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Credit to @Sturgeon for originally coming up with this discussion topic.


As I'm sure you're all aware by now, SLS (Space Launch System) is horribly delayed; it was originally supposed to fly a few years ago, but now isn't supposed to launch until 2020. That will be an unmanned launch of the Block 1 version, the Block 2 version (the one that will rival Saturn V) won't be coming until 2029 per wikiped. Also, it makes the odd (and in my opinion poor) choice of going with solid rocket boosters plus hydrolox on the first stage. With that said, SLS does at least make use of existing hardware such as the RL-10 and derivatives of the Shuttle SRBs and RS-25s, and manufacturing has begun on some components. So it's ahead of the complete train wreck that was Constellation.


The question is, how can SLS be fixed? There's a bunch of options depending how far back in time you're willing to go and how radical of changes you're going to make. I'm going to start by laying out what I see as the facts of the situation, without changing the architecture of the system:


  • SLS is horribly overbuilt for LEO crewed operations, and F9/Dragon (and even Atlas V / Starliner) is much cheaper and better fits that mission.
  • Plans to man-rate Falcon Heavy are canned for the moment, so besides BFR (which will blow everything open if it does what Musk promises) there are no American man-capable launchers that can send a crewed mission beyond LEO. (I don't know anything about plans to stick a capsule on New Glenn or any other amazon rockets)
  • Therefore, SLS has something of a niche as a crewed beyond LEO launcher (again assuming BFR doesn't pan out)
  • In order to become more economical, SLS must launch more frequently than once every few years.
  • The most likely way to do this is by establishing a permanent presence on the moon.
This would require acceleration of the schedule for Block 2 most likely, along with a shitload of money. Still, it should serve as a starting point for the discussion.
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Making a short post here, will edit/expand it when I get home.


The problem itself has two aspects. First, SLS is too expensive to fly more than once per year. What was supposed to be a more reasonable heavy lift rocket, with per-launch costs equal to or less than STS, is now expected to cost well over a billion dollars per launch, precluding launching any more frequently than once per year, and likely much less frequently than even that miserable rate.


Second, it is increasingly looking like even DelayX's BFR will beat SLS Block 2 to flight, meaning that Block 2 either will never fly or will only fly once. So Block 1 is probably it, and we might get 2-3 flights out of it. Yet, through Constellation and SLS, so much time and money has been spent to accomplish... This? Is there any way we can at least squeeze a little more from this program?


Well, realistically, probably not. But let's talk about it anyway.


Ways I see to salvage SLS:


1. Let a new product contract, a la commercial crew, for SLS Service Life Extension Engines. Existing SSMEs should be cheap enough to use, but it's probably not worth making new ones for launches beyond the first four or so (IIRC there are 16 usable SSMEs in inventory, 4 used per launch). An SLS powered by BE-4s or Raptors could potentially be much cheaper than the current design.


2. Let a product contract for SLS powerpack and/or booster recovery. Maybe ULA gets this contract, see if they can actually make their powerpack recovery project from Vulcan work, but on a bigger scale. Alternatively, hire Elon to stick gigantic legs on the SLS core stage, and see if you can fly it back.


3. Let a product contract for liquid fueled boosters using the same tank architecture as SLS. More core tanks per flight = reduced cost, especially if you're only recovering the powerpack. The boosters don't necessarily need to use the same engines, but obviously would need to be liquid-fueled.


4. Let a development contract for booster fly-back. There's no reason at this point that liquid strap-on boosters shouldn't be able to fly back home, given how short their trip with the stack is. Obviously, SpaceX is a shoe-in here, but there's no reason Blue Origin or ULA couldn't make competitive bids, too.


The timeline for these contracts would have to be... Condensed. Four basic SLS flights are likely to occur before any changes like these could be made. Call that 5 years, or 2023, if my proposal magically gains support today. Around about that same time, it's likely that BFR will at least be looming large, if not actually making commercial flights. So ultimately, what's the point of a rejiggered, only partially reusable, not-really-SLS SLS? Well, there probably isn't really one, but SLS does have political support which is why the money going to fund it hasn't been diverted to commercial development contracts and guillotines for all Marshall employees from the past 50 years.


But maybe the future of SLS isn't in it's shaky status as a heavy lift rocket, maybe it's - bear with me, now - as a payload. An SLS core tank may not be too wide to fit inside the maw of a BFR, particularly not if a longer fairing were developed to enclose the whole thing. A few more BFR launches, and now you have a fully fueled SLS stage in orbit, presumably with RL-10s or J-2Xs instead of the SSMEs at the very least, if not quad NERVAs. Throw on an ACES style reclamation system and you've now got a transfer stage that gives over 15,000 delta-v m/s with a 100 tonne payload - enough to fly a manned mission to Jupiter and back.

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An outer planet probe would be excellent. Additionally, it would fit the SLS architecture well, given that it has an upper stage with high specific impulse (RL-10C3 has 470 seconds, which is damn decent).


Sturgeon's idea for a nuclear upper stage would be even better (for a large enough stage), but getting a nuclear rocket and more money in SLS is definitely a bridge too far politically.

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To go back in time, here's a rough, probably optimistic timeline for a non-broken SLS program:


  • 2005: Development of SLS begins with a kerolox or methalox core, liquid boosters (ideally using the same engines as the core), and a hydrolox upper stage. Payload is 70-150 tons to LEO in various configurations.
  • 2006: SLS gets some snazzy name
  • 2008: SLS configuration nailed down, detailed development work ongoing
  • 2009: Work begins on reusability of first stage and boosters (contract out to SpaceX?)
  • 2010: Static and ground testing of SLS commences
  • 2011: Shuttle retires
  • 2012: Block 1 of SLS launches (no side boosters, fully expendable)
  • 2013: First operational flight of SLS Block 1, Test of Block 2 (recoverable boosters, expendable core)
  • 2014: Second operational Block 1 flight, first operational Block 2 flight
  • 2015: Test of Block 1B (recoverable core, also used on Block 2B)
  • 2016-2018: Operational use of Block 1B, Block 2B with recoverable core and boosters
  • 2020?: First flight of Block 3 (max payload, fully recoverable/reusable first stage and boosters)
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Since we've turned this into an althist wank thread (it was already a wank thread tbh), and since this booster is a sort of spiritual successor to both Shuttle and Saturn V, I propose the name Vulcan.

Not to be confused with the Rocket That Is Low Energy and Sad, or ETS's Zenit Gangbang.

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  • 2 months later...

It looks like SLS is salvageable if Boeing stays involved; https://arstechnica.com/science/2018/10/theres-a-new-report-on-sls-rocket-management-and-its-pretty-brutal/


There is a rather remarkable section of the report that discusses the reasons for these delays. Boeing evidently told the inspector general that initial delays for SLS development were caused by "insufficient funding." Notably, Boeing said the SLS contract was underfunded for 2015, and therefore it could not maintain its delivery schedule for the first two core stages.

The inspector general appeared to be having none of this, however. "By the end of FY 2015, the company had received $706 million, only $53 million less than requested for its work to build two core stages," the report states. "In addition, due to a congressional 'plus-up' the following year, Boeing received approximately $200 million more than what NASA estimated was needed to meet the original 2017 launch schedule. Further, in May 2016 NASA added almost $1 billion in additional contract value—bringing the total contract value to $5.2 billion—with only minimal changes in the scope of work."



Between this and other fiascoes like the KC-46, my opinion of Boeing isn't that great right now.

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