Author Topic: Should Super Heavy (BFR/ITS) have a smaller prototype to ease development?  (Read 70189 times)

Offline Lobo

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Re: Should ITS have a smaller prototype to ease development?
« Reply #80 on: 02/21/2017 06:53 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.


Yea, this was discussed on a similar thread.

Myself, I don't think there's a case for a mini-ITS.  For the same reason there was no real need for a "Saturn III" between the Saturn 1B and Saturn V.  For going to LEO, the Saturn 1B was fine.  For sending humans BLEO, you need as much capability as you can get, so you wanted the Saturn V (or even bigger, if it has been feasible).  But not much need in between.  Not even as an interim stepping stone.  NASA went right from the Saturn 1 to Saturn V. 
It's similar for SpaceX.  They already have their "Saturn 1" in Falcon, and now they want as much capability as they can possible get in ITS.  No need to have an intermediate LV.  It is nice to work up in scale, but it also costs a lot to have an entirely new and different intermediate LV to pay for development and testing.  Go do what you really -need- and then focus your funds and efforts there.  Rather than an essentially "dead end" LV.

NOTE:  The one scenario it could make sense, is as a fully reusable Falcon replacement.  Something that would handle all commercial and government payloads fully reusably in a single stick LV.  Something that could launch basically a D4H payload to GTO, have the booster RTLS, and have the upper stage deploy the payload in GTO, and then have enough propellants to deorbit itself form GTO, and land back at the launch site. 
The problem with this, is they already have Falcon in place and all of it's development paid for.  It's probably not the LV they'd be flying if they could do a clean sheet design knowing everything they know right now, but as the bumper sticker says, "Don't laugh, it's paid for".  ;-)

They have launch pads being built for Falcon, and infrastructure in place for it.  And a mini-ITS to replace it would have to be built somewhere near the water or at the launch site like ITS since it couldn't be transported by road...which means starting all over again after they've just barely got their final version of Falcon flying, and FH soon to be flying.  So I don't see them scrapping all of that and starting over, just to replicate the capabilities F9/FH will already have...just with an expendable upper stage rather than a reusable one.


Offline Lobo

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Re: Should ITS have a smaller prototype to ease development?
« Reply #81 on: 02/21/2017 07:12 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.

Yes, I've discussed that before with some folks, I think on the Mini-BFR thread.
The ITS Spacecraft is really it's own SSTO rocket. It will have to get itself off the surface of Mars and get itself all the way back to Earth and land.  It needs help on Earth to get itself all the way over to Mars because of the deeper gravity well, with a usable payload, but without much (or any) payload, it could probably get itself up to LEO on it's own...with some engine modifications as it can't take off with those vacuum nozzles.
And with some tweaking later, it could probably get itself plus some usable payload to LEO.  In which case, it could possibly replace Falcon at some point down the road.  And given how it will be designed to operate on the surface of Mars, it could possibly operate on some large flat pad, or with a simple launch mount, like Redstone or the Early Saturn 1's.  Although they will probably want to direct the thrust in some manner rather than have it go in all directions... and need some sound supression and other things that won't be an issue on Mars.  But you get the idea.  It could really change the whole idea of pad ops to something a little more like an airport.  If not going to Mars, these spacecraft would launch and land themselves in one big flat complex to handle the typical comsat payload or crew shuttle duties to a space station.  And it'd be just a different configuration of the hardware already built for the Mars program.

Offline RonM

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Re: Should ITS have a smaller prototype to ease development?
« Reply #82 on: 02/21/2017 07:15 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.


Yea, this was discussed on a similar thread.

