Author Topic: Hypothetical 1/3 Scale Starship  (Read 13279 times)

Offline FunBobby

  • Member
  • Posts: 36
  • Germany
  • Liked: 18
  • Likes Given: 11
Hypothetical 1/3 Scale Starship
« 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
Cheers,
Bobby

Offline MATTBLAK

  • Elite Veteran & 'J.A.F.A'
  • Senior Member
  • *****
  • Posts: 5362
  • 'Space Cadets' Let us; UNITE!! (crickets chirping)
  • New Zealand
  • Liked: 2240
  • Likes Given: 3883
Re: Hypothetical 1/3 Scale Starship
« Reply #1 on: 02/21/2022 07:01 am »

"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

Offline nacnud

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2691
  • Liked: 981
  • Likes Given: 347
Re: Hypothetical 1/3 Scale Starship
« 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.

Online hektor

  • Senior Member
  • *****
  • Posts: 2738
  • Liked: 1215
  • Likes Given: 55
Re: Hypothetical 1/3 Scale Starship
« Reply #3 on: 02/21/2022 09:28 am »
Not that hypothetical. It is called Terran R.

Offline edzieba

  • Virtual Realist
  • Senior Member
  • *****
  • Posts: 6313
  • United Kingdom
  • Liked: 9651
  • Likes Given: 41
Re: Hypothetical 1/3 Scale Starship
« 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.

Offline envy887

  • Senior Member
  • *****
  • Posts: 8150
  • Liked: 6816
  • Likes Given: 2965
Re: Hypothetical 1/3 Scale Starship
« Reply #5 on: 02/21/2022 12:58 pm »
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.

Offline spacenut

  • Senior Member
  • *****
  • Posts: 5189
  • East Alabama
  • Liked: 2591
  • Likes Given: 2903
Re: Hypothetical 1/3 Scale Starship
« 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. 

Offline nacnud

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2691
  • Liked: 981
  • Likes Given: 347
Re: Hypothetical 1/3 Scale Starship
« 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.

Online Eer

  • Full Member
  • ****
  • Posts: 631
  • Liked: 473
  • Likes Given: 928
Re: Hypothetical 1/3 Scale Starship
« 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 ...
From "The Rhetoric of Interstellar Flight", by Paul Gilster, March 10, 2011: We’ll build a future in space one dogged step at a time, and when asked how long humanity will struggle before reaching the stars, we’ll respond, “As long as it takes.”

Online meekGee

  • Senior Member
  • *****
  • Posts: 14315
  • N. California
  • Liked: 14176
  • Likes Given: 1397
Re: Hypothetical 1/3 Scale Starship
« Reply #9 on: 02/21/2022 02:45 pm »
Remember this is already a half sized Starship.
ABCD - Always Be Counting Down

Offline sebk

  • Full Member
  • ****
  • Posts: 774
  • Europe
  • Liked: 969
  • Likes Given: 27121
Re: Hypothetical 1/3 Scale Starship
« 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.

Offline DreamyPickle

  • Full Member
  • ****
  • Posts: 955
  • Home
  • Liked: 921
  • Likes Given: 205
Re: Hypothetical 1/3 Scale Starship
« 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.

Offline chopsticks

  • Full Member
  • ****
  • Posts: 1109
  • Québec, Canada
  • Liked: 1107
  • Likes Given: 170
Re: Hypothetical 1/3 Scale Starship
« 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).

Online JayWee

  • Full Member
  • ****
  • Posts: 1005
  • Liked: 1002
  • Likes Given: 1893
Re: Hypothetical 1/3 Scale Starship
« Reply #13 on: 02/21/2022 03:51 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.
« Last Edit: 02/21/2022 03:51 pm by JayWee »

Offline DanClemmensen

  • Senior Member
  • *****
  • Posts: 5704
  • Earth (currently)
  • Liked: 4463
  • Likes Given: 1864
Re: Hypothetical 1/3 Scale Starship
« Reply #14 on: 02/21/2022 03:56 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.

Offline FunBobby

  • Member
  • Posts: 36
  • Germany
  • Liked: 18
  • Likes Given: 11
Re: Hypothetical 1/3 Scale Starship
« 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
Cheers,
Bobby

Offline Redclaws

  • Full Member
  • ****
  • Posts: 750
  • Liked: 861
  • Likes Given: 1048
Re: Hypothetical 1/3 Scale Starship
« Reply #16 on: 02/21/2022 04:25 pm »
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.

