Author Topic: Hypothetical 1/3 Scale Starship (Read 16063 times)

FunBobby · « **on:** 02/21/2022 06:51 am »

I have been following this community for a number of years but am posting for the first time. I am NOT advocating for SPACEX to re-design Starship. I simply was looking for your opinions on my long-held belief; In some (not all) aspects Starship would be more successful and further along in development at this stage if it had been initially scaled down to something roughly half-way in between Falcon and the current design. For the sake of this argument, I imagine a launch vehicle that also uses Raptor engines, and the same approaches to material design and fabrication. My hypothetical baby-Starship would have probably had 9-12 Raptors on the booster and 1-2 Raptors on an initially expendable upper stage. I think this hypothetical LV would have produced FH expendable mass to orbit at a cost equal to or less than Falcon 9. Another way to think of it might just be a better/cheaper New Glenn. I realize that most of the design decisions on Starship, including it's massive size, are what enable it to serve its mission as a (Mars Colonial Transporter) and this scaled-down version could never transport 100 humans to the red planet. Consider though please:
1. Could the 1/3 scale Starship have progressed any faster through testing, particularly through the FAA approval process?
2. Would a 1/3 scale Starship be any better to serve existing Starlink / Comsat / NASA / DoD launch requirements?
3. Would a 1/3 scale Starship have been better positioned to improve vs replace the Artemis program?
4. Would a 1/3 scale Starship still have a reasonable upgrade-path to 2nd stage re-use including in-orbit refueling within a few years after initial capability?
5. Would a 1/3 scale Starship have provided a faster path to Mars Exploration while still able to provide support eventual Mars Colonization?
Thanks,
Bobby

MATTBLAK · « **Reply #1 on:** 02/21/2022 07:01 am »

nacnud · « **Reply #2 on:** 02/21/2022 09:26 am »

I don't think a 1/3 scale starship would have the payload and contingency margins to be fully and rapidly reusable. Also I don't think it would be significantly cheaper to develop.

Starship is already a scaled down design of the ITS concept.

hektor · « **Reply #3 on:** 02/21/2022 09:28 am »

Not that hypothetical. It is called Terran R.

edzieba · « **Reply #4 on:** 02/21/2022 11:10 am »

There was a subscale Starship-like upper stage demonstrator for Falcon initially planned. This plan was dropped in favour of moving straight to full-scale.

envy887 · « **Reply #5 on:** 02/21/2022 12:58 pm »

Quote from: FunBobby on 02/21/2022 06:51 am

5. Would a 1/3 scale Starship ... [be] able to provide support eventual Mars Colonization?

No. And as far as SpaceX is concerned, this is probably the end of the discussion. Without a Mars capability beyond flags and footprints, this vehicle would be basically no more useful than Falcon for reaching SpaceX's ultimate goals.

spacenut · « **Reply #6 on:** 02/21/2022 02:19 pm »

I've wondered if a half scale Starship would work. Say 5-6m in diameter. This would replace Falcon Heavy with a single stick launch. Say with 9-12 Raptor engines on the booster. Maybe some subscale Raptors on the upper stage so it could land.

nacnud · « **Reply #7 on:** 02/21/2022 02:29 pm »

Well a full up starship loaded with propellants weighs close to 5000t and has a payload of around 100t. That's a mass fraction of around 2% even with the volumetric efficiencies. In this case larger is better as far as margins go.

Really thought I think that the system is sized for the smallest reasonable SSTO for the return trip from Mars to Earth.

Eer · « **Reply #8 on:** 02/21/2022 02:45 pm »

I've thought the design point for Starship and SH Booster were similar to the DC3 (airplane) or 18-wheel truck. Reusable, cargo focused, able to support passengers, too. Not a 747 or Queen Elisabeth II Ocean liner, but heavy duty, reliable cartage.

There will be room for smaller vehicles - panel vans instead of 18-wheelers - as well as mega cruisers (think rotational artificial gravity) in the medium-to-far future.

One size won't fit all. Any more than a pickup truck would satisfy all heavy trucking needs, or the QEII be the only recreational boat worth building ...

meekGee · « **Reply #9 on:** 02/21/2022 02:45 pm »

Remember this is already a half sized Starship.

sebk · « **Reply #10 on:** 02/21/2022 03:02 pm »

1/3 (mass) scale Starship (~35t to LEO, so no ~FH expendable, farm from it) wouldn't be that much smaller. It would be 6.24m diameter, 83m tall.

