fredinno Posted February 25, 2016 Share Posted February 25, 2016 33 minutes ago, DerekL1963 said: Maximizing performance of the first stage means maximizing the payload while still retaining enough reserve to recover to the landing site. Short term PITA, longer term probably at least a medium win. Indeed, but a diameter change would have been far better- they need a diameter change if they want to use CH4 Lox and/or plan on 2nd stage reuse. Sure, the performance gain would be enormous, but the rocket could be shortened (yes, there would also be pad modifications), then re-legnthened over time as needed. It would also be much more of a long-term investment- yes, Ch4 is cryogenic, but nowhere near that of deep cryo LO2. https://en.wikipedia.org/wiki/Liquid_oxygen https://en.wikipedia.org/wiki/Methane The existing Lo2 cryogen oxidiser tech used on F9 V1.1 (not FT) was more than enough for CH4 cryogenic fuel. Link to comment Share on other sites More sharing options...
Halo_003 Posted February 25, 2016 Share Posted February 25, 2016 (edited) 12 minutes ago, fredinno said: Indeed, but a diameter change would have been far better- they need a diameter change if they want to use CH4 Lox and/or plan on 2nd stage reuse. Sure, the performance gain would be enormous, but the rocket could be shortened (yes, there would also be pad modifications), then re-legnthened over time as needed. It would also be much more of a long-term investment- yes, Ch4 is cryogenic, but nowhere near that of deep cryo LO2. https://en.wikipedia.org/wiki/Liquid_oxygen https://en.wikipedia.org/wiki/Methane The existing Lo2 cryogen oxidiser tech used on F9 V1.1 (not FT) was more than enough for CH4 cryogenic fuel. Why would they need a diameter change to use CH4+LOX? Also, do you know by chance what temperature they're using for the LOX? Edited February 25, 2016 by Halo_003 Link to comment Share on other sites More sharing options...
DerekL1963 Posted February 25, 2016 Share Posted February 25, 2016 19 minutes ago, fredinno said: 1 hour ago, DerekL1963 said: Maximizing performance of the first stage means maximizing the payload while still retaining enough reserve to recover to the landing site. Short term PITA, longer term probably at least a medium win. Indeed, but a diameter change would have been far better- they need a diameter change if they want to use CH4 Lox and/or plan on 2nd stage reuse. Sure, the performance gain would be enormous, but the rocket could be shortened (yes, there would also be pad modifications), then re-legnthened over time as needed. It would also be much more of a long-term investment- yes, Ch4 is cryogenic, but nowhere near that of deep cryo LO2 The only people afraid of deep cryogens (based on well established, well tested, well known technology) are the amateurs in the cheap seats (who prefer untested, unknown, unproven technologies). Theoretical handwaving from the cheap seats is entertaining - but SpaceX has a business to run today. Link to comment Share on other sites More sharing options...
KSK Posted February 25, 2016 Share Posted February 25, 2016 43 minutes ago, fredinno said: Indeed, but a diameter change would have been far better- they need a diameter change if they want to use CH4 Lox and/or plan on 2nd stage reuse. Sure, the performance gain would be enormous, but the rocket could be shortened (yes, there would also be pad modifications), then re-legnthened over time as needed. It would also be much more of a long-term investment- yes, Ch4 is cryogenic, but nowhere near that of deep cryo LO2. https://en.wikipedia.org/wiki/Liquid_oxygen https://en.wikipedia.org/wiki/Methane The existing Lo2 cryogen oxidiser tech used on F9 V1.1 (not FT) was more than enough for CH4 cryogenic fuel. Given the choice between persevering with a known technology (subcooled LOX isn't exactly a new thing, just new for them) or developing an entirely new rocket complete with new tooling, new engines and a new fuel, not to mention new infrastructure to support it, I can't imagine why SpaceX opted to stick with the known technology for the moment. It's not like they're short of other ongoing projects either. Or that subcooled LOX isn't going to give a performance upgrade to any LOX/CH4 they decide to build in future. Link to comment Share on other sites More sharing options...
Red Iron Crown Posted February 25, 2016 Share Posted February 25, 2016 45 minutes ago, Halo_003 said: Why would they need a diameter change to use CH4+LOX? Because liquid CH4 is about half the density of RP-1. They'll need much more volume for the same mass capacity. Link to comment Share on other sites More sharing options...
Halo_003 Posted February 25, 2016 Share Posted February 25, 2016 13 minutes ago, Red Iron Crown said: Because liquid CH4 is about half the density of RP-1. They'll need much more volume for the same mass capacity. Derp, good call, wasn't thinking of that. Link to comment Share on other sites More sharing options...
sevenperforce Posted February 25, 2016 Share Posted February 25, 2016 Odds on a successful landing tonight? Link to comment Share on other sites More sharing options...
