Quote from: Slarty1080 on 03/20/2018 02:26 pmIf BFR could be launched repeatedly, rapidly and cheaply it could eat the space launch market alive, earning a lot of money to fund BFS development. But developing BFS first means it’s going to sit around until BFR is ready to launch it, which seems a waste. Obviously SpaceX must have thought about this a lot more carefully than me; I'm just interested in their reasoning.The above assumes implicitly several things that may not be true.* F9/H is not already capable of eating the market alive, especially with reduced costs with block 5, and reusability of fairings and other components.The initial figure given way back when was that S1 was 60% of the stage cost, making S2 somewhere in the range of 20 million dollars without the fairing.I am unsure if they have published more recently than that on the cost of S2s.It's not unreasonable to suspect it might be considerably lower.* There is no value in repeated F9/H launches that may transfer over to BFS/R operations. At least some aspects - payload preparation, launch licences, ... are going to be similar, and these set a limiting cadence to BFR/S operations.* BFS can't do anything without BFR.Depending on questionable assumptions, it is at least somewhat plausible that BFS-SSTO can launch a large fraction of satellites, with the aid of in-orbit refuelling. BFS - without BFR eats the launch market.* There is no 'political' value for SpaceX in delaying the apparent likely launch date of BFR/S.Developing BFS up until they believe it is orbital-capable can be undersold as 'just tests', leading others to be able to insist to themselves it's not happening, and that full up-launches, for which they need to develop BFR anyway is still some years off.Why they might be doing this is unclear. It could be for example that they want others considering entering the market to do so now, in the knowledge that they can kill them in several years, rather than to invent plans which might actually work in the face of BFR (I don't believe this one).* More money would help the development effort.At some point, if you've got a good team that works well together, and enough equipment, adding more people and equipment may not actually make stuff go faster - at least in a sustainable manner.Being able to go out and buy subassemblies may mean you'd later need to develop that again internally, and face requalifying the systems they interact with.* The architecture we saw at IAC2017 is still accurate.Some of the speculation I did in the above mentioned thread was of a BFS-in-air refuelling. This is at least somewhat plausible, and would enable much, much greater capability for BFS without BFR.Do I believe all of the above are false - no.Do I know which - if any are actually true - no.
If BFR could be launched repeatedly, rapidly and cheaply it could eat the space launch market alive, earning a lot of money to fund BFS development. But developing BFS first means it’s going to sit around until BFR is ready to launch it, which seems a waste. Obviously SpaceX must have thought about this a lot more carefully than me; I'm just interested in their reasoning.
that was an interesting thread.People were talking about what BFS might be able to do on its own. BFR must be much more capable than BFS as it doesn't have all the cargo decks etc.Also it mentioned that the IAC2017 architecture is no longer accurate (extra engine added to BFS):https://www.reddit.com/r/space/comments/76e79c/i_am_elon_musk_ask_me_anything_about_bfr/dodcg22/
How can BFR refer to two distinct things?Surely BFB and BFS as individual items, BFR (or even BFx) should refer to the whole stack?
In my opinion, there is only one business case for an expendable upper stage for BFR:A customer needs to get a massive monolithic payload into LEO (ballpark >300t), and is willing to pay for expending the stage. then a traditional upper stage makes sense.But these customers will be very rare, especially since the BFR can already do monolithic payloads with 130-150t, and even if a 300t payload can't be split up in 2x150t, maybe it can be done at 3x150t.So, SpaceX may not develop that stage because it's useless, and SpaceX already indicated that BFR will not be their biggest system. And suddenly, SX can do 300t reusable.
A single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.
Quote from: TrevorMonty on 03/21/2018 05:33 pmA single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.Yup. As much as the BFR architecture is being sold as "do anything, just refuel more," its biggest weakness is sending a few tonnes to very high delta-V trajectories. Something with much much less dry mass would be better.I think the other weakness that has been minimized by a little Elon slight of hand is that the economics of reusability really only apply for earth orbit. Send a BFS beyond Mars orbit and you have basically expended it. By the time it comes back it will be obsolete.
Quote from: TrevorMonty on 03/21/2018 05:33 pmA single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.Yup. As much as the BFR architecture is being sold as "do anything, just refuel more," its biggest weakness is sending a few tonnes to very high delta-V trajectories. Something with much much less dry mass would be better.
Quote from: groundbound on 03/21/2018 06:52 pmQuote from: TrevorMonty on 03/21/2018 05:33 pmA single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.Yup. As much as the BFR architecture is being sold as "do anything, just refuel more," its biggest weakness is sending a few tonnes to very high delta-V trajectories. Something with much much less dry mass would be better.Depends how much you believe fuel is cheap.Refuel in LEO, and you can throw some tens of tons to 6km/s over LEO (ending up in an orbit you have barely enough fuel to burn back to an earth capture orbit some hours later).Start out in GTO, (requiring twelve launches, filling two upper stages in LEO), and it's more like 8.5.
Quote from: TrevorMonty on 03/21/2018 05:33 pmA single raptor expendable US could be useful for BLEO missions, especially if is refuelled by single tanker launch. Spacex take on ULA DL. Should be good for about 50t, with 150t topup.If SpaceX were to develop a single Raptor expendable US for BLEO, make it in the profile for launch on the F9 or FH.A Europa or Titan mission would see that F9 Raptor US refueled in LEO by a BFS and the refueled US would outperform the SLS at a fraction of the cost.Heading into Kerbal territory, the BFS could add on side strapped propellant tanks (crossfeed zombie rises again) for a real high C3 launch.If you're gonna do expendable, do an inexpensive Falcon class launched Raptor expendable enhanced by LEO refueling.
Quote from: JamesH65 on 03/21/2018 03:52 pmHow can BFR refer to two distinct things?Surely BFB and BFS as individual items, BFR (or even BFx) should refer to the whole stack?Yes, it should.It would be very nice if it did, however Elon does not use these terms precisely, and there is no better one that has come up.Unfortunately, BFR is ambiguous, and may refer to both, or only the booster.I tend to - when I remember use BFR (the booster) the first time in a post, then BFR/BFS.
I don’t believe this is correct. You remember incorrectly. BFR has consistently referred to the stack, with BFB now being used for the booster, and BFS always for the spaceship.
Quote from: Robotbeat on 03/21/2018 11:18 pmI don’t believe this is correct. You remember incorrectly. BFR has consistently referred to the stack, with BFB now being used for the booster, and BFS always for the spaceship.Hey, where's the first use of BFB? I didn't see it in the 2007 IAC, was it in there?
Quote from: QuantumG on 03/21/2018 11:33 pmQuote from: Robotbeat on 03/21/2018 11:18 pmI don’t believe this is correct. You remember incorrectly. BFR has consistently referred to the stack, with BFB now being used for the booster, and BFS always for the spaceship.Hey, where's the first use of BFB? I didn't see it in the 2007 IAC, was it in there?On this site, I think this week.
...and I do believe there is a more recent use of SpaceX themselves using it. Elon, I think.
Quote from: Robotbeat on 03/22/2018 01:15 am...and I do believe there is a more recent use of SpaceX themselves using it. Elon, I think.If you can de-vague that I'll consider it canon (until Elon just makes up some other words), but I think most of us have been using BFS/BFR.