Before flying the first crew, I suspect at least one unmanned passenger BFS round trip to Mars and back would be needed.
I'd think the ratio would be something like 1 BFR: 1 Passenger MCT: 2-4 Tanker BFS: 10-20 Cargo MCTs.
Quote from: TheSpaceRod on 07/04/2016 10:36 amBefore flying the first crew, I suspect at least one unmanned passenger BFS round trip to Mars and back would be needed.Will this be possible? It is my understanding that this would require autonomous refueling on Mars.
Quote from: jpo234 on 07/04/2016 10:54 amQuote from: TheSpaceRod on 07/04/2016 10:36 amBefore flying the first crew, I suspect at least one unmanned passenger BFS round trip to Mars and back would be needed.Will this be possible? It is my understanding that this would require autonomous refueling on Mars.Why would that even be desirable? Mars ascent is by far the easiest part of the mission. The hardest are Mars descent and earth descent. Mars descent will be tested at least twice with cargo BFS and earth descent from interplanetary speed can be tested with a loop around the moon plus maybe an additional acceleration before atmospheric entry to correctly simulate interplanetary speed. Again putting demands on SpaceX that NASA mission plans don't include.
Landing on Mars has been done before.
No-one has EVER launched from Mars.
Earth descent, also been done before.
I'd say it was all very difficult. I wouldn't like to put degrees of risk on it.
Quote from: JamesH65 on 07/04/2016 02:09 pmLanding on Mars has been done before. There was never a propulsive landing without chutes. The landing vehicle always disintegrated during EDL, only the payload survived.Quote from: JamesH65 on 07/04/2016 02:09 pmNo-one has EVER launched from Mars. Things that make a Mars launch easier compared to Earth: No athmosphere and wheather to speek of, shallower gravity well.Quote from: JamesH65 on 07/04/2016 02:09 pmEarth descent, also been done before. Once again: Never a propulsive landing of a complete spacecraft from interplanetary speeds.Quote from: JamesH65 on 07/04/2016 02:09 pmI'd say it was all very difficult. I wouldn't like to put degrees of risk on it.I think we can all agree to this.
Do we know that RD won't be using drogues or chutes of any kind?
My point was though, that as a race, we have experience of landing things on planets (from interplanetary speeds), but nothing on launching.
And is the weather on Mars really that benign? Gravity well is a given of course.
Quote from: Ludus on 07/04/2016 02:41 amI'd think the ratio would be something like 1 BFR: 1 Passenger MCT: 2-4 Tanker BFS: 10-20 Cargo MCTs.I think it really depends what we are looking at: early missions? fully established Mars colonial transport architecture? Obviously, in the long run you want plenty of BFSs (if you want to move 50'000 people to Mars per year, there is no going around it!), but Robobeat was going after the minimum number absolutely necessary to complete a human mission to Mars - and the minimum number is exactly what we can expect for the very first missions. For these very first missions, you clearly don't need "10-20 Cargo MCTs". You can transport all the cargo you need for a scout class mission in a single BFS - just tune down the number of crew members to 4-10 or so, and use the rest of the capacity for cargo. Also, I don't think you need so many tankers if you only have one BFR to launch them anyway. I doubt that the "turn-around" time of the BFS tankers is going to be much longer than the BFR.The absolute minimum is: 1 BFR, 1 tanker BFS, 1 BFS. And thats what we are likely going to see for 2022/2024 (or whenever the first mission happens).
Also worth noting that if they go modular, a passenger module is just another kind of cargo module/container (albeit with very special requirements for power, comms, etc) This was proposed for Shuttle, back in the day...
So landing on Mars is harder than taking off? Really? Landing on Mars has been done before. No-one has EVER launched from Mars. Earth descent, also been done before.
Quote from: JamesH65 on 07/04/2016 06:40 pmDo we know that RD won't be using drogues or chutes of any kind?Why RD? I thought this is about the BFS part of the MCT...And yes, RD will be all about propulsive landing. Quote from: JamesH65 on 07/04/2016 06:40 pmMy point was though, that as a race, we have experience of landing things on planets (from interplanetary speeds), but nothing on launching. We know how to launch from the third planet, aka Earth and its moon.Quote from: JamesH65 on 07/04/2016 06:40 pmAnd is the weather on Mars really that benign? Gravity well is a given of course.Martian athmospheric pressure on the ground is 0.6% of the pressure at sea level on earth. On earth this would count as a low quality vacuum.
Sorry, with my statement about launching, I was clearly talking about off Earth, and aside from the Moon landing launches, there is little to go on. The launches are completely unattended for one, which has never happened before, even on Earth. No chance to pop over to the rocket to attach anything! A considerable number of challenges to overcome, but I am very optimistic. Lots of smart people working on it.
These are all things that anyone doing a sample return mission has to solve. And they are solvable. They have even been done before.
Actually, there have been unattended rocket launches from a planetary body. The Soviet lunar sample return missions.
Luna 20 https://en.m.wikipedia.org/wiki/Luna_20