The remote manipulator deploying SPAS from the shuttle bay. The orbiter then moved away from SPAS for the sequence of burns of the orbital engines. The sensors were boresighted together and pointed by the SPAS attitude-control system.

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Two Space Experiments

Aerospace played major roles in a number of space experiments conducted by the Ballistic Missile Defense Organization. Two notable experiments were the Midcourse Space Experiment (MSX), a free-flying satellite launched in 1996, and the Infrared Background Signature Survey (IBSS), flown as a NASA shuttle mission in 1991. The results of these experiments are particularly relevant to current U.S. initiatives directed toward development and deployment of missile defense systems.

Midcourse Space Experiment

MSX experiments collected and analyzed target and background phenomenology data to address the sensor requirements for defense against ballistic missiles in the midcourse phase of flight. The Spatial Infrared Imaging Telescope (SPIRIT) III, the primary sensor aboard the satellite, consisted of a cryogenic radiometer and spectrometer operating in the middle- and long-wavelength regions of the infrared spectrum (MWIR and LWIR). SPIRIT III, built by Utah State University, is the most sensitive such instrument ever deployed in space. The spacecraft also carried the ultraviolet/visible imaging and spectrographic imaging (UVISI) sensor system, a space-based visible surveillance camera, an onboard signal and data processor, and a suite of instruments to monitor contamination on and around the spacecraft. Cryogen for the infrared sensor lasted about nine months; however, the visible and ultraviolet sensors, not requiring such cooling, continue to function today, supporting space-based space surveillance experiments. The MSX program achieved all objectives.

The MSX satellite, built by Johns Hopkins University Applied Physics Laboratory, was launched from Vandenberg Air Force Base April 24, 1996, aboard a Delta II launch vehicle into a sun-synchronous orbit at 900-kilometer altitude and 99.16-degree inclination. The satellite is 5.2 meters in length and 2400 kilograms in mass.

Critical functions of a midcourse surveillance sensor are the detection, acquisition, tracking, and discrimination of offensive midcourse objects. A surveillance system design must be based on a full understanding of the behavior and resulting hard-body signatures (response of an infrared sensor when observing the targets) of expected targets and the effects of backgrounds against which these targets must be observed. Detailed characterization and careful modeling of the signatures of potential targets and high-fidelity models of terrestrial, Earth limb, and celestial backgrounds are essential. These data and models are required across the optical spectrum, over the entire globe, and for an extended time to account for seasonal and geographic variations.

A visible plume from the orbiter engine viewed by the TV camera aboard SPAS during a burn observed from a range of about one kilometer; the thrust vector was oriented about 90 degrees from the direction of orbital motion. In simultaneous infrared observations, the plume appeared much brighter relative to the sunlit orbiter.

A southern aurora viewed from the shuttle.

Aerospace was responsible for the key target experiments team, which accomplished the planning and data analyses of the highest-priority experiment in the MSX program, the MSX Dedicated Target (MDT)-II. Aerospace also contributed significantly in the areas of LWIR-infrared sensor calibration and spacecraft contamination. Glenn Light coordinated activities in the MSX experiments, which have supplied an unprecedented wealth of MWIR and LWIR data on target, background, and plume signatures. These data provided the basis for functional demonstrations of detection, tracking, and discrimination of midcourse objects.

Infrared Background Signature Survey

The IBSS experiments were carried out on shuttle flight STS-39, launched April 28, 1991, from Cape Canaveral into a circular orbit, 260-kilometer altitude and 57-degree inclination. Infrared, visible, and ultraviolet sensors were mounted on SPAS, the shuttle pallet spacecraft, deployed from the shuttle orbiter to maneuver in its vicinity. The IBSS Science Working Group, staffed in part by Aerospace, recommended two principal missions. In the first experiment, SPAS observed plumes of the orbiter's maneuvering engines as surrogates for the thrusters of postboost vehicles in their interaction with the tenuous atmosphere of near space.

The orbital thrusters were operated in a sequence of burns to simulate those of a typical postboost vehicle in its maneuvers during the deployment of reentry vehicles and other elements of the payload. The observations provided a much-improved basis for estimating the infrared emission from postboost vehicles observable to space-based sensors.

The second mission recorded infrared properties of liquid rocket fuels released from canisters deployed from the orbiter. The experiments characterized the resultant clouds of vapor and frozen particles, which simulated the consequences of propellant tank ruptures in space. The particles scatter sunlight and earthshine, and the fuel vapor reacting with oxygen in its atomic form produces chemiluminescence at infrared wavelengths. The findings of the experiments contributed immensely to the knowledge of such phenomena and their impact on missile surveillance. In other experiments, the mission yielded valuable data on Earth-cloud backgrounds and limb radiances and some of the most spectacular images of auroras ever viewed from space.

Aerospace provided technical advisors to the Commander of the Air Force Space and Missile Systems Center, who was mission director for this flight. The complex operations for the mission were planned and designed at Aerospace. Among others, Thomas Hayhurst, Lindsay Tilney, and Frederick Simmons played key roles in the program. During the flight, Aerospace provided on-orbit support at the NASA Flight Control Center in Houston, including real-time mission timeline changes, problem workarounds, and operations reconfiguring.

A single scan of data from the MSX SPIRIT III in the LWIR band from 6.8 to 10.8 microns observing the target suite in the MDT-II experiment. The targets were launched on a ballistic trajectory by a STARS II missile from the Kauai Test Facility, with ocean impact north of the Kwajalein Atoll. The postboost vehicle, in the upper left corner, successfully deployed 24 objects in space, all apparent in the figure. Object 17 remained on the postboost vehicle. At the time of this scan, all objects were in darkness and observed in self-emission. Additional deployment debris, not apparent in this image, is apparent in the original data.

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