Larger than ITS - The next generation

[DnA915]

I know there was brief talk from Elon about how the next generation of ships may make the ITS look small. I was curious as to the best operation for these ships. Would it make sense to leave these in earth and mars parking orbits and then just use ITS to boost larger occupant capsules of 200 people to and from the larger ship? This would take away the need for extra landing propellent and landing systems and their associated weight. Also, assuming it had the same docking mechanisms, these could easily be refilled with the same ITS style tankers. It would also allow for a piece together style ship that has no need to be aerodynamic so that you could concentrate only on strength (or some artificial gravity).

[GWH]

Was thinking about this also, partly influence by the sheer number of flights a single booster and a couple tankers could perform in their lifetimes, where eventually doing in orbit assembly of a MASSIVE ship would make sense. A cargo ITS would launch passenger modules, which are assembled on top of a ITS tanker to make a massive stage. This gets you more uses per propulsion element (ITS space ship bound for Mars).

They could cluster together ITS tankers in space as the "booster" element to reach near escape velocity from Earth than swing back to aerocapture back in to orbit for refueling while a single ITS tanker derived super stack would complete the burn to Mars.  Aerocapture at Mars and then reusable shuttles from the surface and back to pick up passengers.

My back of the envelope calcs had two variants:
Super ITS:
5 ITS passenger modules assembled on a single ITS tanker, 500 people, 1500kg cargo, 150 meters long when stacked on top of the tanker ITS propulsion element. 
dV of 3.06 km/s all in, and 5.5 km/s when empty to return (zero margin but could make it).
To provide the necessary dV to leave Earth orbit, a cluster of 3 ITS tankers would give it a 3 km/s shove (High elliptical orbit).  Total dV on the way to Mars is 5.5 km/s for the slow 180 day "economy" transit.
6 flights to assemble and 26 tanker flights worth of fuel.

Mega ITS
10 ITS passenger modules assembled on a single ITS tanker, 1000 people, 3000kg cargo, 250 meters long when stacked on top of the tanker ITS propulsion element.
Using only a single propulsion element would leave a big shortfall of dV from High Elliptical Earth Orbit, so instead a partial boostback is going to be used for the boosters.  A ring of 6 tankers would provide a boost of 4 km/s dV and then separate and burn back 1.2km/s. The crew vehicle now can provide 1.7 km/s dV the rest of the way.  Boosters to get back from Mars would be needed.  42 Raptor Vacs would power this vehicle if all lit up at the same time.
11 flights to assemble and 46 tanker flights worth of fuel.

[MATTBLAK]

If and when they manage to get a regular and efficient ISRU and propellant transfer operation(s) up and running for the oceans of LOX & Methane required, there's no reason why they couldn't have giant, in-space only ships that run as 'Super Ferries' and even 'Space Liners' between the planets. I guess we're talking 40-to-50 years down the road, here!

I could also advocate, but not necessarily see happening nuclear-thermal or nuclear gas-core propulsion modules that could facilitate faster transfers between worlds. Though getting big supplies of hydrogen up to the 'nuke tugs' could be an infrastructure challenge. Though I could forsee instead the shipping of cometary or asteroidal water to big, orbiting 'Propellant Farm/Factories' for processing. These Prop Farms could take the water and using solar powered electrolysis split the water into hydrogen and oxygen. The oxygen goes for use with the LOX/Methane fueled ships and the hydrogen could be used both for the nuke tugs and for making methane, when combined with CO2 brought from comets or Mars itself. Or other sources. No volatile gas or liquid need be wasted. Methane could even be cycled in from the Station's own sewage plants and other waste facilities. Maybe the CO2 produced from all the present humans could be trapped and sent to the methane-creating process, too!

Chemistry, biology, geology, geophysics and astronautical engineering; all working closely together to truly leverage a Space-going infrastructure into reality from the pages of science fiction. And for slower-moving, economic cargo runs through the Solar System? A mixture of solar-electric, nuclear-electric and ISRU-chemical propulsion technologies applied where most-needed and most practical.

[Robotbeat]

I think Musk was imagining a much larger booster rocket, not just a big in-orbit ship.

