Spectral Measurements of Atomic Oxygen and Nitrogen During the OSIRIS-REx Re-entry

This paper presents measured spectral irradiance from the OSIRIS-REx Sample Return Capsule reentry (24 September 2023) as measured from one window of the NASA NA522 airborne observation platform. Two instruments with a nominal 10 nm bandwidth and 0.083 nm resolution were successfully used at this window: (1) Instrument 780, targeting atomic oxygen 777 nm emission; and (2) Instrument 820, targeting atomic nitrogen and atomic oxygen emissions in the vicinity of 820 nm. Useful data was acquired for an 8 s period of the re-entry, including at peak radiative heating. The design and calibration of these instruments is presented, along with the image processing methodology used to extract spectral data from the raw images. As the re-entry occurred during daylight hours, the significant sky background was a key consideration in the instrument design. Time resolved spectral irradiance measurements are presented for four bandpasses; one for the oxygen 777 nm triplet, and three for atomic nitrogen lines near 820 nm. No significant atomic oxygen emissions were observed near 820 nm. A 300 ms time-averaged spectrum at predicted peak heating is presented for both instruments. The results presented in this paper are the basis for future analysis of the shock-heated gas emissions from the OSIRIS-REx capsule re-entry.