Author Topic: Larger than ITS - The next generation  (Read 8946 times)

Online DnA915

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Larger than ITS - The next generation
« on: 07/07/2017 04:53 AM »
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).

Offline GWH

Re: Larger than ITS - The next generation
« Reply #1 on: 07/07/2017 05:31 AM »
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.

Offline MATTBLAK

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Re: Larger than ITS - The next generation
« Reply #2 on: 07/07/2017 05:56 AM »
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.
« Last Edit: 07/07/2017 05:57 AM by MATTBLAK »
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Offline Robotbeat

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Re: Larger than ITS - The next generation
« Reply #3 on: 07/07/2017 05:59 AM »
I think Musk was imagining a much larger booster rocket, not just a big in-orbit ship.
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Offline Lars-J

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Larger than ITS - The next generation
« Reply #4 on: 07/07/2017 06:30 AM »
@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.
« Last Edit: 07/07/2017 06:32 AM by Lars-J »

Offline guckyfan

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Re: Larger than ITS - The next generation
« Reply #5 on: 07/07/2017 09:48 AM »
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.

Offline Eerie

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Re: Larger than ITS - The next generation
« Reply #6 on: 07/07/2017 10:23 AM »
At some scale, it will make more sense to build a Lofstrom loop and assemble your mega-ship in orbit.

Offline rakaydos

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Re: Larger than ITS - The next generation
« Reply #7 on: 07/07/2017 10:56 AM »
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.

Online spacenut

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Re: Larger than ITS - The next generation
« Reply #8 on: 07/07/2017 11:57 AM »
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. 

Offline GWH

Re: Larger than ITS - The next generation
« Reply #9 on: 07/07/2017 03:41 PM »
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.
« Last Edit: 07/07/2017 05:11 PM by GWH »

Offline Darkseraph

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Re: Larger than ITS - The next generation
« Reply #10 on: 07/07/2017 04:04 PM »
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.




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Offline gospacex

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Re: Larger than ITS - The next generation
« Reply #11 on: 07/07/2017 04:14 PM »
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.

Offline UberNobody

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Re: Larger than ITS - The next generation
« Reply #12 on: 07/07/2017 04:14 PM »
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!):


Offline RoboGoofers

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Re: Larger than ITS - The next generation
« Reply #13 on: 07/07/2017 04:27 PM »
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.

Offline TomH

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Re: Larger than ITS - The next generation
« Reply #14 on: 07/07/2017 08:12 PM »
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.
« Last Edit: 07/07/2017 10:42 PM by TomH »

Offline Jim Davis

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Re: Larger than ITS - The next generation
« Reply #15 on: 07/07/2017 08:21 PM »
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".

Online DnA915

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Re: Larger than ITS - The next generation
« Reply #16 on: 07/07/2017 08:39 PM »
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

Offline TomH

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Re: Larger than ITS - The next generation
« Reply #17 on: 07/07/2017 10:41 PM »
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.

« Last Edit: 07/07/2017 10:43 PM by TomH »

Online meekGee

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Re: Larger than ITS - The next generation
« Reply #18 on: 07/08/2017 05:46 AM »
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)
« Last Edit: 07/08/2017 07:52 AM by meekGee »
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Online DnA915

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Re: Larger than ITS - The next generation
« Reply #19 on: 07/08/2017 09:23 PM »
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.

Offline TomH

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Re: Larger than ITS - The next generation
« Reply #20 on: 07/08/2017 11:28 PM »
I think a cruise ship has more similarities.

Ocean liner. Cruise ships and ocean liners have different designs. Cruise ships are mainly designed to putter around and have all kinds of recreational activities. Liners, so named because they travel mainly in a straight line, are designed to go from Point A to Point B. While they may have luxuries, the hull, keel, etc. are designed for higher speed, the ability to handle larger waves, and the ship is intended for constant long distance transport; cruise ships are not. Cruise ships are boxier while liners are narrower, sleeker, and have a stronger superstructure. Cruise ships now employ bow planes for stabilization whereas liners avoid them due to drag. QEII, QMII, and SS United States are liners; almost all other ocean going passenger ships are cruise ships.

ITS will be designed to go from Point A to Point B.

https://frugalfirstclasstravel.com/2015/05/29/cruise-ship-vs-ocean-liner-whats-difference/
« Last Edit: 07/09/2017 06:09 AM by TomH »

Online meekGee

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Re: Larger than ITS - The next generation
« Reply #21 on: 07/08/2017 11:46 PM »
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.

