This doesn't solve the problem however. The travel time will be longer than staying on Mars and leaving at the next conjunction if you use the same fuel or less. So there will always be two spacecraft travelling at the same time.
Quote from: high road on 07/07/2017 11:14 amThis doesn't solve the problem however. The travel time will be longer than staying on Mars and leaving at the next conjunction if you use the same fuel or less. So there will always be two spacecraft travelling at the same time.True, but the real problem is getting getting the ships back as fast as possible for relaunch, not the longer travel time of the empty return ships.Having them back on earth within a year and a few months is better from a reusability perspective, than having them back within 3 years and a few months.If the people on mars haven't setup a living quarters and depend on their ship than of course we have no choice but to leave the ship on the surface.
Quote from: high road on 07/07/2017 11:14 amThis doesn't solve the problem however. The travel time will be longer than staying on Mars and leaving at the next conjunction if you use the same fuel or less. So there will always be two spacecraft travelling at the same time.True, but the real problem is getting getting the ships back as fast as possible for relaunch, not the longer travel time of the empty return ships.Having them back on earth within a year and a few months is better from a reusability perspective, than having them back within 3 years and a few months.
What I seem to have missed is who actually pays for the cargo flights - and for the cargo itself - to make the colony work? The $200k/passenger cost seems to be for the people transport to Mars only, and maybe whatever personal luggage they take with them. Who pays for producing the bulk cargo needed by the colony and flying it to Mars?
A few years ago I wrote a simple simulator and played with the orbits.If you have enough dV, you can launch three months too early, travel a higher energy transfer orbit, refuel very quickly, and fly back, launching about 3 months too late.It's expensive, but you get your ship back in time for the next synod.These trajectories result in very high entry speeds.Whether it is a worthwhile exercise is questionable, but it is possible.
This is an important topic. A Mars colony will depend a lot on "tourists" that stay for a year. Ideally even below 4 months, but that is not currently possible.
Otherwise we end up with a 95% male-nerd colony. That's how I see it in my head: nerd males perhaps with some minor autism or social awkwardness. Some sort of Comi-con, perhaps even with females prostitutes.Bottom line: either there is a 1 year "package" for tourists or this can become a joke. "Go to Mars" or "you come from Mars" could easily become catchphrases to call someone a lonely nerd.
Everybody is talking about the technical challenges but nobody is talking about the social challenges. And my experience in management tough me that people management is the hardest thing you can face. And I only manage them during working hours! I don't manage their private life! But any plan for Mars colonization must face the social challenges: maintaining male-female ratio, maintaining a healthy social environment, establishing rules (actually, laws), justice, social security, etc.
I can't find the sim files again, but I remember turn-around had to be very quick.
@high road, your right about the tittle, changed it.My first line of reasoning was the Earth is at the same place every year, unlike mars. So that could mean you have more frequent options for return trajectories.Also ballistic capture and low energy transfer, could have other possibilities back from Mars than towards.
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!
@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.
Quote from: Peter.Colin on 07/09/2017 09:43 amInteresting, 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.Your intuition is correct. The "Aldrin Cyclers" (also described in the JBIS article I linked above) come in two flavors, each of which visit Earth and Mars every 26 months. The Up Cycler takes 147 days to reach Mars, and 21 months to get back; the Down Cycler is roughly the opposite. Again, I would expect that switching from a cycler trajectory to one with briefs stay-overs on each end would cause only a small change in departure/arrival velocity, and probably get rid of the deep-space burns as well as speeding the slow leg a bit. Aldrin's Up cycler has an Earth departure Vinfinity is 6.1 km/s (Vinj= 12.4 km/s = Vcirc+4.8 km/s), and the Mars Vinfinity is a whopping 9.3 km/sec (Vinj = 7.1 km/s), which the ITS ship can barely do with only a 130 ton payload.---It will be interesting to hear if Musk has an opinion on the issue, but I would think in the early years, most Mars passengers would be planning on a stay of 2-4 years, with only 10% or so being "lifers". The lifers would presumably prefer a fast outbound, and slow return of the empty ship. The round trip people might prefer the more balanced 10month/10month out/return, or perhaps 8/12 (assuming that's also possible).---Quote from: ThereIWas3 on 07/09/2017 10:01 pmWith 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.
Someone who knows something about orbits might be able to immediately dismiss this, but I don't suppose there is any possibility of more than one round trip each Synod? I imagine you would be alternating totally different sorts of transfers such as opposition and conjunction, going overboard on one and using the other only for cargo.If you are getting there and back within 6 months, I suppose another way of getting more use out of the ITS would be lunar missions or LEO tourism. Otherwise it is just sitting around for more than a year.
If you can get to mars in under 30 days, like Elon said future ships wil be able to do, you could theoretically do 2 or 3 round trips per Synod, 2 of them in a 6 months window, with the same ship.The 3rd trip back could be a long indirect trip.
Hi just had another random idea. Too small for it's own thread.A big problem with cost effective mars flights is that due to roughly two years between launch windows, you cannot get many uses out of your ITS before it has to be retired.Once you get a significant number of flights, how about a new class of ITS which is really just an ITS-shaped DSH with a heat shield. It has just enough engines and tankage to get to orbit, empty.passengers could dock with it in high orbit. They are packed like sardines in a standard ITS. The DSH version has more space.A full tanker is used as a booster to push it towards mars, on a trajectory that allows the tanker to aerobrake at earth.The DSH is aerocaptured at mars but the passengers have to be shuttled down to mars with another ITS. (Alternatively, this version does have engines and tankage, but only equivalent to what an ITS needs to land on marsThe point is that the ITS at each end can be significantly reused. The DSH version could be much less expensive per passenger since it does not need to maintain engines or store fuel. (or alternatively, if it lands at mars, still not as many or as much)Also, because it's task is much simpler, it may be possible to reuse it a few more synods.
The alternate to all of this is that the ITS is likely to have more usage of about 60-90% within cis-lunar space. Using the ITS multiple times in local space (like 20+ times) prior to using the used vehicle on a Mars trip reduces the build rates and the costs for Mars since the cost of going to Mars is the cost of just one more launch of this used vehicle.
Who pays is a good question.The first return ship could be loaded full with Mars Samples.I'd pay for a real Mars stone from the first Mision.This is probably worth arready as much as the ship cost.
Hi just had another random idea. Too small for it's own thread.A big problem with cost effective mars flights is that due to roughly two years between launch windows, you cannot get many uses out of your ITS before it has to be retired.Once you get a significant number of flights, how about a new class of ITS which is really just an ITS-shaped DSH with a heat shield. It has just enough engines and tankage to get to orbit, empty.passengers could dock with it in high orbit. They are packed like sardines in a standard ITS. The DSH version has more space....The point is that the ITS at each end can be significantly reused. The DSH version could be much less expensive per passenger since it does not need to maintain engines or store fuel. (or alternatively, if it lands at mars, still not as many or as much)...
...The mother ship idea gets a lot more appealing when the mother ship is nuclear powered.
Just to clarify, the central goal I was aiming for was to solve the problem of a super expensive vehicle only being reusable every 2 years
QuoteJust to clarify, the central goal I was aiming for was to solve the problem of a super expensive vehicle only being reusable every 2 yearsIsn't the solution simply "have more destinations", as has been discussed? Earth-Earth, Earth-Moon, and Earth-Venus, etc. So long as a given craft is multipurpose and any internal reconfigurations for different missions don't require an extensive retrofit....