Mission statement: A mission to help evaluate the performance of thermal protection systems of atmospheric entry vehicles returning to Earth at superorbital velocities.
THE MISSION
The airborne observations.
The Hayabusa Re-Entry MAC airborne observing campaign will deploy a wide range of imaging and spectrographic cameras for remote-sensing observations of the artificial meteor to cover spatial resolution, wavelength, spectral resolution, sensitivity, and time.
Weather won't affect the airborne observations. Hayabusa Re-Entry MAC (for "Multi-instrument Aircraft Campaign") offers an international team of researchers a viewing platform above weather at 39,000 ft, from where atmospheric extinction is low even when the spacecraft is still far away.
NASA's DC-8 Airborne Laboratory will deploy from Palmdale in California to Melbourne in Australia. On the day of the entry, it will fly in a race-track pattern at some distance from the landing site so that the entry is visible at low elevation angles out of the left-hand window ports. Windows are optical glass of various kind to provide the best possible view. The DC-8 aircraft is operated out of the NASA Dryden Aircraft Operations Facility in Palmdale, California, where scientists will meet in the weeks prior to the mission to install their instruments.
The participating researchers are from NASA, JAXA, the University of Southern Queensland in Australia, and several other universities and private institutes. They will point high definition TV cameras, intensified cameras, high frame-rate cameras, near-IR sensitive InGaAs cameras, slit-based spectrographs, and slit-less spectrographs to capture the light from the capsule during entry.
The DC-8 floorplan below, showing the distribution of instruments in the aircraft, is preliminary and will be updated as mission preparations unfold.
These will be very challenging observations. Because there is no remaining fuel to divert the main spacecraft, the Hayabusa capsule enters just before the main bus, causing the main target of the campaign to sit just head of a fragmenting fireball that may become 4 magnitudes brighter. The researchers will adapt to this by zooming in on their target and using high framerate cameras to avoid motion blurring. By orienting the grating dispersion perpendicular to the debris train, slit-less spectroscopy can be used to get spectra from the capsule and parts of the rest of the spacecraft at the same time (similar to ATV reentry spectroscopic data shown in figure left, courtesy of Mike Taylor of Utah State University).
The conditions of entry.
The 40-cm diameter capsule will be detached from the main spacecraft when passing the Moon's orbit, put in a 5 rotations/second spin. Depending on the time of release, it will have moved about 2-5 km ahead of the main spacecraft when reaching atmospheric interface at 200 km altitude.
Because Hayabusa is on an asteroidal orbit around the Sun, the time of arrival will not be affected much by last-minute manouvers. The entry will occur in the middle of the night in dark-sky conditions. In close collaboration with JAXA, the latest positional information on the capsule will be communicated to the science team, better preparing the team for the arrival of the capsule.
Below 40 km, the capsule will have been slowed down enough by the atmosphere to no longer emit visible light. Once the capsule reaches 10 km altitude, the heat shield is separated and falls to the ground (see figure above, courtesy of Tetsuya Yamada, JAXA). The exact point of where the heat shield is released (and the parachute is opened) has an uncertainty of about 100 x 15 km. To help recover the heat shield, the trajectory of the capsule is determined from the meteor observations.
The Sample Return Capsule will be floated to the ground by means of a parachute. Due to upper atmosphere winds, the capsule can end up quite far from the point of release. To be able to recover the capsule, the parachute is given a high reflectivity for radar signals, and the capsule has a radio responder.
Ground-based observers will have more difficulty spotting the capsule low near the horizon and in bad winter weather conditions, but can provide triangulation for trajectory reconstruction (in clear weather only) and infrasound detections (all weather).
