Author Topic: Should ITS have a smaller prototype to ease development?  (Read 11324 times)

Offline RotoSequence

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Re: Should ITS have a smaller prototype to ease development?
« Reply #20 on: 02/17/2017 02:05 PM »
The test ITS tank seems to have failed cryo-testing. No details as yet, but it has definitely broken apart.

https://imgur.com/a/bGHR6

"Should they..." is probably only going to get messier based on the number of tanks they go through in testing.

Offline spacenut

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Re: Should ITS have a smaller prototype to ease development?
« Reply #21 on: 02/17/2017 02:22 PM »
Once the Raptor engine is developed.  Then, I have the following questions.

1. Do you have the manufacturing infrastructure to build ITS?
2. Do you have the transportation infrastructure to get ITS to the launch pad?
3. Do you have the launch facilities to handle 20 million or more lbs of thrust?
4. Do you have the landing facilities, either on land or on a ship for such a rocket to land, or is it going to land back at the launch pad?
5. What about sound and vibration of such a launch for nearby areas?  Does such a launch facility need to be remote?, near the equator?, or such?

As you can see, the infrastructure for such a beast is going to cost a lot.  Probably more than one of the ITS rockets itself. 

Things to consider.  Pads 39a and 39b are capable of 12 million lbs thrust now.  Just some modifications needed for something that size or smaller.  Anything larger than 12 m in diameter cannot fit the existing barge, river and inland waterway transportation system in America, and it is extensive already. 

I think it should be no larger than NASA's old Nova rocket of 12 million lbs thrust to use the existing facilities at the Cape.  Maybe scale it down to 50 people and 50 tons to Mars.  Unless Governments chip in and buy's launches for their colonization efforts to not be left out. 

Online envy887

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Re: Should ITS have a smaller prototype to ease development?
« Reply #22 on: 02/17/2017 03:14 PM »
Once the Raptor engine is developed.  Then, I have the following questions.

1. Do you have the manufacturing infrastructure to build ITS?
2. Do you have the transportation infrastructure to get ITS to the launch pad?
3. Do you have the launch facilities to handle 20 million or more lbs of thrust?
4. Do you have the landing facilities, either on land or on a ship for such a rocket to land, or is it going to land back at the launch pad?
5. What about sound and vibration of such a launch for nearby areas?  Does such a launch facility need to be remote?, near the equator?, or such?

As you can see, the infrastructure for such a beast is going to cost a lot.  Probably more than one of the ITS rockets itself. 

Things to consider.  Pads 39a and 39b are capable of 12 million lbs thrust now.  Just some modifications needed for something that size or smaller.  Anything larger than 12 m in diameter cannot fit the existing barge, river and inland waterway transportation system in America, and it is extensive already. 

I think it should be no larger than NASA's old Nova rocket of 12 million lbs thrust to use the existing facilities at the Cape.  Maybe scale it down to 50 people and 50 tons to Mars.  Unless Governments chip in and buy's launches for their colonization efforts to not be left out.

Thrust and diameter aren't really related though. They could build a much shorter 12m booster with say 18 engines, keep the same spaceship, and just reduce the payload to orbit to 125 tonnes (160 tonnes for the tanker). It would just take more launches to refill the ship in orbit. Is that worthwhile? I don't know.

For a minimum viable Mars mission, they don't even need the booster. A 6m diameter version of the spaceship launched on FH could put about 50 tonnes and at least 6 or 8 crew to Mars surface.

Offline Nomadd

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Re: Should ITS have a smaller prototype to ease development?
« Reply #23 on: 02/17/2017 03:21 PM »
The test ITS tank seems to have failed cryo-testing. No details as yet, but it has definitely broken apart.

https://imgur.com/a/bGHR6

"Should they..." is probably only going to get messier based on the number of tanks they go through in testing.
You can't assume there's a problem. Stuff like that is often tested to destruction. Being too strong would point to a problem in their model the same as being too weak.
« Last Edit: 02/17/2017 04:05 PM by Nomadd »

Online envy887

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Re: Should ITS have a smaller prototype to ease development?
« Reply #24 on: 02/17/2017 03:25 PM »
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.

