Should Super Heavy (BFR/ITS) have a smaller prototype to ease development?

[redliox]

Looking over the ITS plans and comparing them to either Mars Direct or SLS...it's on the verge of insanely ambitious.  Bear in mind I'm not saying it's impossible (indeed I pray it succeeds, moreso ahead of the SLS/Orion mess), but the SLS, STS, and Saturn V all suffered growing pains in their development.  Would it be easier to build a smaller version of ITS first beforehand or not?  Say something either at 1/2 or 2/3 scaled compared to the full ITS.

[Steve G]

When I was a kid watching Apollo 11, and 2001: A Space Odyssey, if you asked me back then that in 50 years would Musk's ITS was too large, I would have expected that kind of scale. But I also expected that there would have been moon bases with commercial flights flying there, and man would be on Mars before the end of the 20th century. So back then, looking 50 years ahead, this would make perfect sense. Somehow, we lost the future that looked so promising back then. What ITS does is give us back the future.

HOWEVER

The scale is ludicrous, and there is no business case for it. I understand Musk's rational, to have the economics to go to Mars for less than a quarter million dollars per passenger. But let's put our business hats on. He should build a 1/4 scale lander, focus on orbital space tourism, lunar tourism and even a true space shuttle for space deliveries. The rocket is too large for just about any commercial or government client. Maintain a cash flow while perfecting the technology and let the systems mature. Sure, there will be duplicate costs by building two systems instead of one, but a two pronged approach won't bankrupt him. It reminds me of Howard Hughes' Spruce Goose. Build it and he can only afford one flight with it.

[MATTBLAK]

He's trying to develop the 747 of Mars transports - when nobody has even done a DC-3 for Mars yet. I love, love the overall concept - but I think the vehicle suffers from 'Giantism'. He wants to build a launcher with more than three point five times the thrust of a Saturn V, with 42 engines in the first stage!! To take 100 persons to Mars; to a place where the infrastructure to support them is a distant dream and probably harder to implement and imagine than the I.T.S. itself at this point.

If Elon was building a reusable launcher and Spacecraft with 'only' approximately twice the thrust of a Saturn V, to send crews of about 12 Astronauts to Mars in what amounted to a smaller moldline replica of the ITS - that I feel would still be an enormous technical and logistical challenge, in of itself. With such a vehicle, a decent sized Martian Outpost could be established with this hardware set, including a Freighter version of the 'Mini-ITS'. If this vehicle works well, then it could be scaled up to match Elon's full-sized ambitions. Sort of how Boeing did the 707 first, then super-sized it's ambitions by developing the 747.

But: I'm aware that Musk is trying to cut to the chase and not split the time and relatively scarce money on two separate development projects. Perhaps he's already taken into account that if he runs into major headaches during the ITS development; he could probably downsize the crew size ambition from 100 to 'only' 50 - which would still itself be a dazzling achievement.

[GWH]

I think yes, if it can be made as a reusable upper stage for F9/FH, with the ability to land payloads on planetary surfaces. Provide a commercial lunar or martian lander.

As it sits right now SpaceX hasn't achieved rapid reuse of booster stages, rapid reuse from orbital velocity is going to be a very large challenge if the shuttle is to be used as an example.   What are the challenges there, and the unknowns?  The ITS is very much dependent on this rapid reusability and would be a very steep learning curve depending on the development of a lot of infrastructure to get to the first orbital test.
If they can start testing and refining on a scaled down single raptor upperstage sooner it could prevent a lot of stumbling after.

If the upper stages are reused from previous commercial launches they could be sent on a one way trip to Mars/Moon while maintaining the cost benefits of reuse.

I think a single raptor refuelable upper stage and cargo landers coupled with commercial habitats and Dragon as a crew lander could be quite capable of putting boots on Mars.

[Lar]

no

[MATTBLAK]

What I think Lar meant to say was...

[Lar]

yes

i had surgery today and i came out of the haze to say this.

There have been a lot of threads about this. the conclusion always is that it is a waste of time and money, and actually slows things down. OP should do their homework and link to all of them.  Why is this time different?

[Bynaus]

He's trying to develop the 747 of Mars transports - when nobody has even done a DC-3 for Mars yet.

I actually think that a 100 years from now, the ITS, if it is indeed eventually built and flown, will be seen as a spaceflight analogue to the DC-2/DC-3, rather than the 747 (and the "Heart of Gold" will be more like the DC-1). A very-ambitious-before-built, pushing-the-envelope, early-in-its-era machine that establishes the market it was built to serve. Yes, the DC-3 never had 100 passengers, but passenger numbers are beside the point: what you need is a spacecraft which is large enough to plausibly reach the effects you want - full reusability and big enough so it can carry a useful fuel-production facility to Mars. That it can carry 100 pax if crammed full is just a bonus. The 747s of spaceflight will come much later, once flying between Earth and Mars has become commonplace.

