Quote from: nadreck on 01/23/2016 06:55 pmQuote from: Robotbeat on 01/23/2016 06:50 pmSo just go into very low Orbit and deorbit. That'd take less than ~5km/s delta-v.btw, are you relying on Earth figures, or are you recalculating them for Mars? The lower gravity makes a huge difference here....BTW, this is all off-topic. I just brought up the idea to counter the false (but oft-repeated) claim that abort would be useless for MCT because there'd be no way to get to them.I was using 4.1km/s for surface to LMOyes I was calculating for Mars for the point to point distancescare to show your work?
Quote from: Robotbeat on 01/23/2016 06:50 pmSo just go into very low Orbit and deorbit. That'd take less than ~5km/s delta-v.btw, are you relying on Earth figures, or are you recalculating them for Mars? The lower gravity makes a huge difference here....BTW, this is all off-topic. I just brought up the idea to counter the false (but oft-repeated) claim that abort would be useless for MCT because there'd be no way to get to them.I was using 4.1km/s for surface to LMOyes I was calculating for Mars for the point to point distances
So just go into very low Orbit and deorbit. That'd take less than ~5km/s delta-v.btw, are you relying on Earth figures, or are you recalculating them for Mars? The lower gravity makes a huge difference here....BTW, this is all off-topic. I just brought up the idea to counter the false (but oft-repeated) claim that abort would be useless for MCT because there'd be no way to get to them.
It stands to reason that if a hopper over 700km exceeds orbital delta-V, then an aborted crew would not be more than ~700km away.
That close, and a land-train of pressurized rovers would likely be able to meet them within a couple days of travel (or even 8-10 hours with a slightly prepared path, within EVA+contingency time). If the aborted crew aborted along with a rebreather system, they should be able to hang out in their spacesuits that long.
There would likely be only one orbital track for return from Earth, so you could possibly prepare a route before hand.
No evidence of a depot in LMO. Vastly more likely to launch directly to Earth or possibly visit a depot in high orbit like MSL-2.
BFS should be able to get to orbit in a jiffy. They would only abort if they couldn't make it to orbit (even with secondary thrusters). It doesn't take 10,000km to get to orbit in a BFS with high thrust.
Quote from: Robotbeat on 01/23/2016 08:18 pmNo evidence of a depot in LMO. Vastly more likely to launch directly to Earth or possibly visit a depot in high orbit like MSL-2.Obviously there is no evidence of a depot in orbit around Mars yet, but there are no people, hoppers or vehicles returning to Earth. There is evidence that depots in LMO are a practical solution to a number of issues of the logistics of settling and exploring Mars. If you read the various threads on this forum there is as much evidence of depots as of other systems discussed here.Quote from: Robotbeat on 01/23/2016 08:16 pmBFS should be able to get to orbit in a jiffy. They would only abort if they couldn't make it to orbit (even with secondary thrusters). It doesn't take 10,000km to get to orbit in a BFS with high thrust.HUH again, if we are talking about a failure that causes an abort the failure could take place anywhere between launch and when the final orbit is achieved. So if that failure takes place at 95% of orbital velocity just 100km down range from the launch site, momentum would take them halfway around Mars.
If you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for.
The only reason the crew would be back on the surface is if the vehicle had a really bad day and the crew had to bail out, perhaps in a pod or ejection seats. Probably a pod, since it'd allow survival from Near Mars orbital velocity.Then parachute down, with solid retrorockets to keep parachute size reasonable. The whole abort system could be relatively low mass. 2kg for the chute, 5-10kg for the rockets per passenger, plus whatever the suit would weigh and the pod to protect against the relatively modest Mars reentry (much more modest than. Typical Mars probe which comes in hyperbolically).
Quote from: Robotbeat on 01/23/2016 08:27 pmIf you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for.It is above! You can also do the math yourself see the link I quoted above along with my calculations:https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdfI said that it would take the same ΔV as going to orbit to launch and land 700km down range. You only need half orbital velocity to launch and crash 700km down range.
Quote from: nadreck on 01/23/2016 08:31 pmQuote from: Robotbeat on 01/23/2016 08:27 pmIf you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for.It is above! You can also do the math yourself see the link I quoted above along with my calculations:https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdfI said that it would take the same ΔV as going to orbit to launch and land 700km down range. You only need half orbital velocity to launch and crash 700km down range.What delta-V are you assuming is needed for landing?
Ok Robobeat you modified your post to say calculations with lift, that was not there when I replied. Lift is pretty irrelevant at lower speeds especially since to get efficient ballistic distances from your launch velocity you have to launch at an angle greater than 40 degrees (which means as you approach the surface (and lift can only play a role in the last 10 km or so) you are coming in at the same angle. So lift is not going to increase your range significantly.
Quote from: Robotbeat on 01/23/2016 08:38 pmQuote from: nadreck on 01/23/2016 08:31 pmQuote from: Robotbeat on 01/23/2016 08:27 pmIf you're that close, thrusters could get you to orbit. You just said that more than 700km would take more than orbital velocity, a claim I still have seen no calculations for.It is above! You can also do the math yourself see the link I quoted above along with my calculations:https://www.rand.org/content/dam/rand/pubs/research_memoranda/2008/RM3752.pdfI said that it would take the same ΔV as going to orbit to launch and land 700km down range. You only need half orbital velocity to launch and crash 700km down range.What delta-V are you assuming is needed for landing?Equal to take off, particularly on hops that are less than 2km/s launch velocity since they are also really high angle
Are you assuming the crew would have enough supplies