Myself, I don't think there's a case for a mini-ITS.  For the same reason there was no real need for a "Saturn III" between the Saturn 1B and Saturn V.  For going to LEO, the Saturn 1B was fine.  For sending humans BLEO, you need as much capability as you can get, so you wanted the Saturn V (or even bigger, if it has been feasible).  But not much need in between.  Not even as an interim stepping stone.  NASA went right from the Saturn 1 to Saturn V. 
It's similar for SpaceX.  They already have their "Saturn 1" in Falcon, and now they want as much capability as they can possible get in ITS.  No need to have an intermediate LV.  It is nice to work up in scale, but it also costs a lot to have an entirely new and different intermediate LV to pay for development and testing.  Go do what you really -need- and then focus your funds and efforts there.  Rather than an essentially "dead end" LV.

NOTE:  The one scenario it could make sense, is as a fully reusable Falcon replacement.  Something that would handle all commercial and government payloads fully reusably in a single stick LV.  Something that could launch basically a D4H payload to GTO, have the booster RTLS, and have the upper stage deploy the payload in GTO, and then have enough propellants to deorbit itself form GTO, and land back at the launch site. 
The problem with this, is they already have Falcon in place and all of it's development paid for.  It's probably not the LV they'd be flying if they could do a clean sheet design knowing everything they know right now, but as the bumper sticker says, "Don't laugh, it's paid for".  ;-)

They have launch pads being built for Falcon, and infrastructure in place for it.  And a mini-ITS to replace it would have to be built somewhere near the water or at the launch site like ITS since it couldn't be transported by road...which means starting all over again after they've just barely got their final version of Falcon flying, and FH soon to be flying.  So I don't see them scrapping all of that and starting over, just to replicate the capabilities F9/FH will already have...just with an expendable upper stage rather than a reusable one.

Good points, but I see a problem with your comparison.

Saturn 1B and Saturn V are similar rockets as in they used similar construction and fuel. ITS will have composite fuel tanks and use methane instead of RP-1, major changes from F9. That's a bigger leap than going from Saturn 1B to Saturn V. But it looks like Elon is comfortable with making that leap.

Offline Lobo

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Re: Should ITS have a smaller prototype to ease development?
« Reply #83 on: 02/21/2017 07:37 pm »

Good points, but I see a problem with your comparison.

Saturn 1B and Saturn V are similar rockets as in they used similar construction and fuel. ITS will have composite fuel tanks and use methane instead of RP-1, major changes from F9. That's a bigger leap than going from Saturn 1B to Saturn V. But it looks like Elon is comfortable with making that leap.

True, but it was just for the sake of demonstration.  ;-)

Actually, the original Saturn 1 and Saturn V is probably more correctly comparative of Falcon 9 and ITS.  They used similar fuels, but really had nothing else in common, until the switched from the S-IV upper stage to the S-IVB, so they then both had that in common.

Regardless, it's certainly a big jump.  Bigger in most ways than the Jump from the Saturn 1 to the Saturn V.  But, it still comes back to "build what you need", and not to mess around with an LV that you don't need.  If funds dry up, then you could be stuck with this mini-ITS that's really not capable of the Mars program that Elan wants, without the funds to build the full ITS in addition.

Online wannamoonbase

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Re: Should ITS have a smaller prototype to ease development?
« Reply #84 on: 02/21/2017 08:10 pm »
Saturn 1B and Saturn V are similar rockets as in they used similar construction and fuel. ITS will have composite fuel tanks and use methane instead of RP-1, major changes from F9. That's a bigger leap than going from Saturn 1B to Saturn V. But it looks like Elon is comfortable with making that leap.

Or he doesn't have money to do anything else.

A smaller raptor powered vehicle could have the benefit of doing many more RTLS launches than F9 and fully implementing the reuse lessons they are learning and will continue to learn for years to come.

I still think that F9 to ITS, without every flying raptor, is a massive step, maybe too big of a step.
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Offline hkultala

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Re: Should ITS have a smaller prototype to ease development?
« Reply #85 on: 02/21/2017 08:16 pm »
Saturn 1B and Saturn V are similar rockets as in they used similar construction and fuel. ITS will have composite fuel tanks and use methane instead of RP-1, major changes from F9. That's a bigger leap than going from Saturn 1B to Saturn V. But it looks like Elon is comfortable with making that leap.