KerbonautInTraining Posted February 25, 2016 Share Posted February 25, 2016 I'm still confused as to why they don't have near future plans for an LH2 upper stage. Link to comment Share on other sites More sharing options...
Tex Mechs Robot Posted February 25, 2016 Share Posted February 25, 2016 Coming up on 3 hours to launch. Link to comment Share on other sites More sharing options...
sevenperforce Posted February 25, 2016 Share Posted February 25, 2016 4 minutes ago, KerbonautInTraining said: I'm still confused as to why they don't have near future plans for an LH2 upper stage. Reusability development probably has something to do with it. LH2 destroys tanks. It would require a separate engine and an added fuel type when they are trying to streamline operations by doing everything with a single engine and single fuel type. Finally, its bulk would make the upper stage ungainly. Link to comment Share on other sites More sharing options...
sgt_flyer Posted February 25, 2016 Share Posted February 25, 2016 (edited) 13 minutes ago, KerbonautInTraining said: I'm still confused as to why they don't have near future plans for an LH2 upper stage. they don't have plans for a lh2 one, but they do have plans for a liquid methane one. SpaceX was awarded 33,6M$ in january from the air force to help develop a raptor prototype specifically for a falcon 9 / falcon heavy upper stage. http://spaceflightnow.com/2016/01/14/orbital-atk-spacex-nab-u-s-air-force-propulsion-contracts/ though, Falcon 9 being a two stage rocket, i guess it could benefit even more from a fregat style third stage than an LH2 upperstage Edited February 25, 2016 by sgt_flyer Link to comment Share on other sites More sharing options...
Streetwind Posted February 25, 2016 Share Posted February 25, 2016 13 minutes ago, sevenperforce said: Odds on a successful landing tonight? Not zero, but low. Rumor mill says they're skipping the boostback burn entirely to save fuel, and are letting the stage simply follow its ballistic arc to the barge which would be way further downrange than usual. (Of course, rumors may or may not turn out to be untrue.) Link to comment Share on other sites More sharing options...
sevenperforce Posted February 25, 2016 Share Posted February 25, 2016 Just now, Streetwind said: Not zero, but low. Rumor mill says they're skipping the boostback burn entirely to save fuel, and are letting the stage simply follow its ballistic arc to the barge which would be way further downrange than usual. (Of course, rumors may or may not turn out to be untrue.) So what's the most likely failure mode? Breakup during re-entry, or a missed/hard landing? Link to comment Share on other sites More sharing options...
VirtualCLD Posted February 25, 2016 Share Posted February 25, 2016 15 minutes ago, sevenperforce said: So what's the most likely failure mode? Breakup during re-entry, or a missed/hard landing? I've heard the same rumor so my guess would be a missed/hard landing as the most likely failure mode. Link to comment Share on other sites More sharing options...
Camacha Posted February 25, 2016 Share Posted February 25, 2016 Let us hope they do not scrub this time. Thanks for all the updates! Link to comment Share on other sites More sharing options...
sgt_flyer Posted February 25, 2016 Share Posted February 25, 2016 Weather is still 80% favorable for today's launch - though they are keeping an eye on wind strength at high altitude and ground levels. http://www.spacex.com/webcast Link to comment Share on other sites More sharing options...
DerekL1963 Posted February 25, 2016 Share Posted February 25, 2016 25 minutes ago, sevenperforce said: 27 minutes ago, Streetwind said: Not zero, but low. Rumor mill says they're skipping the boostback burn entirely to save fuel, and are letting the stage simply follow its ballistic arc to the barge which would be way further downrange than usual. So what's the most likely failure mode? Breakup during re-entry, or a missed/hard landing? Part of the the function of the boostback burn is to target the vehicles - skipping it means they have to re-target during the entry burn, which takes more energy and is constrained by aerodynamics. It won't take much of an error during the first stage burn for it to be off by miles... so my guess is the most likely failure mode is a clean miss where the vehicle doesn't even come within a couple of miles of the barge. The next most likely is a near miss or failed landing due to excessive horizontal velocity. Much depends on how well they understand the ballistic performance of the vehicle. Link to comment Share on other sites More sharing options...
