Imagine the Code to do This
JonnyMac
Posts: 9,070
Most of us got very excited when self-balancing robots showed up. Imagine the code to fly and position a booster the size of a 22-story skyscraper so precisely that it can be caught by a pair of mechanical arms. I'm old enough to have watched Neil Armstrong step on the moon live on TV. Like that moment, today's catch of the SpaceX Super Heavy booster was similarly awe inspiring.
Comments
Concur! Here's an interesting video from Ryan Hansen that illustrates his assessment of how the catch works. The animation and graphics are beautiful.
Never mind the code, imagine the rocket motor valves and controls that allowed the code to do its thing.
The rocket has gone up already, and coming down you can see it still smoking-hot, but the rocket motor starts and throttles on demand, as do the side thrusters to gently sway it sideways.
Agree with JMG on this. The hard engineering is handling the heat. The nozzles are still glowing red from reentry when it reignites.
Funny fact: Due to https://en.wikipedia.org/wiki/Moment_of_inertia, which is for a cylinder:
It should be more easy to balance that very long and slender object, than a little robot! The huge Moment of Inertia should be giving plenty of time. It's just a little bit more expensive, if there is a bug....
When the first moon landing has been done, NASA must already have been able to control thrust of rockets rather precisely.
I discovered balancing a very long vertical pole with one hand at the young age of 5 ... I, quite literally, was the "robot" brains for a self balancing robot. .... And yes, the bigger the "pole" the easier it is to balance, because that was the next challenge... to see how long of a pole i could balance.
Another detail, that may have been a coincidence, is reignition occurred as the booster crossed below the sound barrier.
I haven't paid much attention to Falcon 9 landings to know if that is the same there or not. Have they had that level of detail before?
The landing burn for the Falcon 9 booster is always well after the call-out of transonic. In both cases atmospheric drag does most of the work; the landing burn is for final "braking" and positioning. That said, the Falcon cannot hover like Super Heavy, so the goal of the F9 algorithm is to decelerate to 0 just as it touches down. There was a somewhat hard landing recently that broke a leg. The F9 fell over and was lost.
"the Falcon cannot hover like Super Heavy" The Falcon certainly could, it's obviously only using a tiny fraction of its lifting power to land. Maybe there is thermal reasons for minimising the burn though. You can see the Super Heavy venting flames sideways as it hovers next to the tower. That probably ain't for control reasons.
Well, efficiency is a reason to minimise both burn time and thrust on landing. The more fuel available to lifting then the heavier the payload can be, or further it can be lofted. But that's just another way of saying the Falcon can hover but they don't want it to.
It's good to know about the Falcon not burning earlier. So it might be tricky to burn like that at low altitude supersonic. Or at least they're not wanting to try unless they have to.
They say it can't because the Merlin engine cannot be throttled low enough to match the weight of the nearly-empty booster.
There are always at least two burns for the F9: the de-orbit burn and the landing burn (if the booster returns to land it first does a boost-back, like Super Heavy did). The de-orbit burn slows the F9 so that it drops into the thicker part of the atmosphere where the grid fins can affect trajectory.
If SpaceX launches in the evening from Vandenberg, I can step outside and watch it fly by. It's really cool just after sunset because it's dark on land but still sunlit in the upper atmosphere so get really neat effects. It's easy to see stage separation and you can also see the booster reorienting itself with cold gas thrusters. Often times you can see the fairing halves falling away, too.
(Image is from LA, but not taken by me)
Impressive light show for sure. I didn't know it was so visible from the ground.
Ah, that figures about the hover. It's too powerful. Microwave ovens are like that I've noticed. Even the "inverter" models don't go below 50% before they start cycling the relay in place of lowering microwave power.
There's no supersonic effects in space. So those manoeuvrers don't count in terms of how tricky it might be to fire up, head on, at speed, in the low atmosphere.