RCS analysis of the reinforced carbon-carbon tee-seals as potential "Flight Day Two" candidates in support of the Columbia accident investigation

During the Columbia Shuttle Investigation, our office tried to identify a piece of on-orbit debris that originated from the Orbiter during its second day in space. This "Flight Day Two" (FD2) object was detected by UHF radar and tracked for 3 days before falling out of orbit. Extensive RCS measurements performed by the Air Force Research Laboratory (AFRL) and corresponding ballistic analysis by the USAF Space Command narrowed the potential candidates down to just two possible classes of objects: (1) a section of reinforced carbon-carbon (RCC) leading edge panel acreage; (2) a section of RCC "tee-seals". During the investigation, AFRL was asked to estimate the UHF RCS of various whole and fragmentary tee-seals to compare with the on-orbit UHF RCS observations. Since actual Orbiter tee-seal hardware, either whole or fractured, were not available, we predicted UHF RCS on various virtual tee-seal fragment geometries to confirm or eliminate the tee-seal as a candidate for the FD2 object. The paper summarizes our UHF RCS predictions, which definitively show that a whole or partial RCC tee-seal could not be the FD2 object. This left the RCC panel acreage as the only known object that fits both the on-orbit observed ballistic and UHF RCS data, a confirming piece of evidence in the Columbia investigation.