Author Topic: IAC 2017 -- ITS v0.2  (Read 49542 times)

Online Robotbeat

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Re: IAC 2017 -- ITS v0.2
« Reply #160 on: 09/12/2017 10:40 PM »
Okay, but that's just engineering. Nothing fundamentally challenging about that part of it.
In exactly the same way that FH was just hooking 3 F9's together?
Whole point of that clustering is it WOULDN'T require even a concerted reengineering effort of the components. They were wrong. With ITS, that will be needed no matter what and there's no fooling themselves about it so they can plan from the start.

ITS WILL have major challenges. They're not going to necessarily be mundane and easily foreseeable ones like that.

Let's try to ask insightful questions, like how they hope to deal with center of mass during entry, etc.
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Offline Pipcard

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Re: IAC 2017 -- ITS v0.2
« Reply #161 on: 09/12/2017 10:56 PM »
Okay, but that's just engineering. Nothing fundamentally challenging about that part of it.
In exactly the same way that FH was just hooking 3 F9's together?
Whole point of that clustering is it WOULDN'T require even a concerted reengineering effort of the components. They were wrong. With ITS, that will be needed no matter what and there's no fooling themselves about it so they can plan from the start.

ITS WILL have major challenges. They're not going to necessarily be mundane and easily foreseeable ones like that.

Let's try to ask insightful questions, like how they hope to deal with center of mass during entry, etc.
Oh yeah, that. Because I've always wondered why the crew/cargo section isn't in the middle of the spaceship to make the center of mass more manageable (especially if they aren't going to go with an launch escape system). And I wonder how they will address concerns about the lack of an LES. I'm not sure how ready people are to accept the idea that an interplanetary spaceship will be just as reliable as a passenger airliner, or alternatively, the idea that the risks should just be handwaved away.
« Last Edit: 09/12/2017 11:23 PM by Pipcard »

Offline RonM

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Re: IAC 2017 -- ITS v0.2
« Reply #162 on: 09/13/2017 03:16 AM »
Lack of LAS might be an issue with the original ITS design carrying 100 people on colonization flights, but it doesn't have to be an issue for ITSy conducting exploration missions. With a small crew they can launch later in a Dragon.

Offline TomH

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Re: IAC 2017 -- ITS v0.2
« Reply #163 on: 09/13/2017 04:09 AM »
Lack of LAS might be an issue with the original ITS design carrying 100 people on colonization flights, but it doesn't have to be an issue for ITSy conducting exploration missions. With a small crew they can launch later in a Dragon.

And this begs the question, how useful is a LAS when departing the surface of Mars?

Online Robotbeat

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Re: IAC 2017 -- ITS v0.2
« Reply #164 on: 09/13/2017 05:35 AM »
Lack of LAS might be an issue with the original ITS design carrying 100 people on colonization flights, but it doesn't have to be an issue for ITSy conducting exploration missions. With a small crew they can launch later in a Dragon.

And this begs the question, how useful is a LAS when departing the surface of Mars?
Very useful for the vast majority of trips. We ain't doing just flags and footprints, there WILL be substantial infrastructure on Mars including a few long range rovers.
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Online john smith 19

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Re: IAC 2017 -- ITS v0.2
« Reply #165 on: 09/13/2017 10:36 AM »
One short-ish cut available to an over sized single body booster, is to just not sharpen the virtual pencil too much.  Start with the least amount of new technology (alloy not carbon) and make it heavier than optimum.

Build, fly, analyze, repeat.
That's certainly the conservative option and leverages all their knowledge base to date.

It's a question of what that strategy gives you.

I think the F9 is close to maxing out the capacity on their FSW rigs. Maybe another 10cm? That LOX tank demo was huge. So you could get maybe a test vehicle that's a bit bigger than an F9, but what would that teach you about building your ultimate end-game vehicle?