[Lars-J]

@MATTBLAK:
Yes - At some point when you size up everything, landing the whole ship becomes less practical. ITS - as currently envisioned - makes a lot of sense due to the relative lack of in space and on Mars infrastructure. It might even be a "sweet spot". (For example, bigger launchers from Earth would require absurdly large infrastructure)

So I'm not saying it will happen, but I agree that a next level architecture could look very different.

[guckyfan]

I see a much larger interplanetary ship having different propulsion. Tom Mueller talked about using nuclear, probably nuclear thermal. That ship would not land on Mars. It does probably require an industrial support base on Mars. Ferries going up and down between Mars and those ferries need servicing on Mars.

Tom Mueller also said SpaceX can not afford a nuclear drive test stand on earth. Maybe a few decades down the line they could have one on Mars, again with a substantial industrial base.

I remember initial data here on L2 that the BFS would have 15m diameter. That switched to 12m with the IAC presentation. Given an intermediate smaller vehicle I imagine 15m could be back on the table. But somewhere around that value I imagine is the upper limit of what is practical. Except some hypothetical future breakthrough propulsion system comes up which we cannot even speculate on now.

[Eerie]

At some scale, it will make more sense to build a Lofstrom loop and assemble your mega-ship in orbit.

[rakaydos]

At some scale, it will make more sense to build a Lofstrom loop and assemble your mega-ship in orbit.

That -is- where the progression leads, but I suspect it's a generation or two beyond elon's superliner.

If MCT is equivilant to the world's first long range steamship (ACT), a launch loop or space elevator is an equivilant to a modern seaport. No market for it yet, but if "steamships" become popular, they will be inevitable.

[spacenut]

I could see a large ship assembly area at L1 or L2 moon vicinity.  Existing rockets or new ones soon to come on line can get cargo and humans there.  Then the large ship would go to a high Mars orbit to off load to Mars landers.  The large ships would be like Buz Aldrins cycler only faster since it would be nuclear powered ship.  This ship could make quick flights to and from Mars during the proper synod, but would take longer when Mars is further from earth.  These super large ships could also travel to the Astroids or the moons of Jupiter and Saturn. 

[GWH]

I think Musk was imagining a much larger booster rocket, not just a big in-orbit ship.

Maybe, but that doesn't make sense to me economically. Why? Most of the cost is sunk in each individual Mars ship which is stuck on a 2 year cycle, the cost/flight of the booster is pretty trivial in terms of hardware alone.

The expected lifetimes and fabrication costs of each vehicle are as follows:
Booster: 1000 uses, $230M
Tanker: 100 uses, $130M
Ship: 12 uses, $200M

Assuming a 24 year lifetime per booster to match up with the 24 year lifetime of Mars ships, one could use a pair of boosters per pad rotating for periodic refurbishment for 42 flights per year each, 84 flights total per pad.
At 5 tankers per 1 Ship that's 140 tanker flights and 28 Mars ships per synod.
Over 24 years that's 33,600 passengers, 100,800 kg cargo to Mars
Total fab costs:
Booster: 2 required for $460M total - $0.23M hardware cost per flight
Tanker: 17 required for $2,210M total - $1.3M hardware cost per flight
Mars Ship: 28 required for $5,600M total - $16.67M hardware cost per flight
Total fabrication costs: $8,270M
That's just for one launch pad.

If you take the cost difference between the Mars ship and tanker a bare minimum cost of the passenger and cargo compartment would be $70M.
So if one used the "Mega ITS" ship as outlined above you'd need 3 ships transporting 1000 people each, bare minimum cost of 10 passenger/cargo compartments + 1 tanker for each ship would be $830M, and then your 6 tanker boosters that stay in space.
Assuming the scenario above, and the exact same # of tanker flights (this is a little different than my earlier scenario but done this way to be apples to apples).
Booster: 2 required for $460M total - $0.23M hardware cost per flight
Tanker: 17 required for $2,210M total - $1.3M hardware cost per flight
Mars Mega ITS Ship: 3 required for $2,490M total - $207.5M hardware cost per flight
In Space Boosters: 6 required for $130M each, $780M total, $21.7M per Mega ITS departure
Total fabrication costs: $5,940M, total savings $2,330M, or 33% less cost.

