On January 5, 1979, NASA commissioned a second orbiter. Later that month, Rockwell began converting STA-099 to OV-099, later named "Challenger". On January 29, 1979, NASA ordered two additional orbiters, OV-103 and OV-104, which were named "Discovery" and "Atlantis". Construction of OV-105, later named "Endeavour", began in February 1982, but NASA decided to limit the Space Shuttle fleet to four orbiters in 1983. After the loss of "Challenger", NASA resumed production of "Endeavour" in September 1987.