RizzoTheRat Posted February 7, 2018 Share Posted February 7, 2018 From discussion on another forum apparently they'd said they weren't entirely sure how much LOx would boil off in the coasting phase, so running it dry to measure the amount left makes sense Quote Link to comment Share on other sites More sharing options...
Technical Ben Posted February 7, 2018 Share Posted February 7, 2018 3 engine landing is harder than the one. As more engines to startup, and riskier "suicide" burn. They say they may have run out of starting fluid. Bear in mind this was a first time 3x heavy launch. So they had to "guesstimate" some figures on how much fuel/fluid/etc to take. That and/or something got stuck? Quote Link to comment Share on other sites More sharing options...
RizzoTheRat Posted February 7, 2018 Share Posted February 7, 2018 Presumably the core went higher than the usual Falcon 9 stages so faster on the way down and needing more thrust? Quote Link to comment Share on other sites More sharing options...
kerbiloid Posted February 7, 2018 Share Posted February 7, 2018 Spoiler The first stage separation moment (24:34 of the video) reminds me of that gadget from Kill Bill. Quote Link to comment Share on other sites More sharing options...
KSK Posted February 7, 2018 Share Posted February 7, 2018 12 minutes ago, YNM said: You still realize how hard it is to tell amount of fuel on probes do you ? Even back on Earth fuel tank gauges are rarely precision devices, airplanes don't really measure them, cars have a wide error. And that' where the fuel wouldn't come out as tiny particles floating around (or, truer to cryogenic, you've gotten yourself a pressurized tank). Woah - take it easy. I've already admitted that my initial 'why can't they just calculate it' thoughts were too simplistic. And yes, I've read enough to know that spacecraft fuel gauges aren't exactly precision devices. But I was kind of assuming that SpaceX knew how much propellant they put into the second stage, so once they've left a margin (because running a booster stage completely empty isn't a good idea) they should be able to calculate a maximum theoretical performance. 2 minutes ago, RizzoTheRat said: From discussion on another forum apparently they'd said they weren't entirely sure how much LOx would boil off in the coasting phase, so running it dry to measure the amount left makes sense That was the kind of answer I had in mind - cheers. Quote Link to comment Share on other sites More sharing options...
Nefrums Posted February 7, 2018 Share Posted February 7, 2018 3 minutes ago, RizzoTheRat said: Presumably the core went higher than the usual Falcon 9 stages so faster on the way down and needing more thrust? Thrust is not an issue, one engine is capable of slowing down the rocket. But as all KSP players know, a higher TWR means a more efficient landing, with a shorter burn that saves dV. I doubt that was actually needed on this launch. They could most likely have landed the core with one engine. More likely is that they wanted to test yet another new thing on this test flight. Quote Link to comment Share on other sites More sharing options...
Reactordrone Posted February 7, 2018 Share Posted February 7, 2018 31 minutes ago, Nefrums said: did SpaceX try a new landing procedure for the center core? Landing is normally done on one engine, Side boosters landed with one engine. Last week they tried a new shorter landing burn with three engines for soft splashdown on a expendable launch. Now we hear that the core failed to land because only one out of three engines started... The boosters did a 1-3-1 burn for this landing (Lighting the centre engine, briefly firing up two more engines for a fast slowdown, then landing on just one) I assume the core was trying to do the same. Quote Link to comment Share on other sites More sharing options...
Technical Ben Posted February 7, 2018 Share Posted February 7, 2018 (edited) SpaceX reuploaded the cast video with a correction on booster 2 camera. [edit] Ah, the good old 1.3.1. I've been trying to "force" this kind of thing with mechjeb with action keys and toggling on/off engines. I should really learn KOS. Edited February 7, 2018 by Technical Ben Boosters... MOAR. Quote Link to comment Share on other sites More sharing options...
tseitsei89 Posted February 7, 2018 Share Posted February 7, 2018 (edited) 44 minutes ago, Nefrums said: Thrust is not an issue, one engine is capable of slowing down the rocket. But as all KSP players know, a higher TWR means a more efficient landing, with a shorter burn that saves dV. I doubt that was actually needed on this launch. They could most likely have landed the core with one engine. More likely is that they wanted to test yet another new thing on this test flight. The boosters ignited 3 engines during the landing. They used so called 1-3-1 landing. What that means is that: First only the center engine ignites Then 2 more engines ignite for higher thrust more dv efficient slowdown Then at the end those 2 engines shut down to give better control for the final landing You can briefly see it in the video below. @1:27 first engine ignites, @1:29 2 more engines ignite for added thrust (and camera has trouble following), @1:34 when camera gets back you can see the 2 engines just being shut down. So if they did try the same 1-3-1 landing with core stage, the center engine alone wouldn't have enough time to slow it down to landing if those 2 engines didn't ignite Edited February 7, 2018 by tseitsei89 Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted February 7, 2018 Share Posted February 7, 2018 13 hours ago, qzgy said: Seriously?! How big? 3.5 tonnes to trans-Plutonian injection without gravity assists. Requires fully-expendable performance. Quote Link to comment Share on other sites More sharing options...
