Could the SuperHeavy booster be SSTO?

RGClark · 2022-06-30 19:25:12

Running some numbers for the SuperHeavy+Starship launcher, I was surprised to get that an expendable SuperHeavy alone could be SSTO with quite high payload. Wikipedia gives the propellant mass of the SuperHeavy as 3,400 tons, but does not give the dry mass. We can do an estimate of that based on information Elon provided in a tweet:

Elon Musk
@elonmusk
Replying to @Erdayastronaut and @DiscoverMag
Probably no fairing either & just 3 Raptor Vacuum engines. Mass ratio of ~30 (1200 tons full, 40 tons empty) with Isp of 380. Then drop a few dozen modified Starlink satellites from empty engine bays with ~1600 Isp, MR 2. Spread out, see what’s there. Not impossible.
9:14 PM · Mar 29, 2019·Twitter for iPhone 90 Retweets 32 Quote Tweets 1,498 Likes
https://twitter.com/elonmusk/status/111 … SDa_YI0OyA

This is for a stripped down Starship, no reusability systems, no passenger quarters, and reduced number of engines. But this could not lift-off from ground because of the reduced thrust with only 3 engines plus being vacuum optimized these could not operate at sea level. So up the number of engines to 9 using sea level Raptors. According to wiki the Raptors have a mass of 1,500 kg. So adding 6 more brings the dry mass to 49 tons, call it 50 tons, for a mass ratio of 25 to 1.

By the way, there have been many estimates of the capabilities of the Starship for a use other than that with the many passengers, say 50 to 100 , to LEO or as colonists to Mars, for instance, such as the tanker use or only as the lander vehicle transporting a capsule for astronauts for lunar missions. But surprisingly they all use the ca. 100 ton dry mass of the passenger Starship. But without this large passenger compartment it should be a much smaller dry mass used in the calculations. For instance, the Dragon 2 crew capsule dry mass without the trunk is in the range of 7 to 8 tons for up to 7 astronauts. So imagine a scaled up passenger compartment for 50 passengers or more. That passenger compartment itself could well mass over 60 tons.

So the dry mass estimate of a stripped down, expendable, reduced engine Starship of 40 tons offered by Elon does make sense.

Based on this, an expendable Starship with sufficient engines for ground launch could be SSTO:

the ISP of the Raptors for both sea level and vacuum-optimized versions have been given various numbers. I’ll use 358 s as the vacuum ISP of the sea level Raptor. For calculating payload using the rocket equation, the vacuum Isp is commonly used even for the ground stage, since the diminution in Isp at sea level can be regarded as a loss just like air drag and gravity loss for which you compensate by adding additional amount to required delta-v to orbit just like the other losses.

Then 3580ln(1 +1200/(50 + 50)) = 9,180 m/s sufficient for LEO.

But as of now, SpaceX has no plans of making the Starship a ground-launched vehicle. So we’ll look instead at the SuperHeavy. For an expendable version with no reusability systems, we’ll estimate the dry mass using a mass ratio of 25 to 1, same as for a ground-launched expendable Starship. Actually, likely the Superheavy mass ratio will be even better than this since it is known scaling a rocket up improves the mass ratio. So this gives a dry mass of 136 tons. Then the expendable SuperHeavy could get 150 tons to LEO as an expendable SSTO: 3580ln(1 + 3,400/(136 + 150)) = 9,150 m/s, sufficient for LEO.

But what about a reusable version? Reusability systems added to a stage should add less than 10% to the dry mass:

_______________________________________________________________________
From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: The cost (in weight) for Reusable SSTO
Date: Sun, 28 Mar 1999 22:37:10 GMT

In article <kemJ2.876$Vc2.18603@news-west.eli.net>,
Larry Gales <larryg@u.washington.edu> wrote:
>An SSTO with a useful payload using Kero/LOX is easy to do -- provided that
>it is *expendable*. All of the difficulty lies in making it reusable...

