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A reusable SLS?


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 The SLS is now projected to cost $4 .1 billion per flight. Because of that severe cost it is projected to only fly once per year. This can not form the basis of a sustainable Moon colonization plan. But suppose we could make the SLS reusable? It’s already known the side boosters can be made reusable as with the shuttle program. The engines on the SLS core stage were derived from the shuttle engines which were intended to be reused up to 100 times. However, since the SLS was intended to be expendable the shuttle-derived engines on the core were designed cheaper to be expendable. However, any rocket engine even an expendable in reality is reusable at least 10 times or more. This is because they have to be certified for several firings for testing purposes. This is described by the well-regarded space expert Henry Spencer:

_______________________________________________________________________________________________________________

From: Henry Spencer <[email protected]>
Newsgroups: sci.space.tech
Subject: RLV engines (was Re: X-33 Concepts: Lockheed, Mac Dac, Rockwell)
Date: Wed, 19 Jun 1996 13:03:12 GMT

In article <[email protected]> [email protected] (Andy Haber) writes:
>I think this is an area where critics can speak the loudest.  Today's 
>existing engines all leave something be be desired as true, good SSTO engines.
>This is mostly due to history.  Most engines (other than SSME's) were 
>designed for ELV's, not SSTO's.

Actually, this does not have a lot of bearing on their suitability for
RLVs.  Most ELV engines are, despite their application, reusable, because
they have to be developed and tested.  The F-1 was specified for 20 starts
and 2250s of life, the J-2 for 30 and 3750s.  Six F-1s ran over 5000s each
as part of the service-life tests.  DC-X's RL10s looked "pristine" after
20 starts; the RL10 is nominally rated for 10 starts and 4000s of firing.

>...In terms of using SSME's, sure those can used,
>although doing something to reduce the required level on maintenance on
>the existing engines is quite desirable...

Unfortunately, it probably can't go far enough.  Rocketdyne's own estimate
was that, with a *lot* of work, you could probably get SSME maintenance
costs down to $750k/engine/flight, which is unsatisfactory if you're aiming
for really large cost reductions.
-- 
If we feared danger, mankind would never           |       Henry Spencer
go to space.                  --Ellison S. Onizuka |   [email protected]

_______________________________________________________________________________________________________________

https://yarchive.net/space/rocket/engine_reusability.html

 Then even reusing the vehicle 10 times could result in a factor of 10 reduction of launch cost, if the maintenance cost could be kept relatively low. That quote about $750, 000 maintenance cost after a lot of work may seem low but from memory I recall it being in the range of $1 million to $2 million per engine after several years into the shuttle program.

 But how to land the SLS core? Starting the SSME’s is a complex process. Modifying them to be air-startable would not be trivial. Instead, I suggest using the method proposed for making the Centaur a lunar lander, multiple pressure-fed side thrusters for a horizontal landing. 

E9fMgyUXEAUfDvH?format=jpg&name=medium

Robust Lunar Exploration Using an Efficient Lunar Lander Derived from Existing Upper Stages. 

 Note then that for a stage reenterring to Earth broad-side almost all the reentry velocity is burned off aerodynamically just by air drag so that the stage reaches terminal velocity at approx. 100 m/s. For a stage nearly empty of fuel, this low amount of velocity could be cancelled relatively easily by pressure-fed thrusters with the thrusters running on just the residual of propellant left in the tanks.

   Robert Clark

 

Edited by Exoscientist
Clarity
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Nice idea, but...

- It would add even more time and expenses to development process.

- Comes with very high probability of losing very big, very expensive rockets early on in the process of working bugs out of the system.

- It wouldn't be SLS anymore. Not really.

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47 minutes ago, Exoscientist said:

Note then that for a stage reinterring to Earth broad-side almost all the reentry velocity is burned off aerodynamically just by air drag so that the stage reaches terminal velocity at approx. 100 m/s. For a stage nearly empty of fuel, this low amount of velocity could be cancelled relatively easily by pressure-fed thrusters with the thrusters running on just the residual of propellant left in the 

Many things missing:

1: the SLS core is going very fast by the time the EUS is separared. Not orbital, but much faster than the F9 first stage (and closer to the Vucal core). Even F9 requires some heat shielding to be able to return, plus grid fins for steering, plus header tanks for landing & boostback; Vulcan to reuse the engines will need a much bigger heat shield than F9. All of this is weight that you haven't accounted for; that is not to say that reusability is the wrong way to go or anything, but rockets with a large first stage compared to the second (usually hydrolox) are terrible for RTLS or even ASDS. Also, add landing gear and additional pressurization and modifications to avoid sloshing when starting the engines  while horizontal

2: Where does the SLS land?

