I just read this article, in which former director Kraft is described as deriding NASA's current plan to use a single heavy-lift vehicle (Space Launch System, or SLS) as a primary launch platform. Why is NASA doing this?

A single failure destroys an enormous amount of work. Distributing the across rockets increases the possibly of a single failure, but a single failure results in less loss. Furthermore, the smaller rockets exist today, so it doesn't require a huge new new development effort. Since they exist today, a lot of the design flaws have already been discovered and corrected.

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    $\begingroup$ An excellent question! I have had interactions with the planners for human Mars and asteroid missions, and they consider a large number of launches for a mission to be "unrealistic", and is one of their primary metrics for evaluating an architecture (the other being total IMLEO, initial mass in low Earth orbit). I never got a good rationale for why fewer launches is better. $\endgroup$
    – Mark Adler
    Sep 4, 2013 at 1:52
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    $\begingroup$ I'm with you that you reduce your exposure to launch failures when you have more of them. Furthermore, the more you fly, the more reliable they get. So it is not necessarily true that you increase the probability of a single failure. You can have too few launches of a given design for it to be reliable enough. $\endgroup$
    – Mark Adler
    Sep 4, 2013 at 1:53
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    $\begingroup$ Au contrair, an entire Mars mission consisting of 4 Atlas Heavy to dock in LEO, instead of 1 SLS, is scrapped if 1 of the launches fails. Already launched components may have to be deorbited, cryo fuel tanks in LEO boil off and the launch window is lost for 2 years. However, Atlas and Ariane have 97% success rate and its getting better, we're not in the wild 1960s anymore. And I know of none, out of 100+ dockings in LEO or Lunar orbit which has failed catastrophically. I recommend "The Space Show" archive where exactly your question is debated so often that the host is sick and tired of it. $\endgroup$
    – LocalFluff
    Apr 11, 2014 at 9:19
  • $\begingroup$ "Au contrair, an entire Mars mission consisting of 4 Atlas Heavy to dock in LEO, instead of 1 SLS, is scrapped if 1 of the launches fails. Already launched components may have to be deorbited, cryo fuel tanks in LEO boil off and the launch window is lost for 2 years." Unlike SLS, Atlas Vs can launch frequently. There've already been 3 launches in 2014. If one Atlas V fails, a new one can be launched before cyro boils off. $\endgroup$
    – HopDavid
    Apr 11, 2014 at 13:18
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    $\begingroup$ @BCS "you can let the rest of the mission sit in orbit for 2 years without any harm" Assuming, of course, that the hardware is designed to survive an additional two years in at least LEO. Which means you'll need to maintain the orbit (costs fuel, at the very least), you'll likely need additional radiation hardening (which at least costs weight = fuel = more weight = more fuel = ..., and likely costs noticable amounts of cash), and possibly other things I'm not thinking of right now. $\endgroup$
    – user
    Apr 15, 2014 at 9:46

3 Answers 3


Just guesses but:

  • Avoiding rendezvous in orbit and the extra equipment that takes?
  • Amortizing the lift cost of things that scale sub-linearly?

Also, at first blush, it doesn't sound like they are thinking of putting multiple major payloads on a single super-sized booster.

  • $\begingroup$ Do you think they're talking about a single 120-ton component, then? $\endgroup$ Sep 4, 2013 at 0:40
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    $\begingroup$ @DonBranson Given that the N1 has a payload of 100T to LEO and the Saturn V can do 130T, I'd think that would be not unreasonable. Given such a booster, I'd consider things like a 15m space telescope or a multi-rover mars mission. --- OTOH, if you want that class of booster why not just update the S-V designs a bit? $\endgroup$
    – BCS
    Sep 4, 2013 at 1:19
  • $\begingroup$ NASA would also be biased toward big, distinctive projects in part because of the political nature of its funding (being spectacular feeds national pride--politicians winning votes by saying "I supported apple pie^W^Wthat magnificent space mission"--and spending money in more states--"I brought jobs to our fair state"), especially with commercial launch services becoming increasingly more capable in lower investment and more cost-effective areas. $\endgroup$
    – user56
    Sep 4, 2013 at 1:50
  • $\begingroup$ In addition, it simplifies construction, reduces the origami type spacecraft issues, connectors, etc. $\endgroup$
    – PearsonArtPhoto
    Sep 4, 2013 at 16:51
  • $\begingroup$ Re: commercial launch services -> "I support the Capitalist way!" $\endgroup$
    – BCS
    Sep 4, 2013 at 20:24