Saturn IB and Saturn V had quite different first stage tank structures.

But the engine and fuel types were similar, and even same upper stage was used.

Offline gin455res

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Re: Should ITS have a smaller prototype to ease development?
« Reply #86 on: 02/21/2017 08:41 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.


Yea, this was discussed on a similar thread.

Myself, I don't think there's a case for a mini-ITS.  For the same reason there was no real need for a "Saturn III" between the Saturn 1B and Saturn V.  For going to LEO, the Saturn 1B was fine.  For sending humans BLEO, you need as much capability as you can get, so you wanted the Saturn V (or even bigger, if it has been feasible).  But not much need in between.  Not even as an interim stepping stone.  NASA went right from the Saturn 1 to Saturn V. 
It's similar for SpaceX.  They already have their "Saturn 1" in Falcon, and now they want as much capability as they can possible get in ITS.  No need to have an intermediate LV.  It is nice to work up in scale, but it also costs a lot to have an entirely new and different intermediate LV to pay for development and testing.  Go do what you really -need- and then focus your funds and efforts there.  Rather than an essentially "dead end" LV.

NOTE:  The one scenario it could make sense, is as a fully reusable Falcon replacement.  Something that would handle all commercial and government payloads fully reusably in a single stick LV.  Something that could launch basically a D4H payload to GTO, have the booster RTLS, and have the upper stage deploy the payload in GTO, and then have enough propellants to deorbit itself form GTO, and land back at the launch site. 
The problem with this, is they already have Falcon in place and all of it's development paid for.  It's probably not the LV they'd be flying if they could do a clean sheet design knowing everything they know right now, but as the bumper sticker says, "Don't laugh, it's paid for".  ;-)

They have launch pads being built for Falcon, and infrastructure in place for it.  And a mini-ITS to replace it would have to be built somewhere near the water or at the launch site like ITS since it couldn't be transported by road...which means starting all over again after they've just barely got their final version of Falcon flying, and FH soon to be flying.  So I don't see them scrapping all of that and starting over, just to replicate the capabilities F9/FH will already have...just with an expendable upper stage rather than a reusable one.

Good points, but I see a problem with your comparison.

Saturn 1B and Saturn V are similar rockets as in they used similar construction and fuel. ITS will have composite fuel tanks and use methane instead of RP-1, major changes from F9. That's a bigger leap than going from Saturn 1B to Saturn V. But it looks like Elon is comfortable with making that leap.

How long has it taken the Merlin engine to reach it's current level of maturity?


(Maybe a successful and rich SpaceX will have more funds to accelerate Raptor development compared to the historical Merlin development? but Merlin is here and ready right-now-ish - well, assuming block 5 is not a turkey and inherits some of its predecessors' flight-derivable reliability stats. What is the relative timeline, and risks inherent in Raptor compared to block 5?)

By foregoing an intermediate super-heavy merlin-based system are you missing a trick($$). Namely, a window of several years where it may be possible to further slash the cost to orbit; continue to expand the mass and capability of your orbital comms-network, build new markets and value; squeeze competitors; and get on with the initial mars base building without having to wait an extra 3-5?? years for a mature ITS system.

Just because (say) $10? million per person to Mars may not be sustainable long-term, does it mean there mightn't be buyers at levels significantly above Musk's stated goal of $500,000 for a number of years, while ITS becomes operational?

However, the only items an (initially) merlin-based interim system might prototype is TPS and mixed expansion engines (for vertical landing of the upper-stage.) Raptor upper-stages and composites might be optional.


An interim system might act as a lucrative and risk-reducing bridge between falcon heavy and ITS. And the more ITS might move to the right (a clear risk) the more this might hold.

Offline spacenut

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Re: Should ITS have a smaller prototype to ease development?
« Reply #87 on: 02/21/2017 08:53 pm »
The government (NASA), at that time, had unlimited resources, so they could go straight from Saturn I to Saturn V.  SpaceX doesn't have unlimited resources.  That it why I think a step between F9/FH and ITS should be done by them, to utilize existing infrastructures at the Cape, inland waterways and transportation systems.  This would save them costs to build new infrastructures. 

