Determination of Barometric Altimeter Errors for the Orion Exploration Flight Test-1 Entry

摘要

The Exploration Flight Test 1 (EFT-1) mission is the uncrewed flight test for the upcoming Multi-Purpose Crew Vehicle (MPCV). During entry, the EFT-1 vehicle will trigger several Landing and Recovery System (LRS) events, such as parachute deployment, based on on-board altitude information. The primary altitude source is the filtered navigation solution updated with GPS measurement data. The vehicle also has three barometric altimeters that will be used to measure atmospheric pressure during entry. In the event that GPS data is not available during entry, the altitude derived from the barometric altimeter pressure will be used to trigger drogue parachute and main parachute deployment. Therefore it is important to understand the impact of error sources on the pressure measured by the barometric altimeters and on the altitude derived from that pressure. The error sources for the barometric altimeters are not independent, and many error sources result in bias in a specific direction. Therefore conventional error budget methods could not be applied. Instead, high fidelity Monte-Carlo simulation was performed and error bounds were determined based on the results of this analysis. Aerodynamic errors were the largest single contributor to the error budget for the barometric altimeters. The validity of the altitude triggers for LRS events was evaluated given the barometric altimeter altitude budget, and it was determined that even with large errors in the barometric altimeter altitude, LRS events would still occur within acceptable ranges.