There are people who are sufficiently anti-SSTO that they will dispute the
feasibility of even expendable SSTOs (apparently not having read the specs
for the Titan II first stage carefully).

> (1) De-orbit fuel: I understand that it takes about 100 m/s to de-orbit.

That's roughly right. Of course, in favorable circumstances you could play
tricks like using a tether to simultaneously boost a payload higher and
de-orbit your vehicle. (As NASA's Ivan Bekey pointed out, this is one case
where the extra dry mass of a reusable vehicle is an *advantage*, because
the heavier the vehicle, the greater the boost given to the payload.)

> (2) TPS (heat shield): the figures I hear for this are around 15% of the
>orbital mass

Could be... but one should be very suspicious of this sort of parametric
estimate. It's often possible to beat such numbers, often by quite a large
margin, by being clever and exploiting favorable conditions. Any single
number for TPS in particular has a *lot* of assumptions in it.

> (4) Landing gear: about 3%

Gary Hudson pointed out a couple of years ago that, while 3% is common
wisdom, the B-58 landing gear was 1.5%... and that was a very tall and
mechanically complex gear designed in the 1950s. See comment above
about cleverness.

I would be very suspicious of any parametric number for landing gear which
doesn't at least distinguish between vertical and horizontal landing.

> (5) Additional structure to meet loads from differnet directions (e.g.,
>vertical
> takeoff, semi-horizontal re-enttry, horizontal landing). This is
>purely
> guesswork on my part, but I assume about 8%

Of course, here the assumptions are up front: you're assuming a flight
profile that many of us would say is simply inferior -- overly complex,
difficult to test incrementally, and hard on the structure.

>I would appreciate it if anyone could supply more accurate figures.

More accurate figures either have to be for a specific vehicle design,
or are so hedged about with assumptions that they are nearly meaningless.
--
The good old days | Henry Spencer henry@spsystems.net
weren't. | (aka henry@zoo.toronto.edu)
_________________________________________________________________
https://yarchive.net/space/launchers/la … eight.html

The 15% mentioned for thermal protecton(TPS) is for Apollo-era heat shields. But the PICA-X developed by SpaceX is 50% lighter so call it 7.5% for TPS. And for the landing gear ca. 3%, but with carbon composites say half of that at 1.5%.

But this would put the reusable payload at ca. 136 tons which is in the range of 100 to 150 tons of the full two stage reusable vehicle!

How is that possible? A reusable multistage vehicle has a severe disadvantage. The fuel that needs to be kept on reserve for the first stage to slow down and boost back to the launch site subtracts greatly from the payload possible. But for a reusable SSTO it can remain in orbit until the Earth rotates below until the landing site is once again below the vehicle.

Robert Clark

Last edited by RGClark (2022-07-03 08:15:31)

kbd512 · 2022-06-30 21:15:23

RGClark,

If it was possible to recover the engines and to use a low-cost high strength alloy steel with a coating to resist LOX, for single-use, then this might actually make sense if the propellant tanks were robotically fabricated. So long as it was used for cargo-only, there's probably no way to make a cheaper rocket. If the propellant tank steel is $750/t, then that's $26,625 for 35.5t of steel. If it can be made to work using cheap all-welded materials, with engine recovery using another reusable Starship in orbit, then I can't see any real downside to making space launches equivalent to the cost of the steel plus propellant. If it can be made even lighter and cheaper using steel balloon tanks, then that directly translates into payload performance, so a single-use SSTO Starship may end up being a lot cheaper than the alternatives. You could reduce dry mass by about 10t using balloon tanks, so 146t to LEO.

If the goal is to take food, water, parts of larger ships such as my all-steel "large ship" concept, or slit coil steel for on-orbit fabrication of larger ships, then you may not need much of a payload fairing or other nonsense. Assuming that the engines could be taken back to Earth from orbit in a fully reusable starship, then this has to be the cheapest ride out there. All of these changes could also drastically reduce the dry mass of the vehicle, to the point where we end up with almost identical payload performance without paying a lot more for a reusable vehicle.