Offline redliox

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Re: Should ITS have a smaller prototype to ease development?
« Reply #88 on: 02/21/2017 09:52 pm »
Keep in mind that scale models are usually (?) done as proof of concepts. Some of the more successful scale models (DC-X) focus more on specific technologies. Scale models that try to do to much - replicate everything at a smaller scale - like X-33 can run into problems.

So the question is... what specific kinds of challenge technologies do you hope to test and verify using a "small ITS"? And is verifying those really that much more cost-effective using a smaller scale?

I'll start by pointing out three things I see as big challenges:
- ITS reentry shape (scale changes mass properties, for example going from Apollo to Orion was more difficult and costly than imagined *despite* same shape)
- ITS TPS (similar concern as above, scale affects mass and heat loading)
- structural composite cryogenic tanks (this testing can be done all on the ground, no smaller vehicle needed)

I think those both would be good concepts to start with.  Beyond those, it would be a matter of seeing how ISRU on Mars could be done which could be part of a different vehicle, like an experiment on a future Red Dragon for one.  Seeing if the vehicle can reach Mars, retain the majority of its fuel (most likely methalox, although hydrolox may be optional [though not nearly as likely]), and survive EDL is the greatest challenge for HSF engineering.  Life-support and ISRU, by comparison, could be largely lab-tested.

I think arguing for a smaller final ITS system because it would be more affordable is one argument that I might agree with. But I don't think creating a smaller pathfinder system is worth it.

Between the crappy experiences of STS and X-33, you have a painful point that can't be denied.  However, the Mars Pathfinder's designs became the basis for MER and MSL; even the Skycrane could be said to be an evolution of the cable that lowered the probe from its solid-fueled backshell.  All the same, I would agree that any precursor/pathfinder vehicle should be as close as possible to the final vehicle, or barring that as affordable as possible with commonality with the final vehicle; i.e. I'd take your advice 75% to heart with 25% boldness.

In the case of this hypothetical mini-ITS, specifically a mini-Interplanetary Spaceship, it should have raptor engines (just fewer of them), be methalox, fly aboard a full-scale ITS booster, and sit inside a shroud identical to the full IPS so only mass would differ from a future larger spaceship.

It's scale is huge, sure.
But we need to remember that ITS would be a paradigm shift.  And we have to stand on our heads a bit to account for that. 
It's huge...but fully reusable...with not only booster recovery and reuse, but "return to launch site" recovery and reuse.  Right now  F9-FT is technically much larger than necessary for what it needs to do.  But it's grown larger and more powerful as SpaceX has explored booster reusability.   It uses that extra performance to land the booster on a barge or back on land, depending on payload requirements.  But they've squeezed about as much performance out of the hardare and technology as they can.  If SpaceX could redesign Falcon 9 from scratch today, knowing everything they know now, and if road transportation wasn't a consideration, I think it'd be even larger...and probably methane, which would make it even larger yet as CH4 is less dense than RP-1.    That way they could launch all the commercial sats to GTO and still RTLS the booster...which is ideal.   They may even go larger yet, and get up into EELV-heavy payload range and RTLS the booster, but without the need for the complex tri-core booster.  That way they have just one common single-stick booster for pretty much every potential payload, and it could return the booster to the launch site for all of them.  Now, if you added a reusable upper stage to that, then your scale goes up again to account for that.  But while very oversized, it could still be very economical.
ITS is just really an extension of that.

Basically the ITS (especially if you're referring to its booster half) is the supreme evolution of Falcon tech eh?

