Space Nerd Posted September 3, 2020 Share Posted September 3, 2020 Oops, completely missed it. Quote Link to comment Share on other sites More sharing options...
cubinator Posted September 3, 2020 Share Posted September 3, 2020 42 minutes ago, Space Nerd said: Oops, completely missed it. Same. Replays ftw! Only second landing for this booster? It's still fresh! Quote Link to comment Share on other sites More sharing options...
Entropian Posted September 3, 2020 Share Posted September 3, 2020 3 minutes ago, cubinator said: Only second landing for this booster? It's still fresh! Same thing I was thinking! Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted September 3, 2020 Share Posted September 3, 2020 13 hours ago, magnemoe said: Why the 4+4 engines center rater than 1+6 engines? As in is this something official? 1+6 is more compact. If you do one central engine with seven around it, you can certainly do a much smaller footprint. But you lose symmetry. If you want perfectly axisymmetric thrust, you'd have to fire at least 7 engines for the landing burn. Probably fine, but it's hard to know for sure; Raptor has enough throttle range to do other combinations. This gives you a skirt size of 9.2 meters with engines under the leg fairings and 9.8 meters if you want all 20 engines in a perfect circle. This assumes 10 degrees of gimbal range on all eight central engines. Obviously there are tighter packings if the central engines have a constrained gimbal range. Quote Link to comment Share on other sites More sharing options...
tater Posted September 3, 2020 Share Posted September 3, 2020 Why would you need multiple engines for the landing burn? Inner Raptors have 210 tons of thrust per Musk. What's the mass of (nearly empty) SS? The entry burn is multiples, but how important is symmetry for that burn at ~2km/s? Quote Link to comment Share on other sites More sharing options...
magnemoe Posted September 3, 2020 Share Posted September 3, 2020 30 minutes ago, sevenperforce said: If you do one central engine with seven around it, you can certainly do a much smaller footprint. But you lose symmetry. If you want perfectly axisymmetric thrust, you'd have to fire at least 7 engines for the landing burn. Probably fine, but it's hard to know for sure; Raptor has enough throttle range to do other combinations. This gives you a skirt size of 9.2 meters with engines under the leg fairings and 9.8 meters if you want all 20 engines in a perfect circle. This assumes 10 degrees of gimbal range on all eight central engines. Obviously there are tighter packings if the central engines have a constrained gimbal range. Yes, loose of symmetry is not good, yes you can compensate but its not something you want to do. with 4+4 you get 2,4,6 and 8 symmetry and 4 engine pairs. With 1+6 you can get 1 core and 3 pairs letting you do 1-7 engine burns Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted September 3, 2020 Share Posted September 3, 2020 5 minutes ago, tater said: Why would you need multiple engines for the landing burn? Inner Raptors have 210 tons of thrust per Musk. What's the mass of (nearly empty) SS? I'm talking about Superheavy, not Starship. You definitely need more than one engine for the Superheavy landing burn; Elon said the absolute minimum (for hops) is two. They might be able to do a seven-engine hoverslam but that's probably pushing limits even at minimum throttle. With seven engines in a ring you can fire three or four in near-symmetry and use differential throttle to balance thrust. But the more you are throttling your engines to balance thrust, the less effective throttle range you have. 10 minutes ago, tater said: The entry burn is multiples, but how important is symmetry for that burn at ~2km/s? You're right, the entry burn is easy -- you can fire seven or eight there with no problems. 9 minutes ago, magnemoe said: Yes, loose of symmetry is not good, yes you can compensate but its not something you want to do. with 4+4 you get 2,4,6 and 8 symmetry and 4 engine pairs. With 1+6 you can get 1 core and 3 pairs letting you do 1-7 engine burns I agree. But word of Elon says the core is eight engines, not seven. Of course they could still change that. In fact they could even go to a 29-engine approach and do nine engines in the center with a 20-engine ring. Quote Link to comment Share on other sites More sharing options...
RealKerbal3x Posted September 3, 2020 Share Posted September 3, 2020 (edited) Texas Tank Watchers, assemble 3 minutes ago, sevenperforce said: You're right, the entry burn is easy -- you can fire seven or eight there with no problems. Haven't they've talked about skipping the entry burn with Super Heavy? It's meant to stage at a lower altitude and velocity than the F9 first stage, and it's made out of heat-resistant stainless steel which means no thermal protection is required. Edited September 3, 2020 by RealKerbal3x Quote Link to comment Share on other sites More sharing options...