Now, to the main point: I can imagine that there will be more scaled test articles along the way (like the scaled Raptor parts and the shortened tank we have seen), but development of the Heart of Gold will always aim for the real thing. There's simply no point in building an extremely expensive reusable upper stage/interplanetary spaceship/Mars lander/Mars return stage which... cannot make it to Mars and back.

[dror]

It could only be a waste of money if they ever going to build a full size ITS, which I don't think they will.
Since "100 seats, 100 ton" is arbitrary, I see no reason for them to persue the ITS as was presented.
"20 seats 20 tons" makes more sense to me.
I hope they will develope a 9 Raptor SFR with 1 Raptor SFS to replace FH and do all BEO
For F9 I hope they develope the mini raptor reusable 2nd stage sooner rather than later.

[redliox]

It seems an interesting split between going full-bore with ITS or something smaller. It gives me further fuel for thought....

The true strength of ITS comes from the booster half, whereas the Interplanetary Spaceship requies help via refueling. If something had to be prioritized, it should be the booster, i.e. the workhorse of this pair.  What if the booster was built at full scale but the ship at half? Assuming a Mars Direct style basis and a crew of 4, not 100 or 50, and perhaps even expending the booster during these prototype flights (ala the early tests of Falcon 9 landings) wouldn't that produce some productive flights without derailing Musk's plans?

[Semmel]

I think in this thread, as in past threads on the topic, people think a smaller BFR/ITS would be cheaper that the full size one. I respectfully disagree.

The bulk of the money for this launcher at moment is development and infrastructure up front. That includes but is not limited to:
* Design of BFR
* Design of ITS
* Carbon composite tank development
* Analysis and prove of the design
* Refueling capability in orbit
* EDL design development
* Development of re-usability strategy
* Fuel storage in space (on the way to mars and back)
* Fuel production strategy, design and prototype on Mars
* Fuel production plant on Mars
* Engine development
* BFR/ITS Testing and integration
* Tools to manufacture
* BFR/ITS production
* BFR/ITS operation
* Launch pad and GSE design
* Launch pad and GSE construction
* Astronaut training
* Human rating of the vehicle
* Software on all fronts
(And I probably forgot many)

The things that might save money using a smaller vehicle
* Fuel production plant on Mars
* BFR/ITS Testing and integration
* Tools to manufacture
* BFR/ITS production
* BFR/ITS operation
* Launch pad and GSE construction

And I dont think that the savings on these items scale linearly with capability. I think its much less. And that neglects the other items completely.

All in all, I think development, construction and operation of any vehicle that can go to mars and back is only very weakly dependent on its capability in terms of people/cargo.  And once it flies and you are actually putting cargo on Mars, its far far cheaper to have one large vehicle rather than multiple smaller ones. I would even go as far as claiming that one 100T cargo ITS is cheaper after the first flight than 5 20T cargo ITSes.

If you include everything, I think to minimize the cost of BFR/ITS is to go as big as physically possible that does not bankrupt the company.

I think the proper way of approaching the size question of ITS is to argue why its not even bigger.

[KelvinZero]

My layman's guess is that shortening the upper stage (which I understand they are developing first) would be sort of like shortening the space shuttle: a totally different vehicle.

I did wonder about shortening the first stage and having less engines. To what extent would that be a whole new vehicle? I suppose you could also not shorten it, but fill it less and have less engines. The saving would be .. less engines. That is a lot of engines on that thing.

There is also that test vehicle. Is it going to be more like the tanker version of the upper stage? From memory that is like 90 tons dry mass instead of 150 and I assume a lot less parts. That is something.

[R7]

Just build it as planned and lets see what happens then.
Will it be ridiculuously big for the existing launch market? Yes.
Will it be ridiculuously expensive for the existing launch market? Not necessarily if the reusability pans out.
Will smaller vehicle enable the potentially game-changing Mars exodus opening a new market? No.
_{(At least SLS will become so silly NASA is forced to axe it and concentrate on something more sensible, like designing colonization infrastructure.)}

[FutureSpaceTourist]

Here are a couple of threads that have previously discussed smaller BFRs/ITSs:

Re: Speculation: SFR (mini-BFR) as fully reusable Falcon Heavy replacement
http://forum.nasaspaceflight.com/index.php?topic=36508.0

Re: Full diameter shortened ITS as FH replacement?
http://forum.nasaspaceflight.com/index.php?topic=41357.0

I imagine it's come up in the various discussion threads too (but I don't have the time to track them!)

