Rarefied-Flow Transition Regime Orbiter Aerodynamic Acceleration Flight Measurements

Acceleration data taken for the e rst time from the orbital acceleration research experiment during re-entry on Space Transportation System-62 have been analyzed using in situ calibration factors. The re-entry data include the e ight regime from orbital altitudes down to about 90 km, which covers the free-molecule-e ow regime and the upper altitude fringes of the raree ed-e ow transition into the hypersonic continuum. Ancillary e ight data on Orbiter position, orientation, velocity, and rotation rates have been used in models to transform the measured accelerations to the Orbiter center of gravity, from which aerodynamic accelerations along the Orbiter body axes have been calculated. Residual offsets introduced in the measurements by unmodeled Orbiter forces are identie ed and removed.Theresulting aerodynamicacceleration measurementsalong theOrbiter’ sbody axisand thenormal to axialacceleration ratio in thefree-molecule-e owandtransition-e owregimesarepresented,andthereisexcellent agreementwhencompared withnumericalsimulationsfromthreedirectsimulationMonteCarlo codes.Also,there is good agreement with a direct comparison between the experiment e ight data and an independent microgravity accelerometer experiment, the high-resolution accelerometer package, which also obtained e ight data on re-entry during the mission down to about 95 km.