The spacecraft lifted off at 9:03 p.m. Central Asian Time, from Baikonur Cosmodrome in Kazakhstan. The 21st Progress to visit the station is carrying some small crustaceans for a Russian scientific experiment called Aquarium, which will examine the stability of closed ecological systems in microgravity. Researchers think it could provide information useful for lengthy human spaceflights.

Progress is carrying 5,040 pounds of equipment and supplies, including more than 1,900 pounds of propellant, just over 100 pounds of air and oxygen, 661 pounds of water and almost 2,360 pounds of dry cargo.

Its sister cargo carrier and predecessor at the station, Progress 20, will remain at the Pirs docking compartment until mid-June, when it will be de-orbited with a load of trash and surplus equipment and burn up after entry into Earth's atmosphere.

P21 is scheduled to dock with the aft port of the Zvezda service module at 1:40 p.m. Eastern Time Wednesday. NASA Television will cover the docking live, beginning at 1 p.m.

The Progress is similar in appearance and some design elements to the Soyuz spacecraft, which periodically transports crewmembers to the station, serves as a lifeboat while they are there and returns them to Earth. The aft instrumentation and propulsion module is nearly identical.

The second of the three Progress sections is a refueling module, and the third, uppermost as the Progress sits on the launch pad, carries cargo. On the Soyuz, the descent module, where the crew sits at launch and which returns them to Earth, is the middle module and the third is called the orbital module.

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