Delta 181 Thrusted Vector Mission

The second DELTA/SDI mission from the Cape was the DELTA 181 Thrusted Vector Mission (Thrusted Vector Experiment). Like the DELTA 180 mission, DELTA 181 involved the placement of a DELTA second stage in low-Earth orbit, but it included the deployment of two payloads as the object of a series of experiments in orbit. One of the payloads was a plume generator package, and the other was a science package containing eight test objects and four reference objects.

An APL-designed sensor module was launched into orbit and performed a number of significant SDI Delta 181 program experiments. Sensor module on-orbit command and control operations involved a network of worldwide facilities called the control complex. A major component was the sensor module command center, which was designed, installed, and operated by APL. The sensor module, consisting of a command and data handling system and seven scientific experiments, remained with the DELTA's second stage to scan elements of both packages once they were deployed.

The sensor module was equipped with ultraviolet, infrared, radar and laser sensors to gather a tremendous amount of data on the "signatures" generated by the deployed payloads. That data was transmitted via two wideband telemetry downlinks to stations on the ground. Data from approximately 100 ground-based sources funneled into the Cape via communications satellites. The mission required more than 200 radar tracking maneuvers over a period of two days, and recorded data continued to come in for about ten days after the experimental portion of the mission was completed. Put simply, DELTA 181 presented the Eastern Range with one of the most complex support missions in history.

In the late fall of 1985, a conceptual design for a follow-on mission to Delta 180 was developed and briefed to Director, SDIO. This design, with minor re-work to remove some ABM Treaty nonconformities, became the Thrusted Vector Mission. More widely known as Delta 181, the mission was given a "go-ahead" in January 1986 and funded immediately. Aside from some evolutionary changes. Delta 181 was flown as designed 25 months later in February 1988.

The Delta 181 mission objectives centered around the gathering of phenomenology data in support of the SDI midcourse engagement. This included characterization of a variety of test objects (TO'S) against various backgrounds, characterization of the background itself. and maneuvering, pointing, and tracking to acquire and view TO'S. In support of boost and post-boost engagement, plume and background data were to be gathered. Secondary objectives included demonstration of effective management and coordination of large inter-service goverment industry joint projects. The secondary objectives, which were satisfied as demonstrated by the successful development and execution of the mission.

The Delta 181 mission objectives centered around the gathering of SDI phenomenology data including characterization of a variety of test objects and plumes against various backgrounds, characterization of the background itself, and maneuvering, pointing, and tracking to acquire and view targets. The pointing was accomplished by interfacing three of the sensors to the existing Delta attitude control system, via an onboard multisensor/multiobject navigation filter. The tracking sensors were a pulsed ladar, a Ku band Doppler radar, and an IR imager.

The Precision Automated Tracking System (PATS) is a van mounted laser tracking system capable of 3-dimensional position locating of augmented targets such as missiles, aircraft and mortar shells. A compact version of PATS, adapted for a spaceborne tracking experiment, was designed and manufactured by GTE/EOO on a 9 month QRC project for SDIO's Delta 181 mission in 1988. This 200 pound space qualified system successfully tracked multiple targets and provided terminal guidance commands to the host spacecraft. During the Delta 181 mission the FASTBALL system provided the following basic data for each of several cooperative test objects in real time: range, angles (azimuth and elevation), received power, test object identification, and system health and status. This data was provided both to the Delta 181 onboard navigation system for use in real-time attitude control of the spacecraft and via telemetry to mission ground control.

The design was aggressive and intricate requiring nearly continuous maneuvering to obtain observations under various conditions of lighting, background, range, and aspect angle. Accelerating objects, including a ground-launched rocket, were to be tracked and observed to acquire the plume data. The mission scenario, referred to as the Timeline, was iterated nearly continuously in response to engineering realities, evolutionary changes in the mission details, and performance expectations of the vehicle, the satellite, and the test objects. The payload consisted of the Delta second stage, the sensor module. - a satellitete which remained attached to the second stace - test obiects, a plume generator. and the canister cluster which housed and dispensed the test objects.

The flight operations planning and execution were as intricate and challenging as any aspect of the mission. They involved coordination between and cooperation of most of the US's major test range organisations. The fiscal and technical mnnasement of this program also presented some challenges: eighteen different organizations had major roles in the mission.

The mission was launched at 2207 hours UT, 08 February 1988. The countdown marked the second launch attempt for the DELTA 181 mission. The first launch attempt was scrubbed at 2219Z on 4 February 1988 due to a second stage fuel tank valve malfunction. Concerning the launch itself, the countdown for the DELTA 181 mission was picked up at 1557Z on 8 February 1988. It proceeded smoothly to lift-off at 2207:00Z. As the DELTA Model 3910 booster climbed away from Pad 17B, the launch vehicle rolled out of its 115-degree launch azimuth into a flight azimuth of 94 degrees. The DELTA's second stage was injected into a 90 x 120-nautical-mile orbit inclined 28.7 degrees to the equator.

During the 12-hour, $250 million test, Delta 181 ejected 14 objects representing Soviet warheads and decoys and four small, solid-fuel rockets. Data was collected during the first seven orbits, then the second stage boosted itself into a 171-nautical-mile circular orbit during its eighth revolution. During the ninth and tenth orbits, the sensor module's telemetry and tape recorder systems were verified. Over the next ten days, the sensor module transmitted its recorded data to designated ground stations in the DELTA 181 support network.

Data collecticn was accomplished over 12 hours and retrieved from the onboard recorders during the following 10 days. At the conclusion of the planned mission, owing to available power, two additional tasks were undertaken. First, the recorders were played backtwice more in an effort to assure maximum data recovery. Second, the U2 and R experiments were turned on, their data recorded and then played back. Many parts of the mission were executed nominally.

The mission was highly successful. There were, however, anomalies. About 100 different acquisition and track sequences were attempted, and possibly as many as half achieved less than solid track. The mission required nearly continuous maneuvering to view multiple test objects under various conditions of lighting, background, range, and aspect angle. Although tracking exceeded mission data gathering requirements, there were some problems that adversely affected the tracking.

Although the mission timeline was very detailed, the mission events fall into three general categories: test object deployment and observations; plume observations; and background science, and calibration observations. The seven primary instruments were fixed relative to the vehicle centerline and had fields of view the order of 5 degrees; some were gimbaled giving them somewhat larger fields of regard. Six of the instruments had measurement times the order of a second (.2 sec-3 sec); the seventh (13) required 30+ seconds to cycle through its various filters. Since scan times were the order of 35 seconds, there was at least ten fald redundancy in most observations.

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