Are you suggesting 1/2 or 2/3 the diameter? Or 1/2 to 2/3 the mass and volume? There's a big difference since mass and volume scale as diameter cubed.

1/2 scale by diameter could be easily launched on Falcon Heavy, while 1/2 scale by mass/volume would dwarf Saturn V.

Offline john smith 19

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Re: Should ITS have a smaller prototype to ease development?
« Reply #25 on: 02/17/2017 04:58 PM »
The test ITS tank seems to have failed cryo-testing. No details as yet, but it has definitely broken apart.

https://imgur.com/a/bGHR6

"Should they..." is probably only going to get messier based on the number of tanks they go through in testing.
Are we sure this really is a picture of an ITS test tank? I'd expected something "stiffer." This looks like rubber. Also very surprised that is what Hawthorne or Texas looks like.

The tanks seem to be a major part of ITS. Big composites, carrying sub cooled cryogens, multiple cycles of launch/transit/entry/ over decades.

This is not a large soda bottle wrapped in string.  :( It's a long way past the SoA, never mind the common SoP.
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Offline RotoSequence

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Re: Should ITS have a smaller prototype to ease development?
« Reply #26 on: 02/17/2017 05:03 PM »
The test ITS tank seems to have failed cryo-testing. No details as yet, but it has definitely broken apart.

https://imgur.com/a/bGHR6

"Should they..." is probably only going to get messier based on the number of tanks they go through in testing.
Are we sure this really is a picture of an ITS test tank? I'd expected something "stiffer." This looks like rubber. Also very surprised that is what Hawthorne or Texas looks like.

The tanks seem to be a major part of ITS. Big composites, carrying sub cooled cryogens, multiple cycles of launch/transit/entry/ over decades.

This is not a large soda bottle wrapped in string.  :( It's a long way past the SoA, never mind the common SoP.

We're sure it's the tank. The ITS test article was built by Janicki Industries of Sedro-Woolley, Washington; the tank never left the Puget Sound region.

Offline wannamoonbase

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Re: Should ITS have a smaller prototype to ease development?
« Reply #27 on: 02/17/2017 05:16 PM »
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.

Completely agree.

ITS, although bold and sexy on a power point slide, is such a huge step its hard to see how a small company with limited resources can develop such a vehicle without decades of time and money.

Developing a raptor powered F9 replacement with a fully reuseable second stage would provide many learning opportunities and allow flight history for Raptor.  Throw more Raptors underneath a SFR than needed, give it lots of margin for commercial payloads and work on reusability and maybe even the very bold plan for landing on a launch mount. 

I think ITS is a fantasy and won't see the light of day for many years, if ever.
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Offline Oli

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Re: Should ITS have a smaller prototype to ease development?
« Reply #28 on: 02/17/2017 06:13 PM »
A typical mid-L/D Mars lander with 40mt payload has the dimensions 30m x 10m.

ITS has the dimensions 50m x 12m. Only ~1/3 of that volume is available for the payload, so it's questionable whether SpaceX can land much more volume on Mars than a typical 40mt lander from NASA. DRM 5.0 needs 2 40mt landers.

Making ITS smaller in terms of volume might not be an option if SpaceX plans to sells Mars flights to NASA.
« Last Edit: 02/17/2017 06:14 PM by Oli »

Offline philw1776

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Re: Should ITS have a smaller prototype to ease development?
« Reply #29 on: 02/17/2017 06:27 PM »
The ITS is built to the wrong scale, it's a fantasy, etc. crowd simply can't get their heads around the proven fact, time and again, that Musk is a paradigm breaking innovator.  OK, he's not good meeting his schedules.
I have an MBA in finance from a good B school plus my engineering degree.  I was aghast at Musk's business plan to merge Solar City with Tesla and I feared disaster.  But if I knew what I was doing I would have bought Tesla stock just a few months ago and would now have a tidy sum as the stock instead of tanking has skyrocketed.  I was with the financial expert crowd underestimating the guy. But I digress.