Offline envy887

  • Senior Member
  • *****
  • Posts: 8150
  • Liked: 6816
  • Likes Given: 2965
Re: Hypothetical 1/3 Scale Starship
« Reply #17 on: 02/21/2022 05:32 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.

Offline lykos

  • Full Member
  • ***
  • Posts: 354
  • Greece
  • Liked: 220
  • Likes Given: 61
Re: Hypothetical 1/3 Scale Starship
« 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
« Last Edit: 02/21/2022 05:44 pm by lykos »

Offline Asteroza

  • Senior Member
  • *****
  • Posts: 2880
  • Liked: 1105
  • Likes Given: 33
Re: Hypothetical 1/3 Scale Starship
« Reply #19 on: 02/21/2022 09:48 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.

Offline Oersted

  • Member
  • Senior Member
  • *****
  • Posts: 2914
  • Liked: 4123
  • Likes Given: 2782
Re: Hypothetical 1/3 Scale Starship
« Reply #20 on: 02/21/2022 10:08 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.

With an expendable upper stage it would no longer make sense to refer to it as Starship. It is another launch vehicle then. Starship is by definition an attempt to overcome the huge challenge of designing a completely reusable launch system. That's the purpose baked into every facet of Starship as we know it.

Offline Lemurion

Re: Hypothetical 1/3 Scale Starship
« Reply #21 on: 02/22/2022 08:06 am »
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

Part of the problem with a further scaled down Starship is that a whole ton of issues around reusability get much harder to solve as you go smaller. You end up with less mass to play with on the upper stage so it’s less forgiving of mistakes. One of Starship’s advantages is that if they need an extra ton or two of hardware for something it’s not really a big deal. On a smaller ship it would be more of an issue as additional mass added up.

Offline FunBobby

  • Member
  • Posts: 36
  • Germany
  • Liked: 18
  • Likes Given: 11
Re: Hypothetical 1/3 Scale Starship
« Reply #22 on: 02/22/2022 09:01 am »
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.

With an expendable upper stage it would no longer make sense to refer to it as Starship. It is another launch vehicle then. Starship is by definition an attempt to overcome the huge challenge of designing a completely reusable launch system. That's the purpose baked into every facet of Starship as we know it.

True - The name Starship would not have applied.  It would have just been a SPACEX Heavy Lift LV with a more incremental approach than was taken with today's Starship.  It still could have incorporated Rapidly Reusable Raptor engines on the booster, stainless steel construction, perhaps even landing via the chopsticks.  I do think that it's at least remotely possible (given the rate of progress on Starship), that such a vehicle could have already launched it's first revenue generating or Starlink deploying mission by now. 
Cheers,
Bobby

Offline envy887

  • Senior Member
  • *****
  • Posts: 8150
  • Liked: 6816
  • Likes Given: 2965
Re: Hypothetical 1/3 Scale Starship
« Reply #23 on: 02/22/2022 12:56 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.

With an expendable upper stage it would no longer make sense to refer to it as Starship. It is another launch vehicle then. Starship is by definition an attempt to overcome the huge challenge of designing a completely reusable launch system. That's the purpose baked into every facet of Starship as we know it.

There is a logical development sequence that goes through first making and flying an expendable upper stage that basically looks like SN5 or 6. However, the main advantage of that sequence is it spreads out the costs while still moving forward, so it only makes sense if cashflow constrained... which SpaceX is not.
« Last Edit: 02/22/2022 12:57 pm by envy887 »

Offline spacenut

  • Senior Member
  • *****
  • Posts: 5189
  • East Alabama
  • Liked: 2591
  • Likes Given: 2903
Re: Hypothetical 1/3 Scale Starship
« Reply #24 on: 02/22/2022 01:02 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.

The new Starship/Superheavy upgrade with 33 engines on the booster and 6 vacuum engines and 3 sea level engines on the Starship has an estimated payload capability of around 200 tons. 

Offline Twark_Main

  • Senior Member
  • *****
  • Posts: 3763
  • Technically, we ALL live in space
  • Liked: 1950
  • Likes Given: 1217
Re: Hypothetical 1/3 Scale Starship
« Reply #25 on: 02/22/2022 02:57 pm »
Amazing how closely this mirrors Elon Musk statements from over a decade ago.