3: Does it do an RTLS, a boostback burn, an entry burn?

4: How does it steer, and how does it remain horizontal in a very tail heavy configuration?

5: How long does the development for this take? You need new avionics, new aerodynamics to study (because of exposed landing engines and legs), a new set of Grasshopper-like demonstrators plus, of course, the actual changes to the rocket

6: What about the foam? It's likely that the same thing that killed Columbia will still happen with the SLS core, only that this time there's no damage to do thanks to the lack of an orbiter on the side. Now that you've put there engines and landing gear, pieces of foam could hit them and prevent the core from landing, or worse

1 hour ago, Exoscientist said:

It’s already known the side boosters can be made reusable as with the shuttle program

That's wrong; the Shuttle boosters are refurbishable, not reusable. Very few parts other than the shell can survive the rough sea landing, and in fact during the shuttle era this led to basically no cost saving compared to making new SRBs from scratch. With SLS, the velocity is quite a bit higher and would lead to even less parts surviving the return to Earth

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I think throwing out SLS and replacing it with a semi-reusable Starship would make more sense.

It would be rather crude, but something like this-

1. Upper stage developed by old space to satisfy Congress (pork)

2. Throw out the ESM and replace it with a more powerful service module made in the USA, again for the purposes of satisfying Congress (pork). ESA wants to look at a European crewed spacecraft anyways and can have ESM “back”

3. The economy isn’t great anyways and it should be understandable to Congress that we don’t need such an expensive rocket to nowhere when the debt is how it is. We need post-Apollo frugality, of all things. Gateway and Orion are somewhat reasonable as “bones” for US prestige (as opposed to getting rid of crewed space exploration altogether, as was probably on some politicians minds after Apollo 11), but SLS is just dumb now that Starship has come along. Even if it blows up like the N1, surely with the experience SpaceX has with Falcon 9 they can make some sort of functioning HLLV with Raptor and the tanks they have.

A “smart SLS” was something that needed to be decided upon after Constellation got canceled. Invite famous astronauts and scientists onto a commission, come up with a proto-Artemis, all of your mission requirements, and let the designing begin according to those requirements. The Reagan administration actually tried to do this in the 80s with a commission with the likes of Neil Armstrong and Chuck Yeager among its ranks. Instead… I haven’t read much about SLS’ early days, but I am aware of a picture of Bill Nelson pointing at an SLS graphic at some meeting. Was it really just “designed by committee” in the name of randomly doing something after the Shuttle was retired?

But back to my original point- “smart SLS” needed to happen in 2009-2012, not in 2022. People made bad decisions or no decisions at all and here we are. It’s too late for SLS. And that’s nothing to be ashamed of. Energia was the first fully functioning SHLV* since the Saturn V but got canceled after just two flights. The ISS and continued human presence through Soyuz was way cooler than keeping Energia on standby for an eventual lunar program 30 years later though. Sometimes really awesome looking things just need to go away.

*In the context of this sentence, I don’t treat the Shuttle as an SHLV because for it to be considered an SHLV the orbiter needs to be included in the payload. The actual functioning payload is only considered in my sentence. Energia could launch a lunar lander to the Moon for rendezvous with an Energia-launched crew vehicle, Shuttle-launched vehicles would need refueling at a station to do this.

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There isn't any practical way to make SLS reusable, and if you did it would be so different it wouldn't be SLS anymore.

The boosters are barely worth refurbishing even if they were recovered and the best that can be done with the RS25s is a kind of ULA's SMART reuse where the engines alone are recovered.

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The core can't be landed, that's a bridge too far (wow, I remember Henry from the sci.space days, legend). Even if it could, downrange, we have good data on how that impacts payload to LEO—it drops it by ~20% for downrange landing (per SpaceX). A 20% loss of mass to LEO turns SLS from barely capable to useless. That drops the dv in the residuals to the point it can't do a TLI burn, then maybe with EUS it would have ICPS performance.

