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I'm not sure about the total thrust of SLS Block II (Crew Stack). So the math could be wrong. Since the Atlas 5 has a version where 4 SRBs are used, is this also possible for SLS?

Pitto
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Lee JBartholomew Baker
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    It is not, because the core stage as designed cannot withstand the material stresses nor does it have hardpoints to attach a second pair of SRBs. – Anton Hengst Mar 03 '21 at 21:03

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Such a thing might be possible but it would involve a major redesign of the rocket. All of the forces on the central core would be different so the core would need to be reinforced. As SpaceX found when they produced Falcon Heavy from Falcon 9 it is not a straight forward issue.

There are many other issues as well, not show stoppers but they all add complications. When twin side boosters are exhausted and released they symmetrically fall away to either side. But with four one will have to be ejected with an upwards component or the release will need to happen in two stages with a rotation in between.

It would also mess with the aerodynamics of the whole vehicle, the point it reaches Qmax and the throttling arrangements. All of this can be dealt with but the complexities may not be worth it. Rockets aren't Lego.

Slarty
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  • "But with four one will have to be ejected with an upwards component or the release will need to happen in two stages with a rotation in between." Why? Couldn't the boosters be spaced evenly around the core? Some Deltas had 8 boosters, and they didn't eject anything upwards. It sounds to me like you are just making stuff up. – Organic Marble Mar 03 '21 at 23:53
  • @OrganicMarble I think the those large SRB's need a very large separation force when the SLS is pitching down the range. The SRB towards the earth might impact the rocket on separation. – Ashvin Mar 04 '21 at 01:08
  • @Ashvin what's the separation altitude? And what's the SRB velocity vector pointed at, at sep? The shuttle ones continued upwards for quite a while after sep. I doubt the traj is much different at sep for the SLS, but I'm willing to be convinced otherwise, if you have data. – Organic Marble Mar 04 '21 at 01:28
  • @OrganicMarble It was just a thought, i dont have any data. – Ashvin Mar 04 '21 at 03:51
  • Yes the boosters should be spaced evenly around the core. But by the time of booster separation the rocket is leaning towards being parallel with Earths surface so 2 boosters are on either side one is "below" and one is "above" and yes they can all still be released, But my point is that its no longer symmetrical the 4 boosters have to be treated differently in that the one being ejected "above" will require much more force than the two to either side and the one below much less. Or the rocket can be rotated along its axis after the first 2 drop away but that's more complication. – Slarty Mar 04 '21 at 09:33
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    The Russian Soyuz launcher uses four boosters which are jettisoned at the same time. What's the difference? – GordonD Mar 04 '21 at 09:56
  • The Russian Soyuz launcher family was designed right from the start with the aim of using 4 boosters. It was not designed to use 2 boosters and then modified to use 4. Yes 4 or more boosters can and have been used, I'm just pointing out that changing plans from 2 to 4 is not as simple as it looks. – Slarty Mar 04 '21 at 14:45
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    Your comment makes your theory even more confusing. How are four evenly spaced boosters not symmetrical? – Organic Marble Mar 04 '21 at 14:58
  • They are symmetrically placed around the rocket and if booster separation was just after launch each separation would be the same. But separation occurs at high altitude when the rocket is no longer flying vertically up but canted over at a high angle relative to Earths surface in order to gain orbital velocity. At this point they are not symmetrical in terms of the forces acting on them some are above or below or to the side of the trajectory. – Slarty Mar 04 '21 at 16:26
  • Mainly, I wanted to get this on record that 4 SRB's are stackable with the Space Launch System. Exceedingly grateful for the review. Here's why: increasingly, the regime and domain of interplanetary economics is going to gain in some significant measure of notoriety, and with the attention given ("as it should or, perhaps shouldn't be") there absolutely must be ways of diverting attention away from the boeing catastrophe in engineering, public relations and mis-calculation (it is there engineers, afterall, who have caused almost all of the problems with the SLS rocket program; – Lee JBartholomew Baker Mar 12 '21 at 17:48