(Elon said the same thing three times, all I did was arrange the thought process as one "supercut" with all the good bits)

NPC Luncheon with Elon Musk, 2011-09-29:
Quote
... the pivotal breakthrough that's necessary, that some company has got to come up with, to make life multi-planetary is a fully and rapidly reusable orbit class rocket. This is a very difficult thing to do because we live on a planet where that is just barely possible. If gravity were a little lower it'd be easier, but if it was a little higher it would be impossible.

Even for an expendable launch vehicle, where you don't have to have any recovery, after a lot of smart people have done their best to optimize the weight of the vehicle and efficiency of the engines and the guidance systems and everything, you get maybe 2 to 3% of your liftoff weight to orbit. That's not a lot of room for error. If your rocket ends up being just a little bit heavier, you get nothing to orbit, and this is why only a few countries have ever reached orbit.

Elon Musk lecture at the Royal Aeronautics Society, 2012-11-16:
Quote
So okay, well what if you want to add in the reusable bits? Adding the reusability tends to take another 2 to 3%. So then you end up with zero or negative, and there's not much point sending a rocket to orbit with nothing on it.

In the past, things have been cancelled when it looked like success was not one of the possible outcomes. In fact, usually they've been cancelled after it was clear that success was not one of the possible outcomes. [laugh]

So, the trick then, is to make a rocket that is so mass efficient that it gets close to 4% of its payload to orbit in an expendable configuration, and then improve the weight of the reusability bits, push that down to around 2% and you get a net of four minus two - so, on the order of 2% of your payload to orbit in a fully reusable scenario.

That requires paying incredibly close attention to every aspect of the rocket's design. The efficiency of the engine, the weight of the engine, the weight of the tanks, the legs, even the secondary structure, the wiring, the plumbing, and the electronics, making sure your guidance system is extremely precise, and just pulling all sorts of tricks—every trick in the book, and then coming up with some new ones—in order to achieve that level of mass efficiency.

Elon Musk Mars Pioneer Acceptance Speech, 2012-08-09:
Quote
You have to really get straight A across the board in all elements of the rocket design. Every little tiny thing. The engine efficiency, thrust to weight, the engine, the tank mass, the pressurant mass, the secondary structure, the wiring, the weight of the computers, everything matters immensely.

But if you do all those things right, then it is possible to make this work, and this is what has given me hope recently in the last few years. Because I wasn't sure whether it was possible, but in the last few years I've become convinced that it is possible.

Of course, just because something is possible doesn't mean it will occur, but I think it can occur. Success being one of the possible outcomes is very important.

That's the breakthrough that SpaceX is really trying to achieve.
« Last Edit: 02/22/2022 03:33 pm by Twark_Main »

Offline xvel

  • Full Member
  • ****
  • Posts: 620
  • I'm metric and I'm proud of it
  • Liked: 685
  • Likes Given: 266
Re: Hypothetical 1/3 Scale Starship
« Reply #26 on: 02/22/2022 03:14 pm »
Amazing how closely this mirrors Elon Musk statements from over a decade ago.

The laws of physics haven't changed much in the last ten years, so... ;)
And God said: "Let there be a metric system". And there was the metric system.
And God saw that it was a good system.

Offline Khadgars

  • Full Member
  • ****
  • Posts: 1750
  • Orange County, California
  • Liked: 1132
  • Likes Given: 3162
Re: Hypothetical 1/3 Scale Starship
« Reply #27 on: 02/22/2022 03:20 pm »
Interesting quotes from Musk there.  I dont' think SpaceX has even started mass efficiency yet on any part of Starship. 

It may end that reaching orbit was the easy part.
Evil triumphs when good men do nothing - Thomas Jefferson

Offline volker2020

  • Full Member
  • ***
  • Posts: 315
  • Frankfurt, Germany
  • Liked: 324
  • Likes Given: 842
Re: Hypothetical 1/3 Scale Starship
« Reply #28 on: 02/22/2022 03:32 pm »
I think at one point, Elon did mention, that the size of starship matters. Because if it was smaller, to keep the same effectiveness, the walls had to be thinner.

Just think about it. Making it shorter, means to keep the same performance ratios, you need thinner steal ...
At one point, it won't work at all. So I really doubt, that shrinking the design without having a closer look at the production, really makes sense.

At least I am quite optimistic, that they can make it bigger.

