tater Posted November 18, 2018 Share Posted November 18, 2018 10 minutes ago, RedKraken said: Not using 1100t since the twr drops to 1.20 How many engines? Quote Link to comment Share on other sites More sharing options...
RedKraken Posted November 18, 2018 Share Posted November 18, 2018 6 minutes ago, tater said: How many engines? 7 sea level engines on each BFS.... total 21. thrust 200t, isp 330-356s each. Quote Link to comment Share on other sites More sharing options...
tater Posted November 18, 2018 Share Posted November 18, 2018 2 minutes ago, RedKraken said: 7 sea level engines on each BFS.... total 21. thrust 200t, isp 330-356s each. I'd assume that a real version would have more engines on the tankers to meet the same 31 (ish) as the stated booster. What's the spreadsheet say with 12-16 per tanker (You could always run the center raptor on the core for 31 total)? In that case, you can have a full prop load on the crew/payload center core, and use the increased volume on tankers for more propellants. Quote Link to comment Share on other sites More sharing options...
RedKraken Posted November 18, 2018 Share Posted November 18, 2018 (edited) 17 minutes ago, tater said: I'd assume that a real version would have more engines on the tankers to meet the same 31 (ish) as the stated booster. What's the spreadsheet say with 12-16 per tanker (You could always run the center raptor on the core for 31 total)? In that case, you can have a full prop load on the crew/payload center core, and use the increased volume on tankers for more propellants. For 31 engines total, i get about 130t to LEO, compared to about 115t for standard 2018BFR. Dry masses still at ~85t. 1600t propellant in the boosters, 1100t in the core. Edited November 18, 2018 by RedKraken Quote Link to comment Share on other sites More sharing options...
tater Posted November 18, 2018 Share Posted November 18, 2018 So plenty of margin for increased structure if needed and still hit 100t to LEO. Quote Link to comment Share on other sites More sharing options...
ThatGuyWithALongUsername Posted November 18, 2018 Share Posted November 18, 2018 BTW, I tried a "biamese" design with only 2 ships and it didn't really work. TWR was just terrible. This was in RO/RSS with @Nessus_'s configs. Added 2 engines to side BFS. No crossfeed. Long story short, you need 3 cores or more/ better Raptors. Considering the insane performance of Merlin engines, I wouldn't be surprised if the Raptors got another upgrade- and that, combined with adding a few more, just might save this design. Otherwise, looks like you need 3 cores. Quote Link to comment Share on other sites More sharing options...
Mad Rocket Scientist Posted November 19, 2018 Share Posted November 19, 2018 2 hours ago, ThatGuyWithALongUsername said: BTW, I tried a "biamese" design with only 2 ships and it didn't really work. TWR was just terrible. This was in RO/RSS with @Nessus_'s configs. Added 2 engines to side BFS. No crossfeed. Long story short, you need 3 cores or more/ better Raptors. Considering the insane performance of Merlin engines, I wouldn't be surprised if the Raptors got another upgrade- and that, combined with adding a few more, just might save this design. Otherwise, looks like you need 3 cores. What if the BFS-boosters have all the cargo pods replaced with SL raptors? Quote Link to comment Share on other sites More sharing options...
ThatGuyWithALongUsername Posted November 19, 2018 Share Posted November 19, 2018 9 minutes ago, Mad Rocket Scientist said: What if the BFS-boosters have all the cargo pods replaced with SL raptors? I tried a 14 engine booster with no success, but I have not yet tried a full BFR 31 engines quite yet. I had the idea but had no more time to try it. Assuming the Raptors can gimbal a lot... it just might work. Very reminiscent of a certain space shuttle. Perhaps I'll try that next... Quote Link to comment Share on other sites More sharing options...
RedKraken Posted November 19, 2018 Share Posted November 19, 2018 54 minutes ago, tater said: So plenty of margin for increased structure if needed and still hit 100t to LEO. Looks like it. The tankers/boosters have to land downrange or ASDS. RTLS costs way too much at higher speed seps (50% reserve for vhoriz 3300m/s) Tankers might achieve 65t dry by themselves.... 20t worth of structure margin Cargo at 75t ... 10t of margin Crew at 85t .... zero margin Re-done with crew @ 95t (10t margin) gives about 125t to LEO (Engine setup is 12-7-12, ie 12 engines on each tanker, 7 on the center core) Quote Link to comment Share on other sites More sharing options...
tater Posted November 19, 2018 Share Posted November 19, 2018 Is there margin for sep at closer to 2 km/s so that RTLS is a thing? Quote Link to comment Share on other sites More sharing options...
RedKraken Posted November 19, 2018 Share Posted November 19, 2018 (edited) 16 minutes ago, tater said: Is there margin for sep at closer to 2 km/s so that RTLS is a thing? RTLS reserve fuel is ~16% sep@1800m/s (vhoriz 1250) for F9. When i punch in 16% reserve for the tankers, it drops LEO payload to 50 tonnes. Ouch. On the positive side, i'm getting a nice matchup in RO 1.3.1 for the 130t to LEO using ASDS. Edited November 19, 2018 by RedKraken Quote Link to comment Share on other sites More sharing options...
DDE Posted November 19, 2018 Share Posted November 19, 2018 3 hours ago, Mad Rocket Scientist said: What if the BFS-boosters have all the cargo pods replaced with SL raptors? The what? Quote Link to comment Share on other sites More sharing options...
tater Posted November 19, 2018 Share Posted November 19, 2018 2 minutes ago, DDE said: The what? The bottom of the #DearMoon BFS has what looks like petals around the engines. They are in fact cargo pods. Quote Link to comment Share on other sites More sharing options...
