As a SpaceX fanboy engineer I say hot staging was not a success.
It was a success. Booster had issues with engine restart, but that was after rotation and boostback started.
As I recall, Falcon 9's booster needs 13% of its propellants for a return to launch site, but it's moving at about 12,000 km/h. So the Starship booster may only need about 6% in its tanks to get back to the launch site (perhaps even less). Counting pixels on the telemetry image, it looks like they had about 9% remaining. That would allow for hovering/maneuvering at the launch site as well, especially given how light the booster would be at that point.
Thanks, now I get it.
Thanks so much for posting that. Great job by Scott to resynch and do the replay in slo-mo. Now its clear how the inner ring of engines were relit in a specific pattern, that one engine in the ring never ignited, and then one of the center three shutdown and two in the inner ring shut down. So a total of4 out of the planned 10 were out.
Also notice the firing of Starship's engines at hot staging. I assume the intent was to fire the vacuum, outer engines first, then wait two seconds, then fire the sea level, inner engines. The only off-nominal point was that one of the vacuums was slow to fire. I wonder if they gimballed the sea level engines or if firing the vacuum engines gave enough separation to go with them pointed straight.
I think the intent was to fir the vacuums first, but does anyone know why? I would have thought that firing the sea level engines first would have still provided enough thrust for stage separation but would have been 'gentler' on the booster.
That sounds reasonable. I was wondering if for this flight test SpaceX planned to ignite all 6 Starship engines just to test them in a flight environment but that the long term plan is to only ignite the R Vacs for stage sep and ascent to orbit and then only use the center 3 Raptors for landing?
If you look at the geometry of the interstage, you'll see that the vacuum engines point at open space while the sea level engines point at a flat plate. There's very little space between engines and plate, and I doubt that the engines can be fired right away even while gimballed. So they fire the vacuum engines immediately because they can, then fire the sea level engines when they can.
Starship needs the thrust of all six engines to efficiently get clear of the atmosphere. If it was on orbit and in vacuum, it could use as few engines as it likes and just take more time to change its velocity. The single vacuum engine on the Falcon 9 second stage happens to have enough thrust to do the job.
That's an interesting idea, especially given that the mass of the vehicle drops quickly with the use of so much propellant.
Time it from the lighting of the first vacuum engines to the lighting of the sea level engines. It's about two seconds.
Telemetry:
I thought the same thing. Very disappointing, particularly given that during IFT-1 during initial ascent we were briefly treated to a spectacular view from the vehicle looking back towards Earth.
I am as certain as I can be that SpaceX recorded a lot of video from multiple cameras on ship and booster and it will prove useful in the post flight analysis.
They're also very likely to show some of that footage, just as they did after IFT-1. Remember the footage from inside, between the two stages? I suspect that they don't want to show live footage of test flights because of potential abuse by SpaceX detractors. It's all about the propaganda, both for and against.
