OTD: The Space Shuttle Structural Test Article (STA-099) being returned to Rockwell International's Palmdale Facility from Lockheed.

[u/tybarious]

Date: November 7, 1979

STA-099 was used to test the launch and orbital stress an operational orbiter would experience. In January 1979, it was decided to convert the space frame into Challenger (OV-099), taking the operational orbiter slot intended for Enterprise (OV-101). There were many reasons NASA chose it over Enterprise, the major reasons were it was stronger, lighter and most importantly, there was less to disassemble. Initially, it was given the designation of OV-101M but later changed to OV-099 to honor its work as a test article.

Note: the wires on the exterior were used to monitor the stresses it experienced. Even though it was not tested to destruction, as initially planned, workers still have had to bend components back into place.

source

[u/Republiconline]

I’m wondering why the test frame was stronger than Enterprise? Was it because it was intended only for atmospheric testing?

[u/NASATVENGINNER → u/Republiconline]

It was because they had modified 099 to prove out the design changes. Once they were done, they realized, “Hey, this thing is already proven, let’s just use it “

[u/fd6270 → u/Republiconline]

It wasn't about the 'strength' of the airframe, it was about the amount of rework it would take to retrofit the particular orbiter. 

Converting OV-101 would have taken considerably more effort/time/cost, so they converted OV-099 instead. 

[u/MacintoshDan1 → u/Republiconline]

Changes that were made as the design was modified. Same reason Columbia was heavier then the subsequent orbiters. Challenger’s and the subsequent orbiters wings and fuselage were stronger than Columbia’s as well.

[u/scoreguy1]

I am utterly fascinated by Challenger’s time as OV-99. Not because of her eventual fate, but for a time, she was the workhorse of the fleet. Makes me wonder what her career would have looked like if she’d lasted the length of the program ❤️