I remain skeptical about the true cost of fully reusable vehicles that reenter the atmosphere. I think operating them will be some multiple of the fuel and maintenance associated with a very large commercial airliner, so it'd be great if reusable vehicles left with payloads and came back with payloads. Tossing a 25t of low alloy steel into the ocean would require thousands of trips to orbit each year to equal the amount of steel in the old ships sunk every year to create artificial reefs.

Beyond that, we need to keep some engines in orbit at a shipyard, to serve as on-orbit spares. Maybe we can use some of these steels one more time as tugs, and then toss the throwaway steel balloon tanks in the drink.

SpaceNut · 2022-07-01 10:36:33

Change the BFR stage to a starship shape and we got a recoverable rocket.

Void · 2022-07-01 11:09:40

There seem to be many emerging possibilities.

For my part, I would wonder if like kbd512 suggested the engines could be removed to another use.

Then make the cabin easily disconnect able, and make space stations out of those.

As for the rest of the ship make the propellant tanks as part of a fuel depot(s), or recycle the mass through something like a 3D printing process.

No need for landing, no need for Machalilla, no need to stack two stages together. No landing legs, no heat shield.

Eventually we might hope to get building materials for orbit from the Moon or asteroids, but for a while the above might be an option to boot up orbital infrastructure.

Sorry about that OK off topic. Well similar. Maybe you could put a "Cabin" on top of the Super heavy, and then the same logic applies.

Done.

Last edited by Void (2022-07-01 11:11:10)

kbd512 · 2022-07-01 11:48:39

Void,

I have a much better idea that wastes nothing. We use the steel from the now empty propellant tank for the large ship construction, then we take the engines back to Earth using a separate Starship that's reusable. Any residuals in the main tanks we will siphon off prior to disassembly and store that in a single purpose-built cryogenic propellant storage tank. There's always 1% to 3% residual to avoid destroying the engines through cavitation.

RGClark is brilliant.

25t of free sheet steel from the empty propellant tanks, plus the payload steel, plus the LOX/LCH4 residuals extracted before deconstruction, engines go back to Earth every few launches, and some stay in orbit for the tug idea that GW had and on-orbit maneuvering. We get greater total payload performance from the disposable SSTO than we get from the resuable vehicle, and no waste of anything. We spent the energy to get the payload to orbit and cannot recover it, so we use everything on-orbit. The engines, wiring harness, and sensors will go back to Earth. The thrust structure will also be consumed building the large ship.

Maybe, just maybe, we can use disposable vehicles cheaply enough to use conventional chemical propulsion for most of the dV requirement to escape from Earth (TMI), which should make tahanson43206 and FriendOfQuark1 happy, but this will greatly increase the tonnage of the ship due to the tankage and propellant required for Mars Orbital Insertion, because the ship is not a lander. Our total dead head payload is about triple a Starship, which is not inserting into orbit at Mars.

Void · 2022-07-01 12:02:52

kbd512, yes that seems to head in the right direction.

It appears to come down to what is the scrap value of parts of the ships, at the location that they arrive at.

If it is high, then perhaps a SSTO is sensible.

For the Large ship sure. But if it remains more sensible than getting materials from elsewhere, then it makes sense to mass produce the SSTO ships and send as many as the market will bear for price, presuming that you might also manufacture orbital structures as well, that have sufficient value.

I am on board.

Done.

Last edited by Void (2022-07-01 12:03:36)

kbd512 · 2022-07-01 12:57:43

Void,

You have to recover the engines and electronics for this to work. Everything else can be easily scrapped. It's sheet steel. We know how to recycle that stuff. No other materials fabrication technology is as well-developed as steel making and recycling. Even concrete is still undergoing quite a bit of experimentation, by way of comparison. Sure, we have to develop some machinery to do it, but we're not asking for anything fundamentally new. The concept of on-orbit construction is somewhat new, but we've done it over and over again to build space stations. We need a giant space station to put people in orbit, giant ships that can only be built on-orbit, and lots of propellant. Basically, we need to industrialize space so that we can bring the costs down to what we expect from all other forms of mass-manufacturing. We can't do colonization without industrialization, plain and simple.