They've got a "baby Raptor" already. An obvious option would be to build their vehicle around that, so they've the whole suite of materials, propellants and engine cycle tested out before they go full scale. 
Pretty sure no one will be proposing a three core vehicle at the IAC
Never say "never" in this business.  :)

But it does seem a pretty unlikely option.
Whole point of that clustering is it WOULDN'T require even a concerted reengineering effort of the components. They were wrong. With ITS, that will be needed no matter what and there's no fooling themselves about it so they can plan from the start.

ITS WILL have major challenges. They're not going to necessarily be mundane and easily foreseeable ones like that.
Except that IRL they were not foreseen, were they?  :( Hence one (of several) of the reasons for the somewhat protracted FH date. For a successful launch you have to start by getting away from the pad in one piece.  :(
Quote from: Robotbeat
Let's try to ask insightful questions, like how they hope to deal with center of mass during entry, etc.
That's a tough one without wings.

 People keep pointing to those 2 tanks-within-tanks on the cutaway. Given that both propellants are cryogens the tanks can be pressurized by propellant heating so they are likely to be for the landing. Of course that still might not give the necessary control authority to make the problem manageable.

I'd wait for Musk to do his presentation. That might make most questions unnecessary.
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Re: IAC 2017 -- ITS v0.2
« Reply #166 on: 09/13/2017 11:50 AM »
We've been imagining on related threads a vehicle - first stage: booster and second stage: spacecraft - up to 9 meters in diameter. Such a launcher would be fully reusable with a big cluster of 'subscale Version 1.0' Raptors in the first stage (not 42x biguns) and a small cluster of subscale Raptors in the spacecraft. A roughly two-thirds scale ITS to prove out the basic concept without going straight to the behemoth with the 42x Raptors. We can assume a targeted liftoff thrust of probably no more than 11 or 12 million pounds; to keep within the Pad 39A limits.

We'll have to see what happens in due course. It will be very interesting - a vehicle that could have great utility and capability. We'll just have to be patient...
« Last Edit: 09/13/2017 01:32 PM by MATTBLAK »
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Online M.E.T.

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Re: IAC 2017 -- ITS v0.2
« Reply #167 on: 09/13/2017 01:02 PM »
We've been imagining on related threads a vehicle - first stage: booster and second stage: spacecraft - up to 9 meters in diameter. Such a launcher would be fully reusable with a big cluster of 'subscale Version 1.0' Raptors in the first stage (not 42x biguns) and a small cluster of subscale Raptors in the spacecraft. A roughly two-thirds scale ITS to prove out the basic concept without going straight to the gargantuan 42-engine behemoth with the 42 Raptors. We can assume a targeted liftoff thrust of probably no more than 11 or 12 million pounds; to keep within the Pad 39A limits.

We'll have to see what happens in due course. It will be very interesting - a vehicle that could have great utility and capability. We'll just have to be patient...

Still don't understand the value of using 3 times as many subscale Raptors compared to the same vehicle using 3 times fewer full scale Raptors. Surely it just adds 3 times as much risk.

Online AncientU

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Re: IAC 2017 -- ITS v0.2
« Reply #168 on: 09/13/2017 01:05 PM »
IMO, the larger Raptor engine will be on the stand this year (next 12 months) and be used to power the booster.  If the full spaceship is built for the 9m, which I think likely, it may use the smaller version, as may a conventional upper stage use maybe 3 of these engines.  12Mlbs lift-off thrust is almost a given...

I think the planned use and lifetime of this ITSy will be most interesting aspect of IAC 2017 -- when will it be built and when will it head for Mars. 

I don't see this as merely a prototyping effort for the BFR.  It is the BFR for next 10+ years -- the World's BFR.
« Last Edit: 09/13/2017 01:07 PM by AncientU »
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Online M.E.T.

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Re: IAC 2017 -- ITS v0.2
« Reply #169 on: 09/13/2017 01:10 PM »
IMO, the larger Raptor engine will be on the stand this year (next 12 months) and be used to power the booster.  If the full spaceship is built for the 9m, which I think likely, it may use the smaller version, as may a conventional upper stage use maybe 3 of these engines.  12Mlbs lift-off thrust is almost a given...

