What about the structure of the Starship being tanked? Now that we're onto MMOD, I can see that being kinda important for a big gas tank on orbit. The double skin with a thermal break would also seem to work well for cryogenic storage.
Perhaps the welding machine needs more clearance than the stringers would provide. No idea. I'm just thinking out loud as to why they wouldn't want to build something from scratch with the reinforcement only on the outside.
If it was for MMOD protection, I would expect the whole thing, yeah. A tanker is just a lot of plumbing and tanks, so it all needs to be protected. The engine bells would still be exposed, but the engines on a depot wouldn't be needed. As you say, this seems like overkill for a Whipple shield, or a Dewar flask. A shield doesn't need that many supports and a flask wouldn't want that many supports.
If it has structural purpose, why reinforce through the long axis of the ship? It's already reinforced in that direction enough to sustain a couple g of acceleration.
We know that SpaceX is under a lot of pressure from NASA to get HLS on schedule and LEO refueling is required for the mission, so it does seem very likely that S26 could be the first depot vehicle. It can’t be a tanker since it has no tiles or flaps. Will it even have sea level Raptors?
So in the case of a vehicle shaped like Starship, a shield that covered everything back to where the rear skirt starts is going to add a lot of mass. But I suppose MMOD protection is essential for a huge vehicle that is going to remain on orbit for a long time; maybe future versions will remain on orbit for years?
Sure. The primary purpose of the engines on the depot is to get to orbit. Once there, those engines are dead weight. They're too powerful for propellant transfer, and tankers visiting the depot can adjust its orbit if needed (adjust on an empty depot). Starship can't get to orbit on 3 vacuum Raptors, and adding three more would be both suboptimal and require new hardware that we haven't yet seen.
Consider it the initial payload of the depot launch.
Really? It can't get the perigee high enough fast enough with only 3 (or 4) Rvacs? I figured they could loft it and it would just incur more gravity and atmospheric losses.
I assumed losing half of the thrust seems like too great a penalty to make orbit. The thrust:weight ratio drops to 1:1.6. It would have to burn 45% of its propellant load just to reach 1:1. If it makes it, it would be a pretty funky flight profile involving lots of acceleration while in atmosphere and probably some aerodynamic skipping to avoid losing too much altitude and generating too much downward velocity. I don't know how much heating that would produce. Perhaps stainless steel could handle it.
One more point of data about the reinforcement is that they've stopped work. Ship 26 has been disconnected from the crane and is in line with the other vehicles in storage. So they've either proved the technique or they've completed the work they wanted done. If the latter, then it may be reinforcement for the HLS body thrusters that are used for Moon landings and launches.
I just realized that every Starship must have sea level Raptors because it can’t get to orbit without TVC. A Starship with only RVacs can’t steer itself during ascent.
Somewhat, as long as you don't lose one. Also may need a lot of thurster action to correct any yaw.
Do you mean roll? Pitch and yaw can be addressed with asymmetrical thrust. Roll should be pretty minor given the lack of any force driving it. Except perhaps the Starship flaps while in atmosphere. Adjustable tabs could be put on the flaps to counter that.
Yeah
Odd that they're working on it without having a crane to stabilize it, and it's more top heavy than before. Maybe it's the OSHA guy's day off.
Bleh. I understand rocket yaw/pitch because each engine is offset from the centerline. I can imagine a slight rocket roll because the engine may not be perfectly aligned with the rocket body long axis. But I'm confused by your saying "yaw" then "spin" as if they're the same thing. Are you talking about engine yaw to correct for rocket spin?
OMG my brain is broken. I was trying to agree with you and typed yaw again instead of roll.Odd that they're working on it without having a crane to stabilize it, and it's more top heavy than before. Maybe it's the OSHA guy's day off.
Bleh. I understand rocket yaw/pitch because each engine is offset from the centerline. I can imagine a slight rocket roll because the engine may not be perfectly aligned with the rocket body long axis. But I'm confused by your saying "yaw" then "spin" as if they're the same thing. Are you talking about engine yaw to correct for rocket spin?
This is my mental model of a rocket's control axes:
In the end, if we're going exclusively with vacuum engines, gimbal them. Bring them in a bit so that they have room for roll authority, and put one in the middle if that still allows the needed bell movements.
That is the peril of being respected - whatever you write is assumed to be accurate
If I don't have a link, beware what I thinkThat is the peril of being respected - whatever you write is assumed to be accurate