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 39284
  • Minnesota
  • Liked: 25279
  • Likes Given: 12125
Re: Hypothetical 1/3 Scale Starship
« Reply #29 on: 02/22/2022 03:48 pm »
Interesting quotes from Musk there.  I dont' think SpaceX has even started mass efficiency yet on any part of Starship. 

It may end that reaching orbit was the easy part.
Starship doesn’t need much design efficiency to be viable for initial uses because it can be refueled.

Starship, like Falcon 9, will be continually optimized over time.

I’d say orbit and recovery (and turnaround for relaunch) are the hard parts because once that is accomplished, you have a viable vehicle for Starlink and HLS.

You need 5 launches vs 15 launches per HLS mission depending on mass efficiency… but it can still work.

Getting it to work is the hardest part. Optimizing it will happen over time.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 39284
  • Minnesota
  • Liked: 25279
  • Likes Given: 12125
Re: Hypothetical 1/3 Scale Starship
« Reply #30 on: 02/22/2022 03:50 pm »
I think at one point, Elon did mention, that the size of starship matters. Because if it was smaller, to keep the same effectiveness, the walls had to be thinner.

Just think about it. Making it shorter, means to keep the same performance ratios, you need thinner steal ...
At one point, it won't work at all. So I really doubt, that shrinking the design without having a closer look at the production, really makes sense.

At least I am quite optimistic, that they can make it bigger.
Steel can be extremely thin. Atlas Centaur has stainless steel tank thickness of jus 0.5mm, versus 3-4mm for Starship.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Okie_Steve

  • Full Member
  • ****
  • Posts: 1886
  • Oklahoma, USA
  • Liked: 1141
  • Likes Given: 726
Re: Hypothetical 1/3 Scale Starship
« Reply #31 on: 02/22/2022 04:01 pm »
In the past Musk made comments that some interpreted as a larger future 18 meter rocket was under consideration. He also made comments that maybe a smaller 7 meter rocket would have been an easier choice than 9 meters. Neither of which matters at this point of course since, as he observed when discussing stretching things, longer is relatively straight forward while changing the diameter is incredibly hard.

So, there might be a case for a slightly smaller reusable rocket but larger apparently has a stronger case.

Offline sebk

  • Full Member
  • ****
  • Posts: 774
  • Europe
  • Liked: 969
  • Likes Given: 27121
Re: Hypothetical 1/3 Scale Starship
« Reply #32 on: 02/22/2022 04:30 pm »
I think at one point, Elon did mention, that the size of starship matters. Because if it was smaller, to keep the same effectiveness, the walls had to be thinner.

Just think about it. Making it shorter, means to keep the same performance ratios, you need thinner steal ...
At one point, it won't work at all. So I really doubt, that shrinking the design without having a closer look at the production, really makes sense.

Steel can be thinner. But heatshield tiles can't. And they do not weigh nothing, far from it. The shield must be very roughly 10cm thick, and at 144kg/m^3 this means 14kg per m^2. With 500-600m^2 of shield this is 8 tonnes. It's about 7% of payload mass. If you'd go with 1/3 mass SSH your shield mass would not decrease 3x but about 2x.

[zubenelgenubi: edit for legibility]
« Last Edit: 02/22/2022 07:14 pm by zubenelgenubi »

Offline volker2020

  • Full Member
  • ***
  • Posts: 315
  • Frankfurt, Germany
  • Liked: 324
  • Likes Given: 842
Re: Hypothetical 1/3 Scale Starship
« Reply #33 on: 02/22/2022 04:56 pm »
I think at one point, Elon did mention, that the size of starship matters. Because if it was smaller, to keep the same effectiveness, the walls had to be thinner.

Just think about it. Making it shorter, means to keep the same performance ratios, you need thinner steal ...
At one point, it won't work at all. So I really doubt, that shrinking the design without having a closer look at the production, really makes sense.

At least I am quite optimistic, that they can make it bigger.
Steel can be extremely thin. Atlas Centaur has stainless steel tank thickness of jus 0.5mm, versus 3-4mm for Starship.
Yes Steel can be extremely thin, but it only works, when under pressure. Not having that pressure at production, means you need extensive skeletons to keep the structures in places, which is a hazard for production. Everything becomes more complicated, starting with welding. I did not say, that it was impossible to build it, but that you need to have a look at the production costs.

