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RCgothic

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    Could the SuperHeavy booster be SSTO?

    in Science & Spaceflight

    Posted

    Making a recoverable SSTO Superheavy would require:

    Stretching it to accommodate more fuel.

    Adding a payload fairing and cargo door.

    The engines are less protected than on Starship so that's additional mass for a wider and more substantial base skirt.

    It'd also need fins like starship to prevent it orienting engines-first on re-entry, and they'd need to be a lot bigger than starship's. 

    A full-length heat shield.

    And structural reinforcements to cope with the horizontal entry and fin loading.

    A normal Superheavy starts off at about 160-180t dry. All of the above could easily take it above 300t. The only positive is that there's no longer any need for grid fins.

    Could the SuperHeavy booster be SSTO?

    in Science & Spaceflight

    Posted · Edited by RCgothic

    Even if an upscaled EXPENDABLE SSTO SUPERHEAVY could put 150t pure payload in orbit, that:

    1) DOES NOT match the 250t-300t of a similar expendable Starship/recovered Superheavy can manage whilst throwing away 24 or 27 fewer engines.

    2) DOES NOT match the cheapness of a completely reusable Starship/Superheavy that throws nothing away.

    Generously, if the dry mass of an upscaled SSTO Superheavy would be around 80-90t, then that'd be 230-240t to orbit total. The dry mass of a RECOVERABLE SSTO SUPERHEAVY would be around 160-180t, and the fuel reserves for landing would be around 50t, so the payload would be maybe 10-30t for basically the same fuel expenditure as the TSTO. So the SSTO recoverable Superheavy (if it even works):

    3) COSTS 5-15 X AS MUCH PER KG as a fully recoverable TSTO in terms of the only substantial consumable, propellant.

    Seriously, the TSTO performance and price is unassailable by an SSTO, even being generous. If recoverable SSTO Superheavy were preferable to TSTO Starship/Superheavy, that's what SpaceX would be building.

    Could the SuperHeavy booster be SSTO?

    in Science & Spaceflight

    Posted

    2 hours ago, Exoscientist said:

     I’ve acknowledged the expendable TSTO gets more payload to orbit than the expendable SSTO. The point I’m making is the reusable SSTO meets or exceeds the reusable TSTO payload. The reason is the fully reusable TSTO loses 50% of its payload due to the large amount of propellant that has to remain unused on ascent to orbit in order to cancel out the first stage forward motion and to boost it back to the launch site. Note this unused propellant is doubly disadvantage as far as orbital payload is concerned. First, it adds deadweight on ascent to orbit, and secondly it reduces the propellant load that can be used for that ascent.

    No, SSTO never matches TSTO. 

    The reuse penalty is *already included* in the 150t to LEO. That's 100% reusable Starship, 100% reusable Superheavy. 

    The Starship expendable payload is 250t to 300t. Superheavy is still recovered in this figure.

    The *fully expendable* Starship/Superheavy combo is somewhere between 420-500t .

     

    Superheavy SSTO can do maybe 50t payload expendably and does not have enough margin for recovery.

    Could the SuperHeavy booster be SSTO?

    in Science & Spaceflight

    Posted · Edited by RCgothic

    Yes, the TSTO fully reusable payload of Starship Superheavy is ~150t. This is *already* with the reuse penalty applied.

    Total mass to orbit is ~265t (150t payload plus 30t landing propellant + 85t ship). Assuming a 40% mass to LEO penalty from booster reuse, the total mass to LEO expendably would be 475t. With an expendable 40t ship with no landing fuel, fins, heat shield etc, that's an expendable TSTO payload of 435t.

    That's your apple for comparison with the SSTO.

    And now we go back and see that even expendably an SSTO Superheavy would put up *maybe* 50t expendably. Then we note that making Starship reusable (an equivalent task to reusing Superheavy SSTO)  more than doubles the structural weight, plus requires over 30t of reserved landing propellant and oh look we're all out of payload. Superheavy SSTO reusable doesn't close.

    SSTO *never* wins against TSTO

    Weird Facts About Spacecraft Maneuvers And Orbital Maneuvers.... Am I Right Or Wrong?

    in Science & Spaceflight

    Posted · Edited by RCgothic

    If you have a drive capable of constant acceleration, don't worry about fuel efficiency when catching a target ahead of you in the orbit. You can brute-force it.

