Quote from: edzieba on 12/14/2022 07:14 pmOther than Falcon 9's 'load and go', all other crew launch systems (both cryogenic and hypergolic) load propellants first, then have crew and ground teams approach the active vehicle for boarding.But nobody's doing "disembark with prop still onboard after an emergency landing".
Other than Falcon 9's 'load and go', all other crew launch systems (both cryogenic and hypergolic) load propellants first, then have crew and ground teams approach the active vehicle for boarding.
Quote from: TheRadicalModerate on 12/14/2022 08:59 pmQuote from: edzieba on 12/14/2022 07:14 pmOther than Falcon 9's 'load and go', all other crew launch systems (both cryogenic and hypergolic) load propellants first, then have crew and ground teams approach the active vehicle for boarding.But nobody's doing "disembark with prop still onboard after an emergency landing".They do, for the all of three cases of emergency landings that have occurred (all Soyuz). No RCS prop is dumped as part of the abort, just like all the nominal landings where RCS prop remains on-board.
Quote from: chopsticks on 12/14/2022 09:48 pmQuote from: edzieba on 12/14/2022 07:14 pmOther than Falcon 9's 'load and go', all other crew launch systems (both cryogenic and hypergolic) load propellants first, then have crew and ground teams approach the active vehicle for boarding.So what makes F9 different in this regard? Is it the load and go that is more risky? It appears that Starship will also be load and go.F9 has to out of necessity, or it would have to give up the use of subchilled propellants. The theory behind the 'load first' COOPS is that you load propellants, let everything pressurise and settle down, and then let people approach; the idea being that the loading process itself is the riskiest part.
Quote from: edzieba on 12/14/2022 07:14 pmOther than Falcon 9's 'load and go', all other crew launch systems (both cryogenic and hypergolic) load propellants first, then have crew and ground teams approach the active vehicle for boarding.So what makes F9 different in this regard? Is it the load and go that is more risky? It appears that Starship will also be load and go.
Or just flare it off.
Quote from: Robotbeat on 12/15/2022 12:09 amOr just flare it off.Yep. A flare generates its own wind, so the flame is not directly touching the material of the orifice. The entrained air blows the flame away from the orifice.
Let's do a little math on methane venting.Assuming the Starship is floating horizontally after an abort.Assume a 3m/sec wind.assume the vent distance is 9m, with an average width of 3m.That's 27x3x3 = 243 cubic meters of fresh air per second over that vent area.The maximum allowable methane concentration before ignition can occur is 5%.243*.05 = 12 cubic meters of gaseous methane vented per second. 12 cubic meters of gaseus methane weighs in at 8kg.1 hour is 30t of methane. That's more methane than should remain in main and header tanks.The above is a very pessimistic calculation. I suspect all the remaining methane can be vented in 15 minutes safely, especially if there's more than one vent along the length of the Starship.Contrast this to 1 second of 33 engines methane output underneath the OLM. About 1 second at a flow rate of 100kg/sec for each engine. There was no wind.33 * 100kg = 3300kg of methane or 5000 cubic meters of gaseous methane. underneath the OLM which is about 1000 cubic meters. No wonder it went boom.TL;DR - the worry about venting the excess methane is a non-problem on a water landing where all heat sources are snuffed out and the vent rate keeps the concentration below ignition point.
I'm not referring to water landings or even necessarily emergency landings. Just regular landings and the safety concerns surrounding them, and why you'll probably want pad abort capability. Why did it take crews hours to approach SN15 after it landed?It's not just the venting of methane, it's the combination of that possibility and the fact that the vehicle remains pressurized (with propellant).
With proper software, an early BECO and separation would allow Starship to abort to a suborbital flight and land downrange on a prepared tower or pad (e.g. Florida).in fact w/o cargo abort-to-orbit would have been possible today (mass ratio of 11). So another abort "option" is excess fuel on Starship allowing abort-to-orbit.This would allow aborts on excessive Booster engine outs and other damage such as to the steering system.But it's far too early to program such scenarios. So today we got the automated FTS instead.