Offline Keldor

  • Full Member
  • ****
  • Posts: 722
  • Colorado
  • Liked: 896
  • Likes Given: 127
Re: Hypothetical 1/3 Scale Starship
« Reply #34 on: 02/27/2022 10:13 pm »
I think at one point, Elon did mention, that the size of starship matters. Because if it was smaller, to keep the same effectiveness, the walls had to be thinner.

Just think about it. Making it shorter, means to keep the same performance ratios, you need thinner steal ...
At one point, it won't work at all. So I really doubt, that shrinking the design without having a closer look at the production, really makes sense.

At least I am quite optimistic, that they can make it bigger.
Steel can be extremely thin. Atlas Centaur has stainless steel tank thickness of jus 0.5mm, versus 3-4mm for Starship.
Yes Steel can be extremely thin, but it only works, when under pressure. Not having that pressure at production, means you need extensive skeletons to keep the structures in places, which is a hazard for production. Everything becomes more complicated, starting with welding. I did not say, that it was impossible to build it, but that you need to have a look at the production costs.

The thickness they need increases proportionally to radius (as the curvature decreases, tension increases at a constant pressure), as well as height (a taller fuel stack means more pressure at the bottom).  Starship is 3 times wider and the fuel tank is also 2-3 times as tall, so if we were to just scale Atlas-Centaur up, naively we'd need walls 6-8 times thicker, which just happens to be 3-4mm.

Offline Nomadd

  • Senior Member
  • *****
  • Posts: 8853
  • Lower 48
  • Liked: 60522
  • Likes Given: 1316
Re: Hypothetical 1/3 Scale Starship
« Reply #35 on: 02/27/2022 10:28 pm »


Steel can be thinner. But heatshield tiles can't. And they do not weigh nothing, far from it. The shield must be very roughly 10cm thick, and at 144kg/m^3 this means 14kg per m^2. With 500-600m^2 of shield this is 8 tonnes. It's about 7% of payload mass. If you'd go with 1/3 mass SSH your shield mass would not decrease 3x but about 2x.

Where in the world are you getting 10cm for the heat shield?
Those who danced were thought to be quite insane by those who couldn't hear the music.

Offline sebk

  • Full Member
  • ****
  • Posts: 774
  • Europe
  • Liked: 969
  • Likes Given: 27121
Re: Hypothetical 1/3 Scale Starship
« Reply #36 on: 02/28/2022 11:06 am »


Steel can be thinner. But heatshield tiles can't. And they do not weigh nothing, far from it. The shield must be very roughly 10cm thick, and at 144kg/m^3 this means 14kg per m^2. With 500-600m^2 of shield this is 8 tonnes. It's about 7% of payload mass. If you'd go with 1/3 mass SSH your shield mass would not decrease 3x but about 2x.

Where in the world are you getting 10cm for the heat shield?

From different thread (about Starship heatshield). To ensure acceptable skin under the heatshield temperature you need about 11cm thick Li-900 heatshield for aluminum structures, but about 8-9cm for stainless steel.

 Note that in the case of Starship you have not only just the tiles but also the "mineral felt" backing material. Looking at photos and stuff it seems that both materials together are in the order of 3 inches thick. Am I wrong?

Offline livingjw

  • Senior Member
  • *****
  • Posts: 2380
  • New World
  • Liked: 5901
  • Likes Given: 2909
Re: Hypothetical 1/3 Scale Starship
« Reply #37 on: 02/28/2022 03:35 pm »
I put together a quick scaling model. You start with an existing vehicle's mass breakdown. Different items scale at different rates.

Note: Weight spread sheet available here:
 https://forum.nasaspaceflight.com/index.php?topic=50049.msg2149131#msg2149131
I don't know if it has been updated. We should ask equiserre.

John
« Last Edit: 02/28/2022 03:56 pm by livingjw »

Offline Nomadd

  • Senior Member
  • *****
  • Posts: 8853
  • Lower 48
  • Liked: 60522
  • Likes Given: 1316
Re: Hypothetical 1/3 Scale Starship
« Reply #38 on: 02/28/2022 04:19 pm »


Steel can be thinner. But heatshield tiles can't. And they do not weigh nothing, far from it. The shield must be very roughly 10cm thick, and at 144kg/m^3 this means 14kg per m^2. With 500-600m^2 of shield this is 8 tonnes. It's about 7% of payload mass. If you'd go with 1/3 mass SSH your shield mass would not decrease 3x but about 2x.

Where in the world are you getting 10cm for the heat shield?

