sevenperforce Posted July 25, 2017 Share Posted July 25, 2017 18 minutes ago, tater said: Cosine losses are not undesirable in 2 regimes. For entry, they increase the effective area contributing to drag via the larger bow shock, and for landing when a craft cannot throttle deeply enough to hover. But they're a pain if you wanna use the same engines to take off and head to orbit. Quote Link to comment Share on other sites More sharing options...
tater Posted July 25, 2017 Share Posted July 25, 2017 (edited) 6 minutes ago, sevenperforce said: But they're a pain if you wanna use the same engines to take off and head to orbit. Agreed, but gimbal can obviously deal with some or all of this. D2 was never going to take off from Mars, it was a 1-way trip, so TO not an issue. ITS(y) has engine gimbal, so it can cant them out for entry or intentional cosine loss as a form of throttling, or along centerline for TO. (why would autocorrect change along to alone? Sheesh) Edited July 25, 2017 by tater Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted July 25, 2017 Share Posted July 25, 2017 On the subject of the 9-meter BFR... Presumably SpaceX will attempt to pack as many engines as possible into those nine meters. This presents a few possibilities: Spoiler Interestingly, the 22-engine one has only bilateral symmetry, not triangular symmetry, so SpaceX may go back to 4-symmetry rather than 3-symmetry for legs and grid fins. It may be possible to pack more than 22 engines using advanced circle packing, though you run into rather aggressive engine asymmetry. 7 minutes ago, tater said: Agreed, but gimbal can obviously deal with some or all of this. D2 was never going to take off from Mars, it was a 1-way trip, so TO not an issue. ITS(y) has engine gimbal, so it can cant them out for entry or intentional cosine loss as a form of throttling, or along centerline for TO. (why would autocorrect change along to alone? Sheesh) ITS(y) uses biconic entry, so its engines are not pointed retrograde on entry anyway. Its turbopump can also throttle aggressively, so no need to cosine out for throttling losses. And even if it pointed its engines out, this wouldn't help with plume impingement leading to engine bell damage. Its vacuum engines don't gimbal at all. Quote Link to comment Share on other sites More sharing options...
tater Posted July 25, 2017 Share Posted July 25, 2017 The closest packing ideas don't account for gimbal. The previous design had the center core engines more spaced for that reason. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted July 25, 2017 Share Posted July 25, 2017 Does anyone know roughly what gimbal range the Raptor will have? Or, if not, what gimbal range the Merlin 1D currently has? Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted July 25, 2017 Share Posted July 25, 2017 After glancing at a few landing videos, this is about the hardest single-engine gimbal I saw: It's roughly 8 degrees. I'll take a look at Raptor's design and see what kind of planar displacement clearance would be required. Quote Link to comment Share on other sites More sharing options...
IncongruousGoat Posted July 25, 2017 Share Posted July 25, 2017 1 hour ago, sevenperforce said: Presumably SpaceX will attempt to pack as many engines as possible into those nine meters. Considering the difficulties they've been having with clustering 27 engines on FH, they might not want to try and cram as many engines in as possible, if it means compromising combustion/structural/aerodynamic stability. Furthermore, superficially it makes sense that they would try and have as many engines as possible, so they can have a bigger tank and carry a larger payload. However, they can't just extend the tank ad infinitum-F9, for example, is as long as it can physically be without compromising its ability to withstand aerodynamic forces. Also, all of this begs the question: How are they going to transport a 9m booster from Hawthorne to the Cape? They can't use the Interstate like they do for F9-they'd have to use a boat (slow, comes with risk of saltwater corrosion) or a custom-built airplane (expensive) Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted July 25, 2017 Share Posted July 25, 2017 The Raptor engine bell appears to be about 1.8 meters long. I don't know if the gimbal is at the throat or at the chamber, but it's not going to make much of a difference; it'll need about 24 cm of clearance in every direction. However, the engines will gimbal together for pitch and yaw and in opposite directions for roll control, so the core, gimballed engines can be packed closely, just as shown here: Spoiler This, I believe, is the ideal layout for fitting 1.5-meter engines in a 9-meter cross-section with optimal packing and over 8 degrees of gimbal space for the core: Spoiler If seven core engines are enough to land a booster that uses 42 engines, four should be plenty for a 22-engine booster. 5 minutes ago, IncongruousGoat said: Considering the difficulties they've been having with clustering 27 engines on FH, they might not want to try and cram as many engines in as possible, if it means compromising combustion/structural/aerodynamic stability. Furthermore, superficially it makes sense that they would try and have as many engines as possible, so they can have a bigger tank and carry a larger payload. However, they can't just extend the tank ad infinitum-F9, for example, is as long as it can physically be without compromising its ability to withstand aerodynamic forces. The limiting factor for the dimensions of the original ITS is diameter, not length. F9 has a much higher fineness ratio than the ITS model. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted July 25, 2017 Share Posted July 25, 2017 (edited) Layout in KSP, Tweakscaled, showing gimbal action (8 degree limit): Spoiler A major advantage of this layout is that every engine has pairwise symmetry, meaning that if you have a single engine-out, you need only shut down one opposite engine to balance thrust, rather than shutting down two as with triplicate symmetry. Edited July 25, 2017 by sevenperforce Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted July 25, 2017 Share Posted July 25, 2017 30 minutes ago, IncongruousGoat said: Also, all of this begs the question: How are they going to transport a 9m booster from Hawthorne to the Cape? They can't use the Interstate like they do for F9-they'd have to use a boat (slow, comes with risk of saltwater corrosion) or a custom-built airplane (expensive) Easy answer: launch from Boca Chica? Or maybe go full Buck Rogers and fly the dang thing to the Cape. yeah, right Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted July 25, 2017 Share Posted July 25, 2017 Also, I see CRS-12 has been bumped to TBD. Anyone know why? Quote Link to comment Share on other sites More sharing options...
