PROGRESS 31 (also known as Progress-31) is a cargo satellite launched on August 3, 1987, from the Tyuratam Space Center's LC1 pad by the Soviet Union using a Soyuz-U2 launch vehicle. The spacecraft has dimensions of 7.9 meters in length and diameter, with a dry mass of 4,771 kg and a launch mass of 7,212 kg. It was manufactured by NPOE (NPO Energia) and used batteries for power supply. Equipped with a KTDU-80 motor, PROGRESS 31 served as part of the Progress 7K-TG series with the specific unit being No. 138. Its shape is described as a combination of sphere, cone, cylinder, and pan sections. The satellite's purpose was to transport cargo, though specific details about its mission are not provided in the given data.