Mad Rocket Scientist Posted November 19, 2018 Share Posted November 19, 2018 Just now, DDE said: The what? https://i.redd.it/zg9lfqobgwm11.jpg During the 2018 announcement, they said that you could pull out 2 of those aft cargo pods at a time to upgrade a single of the outer SL raptors to Vac. I was suggesting removing all of them and adding a ring of 6 more SL raptors to the BFboosters. Quote Link to comment Share on other sites More sharing options...
DDE Posted November 19, 2018 Share Posted November 19, 2018 1 hour ago, tater said: The bottom of the #DearMoon BFS has what looks like petals around the engines. They are in fact cargo pods. Yeah, sorry, I tuned out on the new BFR after hearing (probably wrongly) that a slightly intoxcated Musk called it “just like the Tin-Tin rocket”. Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted November 19, 2018 Share Posted November 19, 2018 41 minutes ago, DDE said: Yeah, sorry, I tuned out on the new BFR after hearing (probably wrongly) that a slightly intoxcated Musk called it “just like the Tin-Tin rocket”. Well, it does bare a pretty strong resemblance as of the last official update. Quote Link to comment Share on other sites More sharing options...
Green Baron Posted November 19, 2018 Share Posted November 19, 2018 Proposal to paint a red checker board pattern on it and design specesuits for the pets. Also, before lauch, thoroughly search the cargo bay / pods for scatterbrained detectives and agents. Quote Link to comment Share on other sites More sharing options...
magnemoe Posted November 19, 2018 Share Posted November 19, 2018 18 hours ago, ThatGuyWithALongUsername said: I'm not kidding, I just had a similar idea, but you beat me to it More specifically, why would we need 3 BFS's (?)? One on it's own can SSTO, albeit without much payload, so just strap one tanker BFS to the side and call it a day- that should be enough. Don't think they go parallel staging they have had very good track record with an two stage design so I think they stick with that. They will also not use wings. Design changes, 4 fins? And yes making an smaller, MFS first makes some sense, a bit better capacity than falcon 9 but worse than falcon heavy disposable. Rolle would be satellite launches and perhaps an manned version later. This would continue to be useful even after BFR is in active use as an smaller launcher who is cheaper to operate. Quote Link to comment Share on other sites More sharing options...
DDE Posted November 19, 2018 Share Posted November 19, 2018 4 minutes ago, magnemoe said: an smaller launcher who is cheaper to operate. Their whole shtick is bigger = cheaper. Quote Link to comment Share on other sites More sharing options...
Xd the great Posted November 19, 2018 Share Posted November 19, 2018 30 minutes ago, DDE said: Their whole shtick is bigger = cheaper. Well, cheaper per pound, but more expensive to build. Quote Link to comment Share on other sites More sharing options...
mikegarrison Posted November 19, 2018 Share Posted November 19, 2018 26 minutes ago, DDE said: Their whole shtick is bigger = cheaper. Obviously that's not true. Bigger is not cheaper. Bigger *may* be more efficient. If you need to launch 100 tonnes of payload, doing it in one big rocket may be cheaper than 100 small rockets. But if you need to launch 1 tonne of payload, it will likely be cheaper to launch it with a smaller rocket. (This assumes all else is equal.) Quote Link to comment Share on other sites More sharing options...
Xd the great Posted November 19, 2018 Share Posted November 19, 2018 22 minutes ago, mikegarrison said: Obviously that's not true. Bigger is not cheaper. Bigger *may* be more efficient. If you need to launch 100 tonnes of payload, doing it in one big rocket may be cheaper than 100 small rockets. But if you need to launch 1 tonne of payload, it will likely be cheaper to launch it with a smaller rocket. (This assumes all else is equal.) Not with the bfr. 7 million per launch? A 1 tonne rocket be like 15 million. Quote Link to comment Share on other sites More sharing options...
magnemoe Posted November 19, 2018 Share Posted November 19, 2018 32 minutes ago, Xd the great said: Not with the bfr. 7 million per launch? A 1 tonne rocket be like 15 million. BFR is fully reusable, this makes it cheap to operate compared to other rockets even for its size. Still its cheaper to charter an business jet over an 747 as the 747 require more maintenance and fuel. Quote Link to comment Share on other sites More sharing options...
tater Posted November 19, 2018 Share Posted November 19, 2018 I think Raptor is not changing, nor is size (they have the engines, they have the tooling for 9m). Quote Link to comment Share on other sites More sharing options...
tater Posted November 19, 2018 Share Posted November 19, 2018 A good point was made regarding the delightfully counter-intuitive, radical changes to BFR design over at NSF. Since they are working on BFS (note the S) right now, already, what's to say the change isn't to the BFBooster part of BFR, not the spacecraft? They've built exactly nothing for the booster yet, it's considered the short pole, since it's F9 writ large. What could be delightfully counter-intuitive in that part of the vehicle (assume BFS remains unchanged until they do testing with fins on F9 stage 2 next summer)? People there were suggesting multiple F9s to launch the thing (a booster built like Saturn 1b), but I think that is unlikely. Still, that makes his tweet a lot less radical overall. Ditching landing on launch clamps couldn't hurt, for example. Quote Link to comment Share on other sites More sharing options...
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