It would test flight conditions at the edge of Earth's atmosphere.

VOA: special.2010.07.07

It is launching a fleet of spy satellites and plans to test a rocket that can reenter the atmosphere--officially, for space shuttle research.

FORBES: Japan Weapons, Inc.

So it would be nice to test those models by observing a planet whose atmosphere is already well known: Venus.

ECONOMIST: Transits of Venus

Test pilots demonstrated that it could fly and land in the atmosphere like airplanes, but the Enterprise never flew in space.

CNN: Space shuttle Enterprise flies again