Quote from: meekGee on 07/08/2017 12:50 pmI can't find the sim files again, but I remember turn-around had to be very quick.How did your trajectories differ from those that can be found with NASA's trajectory browser?E.g. Shortened URL!
I can't find the sim files again, but I remember turn-around had to be very quick.
@Oli: Thanks for the link very useful!So it seems possible for the ships to be back to Earth before the next departure.It's typical that for all the calculated trajectories that the stay time on Mars is either 30 days or 112 days.What's unclear to me is whether a re-entry speed would prohibit the trajectory or not?The BFS can decelerate from entry velocities in excess of 12,5km/s.I suposse before re-entry it could flip and slow down with its engines first, how much depends on multiple things.
A few years ago I wrote a simple simulator and played with the orbits.If you have enough dV, ...It's expensive, but you get your ship back in time for the next synod.
Going slow is counterintuitive here. It takes longer because Mars and Earth are further away from each other, not because the spacecraft is actually "going slower". In fact, the rocket would have to move much faster to catch up with Earth during the same synod, while avoiding to be flung out to Jupiter or dropping towards the sun.
Interesting, why do you you suspect both have to be slow (10 months each way)?Is there no possibility you go to Mars fast, and go back slow, so you are still back in the same Synod?I'm no expert, just asking question. ;-) This orbital mechanics stuff in hard, taking for example also deep space burns into account.
With the number of trips Musk is talking about, I would think they will have enough spacecraft for two fleets. ... each Synod without having to rush the turnaround, and allowing for repairs, etc.
Well, Musk did an optimistic analysis to show how low the cost might go, and assuming the ship is calendar-life limited to say 21 years, flying each ship every synod gets you twice as many flights per ship life; this saves about 20% off the average trip cost.
Quote from: high road on 07/09/2017 06:46 pmGoing slow is counterintuitive here. It takes longer because Mars and Earth are further away from each other, not because the spacecraft is actually "going slower". In fact, the rocket would have to move much faster to catch up with Earth during the same synod, while avoiding to be flung out to Jupiter or dropping towards the sun.I agree. Any flight time that is not ~6 month takes more energy from the rocket too. Whether longer or shorter doesn't matter. More energy means faster. So if a trajectory takes 10 month instead of 6, it takes much much more fuel to fly it.
...Any flight time that is not ~6 month takes more energy from the rocket too. Whether longer or shorter doesn't matter. More energy means faster. So if a trajectory takes 10 month instead of 6, it takes much much more fuel to fly it.
Quote from: Semmel on 07/10/2017 05:53 am...Any flight time that is not ~6 month takes more energy from the rocket too. Whether longer or shorter doesn't matter. More energy means faster. So if a trajectory takes 10 month instead of 6, it takes much much more fuel to fly it.Actually, the minimum energy trajectory is the Hohmann transfer, which takes 258 days (8.4 months); from Zubrin's The Case for Mars, p. 79. The issues is that the Hohmann transfer rounds trip does not complete in one synod (I don't know the exact total, but the normal "piloted conjunction" mission with 6 month transfers has a 910 day round trip = 1.2 synods). The one-synod transfers (including the 10 month transfers) use more propellant because the departure windows are sub-optimal.
Quote from: Semmel on 07/10/2017 05:53 amI agree. Any flight time that is not ~6 month takes more energy from the rocket too. Whether longer or shorter doesn't matter. More energy means faster. So if a trajectory takes 10 month instead of 6, it takes much much more fuel to fly it.That isn't true. There are complicated routes that are very efficient but which take longer than 6 months.
I agree. Any flight time that is not ~6 month takes more energy from the rocket too. Whether longer or shorter doesn't matter. More energy means faster. So if a trajectory takes 10 month instead of 6, it takes much much more fuel to fly it.
Except Musk explicitly mentions a full reuse cycle every synod. You can read it in the recently released white paper version of the IAC presentation.
Or maybe some Venus flyby. But these windows do not occur every synode or are not practical every time.