|Mission type||ISS resupply|
|Mission duration||148 days|
|Spacecraft type||Progress-M s/n 356|
|Start of mission|
|Launch date||24 April 2006, 16:03:25 UTC|
|Launch site||Baikonur, Site 1/5|
|End of mission|
|Decay date||19 September 2006,|
|Perigee altitude||337 km|
|Apogee altitude||348 km|
|Epoch||24 April 2006|
|Docking with ISS|
|Docking port||Zvezda aft|
|Docking date||26 April 2006, 17:41:31 UTC|
|Undocking date||19 September 2006,|
|Time docked||146 days|
Progress M-56 (Russian: Прогресс М-56), identified by NASA as Progress 21P, was a Progress spacecraft used to resupply the International Space Station. It was a Progress-M 11F615A55 spacecraft, with the serial number 356.
Progress M-56 was launched by a Soyuz-U carrier rocket from Site 1/5 at the Baikonur Cosmodrome. Launch occurred at 16:03:25 UTC on 24 April 2006. Also carried to the ISS was an experimental MIT students-built picosatellite, named SPHERE, that will float inside the station, strictly maintaining its location inside.
The spacecraft docked with the aft port of the Zvezda module at 17:41:31 UTC on 26 April 2006. It remained docked for 146 days before undocking at 00:28:17 UTC on 19 September 2006 to make way for Soyuz TMA-9. It was deorbited at 03:28 UTC on 19 September 2006. The spacecraft burned up in the atmosphere over the Pacific Ocean, with any remaining debris landing in the ocean at around 04:14:40 UTC.
Progress M-56 carried supplies to the International Space Station, including food, water and oxygen for the crew and equipment for conducting scientific research.