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This answer has a lot of images that I shouldn't need to repost here, and is supplemental to this answer to the question Help me understand what Farside, a ten “stage” rockoon looked like? How was it configured?

All available sources quoted in both answers state that Farside is a four stage rocket, with the 3rd stage being four parallel Asp's and 4th stage being a single one. But all images shown in both answers just seem to show the four cores of the 3rd stage topped with what looks like a large badminton birdie which is the payload.

Where is the fourth stage?

uhoh
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Pure speculation (just from looking at the photo): it's within the third stage.

While the cylinders for the first stage are either touching or nearly touching, the cylinders on the third stage are separated by a significant distance. It appears to be sufficient for a similar cylinder to be located within.

I have no idea why you wouldn't simply burn all 5 simultaneously as the third stage, but if that is how it's configured, it would match the numbers given.

BowlOfRed
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  • This really sounds plausible. Wouldn't 4 then 1 rather than 5 at once just be an example of staging? Tsiolkovsky etc.? – uhoh May 19 '19 at 09:03
  • As long as they're fired sequentially, yes I'd say they're true stages. I was just questioning what reason would be to do so. My assumption is that firing them simultaneously would be better for performance. But that's just my guess, not a calculation. – BowlOfRed May 19 '19 at 09:09
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    I'm now thinking that rather than the fifth cylinder in the center being captive, is a proper, separate stage that "shoots out" of the structure holding the other four when it's ignition time comes, leaving the four spent elements behind. – uhoh May 19 '19 at 09:13
  • Yes, it has to be able to release the earlier ones. Staging it separately would be a guaranteed loss if it couldn't drop the dry mass of the previous stage. – BowlOfRed May 19 '19 at 09:16
  • okay, in that case I can't understand why you said "I have no idea why you wouldn't simply burn all 5 simultaneously as the third stage..." Isn't the delta-v advantage of staging clear? – uhoh May 19 '19 at 10:34
  • fyi I've just asked How common are “parallel stages” in a launch vehicle? – uhoh May 19 '19 at 12:09