cubinator Posted February 7, 2018 Share Posted February 7, 2018 Well, goodbye car. I don't think I've been that excited for a launch since the Shuttle days. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted February 7, 2018 Share Posted February 7, 2018 12 hours ago, GoSlash27 said: I played hooky from a work- related class to witness the launch as it happened, and it was everything I expected it to be. Doubly- exciting since there were no spoilers. I was cheering like a maniac during all of the landmarks that went right, plus the absurdity of watching Spaceman chillin' in his roadster :D. Simultaneous booster flyback in formation... How cool was that?? Pure rocket porn. 12 hours ago, StrandedonEarth said: I'm sure the Starman suit must be loaded with sensors, Musk is not the type to waste an opportunity to do MOAR SCIENCE!! But I agree, the speedo needed to be pegged, perhaps at Ludicrous Speed. Maybe a "Plaid" spot on the speedo? To my surprise, Elon said that Starman was just a plain mannequin, no sensors or anything else. Quote Link to comment Share on other sites More sharing options...
cypher_00 Posted February 7, 2018 Share Posted February 7, 2018 I showed my mother a picture of Spaceman chilling in his car with earth in the background and the first thing she said was omg is there a real person in that car! Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted February 7, 2018 Share Posted February 7, 2018 12 hours ago, YNM said: Given the fact that there's no crossfeed on this one yet, I think the margin for the centre stage was pretty low. They only lowered the throttle then raise it up again after side separation. From the views I saw, it looked like the center core was already throttled down when it cleared the towers: That might just be plume interaction, though. 10 minutes ago, cypher_00 said: I showed my mother a picture of Spaceman chilling in his car with earth in the background and the first thing she said was omg is there a real person in that car! My 24-year-old brother had the same question. I mean, dude. C'mon. 9 hours ago, Brotoro said: I don't know... when you show before the launch that you are going to aim for an orbit that just touches Mars orbit, but then you put your payload into an orbit out to the asteroid belt...it kind of looks like a miss. Minimum residual shutdown post-coast to measure boil-off rates. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted February 7, 2018 Share Posted February 7, 2018 8 hours ago, Vanamonde said: Really, guys? We're going to get into a fight about whether a launch was 100% successful or 80% successful, or whatever? Can't we all just be happy that something is happening in space? I mean, as players of a space game, we can all agree this is at least cool and interesting, right? Thank you. 7 hours ago, tater said: The core was still not a block 5 core, and none of the FH boosters from today were every intended to fly again. Musk said that the center booster failed due to running out of igniter for the side 2 M1Ds (they did 3 engine-->1 engine landing burns I think, if you look closely). Sounds like they know what happened. The FH core stage is not identical to the other F9s, perhaps the issue is related to that (lower igniter fuel volume due to increased structure?). As @Brotoro said, it was a test flight to suss out exactly these sorts of issues. The Apollo 6 flight, for example discovered the pogo problem with Saturn V had not been fixed. Apollo 6 also had igniter problems I think, as well. Anyway, the FH test was short of perfect, but pretty good for a first flight of a rocket, honestly. They also have the benefit of being able to use hardware and simply try things. We'll likely hear more about the landing failure, particularly since I think he said they might do a blooper video of it. As long as they are confident they know what happened, and how to fix it I think it's not a big deal. I'm just glad it didn't wreck 39A, since that pad is needed for crew. The core did a boostback burn, but we don't know how much of a boostback burn it did (though very careful analysis of the net webcast might suss it out). Did the boostback bring it down to single-stick GTO velocities? If not, then perhaps hitting the atmosphere at far higher velocities than normal caused ignition problems, requiring a longer shot of TEA-TEB and depleting the supply. Something to fix, yes. But that's the point of a test flight. 5 hours ago, Josh IN SPACE said: -Side note. I hope maybe there is footage to come of the core booster diving into the drink. Watching that sounds almost as entertaining as watching the actual launch. I wonder if the core had enough margin to do a 1-0 landing burn like CRS-8. I doubt it; if they had the margin, they would have used it. 1 hour ago, Nefrums said: did SpaceX try a new landing procedure for the center core? Landing is normally done on one engine, Side boosters landed with one engine. Last week they tried a new shorter landing burn with three engines for soft splashdown on a expendable launch. Now we hear that the core failed to land because only one out of three engines started... They have three landing burn configurations: 1-0, 1-3-1-0, and 1-3-0. In 1-0, they perform the entire landing burn with the center engine and shut it down at zero-zero (that's zero velocity, zero altitude). In 1-3-1-0, which has been the approach for almost all ASDS landings, they start the burn with one engine, ignite two side engines to kill almost all the velocity, and then shut those two down and use the center engine with fine throttle control for the landing. 