Yes, I've discussed that before with some folks, I think on the Mini-BFR thread.
The ITS Spacecraft is really it's own SSTO rocket. It will have to get itself off the surface of Mars and get itself all the way back to Earth and land.  It needs help on Earth to get itself all the way over to Mars because of the deeper gravity well, with a usable payload, but without much (or any) payload, it could probably get itself up to LEO on it's own...with some engine modifications as it can't take off with those vacuum nozzles.
And with some tweaking later, it could probably get itself plus some usable payload to LEO.  In which case, it could possibly replace Falcon at some point down the road.  And given how it will be designed to operate on the surface of Mars, it could possibly operate on some large flat pad, or with a simple launch mount, like Redstone or the Early Saturn 1's.  Although they will probably want to direct the thrust in some manner rather than have it go in all directions... and need some sound supression and other things that won't be an issue on Mars.  But you get the idea.  It could really change the whole idea of pad ops to something a little more like an airport.  If not going to Mars, these spacecraft would launch and land themselves in one big flat complex to handle the typical comsat payload or crew shuttle duties to a space station.  And it'd be just a different configuration of the hardware already built for the Mars program.

If you're referring to the spaceship half of the ITS, mini or full, I disagree on re-purposing it for use on Earth.  You may as well be asking the Apollo LEM to do likewise.  The furthest the full-scale could go alone would be to LEO, but not to GTO or Luna so its applications would be limited much as the weight of the space shuttle's wings limited its operations.  At Mars it could indeed a SSTO godsend, but it is going to be some time before Martian manufacturing gets setup.

However, if you're talking about the ITS BOOSTER, you have a far better alley to tread.  It's a beautiful example of what a HLV should be.  The SLS, as an example, has more potential than the STS because it has cargo capacity unseen since Saturn's days; it's main limitations are it's Orion's mule and it is very old-school (since, during the Augustine days, it was viewed that the limited reusability of the shuttle was part of its downfall [since then SpaceX has improved on it heavily]).  The ITS booster is a single rocket doing a superior job compared to either Falcon Heavy or SLS, both of which require setups of multiple rockets.  I wouldn't wish to scale down the ITS booster even for simplicity-sake because it (and perhaps whatever Blue Origin can generate) would be the best rocket ever developed in either the 20th or 21st centuries!

So, while this thread is meant to apply towards both the booster and spaceships halves of ITS, IMPO thus far I think any scaling should be done to the spaceship but not the booster.  The booster is going to be used exclusively at Earth so obviously testing it here is easier whereas the conditions the spaceship encounters are literally on another planet.  Outside of rocket fuel explosions, what precautions should be taken would be with the conditions the spaceship and its crew face on Mars, especially EDL.
« Last Edit: 02/21/2017 10:10 pm by redliox »
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Offline Khadgars

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Re: Should ITS have a smaller prototype to ease development?
« Reply #89 on: 02/21/2017 10:21 pm »
Elaborate on scale models.  I'm curious is there's an optimal scale that is best for testing, not to mention whether it's better to scale by volume or by mass.

More recently, a deliberately scaled model of the Raptor engine was produced for testing, and has so far been successful. However, the test carbon fuel tank was almost full size for the ITS spaceship, and failed in an early test. With the benefit of hindsight, perhaps a smaller scale model would have been a cheaper first iteration?


I had not heard about the failed test.  Can you provide any specifics?
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Offline envy887

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Re: Should ITS have a smaller prototype to ease development?
« Reply #90 on: 02/21/2017 10:43 pm »
There are pictures of the remains of the tank in the ITS development thread.

Offline redliox

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Re: Should ITS have a smaller prototype to ease development?
« Reply #91 on: 02/21/2017 10:55 pm »
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.

How is that number, 0.8 generated?  I assume it's not merely implying this instance of a mini-ITS is 80% the linear dimensions of a full-ITS.  Same as a 4:5 ratio?  How would that translate to both dimensions and mass?
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Offline Lars-J

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Re: Should ITS have a smaller prototype to ease development?
« Reply #92 on: 02/21/2017 11:24 pm »
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.

How is that number, 0.8 generated?  I assume it's not merely implying this instance of a mini-ITS is 80% the linear dimensions of a full-ITS.  Same as a 4:5 ratio?  How would that translate to both dimensions and mass?