They could have opted for something like SMART, shedding the engines, then recovering them, and at the ridiculous price we are paying for RS-25s, that might be worth it (nearly $100M each). Course the added mass, etc likely also reduces performance, and SLS has no margin, since even "best" proposed versions under-perform so much they are not useful.

 

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The core absolutely cannot be landed. Those engines each have a mass of over 3 tonnes. The center of mass is much too far aft for any sort of controlled biaxial entry.

Bereft of its upper stage and the gimbal on its firing RS-25s, the SLS core is a lawn dart. And the SLS is jettisoned while in an actual elliptical earth orbit; it hits the atmosphere faster than a re-entering Crew Dragon. The engines will melt to slag immediately.

What you could do, though, is give it wings. And control surfaces. That way it can re-enter on its side and shield the engines from re-entry heat. The heat shield will be very heavy though. Oh wait, that’s the Shuttle. 

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23 minutes ago, sevenperforce said:

And the SLS is jettisoned while in an actual elliptical earth orbit

I forgot about that above. Even with SLS as a Kerbal rocket where enough entry burn will land literally anything, and magical SAS can keep the thing pointing, the payload hit for the reserved props makes it a non-starter, the hit would be way worse than a 40% loss from RTLS.

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8 hours ago, kerbiloid said:

They should make the nozzles jettisonnable and separate the disnozzled engine module with a heatshield on top of it, return, reeenter, chute.

This is what ULA plans for Vulcan, "SMART" reuse.

20150413_ula-smart-system.jpg.webp

They'd spend billions to dev this, then spend so much refurbing the engines it would not pay for itself until Artemis C (Roman numeral ;) )

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9 minutes ago, kerbiloid said:

Soon (tm)

Same can be said for SLS/Orion, first all-up launch is Artemis II (Orion is not complete for the one on the pad now). Artemis II is in maybe 2024, possibly 2025.

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On 6/16/2022 at 9:09 AM, Scotius said:

Nice idea, but...

- It would add even more time and expenses to development process.

- Comes with very high probability of losing very big, very expensive rockets early on in the process of working bugs out of the system.

- It wouldn't be SLS anymore. Not really.

It certainly will not happen with SLS. It is more political subsidization program than real space program with technical and scientific objectives.

But Falcon9 overcame that second issue with clever way. They used it as expendable rocket and made landing experiments after sending 2. stage and payload to trajectory. Commercial missions succeeded and company got money even many landings failed before they got all systems work reliably. It certainly could work as development step for expendable SLS too.

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SLS requires all of its performance for its primary mission though. There isn't any spare capacity to waste on recovery experiments, even if recovery of any portion of it were feasible (which is not likely).

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17 minutes ago, RCgothic said:

SLS requires all of its performance for its primary mission though. There isn't any spare capacity to waste on recovery experiments, even if recovery of any portion of it were feasible (which is not likely).

This. Reuse uses capability margin, even ignoring the fact that the core SLS stage is effectively put into orbit, so SLS core recovery is the same problem as Starship/Shuttle recovery. Falcon 9 S1, Electron S1, and NG S1 are all recoverable (the last assuming it flies at some point) because they stage off at ~2 km/s. The only possible recover for SLS would be a passive system for the RS-25s, or perhaps reusable boosters. Not SRBs, however, they'd have to be more like F9, SRB reuse never saved money. It's astounding how expensive the SRBS are, almost a billion $ a pair.

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Super Falcon (Falcon 19!) would actually make for a great SRB replacement.

Just a little larger diameter (4.5m), basically the same thrust, lighter overall, much better ISP, and recoverable.

Edited by RCgothic
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1 hour ago, RCgothic said:

Super Falcon (Falcon 19!) would actually make for a great SRB replacement.

Just a little larger diameter (4.5m), basically the same thrust, lighter overall, much better ISP, and recoverable.

The trouble is that I’d wager falcon 19/whatever would be the bones of a LV that would make SLS obsolete. Can’t run numbers right now, but why not just dump SLS and use Falcon 19 Heavy? In order to use falcon-ish boosters they’d have to be crew rated, at which point dump the grossly overpriced Core/EUS in the middle entirely.

