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.
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.
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....