On topic, the ITS will be tested as Musk outlined in his Powerpoint show.  He can't afford the dollars and more importantly to him personally the TIME wasted in mini-ITS whatevers that do not lead directly to his goal. Per his presentation, instead of building & testing the 42 engine booster first, he moves right to the 2nd stage.  Here's one scalable, incremental, direct pathway SX engineers could follow.

Build the simpler to outfit 90 tonne ITS stage 2 Tanker version first.
Equip with just the 3 SL Raptors to flight test them and the stage 2 airframe, TPS & avionics
~700 tonnes of propellant and the 90 tonne craft can get up to ~5 Km/sec (rocket equation)
Fly & recover, testing heat shield and airframe at lower stress and qualifying the avionics

Next build initial booster stage with ~ half the engines, but full sized airframe & tanks (no extra tooling costs)
Maybe equip 2nd stage with some Rvacs, or do so later after 1st flights
Then
Execute orbital tests & re-entry with minimal "payload" to LEO
Proves out landing technique for booster stage & more Raptor engine flight experience

and so on...

I'm convinced SpaceX's engineers will come up with a more clever, lower cost approach than this, an approach that does not divert them from their goal and require non-essential R&D time and money for spacecraft not utilized in the Mars settlement core mission.

« Last Edit: 02/17/2017 06:28 PM by philw1776 »
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Offline MikeAtkinson

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Re: Should ITS have a smaller prototype to ease development?
« Reply #30 on: 02/17/2017 06:29 PM »
A typical mid-L/D Mars lander with 40mt payload has the dimensions 30m x 10m.

ITS has the dimensions 50m x 12m. Only ~1/3 of that volume is available for the payload, so it's questionable whether SpaceX can land much more volume on Mars than a typical 40mt lander from NASA. DRM 5.0 needs 2 40mt landers.

Making ITS smaller in terms of volume might not be an option if SpaceX plans to sells Mars flights to NASA.

So about 1,800 m3 of volume for payload, at CRS payload densities that is over 200 tonnes, SpaceX say that they will land 100 tonnes (maybe more later).

Offline guckyfan

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Re: Should ITS have a smaller prototype to ease development?
« Reply #31 on: 02/17/2017 06:54 PM »
Build the simpler to outfit 90 tonne ITS stage 2 Tanker version first.
Equip with just the 3 SL Raptors to flight test them and the stage 2 airframe, TPS & avionics
~700 tonnes of propellant and the 90 tonne craft can get up to ~5 Km/sec (rocket equation)
Fly & recover, testing heat shield and airframe at lower stress and qualifying the avionics

I like that approach, a lot. As far as I remember, a completely new suggestion that makes a lot of sense to me. But I am not an expert.

Online envy887

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Re: Should ITS have a smaller prototype to ease development?
« Reply #32 on: 02/17/2017 07:37 PM »
A typical mid-L/D Mars lander with 40mt payload has the dimensions 30m x 10m.

ITS has the dimensions 50m x 12m. Only ~1/3 of that volume is available for the payload, so it's questionable whether SpaceX can land much more volume on Mars than a typical 40mt lander from NASA. DRM 5.0 needs 2 40mt landers.

Making ITS smaller in terms of volume might not be an option if SpaceX plans to sells Mars flights to NASA.

So about 1,800 m3 of volume for payload, at CRS payload densities that is over 200 tonnes, SpaceX say that they will land 100 tonnes (maybe more later).
The IAC presentation says up to 450 tonnes landed. Nominally 300.

Offline MikeAtkinson

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Re: Should ITS have a smaller prototype to ease development?
« Reply #33 on: 02/17/2017 08:10 PM »
A typical mid-L/D Mars lander with 40mt payload has the dimensions 30m x 10m.

ITS has the dimensions 50m x 12m. Only ~1/3 of that volume is available for the payload, so it's questionable whether SpaceX can land much more volume on Mars than a typical 40mt lander from NASA. DRM 5.0 needs 2 40mt landers.

