Concept

Orbital rendezvous — where it appears

Bringing two spacecraft to the same place with the same velocity. The far phase is a matter of orbital periods and takes hours; the near phase is governed by the relative-motion equations and is counterintuitive, since a burn along the track moves the chaser backwards.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

A Hohmann transfer, 2.6 to 1 in radius. Two circular orbits and the ellipse that touches both. The first burn raises the far point to the outer orbit; the second, half an orbit later, circularises. The costs are computed from the vis-viva relation.

The cheapest way between two orbits, and why it is so slow

Two burns and a long coast is the least fuel that will move a spacecraft between two circular orbits. It is also, for anything beyond the Moon, an unreasonably long wait.

spaceflight · Orbital transfer

Catching a target 40° ahead. A phasing manoeuvre. Dropping into an orbit 6% lower shortens the period to 0.9553 of the target's, so the chaser gains 16.1° each lap and closes 40° in 3 revolutions. Speeding up would have lost ground instead.

Catching up by slowing down, which cost Gemini 4 its fuel

To reach something ahead in the same orbit, a spacecraft must fire backwards. Pointing at the target and thrusting makes the gap grow, and a crew found that out in orbit before anyone had flown the correct manoeuvre.

spaceflight · Rendezvous

Named alongside it

The objects these essays reach for when they reach for this one.

Launch window Synodic period Δv Gravity assist Hohmann transfer Lagrange points Oberth effect Phasing orbit R-bar approach Relative motion Vis-viva

All concepts