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#1 2022-06-16 08:44:21
A reusable SLS?
Posted 9 hours ago (edited)
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 <henry@zoo.toronto.edu>
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 <4q6am4$46s@ns.hcsc.com> andyh@hcxio.hdw.hcsc.com (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 | henry@zoo.toronto.edu
_______________________________________________________________________________________________________________
https://yarchive.net/space/rocket/engin … ility.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.
Robust Lunar Exploration Using an Efficient Lunar Lander Derived from Existing Upper Stages.
https://www.ulalaunch.com/docs/default- … )-2009.pdf
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
Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):
“Anything worth doing is worth doing for a billion dollars.”
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#2 2022-06-16 18:47:02
- SpaceNut
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- From: New Hampshire
- Registered: 2004-07-22
- Posts: 29,436
Re: A reusable SLS?
based on the need to do a first stage recovery the stage would need to reserve 25% of the tank and add control plus legs to make a vertical landing of it possible. with as you noted a re-start able engine for the stage. But that means the second stage would need to be stronger and less payload to orbit would occur.
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