Yes and no...  Manned trips to Mars will be 3-monthish, and will be a one-in-a-life time thing.  Immigration, not commuting.

Even if you're only going for 2 years (minimum stay), that's still acceptable.

In that context, 3 months in a space that gives you a cot and communal areas - I think that's acceptable

Other than number of flights, I think we'll see faster ships.  I can see an advanced electric drive ship going back and forth (still once every two years) - but faster.

Actually, the ability to travel faster will reduce the need for larger ships.

So I'm sticking with "large airplane" size, and not "cruise ship"/"battlestar" size...

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Offline ChrisWilson68

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Re: Larger than ITS - The next generation
« Reply #22 on: 07/09/2017 06:57 AM »
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.

I don't agree.  Rockets really are more efficient than most people give them credit for.  Once they're completely reusable and scaled up, they can be more efficient than Lofstrom loops or space elevators or orbital rings or any other megastructures, no matter how much we're launching to space and no matter how far in the future we go.

The cost comparisons for these megastructures tend to compare costs against today's expendable rockets.  That's not the right comparison.  The right comparison is against the optimized reusable rockets of the future when we're carrying large volumes of cargo to and from space.

Offline RoboGoofers

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Re: Larger than ITS - The next generation
« Reply #23 on: 07/11/2017 05:30 PM »
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.

I don't agree.  Rockets really are more efficient than most people give them credit for.  Once they're completely reusable and scaled up, they can be more efficient than Lofstrom loops or space elevators or orbital rings or any other megastructures, no matter how much we're launching to space and no matter how far in the future we go.

The cost comparisons for these megastructures tend to compare costs against today's expendable rockets.  That's not the right comparison.  The right comparison is against the optimized reusable rockets of the future when we're carrying large volumes of cargo to and from space.

I don't know, that sounds like you're saying, by analogy, ferries can be cheaper than bridges. it depends on your metric. maybe the ferry ticket cost is cheaper than the bridge toll, but thinking of them as whole systems, the bridge is far cheaper/efficient.

Online DnA915

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Re: Larger than ITS - The next generation
« Reply #24 on: 07/11/2017 06:10 PM »
I don't know, that sounds like you're saying, by analogy, ferries can be cheaper than bridges. it depends on your metric. maybe the ferry ticket cost is cheaper than the bridge toll, but thinking of them as whole systems, the bridge is far cheaper/efficient.

Not to start arguing way off topic, but saying the statement broadly "the bridge is far cheaper/efficient" is not true. If it were, we would never use boats on a regular basis and would simply always build bridges. Its all about distance, efficiency, cost and convenience. I think the previous commenters point was that he thinks it would no longer make economical sense, at least in the timeframes that governments paying would be able to swallow.

Offline oldAtlas_Eguy

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Re: Larger than ITS - The next generation
« Reply #25 on: 07/13/2017 03:57 PM »
I believe with the advent of a in-space propellant ISRU infrastructure that the cruise ship vs airplane analogies for what each would be but that it delineates how such planetary in-space only vs the surface shuttles  to orbit would be designed. The shuttles would look similar but maybe larger than the ITS. They would be Airplane like in their packing the passengers in since they would have at most a 3 day trip. The in-space planetary craft would be massive comfortable travel space for passengers in the thousands or 10s of thousands. Imagine a torus colony like moving vehicle using Nuclear Thermal or such like 900+ ISP engines. The crew including their families would live simi-permanently on the vehicle almost like its own in-space city. 

The key here is that even just the original ITS sized craft when used as a orbital shuttle could transport over 400 people at at time if the duration of the trip is short as in a few days. My original estimate was a value of 4 to 1 for number of short duration (3+ days) passengers to the longer duration (3+ months) numbers. This was for a Earth to Moon surface passenger service evaluation using a customized ITS). If the number is 200 for long duration this would then give a shuttle to orbit number at 800. To load then this massive 10,000 passenger in-space cruise ship would take just 2 tankers and the one ITS passenger flight to get from Earth to L2 and on Mars it needs no Tankers at all to get to Deimos orbit. That then makes for the transport of 10,000 people from Earth to Mars requiring 12.5 ITS passenger flights and 25 Tankers for every 10,000 people. So at 100 ITS and 200 tankers that would then be in this scenario for one or several "cruise" ships the transport of 80,000 people between planets every synod without much change to the surface infrastructures (Pads required or even LVs designs). This would be vs the use of only ITS and no in-space ISRU propellant sources only 50 ITS transporting just 200 each for a total of 10,000 passengers. This is a 8 to 1 cost reduction in transport costs for this first part of the leg of the journey. The massive cruise ships could have lifetimes measured in decades where the number of persons tranport in just one direction at 10,000 at a time would be over 30 years 150,000. If each such vehicle cost $10B even to build than that is a per person cost of $67K. The operations costs would nearly equal that cost putting the tiket price to travel on these very comfortable vehicles at ~$100K. Now add the surface shuttles cost at $100K at Earth and $30K at Mars the total trip price would be $230K. This also give the prices for going anywhere in Cis-Lunar space even the Lunar surface at about $100K. This then makes going to Mars vs just the Moon is only 2X as much.

