Author Topic: ITS Spaceship Round-trip each Synod possible?  (Read 8506 times)

Offline Hotblack Desiato

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #40 on: 07/23/2017 05:05 PM »
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.

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.
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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).
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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.

That actually solves another problem I have with flights once every synode. And besides, it solves the problem that people who want to leave Mars have to stay on the ITS back home for a long time.

The problem I see is: with the fleet of ITS cycling every 26 monts, they will all stay together for a brief period of time on Mars and a similar period on Earth. During that time, they need to receive maintenance etc. Sure, you can use the production personell for the mainentance, leading to 25 months working on new ITS and spare parts, and 1 month of actual maintenance for the fleet in use. By using the up-cycles and the down-cycles, the time available for maintenance doubles. Cargo-ITS go to Mars via down-cycles (18m trajectory), and allow people to travel back to Earth on a quick 6m trajectory (or even faster). And people who want to go to Mars can use the up-cycles with fast trajectories to Mars and slow ones back to Earth.

This will also help the fuel production and storage on Mars, since it lowers the amount of fuel that needs to be kept in stock on Mars.

Offline Peter.Colin

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #41 on: 07/23/2017 10:08 PM »
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.
« Last Edit: 07/23/2017 10:10 PM by Peter.Colin »

Offline KelvinZero

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #42 on: 07/23/2017 10:28 PM »
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.
I was hoping for something less brute force, eg where you at least leave at the right time for whatever transfer type in both cases. I was wondering if by freak coincidence the 6month round trip time Elon mentioned (opposition-class?) would leave time for a slower conjunction-class mission.

Anyway, I guess using it for a couple of cis-lunar flights during the off-season would be a lot less complicated (leo tourism or lunar base). I guess if the trip takes 6 months including return you have about 1.5 years when it is just sitting around.

Offline KelvinZero

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #43 on: 09/04/2017 12:49 PM »
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 mars

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)

Also, because it's task is much simpler, it may be possible to reuse it a few more synods.

Online oldAtlas_Eguy

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #44 on: 09/04/2017 07:06 PM »
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 mars

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)

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.

Offline KelvinZero

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #45 on: 09/05/2017 12:31 AM »
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.
I think you are very likely right.

I still sort of like this ITS+Tanker+ trajectory that immediately recovers Tanker by skimming earth. We will have to think up some use for that :)

Offline QuantumG

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #46 on: 09/05/2017 12:34 AM »
Not yet mentioned on this thread, as far as I can see. Fast transfers are good for mitigating both radiation and zero-g exposure concerns. Also this plot.




Jeff Bezos has billions to spend on rockets and can go at whatever pace he likes! Wow! What pace is he going at? Well... have you heard of Zeno's paradox?

Offline ChrML

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #47 on: 09/06/2017 08:32 PM »
Elon has previously confirmed out-of-synod return trips being possible with the 12m ITS.

How feasible is a longer trajectory of maybe 3-4 months from Mars, past the sun (maybe even a Venus flyby for sightseeing) and back to the earth? Or the other way around. E.g. 1 fast trip, then two slow. Perhaps cargo only in the 4 month trips.

That could increase lifecycles from approximately 15 to 45 uses, which would significantly reduce the number of ITS ships needed to build the colony and leave more money for building the colony.

Offline Rei

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Re: ITS Spaceship Yearly Mars return possible?
« Reply #48 on: 09/29/2017 02:04 PM »
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.

There's lots of different ways to help pay for offworld settlement activity.  This (ch. 8, p.213-228) is for Venus, but a lot of the same aspects can also apply to Mars as well. As for the specific one mentioned above: certainly public sales of mineral sample sales are among the ways for a colony to earn income. An even larger market is if you can return minerals that are workable in the super-premium end of the decorative stone market, for a low enough price (reasonable hardness / workability / aesthetics). "Oh, your countertop is made from brazilian agate?  Mine is made from polished basalt from freaking Mars.;)  It's not a limitless market, but when you're talking about the sort of payload return costs that SpaceX is, there's potential.

That said, there's no question that someone is going to have to put forward the capital costs. In Musk's previous IAC presentation, they left it as a big blank as to who was supposed to pay for it. In the current one, it sounds like SpaceX themselves thinks that they can cover the initial capital costs.

