SpaceX (Vol. 2)
Discussion
Arnold Cunningham said:
LivLL said:
I thought they were waiting for a second site to be finished before catch attempt just In case it all goes wrong.
3 weeks to go now
Or they plan that site 2 will be finished in time for flight 6, regardless. Or maybe the last promo video was just a tease. 3 weeks to go now
Perhaps not as tongue in cheek as you'd think. They're not afraid of blowing stuff up in the interests of learning more, more quickly. So I could well see that as long at they think there's a better than 50/50 chance of landing it, they'll have a go, log all the data, and learn from it.
Arnold Cunningham said:
Perhaps not as tongue in cheek as you'd think. They're not afraid of blowing stuff up in the interests of learning more, more quickly. So I could well see that as long at they think there's a better than 50/50 chance of landing it, they'll have a go, log all the data, and learn from it.
Delays cost more than rebuilding stuff, especially as the new tower has different plumbing (vacuum-insulated like a thermos) than the old.The real difficulties come in getting signoff to blow your own stuff up and/or approval to try again after you have.
Legmaster said:
Arnold Cunningham said:
LivLL said:
I thought they were waiting for a second site to be finished before catch attempt just In case it all goes wrong.
3 weeks to go now
Or they plan that site 2 will be finished in time for flight 6, regardless. Or maybe the last promo video was just a tease. 3 weeks to go now
It rocketing off into the sunset and the abort system being triggered would be an investigation.
How much of an explosion would it be with so little propellant left in the tank at the point of reaching the tower? How much does an empty booster weigh? Maybe if the worst happened it might not cause all that much damage..? 
Remember they've had several crashes in that area when they were testing the first few Starship prototypes - didn't seem to cause much of a problem with the infrastructure!
Remember they've had several crashes in that area when they were testing the first few Starship prototypes - didn't seem to cause much of a problem with the infrastructure!
AJLintern said:
How much of an explosion would it be with so little propellant left in the tank at the point of reaching the tower? How much does an empty booster weigh? Maybe if the worst happened it might not cause all that much damage..?
Remember they've had several crashes in that area when they were testing the first few Starship prototypes - didn't seem to cause much of a problem with the infrastructure!
Explosive effects fall off by the cube of distance. The booster will likely have about 10-20 tonnes of propellant, not all of that manages to deflagrate but it would still be equal to multiple tonnes of explosive going off a short distance away.Remember they've had several crashes in that area when they were testing the first few Starship prototypes - didn't seem to cause much of a problem with the infrastructure!
You also have a 300 tonne booster hitting the launch mount at high speed car crash velocity.
I thought the idea was to slow down to a hover some way over to the side and gradually move across into the chopsticks - that way if it's coming in too hot it won't crash directly into the tower. I guess it depends how confident they are with the accuracy of the trajectory - seem to manage pretty well with the Falcon 9s.
Beati Dogu said:
It wont be hovering, it’ll be descending the whole time.
They’ll arc it in like they do with Falcon 9 boosters, so if if loses control it will safely ditch itself.
Interesting.They’ll arc it in like they do with Falcon 9 boosters, so if if loses control it will safely ditch itself.
When landing, F9 booster has more thrust at its lowest power setting than the weight of the rocket, so it cannot hover. This leads to the practise of hoverslam landings for F9 boosters
Starship booster can hover, it's engines can throttle down enough to achieve this when it's empty, so while it may waste fuel, I don't know why it would actually need to descend the whole time in a test scenario.
SpaceX started hover testing the ship as practically the first set of flight tests years ago.
Have they published a flight test plan for ift5?
Yes that was my understanding, that they can throttle back enough to hover - something they can't do with the F9. Otherwise there's no way they could achieve being caught by the chopsticks - it needs to be static so they can reposition and engage those relatively tiny pins that stick out!
Edited to add - here's an animation of it: https://www.youtube.com/watch?v=Y-k8QjIF-uI
Edited to add - here's an animation of it: https://www.youtube.com/watch?v=Y-k8QjIF-uI
Edited by AJLintern on Wednesday 10th July 08:22
As far as I'm aware, the plan is for the booster to get into position and slow its descent to about 2-3 meters per second (4.5 to 6.7 mph).
The arms will close around the smooth upper methane tank once the lower part (and its protruding chines) have passed by.
Then it catches the lifting lugs located just under the grid fins
Simples...
Let's not forget that the booster is ~70 meters tall, so even at 3 m/s it will still take ~23 seconds for it slip through to capture.That'll seem like an age, I'm sure.
The arms' shock absorbers have then got to absorb any kinetic energy without snapping off or crushing anything. We know it can take the ~220 ton dead weight as it has done that several times already.
Oh lawd, she comin!: Booster 12 was wheeled out to the pad yesterday:
The arms will close around the smooth upper methane tank once the lower part (and its protruding chines) have passed by.
Then it catches the lifting lugs located just under the grid fins
Simples...
Let's not forget that the booster is ~70 meters tall, so even at 3 m/s it will still take ~23 seconds for it slip through to capture.That'll seem like an age, I'm sure.
The arms' shock absorbers have then got to absorb any kinetic energy without snapping off or crushing anything. We know it can take the ~220 ton dead weight as it has done that several times already.
Oh lawd, she comin!: Booster 12 was wheeled out to the pad yesterday:
AJLintern said:
I thought the idea was to slow down to a hover some way over to the side and gradually move across into the chopsticks - that way if it's coming in too hot it won't crash directly into the tower. I guess it depends how confident they are with the accuracy of the trajectory - seem to manage pretty well with the Falcon 9s.
Nobody has done this before so there will be a bunch of never demonstrated failure modes.Booster is ~250 tonnes, the Raptor can throttle down to about 90 tonnes so it could hover on as many as three engines. (all masses/thrust highly variable). Hovering is still pretty bad for payload so needs to be minimised, I would expect that the booster will do something akin to the hover slam slightly off center before vectoring over to the arms in a hover.
The height at which is does this will be a compromise between wanting to minimise the impact of the rocket plum as it "spashes" over the edge of the edge of the launch mount vs the additional kinetic energy of a failed booster dropping on said launch mount. I'd optimise for the former.
In terms of fun new failure modes:
1: The impact of the plume on the launch mount and its reflection back at the booster.
2: The plume detaching stuff from the launch mount and these things striking the booster
3: The booster touching launch mount, not least because this could cause the booster to do something odd as the control laws for a booster in free air vs one pivoting on a hard point will be different.
4: The failure of an engine while recoverable likely results in the booster moving large distances horizontally while the remaining engines re-orientate, this distance is likely to overlap with something solid when in close proximity to the tower.
5: Multiple new ways for fuel to slosh and set up fun dynamic effects, particularly when the booster is grabbed.
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