Making ITS smaller in terms of volume might not be an option if SpaceX plans to sells Mars flights to NASA.

Yes, my mistake. Still anything over about 200 tonnes would require a greater density than CRS cargo to the ISS. Not impossible for bulk products (metals/chemicals, dry/frozen foodstuff, etc.)

So about 1,800 m3 of volume for payload, at CRS payload densities that is over 200 tonnes, SpaceX say that they will land 100 tonnes (maybe more later).
The IAC presentation says up to 450 tonnes landed. Nominally 300.

Online Rei

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Re: Should ITS have a smaller prototype to ease development?
« Reply #34 on: 02/18/2017 01:41 AM »
The test ITS tank seems to have failed cryo-testing. No details as yet, but it has definitely broken apart.

https://imgur.com/a/bGHR6

"Should they..." is probably only going to get messier based on the number of tanks they go through in testing.

And they're only doing the most basic, inert testing right now...

Composites are tough.  Composites with cryogenics, incredibly tough.  I hope they can pull it off.  I really don't know if they can.

I don't recall, is the ultimate plan to have the tank lined or unlined?  At least with lined you can get rid of a lot of the oxygen/CF reaction concerns.

Online Rei

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Re: Should ITS have a smaller prototype to ease development?
« Reply #35 on: 02/18/2017 01:44 AM »
A typical mid-L/D Mars lander with 40mt payload has the dimensions 30m x 10m.

ITS has the dimensions 50m x 12m. Only ~1/3 of that volume is available for the payload, so it's questionable whether SpaceX can land much more volume on Mars than a typical 40mt lander from NASA. DRM 5.0 needs 2 40mt landers.

Making ITS smaller in terms of volume might not be an option if SpaceX plans to sells Mars flights to NASA.

So about 1,800 m3 of volume for payload, at CRS payload densities that is over 200 tonnes, SpaceX say that they will land 100 tonnes (maybe more later).
The IAC presentation says up to 450 tonnes landed. Nominally 300.

Yeah, they're looking at non-Hohmann transfers.  Which actually is pretty reasonable when you start digging down into the numbers.  You get a lot of trip shortening with that first extra bit of delta-V (it's a case of diminishing returns after that).  And from an economics perspective, they have a lot of sunk costs in that ship doing nothing when it's just drifting through space.  The sooner they can get it back to earth and relaunch, the better their economics work out to be.  So it's worth sacrificing cargo.

Online envy887

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Re: Should ITS have a smaller prototype to ease development?
« Reply #36 on: 02/18/2017 02:13 AM »
A typical mid-L/D Mars lander with 40mt payload has the dimensions 30m x 10m.

ITS has the dimensions 50m x 12m. Only ~1/3 of that volume is available for the payload, so it's questionable whether SpaceX can land much more volume on Mars than a typical 40mt lander from NASA. DRM 5.0 needs 2 40mt landers.

Making ITS smaller in terms of volume might not be an option if SpaceX plans to sells Mars flights to NASA.

So about 1,800 m3 of volume for payload, at CRS payload densities that is over 200 tonnes, SpaceX say that they will land 100 tonnes (maybe more later).
The IAC presentation says up to 450 tonnes landed. Nominally 300.

Yeah, they're looking at non-Hohmann transfers.  Which actually is pretty reasonable when you start digging down into the numbers.  You get a lot of trip shortening with that first extra bit of delta-V (it's a case of diminishing returns after that).  And from an economics perspective, they have a lot of sunk costs in that ship doing nothing when it's just drifting through space.  The sooner they can get it back to earth and relaunch, the better their economics work out to be.  So it's worth sacrificing cargo.

The transfer windows don't really work out that way. If you get to Mars faster, you just end up having to wait longer to launch back to Earth, and you get back at the same time. Unless you're flying a opposition class mission with a 30-day stay, a return inside the orbit of Venus, and a 15-20 km/s reentry, you always get back too late for the next launch opportunity.