tater Posted September 3, 2020 Share Posted September 3, 2020 10 minutes ago, sevenperforce said: I'm talking about Superheavy, not Starship. You definitely need more than one engine for the Superheavy landing burn; Elon said the absolute minimum (for hops) is two. They might be able to do a seven-engine hoverslam but that's probably pushing limits even at minimum throttle. Doh! My bad. Was writing about SH, thinking SS in my head. What's the landing mass of SH? I see 300t thrown around, so that's 2 engines. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted September 3, 2020 Share Posted September 3, 2020 26 minutes ago, RealKerbal3x said: Haven't they've talked about skipping the entry burn with Super Heavy? It's meant to stage at a lower altitude and velocity than the F9 first stage, and it's made out of heat-resistant stainless steel which means no thermal protection is required. I haven't heard of them saying that, no. New Glenn is supposed to skip the entry burn but all renders and discussion from SpaceX has shown both boostback and entry. I'm not sure which way altitude and velocity go at this point. I don't think we've gotten any actual numbers for staging velocity since the 12-meter carbon-fiber BFR design. 14 minutes ago, tater said: What's the landing mass of SH? I see 300t thrown around, so that's 2 engines. Sounds about right! Quote Link to comment Share on other sites More sharing options...
RealKerbal3x Posted September 3, 2020 Share Posted September 3, 2020 3 minutes ago, sevenperforce said: I haven't heard of them saying that, no. New Glenn is supposed to skip the entry burn but all renders and discussion from SpaceX has shown both boostback and entry. I'm not sure which way altitude and velocity go at this point. I don't think we've gotten any actual numbers for staging velocity since the 12-meter carbon-fiber BFR design. I feel like I saw it in one of Elon's tweets a while back. But my memory is fuzzy. Quote Link to comment Share on other sites More sharing options...
magnemoe Posted September 3, 2020 Share Posted September 3, 2020 43 minutes ago, RealKerbal3x said: Texas Tank Watchers, assemble Haven't they've talked about skipping the entry burn with Super Heavy? It's meant to stage at a lower altitude and velocity than the F9 first stage, and it's made out of heat-resistant stainless steel which means no thermal protection is required. Yes, SH is supposed to don't need an entry burn, steel+ some thermal coating on parts who get hot and its should work. Good chance they have an floor to protect the engine mechanic too, look at N1 images for an idea, have an hatch for entry into the engineering space and this is removable sections if you need to pull stuff out. Quote Link to comment Share on other sites More sharing options...
tater Posted September 3, 2020 Share Posted September 3, 2020 Course if SS can TO and land with1 off center engine, what can't SH land with 2 un-centered engines? Quote Link to comment Share on other sites More sharing options...
Ultimate Steve Posted September 3, 2020 Share Posted September 3, 2020 4 ish minutes until hop assuming siren is accurate. Quote Link to comment Share on other sites More sharing options...
Commodore_32 Posted September 3, 2020 Share Posted September 3, 2020 SUCCESSFUL SN6 HOP!! Quote Link to comment Share on other sites More sharing options...
RealKerbal3x Posted September 3, 2020 Share Posted September 3, 2020 HOP! Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted September 3, 2020 Share Posted September 3, 2020 Hop, skip and a jump! Quote Link to comment Share on other sites More sharing options...
Commodore_32 Posted September 3, 2020 Share Posted September 3, 2020 Its leaning! Quote Link to comment Share on other sites More sharing options...
Spaceception Posted September 3, 2020 Share Posted September 3, 2020 Could SN5 take another leap this month, followed by SN8? Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted September 3, 2020 Share Posted September 3, 2020 22 minutes ago, Commodore_32 said: Its leaning! Is it though? Or is it just perspective? I think they keep landing hard on one leg and using that crush core. Quote Link to comment Share on other sites More sharing options...
Commodore_32 Posted September 3, 2020 Share Posted September 3, 2020 No, it leans because the CoT is not aligned with the CoM So they need to lean to one side so it doesnt flip over, and the landing legs have suspention so it keeps leaning even in the ground. Quote Link to comment Share on other sites More sharing options...
Entropian Posted September 3, 2020 Share Posted September 3, 2020 I thought the CoG is relatively inline with the "center of landing legs." You're talking about it when landed, right? Quote Link to comment Share on other sites More sharing options...
Nightside Posted September 3, 2020 Share Posted September 3, 2020 15 minutes ago, Entropian said: I thought the CoG is relatively inline with the "center of landing legs." You're talking about it when landed, right? well if it lands hard at an angle some of the suspension could crush. Quote Link to comment Share on other sites More sharing options...
Entropian Posted September 3, 2020 Share Posted September 3, 2020 Just now, Nightside said: well if it lands hard at an angle some of the suspension could crush. Yes, but the CoT should have no effect on the position of the vehicle when landed. I think it's at a slight angle, but I could be wrong. Quote Link to comment Share on other sites More sharing options...
RealKerbal3x Posted September 3, 2020 Share Posted September 3, 2020 1 minute ago, Entropian said: Yes, but the CoT should have no effect on the position of the vehicle when landed. I think it's at a slight angle, but I could be wrong. Just looking at it, it seems that it's at more of a tilt than SN5 was. Quote Link to comment Share on other sites More sharing options...
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