By this time the demand for travel may be much more than this level of infrastructure can handle.

If you increase the sizes of the surface to orbit craft then that also would make the size or number of in-space cruise ships grow. Eventually with enough DV from high thrust high ISP engines the departures would no longer be limited to the synods.

Offline RoboGoofers

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Re: Larger than ITS - The next generation
« Reply #26 on: 07/13/2017 06:41 PM »
I believe with the advent of a in-space propellant ISRU infrastructure that the cruise ship vs airplane analogies for what each would be but that it delineates how such planetary in-space only vs the surface shuttles  to orbit would be designed. The shuttles would look similar but maybe larger than the ITS. They would be Airplane like in their packing the passengers in since they would have at most a 3 day trip. The in-space planetary craft would be massive comfortable travel space for passengers in the thousands or 10s of thousands. Imagine a torus colony like moving vehicle using Nuclear Thermal or such like 900+ ISP engines. The crew including their families would live simi-permanently on the vehicle almost like its own in-space city. 

The key here is that even just the original ITS sized craft when used as a orbital shuttle could transport over 400 people at at time if the duration of the trip is short as in a few days. My original estimate was a value of 4 to 1 for number of short duration (3+ days) passengers to the longer duration (3+ months) numbers. This was for a Earth to Moon surface passenger service evaluation using a customized ITS). If the number is 200 for long duration this would then give a shuttle to orbit number at 800. To load then this massive 10,000 passenger in-space cruise ship would take just 2 tankers and the one ITS passenger flight to get from Earth to L2 and on Mars it needs no Tankers at all to get to Deimos orbit. That then makes for the transport of 10,000 people from Earth to Mars requiring 12.5 ITS passenger flights and 25 Tankers for every 10,000 people. So at 100 ITS and 200 tankers that would then be in this scenario for one or several "cruise" ships the transport of 80,000 people between planets every synod without much change to the surface infrastructures (Pads required or even LVs designs). This would be vs the use of only ITS and no in-space ISRU propellant sources only 50 ITS transporting just 200 each for a total of 10,000 passengers. This is a 8 to 1 cost reduction in transport costs for this first part of the leg of the journey. The massive cruise ships could have lifetimes measured in decades where the number of persons tranport in just one direction at 10,000 at a time would be over 30 years 150,000. If each such vehicle cost $10B even to build than that is a per person cost of $67K. The operations costs would nearly equal that cost putting the tiket price to travel on these very comfortable vehicles at ~$100K. Now add the surface shuttles cost at $100K at Earth and $30K at Mars the total trip price would be $230K. This also give the prices for going anywhere in Cis-Lunar space even the Lunar surface at about $100K. This then makes going to Mars vs just the Moon is only 2X as much.

By this time the demand for travel may be much more than this level of infrastructure can handle.

If you increase the sizes of the surface to orbit craft then that also would make the size or number of in-space cruise ships grow. Eventually with enough DV from high thrust high ISP engines the departures would no longer be limited to the synods.

If i'm following, you would jam pack an ITS shuttle with people? So are you accounting for the cargo flights required for supplies?

Also you seem to be assuming that a 10000 person ship would scale linearly. I think that's unlikely. 10k people is ~1.5 million pounds just in flesh and bones. Not to get crude and into any IAC-question territory, but you'd need a full sewage plant to deal with all those people, and that equipment alone wouldn't scale linearly.

 Such a large ship might be much slower and require more supplies and room for the passengers, even assuming Nuclear thermal since 1st generation engines are likely to be sub-optimal.

Offline original_mds

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Re: Larger than ITS - The next generation
« Reply #27 on: 07/13/2017 11:25 PM »
If i'm following, you would jam pack an ITS shuttle with people? So are you accounting for the cargo flights required for supplies?

Also you seem to be assuming that a 10000 person ship would scale linearly. I think that's unlikely. 10k people is ~1.5 million pounds just in flesh and bones. Not to get crude and into any IAC-question territory, but you'd need a full sewage plant to deal with all those people, and that equipment alone wouldn't scale linearly.
...