[uhuznaa]

Both Musk and many people here think it would be wasted effort. I think it could have the advantage of building something to use as a fully reusable workhorse launcher (replacing the F9), especially since SpaceX is developing a scaled down Raptor engine contracted by USAF anyway.

Then use more generous mass fractions to ease development of both stages -- you don't need 100t payload to LEO for any commercial payloads anyway and if you can go aluminum instead of composites things get much faster and easier. Then you could get something that you can debug and optimize on a smaller scale, while earning money with it.

Personally I think that the span between what SpaceX is actually flying now on one end and ITS on the other end is so big that nobody really is convinced enough to give them the money to go there. And without money SpaceX will never get around to actually build ITS. They need to add a rung more to that ladder so they can climb it.

From a purely engineering point of view ITS is a bit much to eat with one bite. Starting smaller and with more elbow room in terms of mass fractions would make this much more doable.

[IRobot]

Personally I think that the span between what SpaceX is actually flying now on one end and ITS on the other end is so big that nobody really is convinced enough to give them the money to go there. And without money SpaceX will never get around to actually build ITS.

Musk could personally finance the first few missions. And with a lot of hype, I'm sure he could make an IPO of SpaceX or a specialized Mars colonization company.

I think he is betting on some of the following sources of money:

- SpaceX
- own money
- NASA
- LEO tourism, ex: Bigelow
- asteroid mining companies

If he proves the capability (with SpaceX and own money), he is hoping that some of those potential customers jump in.

[DOCinCT]

... and if you can go aluminum instead of composites things get much faster and easier...

Is there any research or studies out there that support the idea that building the LH2 tank for SLS was any faster or substantially less expensive than building the LOX test article out of carbon composite?

[su27k]

smaller prototype

Depends on what you mean by this. It seems most people read this as a mature subscale system that is ready to take human to Mars, which is strange since in my mind a smaller prototype is something like DC-X or X-33, a test vehicle that is never meant for real missions.

I think it's entirely possible they'll do small prototype vehicle which is used for pathfinding and testing, after all the Raptor being tested is already subscale, so in a sense they're already doing it. It is also possible they'll have to abandon the original ITS size and scale it back to say 1/3 of the original size, due to some constraints (funding, launch site availability, etc). What they will not do, in my opinion, is to develop a subscale fully mature ITS then goes on to develop a full scale ITS, it just serves no purpose and waste a lot of time and resources.

[uhuznaa]

smaller prototype

Depends on what you mean by this. It seems most people read this as a mature subscale system that is ready to take human to Mars, which is strange since in my mind a smaller prototype is something like DC-X or X-33, a test vehicle that is never meant for real missions.

I think it's entirely possible they'll do small prototype vehicle which is used for pathfinding and testing, after all the Raptor being tested is already subscale, so in a sense they're already doing it. It is also possible they'll have to abandon the original ITS size and scale it back to say 1/3 of the original size, due to some constraints (funding, launch site availability, etc). What they will not do, in my opinion, is to develop a subscale fully mature ITS then goes on to develop a full scale ITS, it just serves no purpose and waste a lot of time and resources.

Of course a scaled down ITS with more lenient mass fractions wouldn't be an "Interplanetary Transport System" anymore. It would just be a fully reusable two stage orbital launcher. Useful for earning money by selling launches and also by launching the 4000 satellites SpaceX is talking about. And for learning how to build and operate such a thing before going all the way and building a Mars craft.

And at the moment I just can't see ITS ever happening. Musk talked about $5m that SpaceX will invest in development each year. This is basically nothing. Without a few billions from others ITS will never happen. And without showing others that the concept is valid nobody will invest that kind of money.

[uhuznaa]

... and if you can go aluminum instead of composites things get much faster and easier...

Is there any research or studies out there that support the idea that building the LH2 tank for SLS was any faster or substantially less expensive than building the LOX test article out of carbon composite?

Using the money spent on SLS as a yardstick is pointless. Fact is that SpaceX is already using aluminum for the Falcon 9 first and second stages all the time and scaling this up for a smaller ITS-like launcher would be much cheaper and easier than using composites, especially for a reusable craft that goes through lots of hard thermal cycles and mechanical loads. The fact that they had a failing small composite tank ruin a rocket and payload and launchpad a few months ago doesn't exactly instill confidence here.

And it doesn't matter anyway what you or me believe: SpaceX will need to convince people to bet billions of dollars on them being able to do this. Right now this is very hard to do. Staying in their comfort-zone as far as possible and proving the concept would be the way to go and if they get an orbital workhorse by doing this, all the better.