The 0.8 figure presumably comes from how mass scales with linear dimension change.

For example... If you want an ITS that is half the liftoff weight of a full ITS, then the linear scale change is 0.8.  (0.8 ^ 3 = ~0.5) So it is not going to be as much smaller as you might think.

Offline Lobo

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Re: Should ITS have a smaller prototype to ease development?
« Reply #93 on: 02/21/2017 11:57 pm »

Basically the ITS (especially if you're referring to its booster half) is the supreme evolution of Falcon tech eh?

In a sense, yes.  I don't know for sure, but I bet if you sat Musk and SHotwell down and asked them how they would design a clean sheet sat launcher knowing what they know now, I'm guessing they wouldn't draw up Falcon.  They'd draw up a mini-ITS.  A single stick two-stage system that's fully reusable.  They'd have some method of unmanned payload deployment in the upper stage.  It'd be like a smaller unmanned shuttle with perhaps a dorsal payload bay.  It would deploy sats in GTO, and then circle back close to Earth where it could do a deorbit burn, and then land.  It'd be size to handle the largest expected payload (something D4H-class to GTO) and with that it could RTLS both the booster and upper stage.  That'd be a nice slick, simple and efficient system.
I think ITS is that...but they already have invested heavily in Falcon, and it already works pretty well, and it's paid for, so no need to replace it.  But a new heavy launch system for going to Mars doesn't exist yet, and I think it's just what a clean-sheet Falcon would be...but much bigger.



If you're referring to the spaceship half of the ITS, mini or full, I disagree on re-purposing it for use on Earth.  You may as well be asking the Apollo LEM to do likewise.  The furthest the full-scale could go alone would be to LEO, but not to GTO or Luna so its applications would be limited much as the weight of the space shuttle's wings limited its operations.  At Mars it could indeed a SSTO godsend, but it is going to be some time before Martian manufacturing gets setup.

However, if you're talking about the ITS BOOSTER, you have a far better alley to tread.  It's a beautiful example of what a HLV should be.  The SLS, as an example, has more potential than the STS because it has cargo capacity unseen since Saturn's days; it's main limitations are it's Orion's mule and it is very old-school (since, during the Augustine days, it was viewed that the limited reusability of the shuttle was part of its downfall [since then SpaceX has improved on it heavily]).  The ITS booster is a single rocket doing a superior job compared to either Falcon Heavy or SLS, both of which require setups of multiple rockets.  I wouldn't wish to scale down the ITS booster even for simplicity-sake because it (and perhaps whatever Blue Origin can generate) would be the best rocket ever developed in either the 20th or 21st centuries!

So, while this thread is meant to apply towards both the booster and spaceships halves of ITS, IMPO thus far I think any scaling should be done to the spaceship but not the booster.  The booster is going to be used exclusively at Earth so obviously testing it here is easier whereas the conditions the spaceship encounters are literally on another planet.  Outside of rocket fuel explosions, what precautions should be taken would be with the conditions the spaceship and its crew face on Mars, especially EDL.

I address some of this in my PM back to you.  But I disagree.  Using the ITS spaceship to go to LEO would not be like repurposing the LEM, because it's already designed to launch in an atmosphere, and do EDL in an atmosphere.  Specifically Earth's on it's return trip.  Really it'd just need some engine and MPS tweaking so it has sufficient sea level Raptors that can get it off the ground and high enough to shut them down and light say a pair of Vacuum Raptors.  By that time it'd have burned enough fuel that two should be plenty of thrust.  Now, what could it in LEO?  Well, it could deploy sats with kick stages to get them to GTO, or GSO/GEO.  Or the comsats could be designed with enough on board fuel to get themselves form LEO to GSO/GEO.  (most are already designed to get themselves from GTO to GSO/GEO, so it'd be a matter of giving it sufficient propellant capacity.)
It could also serve as a LEO crew taxi to a space station.  Some folks have done some calculations and figured conservatively, with the correct engine config, it should be able to get itself plus around 20mt of payload to LEO.
But this would only be for a theoretical eventual Falcon replacement.  No real need for it other than that.