One person's garbage is another person's gold mine.  More biomass and fertilizer to support agriculture at the end point.

On the sewage plant note, are you implying there would be ELCSS economies of scale?

Offline oldAtlas_Eguy

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Re: Larger than ITS - The next generation
« Reply #28 on: 07/13/2017 11:29 PM »
The idea is that even though these vehicles would be very large and complex they would also  be significantly self sufficient in recycling/food production (using on-board farm) such that the supplies to be on loaded are very minimal. Most of the cargo to be loaded would be the individuals personal cargo. This vehicle would in essence be a mobile in-space colony. You are correct in that the key to such huge craft is high ISP/ high thrust systems of which some sort of Nuclear implementation seems to be the answer at this point in time. The advantage of such huge spacecraft is the safety factor that size itself creates.

The negative is the increase in kg per person transported over that of a smaller less "roomy" transport. But the direction that the market will push is for these "luxury liner" transports over that of a "cattle car". Musk already has indicated that the ITS could take more people but would be counterproductive from enticing or getting people to ride in it. For the short 3+ day intervals people will tolerate crowding but not for 3 months.

Offline IRobot

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Re: Larger than ITS - The next generation
« Reply #29 on: 07/14/2017 08:10 AM »
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.
On a typical vertical launch chemical rocket, don't we hit other limits before we ran out of money? What about acoustic and vibration issues with huge rockets? Can we make a pad that survives such a beast?

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Re: Larger than ITS - The next generation
« Reply #30 on: 07/14/2017 12:17 PM »
As far as pad's and proximity to people/structures. I think we will see offshore platforms for the really big rockets.
bob

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Re: Larger than ITS - The next generation
« Reply #31 on: 07/14/2017 12:45 PM »
So instead of talking about a self sufficient city on Mars, you are now talking about a self sufficient space ship that brings people to Mars. Maybe you are overcooking it a bit?

Offline IRobot

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Re: Larger than ITS - The next generation
« Reply #32 on: 07/14/2017 03:13 PM »
As far as pad's and proximity to people/structures. I think we will see offshore platforms for the really big rockets.
I was talking about the pad itself. Can it resist such a big rocket launch?

Online rsdavis9

Re: Larger than ITS - The next generation
« Reply #33 on: 07/14/2017 03:16 PM »
As far as pad's and proximity to people/structures. I think we will see offshore platforms for the really big rockets.
I was talking about the pad itself. Can it resist such a big rocket launch?

There has got to be something that can resist it.
Inconel water cooled!
After all the rocket engine itself is made of something...
bob

Offline original_mds

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Re: Larger than ITS - The next generation
« Reply #34 on: 07/14/2017 03:59 PM »
As far as pad's and proximity to people/structures. I think we will see offshore platforms for the really big rockets.
I was talking about the pad itself. Can it resist such a big rocket launch?

There has got to be something that can resist it.
Inconel water cooled!
After all the rocket engine itself is made of something...

Water launch it.  http://www.astronautix.com/s/seadragon.html

Even if salt corrosion is an issue at sea, there are enough fresh water bodies, both natural and unnatural, that it should be feasible (although I suspect environmentalist concerns about aquatic life will push it towards artificial bodies of water).

Offline DAZ

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Re: Larger than ITS - The next generation
« Reply #35 on: 07/15/2017 12:47 AM »
Would something like this https://www.nextbigfuture.com/2017/07/air-enhanced-nuclear-thermal-rocket-by-x-spacex-engineer.html lead to the next generation or the generation after the next?

Offline Eerie

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Re: Larger than ITS - The next generation
« Reply #36 on: 07/15/2017 01:06 PM »
Would something like this https://www.nextbigfuture.com/2017/07/air-enhanced-nuclear-thermal-rocket-by-x-spacex-engineer.html lead to the next generation or the generation after the next?

I am willing to bet that the first operational nuclear rocket (of any kind) will be built outside of Earth and operate far away from Earth.

Offline Robotbeat

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Re: Larger than ITS - The next generation
« Reply #37 on: 07/15/2017 02:06 PM »
It will be built on Earth but operated only in space.
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Offline Eerie

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Re: Larger than ITS - The next generation
« Reply #38 on: 07/15/2017 03:20 PM »
It will be built on Earth but operated only in space.

Well, this is pure sci-fi speculation, but I just don't see it happen like this. People won't want to test the nuclear rocket on Earth. People won't want to launch nuclear fuel from Earth either. And when you have the capability to mine and produce nuclear fuel in space, you are not that far from being able to build the rocket in space, too. And this is a point where you have an extensive space economy, which we have no idea how it would look like.