I think the planned use and lifetime of this ITSy will be most interesting aspect of IAC 2017 -- when will it be built and when will it head for Mars. 

I don't see this as merely a prototyping effort for the BFR.  It is the BFR for next 10+ years -- the World's BFR.

Just to clarify, do you mean the original ITS Spaceship being built as the 2nd stage for the mini-ITS first stage? Meaning that only the first stage is downscaled to 9m? How would that work with the factory constraints that limit the first stage to a 9m diameter? Surely both stages need to be downscaled.
« Last Edit: 09/13/2017 01:12 PM by M.E.T. »

Offline rsdavis9

Re: IAC 2017 -- ITS v0.2
« Reply #170 on: 09/13/2017 01:27 PM »
I think the cheapest path is to go for the final 9m booster and spacecraft from the start.

Using subscale raptors will cost more in the long run.
Assuming that going from subscale to full scale isn't VERY hard.
Go for composites from the start. Maybe metal lined tanks.
Many other things can probably be skimped on and done later.

But the major components will benefit the cost by being done in final form from the start. Having the same engines for both stages is a known benefit. All composite will take longer but avoids a major redesign later.

Its all about how much effort later to change versus how much easier it is now.

bob

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Re: IAC 2017 -- ITS v0.2
« Reply #171 on: 09/13/2017 01:37 PM »
Then forget about subscale Raptors - go for the full size, 'Version 1.0'. Put as many as possible on the 9 meter design, albeit trying to keep within the approximate 12 million pound thrust range. As someone just said - make this the BFR, prove out big-scale orbital propellant transfer and reusability...

...Then raise the bar and set the standard for many years to come.
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Offline guckyfan

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Re: IAC 2017 -- ITS v0.2
« Reply #172 on: 09/13/2017 01:40 PM »
Flight qualifying the subscale Raptor would enable them to fly a methane vehicle in 2020. Later they can change the thrust structure and stretch the tanks going for a bigger even more capable vehicle.

Offline rsdavis9

Re: IAC 2017 -- ITS v0.2
« Reply #173 on: 09/13/2017 01:47 PM »
Flight qualifying the subscale Raptor would enable them to fly a methane vehicle in 2020. Later they can change the thrust structure and stretch the tanks going for a bigger even more capable vehicle.

So the redesign of the vehicle for 3x raptor is not VERY hard?
How about the factory line for subscale first then full scale?
Is there a use for a subscale that will exist after full scale is available?
Thereby justifying the expense.
bob

Online AncientU

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Re: IAC 2017 -- ITS v0.2
« Reply #174 on: 09/13/2017 01:52 PM »
IMO, the larger Raptor engine will be on the stand this year (next 12 months) and be used to power the booster.  If the full spaceship is built for the 9m, which I think likely, it may use the smaller version, as may a conventional upper stage use maybe 3 of these engines.  12Mlbs lift-off thrust is almost a given...

I think the planned use and lifetime of this ITSy will be most interesting aspect of IAC 2017 -- when will it be built and when will it head for Mars. 

I don't see this as merely a prototyping effort for the BFR.  It is the BFR for next 10+ years -- the World's BFR.

Just to clarify, do you mean the original ITS Spaceship being built as the 2nd stage for the mini-ITS first stage? Meaning that only the first stage is downscaled to 9m? How would that work with the factory constraints that limit the first stage to a 9m diameter? Surely both stages need to be downscaled.