Currently there are plenty of launch system available in the world for the 10t - 20t range, but none which can get more than 23 tons to low earth orbit. The SLS, however, will have a LEO capacity of 70t - 130t. That would open up a whole new market segment on which neither ESA nor Roskosmos can offer anything.

There is, however, another player who emerges on the market for launch systems and who is currently developing a rocket with LEO capacity in that scale: China with its Long March 9. Leaving that market exclusively to the Chinese could be a dangerous move from a geopolitical point of view. The Chinese having a world-wide monopoly on launching 100t chunks into orbit would be quite a problem for US international interests.

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    $\begingroup$ What market? Using an HLV to deliver sats is like using a Mack truck to deliver pizza. Same goes for delivering supplies to the I.S.S. If we wanted to send humans beyond LEO, there are alternatives to HLV. For example ulalaunch.com/site/docs/publications/… $\endgroup$
    – HopDavid
    Apr 11, 2014 at 13:46

From the article:

It's been derisively referred to as the "Senate Launch System" in a lot of places, because it's being designed and built in a very distributed manner, with work being spread across many different contractors in many different states.

That says it for me. The SLS is a make work program that provides employment in areas the senators represent. Also known as pork.

  • $\begingroup$ That's necessarily the way governments do things. So I think it is an irrelevant criticism, it is just stating the bleeding obvious. It's either SLS, another as inefficient governmental small rocket program, or no governmental rocket program. Personally, I'm looking forward to the huge SLS. Private sector or the much smaller foreign space agencies would never develop such a heavy lift so it's NASA or noone. Once it exists there'll be political pressure to make up missions for it, and that'll be exciting. $\endgroup$
    – LocalFluff
    Apr 11, 2014 at 9:35
  • $\begingroup$ * Private sector or the much smaller foreign space agencies would never develop such a heavy lift so it's NASA or noone." Correct, NASA or noone. A competitive market needs several providers. A single provider monopoly has less incentive to keep costs down. In fact if it's a cost plus contract, they have incentive to boost costs. "Once it exists..." There's no guarantee it will exist. The Ares rockets did not come to pass. "there'll be political pressure to make up missions " So far political pressure hasn't provided the needed funding. $\endgroup$
    – HopDavid
    Apr 11, 2014 at 12:36
  • $\begingroup$ Maybe the military wants the SLS for some secret monster mission. And when the US military wants something, costs are completely ignored as a parameter in decision making. I mean, they do rule the government, no one else has a say about what the military does or doesn't. And to make it look better NASA might be allowed to use it once or twice for science or human missions. $\endgroup$
    – LocalFluff
    Apr 11, 2014 at 16:33
  • $\begingroup$ "Maybe the military wants the SLS for some secret monster mission" Unfounded speculation. Besides the military has it's own aerospace program en.wikipedia.org/wiki/Air_Force_Space_Command $\endgroup$
    – HopDavid
    Apr 11, 2014 at 17:03
  • $\begingroup$ Yes, it's bleedingly obvious that our elected reps look after their constituents. But when they do so at the expense of the greater good, that's pork. Right now Senator Shelby et al are trying to protect the status quo from upstarts like SpaceX or Blue Origin. Much like Senator Owen Brewster tried to protect his supporters from that upstart Howard Hughes. en.wikipedia.org/wiki/Owen_Brewster#Opposition_to_Howard_Hughes $\endgroup$
    – HopDavid
    Apr 11, 2014 at 17:10

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