StupidAndy Posted July 25, 2017 Share Posted July 25, 2017 Wikipedia says August 14 Quote Link to comment Share on other sites More sharing options...
tater Posted July 25, 2017 Share Posted July 25, 2017 Atlas was moved, and perhaps it bumps SX. Quote Link to comment Share on other sites More sharing options...
Racescort666 Posted July 26, 2017 Share Posted July 26, 2017 STP-2 is now NET April 30th. I have a buddy with a payload on that flight so I'm pretty excited. I'm also excited for the FH demo which is still supposed to be this year. I wonder what they are going to do with it? Quote Link to comment Share on other sites More sharing options...
TheEpicSquared Posted July 26, 2017 Share Posted July 26, 2017 (edited) 1 minute ago, Racescort666 said: I'm also excited for the FH demo which is still supposed to be this year. I wonder what they are going to do with it? Hope it doesn't damage the pad if it fails Edited July 26, 2017 by TheEpicSquared Quote Link to comment Share on other sites More sharing options...
kerbinorbiter Posted July 26, 2017 Share Posted July 26, 2017 Kerbal Musk SpaceX Program just thought i would share that Quote Link to comment Share on other sites More sharing options...
tater Posted July 26, 2017 Share Posted July 26, 2017 20 hours ago, tater said: Atlas was moved, and perhaps it bumps SX. Quote Link to comment Share on other sites More sharing options...
StupidAndy Posted July 26, 2017 Share Posted July 26, 2017 they're launching a tardis into space?!?! does this mean that CRS-12 will go after? Quote Link to comment Share on other sites More sharing options...
insert_name Posted July 26, 2017 Share Posted July 26, 2017 High probability of failure on initial f9h launch https://spaceflightnow.com/2017/07/25/musk-sets-expectations-low-for-maiden-falcon-heavy-launch/ Quote Link to comment Share on other sites More sharing options...
CatastrophicFailure Posted July 26, 2017 Share Posted July 26, 2017 1 minute ago, insert_name said: High probability of failure on initial f9h launch https://spaceflightnow.com/2017/07/25/musk-sets-expectations-low-for-maiden-falcon-heavy-launch/ Yes, um, we've been commiserating over this for the last couple pages... ...yet they remain confident enough in the second launch that it's got a paying customer (ArabSat 6). Quote Link to comment Share on other sites More sharing options...
CastleKSide Posted July 26, 2017 Share Posted July 26, 2017 The second launch could easily become the 3rd if there is a failure Quote Link to comment Share on other sites More sharing options...
Kryten Posted July 26, 2017 Share Posted July 26, 2017 1 hour ago, CatastrophicFailure said: ..yet they remain confident enough in the second launch that it's got a paying customer (ArabSat 6). Arabsat-6A isn't your average payload either, it cost somewhere in the region of $300 million: about twice as much as Amos-6. There could be quite a kerfuffle should it end up in the Atlantic. Quote Link to comment Share on other sites More sharing options...
StupidAndy Posted July 26, 2017 Share Posted July 26, 2017 (edited) Wikipedia says now that the 2nd flight of the Falcon Heavy is the last of 2017...? actually it says that that is the FIRST?!?! WHAAAT??!?! am I just looking at a wrong manifest? Edited July 26, 2017 by StupidAndy Quote Link to comment Share on other sites More sharing options...
Kryten Posted July 26, 2017 Share Posted July 26, 2017 Has anybody successfully fired a rocket engine with gel/liquid prop combination? Trying to do stuff that hasn't been done before doesn't seem sensible for an amateur effort. Quote Link to comment Share on other sites More sharing options...
sevenperforce Posted July 26, 2017 Share Posted July 26, 2017 5 minutes ago, Kryten said: Has anybody successfully fired a rocket engine with gel/liquid prop combination? Trying to do stuff that hasn't been done before doesn't seem sensible for an amateur effort. Wrong thread, but yes. The very first "liquid-fueled" rocket ever designed and flown by the Soviet Union was napalm and LOX. Quote Link to comment Share on other sites More sharing options...
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