1
$\begingroup$

I would like to clarify what is a staging event. Maybe there is no definite definition. First I though it was easy as the Nasa definition is clear. Then I though of the stage-and-a-half Atlas SLV-3, and the Space shuttle for which one separation event consists in only dropping a tank.

Then, I thought of Apollo missions. A typical Apollo mission involved many separation events, some of which can clearly be qualified as staging, but what about the others?

Here is a quick list of the separation events:

  • S-IC few minutes after take off (clearly a staging event)
  • S-II during initial ascent (clearly a staging event)
  • separation of S-IV B on one hand, the LM+CSM on the other hand. Not clear if this was considered to be a staging event.
  • separation of LM and CSM in lunar orbit. I don't think this was a staging event, but I'm not quite sure.
  • separation of ascent and descent stage for the LM. I don't think this was a staging event as the tank and engines of the descent stage play no role during this launch.
  • separation of LM and CSM. I don't think this was staging event.
  • separation of CM and SM just before reentry. I've never heard staging for separation of reentry vehicle, yet the CM let behind a stage with empty propellant tank and a rocket engine and it looks like a serial staging.

During a typical Apollo mission, what separation events were considered as staging?

$\endgroup$
3
  • 1
    $\begingroup$ Are you looking for official Apollo program terminology? $\endgroup$ – SE - stop firing the good guys Nov 2 '20 at 13:29
  • $\begingroup$ @SE-stopfiringthegoodguys Do you mean there are multiple authoritative sources contradicting each other? $\endgroup$ – Manu H Nov 4 '20 at 17:05
  • $\begingroup$ No, though there may be. I'm simply asking if that's what your question is about, since there are other ways of interpreting this question. $\endgroup$ – SE - stop firing the good guys Nov 4 '20 at 17:06
4
$\begingroup$

Warning: this answer contains unsupported opinions.

I don't believe the events after dropping the S-II are generally referred to as staging, but I think at least the S-IVB/CSM separation event could be considered staging.

Separation of S-IVB on one hand, the LM+CSM on the other hand. Not clear if this is considered as a staging event.

While not usually thought of as staging, the "transposition, docking, and extraction" maneuver separating the S-IVB from the CSM/LM satisfies the basic definitions of a staging event. An expended lower stage (the S-IVB) is separating from a fully fueled stage (the CSM) which will go on to make propulsive maneuvers later (mid-course corrections, lunar orbit insertion, and so on). The post-staging coast phase is unusually long, but that's an arbitrary distinction; the CSM is usually referred to as a spacecraft rather than a stage, but that's also arbitrary. The S-IVB did some maneuvering after separation to meet its eventual fate, but that's not unique (consider the Falcon 9 first stage). The separation is more complex, and gentler, than other staging events, but that doesn't seem particularly definitive to me. I can't think of anything that is fundamentally different between this and other staging events.

Separation of LM and CSM in lunar orbit. I don't think this is a staging event, but I'm not quite sure.

The most obvious distinction to me from "staging" is that the CSM is not discarded, and the LM will eventually return to the CSM. I've always seen this described as "separation" or "undocking", never as "staging".

separation of ascent and descent stage for the LM. I don't think this is a staging event as the tank and engines of the descent stage play no role during this launch.

This was, in fact, referred to as staging during the Apollo program. While the normal mission plan had the descent stage resting gently on the lunar surface when the ascent stage separated and fired, an abort from low altitude on the landing descent would look much like any other staging event. On the LM control panel were two prominent buttons: ABORT and ABORT STAGE. The ABORT button would abort the landing and return to safe lunar orbit using the descent engine; ABORT STAGE would shut off the descent engine, separate the two stages, and fire the ascent engine to return to orbit.

Close up of LM control panel showing ABORT and ABORT STAGE buttons

separation of LM and CSM. I don't think this is staging event.

This is just referred to as a jettison. The distinction I see from staging is that the LM is discarded, but at no point was the LM engine pushing the entire stack (except on Apollo 13!).

separation of CM and SM just before reentry. I've never heard staging for separation of reentry vehicle, yet the CM let behind a stage with empty propellant tank and a rocket engine and it looks like a serial staging.

The usual purpose of staging is to discard mass so that a following burn can be more mass-efficient, which isn't relevant to the CSM/LM separation, so it makes sense to me to classify it as a jettison rather than a staging.

$\endgroup$
3
$\begingroup$

Looking at for instance the list of events for Apollo 11, there are no "staging events", just a number of "separations".

On the other hand, if we are counting everything with a "stage" in the name, there are a total of five stages, three on the Saturn V and two on the lunar module.

To make a slightly different point than Russell Borogove's answer, I'm including the same disclaimer: "Warning: this answer contains unsupported opinions."

The staging page you linked does not go much farther than explaining that staging is getting rid of spent hardware to save having to carry the dead weight for further velocity changes. That leads to at least two reasonable interpretations:

1. Several parts contributing to the same manoeuvre, with one being discarded before the manoeuvre is complete.

Under this interpretation, only the S-IC and S-II separation events are staging events.

2. Discarding spent hardware in between maneuvres also counts

Under this interpretation, the S-IV separation, LM descent stage separation, LM ascent stage separation and the service module separation would also have to be counted.

$\endgroup$
5
  • 1
    $\begingroup$ Not Apollo, but on shuttle losing the SRBs was "staging", losing the ET was "separation". $\endgroup$ – Organic Marble Nov 2 '20 at 22:02
  • $\begingroup$ "Same manoeuvre" is doing some heavy lifting here. Why is staging during ascent to orbit part of the same maneuver, but staging during TLI not? $\endgroup$ – Russell Borogove Nov 2 '20 at 22:13
  • 1
    $\begingroup$ @RussellBorogove It's a rabbit hole of fuzzy terminology indeed. What I'm trying to express is if the separation is during a large velocity change or not. S-IV is separated after the TLI velocity change is over. $\endgroup$ – SE - stop firing the good guys Nov 2 '20 at 22:17
  • $\begingroup$ Not if you count MCC-1 as part of the TLI velocity change. $\endgroup$ – Russell Borogove Nov 2 '20 at 22:35
  • $\begingroup$ The problem with the terminology is that both answers are somewhat right, from a certain PoV. I've upvoted both, because both make good points, and there is no authoritative source. In the end, its up to the one writing the flight plan what they call which event, with certainly some leeway in both directions. I would be surprised to see first stage separation be described as undocking and not staging, but simply calling it "separation" also occurs in alot of documents. $\endgroup$ – Polygnome Nov 3 '20 at 9:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.