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1 hour ago, tater said:

The trouble is that I’d wager falcon 19/whatever would be the bones of a LV that would make SLS obsolete. Can’t run numbers right now, but why not just dump SLS and use Falcon 19 Heavy? In order to use falcon-ish boosters they’d have to be crew rated, at which point dump the grossly overpriced Core/EUS in the middle entirely.

True actually. Falcon 19 Heavy would probably not be taller, the engines can only lift so much.

So if it's not stretched, it would perform a similar flight profile to Falcon 9. Direct scaling of thrust to payload would give a payload for Falcon19!Heavy of 133t expendable.

Probably a bit better due to beneficial square/cube law. Recovery modes would also be easier due to better aspect ratio and more body lift.

Directly competitive to SLS to LEO. Cheaper, due to leveraging the cost-effective Merlin engines. Plus more flexible due to scalable recovery options. With high energy 2nd and 3rd stages it'd be very superior.

57 main engines would be charting new territory though.

Edited by RCgothic
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2 hours ago, RCgothic said:

57 main engines would be charting new territory though.

Or they could use a 33 engine rocket... which is ready for testing.

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 This report estimates the launch market as approx. $48 Billion per year by 2030:

Global Space Launch Services Market is projected to reach at a market value of US$ 47.6 Billion by 2030: Visiongain Research Inc October 05, 2021 09:33 ET | Source: Visiongain Ltd https://www.globenewswire.com/news-release/2021/10/05/2308874/0/en/Global-Space-Launch-Services-Market-is-projected-to-reach-at-a-market-value-of-US-47-6-Billion-by-2030-Visiongain-Research-Inc.html

 At a going rate of approx. $10,000 per kilo to LEO that would amount to 4,800 tons to orbit.  For a SLS lofting nearly 100 tons to orbit even in SLS 1 form, that’s quite a lot of launches it could take part in per year IF it could do it at a competitive price. If  it could do 10 reuses, that could bring the price down to $400 million per flight, or $4,000 per kilo, about the price of the reusable F9 when new, or a bit more than $3,000 per kilo of the used F9. But IF it could do 20 reuses, within the capabilities of some expendable engines, it would be $2,000 per kilo which would beat even the F9 used reusable price.

 About the landing, there would be additional development cost for the horizontal landing thrusters.  But pressure-fed thrusters are a relatively simple technology. Compare for example the time SpaceX spent developing the Draco thrusters on the Dragon to the time developing the Merlin engine. And from discussion of the thrusters on the Starship they seem more like an afterthought compared to the cost, time, and complexity put into the Raptor engines.

 How about giving the RS-25’s on the SLS core restart capability? Again I’ll refer to the redoubtable Henry Spencer:


Newsgroups: sci.space.shuttle
From: [email protected] (Henry Spencer)
Subject: Re: One part Oxygen, two parts Hydrogen and BOOM!
Date: Sat, 14 Oct 2000 03:37:23 GMT

In article <[email protected]>,
Pete Zaitcev <[email protected]> wrote:
>> The SSMEs use "torch" igniters, little oxygen/hydrogen burners firing into
>> the preburners and chambers.  The igniters themselves are ignited by,
>> essentially, high-tech spark plugs.
>
>I see... obviously there cannot be a spark in a vacuum.

Not entirely true, but irrelevant -- when the igniter fires up, there's an
oxygen/hydrogen gas mixture there for the spark to travel through.

>Is the plug the reason engines cannot be restarted in orbit or
>there is more to the story?

There's nothing *fundamental* in the SSME which makes an in-space restart
impossible -- no one-shot parts or anything like that -- but it's a
complicated engine which has to be set up exactly right for a successful
start, and ground equipment (and gravity!) helps out with that.  It would
not be difficult to develop a variant which could start itself in space,
but there has been no reason to do that.
--
Microsoft shouldn't be broken up.       |  Henry Spencer   [email protected]
It should be shut down.  -- Phil Agre   |      (aka [email protected])

https://yarchive.net/space/shuttle/ssme_ignition.html

 So likely it could be done by Aerojet, but I have no confidence they could do it in an affordable manner. Or more precisely, I have no confidence they would do it at an affordable price charged to NASA. For instance the RS-25 engine used on the SLS is derived from the SSME. It was expected to be cheaper than the SSME as it it used a lower parts counts and was not required to have the 100 times reusability of the SSME. But instead Aerojet charged more for this engine than the SSME even when accounting for inflation:

