mfck you had it right, I am saying their is an irrational fear of rendezvouses in mission planning. ....NASA assesses the chance of a crewed Orion capsule with a contingency EVA option failing to dock with a lunar assent vehicle at just 1 in 546. https://www.nasa.gov/pdf/140639main_ESAS_08.pdf (Page 13)...So I would estimate a failure chance of the BFS to achieve refueling in Mars orbit at around 1:1000 and not at all something worth of concern. ....
Quote from: Impaler on 07/20/2016 02:31 ammfck you had it right, I am saying their is an irrational fear of rendezvouses in mission planning. ....NASA assesses the chance of a crewed Orion capsule with a contingency EVA option failing to dock with a lunar assent vehicle at just 1 in 546. https://www.nasa.gov/pdf/140639main_ESAS_08.pdf (Page 13)...So I would estimate a failure chance of the BFS to achieve refueling in Mars orbit at around 1:1000 and not at all something worth of concern. ....I am not an engineer, but those risk figures seem odd. 1:546 might be considered OK for Orion, a craft that will hardly (imo) fly 100 missions combined, but a 1:1000, for a mass transportation architecture that MCT is, seems unacceptable. What am I missing? What are the comparable risks in, say, aviation?
We don't know isn't a valid reason. Same line of reasoning would give us Apollo-like hypergols.SpaceX is going to find out. So make a first-try estimate. You'll see that a ton of water per day isn't unreasonable to harvest since you need to harvest at least hundreds of kilograms per day anyway. Better than tripling the required number of launches and the complexity of the architecture.
While 936 might seem prohibitive, it is substituting for 600 mt of propellant MADE on the surface of Mars, so the ratio of substitution is ~3:2 when propellant is delivered to a high Mars orbit. This is quite different then the traditional view that Mars ISPP will have a IMLEO reduction factor of 10x - 20x but thouse estimates are based on taking all propellant down to the Martian surface which is an additional 10 km/s DeltaV, this scenario puts the refueling at the optimum point for efficient delivery.
A stage with all of the capabilities I've described for the 2nd stage is a necessity under any architecture, others have simply been calling it a 'BFS-Tanker' as it is clear that the cargo carrying BFS vehicle would not be an efficient tanker to LEO and something specialized for that purpose is necessary....
Quote from: Impaler on 07/21/2016 10:21 pmA stage with all of the capabilities I've described for the 2nd stage is a necessity under any architecture, others have simply been calling it a 'BFS-Tanker' as it is clear that the cargo carrying BFS vehicle would not be an efficient tanker to LEO and something specialized for that purpose is necessary....Musk said that (paraphrasing) "he's tempted to pursue stage 2 reuse on FH, but it's probably better to focus on Mars architecture".Since a reusable upper stage on FH is a natural iterative development towards any potential reusable S2 on BFR, I think it's highly probable based on this statement that the Mars architecture won't include a S2 at all. If BFR did have a S2 on it, any focus on developing a smaller version would help (not detract from) focus on the larger one.So I think the Falcon upper stage is an architectural dead end, and BFR/BFS will derive from the vehicles SpaceX is currently reusing: Falcon Stage 1, and Dragon. That wouldn't mean that specialized (e.g. Tanker) version wouldn't exist, just that they would share heritage with Dragon and not with the F9 S2.Most of the specializations (lightweight legs, insulation, cryocoolers, extra PV arrays, bigger tanks) will fit just as well in a similar outer mold line to BFS, even though internal and structural components would differ. It would be more like the relation between FH center and side boosters than between F9 S2 and Dragon: looks very much the same, but a bit different inside.
...But we now know that a Raptor upper stage is being made, which IS exactly what would make sense as a for runner to a reusable BFS upper stage, the new F9 upper stage can do controlled re-entry burn tests while still being disposed of, just as the F9 first stage was splashed into the ocean several times before even trying to put legs on it. The new upper stage lets SpaceX do it's tests at customer expense, which is how they like to do all their testing.
Err, how exactly do we now know that a Raptor upper stage is being made? I thought the only things we know are (1) The Air Force has thrown some money SpaceX's way to develop a Raptor vac engine, and (2) Musk has recently said that doing a new, reusable upper stage for Falcon is tempting, but SpaceX will be concentrating on developing the 'Mars rocket' instead. This would imply to me that (sadly) there is no effort underway to do a new upper stage for Falcon, and likely won't be in the future.
This other transaction agreement requires shared cost investment with SpaceX for the development of a prototype of the Raptor engine for the upper stage of the Falcon 9 and Falcon Heavy launch vehicles.
Outer mold line similarities are n8ot en8ough t8o c8onsider 8one vehic2le derived
...the new F9 upper stage can do controlled re-entry burn tests while still being disposed of...
Quote from: GORDAP on 07/28/2016 08:35 amErr, how exactly do we now know that a Raptor upper stage is being made? I thought the only things we know are (1) The Air Force has thrown some money SpaceX's way to develop a Raptor vac engine, and (2) Musk has recently said that doing a new, reusable upper stage for Falcon is tempting, but SpaceX will be concentrating on developing the 'Mars rocket' instead. This would imply to me that (sadly) there is no effort underway to do a new upper stage for Falcon, and likely won't be in the future.The Air Force said specifically that the engine is for F9.Quote This other transaction agreement requires shared cost investment with SpaceX for the development of a prototype of the Raptor engine for the upper stage of the Falcon 9 and Falcon Heavy launch vehicles.http://www.defense.gov/News/Contracts/Contract-View/Article/642983
... Find out whether a Rapter VAC could be use on an F9 U/S
Quote from: JamesH65 on 07/28/2016 01:44 pm... Find out whether a Rapter VAC could be use on an F9 U/SAlmost certainly yes. Read the last few pages of the Raptor on F9/FH discussion: http://forum.nasaspaceflight.com/index.php?topic=39314
"Almost certainly" is "almost certainly" not good enough for the US DoD!
It could be, but it's not going to. At least not before MCT flies.I started at least one thread speculating about a Raptor-based reusable upper stage for Falcon 9/FH, given that hint from the Air Force (which is not new, we've known about that for a quite long while). But now we know from Musk that they're not going to pursue that right now.