Mir/Salyut Space Station Refuelling and Resupply

Copyright (C) 1993, by Dennis Newkirk

For those who don't know, Salyut 6-7 and Mir use a pressure fed storable propellant propulsion module at the rear of the station designated OUD. The system includes 2 main engines (1 on Mir), 4 blocks of attitude control thrusters and 6 propellant tanks positioned around the rear docking port. The main engines are rarely used since spacecraft are usually docked at the port (and not really trusted after many years of disuse). When this is so, the docked spacecraft are used to boost the stations orbit whenever propellant supplies allow.

Progress Description

The Progress was a highly modified version of the Soyuz, used to automatically deliver cargo to the space stations. The Soyuz design was altered by replacing the capsule with a tankage section. The Progress spacecraft usually weighed about 7,020 kg. at launch depending on the amount of cargo. Payload capacity was 2300 kg. of which about 1000 kg. was maximum weight of propellants, and 1300 kg. maximum orbital module cargo. It was 7.94 meters long and 2.7 meters diameter at the base. Internal volume of the cargo module was 6.6 cubic meters. The docking collar of the Progress includes propellant line connectors in addition to the standard electrical and communication connections. The Progress docked only at the aft port of Salyut 6 and 7 stations because it was the only port with propellant line connections. Mir forward and aft (and Kvant) ports are equipped with the connections. The Progress service module used a modified version of the OUD pressure feed engine system. The Progress was also used to test the new engine system before the beginning the Soyuz T flights, which used the same system.

The pressurized instrument section of the service module was lengthened and equipment for automatic docking was apparently installed in this additional space. The Progress carried twice as much instrumentation for rendezvous and docking as the Soyuz. In the cargo section, pressure was maintained at 760 mm. but temperature varied from 3 to 30 C during flight. Special equipment carrying racks were installed depending on the cargo to be carried. The hatch, with the docking probe, could be opened automatically or manually. Another feature of the docking hatch and probe was the ability to remove the entire hatch from its mounting, to facilitate movement of cargo. The probe is stored in the space station and installed or stowed in the Progress before undocking.

The Progress could carry enough cargo to supply a Salyut with two or three cosmonauts for three to six weeks. One figure quoted by the soviets was 30 kg. supplies per-person per-day. A typical cargo consisted of 200 kg. of water, 600 kg. of propellant, 250 kg. of food, 450 kg. of air, experiments, mail, replacement parts, materials samples, fresh food, video taped movies, concerts and cartoons, clothes, books and music and nature sound cassettes.

Propellant was transferred from the Progress to the station by closing off the stations tanks and using a pump to lower the pressure of the tanks from an operational pressure of 220 Atmospheres, to about 3 Atmospheres by extracting nitrogen from the tanks flexible bellows. This took several hours because the pumping consumed a quarter of the Salyut station's electrical power (one kilowatt) and the Salyut's batteries had to be recharged periodically during the process. The Progress tanks were pressurized to 8 Atmospheres using its own nitrogen supply. When the valves were opened, most of the propellant flowed to the stations tanks which were then closed off refilled. The same process was used for both fuel and oxidizer tanks. The lines in the docking collar were then purged with nitrogen after refueling, to prevent the volatile fuel and oxidizer residue from spilling out onto the station after undocking. It was not uncommon for fuel and oxidizer transfers to be done days apart, and never at the same time probably due to power constraints and safety concerns. All refuelling operations can be done remotely from mission control, and usually cosmonauts only observe.

The cosmonauts usually observe the docking of the Progress from 10 km. distance and could boost the station away from a malfunctioning ship. The cosmonauts could orient the station manually during the docking or let the stations automatic systems point the station. The Progress' were unloaded and refilled with waste, used equipment and air regenerators. Special tools for unfastening the equipment in Progress were carried on Salyut stations including a recoilless hammer, a lock-on screwdriver, pliers, and a power screwdriver. Many items like air regeneration tanks, clothes and human wastes were disposed of using Progress ships that burn up on re-entry. When a Progress was not available, the cosmonauts put the small trash in bags and put it out through the scientific airlocks. These bags quickly fell into the atmosphere and reentered due to atmospheric drag after about a month. This is used rarely on Mir.

Progress M Description

Revised Progress design using a Soyuz TM service module, Kurs (enabling docking at the forward Mir port which does not have Igla), and solar panels. The propellant section was connected to the propulsion section so propellant can be shared and unused orbital maneuvering propellant transfered to the station. The cargo compartment (orbital module) was slightly lengthened adding 1 cubic meter to the volume, and payload capacity was increased by 200 kg. (2700 kg. total). Capable of independent flight for up to 30 days. Docked lifetime is 108 days.

The orbital module also can be equipped with a NPO Energia return capsule capable of carrying 100-150 kg.. The capusle is carried in the orbital module and is used to replace the docking probe after filling the Progress with trash, and the old probe. The capsule is 60 cm. in diameter. After retrofire the capsule seperates and pressure sensors trigger parachutes after reentry.