sevenperforce Posted February 25, 2016 Share Posted February 25, 2016 3 minutes ago, DerekL1963 said: Part of the the function of the boostback burn is to target the vehicles - skipping it means they have to re-target during the entry burn, which takes more energy and is constrained by aerodynamics. It won't take much of an error during the first stage burn for it to be off by miles... so my guess is the most likely failure mode is a clean miss where the vehicle doesn't even come within a couple of miles of the barge. The next most likely is a near miss or failed landing due to excessive horizontal velocity. Much depends on how well they understand the ballistic performance of the vehicle. And the ballistic performance of a cylindrical rocket is anything but simple. Link to comment Share on other sites More sharing options...
sgt_flyer Posted February 25, 2016 Share Posted February 25, 2016 1 minute ago, DerekL1963 said: Part of the the function of the boostback burn is to target the vehicles - skipping it means they have to re-target during the entry burn, which takes more energy and is constrained by aerodynamics. It won't take much of an error during the first stage burn for it to be off by miles... so my guess is the most likely failure mode is a clean miss where the vehicle doesn't even come within a couple of miles of the barge. The next most likely is a near miss or failed landing due to excessive horizontal velocity. Much depends on how well they understand the ballistic performance of the vehicle. do you know it they will still make a reentry burn ? if they can steer a bit at this point, it could help for minimizing the deviations. (and i wonder how much just changing the booster's attitude could help them compensate deviation too - through the grid fins and the cold gas thrusters - especially as the booster is round, there's not much lifting body effect - though the drag profile would increase - so a bit of control in how far it will go, but less control over lateral deviations .) Link to comment Share on other sites More sharing options...
sevenperforce Posted February 25, 2016 Share Posted February 25, 2016 16 minutes ago, sgt_flyer said: do you know it they will still make a reentry burn ? if they can steer a bit at this point, it could help for minimizing the deviations. (and i wonder how much just changing the booster's attitude could help them compensate deviation too - through the grid fins and the cold gas thrusters - especially as the booster is round, there's not much lifting body effect - though the drag profile would increase - so a bit of control in how far it will go, but less control over lateral deviations .) I can't see how they could get away without a reentry burn. Otherwise that booster will smack into the atmosphere like an egg hitting concrete. Link to comment Share on other sites More sharing options...
DerekL1963 Posted February 25, 2016 Share Posted February 25, 2016 15 minutes ago, sgt_flyer said: do you know it they will still make a reentry burn ? if they can steer a bit at this point, it could help for minimizing the deviations. They're going to have to slow down *somehow*. And if they are in fact skipping the boostback burn and simply going the full ballistic route, it's their only chance to re-target. 18 minutes ago, sgt_flyer said: (and i wonder how much just changing the booster's attitude could help them compensate deviation too - through the grid fins and the cold gas thrusters - especially as the booster is round, there's not much lifting body effect - though the drag profile would increase - so a bit of control in how far it will go, but less control over lateral deviations .) Unless they're flying due east, a correction in the plane of the flight path will move the impact point both downrange and crossrange. And now I'm having flashbacks to MK5 guidance school.... Link to comment Share on other sites More sharing options...
sgt_flyer Posted February 25, 2016 Share Posted February 25, 2016 (edited) 15 minutes ago, DerekL1963 said: They're going to have to slow down *somehow*. And if they are in fact skipping the boostback burn and simply going the full ballistic route, it's their only chance to re-target. Unless they're flying due east, a correction in the plane of the flight path will move the impact point both downrange and crossrange. And now I'm having flashbacks to MK5 guidance school.... yes,changing the drag profile would affect both the downrange and crossrange position of the landing zone if not moving due east (or west ;)) - but wouldn't they both be affected at the same time if you can only act on the drag profile without at least a lifting body ? - if (for example) the longitude of the projected landing zone is correct, but not the latitude once the ballistic phase starts ? (i meant, they won't be able to correct one without affecting the other with only a tubular shape) Edited February 25, 2016 by sgt_flyer Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted February 25, 2016 Share Posted February 25, 2016 Anyone else getting some weird behavior from the live streams? They all say they don't start till about 3:45 (PST), but that's when liftoff is? Link to comment Share on other sites More sharing options...
Mad Rocket Scientist Posted February 25, 2016 Share Posted February 25, 2016 2 hours ago, sevenperforce said: Odds on a successful landing tonight? Slim, but not quite zero. I think it's most likely to break up/burn up during reentry. 11 minutes ago, CatastrophicFailure said: Anyone else getting some weird behavior from the live streams? They all say they don't start till about 3:45 (PST), but that's when liftoff is? Maybe they don't know when the video will start yet? Link to comment Share on other sites More sharing options...
Scotius Posted February 25, 2016 Share Posted February 25, 2016 Webcast is starting now. Go Falcon! Link to comment Share on other sites More sharing options...
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