Offline Nathan2go

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #49 on: 10/01/2017 06:36 PM »
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)
...
There are two issues: passenger volume, and ship reuse.

For ship reuse, maybe you make the ship as two modules: a passenger compartment, and a separable propulsion module.  The propulsion module, with an added nose cone (with nose tank for balance at landing), could be used as a tanker.  You'd use it as a tanker for say 50 flights, then convert it to passenger duty, for 10 more flights to complete its service life.   

Musk said last year that the tanker was the same as the ship, but filled all the way with propellant: I don't think this has to be done this way.  If the tanker propellant volume is the same as for the passenger ship, the payload capacity only drops a bit (7% ?), since the 2nd stage gross mass is 85% propellant anyway, and reducing the mass of the 2nd stage will boost the performance of the 1st stage.

Or maybe you use the ship for monthly Lunar tourism flights for a few years to improve utilization.

As far as having the passengers ride a tightly packed ship to orbit, then meet a larger ship there (i.e. mother ship):  yes, it "feels" right.  But in practice, there are many problems.  If the larger ship has more mass, then perhaps it will need in-space construction (e.g. maybe it launches with the big passenger volume empty, and the interior features get installed through a large cargo hatch), which implies the in-space labor must be cheap.  Also, maybe you need a dedicated flight to load consumable, in addition to the passenger flight.  Also, if it is too heavy to land, it must receive all maintenance while in orbit.

Note that is not a very effective way to reduce the amount of fuel that gets lifted off planet surfaces.  Starting in low Mars orbit, you still need a methalox burn with mass_ratio = 2 to return to Earth.  If you get the fuel from Mars surface, it's about a 2x savings if the ship starts in orbit instead of on the surface; easy to eat up that savings with a heavy ship.  So returning spacious (heavy) ships will still take a lot of fuel. 

The mother ship idea gets a lot more appealing when the mother ship is nuclear powered.

Offline KelvinZero

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #50 on: 10/01/2017 10:59 PM »
...
The mother ship idea gets a lot more appealing when the mother ship is nuclear powered.

Hi Nathan,

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.. so I was setting out to make that bit as cheap and low maintenance as possible.

My solution was an interplanetary vehicle that was little more than an empty husk of a BFS.. a BFS with no engines or fuel tanks. Just one big pressurised volume inside the exact same aerodynamic hull.. It is only bigger in the sense of having more living space because you took the tanks out. All it has is a heat shield to brake into orbit at the other end and some minor rockets to correct its trajectory.

The expensive part would be a conventional tanker as Elon Musk has presented. This aerobrakes back to earth immediately after pushing the husk ship on its way, so it's part of the mission is mere days and it can immediately  be used again.

Offline Rei

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #51 on: 10/01/2017 11:41 PM »
Quote
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

Isn'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 multiyear retrofit....  A retrofit that takes a couple days, weeks, even months would be fine, so long as the craft itself can handle different missions.
« Last Edit: 10/01/2017 11:50 PM by Rei »

Offline KelvinZero

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #52 on: 10/01/2017 11:54 PM »
Quote
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

Isn'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....
That is true.. it is not 2 years that the vehicle is out of use, it could be as low as 6 months if we have 3 months both ways. Still, 6 months is a lot longer than typical mission times of a day to LEO tourism or a week to the moon and back. (passengers to the moon could stay as long as they like, but it is cheaper to reuse the BFR immediately bringing other passengers home)

This is also dedicated to just one purpose, shovelling passengers to mars as cheaply as possible, and it is not something you would consider until a long time in the future: when you had ITS being used purely as shuttles around mars, and so also repaired and serviced at mars.

Offline wes_wilson

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Re: ITS Spaceship Round-trip each Synod possible?
« Reply #53 on: 10/02/2017 03:33 AM »
Wonder how the return trip time would improve if:
- a couple of the tanker BFS's were taken to Mars in addition to a passenger ship (these could remain for reuse at mars)
- passenger ship flies into mars orbit and is refuelled by the tankers (just like at earth)
- BFS leaves from Mars orbit for Earth with full tanks of fuel

Basically all the same process they're proposing at Earth; just without the need for BFR due to lower gravity.



 
@SpaceX "When can I buy my ticket to Mars?"

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