If you'd like something comparable to FH expendable lift to LEO, it would be 1/2 (mass) scale, so about 95m tall 7.14m diameter. It would be about New Glenn planned size.

In both cases you'd have still a big rocket. Too big for road transportation and like efficiencies.

Moreover it would have troubles with landing:

1/3 scale Starship would be 2 Raptors orbital vehicle + 11 Raptors booster; 1/2 scale one would be 3 Raptors orbital vehicle + 16 Raptors booster.

And here's the problem. 2 Raptors means one SL and on Vac -- no redundancy. Moreover the engines would be off axis, so landing would be harder to develop. With 3 Raptors variant we'd need to RVacs and 1 SL -- again no redundancy for landing and off-center propulsion.

DreamyPickle · « **Reply #11 on:** 02/21/2022 03:17 pm »

It would certainly help with FAA approval!

One issue is that you would also need to rescale the raptors if you want to maintain engine redundancy on landing.

Then again, the most recent design calls for 9 raptors on the upper stage. Maybe they could find a way to provide landing redundancy using the vacuum raptors.

chopsticks · « **Reply #12 on:** 02/21/2022 03:22 pm »

I have thought for awhile that for LEO operations, a smaller version of a Starship could be quite practical - especially for crew and ISS/future space station ferries (cargo as well).

Docking the regular sized Starship right now seems a little dubious just due to the sheer mass of it and likely impringement of RCS plumes on the solar panels. A smaller vehicle could mitigate this while still providing plenty of space.

I don't think that a rapidly reusable vehicle for LEO has to be as big as the current Starship. Starship is ultimately meant for Mars, but something designed for LEO could be smaller in my opinion. Ground ops would probably be simplified as well (less fuel, less TPS for example).

JayWee · « **Reply #13 on:** 02/21/2022 03:51 pm »

Quote from: Eer on 02/21/2022 02:45 pm

I've thought the design point for Starship and SH Booster were similar to the DC3 (airplane) or 18-wheel truck. Reusable, cargo focused, able to support passengers, too. Not a 747 or Queen Elisabeth II Ocean liner, but heavy duty, reliable cartage.

There will be room for smaller vehicles - panel vans instead of 18-wheelers - as well as mega cruisers (think rotational artificial gravity) in the medium-to-far future.

One size won't fit all. Any more than a pickup truck would satisfy all heavy trucking needs, or the QEII be the only recreational boat worth building ...

When you go bigger than Starship you start to run into noise issues. Definitely would have to launch from offshore. I wonder if someone calculated maximal reasonable liftoff thrust noise limit.

When you go smaller.... There are certain efficiencies of scale. I do believe there IS a certain minimal second stage size, where you start having either material issues(walls too thin) or mass fraction issues (ie, heatshield masses too much)

And, I think Elon once mentioned he thought maybe it could have been a bit smaller, but not sure about it.

DanClemmensen · « **Reply #14 on:** 02/21/2022 03:56 pm »

Quote from: chopsticks on 02/21/2022 03:22 pm

I have thought for awhile that for LEO operations, a smaller version of a Starship could be quite practical - especially for crew and ISS/future space station ferries (cargo as well).

Docking the regular sized Starship right now seems a little dubious just due to the sheer mass of it and likely impringement of RCS plumes on the solar panels. A smaller vehicle could mitigate this while still providing plenty of space.

I don't think that a rapidly reusable vehicle for LEO has to be as big as the current Starship. Starship is ultimately meant for Mars, but something designed for LEO could be smaller in my opinion. Ground ops would probably be simplified as well (less fuel, less TPS for example).

Opinion:Starship will be cost-effective for all LEO missions, so a development effort for a small versions is not cost-effective. The exception is docking to ISS and possibly to follow-on stations. For this exception, it is cheaper to design and build a tailored solution such as an in-orbit taxi for crew and an ISS cargo/service module to serve the six-month sustaining role of the crew and cargo Dragons.