None of this is even remotely close, of course, so who knows. Personally, I don't believe SpaceX will land people on Mars before 2030 or having the Internet constellation operate before 2025 (sure would love to be mistaken on both accounts). And both of these things are achievable with chemical rockets.

Offline DAZ

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Re: Larger than ITS - The next generation
« Reply #39 on: 07/15/2017 10:07 PM »
It will be built on Earth but operated only in space.

Well, this is pure sci-fi speculation, but I just don't see it happen like this. People won't want to test the nuclear rocket on Earth. People won't want to launch nuclear fuel from Earth either. And when you have the capability to mine and produce nuclear fuel in space, you are not that far from being able to build the rocket in space, too. And this is a point where you have an extensive space economy, which we have no idea how it would look like.

None of this is even remotely close, of course, so who knows. Personally, I don't believe SpaceX will land people on Mars before 2030 or having the Internet constellation operate before 2025 (sure would love to be mistaken on both accounts). And both of these things are achievable with chemical rockets.

The comments say more about the sorry state of society then as to the technical merits of the concept.  Admittedly, we are approaching the point of total paralysis on just about every conceivable front.  In the 80s, when the anti-nuclear front was hitting its stride, it was being quietly backed by the petroleum industry.  Such backing with the advent of the Internet (see the book twitter and tear gas) is becoming totally unnecessary.  Smaller, less organized, less educated, minimally funded, ad hoc organizations are now swinging way above their apparent size.  It is now taking 2 to 3 times longer and 2 to 3 times more money to accomplish a project that the majority of the public agrees with but because of the influence of these microscopic groups and their tactics, almost nothing is getting accomplished.  A bridge across the waterway that should’ve taken 5 to 10 years is now taking 15 to 30 years.  A simple sewage treatment plant can now take decades to build and is almost unaffordable.  I personally do not believe we will actually reach total paralysis.  Other forces will come into play to counteract the forces attempting to reach paralysis for no other reason than simple day-to-day survival will dictate this.  Exactly how these counter forces will emerge and play out I do not know but I do know history teaches us that these things will eventually change to attempt to get more toward a balance.

On to something more on-topic.

It is been said that once you are in orbit around the earth that you are 50 to 70% of the way to anyplace else in the solar system.  This would be measured not only in energy but also in dollars.  If nuclear rockets are only built and operated in space you are essentially 95% plus of the way to every place in the solar system.  Building these nuclear rockets at that time might be financially impossible/unnecessary due to the upfront costs necessary before you even have your 1st rocket.

The biggest problem with building any kind of nuclear rocket on earth (aside from the anti-nuclear paranoia groups) is the extremely large upfront costs and the generally unacceptable thrust to weight ratios of the most easily built (and low risk, acceptable) Nuclear Thermal Rocket.  The nuclear lightbulb, nuclear saltwater rocket, or the nuclear pulsed detonation (Orion) rocket would probably be more effective but much higher risk/danger that even the general public would not accept.  Their costs would also be many orders of magnitude higher to build even the smallest versions.

The Air Enhanced Nuclear Thermal Rocket would overcome much of this.  Much of the biggest uncertainties have already been built and tested in full-scale working prototypes like NERVA (Nuclear Engine for Rocket Vehicle Application).  The other parts of this system that are non-nuclear could be built and tested in non-nuclear forms.  These would be the turbocharged parts (air enhanced) of the Nuclear Thermal Rocket.  The system as described by John Bucknell would have many times the mass fraction of any other conceived non-nuclear system.  Including even a much bigger ITS type rocket.  If scaled up could achieve payloads to the moon many times larger than the ITS could achieve even with multiple refueling’s in orbit and it could do this from a direct launch on the earth.  This could mean the costs to orbit could be in the tens of dollars per pound on the low side to maybe only a few hundreds of dollars per pound on the high side.  This could make it cheaper to go to orbit than to fly from the United States to Australia.

So once in space, you can come up with all kinds of relatively cheaper more efficient ways to get around but unless you can tackle the problem of getting from the Earth’s surface into orbit you are essentially dealing with the smaller part of the problem.  And that’s what makes this concept so interesting as it takes such a large upfront bite out of the problem.