I didn't include any refurbishment costs in the above to keep it simple, the Mars ship refurb costs are estimated at $10M/synod, so if a larger in space ship and then cycling shuttles would require less refurb overall than the costs would drop even more in comparison.

[Darkseraph]

ITS as currently envisioned ought to be the next generation system. A system closer in size to New Glenn or SLS, probably makes more sense in the nearer term. Since Falcon Heavy turned out to be 'harder than you would think', that doesn't bode well for the cost and schedule of ITS, as it has been described.

This architecture is crammed full of novel technologies SpaceX have little experience with such as second stage reuse, lifting bodies, orbital refueling, methane engines, large composite tanks, precision mars landing, cradle landing, rapid reuse, 51 total engines, low boiloff propellant management and the list goes on. Absolutely not confident based on their previous performance meeting goals.

[gospacex]

I know there was brief talk from Elon about how the next generation of ships may make the ITS look small.

I think a look at evolution of sizes of ocean going cargo ships would let you make good predictions.

Really huge ships are limited by infrastructure (depth of ports and seaways, width of Panama Canal etc). Therefore their sizes increase rather slowly - only in sync with infrastructure upgrades.

Current embryonic state of our civilization's space capabilities require, at max, 12-15m diameter launcher. Anything larger would require humongous (meaning very expensive) launch pads, and would provide lift capability way in excess of the needs.

Some 100 years from now, when demand increase, and space infrastructure grows in response to that, a slow increase in launcher diameter will occur.

[UberNobody]

Personally, I don't think we'll go much beyond a 15m-17m ITS v.3 before more radical changes take over.  We might see ITS be complimented by in-space mining efforts that put fuel depots in Earth/Mars orbits.  After that, you pretty much need an orbital ring or fusion rockets to make further efficiency gains (without the political nightmare that is fission).

With a beefed up ITS and some in-space mining, an orbital ring is definitely within reach.  Learn more about it here if you aren't familiar (the channel is 100% epic!):

[RoboGoofers]

I know there was brief talk from Elon about how the next generation of ships may make the ITS look small.

I think a look at evolution of sizes of ocean going cargo ships would let you make good predictions.

Really huge ships are limited by infrastructure (depth of ports and seaways, width of Panama Canal etc). Therefore their sizes increase rather slowly - only in sync with infrastructure upgrades.

Current embryonic state of our civilization's space capabilities require, at max, 12-15m diameter launcher. Anything larger would require humongous (meaning very expensive) launch pads, and would provide lift capability way in excess of the needs.

Some 100 years from now, when demand increase, and space infrastructure grows in response to that, a slow increase in launcher diameter will occur.

Also consider the sunk cost involved in infrastructure. Wider trains would be useful, but that'd require changing all the tracks, tunnels, etc. etc.
Bottom line is that it's never going to change if there's a hundred years of built up infrastructure around a specific size. it'll be 'good enough. why bother?'

That's when something like a launch loop becomes compelling. it might actually be cheaper than upgrading everything.

[TomH]

Predicting the near future is something that can be extrapolated by extending existing technology and tech that is theoretically possible via known science. Predicting the distant future is a dicey proposition because of unknown discoveries that are likely to happen.

Thomas Jefferson thought it would take a hundred generations from Lewis & Clark until the time the west was populated. It took 2.5. What he could not foresee were the steam engine and industrial revolution which were around the corner.

We have no way of knowing discoveries that will be made in coming decades and how those will affect the unfolding of history.

If Meriwether Lewis, sitting in his canoe near the confluence of the Willamette and Columbia Rivers in 1806, could have taken a 10 second glimpse two centuries into the future, he would have seen skyscrapers, massive steel bridges, huge steel container ships, and wide bodied airliners on glide slope into PDX. It would have been like nothing he could have expected. Our future is likely as obscured to us as his was to him.

[Jim Davis]

Thomas Jefferson thought it would take a thousand generations from Lewis & Clark until the time the west was populated.

He wrote that, but it's pretty clear he did not really think that. A thousand generations is about 20,000 years and that would be very pessimistic even by early 19th century standards.

