Accession Number:

ADA510202

Title:

Analysis of Space Shuttle Primary Reaction-Control Engine-Exhaust Transients

Descriptive Note:

Journal article

Corporate Author:

AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE

Report Date:

2008-10-01

Pagination or Media Count:

11.0

Abstract:

A series of 22 primary reaction-control-system engine attitude-control firings were observed from the Maui Space Surveillance Site during the space shuttle STS-115 mission. The firings occurred during a pass over Maui on 19 September 2006 during which the orbiter was in sunlight and the observatory was in darkness. The observed attitude maneuvers maintained the orbiter in an orientation in which its long axis was aligned with the line of sight from the observatory. This ensured that the thrust vectors of all the observed engine firings were perpendicular to the line of sight, providing an optimal side-on observation of the exhaust. The firings ranged between 80 and 320 ms in duration and involved 2 or 3 engines for pitch, roll and yaw adjustments. A 0.328 deg field-of-view acquisition scope of the 3.6 m telescope of the Advanced Electro-Optical System provided unfiltered imagery in the near-ultraviolet visible spectral region. The most interesting white-light features were transients, one observed at engine start up and two at shutdown. The analysis of the transient speeds reveals that the startup transient consists of either unburned propellant droplets or higher-pressure gas evaporated from droplets and that the shutdown transients are attributable to a slightly staggered release of unburned oxidizer and fuel, respectively. The first oxidizer shutdown transient is the brightest feature, for which an intensity evolution analysis is conducted. The analysis of the ground-based data is fully consistent with spectral features attributable to primary reaction-control-system engine transients observed in previous measurements from the space shuttle bay using an imager spectrograph.

Subject Categories:

  • Astronautics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE