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Upper stage

The part of a rocket that fires after the first stage separates, doing the precise work of placing a payload into its final orbit.

Why it matters

The upper stage is where the mission actually succeeds or fails. It fires in vacuum, often restarts hours later to circularise an orbit, and its accuracy determines whether a satellite arrives where it was sold to arrive. It is also almost always expended - and that is a problem in its own right, because a spent upper stage is a large, uncontrolled object left in orbit. Many of the most worrying debris objects are not satellites at all but abandoned upper stages.

In our data

Where the upper stage earns its keep is visible in the 23 missions we track that stop at geostationary transfer orbit: the stage delivers the satellite to a long ellipse and then stops, leaving the spacecraft to raise itself the rest of the way over the following months. Those 23 flights are also where a spent stage is left in a high, long-lived orbit rather than re-entering within years.

Missions we track
Where we use it
Not to be confused with

A kick stage, a small extra stage added on top to fine-tune the final orbit or to deploy several payloads to different orbits - common on smaller vehicles. Also distinct from the booster, which does the heavy lifting off the pad and, on a reusable vehicle, is the part that comes back.