rendezvous

In orbital mechanics, a rendezvous is a series of calculated burns and trajectory adjustments that bring two spacecraft into the same orbit and position them within docking distance, typically a few meters. This is not a spontaneous event but a choreographed sequence of maneuvers, usually taking several hours or days, in which the chaser vehicle (often a crewed spacecraft or cargo vehicle) closes on a target vehicle (a space station, another spacecraft, or an orbital facility) that is already in a stable orbit.

The classical rendezvous profile begins with the chaser in a lower, faster orbit than the target. An initial burn raises the chaser's orbit to an intermediate altitude where the two spacecraft have nearly matched orbital periods. A second corrective burn circularizes the chaser's orbit, placing both vehicles in the same orbital plane and altitude. Throughout this sequence, controllers continuously refine relative velocity and alignment to bring the gap between them to zero at the moment of closest approach.

Variants and real-world practice

Modern crewed rendezvous to the International Space Station typically use a phased approach lasting six to eight hours from launch to docking, though the actual closure from holding point to contact may take only a few minutes. Automated cargo vehicles like the Progress, ATV, and Cygnus spacecraft conduct autonomous rendezvous, with ground controllers monitoring and ready to intervene. The Soyuz spacecraft uses a mix of automatic and manual phases, allowing the commander to take manual control during the final approach if needed. Orbital rendezvous requires precise knowledge of the target's orbit, continuous communications, and on-board navigation systems capable of measuring relative position and velocity to within centimeters and millimeters per second.

The term itself comes from French military usage, where a rendezvous was a prearranged meeting point. In spaceflight, the word retained its sense of planned encounter but acquired the technical meaning of matching orbits as a prerequisite. The maneuver is fundamental to all crewed spaceflight beyond Earth orbit, supply missions to space stations, on-orbit assembly, and satellite servicing. Without reliable rendezvous capability, the sustained operation of orbital infrastructure becomes impossible.