But that is also the biggest part of the problem as you have to eat the entire elephant all in one bite.  This is been part of the genius that SpaceX and Blue Origin are trying to accomplish.  They have found a way to eat the elephant in smaller bite-size pieces.  For example, SpaceX is not starting with the ITS it started with the Falcon 1.  SpaceX incrementally increased and improved their system and found ways to pay for it as they were going.  The problem with the NTTR (Nuclear thermal turbo rocket) is that you essentially have to do this as in all up project.  You have to find all of the money(s) to build your entire project before you can really start earning money from the project.  Now, this is not normally inconceivable or even an extremely difficult problem.  We do this all the time with things like cars, cell phones, and airplanes.  But normally you have a proven market, as it were, in order to attract financing.  This is why I think this would be a follow-up project for somebody (to possibly leapfrog past) the ITS.  The ITS opens and shows the possible market potentials.  But something like the NTTR is what may follow and be the equivalent of the airplane that eventually ended the era of the liner crossing the Atlantic.

Offline Robotbeat

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Re: Larger than ITS - The next generation
« Reply #40 on: 07/15/2017 11:17 PM »
Fissionable nuclear fuel is less dangerous than the radioisotope fuel we launch on every outer planets mission.

And NASA has recently tested an actual active fission reactor (although of a very simple design different than would be used in flight) with DoE's help in the last few years. This could be used for nuclear electric propulsion, probably for robotic missions.

Nuclear is not prohibited. Just need to use common sense. Doesn't make sense to use for Earth launch (chemical rockets work very well and affordably for launching into LEO), but could be useful once in orbit.
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline DAZ

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Re: Larger than ITS - The next generation
« Reply #41 on: 07/16/2017 01:09 AM »
Fissionable nuclear fuel is less dangerous than the radioisotope fuel we launch on every outer planets mission.

And NASA has recently tested an actual active fission reactor (although of a very simple design different than would be used in flight) with DoE's help in the last few years. This could be used for nuclear electric propulsion, probably for robotic missions.

Nuclear is not prohibited. Just need to use common sense. Doesn't make sense to use for Earth launch (chemical rockets work very well and affordably for launching into LEO), but could be useful once in orbit.

I readily agree with all of your statements except for your last sentence.  Chemical rockets don’t work very well they barely work at all.  Any object they place into orbit ends up costing more than their weight in gold or platinum.  SpaceX and Blue Origin are working very hard to get the price down below the cost of gold.  This is essentially what the whole ITS project is about.  By scaling up to such a large size they hope to bring the cost down.  This is primarily the reason why a smaller ITS doesn’t make economic sense.  Making it half the physical size costs 80 to 90% of the full-size version but you only get 10 to 20% of the economic advantages.  A very much larger ITS (which is what this topic is about) could possibly be even more economically advantageous.  But no matter how big you make the ITS it may not be as economically advantageous as an NTTR that is the same size as the presently envisioned ITS.  In fact, as you scale up both vehicles the NTTR will always come out ahead for the same size vehicles.  Of course, that assumes that the NTTR works as envisioned.

Up thread, it was mentioned about different generations of these vehicles.  It is definitely possible that a much bigger version of the ITS type vehicle could be built.  But it will be approaching the physical limits for just handling such a large vehicle.  And as mentioned up thread some much more advanced concept will need to come along.  The NTTR may be that concept.

Offline Robotbeat

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Re: Larger than ITS - The next generation
« Reply #42 on: 07/16/2017 02:41 AM »
Nah, brah, that's completely off-base. Gold and platinum are on the order of $100,000/kg. Falcon Heavy is on the order of $2000/kg. ITS is hoped to get around $10/kg because the actual cost of chemical propellants is very low. It's not the chemical aspect that makes current space launch expensive, it's the cost of throwing away aerospace hardware every flight.

And you think nuclear thermal would help?

A nuclear thermal rocket would be a very fast way to make your space launch even more expensive and approach the cost you mentioned before.

And you don't even get the benefit of lower propellant costs as nuclear thermal rockets generally use pure hydrogen, which is a LOT more expensive per kilogram ($10 or so) than liquid oxygen ($0.10 per kilogram or even less) which makes up the vast majority of a chemical rocket's propellant and liquified natural gas is also super cheap ($0.25/kg in the US). So even though an NTR would use less propellant, the cost of that propellant would be actually more.

This is only partly why nuclear thermal (especially the high Isp kind) is not a good idea for Earth launch. There are also technical reasons why it's a bad idea.

Might be good for very high delta-V trajectories.
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Offline DAZ

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Re: Larger than ITS - The next generation
« Reply #43 on: 07/16/2017 03:01 PM »
Nah, brah, that's completely off-base. Gold and platinum are on the order of $100,000/kg. Falcon Heavy is on the order of $2000/kg. ITS is hoped to get around $10/kg because the actual cost of chemical propellants is very low. It's not the chemical aspect that makes current space launch expensive, it's the cost of throwing away aerospace hardware every flight.

And you think nuclear thermal would help?

A nuclear thermal rocket would be a very fast way to make your space launch even more expensive and approach the cost you mentioned before.

And you don't even get the benefit of lower propellant costs as nuclear thermal rockets generally use pure hydrogen, which is a LOT more expensive per kilogram ($10 or so) than liquid oxygen ($0.10 per kilogram or even less) which makes up the vast majority of a chemical rocket's propellant and liquified natural gas is also super cheap ($0.25/kg in the US). So even though an NTR would use less propellant, the cost of that propellant would be actually more.

This is only partly why nuclear thermal (especially the high Isp kind) is not a good idea for Earth launch. There are also technical reasons why it's a bad idea.

Might be good for very high delta-V trajectories.

Well, you are partly right and I’m partially wrong.  In the last 10 to 15 years the price of gold (and platinum) has gone totally wacky.  It is gone up multiple hundreds of percent.  Traditionally platinum is more expensive than gold but at this time it’s the other way around.

So at the present price of gold, you are correct.  I was speaking and thinking of the more traditional prices of gold and launch costs from like 10 to 15 years ago.  This incidentally was before SpaceX.  SpaceX has managed to bring the price to launch into orbit to below the traditional costs of gold that I was thinking of.  They are on course with the ITS to get launch costs down to the traditional costs of silver.  The problem is we’re still thinking of these launch costs like the costs of precious metal.  Ideally, we need to get the cost down to below dirt and water like most of our other transportation costs.  We will obviously not reach that idea but the closer we can get the better.  The ITS will probably get down into the hundreds of dollars but is doubtful that this type of system will get all the way down to $10.  A 2nd generation ITS will probably get us very close but still not as low as obviously desirable or that can be obtained.

As you said, the cost of the fuel is not the most important parameter.  It is more how often you can use the vehicle AND how much it can carry at one time for a given size vehicle.  This is why a bigger ITS would be better.  This is also why a theoretical NTTR could be better.  It could carry more for the same size vehicle.  Possibly as much is 2 to 3 times more.  And yes it does use hydrogen (which is more expensive than methane obviously) but it will use more air than hydrogen.  When you take into account the free air as propellant it could be as cheap as methane/LOX.

The NTTR is among the 1st truly new ideas to launch much cheaper into orbit that is come out in decades.  Another has been a laser launch system.  To get past limitations of a chemical system a new system not based on chemical propellants will be needed.  Maybe this will be a laser derived launch system but such a system would require an absolutely huge ground infrastructure be built to compete with something like an ITS at each launch location.  On the other hand, maybe it could be something like an NTTR that would still require a large upfront investment to develop but once developed could be scaled at a much lower cost than a laser launched system.  No matter how you look at it the future looks to be very interesting past the ITS.

Offline DreamyPickle

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Re: Larger than ITS - The next generation
« Reply #44 on: 07/16/2017 09:11 PM »
People seem to assume that the main point of ITS is the scale but I think it's actually the full reusability that is key to reducing costs. Since reusability eats into payload fraction you still need a bigger rocket, but not that much bigger. I suspect Elon's initial presentation was scaled up intentionally so that people wouldn't see it as a threat to projects like SLS.

In order for the project to be successful all it needs is a payload capacity similar to the Falcon Heavy, maybe even smaller. Then you complete with EELV-class launchers by having high flight rates and not throwing away hardware. Key features would be:

* Fully reusable second stage entering on it's side.
* No manual inspection of the heat shield.
* Second stage capable of reentering from higher orbits like GTO or Mars/Moon return.
* Payload bay instead of disposable fairing.
* Orbital refueling for sending large payloads outside LEO.
* Three configurations: cargo, tanker and manned.

There are also benefits to scaling up such as the fact that you don't need to split manned missions into small chunks. But these additional advantages are small.

Offline JamesH65

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Re: Larger than ITS - The next generation
« Reply #45 on: 07/17/2017 12:53 PM »
Nah, brah, that's completely off-base. Gold and platinum are on the order of $100,000/kg. Falcon Heavy is on the order of $2000/kg. ITS is hoped to get around $10/kg because the actual cost of chemical propellants is very low. It's not the chemical aspect that makes current space launch expensive, it's the cost of throwing away aerospace hardware every flight.

And you think nuclear thermal would help?

A nuclear thermal rocket would be a very fast way to make your space launch even more expensive and approach the cost you mentioned before.

