Station-to-Shuttle Power Transfer System

The Station-to-Shuttle Power Transfer System (SSPTS; pronounced "spits") allows a docked Space Shuttle to make use of power provided by the International Space Station's solar arrays. Using this system reduces usage of a shuttle's onboard power-generating fuel cells, allowing it to stay docked to the space station for an additional four days.

SSPTS is a shuttle upgrade that replaces the Assembly Power Converter Unit (APCU) with a new device called the Power Transfer Unit (PTU). The APCU had the capacity to convert shuttle 28VDC main bus power to 124VDC compatible with ISS's 120VDC power system. This was used in the initial construction of the space station to augment the power available from the Russian "Zvezda" service module. The PTU adds to this the capability to convert the 120VDC supplied by the ISS to the orbiter's 28VDC main bus power. It is capable of transferring up to eight kilowatts of power from the space station to the orbiter. With this upgrade both the shuttle and the ISS are now able to use each other's power systems when needed, although it is not expected that the ISS will ever again require the use of an orbiter's power systems. [cite web
url = http://shuttlepayloads.jsc.nasa.gov/data/PayloadDocs/documents/07700/App_03.pdf?page=66| title = Space Shuttle Program "System Description and Design Data - Electrical Power and Avionics (NSTS 07700, Vol. XIV, Appendix 3)"| accessdate =| publisher = NASA| pages = 111Section 8.5, page 66]

During mission STS-116, PMA-2 was rewired to allow for the use of the SSPTS.cite web |url=http://www.nasa.gov/centers/johnson/pdf/163524main_ASC_116_F_B_1.pdf?page=174 |page=174|title=Ascent Checklist STS-116 | accessdate =|publisher=Mission Operations Directorate Flight Design and Dynamics Division| date= page 174: AFT FLIGHT DECK PAYLOADS SWITCH LIST FOR HANDOVER] The first mission to make actual use of the system was STS-118 with Space Shuttle "Endeavour". [cite web | url = http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts118/news/STS-118-05.html | title = STS-118 MCC Status Report #05 | publisher = NASA]

Currently only "Discovery" and "Endeavour" are equipped with the SSPTS. After "Atlantis" returns from the STS-125 servicing mission to the Hubble Space Telescope, it too will be equipped with the SSPTS for its two remaining ISS missions.Fact|date=October 2008

See also

* Extended Duration Orbiter

References

External links

* [http://www.boeing.com/defense-space/space/returntoflight/vehicleupgrades/sspts.html SSPTS information from Boeing]