The spaceship built for the 9m booster will be a sub-scale ITS upper stage from that described last IAC, IMO.  As a sub-scale vehicle, it will be difficult to use a redundant set of full vacuum optimized nozzles plus landing engine considerations if the full scale Raptor is the engine.  Therefore, I believe the subscale engine would be best for the 9m spaceship/upper stage (OML might be 12m, just as OML for 12m spaceship was 17m).
« Last Edit: 09/13/2017 01:55 PM by AncientU »
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Offline envy887

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Re: IAC 2017 -- ITS v0.2
« Reply #175 on: 09/13/2017 01:56 PM »
Flight qualifying the subscale Raptor would enable them to fly a methane vehicle in 2020. Later they can change the thrust structure and stretch the tanks going for a bigger even more capable vehicle.

So the redesign of the vehicle for 3x raptor is not VERY hard?
How about the factory line for subscale first then full scale?
Is there a use for a subscale that will exist after full scale is available?
Thereby justifying the expense.

Likely about as hard as redesigning F9 from v1.0 to v1.1 and the octaweb.

Online ZachF

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Re: IAC 2017 -- ITS v0.2
« Reply #176 on: 09/13/2017 02:13 PM »
IMO, the larger Raptor engine will be on the stand this year (next 12 months) and be used to power the booster.  If the full spaceship is built for the 9m, which I think likely, it may use the smaller version, as may a conventional upper stage use maybe 3 of these engines.  12Mlbs lift-off thrust is almost a given...

I think the planned use and lifetime of this ITSy will be most interesting aspect of IAC 2017 -- when will it be built and when will it head for Mars. 

I don't see this as merely a prototyping effort for the BFR.  It is the BFR for next 10+ years -- the World's BFR.

Just to clarify, do you mean the original ITS Spaceship being built as the 2nd stage for the mini-ITS first stage? Meaning that only the first stage is downscaled to 9m? How would that work with the factory constraints that limit the first stage to a 9m diameter? Surely both stages need to be downscaled.

The spaceship built for the 9m booster will be a sub-scale ITS upper stage from that described last IAC, IMO.  As a sub-scale vehicle, it will be difficult to use a redundant set of full vacuum optimized nozzles plus landing engine considerations if the full scale Raptor is the engine.  Therefore, I believe the subscale engine would be best for the 9m spaceship (OML might be 12m, just as OML for 12m spaceship was 17m).

yeah, I was going over engine placement scenarios, and the full scale vacuum raptor does not fit well in a 9m diameter.

I personally think the ITSy/BFR2.0 will be a little over 4,000 tonnes GTOW, about 42% the size of the ITSv16. It will be about 107m tall.

The full scale raptor Vacs, if you pixel measure the old ITSv16 had bell diameters of ~4 m. In order to fit 3 you would probably have to reduce the expansion ratio slightly, and you would not have a center engine, and 3 sea level raptors would be way overpowered, so you would need to develop an entirely new landing engine.

A Raptor Vac, based on the 1MN test version, with thrust of about 1.4-1.5MN, would have a bell diameter of around 2.6m, so you could fit 6 of them in a 9m diameter easy, perhaps even with an increased expansion ratio of ~250:1, and get a few more seconds of ISP, and therefore reach performance goals with less of a need to use exotic carbon fiber materials (save that for the next, larger version of ITS) It would also be able to fit a ~1.8m diameter Sea level Raptor engine in the middle for landing.

Such a Raptor could also fit on the US of a Falcon if they chose to do so.

The booster will use ~18 of the original sized 3MN sea level Raptors. That number fits perfect in a 9m diameter, and also is divisible by 3. With a ~4,100 tonne vehicle this would increase liftoff TWR from ~1.38 in the original design to ~1.47. The higher liftoff TWR may again allow less aggressive use of advanced materials because of less gravity losses. Smaller rockets (with the same shape) have a higher frontal sectional density, allowing higher potential thrust/weight.

I think the original ITS booster stage had placeholder engines in the CAD that were slightly smaller than the actual engines. In order to fit all 42 engines the ITSv16 would probably have needed a small skirt on the bottom.