Jefferson was indulging in a rhetorical flourish like the Labour politician who claimed he was descended from a "thousand generations of coal miners".

[DnA915]

Predicting the near future is something that can be extrapolated by extending existing technology and tech that is theoretically possible via known science. Predicting the distant future is a dicey proposition because of unknown discoveries that are likely to happen.

I agree with this to a point. If however, SpaceX manages to stay on their own timeline, I don't think the larger version is more than 30 years out. That being said, I would hope that something like the EM-Drive will be proved on a large scale which would definitely change deep space propulsion methods and the likelihood of in-space only optimized vehicles

[TomH]

He wrote that, but it's pretty clear he did not really think that.

My apologies, My addled old brain added an extra zero. It was 100 generations. Jefferson had instructed Lewis to search for a water route. At this point in history, great canal projects were complete or underway in Britain and the European continent. Surveying and preliminary engineering were underway for the Erie Canal which would connect the Hudson River with Lake Erie while the Illinois and Michigan Canal would connect Erie with the Mississippi via the swamp just south of the Chicago River. This would open the central third of present day US to commercial transportation. Jefferson's hope was that such a canal could connect the headwaters of the Missouri and Columbia Rivers.

Lewis returned, telling of their travails in the Bitterroots, of the snow and the immense steep grades. Jefferson was dejected. It had taken 200 years from Jamestown until settlers had penetrated 50 miles with much population density on the eastern seaboard on level ground.

Jefferson also did not state that it would take 100 generations for any settlers to enter the west. His words were in relation to a populated territory. In relation to the time it had taken to penetrate the eastern interior, 2,200 years would have been a reasonable estimate on his part for the west to become populated.

Jefferson did indeed believe what he wrote. He was a man of logic and science, not prone to hyperbole of any kind. Without knowledge of improvements in sea craft, South Pass through the Rocky Mountains, passes that would be discovered, and the imminent invention of steam power, he did believe it would take 100 generations to settle the west. Again, my apologies in relation to 1000 vs. 100.

[meekGee]

If you look at airplanes, they stopped getting larger in any significant way after the B747.  They actually shrunk, so it wasn't infrastructure that was driving it... and the A380 is limited mostly by market forces.

What did explode instead was the amount of traffic.  10,000 flights in the air over the US during daytime...  An unthinkable number 30 years earlier.

I don't see why we need anything larger than a B747 for Mars.  So maybe one iteration beyond ITS.

However, I do think we will see 100 launch pads (probably offshore), and thousands of rockets flying up and down like airplanes from an airport.

I don't see the equivalent of sea transport happening, because I don't think you'll ever have a solar system global economy in the way you have it on Earth, because of the time constants.  (no real time communication, or any kind of reasonable transport times)

[DnA915]

If you look at airplanes, they stopped getting larger in any significant way after the B747.  They actually shrunk, so it wasn't infrastructure that was driving it... and the A380 is limited mostly by market forces.

What did explode instead was the amount of traffic.  10,000 flights in the air over the US during daytime...  An unthinkable number 30 years earlier.

I don't see why we need anything larger than a B747 for Mars.  So maybe one iteration beyond ITS.

However, I do think we will see 100 launch pads (probably offshore), and thousands of rockets flying up and down like airplanes from an airport.

I don't see the equivalent of sea transport happening, because I don't think you'll ever have a solar system global economy in the way you have it on Earth, because of the time constants.  (no real time communication, or any kind of reasonable transport times)

The plane analogy stands up somewhat, but for a trip to mars, as far as the ideal setup, I think a cruise ship has more similarities. You can't ask people to sit on a plane or something like a plane for 9 months; they would go crazy. You need room for privacy, room for socializing, and for a 9 month period which if far longer than most cruises, you are going to need some form of entertainment. If there is a large demand for trips to mars in the not too distant future, people will want to go in the largest and the most comfortable if the price is not too high, and that would add demand for bigger ships. I think Elon does an amazing job in his companies in realizing that looking and feeling cool and inspiring will eventually drive the success of the endeavor. We see this in ITS and its description and I think it will continue to get bigger for this reason.