Tuesday, November 17, 2009

Space Station Assembly

Russian Progress Spacecraft

The Progress resupply vehicle is an automated, unpiloted version of the Soyuz spacecraft that is used to bring supplies and fuel to the International Space Station. The Progress also has the ability to raise the Station's altitude and control the orientation of the Station using the vehicle's thrusters.

Image to right: A Progress spacecraft sits atop a Soyuz rocket at Baikonur Cosmodrome. Credit: NASA

Both the Progress M and M1 versions have a pressurized Cargo Module to carry supplies, a Refueling Module that holds fuel tanks containing propellant and pressurized gases, and an Instrumentation/Propulsion Module where the Progress systems equipment and thrusters are located.

The Progress spacecraft is launched to the Space Station from the Baikonur Cosmodrome in Kazakhstan aboard a Soyuz rocket. It normally docks to the end of the Station's Zvezda Service Module, but it can also dock to the bottom of the Pirs Docking Compartment.

Cargo Module

The Progress Cargo Module -- which is similar in construction to the Soyuz Orbital Module -- can carry up to 1,700 kilograms (3,748 pounds) of supplies to the Space Station in a pressurized volume of about 6 cubic meters (212 cubic feet). Once the Progress docks with the Space Station, the crew enters the Cargo Module through the docking hatch.

After the cargo is removed and before the Progress undocks, the crew refills it with trash, unneeded equipment and wastewater, which will burn up with the spacecraft when it re-enters the Earth's atmosphere. The Cargo Module can hold 1,000 to 1,700 kilograms (2,205 to 3,748 pounds) of trash.

Refueling Module
In place of the Soyuz Descent Module, the Progress has a Refueling Module. The Progress M1 Refueling Module has eight propellant tanks that can hold up to 1,740 kilograms (3,836 pounds) of fuel, depending on how much weight is carried in the Cargo Module. Four of the tanks contain fuel, while the other four contain the fuel's oxidizer. The Progress M has four tanks -- two for fuel and two for oxidizer -- and two water tanks. The M1 has no water tanks.

The contents of the fuel and oxidizer tanks can be transferred to the Space Station's own propulsion system through fluid connectors in the docking ring. This propellant can also be used by the Progress' thrusters to boost the Station altitude or to change its orientation, or attitude, in space.

Instrumentation/Propulsion Module

This module contains the electronic equipment, or avionics, for the Progress' systems and sensors. It is similar in design to the Soyuz Instrumentation/Propulsion Module. Any fuel in this module that is not used to get the Progress to the Station or for undocking and deorbit can be used to boost the altitude of the Space Station. Surplus fuel amounts can vary from 185 to 250 kilograms (408 to 551 pounds).

Rendezvous, Docking and Undocking

The Progress normally takes two days to reach the Space Station. The rendezvous and docking are both automated, although once the spacecraft is within 150 meters (492 feet) of the Station, the Russian Mission Control Center just outside Moscow and the Station crew monitor the approach and docking.

The Progress uses an automated, radar-based system called Kurs to dock to the Station. The active portion of the Kurs is on the Progress and the passive equipment is on the Station. The Station crew can also dock the Progress using the TORU system, a backup remote control docking system in the Station's Zvezda Service Module.

Once the Progress is filled with trash, usually a day before the launch of the next Progress vehicle, the Station crew closes the hatches and initiates the undocking process. Once the Progress has undocked, the vehicle's thrusters are fired to maneuver it into an orbit that will send it into the Earth's atmosphere, where it will burn up on re-entry over the Pacific Ocean.