From different thread (about Starship heatshield). To ensure acceptable skin under the heatshield temperature you need about 11cm thick Li-900 heatshield for aluminum structures, but about 8-9cm for stainless steel.

 Note that in the case of Starship you have not only just the tiles but also the "mineral felt" backing material. Looking at photos and stuff it seems that both materials together are in the order of 3 inches thick. Am I wrong?
The underlayment varies, but the tiles are only about an inch thick at the edges and where the brackets are, and only about 5/8 inch for the rest. That's from pre SN15 samples. (Most of which were used up in an attempt to build a heat shield for a Harley exhaust pipe)
« Last Edit: 02/28/2022 04:29 pm by Nomadd »
Those who danced were thought to be quite insane by those who couldn't hear the music.

Offline FunBobby

  • Member
  • Posts: 36
  • Germany
  • Liked: 18
  • Likes Given: 11
Re: Hypothetical 1/3 Scale Starship
« Reply #39 on: 02/28/2022 05:04 pm »
So, the scaling guide posted above is quite interesting.  If I am reading it correctly, one of the big advantages of really large rockets is that the mass percentage of TPS scales as a less than linear function and TPS is one of if not the biggest dry mass addition for a reusable rocket.  Does that also then support the argument for short stubby rocket stages since they will have reduced surface area to hold a given amount of fuel and propellant and that is less to shield?  At least maybe that argument is valid for something entering ballistic, maybe it no longer applies if you need to generate lift as well.  I also understand that a rocket stage shaped like a beach ball would introduce other challenges for construction and transportation. 

As far as transportation, I had a University Professor over 20 years ago who liked to say that the SRB diameter for the Shuttle was set by the width of a horses ass..........Initial rail lines in Europe and N.A. where of course based on a standardized track width to worth with a standardized train size.  Many of those lines were built on high volume roads that had existed for centuries which needed to allow passage of horse drawn traffic in both directions.  Due to SRBs being built in Utah and the Shuttle launching from Florida, rail transit was highly desired so the segments had to fit onto rail cars.......as part of trains.......running on standardized tracks.........okay so maybe embellished a little, but a maybe a little bit of truth to it.  So the so what for me is that once your rocket stage is already to big to put on railroad cars or pass under highway bridges or load onto airplanes, why not just make it in the optimized shape/size relative to the mass of your launch vehicle? 
Cheers,
Bobby

Offline livingjw

  • Senior Member
  • *****
  • Posts: 2380
  • New World
  • Liked: 5901
  • Likes Given: 2909
Re: Hypothetical 1/3 Scale Starship
« Reply #40 on: 03/01/2022 12:33 am »
So, the scaling guide posted above is quite interesting.  If I am reading it correctly, one of the big advantages of really large rockets is that the mass percentage of TPS scales as a less than linear function and TPS is one of if not the biggest dry mass addition for a reusable rocket.  Does that also then support the argument for short stubby rocket stages since they will have reduced surface area to hold a given amount of fuel and propellant and that is less to shield?  At least maybe that argument is valid for something entering ballistic, maybe it no longer applies if you need to generate lift as well. ....

If you want similar heating loads you need to maintain similar Ballistic Coefient (BC) and CL capabilities for the scaled vehicle. You should be able to maintain these as you scale down, it might even be a little easier at a smaller scale since BC is proportional to W/(CD*A). CD will stay about the same, weight will scale with SFv and A will scale with SFa.

John

Offline FunBobby

  • Member
  • Posts: 36
  • Germany
  • Liked: 18
  • Likes Given: 11
Re: Hypothetical 1/3 Scale Starship
« Reply #41 on: 03/06/2022 09:22 am »
Is it possible to circumvent some of the scaling issues if you employ non-structural re-entry devices?  Specifically what I was thinking about is reducing structural heating by changing the BC through the use of something like a Ballute?  I know that SpaceX briefly considered this as a strategy to recover a Falcon 9 upper-stage with minimal TPS.  I understand that you are basically inflating a structure with gas that increases surface area and drag for ballistic re-entry.  I think this has also been considered as a strategy for Mars atmospheric entry.  This is probably not the best technology for rapid-reuse with minimal refurbishment since I can't imagine the ballute itself being reusable, so it doesn't really have an application for a Starship-like vehicle.  Instead it might be something that Rocket Lab considers if/when they try and develop a reusable 2nd stage.
Cheers,
Bobby

 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1