Electrical system of the International Space Station#Station to shuttle power transfer system

The Station -to- Shuttle Power Transfer System ( SSPTS; pronounced spits ) allowed the Space Shuttle, the energy available from the International Space Station. The decreased use of the on-board fuel cells and prolonged the duration of possible coupling to the ISS by four days.

SSPTS was called to upgrade the shuttle 's Assembly Power Converter Unit ( APCU ) with a new unit, Power Transfer Unit ( PTU). The APCU presented the option available energy to be transferred from the 28- V DC power supply for the shuttle to the 120 V power supply to the ISS. This could be the beginning of the construction of the space station to increase the available power of the Russian Zvezda module. The PTU allowed now to feed from the 120 V DC voltage of the ISS in the 28- V power supply of the orbiter. The maximum transmission power was eight kilowatts. Thus, space shuttle and space station could now, if necessary, provide each other with energy. However, it has made ​​no use of the possibility of the transfer of the Space Shuttle to the ISS.

During the STS-116 mission of the coupler port PMA -2, where the space shuttle docked, rebuilt around the SSPTS was to use. The first mission took advantage of the new system, was STS -118 Space Shuttle Endeavour with.

Only the Discovery and Endeavour were equipped with the SSPTS. The Atlantis without SSPTS was not so long used to the ISS, as the other two orbiters in the fleet.