ISS Propulsion Module

Purpose for an ISS Propulsion module. Critical ISS GN&C/Propulsion functionality currently only resides in Russian (Zvezda and Progess) and European (ATV) assets. A Propulsion Module is needed for ISS altitude maintenance and reboost, debris avoidance maneuvers, attitude control and propellant supply. A . Propulsion Module would be needed in the event the Zvzedza Service Module was not available (launch failure, etc) to the International Space Station. If the Zvzedza had not been available, the Interim Control Module would have been used. It only had a lifetime of 3 years, then the Propulsion Module would have been necessary.

The ISS needs a average of 7000 kg of propellant each year for altitude maintenance, debris avoidance and attitude control. It will need 105,000 kg throught 2014.

A Propulsion Module would provide reserve propellant provides one year of ISS orbit life in case of supply interruption. A Propulsion Module would have been attached to the Unity end of the ISS.

Why build a Propulsion module? Multiple supply vehicles are required to satisfy the ISS's 7000 kg annual average propellant need. Current plan for 6 Progress M1 spacecraft per year meets need.

The Propulsion module would hold 9808 kg fuel. Zarya FGB holds 5500 kg. Zvezda Service module holds 860 kg. Progress M holds 1100 kg, Progress M1 holds 1950 kg. ESA ATV holds 4000 kg. The cancelled U.S. Interim Control Module holds 5000 kg of fuel. A Shuttle Orbiter ISS generic reboost has 232 kg of fuel available. An Orbiter Max reboost mission has 1626 kg of reboost fuel available.

As it turned out, the successful launch of the Zvezda Service module and continued Progress flights made the Propulsion module unnecessary and it was cancelled. The ESA ATV will also be capable of ISS reboosts.