The flight tested the heat shield. The shield protected the spacecraft from the great heat produced when it returned through the Earth's atmosphere.

VOA: special.2009.06.10

It would leave the atmosphere briefly, then return, testing the effects of the extreme heat of re-entry.

VOA: special.2010.07.07

That involves preventing industrial gases from escaping into the atmosphere where they can trap heat.

VOA: special.2009.11.21

But the intense heat of passing through the Earth's atmosphere likely damaged those molecules.

VOA: special.2011.06.22

Carbon dioxide and other gases in the atmosphere trap heat from the sun.

VOA: special.2010.01.19