5. Would a 1/3 scale Starship ... [be] able to provide support eventual Mars Colonization?
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 ...
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).
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
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
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
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.
Quote from: FunBobby on 02/21/2022 04:16 pmThank 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.
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 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.
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.
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.
Amazing how closely this mirrors Elon Musk statements from over a decade ago.
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.
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.
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.
Quote from: volker2020 on 02/22/2022 03:32 pmI 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.
Quote from: Robotbeat on 02/22/2022 03:50 pmQuote from: volker2020 on 02/22/2022 03:32 pmI 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.
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.
Quote from: sebk on 02/22/2022 04:30 pmSteel 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?
Quote from: Nomadd on 02/27/2022 10:28 pmQuote from: sebk on 02/22/2022 04:30 pmSteel 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?
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. ....