That's just my guess after ruminating over the numbers. We'll all find out in a few weeks.  8)


Offline rsdavis9

Re: IAC 2017 -- ITS v0.2
« Reply #177 on: 09/13/2017 02:15 PM »
IMO, the larger Raptor engine will be on the stand this year (next 12 months) and be used to power the booster.  If the full spaceship is built for the 9m, which I think likely, it may use the smaller version, as may a conventional upper stage use maybe 3 of these engines.  12Mlbs lift-off thrust is almost a given...

I think the planned use and lifetime of this ITSy will be most interesting aspect of IAC 2017 -- when will it be built and when will it head for Mars. 

I don't see this as merely a prototyping effort for the BFR.  It is the BFR for next 10+ years -- the World's BFR.

Just to clarify, do you mean the original ITS Spaceship being built as the 2nd stage for the mini-ITS first stage? Meaning that only the first stage is downscaled to 9m? How would that work with the factory constraints that limit the first stage to a 9m diameter? Surely both stages need to be downscaled.

The spaceship built for the 9m booster will be a sub-scale ITS upper stage from that described last IAC, IMO.  As a sub-scale vehicle, it will be difficult to use a redundant set of full vacuum optimized nozzles plus landing engine considerations if the full scale Raptor is the engine.  Therefore, I believe the subscale engine would be best for the 9m spaceship/upper stage (OML might be 12m, just as OML for 12m spaceship was 17m).
Engine redundancy is nice to have but it isn't a necessary design requirement.
bob

Online AncientU

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Re: IAC 2017 -- ITS v0.2
« Reply #178 on: 09/13/2017 02:25 PM »
IMO, the larger Raptor engine will be on the stand this year (next 12 months) and be used to power the booster.  If the full spaceship is built for the 9m, which I think likely, it may use the smaller version, as may a conventional upper stage use maybe 3 of these engines.  12Mlbs lift-off thrust is almost a given...

I think the planned use and lifetime of this ITSy will be most interesting aspect of IAC 2017 -- when will it be built and when will it head for Mars. 

I don't see this as merely a prototyping effort for the BFR.  It is the BFR for next 10+ years -- the World's BFR.

Just to clarify, do you mean the original ITS Spaceship being built as the 2nd stage for the mini-ITS first stage? Meaning that only the first stage is downscaled to 9m? How would that work with the factory constraints that limit the first stage to a 9m diameter? Surely both stages need to be downscaled.

The spaceship built for the 9m booster will be a sub-scale ITS upper stage from that described last IAC, IMO.  As a sub-scale vehicle, it will be difficult to use a redundant set of full vacuum optimized nozzles plus landing engine considerations if the full scale Raptor is the engine.  Therefore, I believe the subscale engine would be best for the 9m spaceship/upper stage (OML might be 12m, just as OML for 12m spaceship was 17m).
Engine redundancy is nice to have but it isn't a necessary design requirement.

When I go to Mars, I would prefer to have redundancy.
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Online ZachF

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Re: IAC 2017 -- ITS v0.2
« Reply #179 on: 09/13/2017 02:29 PM »
Just chiming in, I'm thinking (and hoping) that AMOS-6 and the subsequent COPV testing showed them a LOT about what carbon fiber can and cannot do. Hopefully that will help prevent an AMOS-6 2.0, where instead of just the pad being wrecked (F9), Florida's Eastern coast explodes (ITS).

As I posted above, using a vacuum variant of the subscale Raptor may allow a higher expansion ratio than the original design, increasing ISP in the upper stage. A shorter length will also present a greater relative frontal (and rearward) area, allowing a higher thrust/weight ratio.

A higher TWR in the lower stage, and higher ISP in the upper stage would allow equal performance with with lower mass ratios. I strongly suspect this is why we haven't heard anything about the carbon tank since they kaboomed it. They aren't going to need to use advance materials to reach performance goals for the 9m version. Retire the risk on that unproven tech, and save it for the next, larger, version of ITS/BFR... Bring it out earlier.
« Last Edit: 09/13/2017 02:34 PM by ZachF »

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