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The Safety Of SLS

8 Comments

Steven Squyres is concerned.

Here’s what I wrote in the book on that topic:

It should be noted that NASA currently plans only two flights for the SLS — one in 2017 to demonstrate the 70-ton capability, and one with a crew in 2021, to… somewhere. They have said that, when operational, it may only fly every couple of years. What are the implications of that, in terms of both cost and safety?

Cost wise, it means that each flight will cost several billion dollars, at least for those first two flights. If, once in operation, it has a two- or three-billion-dollar annual budget (a reasonable guess based on Shuttle history), and it only flies every couple of years, that means that each subsequent flight will cost anywhere from four to six billion dollars.

From a safety standpoint, it means that its operating tempo will be far too slow, and its flights far too infrequent, to safely and reliably operate the system. The launch crews will be sitting around for months with little to do, and by the time the next launch occurs they’ll have forgotten how to do it, if they haven’t left from sheer boredom to seek another job.

As a last-ditch effort to try to preserve the Shuttle in 2010, some suggested that it be maintained until we had a replacement, but to fly it only once per year to save money. The worst part of such a proposal would have been the degree to which the system would have been even less safe, given that it was designed for a launch rate of at least four flights per year. It was unsafe to fly it too often (as NASA learned in the 80s as it ramped up the flight rate before Challenger), and it would be equally so to fly it too rarely. NASA’s nominal plans for SLS compound this folly, which is magnified by the fact that both internal NASA studies and independent industry ones have demonstrated that there is no need for such a vehicle to explore beyond earth orbit (existing launchers could do that job just fine, with orbital mating and operations), and it is eating up all the funding for systems, such as landers and orbital propellant storage facilities, that are necessary. All of this is just more indication that actually accomplishing things in space is the lowest priority for Congress (and unfortunately, the space agency itself, otherwise, the administrator would be more honest with the appropriators on the Hill).

More people need to point this out.

8 thoughts on “The Safety Of SLS”

  1. I generally liked shuttle, except for the cost.

    Seems to me that what NASA is trying for with SLS is an even more expensive system with far fewer capabilities, plus it’s less safe.

    Seems to me it would have been cheaper to keep Shuttle by building a few new orbiters. Hopefully they could have been improved to cut maintenance costs, but even if not, they’d have been better than SLS. (Still way too expensive IMHO, but better than SLS).

    I guess SLS really is shuttle-derived; it’s keeping almost all of Shuttle’s bad points and adding a few more, for a less capable, less safe, system.

    BTW, ONE test flight and then a four to five year downtime before SLS goes operational? This will not end well.

  2. I think the Shuttle suffered from the usual problems of any first generation system. It was a prototype and it suffered from the typical problems that prototypes have. i.e. unreliability and expensive maintenance costs.
    Over the years many Shuttle replacement proposals were suggested and money was invested in various of these. NASP, Delta Clipper, X-33, X-34, SLI, etc. I think of these proposals the Delta Clipper, X-34, and SLI were the most viable. However for political or economic reasons these projects were eventually canceled. The only remaining RLV with flyback capability is the X-37 and that had to be “rescued” from the political swamp that is NASA funding by the USAF. In the end it is a much smaller automated vehicle than the final Shuttle design. However it can likely do several of the orbital lab missions originally done with Shuttle while launching is done using the EELVs. In the end the Shuttle Launch System simply couldn’t compete economically for satellite launch against ELVs in general.
    One thing the Shuttle had going for it was the emphasis on reduction of launch costs to LEO. It was expected that large deep space missions would be assembled in space with multiple launches. Even after the Shuttle proved that this was perfectly possible with the Hubble servicing and ISS construction milestones there was some sort of nostalgia for the Moon missions. The entire NASA strategy for long term development of space as a step by step gradual increase of manned presence in space in order to reach a sustained manned presence in Cislunar space was thrown out of the window. This was IMO a major mistake. I think the step by step strategy is still the most viable.

    SLS, as it stands, is going to spend a lot of cash to redevelop Apollo Project era gas-generator engine technology. So the technological advances are going to be negligible at best and may detract from commercial efforts by poaching the limited engine design talent available. In addition the rocket is going to have limited uses other than the Moon missions because of the sheer per flight cost. In the end it is a throwback to an approach which was abandoned in the 1970s as too expensive at a time the US had a much better manufacturing base than it has today. The whole endeavor makes little sense.

    Existing US launch systems, and their proposed near term extensions, are more than enough to supply the requisite launch mass for currently foreseeable needs. Including Moon and asteroid missions. Instead of just working on how to do the missions with existing launch vehicles and then developing better vehicles if demand increased everything is being done the other way around.

    1. I agree. The Shuttle was to RLVs as the P-59 was to the P-80. What NASA needed was a TSTO based on the experienced gain with the Shuttle. Instead NASA wasted its money on ISS.

  4. The SLS will have far lower maintenance costs than the Shuttle, especially SSME rebuilds and tile inspections. It won’t have the risks of main tire blowouts or break pad overheating during landings, and during the landings will be much less likely to encounter pilot induced oscillations.

    How am I doing so far?

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