    Basically, you accelerate so you are going faster, so gravity is no longer enough to hold you at that radius and so your orbit would expand, but then you just thrust inwards to compensate. You'll catch the target much sooner than playing games with orbital mechanics.

    Also, most rendezvous dependent on orbital mechanics assumes a cooperative target. It can be very hard to next to impossible to catch an actively manoeuvring opponent if you're fuel-limited.

    Could the SuperHeavy booster be SSTO?

    in Science & Spaceflight

    Posted · Edited by RCgothic

    5 hours ago, sevenperforce said:

    Plugging in realistic numbers for the mass of Superheavy and adding a payload fairing no longer than the one on Falcon 9, Silverbird gives me an 88.6 tonne payload with 33 engines and an 84.4 tonne payload with 27 engines.

    And this is all extremely silly because why would you expend an entire booster for an 80-90 tonne payload when you could recover the booster and expend only an upper stage to get 3x as much payload into LEO??

    Anything an SSTO can do, a TSTO can do better. 

    It's actually quite remarkable that the SSTO performance could even be as good as 1/3 the TSTO performance.

    43 minutes ago, Exoscientist said:

     The military is considering using the Starship for troop transport:

    TECH & SCIENCE

    Pentagon Mulls Using Elon Musk's Rockets to Deploy Troops From Space

    BY ED BROWNE ON 6/24/22 AT 12:33 PM EDT

    https://www.newsweek.com/pentagon-military-elon-musk-starship-deploy-troops-space-1718969

     Clearly for such a use it would be better to have this capability as a single stage. Considering that the military, like NASA, overpays for everything SpaceX could probably get a billion dollar deal for developing this capability.

     Having a SSTO capability would be a great selling point for this purpose.

       Robert Clark

    Rockets are not remotely combat hardenable. It's akin to trying to land a very large and very delicate bomb near your own positions. Not remotely recommended anywhere even remotely unsecured. Add in that opponents are liable to view it as an incoming ICBM (and react to it as such) and this is probably not an idea that will reach widespread implementation.

    Artemis Discussion Thread

    in Science & Spaceflight

    Posted

    3 hours ago, SunlitZelkova said:

    I know many like to say “it’s all because of SLS”, but to what extent does Congress actually hold sway over NASA planning?

    Why hasn’t doing an architecture with the Commercial Crew vehicles and LSS in LEO and then traveling to the Moon been at least been mentioned as a possibility? 1960s NASA documents are full of proposals denying their own purpose if something more efficient for the same job comes along.

    If they do have some reason not to adopt such an architecture, they ought to inform the public. If we get one Moon landing in 2026 and nothing happens for five years, can you imagine the hard time the media is going to give NASA for choosing the mission profile they did and rejecting other concepts? Especially if Starship is flying regularly by then and perhaps done a few crew missions.

    Apollo literally began with North American offering to build a direct ascent lunar lander but then agreeing to shave off part of their role in the program (and thus income) in favor of LOR with Grumman’s LM. Why would it be so difficult to cut Gateway or even SLS out of the picture?

    The current situation says something rather sad about NASA planners, as this is the “almost like someone playing KSP” type of concept that can be found in many 1960s studies and concepts.

    For Apollo, the goal was commanded, the method was flexible.

    For Artemis, the method is commanded, the goal is flexible.

    If Congress says they have to build and use SLS, they have to do it. If Congress doesn't give them funds to study other architectures, they can't.

    SpaceX Discussion Thread

    in Science & Spaceflight

    Posted

    12 minutes ago, Pthigrivi said:

    Yeah starship itself doesn't make much sense as a military platform. Reusability is the whole point and that still takes a lot of ground infrastructure. Like you could use it to deliver a few dozen armed drones that deploy seconds after landing to secure a perimeter, but then it's basically stuck there. It's also going to be hugely vulnerable to SAM fire during belly flop. 

    I suppose it could Adama-manoeuvre a load of drones at a height above conventional SAM ceiling and then additionally pancake on a target, but that's kind of ICBM-adjacent. I suspect other nations are unlikely to approve.

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