NASA - National Aeronautics and Space Administration

Under the direction of prime contractor, the Boeing Company, Khrunichev State Research and Production Space Center in Moscow added enhancements to Zarya that include:

• greater attitude control functions
• orbital refueling potential at its nadir, or down-facing, docking port
• upgraded avionics
• additional docking capabilities

Other modifications included the refueling system to allow Zarya to accept fuel at its nadir port from the Progress, a Russian logistics resupply vehicle, in the absence of the Service Module, a key station element that must work in concert with Zarya. Without this modification, fuel reception, storage and distribution would occur only when the Service Module is present through Zarya's aft port. Also, power will be added at the nadir port for a Soyuz crew return vehicle or a Progress vehicle.

The enhancements will provide additional backup capabilities for the early International Space Station.

"These modifications make (Zarya) a more robust vehicle," said Michael Wood, Boeing FGB deputy program manager. "Additional attitude control and avionics will maintain the station in the assembly as components are added. Modifications to the aft port will allow docking of either the Russian Service Module (SM) or an interim control module."