Void · 2022-07-01 13:43:12

If you will tolerate a few words about Starship 2.0, it seems to me that prior to the full building of that version, an SSTO of that size might be created, it should punch through the Earth's atmosphere more effectively as per surface area and volume, and while you might scrap the steel in some cases, it may be that a very large volume would have it attractions as well.

As it would not land, you eliminate that possible source of explosion. I am just saying that down the road if 1.0 works for SSTO then a larger 2.0 version might have merit.

It does depend on relative value of the scrap to other options.

Done

Calliban · 2022-07-01 17:44:09

Repurposing rather than reuse. It does make certain amount of sense. The original ITS had a 550te payload in expendable mode and only 300te in reusable mode. A single use vehicle could be lighter, with smaller design factors, as fatigue life does not need to be so long. The effective life of the tanks need to no greater than a few days, with onky a handful of pressure cycles. For the plan to work, the vehicle must be modular in construction, allowing engines, navigation and thruster modules to be decoupled easily.

SpaceNut · 2022-07-01 20:41:26

So, the real question for the scrap yard is what sort of shipyard can be constructed to allow for this size ship to be cannibalized in. As we need to have staff there with the correct tools to rip it apart.

kbd512 · 2022-07-01 21:22:53

SpaceNut,

As thin as the sheet metal will be, you could take it apart with a pair of tin snips. We probably won't use implements quite that crude, but most sheet metal tools don't require gravity or an atmosphere to use. You're correct about the first use case I have for the material, though. We need a shipyard to help fabricate the ships. We need the ability to fixture parts in place for welding.

SpaceNut · 2022-07-01 21:34:25

Sounds like we need a Canadian arm as space suits and sharp edges do not mix.

kbd512 · 2022-07-02 00:12:20

SpaceNut,

Nobody will be venturing outside a spacecraft. That's a non-starter. A shipyard is a dangerous place on Earth, never mind orbit.

SpaceNut · 2022-07-02 10:40:11

I know of Naval shipyard dangers all too well.

Well since the items are to be taken apart then we have an issue of risk mitigation. This what the ISS is doing for all space walks. It is our only model currently in use that allows for the learning of how to progress towards what we want. Even with the Hubble upgrades we learned that a stable platform to work from was required.

SpaceNut · 2022-08-16 18:30:06

A recent test saw the failure on the 6th of hydraulics. The Mechazilla robot arms created by SpaceX are lovingly referred to as chopstick arms. These mechanical arms have been built to make lifting, moving and stacking the SpaceX Starship and Super Heavy boosters easier and quicker. So more testing and modification still possible before its going to leave the launch pad.

Calliban · 2023-04-25 14:53:45

One way we could use Starship as an SSTO, would be to build an orbital chandelier platform. This works rather like a space elevator on a smaller scale. We launch a counterweight satellite loaded with ballast to an orbital altitude of say, 2000km above Earth. We extend cables down to a suspended platform with an orbital altitude of ~200km. The platform, cables and counterweight, will orbit at the orbital velocity corresponding to the altitude of the centre of mass of the whole structure, which will be much closer to the counterweight than the platform. Given that the counterweight is in a higher orbit, this means that the suspended platform will be orbiting at a velocity substantially lower than local orbital velocity. This will place the cables under tension, but not so much tension as to require the use of flawless diamond filaments as cable material.

A Starship would be launched from Earth surface to land on the platform. It's dV will be a function of the change in gravitational potential energy between 0m and 200,000m, plus the kinetic energy needed to achieve orbital velocity at 2000km. Since orbital velocity at 2000km is substantially lower than orbital velocity needed for a 200km circular orbit, the total dV required to reach and land on the platform, would be lower than that needed to achieve a 200km circular orbit. Once on the platform, passengers and cargo would disembark and would be lifted up the cable to the counterweight satellite. The Starship would return to Earth from the platform. This would involve entering the atmosphere at less than typical orbital velocity, which should reduce the design requirements of the heat shield.