FunBobby · « **Reply #15 on:** 02/21/2022 04:16 pm »

Thank you all for you replies and constructive criticism. It seems to be a consensus opinion that the second stage "Starship" would not scale down well and maintain it's planned functionality including EDL, That is certainly valid. I perhaps should have chosen my terms better in that I was thinking more of the entire launch system including the booster which is also referred to as "Starship". My hypothetical vehicle would have began as a 1/3 to 1/2 scale booster with an expendable (no aero surfaces / no thermal protection) upper stage. I am imagining a booster that still is 9M or 8M diameter but much shorter (less than 40M). Perhaps that could have provided growth opportunities by adding rings and engines to the booster later to facilitate later adding a re-usable upper stage vehicle similar to the current design. Regardless, I understand completely that this path is moot as the "growth option" as I was describing eventually looks identical to the design as it stands today. As another poster pointed out, if Terran R manages to reach operational status that might show if there was any validity to that approach. Thanks Again - Bobby

Redclaws · « **Reply #16 on:** 02/21/2022 04:25 pm »

Quote from: FunBobby on 02/21/2022 06:51 am

I have been following this community for a number of years but am posting for the first time. I am NOT advocating for SPACEX to re-design Starship. I simply was looking for your opinions on my long-held belief; In some (not all) aspects Starship would be more successful and further along in development at this stage if it had been initially scaled down to something roughly half-way in between Falcon and the current design. For the sake of this argument, I imagine a launch vehicle that also uses Raptor engines, and the same approaches to material design and fabrication. My hypothetical baby-Starship would have probably had 9-12 Raptors on the booster and 1-2 Raptors on an initially expendable upper stage. I think this hypothetical LV would have produced FH expendable mass to orbit at a cost equal to or less than Falcon 9. Another way to think of it might just be a better/cheaper New Glenn. I realize that most of the design decisions on Starship, including it's massive size, are what enable it to serve its mission as a (Mars Colonial Transporter) and this scaled-down version could never transport 100 humans to the red planet. Consider though please:
1. Could the 1/3 scale Starship have progressed any faster through testing, particularly through the FAA approval process?
2. Would a 1/3 scale Starship be any better to serve existing Starlink / Comsat / NASA / DoD launch requirements?
3. Would a 1/3 scale Starship have been better positioned to improve vs replace the Artemis program?
4. Would a 1/3 scale Starship still have a reasonable upgrade-path to 2nd stage re-use including in-orbit refueling within a few years after initial capability?
5. Would a 1/3 scale Starship have provided a faster path to Mars Exploration while still able to provide support eventual Mars Colonization?
Thanks,
Bobby

Bobby,

Welcome to the forum! And thank you for positing your thoughts as *ideas* to be discussed rather than as declared certainties. These are neat questions.

envy887 · « **Reply #17 on:** 02/21/2022 05:32 pm »

Quote from: FunBobby on 02/21/2022 04:16 pm

Thank you all for you replies and constructive criticism. It seems to be a consensus opinion that the second stage "Starship" would not scale down well and maintain it's planned functionality including EDL, That is certainly valid. I perhaps should have chosen my terms better in that I was thinking more of the entire launch system including the booster which is also referred to as "Starship". My hypothetical vehicle would have began as a 1/3 to 1/2 scale booster with an expendable (no aero surfaces / no thermal protection) upper stage. I am imagining a booster that still is 9M or 8M diameter but much shorter (less than 40M). Perhaps that could have provided growth opportunities by adding rings and engines to the booster later to facilitate later adding a re-usable upper stage vehicle similar to the current design. Regardless, I understand completely that this path is moot as the "growth option" as I was describing eventually looks identical to the design as it stands today. As another poster pointed out, if Terran R manages to reach operational status that might show if there was any validity to that approach. Thanks Again - Bobby

A stubby booster and/or expendable upper is a growth path that SpaceX might have chosen if they were cashflow-constrained, but that isn't really a problem for them right now. Since capital is available, they want to tackle the toughest issues ASAP. And those issues are entry and landing, which could be done with a stubby booster but can't be done with a "short" ship. An expendable upper stage doesn't help with solving those issues, either.

I don't think Terran R is stubby. It looks to have about the same aspect ratio as Starship.

lykos · « **Reply #18 on:** 02/21/2022 05:42 pm »

Something like that may be growing in China.
CALT: Methalox engine, shape of Starship with 20 t payload.

https://spacenews.com/starship-lookalike-among-chinas-new-human-spaceflight-concepts

Asteroza · « **Reply #19 on:** 02/21/2022 09:48 pm »

Quote from: lykos on 02/21/2022 05:42 pm

Something like that may be growing in China.
CALT: Methalox engine, shape of Starship with 20 t payload.

https://spacenews.com/starship-lookalike-among-chinas-new-human-spaceflight-concepts

Isn't that "full-size" though (but not full flavor since they use methalox gas generator engines)? The concept JAXA is rolling around can be charitably be called a mini-starship though.