SESAT: separate a spacecraft from the capacity sold on it

SESAT launched from Baikonur in April 2000 for Eutelsat. Reshetnev’s history records development beginning in 1995 with French Alcatel participation. NASA’s launch bulletin describes a communications spacecraft with eighteen Ku-band transponders. The archive card uses the title Sesat. The project connects Russian spacecraft manufacturing with a European operator and a cross-border payload partnership.

The operator’s 2005–06 report describes SESAT 1 serving communications at 36° East, with coverage linking Europe and regions farther east and south. This is a dated service description. It should not be treated as the satellite’s position throughout its entire history. A spacecraft can be relocated or replaced at a service position without becoming a new physical object.

Eutelsat also marketed capacity under the name SESAT 2. Its operating reports distinguish this from SESAT 1: the later service used leased capacity — open definition on an RSCC spacecraft. A customer might buy access through one operator while the hardware belonged to another. Counting every marketed name as a separately owned satellite would therefore inflate the physical fleet.

Imagine a hypothetical spacecraft with twenty-four comparable capacity units. Operator A leases twelve and operator B uses the other twelve. There are two service allocations but still one spacecraft. If either operator gives its allocation a new commercial name, the number of satellites does not increase. This simplified example is about identity and allocation, not the detailed performance of a particular transponder.

Count hardware and allocations separately

Eutelsat’s 2011 partnership announcement records that W7 replaced SESAT 1 at 36° East in January 2010. Its 2014–15 report separately describes replacing the SESAT 2 lease with capacity on Express-AM6. These are distinct changes: replacing an orbital service role and replacing a leased allocation. Neither should be collapsed into a story of two identical spacecraft being exchanged.

To follow a customer service over time, record the spacecraft identifier, owner, operating organization, allocated capacity and date. Each answers a different question. A user may experience continuity while the physical satellite changes, or retain the same satellite while the provider’s branding changes. SESAT shows why a connected archive needs relationships between programmes, hardware and services rather than a simple list of names.