At the counterweight satellite, passengers would board a ferry vehicle, which would transfer them to an Earth-Moon cycler. Cargo would be lifted to higher orbits using low thrust propulsion.

The reduced dV needed to reach the platform, reduces the mass ratio required to achieve a practical SSTO. If dV is reduced sufficiently to allow Starship upper stage to be used as an SSTO, then we eliminate the requirement for a booster and all of the infrastructure needed to recover and service that booster. If a launch assist could be used to boost Starship takeoff velocity to ~Mach 1, then gravity losses are reduced substantially, increasing the effective payload capacity.

Last edited by Calliban (2023-04-25 15:03:33)

Void · 2023-04-25 20:45:38

Technically, that would be staging of a sort, but please continue.

I have had a notion in time that a solar power platform might able to have cables down to a location where atmosphere could be collected. In order to do this however then a propulsion is needed. The Europeans have a Electric Ion engine which can act on the atmosphere's Nitrogen.
It seems far fetched to use it at this time, but remember that the electricity would come from solar panels high up enough to not have a lot of drag.

Now, there is this: https://www.nasa.gov/directorates/space … ploration/
Quote:

Jan 9, 2023
Photophoretic Propulsion Enabling Mesosphere Exploration
Igor Bargatin
University of Pennsylvania

Their numbers converted to Millibar are .01 to 1 Millibar., or possibly allowing 10 Millibar

They seem to be primarily using the propulsion to levitate. With Tethers, that may not be what is wanted.

What if we have a device that heats up with Microwaves? The Microwaves coming from the solar panels some distance higher in an orbital position, but probably cutting more degrees of position than it should, due to the tethers.

The point being could we sort of create a scramjet powered by microwaves?

I admit, this is a very unsure grip I have on it. Where from my point of view is to keep the apparatus elevated and not dragged down, I also would hope to collect atmospheric Gasse, mine the atmosphere, and then bring that to orbit.

But down the road, perhaps solid loads could be landed in a fashion similar to your notions.

And we might hope to do the same for Mars as well.

Last edited by Void (2023-04-25 20:58:03)

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#1 2022-06-30 19:25:12

Could the SuperHeavy booster be SSTO?

#2 2022-06-30 21:15:23

Re: Could the SuperHeavy booster be SSTO?

#3 2022-07-01 10:36:33

Re: Could the SuperHeavy booster be SSTO?

#4 2022-07-01 11:09:40

Re: Could the SuperHeavy booster be SSTO?

#5 2022-07-01 11:48:39

Re: Could the SuperHeavy booster be SSTO?

#6 2022-07-01 12:02:52

Re: Could the SuperHeavy booster be SSTO?

#7 2022-07-01 12:57:43

Re: Could the SuperHeavy booster be SSTO?

#8 2022-07-01 13:43:12

Re: Could the SuperHeavy booster be SSTO?

#9 2022-07-01 17:44:09

Re: Could the SuperHeavy booster be SSTO?

#10 2022-07-01 20:41:26

Re: Could the SuperHeavy booster be SSTO?

#11 2022-07-01 21:22:53

Re: Could the SuperHeavy booster be SSTO?

#12 2022-07-01 21:34:25

Re: Could the SuperHeavy booster be SSTO?

#13 2022-07-02 00:12:20

Re: Could the SuperHeavy booster be SSTO?

#14 2022-07-02 10:40:11

Re: Could the SuperHeavy booster be SSTO?

#15 2022-08-16 18:30:06

Re: Could the SuperHeavy booster be SSTO?

#16 2023-04-25 14:53:45

Re: Could the SuperHeavy booster be SSTO?

#17 2023-04-25 20:45:38

Re: Could the SuperHeavy booster be SSTO?

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