1-3-0, which they tested on Govsat, burns all three engines all the way to zero-zero. This was most likely a 1-3-1-0, but if one of the two side engines failed to ignite, the center engine would continue to burn merrily away as it plunged into the ocean. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted February 7, 2018 Share Posted February 7, 2018 1 hour ago, RizzoTheRat said: Presumably the core went higher than the usual Falcon 9 stages so faster on the way down and needing more thrust? The stage hits terminal velocity before the landing burn start, so that's not the issue. They probably know exactly why they ran out of TEA-TEB. Not going to be a problem with BFR, since production Raptor will use spark ignition. 1 hour ago, Nefrums said: Thrust is not an issue, one engine is capable of slowing down the rocket. But as all KSP players know, a higher TWR means a more efficient landing, with a shorter burn that saves dV. I doubt that was actually needed on this launch. They could most likely have landed the core with one engine. More likely is that they wanted to test yet another new thing on this test flight. I'd guess that they didn't have QUITE enough margin for a 1-0 landing. The dV difference between a 1-0 and a 1-3-1-0 is stark. The difference between a 1-3-1-0 and a 1-3-0 is less so. Quote Link to comment Share on other sites More sharing options...
Nefrums Posted February 7, 2018 Share Posted February 7, 2018 19 minutes ago, sevenperforce said: Thank you. The core did a boostback burn, but we don't know how much of a boostback burn it did (though very careful analysis of the net webcast might suss it out). Did the boostback bring it down to single-stick GTO velocities? If not, then perhaps hitting the atmosphere at far higher velocities than normal caused ignition problems, requiring a longer shot of TEA-TEB and depleting the supply. Something to fix, yes. But that's the point of a test flight. I wonder if the core had enough margin to do a 1-0 landing burn like CRS-8. I doubt it; if they had the margin, they would have used it. They have three landing burn configurations: 1-0, 1-3-1-0, and 1-3-0. In 1-0, they perform the entire landing burn with the center engine and shut it down at zero-zero (that's zero velocity, zero altitude). In 1-3-1-0, which has been the approach for almost all ASDS landings, they start the burn with one engine, ignite two side engines to kill almost all the velocity, and then shut those two down and use the center engine with fine throttle control for the landing. 1-3-0, which they tested on Govsat, burns all three engines all the way to zero-zero. This was most likely a 1-3-1-0, but if one of the two side engines failed to ignite, the center engine would continue to burn merrily away as it plunged into the ocean. Ok, that makes sense. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted February 7, 2018 Share Posted February 7, 2018 56 minutes ago, Technical Ben said: Ah, the good old 1.3.1. I've been trying to "force" this kind of thing with mechjeb with action keys and toggling on/off engines. I should really learn KOS. If you wanna replicate this... Spoiler Build a booster with a single engine on the tank attachment node and then put down 8 cubic struts in 8-way symmetry around it. Then, attach engines to those 8 struts one by one, rather than using symmetry. You can rotate/translate the struts to move all the engines together, but you can select the engines individually in the action group editor. Set AG1 to shut down all engines, to lock gimbal on all outer engines (but not the core), and to stage your stack decoupler. Turn off staging on the decoupler itself. Set AG2 to toggle the core engine, and set AG3 to toggle two opposite engines. At the desired staging velocity, punch 1 to stage, then switch views to your upper stage and spacebar to stage its engine. Switch back to the booster and start your RCS flip, and press Z to make sure your throttle is full-up. If you're using airbrakes, toggle these on as well. Near the end of your flip, tap 2 to bring your core engine back up and use its gimbal to fix your boostback vector, then press 3 to bring the two side engines online to complete the boostback. Once you've neared your desired boostback velocity, press 3 again to turn them off, then throttle down the core to refine your trajectory. At this point, I switch back to my upper stage to make sure it is ascending well. If it has a high enough TWR, I like to complete its orbital insertion here. After your upper stage is dealt with, jump back over to your booster. Set heading to hold-retrograde. Press X to cut throttle and 3 to bring your side engines back online. Z throttles up all three engines together for the entry burn and tapping 1 kills all three engines together. As you descend, keep an eye on your acceleration gauge. It will jump pretty high, then drop gradually to around 1 when you hit terminal velocity. If you used the entry burn, you'll be coming in almost vertical now, so you have a few seconds past terminal velocity to tap 2 and ignite your core engine. Keep an eye on the ground; it helps if your targeting is good enough that you know roughly the ground-level altitude of your landing site. Just when you start to get nervous (this is the part that requires the most trial-and-error), punch 3 to turn on your side engines. They should only need a couple of seconds max; then punch 3 again, deploy your landing gear, and use Shift to slowly throttle down the core engine to a hoverslam landing. Do it fifty times or so and you start to get really good at it. Quote Link to comment Share on other sites More sharing options...