And you don't even get the benefit of lower propellant costs as nuclear thermal rockets generally use pure hydrogen, which is a LOT more expensive per kilogram ($10 or so) than liquid oxygen ($0.10 per kilogram or even less) which makes up the vast majority of a chemical rocket's propellant and liquified natural gas is also super cheap ($0.25/kg in the US). So even though an NTR would use less propellant, the cost of that propellant would be actually more.

This is only partly why nuclear thermal (especially the high Isp kind) is not a good idea for Earth launch. There are also technical reasons why it's a bad idea.

Might be good for very high delta-V trajectories.

Gold right now is $39k per kilo. Nowhere near $100k and platinum is about $29k, even further away. I didn't look up any of the other figures.

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Re: Larger than ITS - The next generation
« Reply #46 on: 07/17/2017 01:01 PM »
People seem to assume that the main point of ITS is the scale but I think it's actually the full reusability that is key to reducing costs. Since reusability eats into payload fraction you still need a bigger rocket, but not that much bigger.
...

Exactly. Doubling the size only nets a ~10% reduction in cost per kg to orbit. Doubling the reusability nets a ~50% or more reduction.

I suspect there will eventually be a larger rocket than the 42 Raptor ITS, if only to eke out a few more 10 percents reduction in cost. But that size isn't necessary to start with.

Offline Robotbeat

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Re: Larger than ITS - The next generation
« Reply #47 on: 07/17/2017 01:06 PM »
Nah, brah, that's completely off-base. Gold and platinum are on the order of $100,000/kg. Falcon Heavy is on the order of $2000/kg. ITS is hoped to get around $10/kg because the actual cost of chemical propellants is very low. It's not the chemical aspect that makes current space launch expensive, it's the cost of throwing away aerospace hardware every flight.

And you think nuclear thermal would help?

A nuclear thermal rocket would be a very fast way to make your space launch even more expensive and approach the cost you mentioned before.

And you don't even get the benefit of lower propellant costs as nuclear thermal rockets generally use pure hydrogen, which is a LOT more expensive per kilogram ($10 or so) than liquid oxygen ($0.10 per kilogram or even less) which makes up the vast majority of a chemical rocket's propellant and liquified natural gas is also super cheap ($0.25/kg in the US). So even though an NTR would use less propellant, the cost of that propellant would be actually more.

This is only partly why nuclear thermal (especially the high Isp kind) is not a good idea for Earth launch. There are also technical reasons why it's a bad idea.

Might be good for very high delta-V trajectories.

Gold right now is $39k per kilo. Nowhere near $100k and platinum is about $29k, even further away. I didn't look up any of the other figures.
39k is proportionally much closer to 100k than it is to 2k, but correction noted.
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Online spacenut

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Re: Larger than ITS - The next generation
« Reply #48 on: 07/17/2017 01:50 PM »
If they build "in space" nuclear spacecraft for transfer of goods and people to and from Mars.  There is no danger of nuclear problems on earth on in the atmosphere.  An ITS would be sufficient for transfer of goods to a large space only vehicle.  Then another ITS at Mars for off loading stuff.  Trips to Mars would be greatly reduced in time traveled to and from Mars with a nuke spacecraft.  It could be assembled in LEO from components brought up by ITS.  It would be like a large NautilusX type spacecraft.  Standardized cargo modules could be transferred.  Also, standardized human modules could be transfered without anyone getting out.   

Offline alexterrell

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Re: Larger than ITS - The next generation
« Reply #49 on: 07/19/2017 04:42 PM »
I would build the next generation of space craft on Phobos. Perhaps an inflatable torus could be made on earth, and inflated and out fitted at Phobos, where most of the mass is shielding (radiaton and micro meteorite). I was thinking two torus, of major radius 12m and minor radius 6m, counter rotating, inside a non rotating shield.

They would just shuttle between Phobos and High Earth Orbit. If there's fuel at Phobos (ie water or hydrocarbons) they would fuel up there for the return trip.

These would carry a few hundred people - probably no reason to go for more as economies of scale break down. A 40m diameter ship could still have a heat shield for some form of aerocapture.

Online DnA915

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Re: Larger than ITS - The next generation
« Reply #50 on: 07/19/2017 05:00 PM »
I would build the next generation of space craft on Phobos.

Not really understanding the benefit of this vs assembly in LEO. LEO would have plenty of radiation shielding and micro-medeorites have yet to destroy the ISS. Also, if assembled in LEO, you have way less fuel use during assembly and you can also lift larger parts at a time with smaller rockets.

Tags: ITS SpaceX Mars BFR