MCT launch-escape architecture
I guess the r/SpaceX guys couldn't sprint fast enough from the front row to the mic stands.
Lots of issues to be addressed for the safety of passengers on the way to Mars.
He did, but non pressure-fed non-hypergolic engines take some time to spin up their turbopumps, bring the chamber up to operating pressure, and ignite before ramping up to maximum thrust (the the Raptor not only has an extremely chamber pressure, but has two independent turbopumps as part of it's full-flow staged combustion cycle). Unlike with Dragon 2, whose Superdraco engines are Hypergolic and pressure-fed - so will ignite and ramp up to full thrust in a few milliseconds just by opening a valve - the MCT would be sitting on a RUD for several seconds before the Raptors could start moving it away (and they would be exhausting directly into the interstage chamber, which risks damaging the Raptors themselves in the enclosed space). Plus several of the Raptors have extended nozzle bells for vacuum use, so these would need to be jettisoned (tricky, you won;t want to add the mass of an explosive cleaver to the nozzle extension), have thrust severely ramped down, to just blast away and hope the flow separation doesn't fire bits of shattering nozzle extension into the adjacent engines.In the impromptu press-only Q&A afterwards, Musk said the MCT engines double as the abort engines.
That big window does make me wonder how well it could take possible debris impacts at cruising speeds.
He did, but non pressure-fed non-hypergolic engines take some time to spin up their turbopumps, bring the chamber up to operating pressure, and ignite before ramping up to maximum thrust (the the Raptor not only has an extremely chamber pressure, but has two independent turbopumps as part of it's full-flow staged combustion cycle). Unlike with Dragon 2, whose Superdraco engines are Hypergolic and pressure-fed - so will ignite and ramp up to full thrust in a few milliseconds just by opening a valve - the MCT would be sitting on a RUD for several seconds before the Raptors could start moving it away (and they would be exhausting directly into the interstage chamber, which risks damaging the Raptors themselves in the enclosed space). Plus several of the Raptors have extended nozzle bells for vacuum use, so these would need to be jettisoned (tricky, you won;t want to add the mass of an explosive cleaver to the nozzle extension), have thrust severely ramped down, to just blast away and hope the flow separation doesn't fire bits of shattering nozzle extension into the adjacent engines.
The M1Dvac's nozzle extension is welded to the bell (on the second F9 mission where the extension was damaged in transit, they literally took a set of tin-snips to it to trim it off and used excess fuel to counter the loss in efficiency). The RL10B-2 on the Centaur variant used on the Delta IV has a moveable nozzle extension, as does the yet-to-fly Vinci motor.Very good points. But SpaceX is already using a design for bells where the vacuum extension is a separate part which is extended after stage separation on their transfer stage on falcon, so maybe they'll just have something like that?
That might be tricky. The turbopumps are driven by full-flow gas generators which cannot operate independently of the pumps, so having the pumps spun up would require effectively pumping fuel and oxidiser out of the nozzle at flight flow-rates (tons per second) but not igniting it. Which would then hit the hot gas-generator exhaust that feeds into the bell, and would probably ignite in a nice kaboom between the first and second stages.Could there be a way to let the turbopumps run on "standby", generating fuel pressure towards the exhaust without opening the exhaust valve?
JRTI
This launch was from Vandenberg rather than CCAFS, so maybe they managed to wrangle some time on one of the high-gain tracking antennas there (normally used for ICBM test launches)? They had some beautiful IR tracking shots too.Also holy smoke, they got a steady stream from the rocket down to the landing? Did they change something about their setup?