Confused Scientist Posted February 7, 2018 Share Posted February 7, 2018 (edited) One thing that I haven't seen much of so far is how big of a PR success this is. Only SpaceX would put a car in orbit and send back the first pictures while playing a David Bowie song at the faring deployment. The hours-long live video of Starman is also pure gold, along with two boosters landing simultaneously. They also did a fantastic job of hyping things up beforehand with all of their animations even though it was really hard to find the launch date. So, with the successful launch and all of the video they sent back, I have this to say: Good job, SpaceX. The world loves you. Edited February 8, 2018 by Confused Scientist Quote Link to comment Share on other sites More sharing options...
PakledHostage Posted February 7, 2018 Share Posted February 7, 2018 (edited) 44 minutes ago, Confused Scientist said: One thing that I haven't seen much of so far is how big of a PR success is. Only SpaceX would put a car in orbit and send back the first pictures while playing a David Bowie song at the faring deployment. Which was watched live by over 2 million people on YouTube. And if a lot of those 2 million plus YouTube instances were anything like the one playing at my own desk, then the number of people watching live could have been well higher than that; I had a whole crowd of co-workers watching with me. Congratulations SpaceX on a great test flight and for creating a fun STEM spectacle! Edited February 7, 2018 by PakledHostage Quote Link to comment Share on other sites More sharing options...
tater Posted February 7, 2018 Share Posted February 7, 2018 I showed Starman Live to the grocery checker and bagger, and they were astounded and amazed. It's remarkable how little "regular" people pay attention to this stuff. Quote Link to comment Share on other sites More sharing options...
Just Jim Posted February 7, 2018 Share Posted February 7, 2018 10 minutes ago, tater said: I showed Starman Live to the grocery checker and bagger, and they were astounded and amazed. It's remarkable how little "regular" people pay attention to this stuff. I just got home from a friends I was hanging out with this morning, and while he knew about the launch, he didn't understand how the booster landing worked... So I played him the animated Falcon Heavy video SpaceX posted a few days ago: Man... let me tell you, when my friend saw the boosters eject, then spin 180° and punch it back towards Earth... The look on his face was truly priceless!!! Quote Link to comment Share on other sites More sharing options...
Nightfury Posted February 7, 2018 Share Posted February 7, 2018 Don't know if there is a answer yet, but is there any new infornation about the center core? Hopyfully not, but in the webcast you saw smoke and stuff, but nothing more which could be a sign of the stage exploding right next to the ship Besides this it's weird that it takes so long to get any telemetry of the ASDS or S1... Quote Link to comment Share on other sites More sharing options...
RCgothic Posted February 7, 2018 Share Posted February 7, 2018 After rewatching, the abruptness of the ASDS getting swamped and then cutting out fits with a nearby splashdown at 300mph. Nothing new beyond the outer engines ruining out of igniter. Quote Link to comment Share on other sites More sharing options...
tater Posted February 7, 2018 Share Posted February 7, 2018 15 minutes ago, Nightfury said: Don't know if there is a answer yet, but is there any new infornation about the center core? Hopyfully not, but in the webcast you saw smoke and stuff, but nothing more which could be a sign of the stage exploding right next to the ship Besides this it's weird that it takes so long to get any telemetry of the ASDS or S1... It hit the ocean at 300 mph. The 2 side engines failed to ignite (they ran out of TEA-TEB). Quote Link to comment Share on other sites More sharing options...
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