Even a opposition class mission would likely allow ITS to carry 350 to 400 tonnes of cargo, though it's return cargo would likely be limited to less than 50 tonnes.

Offline redliox

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Re: Should ITS have a smaller prototype to ease development?
« Reply #37 on: 02/18/2017 04:51 AM »
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.

Are you suggesting 1/2 or 2/3 the diameter? Or 1/2 to 2/3 the mass and volume? There's a big difference since mass and volume scale as diameter cubed.

1/2 scale by diameter could be easily launched on Falcon Heavy, while 1/2 scale by mass/volume would dwarf Saturn V.

Specifically mass since that influences a rocket's ability to escape Earth.

Going by some of the statistics the ship and tanker have, the crew ship dry mass is supposed to be 150 (metric I presume) tons and the tanker 90; the difference between the 2 no doubt because of crew needs.  Propellant for each adds 1950 and 2500 tons respectively.  A fully fueled crew spaceship would thus weigh 2100 mt.

Compared to Zubrin's Mars Direct vehicles this is a huge difference; nearly 100 times more massive than the Hab lander's mass of 25mt.  Elon Musk is obviously planning big to accommodate future economics, but even if scaled down this means a smaller version of the ITS ship would be a great asset.  A half-scale prototype would still be 75 mt, or otherwise 3 times the size of Zubrin's vehicles and even larger than some of NASA's plans (which I think I saw as high as 60 mt).  While no cruise ship, this would be more than sufficient for NASA or anyone's needs.  Before I forget, including fuel (also reduced by 50% resulting in 975 mt of methalox) the total mass of a mini-Interplanetary Spaceship comes to 1050 mt.

Doing a few delta-v calculations assuming 2 things:
1) Specific Impulse of 360ISP for methalox
2) Use of a full scale ITS booster while flying a 1/2 scale spaceship atop it

An ITS booster (again at FULL scale and going by SpaceX figures) is 275 mt dry mass with 6700 mt of propellant.  Coupled with 1050 of a mini-ship, the whole thing at launch would be 8025 mt.  The booster would give the ship about 6.3 km/s of delta-v, assuming a full burn and no recovery.  The mini-ship would then have to burn roughly 670 mt of its own fuel to enter solid LEO (which requires better than 9 km/s to hit).

In LEO without any refueling, this mini-ship would weigh a total of 380 mt with 305 of methalox still available.  Assuming 4 km/s to reach and manage a Hohmann transfer orbit, 260 mt would be burned to reach Mars.  The remaining 45 mt of methalox would grant a further 1.6 km/s.  While 1.6 km/s is meager, this would be sufficient to split between orbital capture and landing with aerobraking between the 2.

Someone double-check my figures to be certain; however I think for a smaller mission this could suffice to get the ship to Mars even without the tanker Elon wants in the full version.
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Offline OneSpeed

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Re: Should ITS have a smaller prototype to ease development?
« Reply #38 on: 02/18/2017 10:59 AM »
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.

Are you suggesting 1/2 or 2/3 the diameter? Or 1/2 to 2/3 the mass and volume? There's a big difference since mass and volume scale as diameter cubed.

1/2 scale by diameter could be easily launched on Falcon Heavy, while 1/2 scale by mass/volume would dwarf Saturn V.

...

Someone double-check my figures to be certain; however I think for a smaller mission this could suffice to get the ship to Mars even without the tanker Elon wants in the full version.

Not suggesting there is anything wrong with your ΔV calculations, but when you talk about a scale model, that refers to a linear dimension, not to mass. What you are describing is roughly a 0.8 scale model of the ITS.

Offline Lar

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Re: Should ITS have a smaller prototype to ease development?
« Reply #39 on: 02/18/2017 11:11 AM »
Reasons to close this thread
- So much concern trolling
- So little that's not been said in other threads.
- So many incorrect statements
- So much lack of understanding of Musk's plans

Reasons to leave this thread open
- It's a place to send the concern trolls so we can keep them out of other threads.

That one's winning, so far.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY