Quote from: GWH on 01/30/2018 05:25 pmQuote from: freddo411 on 01/30/2018 04:42 pmI'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.Turning your point around please prove out how you've reached the conclusion that TPS and structures can be designed and built to require only minimal, economic amounts of refurb between flights. In particular, how does one asses and ensure the life of these components? How does one optimize their processing to deal with something such as micrometeorite and orbital debris impacts? It is an unproven assertion so far. SpaceX has quite a track record at this point of taking previously difficult, expensive and time consuming tasks (rocket engine refurb, capsule heat shield construction) and re-engineering them into reliable, inexpensive solutions. I suspect that this is the case because they actually set out to make things into reliable, inexpensive solutions.We'll just have to wait and see how difficult this ends up being for the TPS on BFS.
Quote from: freddo411 on 01/30/2018 04:42 pmI'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.Turning your point around please prove out how you've reached the conclusion that TPS and structures can be designed and built to require only minimal, economic amounts of refurb between flights. In particular, how does one asses and ensure the life of these components? How does one optimize their processing to deal with something such as micrometeorite and orbital debris impacts?
I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.
I wouldn't put it past SpaceX to throw some TPS and a parachute on a 2nd stage for a Falcon 9 launch with a particularly light LEO payload.SpaceX is king of "we're probably not going to do this thing" then "well, we changed our minds."
I know SpaceX wants to put all its resources into BFR, but is it really not worthwhile for SpaceX to invest a couple hundred million in adding TPS and fins to the upper stage, with the chance to save $1-2 billion in upper stage costs?Even if performance is poorer and a FH is required instead of an F9, this could be worthwhile if the hope of a block 5 cost of a couple million to refly a booster works out.
Has there been any concrete recent statement about second stage costs?Is it possible they've dropped from 40% to 20 or lower?That would drastically change the economics of actually bothering at all.
Quote from: hplan on 02/24/2018 06:22 pmI know SpaceX wants to put all its resources into BFR, but is it really not worthwhile for SpaceX to invest a couple hundred million in adding TPS and fins to the upper stage, with the chance to save $1-2 billion in upper stage costs?Even if performance is poorer and a FH is required instead of an F9, this could be worthwhile if the hope of a block 5 cost of a couple million to refly a booster works out.They have said that they are planning on doing BFS first, then BFR.BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.
Quote from: speedevil on 02/24/2018 06:58 pmThey have said that they are planning on doing BFS first, then BFR.BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.Which LEO and which payloads?Practically no payload wants to go to such orbit that BFS could launch them as SSTO.<snip>of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.
They have said that they are planning on doing BFS first, then BFR.BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.
Next step will be doing orbital velocity Ship flights, which will need all of the above. Worth noting that BFS is capable of reaching orbit by itself with low payload
Quote from: hkultala on 02/26/2018 10:11 amQuote from: speedevil on 02/24/2018 06:58 pmThey have said that they are planning on doing BFS first, then BFR.BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.Which LEO and which payloads?Practically no payload wants to go to such orbit that BFS could launch them as SSTO.<snip>of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.At least several hundred do.Starlink, specifically."Both of these satellites will be deployed in one mission aboard a SpaceX Falcon-9 v1.2 launch vehicle into an orbital plane of 514 km circular at 97.44 degrees inclination. After insertion, the satellite orbits will be raised to the desired mission altitude of 1125 km circular. ".They have at least some manoeuvring capability. Having the capability to fit somewhat larger tanks to raise from 200km seems wholly plausible, or for very small inclination trims.SSTO capacity depends on the details of course, BFR/S can sort of manage if large parts of the architecture wholly fail. BFS, everything has to work. QuoteNext step will be doing orbital velocity Ship flights, which will need all of the above. Worth noting that BFS is capable of reaching orbit by itself with low payload (Elon - Reddit).If you take various assumptions that seem plausible, you get answers from 10-40 tons or so to SSTO. The latter is almost certainly wrong - but note for example that the mass for BFS given at IAC was 85 tons, with massive passenger windows, and in principle removing those and leaving an empty shell may be lighter, so who knows.The raw numbers for payload are uncertain, but the most basic calculations indicate it can get several Starlink to orbit, and allow them to do interesting things they need to practice for BFS anyway - orbital fuel transfer, ...Paying for your launch vehicles testing with actual operational uses seems a very Elon thing to do.As to 28 degrees - well, there is 25 degrees as well - for Texas, or 9 if they go back to Omelek.It can't do large inclination changes, direct launch to circular (even 1100km) orbit, ...But can it launch a large subset of Starlink sats, perhaps most if you make different assumptions (that a couple of refuellings are OK, doubling the prop on the sats ...) - perhaps.
Starlink plans 7500 sats in 300 km VLEO, which is likely reachable with BFR as SSTO. Some of the inclinations would require launching out of VAFB, which shouldn't really be an issue.
I find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.A stretched chomper-style BFS with extra SL Raptors? Yes, please.
Quote from: dglow on 03/03/2018 03:41 pmI find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.A stretched chomper-style BFS with extra SL Raptors? Yes, please.Modifying BFS much makes absolutely no sense for this, if it works at all, and if you are deviating from getting BFR up and running.
BFS+BFRs payload is just too big, and the flight rate is just too high to make a new vehicle make sense, even for Starlink.
Quote from: speedevil on 03/03/2018 04:04 pmQuote from: dglow on 03/03/2018 03:41 pmI find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 – while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.A stretched chomper-style BFS with extra SL Raptors? Yes, please.Modifying BFS much makes absolutely no sense for this, if it works at all, and if you are deviating from getting BFR up and running.Operationally, yes, but financially? BFR's bread is buttered by Starlink's revenues.
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.
Quote from: Robotbeat on 03/04/2018 04:28 pmTwo stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield. Less wear on the heatshield – why?Greater fuel margins allow for more retropropulsion?
Quote from: hkultalaof these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.At least several hundred do.Starlink, specifically.
of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.