Not sure what you mean to do with the ITS booster by itself.  Maybe put an expendable (or smaller reusable) upper stage on it for deploying sats, and then it's propellant load can be taylored for each payload.  It wouldn't need near a full prop load for many sats.
But...if you are going to do that, then just put a version of the Spacecraft on top, set up to deploy unmanned sats in GTO, and then return to the launch site.  The stack should be able to get a stripped down spaceship plus a sat of up to ~13mt (I think is D4H's max capacity.) to GTO easily. 
I could see ITS used for this purpose instead of FH, and FH retired.  And F9 handling all the payloads smaller than that (which would be the vast majority).

Offline redliox

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Re: Should ITS have a smaller prototype to ease development?
« Reply #94 on: 02/22/2017 12:08 am »
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.

How is that number, 0.8 generated?  I assume it's not merely implying this instance of a mini-ITS is 80% the linear dimensions of a full-ITS.  Same as a 4:5 ratio?  How would that translate to both dimensions and mass?

The 0.8 figure presumably comes from how mass scales with linear dimension change.

For example... If you want an ITS that is half the liftoff weight of a full ITS, then the linear scale change is 0.8.  (0.8 ^ 3 = ~0.5) So it is not going to be as much smaller as you might think.

That actually seems like a good thing.  The mini-ITS in this case would be 80% the same dimensions as its big brother and light enough not to require a tanker to get to Mars.  Handling how the mass would double would become the final issue; given how the test tank blew maybe a slightly smaller tank might be a wise start.
« Last Edit: 02/22/2017 12:15 am by redliox »
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Offline envy887

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Re: Should ITS have a smaller prototype to ease development?
« Reply #95 on: 02/22/2017 12:23 am »
The mini-ITS in this case would be 80% the same dimensions as its big brother...

I like how "mini" in this case refers to something nearly twice as powerful as Saturn V.

Offline OneSpeed

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Re: Should ITS have a smaller prototype to ease development?
« Reply #96 on: 02/22/2017 01:49 am »
That actually seems like a good thing.  The mini-ITS in this case would be 80% the same dimensions as its big brother and light enough not to require a tanker to get to Mars.  Handling how the mass would double would become the final issue; given how the test tank blew maybe a slightly smaller tank might be a wise start.

Why would the ship not require a tanker to get to Mars?


Offline darkenfast

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Re: Should ITS have a smaller prototype to ease development?
« Reply #97 on: 02/22/2017 03:33 am »
If a scaled ITS is such a good idea, then why haven't the SpaceX design team (who presumably have done all the trades on this), come out with a proposed smaller prototype?
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Offline Lar

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Re: Should ITS have a smaller prototype to ease development?
« Reply #98 on: 02/22/2017 03:53 am »
An alternative would be to have a full size (dimensions) ITS prototype, but at lower performance.

So lower numbers of lower thrust Raptor on the booster. Only part fill the tanks. Aim for 50 tonnes of payload, rather than 300 tonnes.

Finally one I kinda like.

One could argue they did this with F9, actually. Over time it's gotten more payload, more thrust, more tank capacity, etc. Without changing the OML or basic size (much).
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Offline redliox

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Re: Should ITS have a smaller prototype to ease development?
« Reply #99 on: 02/22/2017 04:28 am »
That actually seems like a good thing.  The mini-ITS in this case would be 80% the same dimensions as its big brother and light enough not to require a tanker to get to Mars.  Handling how the mass would double would become the final issue; given how the test tank blew maybe a slightly smaller tank might be a wise start.

Why would the ship not require a tanker to get to Mars?

A smaller-scale spaceship would be lite enough to fly directly to Mars using a full-scale ITS booster and a bit of its own fuel is why.
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Tags: Space X ITS 
 

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