Quote from: dglow on 03/05/2018 07:29 amQuote 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?Just because TSTO can launch more payload for the same number of burnt heatshields.
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?
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.
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: envy887 on 03/05/2018 03:50 pmQuote from: dglow on 03/05/2018 07:29 amQuote 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?Just because TSTO can launch more payload for the same number of burnt heatshields.Actually the "wear and tear" metric is pretty useless. We are talking about depreciation which is a component of launch cost which is the only thing that matters. Considering the whole launch cost is supposed to be less than an F1 launch, BFS depreciation could very well be less than the fuel cost of the BFR.
It would probably be wise to see the projected dry mass and payload capabilities of BFR/BFS (including the theoretical SSTO capability) as the end result AFTER several iterations, with the first "block" having considerably less payload than that. Just as SpaceX didn't build the reusable F9 FT Block 5 right after the Falcon 1 they probably will be happy if the first BFR/BFS will make it to orbit and back undamaged with a very small payload and allows them to look over it to improve the next one they will build. If there will be a BFS that can do SSTO it might be the third, fourth or fifth iteration but certainly not the first.
Quote from: Negan on 03/05/2018 06:53 pmQuote from: envy887 on 03/05/2018 03:50 pmQuote from: dglow on 03/05/2018 07:29 amQuote 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?Just because TSTO can launch more payload for the same number of burnt heatshields.Actually the "wear and tear" metric is pretty useless. We are talking about depreciation which is a component of launch cost which is the only thing that matters. Considering the whole launch cost is supposed to be less than an F1 launch, BFS depreciation could very well be less than the fuel cost of the BFR.Same thing. What's cheaper if you have to launch 12,000 satellites: $3M for 10 tonnes or $5M for 150 tonnes?
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?
Quote from: Negan on 03/06/2018 12:52 amHighly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?Any sort of commodity bulk carrier on a predictable set of routes?
Quote from: Negan on 03/06/2018 12:52 amHighly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?Can someone unring this bell? Perhaps reframe what is being discussed? I think you two are talking past each other.
Only if all <10 ton payloads cease to exist. BFS's useful life will be determined by frequency of use not tonnage to orbit. Depreciation equals cost divided by estimated useful life.
Quote from: dglow on 03/05/2018 07:29 amQuote 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?Also because you're not taking very large tanks to very high velocities.Staging hides in the"dry mass" portion of the rocket equation, once you taken into account a finite payload ratio.ABCD: Always Be Counting Down
And here I am thinking about 3 stage vehicles. It would make the orbital stage easier.
Quote from: wannamoonbase on 03/09/2018 03:00 pmAnd here I am thinking about 3 stage vehicles. It would make the orbital stage easier.If you've solved stackability, and orbital recovery, three stage is an interesting option.It allows large payloads to very, very high energies.But, that is a pretty large 'if'.Any non-trivial 'zeroth'' stage for almost all useful purposes means a much higher velocity at the next stage burnout, and for it to be far downrange.About the only exception would be if it was a slow ballistic stage to lift the stage off the pad at low speed, to clear weather, and to allow for use of vacuum engines on the main stage.But, even if you wanted to do this, you can't, unless your engines are on a considerably wider part of the stage, because you don't have the area.A 'low' speed at staging, as implied by a two stage vehicle with an energetic second stage means recovery is so much simpler.F9 - no way would it make sense in the context of reusability.
Quote from: meekGee on 03/05/2018 05:20 pmQuote from: dglow on 03/05/2018 07:29 amQuote 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?Also because you're not taking very large tanks to very high velocities.Staging hides in the"dry mass" portion of the rocket equation, once you taken into account a finite payload ratio.ABCD: Always Be Counting DownAnd here I am thinking about 3 stage vehicles. It would make the orbital stage easier.
Posted on the TESS thread, but:Elon: https://twitter.com/elonmusk/status/985654333860601856?s=21
Quote from: Robotbeat on 04/15/2018 11:14 pmPosted on the TESS thread, but:Elon: https://twitter.com/elonmusk/status/985654333860601856?s=21Too much Teslaquila again. April fools was 2 weeks ago.