The Soyuz 40 mission was a 1981 Soviet crewed spaceflight and the final flight of the Soyuz 7K-T spacecraft. It was a collaboration between the Soviet Union and Romania.^[1]

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Soyuz 40

Soyuz 40 is launched from the Baikonur Cosmodrome on 14 May 1981.
COSPAR ID	1981-042A
SATCAT no.	12454
Mission duration	7 days, 20 hours, 41 minutes, 52 seconds
Orbits completed	124
Spacecraft properties
Spacecraft type	Soyuz 7K-T
Manufacturer	NPO Energia
Launch mass	6,800 kilograms (15,000 lb)
Crew
Crew size	2
Members	Leonid Popov Dumitru Prunariu
Callsign	Dnieper
Start of mission
Launch date	14 May 1981, 17:16:38 (1981-05-14UTC17:16:38Z) UTC
Rocket	Soyuz-U
Launch site	Baikonur 1/5
End of mission
Landing date	22 May 1981, 13:58:30 (1981-05-22UTC13:58:31Z) UTC
Landing site	225 km SE of Dzhezkazgan
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Perigee altitude	198.1 kilometres (123.1 mi)
Apogee altitude	287 kilometres (178 mi)
Inclination	51.6 degrees
Period	89.6 minutes
Docking with Salyut 6
L-R: Popov and Prunariu Soyuz programme (Crewed missions) ← Soyuz 39 Soyuz T-5 →

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• Mass: 6800 kg
• Perigee: 198.1 km
• Apogee: 287 km
• Inclination: 51.6°
• Period: 89.06 minutes

Soyuz 40 was the 16th expedition to Salyut 6 and carried the ninth international crew. It also ended the first phase of the Intercosmos program by carrying Romanian cosmonaut Dumitru Prunariu and Soviet cosmonaut Leonid Popov to the station. In all, nine Intercosmos missions were launched between 1978 and 1981.

Soyuz 40 was the last of the original Soyuz spacecraft (due to its replacement by the Soyuz-T) and the last Soyuz spacecraft to dock with Salyut 6. During the crew's stay, Prunariu studied the Earth's magnetic field. Earth observations had to be delayed until the last day of the flight, when Salyut 6 passed over Romania in daylight. During this time the crew also tested the station's orientation system.

• List of human spaceflights to Salyut space stations
• List of Salyut expeditions