater with arms outstretched" phenomenon (changed moments of inertia) slowing it down... which I guess has a lot of validity, because a single rocket engine basically has NO control over roll along the long axis of the rocket-- that has to be controlled by a side-mounted set of thrusters firing laterally to the rotational axis of the stage... a gimballing single engine can ONLY control a stage in pitch and yaw, NOT roll... (a PAIR of engines could, since they could be gimballed in opposite directions of each other, inducing a roll around the centerline in the desire direction, but this is not the case on Falcon 9). Anyway, the stage stopped rotating, hovered down in a slow descent until the rocket engine was literally blowing spray and steam away from the surface of the ocean as the landing gear touched down, then it extinguished its rocket engine, splashed down into the water, floated upright for a second or so, then keeled over horizontal into the water and remained floating. It landed softly and in a controlled fashion, just over water instead of Landing Zone 1's landing pad.

They have even talked about re-flying it on a SpaceX mission; if for nothing else than "proof of concept" I suppose... it was an all-new stage, as SpaceX will no longer be repainting the stages after they have gotten sooty and burned from flights and previous reentry burns and landings... so if you see a pristine, clean, new white stage, it's a new stage and not a flown one, at least that's what they're saying...

There's plenty about it on Youtube, including some amazing footage if one is interested. Basically, it was a "successful failure" in that the stage performed correctly after the failure, flew to the correct spot (the pre-targeted offshore impact point, chosen to protect property and people on land) and even managed, somewhat unexpectedly, to overcome the problems induced by the failed grid-fin system on the stage's motions prior to landing-- remember SpaceX had one stage crash land because its rate of spin was too high, and this slung the propellant up the sides of the tanks and away from the propellant duct in the center of the bottom dome of the tank, thus starving the engines of fuel and preventing them from bringing the vehicle to a safe landing speed... Amazingly, this didn't happen this time-- the landing engine actually ignited and burned correctly, and fought for and gained control of the stage and brought it down to a correct soft landing, though of course over water 2 miles or so offshore rather than on the pad at LZ-1...

Elon said that basically the landing hydraulic pump is a 'single string' system, meaning "no backups" as they are not considered "mission critical" but are "landing critical" and so in all likelihood, they'll probably add redundant capabilities to the system in the future-- possibly a second pump and backup hydraulic lines in case the primary system fails, so they'll still have control by switching to the backup pump and lines...

Later! OL J R :)
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#3 Re: Space X dumps a booster

Post by Rocket Babe »

And in only 40 years we'll be where we were in 1974. :x
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#4 Re: Space X dumps a booster

Post by luke strawwalker »

Rocket Babe wrote: Sat, 08 Dec 18, 22:45 pm And in only 40 years we'll be where we were in 1974. :x
I'm sorry I don't quite follow...

Later! OL J R :)
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#5 Re: Space X dumps a booster

Post by Commander »

I think she is saying (although it is almost always dangerous to try and read a lady's mind) that at the present time we are so far behind were we were when the Shuttle concept was being first worked on, that it will take the current NASA 40 years to get back to that beginning point.
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#7 Re: Space X dumps a booster

Post by luke strawwalker »

Meh, NASA's stuck in the past with their booster designs anyway...

SpaceX and everyone else is going to leave them in the dust. SLS is cancellation bait strictly on cost if nothing else, and there's a lot of other reasons. Just a matter of time and circumstances before it's dumped...

SpaceX is perfecting reusability and doing it without complicated space-planes... lifting body and space-plane designs really are no use beyond low Earth orbit anyway-- carrying the weight of wings and landing gear is simply too inefficient and too heavy for deep-space operations-- it drags you entire mission capability into the mud and propulsion requirements in the form of delta-V through the roof...

I'd like to see Sierra Nevada finish Dream Chaser and hire SpaceX to launch them; other than that, Crew Dragon all the way...

Later! OL J R :)
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#8 Re: Space X dumps a booster

Post by bernomatic »

Yes, I am a Blue Origin fan commander, so I have to say B.O. is getting their New Glen ready to launch in early 2019. Here is a good take on it and some good comments below.


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