NASA will pay a staggering $146 million for each SLS rocket engine. The rocket needs four engines, and it is expendable. ERIC BERGER - 5/1/2020, 6:55 PM https://arstechnica.com/science/2020/05/nasa-will-pay-a-staggering-146-million-for-each-sls-rocket-engine/

 About the payload lost on reusability, a stage that goes to LEO can remain in orbit for a few orbits to come back over the landing site so minimal propellant is burned to return to launch site. 

 If we do use a large upper stage, then the SLS would not go to orbit and as SpaceX showed you would need minimal fuel burned if landed down range, and so minimal payload lost, rather than returning to launch site. However, there is then the cost of the upper stage. If it were the Ariane 5/6, the cost of the Ariane 6 being as low as $77 million, it should be even lower than that without the Ariane side boosters or upper stage. 

ARIANE 6 VS. SPACEX: HOW THE ROCKETS STACK UP The European Space Agency is planning to use the Ariane 6 for a variety of missions. ESA MIKE BROWN 1.24.2022 2:00 PM In January 2021, Politico reported that the Ariane 6 could launch for as little as $77 million. That’s a steep discount from the $177 million price tag for the Ariane 5. https://www.inverse.com/innovation/ariane-6-vs-spacex

  About the landing thrusters, I wouldn’t give a contract for it to any of the usual aerospace companies under NASA’s cost-plus contracts. Instead I would prefer doing it “in house”, so to speak. I was quite impressed by a team at Johnson Space Center led by chief NASA engineer Stephen Altemus developing an unmanned lunar lander for only $14 million development cost:

The Morpheus lunar lander as a manned lander for the Moon. http://exoscientist.blogspot.com/2014/06/the-morpheus-lunar-lander-as-manned.html

  The approach the NASA team used on saving costs was likely analogous to that used by commercial space in cutting costs.  No doubt also the pressure-fed engines being used rather than complex turbo-pump engines contributed to the low development cost.

 

  Robert Clark

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58 minutes ago, Exoscientist said:

At a going rate of approx. $10,000 per kilo to LEO that would amount to 4,800 tons to orbit.  For a SLS lofting nearly 100 tons to orbit even in SLS 1 form, that’s quite a lot of launches it could take part in per year IF it could do it at a competitive price. If  it could do 10 reuses, that could bring the price down to $400 million per flight, or $4,000 per kilo, about the price of the reusable F9 when new, or a bit more than $3,000 per kilo of the used F9. But IF it could do 20 reuses, within the capabilities of some expendable engines, it would be $2,000 per kilo which would beat even the F9 used reusable price.

As mass to LEO increases, and with more than one provider doing so, cost decreases for the end user—that's the point. Assume BO gets New Glenn going, and a race to the bottom of prices ensues. National launches will use national launchers, so much of the $48B is not available. For the commercial market, the total is lower, and if costs are an order of magnitude lower, 48 becomes 4.8, if they are 2 orders of magnitude lower, then $480M.  Bottom line is (IMHO) that until new businesses are created because of low cost (asteroid mining?), the launch market is chump change. Amazon makes nearly $48B in a month, as an example.

 

58 minutes ago, Exoscientist said:

 About the landing, there would be additional development cost for the horizontal landing thrusters.  But pressure-fed thrusters are a relatively simple technology. Compare for example the time SpaceX spent developing the Draco thrusters on the Dragon to the time developing the Merlin engine. And from discussion of the thrusters on the Starship they seem more like an afterthought compared to the cost, time, and complexity put into the Raptor engines.

 How about giving the RS-25’s on the SLS core restart capability? Again I’ll refer to the redoubtable Henry Spencer:

Doesn't matter, SLS core is put into a highly elliptical orbit as @sevenperforce observed. More specifically, they keep the perigee low for disposal, and the perigee raising is a tiny amount of dv. Core is coming back at orbital velocity. Landing SLS core is the same problem as landing Starship, and will take more work. It's not worth bothering.

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