Integrated spacecraft environments model (ISEM)

Capabilities of the ISEM code are presented that can aid in the understanding of the complex interactions between a space system and the ambient environment. The development of ISEM has been funded primarily by NASA over a period of 7 years. The code was developed as a flexible engineering tool to model the neutral molecular environment and it's interactions with the spacecraft based on orbital conditions and spacecraft molecular sources. Ionization of neutrals and charge exchange are added features. ISEM is a next generation of contamination models developed by the authors for Skylab (ODRAP), Outgassing Deposition Rate Assessment Program and Shuttle (SPACE), Shuttle Payload Contamination Evaluation. A predecessor to the ISEM code was called RAMDEN. Verification of the ISEM code has been made by comparing model results to experiment data both on orbit and in vacuum tests. Atmosphere Explorer-D was modeled and the results compared to flight data for the return flux of Neon to a mass spectrometer with very good results. Far field glow predictions by ISEM, from excited gas species, have been compared to the UV measurements made by the Imaging Spectrometric Observatory flown on Shuttle and the UV measurements made as a function of altitude on the S3-4 satellite with excellent results. ISEM was also compared to a series of vacuum environment tests at Arnold Engineering Development center with good success. Several matches with in flight mass spectrometer data of launched systems have been made. To date the physical systems for which ISEM codes exist include the Space Station Freedom, Shuttle, AE-D, EUVE, EMP, LDEF and many others. A description of the ISEM code, future plans and examples of it's predictions for the systems mentioned above are presented.