Quote from: InterestedEngineer on 04/20/2023 09:23 pmWith proper software, an early BECO and separation would allow Starship to abort to a suborbital flight and land downrange on a prepared tower or pad (e.g. Florida).in fact w/o cargo abort-to-orbit would have been possible today (mass ratio of 11). So another abort "option" is excess fuel on Starship allowing abort-to-orbit.This would allow aborts on excessive Booster engine outs and other damage such as to the steering system.But it's far too early to program such scenarios. So today we got the automated FTS instead.If the SH is having trouble though, you won't get the twist throw of a normal separation though, so escape separation will be very soviet style with the Starship raptors lighting up while still contained within the interstage area. Hope the larger panel area between grid fins can blow out...
No. Doesn’t work for Florida launches. No down range land mass. Can’t say abort to abort was feasible. The stage was already under performing
Quote from: Jim on 04/21/2023 01:52 amNo. Doesn’t work for Florida launches. No down range land mass. Can’t say abort to abort was feasible. The stage was already under performingJim is it feasible for flight computers to shut off engines diametrically opposite to ones that flamed out, in order to increase thrust symmetry and control authority? Would that have been useful in today's flight test?
Quote from: InterestedEngineer on 04/20/2023 09:23 pmWith proper software, an early BECO and separation would allow Starship to abort to a suborbital flight and land downrange on a prepared tower or pad (e.g. Florida).in fact w/o cargo abort-to-orbit would have been possible today (mass ratio of 11). So another abort "option" is excess fuel on Starship allowing abort-to-orbit.This would allow aborts on excessive Booster engine outs and other damage such as to the steering system.But it's far too early to program such scenarios. So today we got the automated FTS instead.No. Doesn’t work for Florida launches. No down range land mass. Can’t say abort to abort was feasible. The stage was already under performing
Quote from: edzieba on 05/05/2023 11:53 amAFTS is still necessary for a crewed vehicle. Shuttle flew with an FTS system, initially for both the SRBs and ET, later just for the SRBs after the decision was made to remove charges from the ET rather than to implement a selective destruct system that would allow firing of the ET charges to be inhibited (after removal, aborts after SRB separation would be via comms to terminate the SSME thrust, or in case of comms failure the FTS command from the range would illuminate a RANGE SAFETY indicator for the crew to manually terminate SSME thrust. Loss of control by the crew would leave no FTS options). Termination of the SRBs (or the ET when charges were present) would have as a near-certainly mean loss of crew. Just because Starship may be flying 1000 tonnes of propellant with people on top, does not mean that is is not still flaying 1000 tonnes of propellant. Keeping that big explosive tank away from population centres must trump the lives of any crew on board. FTS would be only one of the many risks accepted by any spaceflight participants.Dragon flights has AFTS on booster, 2nd stage. Yes?Is there AFTS on dragon? I don't think so. It does have a load of hypergolic fuel but probably is not a huge risk to population on the ground.Obviously with super heavy and starship we have combined 2nd stage with dragon so it is different.
AFTS is still necessary for a crewed vehicle. Shuttle flew with an FTS system, initially for both the SRBs and ET, later just for the SRBs after the decision was made to remove charges from the ET rather than to implement a selective destruct system that would allow firing of the ET charges to be inhibited (after removal, aborts after SRB separation would be via comms to terminate the SSME thrust, or in case of comms failure the FTS command from the range would illuminate a RANGE SAFETY indicator for the crew to manually terminate SSME thrust. Loss of control by the crew would leave no FTS options). Termination of the SRBs (or the ET when charges were present) would have as a near-certainly mean loss of crew. Just because Starship may be flying 1000 tonnes of propellant with people on top, does not mean that is is not still flaying 1000 tonnes of propellant. Keeping that big explosive tank away from population centres must trump the lives of any crew on board. FTS would be only one of the many risks accepted by any spaceflight participants.