The solid boosters of Shuttle/SLS fly in pairs. Could a pair of them fly without SLS, carrying a smaller second stage and payload to orbit? What capacity would it have?

A rescue launcher needs to launch on short notice, hence solid first stage. The second stage still has to be fueled. The prepared payload could be a space tug that for example could prevent a predicted debris collision in LEO from happening.

  • $\begingroup$ Predicted debris collision in LEO isn't currently a good rescue mission - we don't track debris accurately enough to make good conjunction predictions. At the time of the Iridium-Cosmos collision the Iridium constellation was getting 400 conjunction notices per week in 2007 and the collision wasn't the closest predicted collision of the day (and I hear some operators get 20k+ notices a week). $\endgroup$
    – 1337joe
    Jul 22 '15 at 15:44
  • $\begingroup$ Why do you ask? $\endgroup$ Jul 22 '15 at 20:50
  • $\begingroup$ @RussellBorogove Why? I just found a couple while cleaning up my garage... I guess that a solid launcher standing by on short notice would give more flexibility if something important is misplaced in orbit. $\endgroup$
    – LocalFluff
    Jul 22 '15 at 21:41
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    $\begingroup$ It doesn't seem like a great use of a big and relatively fancy SRB. Keeping something like an Athena (en.wikipedia.org/wiki/Athena_II) or Minotaur around might be more sensible, depending on the payload. $\endgroup$ Jul 22 '15 at 21:59
  • $\begingroup$ I may be an old cynic, but we already have something of this kind: SM-3 ASAT. $\endgroup$ Jul 24 '15 at 16:47

By themselves, a pair of SRBs with no payload would produce about 5500 m/s of ∆v, which gets them something more than half-way to orbit. They have a fairly poor ISP and propellant mass fraction.

If you added a 100-ton second stage using storable hydrazine-family propellants, you could get about 5 tons of payload to LEO if that's your goal.

enter image description here

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    $\begingroup$ Invisible Second Stage! $\endgroup$ Jul 24 '15 at 16:20
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    $\begingroup$ That's some serious stealth for you. NRO has cleared this shot for public release. $\endgroup$ Jul 24 '15 at 16:44
  • $\begingroup$ "Boss....we forgot something..." $\endgroup$ Jul 24 '15 at 17:21

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