Match the launcher to the mission

A payload capacity needs an accompanying orbit and configuration. A figure for low Earth orbit cannot simply be reused for geostationary transfer orbit. A transfer orbit is also different from the final geostationary orbit: the mission must allocate the remaining maneuvers to a stage or the spacecraft. A number detached from its destination can make an unsuitable vehicle appear adequate.

Consider a fictional 4-tonne spacecraft. One proposal advertises 6 tonnes to a low circular orbit; another gives 4.5 tonnes to the required transfer orbit. The first is not proven adequate just because six exceeds four. Request performance for the actual orbit, including inclination, plus the adapter allowance and agreed mission margins.

Yang Liwei launched aboard Shenzhou 5 on a Long March 2F in October 2003. Its crew-transport configuration includes an escape system. Carrying people therefore involves requirements beyond lifting the spacecraft’s mass. A cargo-launch success alone is not evidence that another configuration has met those crew requirements.

Chang Zheng 5B launched the Tianhe station module in April 2021, while Chang Zheng 7 Y6 launched Tianzhou 5 in November 2022. These station-related missions delivered different payloads. The accompanying photos show the 5B module launch and the 7 Y6 vehicle before its cargo flight. Neither photo should be labeled as the crew launch described above.

Mass is only one constraint. A payload needs a suitable fairing envelope, mechanical attachment, electrical interfaces and a compatible launch environment. The larger fairing was a meaningful part of the original 5B station-module design. A spacecraft that is light enough can still be too wide or require an incompatible interface.

Finish the fictional selection with a handoff table: who delivers the target orbit, when separation occurs, what state the spacecraft must be in, and which post-separation operations belong to it. For a station mission, orbit insertion is not docking. Define acceptance evidence for each phase so a successful launch is not mistaken for completion of the whole spacecraft mission.