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As I understand it once a spacecraft reaches low earth orbit it may have to do another burn to reach a different orbit. Would that change in orbit be considered an orbital insertion burn? Do any spacecraft do an orbital insertion burn during the initial lift off to orbit. I was under the impression there is one "burn" from lift-off to reaching orbit.

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    $\begingroup$ Shuttle always had a burn to improve the orbit after the main engines shut down. Is that an orbital insertion burn? As you say, it's terminology. More info here space.stackexchange.com/questions/29839/… And, welcome back to space! $\endgroup$ Nov 8, 2021 at 2:20
  • $\begingroup$ @OrganicMarble Thank you, and thanks. $\endgroup$
    – Bob516
    Nov 8, 2021 at 2:46

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Wikipedia defines “orbital insertion” as either acceleration or deceleration to allow entry into a stable orbit.

To answer your question, where a spacecraft has been launched into low earth orbit and performs another burn to reach another orbit, this is by definition an orbital insertion.

The other part of your question, “do any spacecraft do an orbital insertion burn during lift off ?” is awkward semantics. Most launches place their payload in low Earth orbit, so the launch itself is technically an orbital insertion. But this is not the usual use of the term.

The term is more typically used to describe a burn for the purpose of entry into orbit around a celestial body following a transfer, such as Apollo’s Lunar Insertion or transfer from low Earth orbit to a geosynchronous orbit.

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Geostationary satellites are usually launched into a geostationary transfer orbit https://en.wikipedia.org/wiki/Geostationary_transfer_orbit This highly elliptical orbit has an apogee that extends out geostationary orbit and a perigee in low earth orbit. The initial launch burn places the satellite into the transfer orbit and hours later at apogee a second burn is required to circularise the orbit so that it becomes geostationary.

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    $\begingroup$ "Would that change in orbit be considered an orbital insertion burn?" Would that be a "yes"? $\endgroup$
    – uhoh
    Nov 7, 2021 at 23:17
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    $\begingroup$ Well its clearly a separate burn as it happens hours after launch. And its required to insert the spacecraft into geostationary orbit otherwise it would loop back down to LEO on the elliptical transfer orbit. The transfer orbit is a hohmann orbit between LEO and geostationary so I think so yes $\endgroup$
    – Slarty
    Nov 8, 2021 at 8:31
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To put a spacecraft into orbit, you need to do two things:

(1) Get it high enough to avoid excess friction from the body's atmosphere and/or surface (e.g., mountains).

(2) Get it going fast enough in the horizontal direction. This is "insertion".

From the start, on pad, the rocket's usually going straight up, purely working on (1). But then, it pitches over, and works on a combination of (1) and (2). The final burn to achieve the desired orbit is the "insertion" burn: it may be pure (2). The burns may be continuous from liftoff to insertion, so there's no clear distinction. Or, there may be a coast phase between the earlier burn(s) and the final insertion burn. There may be more than one insertion: you may insert into a transfer orbit before inserting into the final orbit.

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    $\begingroup$ Or get it going slow enough. Many orbital insertion burns are "capture" burns where a burn is needed to reduce the spacecraft's velocity below escape velocity. $\endgroup$
    – johnDanger
    Nov 8, 2021 at 17:57
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The following is a highly simplified version of orbital mechanics, but I believe it may help answering the question.

To some approximation all (non-escape) orbits around earth are ellipses, having the center of the earth at one of their two focal points. The only way to change the orbit from one of those ellipses to another is by firing the rocket engine. In particular this means that when you stop firing, you are stuck on an ellipse that goes through the point you are currently at.

So if you want to get to any useful orbit, say a circular at x km above the surface, then necessarily the point where the rocket was last firing also has to be on that orbit and thus at x km altitude (and it has to move fast enough and in the right direction at that point). And of course the rocket also needs to fire at launch, to get you up there in the first place. Anything in between is variable.

If your target orbit is rather low, continuously firing the engine from launch to final orbit (with a short break for stage separation) might be the way to go, because you need every second of acceleration time you can get. If your target orbit is something high, then you might want to split the burn into an initial launch phase to get you on an ellipse with the highest point touching your target orbit (a transfer orbit, or sub-orbit, if the ellipse touches earth) and then a second burn, once you reach that point, to get you into the actual orbit.

In the latter case, the final burn would be the orbital insertion burn. In the continuous firing case things are a bit muddled. The last bit of firing would definitely count, but the point at which the launch burn becomes an orbital insertion burn is a bit arbitrary and up for definition.

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Your question forgets an entire category of launches: interplanetary launches. Those tend to (but aren't always) straight out, they don't have an earth-orbital component at all.

This was also planned for some scenarios considered for the Apollo program (and possibly used in other lunar launches).

So no, not all launches from earth have an earth-orbit insertion burn.

If it is for reaching orbit explicitly, as said there's typically multiple burns. This is true implicitly for most any multi-stage rocket as there's typically a small delay between one stage burning out and the next stage firing. The timing of these delays in part determines the initial orbit. Multiple subsequent burns afterwards can (depending on the vehicle) be then used to reach the final orbit or ejection trajectory.

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