Author Topic: NASA is trying to make the Space Launch System rocket more affordable (Ars)  (Read 6299 times)

Offline Rocket Science

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New Glenn has a max thrust  3,850,000lbs  which is very close to that of the five segment RSRM which is around 3,600,000lbs.
They would stage higher and faster but probably not as much as the Dynetics Pyrios booster would have since they would normally be saving some of the propellant for landing.

You probably could deal with it by just throttling back the RS-25s for part of the flight .

At shutdown it'll be producing a lot of thrust still (while solids "throttle" almost to zero), unless they shut down all but the center engine or something. This was a problem for all previously-studied liquid boosters, the loads from the boosters pushing on the core stage just before BECO are too high. Even with RSRMV they've already had to alter the core stage throttle profile to mitigate this, but with any liquid option they'll probably have to add a 5th RS-25 to minimize the relative acceleration (and, unless thats coupled with some sort of engine reuse, this only exacerbates the most critical cost and schedule problem of the program)

The F-1B only had two throttle settings, and the lowest was 72% of max. And with two off-center engines on Pyrios they could not shut some of them down to "throttle".

BE-4 will throttle much lower, somewhere around 30%, and is much more controllable since it's a requirement for landing. If they need to, they can shut down 2, 4 or 6 engines leading up to separation. The extra 80+ seconds of burn time will allow the RS-25s to burn an extra 140 tonnes of fuel, increasing the core stage TWR at booster sep and further reducing the difference in acceleration of the boosters and core.

With the relatively slow liftoff (~1.23 TWR at liftoff) and the large mass of the core stage (at staging it will mass 50% more than two NG upper stages), the boosters should be going fairly slow at staging compared to New Glenn, although much faster than RSRMs will be. I figure about 2.3 km/s at booster sep for NG booster SLS, vs 2.5 km/s for NG, vs 1.4 km/s for RSRM boosted SLS.

The extra velocity at staging with NG boosters is sufficient to put the entire EUS and Orion in orbit with only a small circularization burn from the EUS (even with downrange recovery of the boosters).
Now if we can recover the core main engines in a "pod" as has been studied over the years we will begin to see potentially real cost savings in the out years with a flyback/boostback architecture...

This "pod" would be coming back from orbit. Might be a lot cheaper to shorten the core and land it downrange, and use the difference in height to build a large 2nd stage.
Yes that would mean a heat-shield with prop doors and chutes. Two stage is also interesting a cost/benefit analysis of each proposal would be revealing. I just recalled the old Saturn S-1D proposal of partial main engine re-usability as well...
http://lostinthisspace.blogspot.ca/2013/01/s-1d-first-stage.html
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Offline Proponent

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At the low flight rates envisioned for SLS, I suspect that reusability would cost more than it saved.

Offline Rocket Science

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At the low flight rates envisioned for SLS, I suspect that reusability would cost more than it saved.
I said pretty much the same on the previous page unless NASA is just throwing out a "red herring"...
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Online mike robel

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1.  Rockets, for the most part, are not LEGOs, {edit:not even the much heralded Falcon 9 which is not as interchangeable from core to core as they thought it would be.  (Which, by the way, I am eager to see launch.)}

2.  It may SpaceX, Blue Origin, and any other companies might not want to bid on the item because of the great uncertainty in funding and contract processes.

3.  Changing engines will require design changes that will cascade from the engine to the rocket to the launch pad plumbing to the VAB doors (maybe) and to the MLP swing arms.  This will drive up the cost and increase the time to do anything.

4.  Restricting this to the SLS, it will probably be cheaper and more effective to just stick to the current plan, such as it is.

$0.02...
« Last Edit: 12/20/2017 03:46 PM by mike robel »

Offline bad_astra

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SLS does not need to be made cheaper, but there does need to be the appearance of constantly making it look as if attempts are made to keep it cheaper. That allows SLS to remain in a perpetual development cycle while at the same time showing off the hardware in flight every couple of years until the political momentum for SLS dissipates and the program can be laid to rest.
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Online envy887

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At the low flight rates envisioned for SLS, I suspect that reusability would cost more than it saved.
Depends how much of it is custom. If Blue is already operating NG as a reusable human-rated vehicle, and already has recovery ships and all the hardware figured out, and the only vehicle change is a custom interstage/nose cone/thrust beam attachment, then it might not be very expensive. Especially considering the huge payload capability upgrade.

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