A typical 6-month return is only about 6.5 to 7 km/s from Mars surface to Earth surface (5.25 for launch to escape, 1 to 1.5 for transfer injection, 0.35 for EDL).
Quote from: envy887 on 06/28/2016 04:26 pm A typical 6-month return is only about 6.5 to 7 km/s from Mars surface to Earth surface (5.25 for launch to escape, 1 to 1.5 for transfer injection, 0.35 for EDL).We had already established that the trip would be 3 months?
The return flight will not likely be in the exact optimum window. Also, it'll likely be less than 6 months.Remember, SpaceX wants the vehicle back each time.
Why rush faster than 6 months on return? Take 3-4 months Earth to Mars with humans. One month or less on Mars. 6 months return, some little cargo and a few possible humans. Plenty of time to get the BFS ready for the next synod which is the goal.
Quote from: Robotbeat on 06/28/2016 06:07 pmThe return flight will not likely be in the exact optimum window. Also, it'll likely be less than 6 months.Remember, SpaceX wants the vehicle back each time.I don't think it's feasible or necessary for early missions to return the vehicle for launch the next synod. IMO that won't happen until LMO refueling is possible and all the kinks/upgrades are worked out of the system. Probably 2030's. That requires a lot of pre-positioned assets to support fast ground unloading/refueling and LMO refueling.
...Orbital mechanics generally preclude having both short stays and fast transits.
Quote from: envy887 on 06/28/2016 08:06 pm...Orbital mechanics generally preclude having both short stays and fast transits.That changes if you're using massive amounts of ISRU propellants.
Quote from: Robotbeat on 06/28/2016 08:32 pmQuote from: envy887 on 06/28/2016 08:06 pm...Orbital mechanics generally preclude having both short stays and fast transits.That changes if you're using massive amounts of ISRU propellants.You are right that in orbit refuelling is not necessary. It would make using massive amounts of propellants much easier though. Especially if there were in orbit ressources for fuel available.
Quote from: Impaler on 06/28/2016 08:24 amYour payload is too small at 100 mt, I'm thinking payload to LEO of around 200 mt even after engine loss, so that would require 4 functional engines and 6 total.But why would you want that? Staging to LEO and LEO to Mars surface have almost exactly the same DV requirements, so the vehicle should be optimized to deliver the same payload to both. A typical fast transit and EDL only requires ~6 kms. Launching 200t payload and 100t ship into LEO requires about 1400t of propellant in the US, but transit and EDL of 100t payload and 100t ship only require about 800t. You're shipping an extra 20% to 30% of useless dry mass (engines and tankage) to Mars and back. For LEO tanker runs the 200t payload is useful, but that can be accomplished with larger tanks that the Mars transit ship doesn't need. And it still doesn't really need 6 engines for high-thrust engine out capability, because a tanker won't be carrying people and it can always use some of it's extra fuel load for margin. An off-nominal LEO launch has a lot of options for abort, particularly if a rapid launch cadence, on-orbit refueling, and LEO rendezvous are SOP.
Your payload is too small at 100 mt, I'm thinking payload to LEO of around 200 mt even after engine loss, so that would require 4 functional engines and 6 total.
... The ideal Earth launch vehicle is thus a simple 2nd stage with a payload fairing which can launch any cargo imaginable, and the ideal mars lander is a modest size capsule that can fit on top of it as a 3rd stage....
Richard Heidmann (Snecma and Ariane) about the MCT.
A winged belly-landing super-shuttle?
Quote from: envy887 on 07/11/2016 01:48 pmA winged belly-landing super-shuttle? In the latest article the "super-shuttle" is not really a shuttle. It's more about maximizing the surface available for aerobraking. This is at least how I interpret the renders.
Quote from: jpo234 on 07/11/2016 01:59 pmQuote from: envy887 on 07/11/2016 01:48 pmA winged belly-landing super-shuttle? In the latest article the "super-shuttle" is not really a shuttle. It's more about maximizing the surface available for aerobraking. This is at least how I interpret the renders.It's maximizing the surface available for aerobraking by entering with the ventral side forward, like the shuttle. That's great for increasing ballistic drag, but not great for optimizing structural mass. And the horizontal take-off/landing is interesting.
That image is from the older article. The article from 07/09/2016 shows a different BFS: just small winglets. IMHO this one is meant to actually land vertically.EDIT: Of course it will enter "with the ventral side forward", but later on reorient for a vertical landing. I don't know whether this is actually possible.