Delta Star satellite atop the booster at the launchpad at Cape Canaveral Air Force Station. (SDIO)

Delta Star: an SDIO Space Experiment

Frederick Simmons and Peter Bythrow

The Delta 183 program was proposed in 1988 by the Strategic Defense Initiative Organization (SDIO), originally as a joint effort between the United States and the Soviet Union involving the Russian Mir space station. When the Soviets decided not to participate, SDIO proceeded unilaterally to conduct the mission without direct involvement of Mir.

The primary motivation for the experiment was to engage the U.S.S.R. in joint activities to allay their concerns about the threat posed by the SDIO missile-defense activities being pursued at the time. A secondary objective was to demonstrate that space experiments could be conceived and executed rapidly and cost-effectively. Indeed, from its conception to launch, the Delta 183 program cost approximately $200 million and took just 14 months, three spent waiting for access to the launch facility.

With the withdrawal of the Soviets, an alternative set of experiments was selected. Those space experiments were remarkably successful. Notable accomplishments of the program included several "firsts": for example, the first closed-loop tracking of a foreign launch vehicle from a platform in space and the first observations from space of booster rocket contrails viewed in negative contrast against a warmer Earth below. The most significant accomplishment, however, was the collection of multispectral data from observations of launches of U.S. and Soviet space launch vehicles.

Launch of Delta 183 from Cape Canaveral March 24, 1989. (U.S. Air Force)

The Delta 183 Program

When President Ronald Reagan introduced the Strategic Defense Initiative (SDI) in 1983, he offered the Soviet Union the opportunity to participate in the development of a ballistic missile defense system for the mutual benefit of the two nations. The Soviet Union and the United States had already cooperated in a joint space operation in the 1970s, culminating in the hookup of a Soyuz and an Apollo spacecraft in July 1975. The onboard greetings of the two crews and some of their activities were televised to viewers on Earth. At the time of President Reagan's offer, relations between the United States and the Soviet Union were somewhat strained, and the Soviets declined.

The Delta 183 program in 1989 was to be another collaborative effort between the U.S.S.R. and the United States, this time space experiments involving Mir. Specifically, an unmanned spacecraft would be deployed and maneuvered into the vicinity of Mir. An American astronaut and a Soviet cosmonaut aboard Mir would engage in extravehicular experiments using National Aeronautics and Space Administration (NASA) space-maneuvering backpacks to inspect the spacecraft, examine material samples, and perform other tasks. Unfortunately, before negotiations were completed, a premature report of the discussions appeared in The Washington Post, and the Soviet Union withdrew.

Proceeding without Soviet participation, SDIO planned the reconfigured program. Johns Hopkins University Applied Physics Laboratory (APL) assembled the sensors, and designed and operated the ground station. The Aerospace Corporation played a key role in planning several of the experiments and analyzing the resultant data.

Configuration of the Delta 183 spacecraft and payload.

Delta Star

The program's name, Delta 183, was derived from the designation of the launch vehicle; the spacecraft itself was called Delta Star. It consisted of two sections: the McDonnell Douglas orbital operations control assembly mated to the sensor module. The instruments were boresighted together parallel to the axis of the module; pointing was provided by the spacecraft's attitude-control system. The sensor ensemble included

• an infrared imager, operating much like a video camera in any of three spectral bands in the short- to mid-wave region
• a long-wave infrared imager adapted from the guidance and control section of a Maverick missile
• an ensemble of three imagers and four photometers, which produced imagery and intensity data in several visible and ultraviolet bands
• an ultraviolet-intensified CCD (charge- coupled device) video camera
• a laser detection and ranging device

Delta Star was launched on March 24, 1989, into a circular orbit of 48-degree inclination and about 360-kilometer altitude. This orbit provided for a repeating ground trace every five revolutions to pass near Cape Canaveral, Florida, and other ground sites to facilitate the observations of "targets of opportunity" and other experiments. The satellite was deactivated the following December 27.

The Experiments

Aerospace was responsible for planning several specific experiments, performing most remote observations with the infrared sensors, and analyzing the resultant data, in particular those from the observations of space launch vehicles as targets of opportunity. Several organizations carried out other experiments, including one concerned with space materials carried aboard the sensor module.

Design features of the Delta Star spacecraft. The sensors, housed in seven panels, were boresighted together and pointed collectively by the attitude-control system.

Multispectral Data of Vehicle Launches

As one of the program's more significant accomplishments, Delta Star observed the launches of a Delta space vehicle out of Cape Canaveral and four Mir resupply vehicles out of the Tyuratam cosmodrome near the Aral Sea.

False color display of a spatially resolved upper-stage plume observed in the ultraviolet spectrum, one of the unique products of the program.

Of themselves, sightings of launches are hardly noteworthy; the satellites of the Defense Support Program have routinely reported such events for more than 30 years. (See Crosslink, Summer 2000.) The Delta Star observations, however, were unique in that the sensors provided multispectral data, ranging from the vacuum ultraviolet to the long-wave infrared. Aerospace analyzed the infrared data that were generated by these experiments, which were prompted by a need to evaluate the reliability of theoretical models for rocket exhaust plumes emission.

The long-wave infrared sensor, a modified Maverick seeker, produced a signal that, coupled to the Delta Star attitude control system, provided closed-loop tracking of a launch vehicle, the first time this had been done from a platform in space. In another interesting event that occurred when a cloud deck obscured the launch site, the ignition was observed by the multiple scattering of visible light through the clouds, whereas the infrared sensors sighted the vehicle only after cloud break.

Booster Contrails

The long-wave infrared imager observed not only the intense plumes from the burning rockets, but also their contrails. In those first such observations from space, the imager recorded the contrails in negative contrast against a warmer Earth below. On the other hand, the shortwave and visible imagers recorded those sunlit trails in positive contrast. Analysis of those persistent trails was also done at Aerospace.

Long-wave infrared observation of a Delta launch from Cape Canaveral shortly after the tracker broke lock. The bright plume is seen at the lower right. The contrail of condensed water vapor and alumina particles appears dark, as do the clouds, against the warmer Earth below, which appears brighter. In a visible-wavelength image, the sunlit clouds would, of course, appear brighter relative to Earth.

Clouds from Vented Liquid Propellants

Aerospace planned and directed a series of experiments involving the launches of rockets out of the NASA Wallops Island facility in Virginia, precisely timed to the arrival of the Delta Star satellite. The Black Brant rockets carried payloads consisting of canisters of liquid propellants, which were released at high altitudes in the fields of view of the sensors aboard Delta Star. The objective was to observe the flash evaporation of the liquids in the near-vacuum environment and to characterize the resulting expanding cloud of frozen particles embedded in the more rapidly expanding vapor, thus to assess the validity of an Aerospace model describing those processes.

Model for a liquid propellant vented into the upper atmosphere. The liquid undergoes a flash evaporation and partial freezing. The solid particles are embedded in a more rapidly expanding cloud of the remaining vapor, which interacts with atomic oxygen to produce chemiluminescent emission. The smaller particle cloud scatters sunlight, preferentially in the forward direction.

Plan for the Delta Star observations of propellants vented into the upper atmosphere. In addition, the releases were observed by the two satellites in high orbits, by instrumented aircraft, and by an astronomical observatory in Massachusetts.

Launch of a Black Brant from Wallops Island, Virginia, for a rendezvous with Delta Star. (Photo courtesy of NASA)

Such clouds, produced by the release of liquid propellants into the upper atmosphere, could interfere with the tracking of vehicles by infrared sensors incorporated into space-based defense systems. Four such experiments were carried out. One booster failed to fly a nominal trajectory, but three launches performed as planned, and the clouds appeared on schedule in the Delta Star fields of view. Unfortunately, just prior to the sequence of the launches, the Delta Star satellite was struck with the flux from an extraordinarily intense solar flare that ruined the sensitivity of the shortwave infrared imager.

Remote observations of one of the propellant releases from a Black Brant rocket launched from Wallops Island. The sensors were located in geostationary orbits above the Atlantic and Pacific Oceans. The symbols denote the positions in satellite coordinates; the numbers are the times in seconds, Greenwich Mean Time.

Nevertheless, the cloud was observed by the ultraviolet sensors aboard Delta Star, by infrared sensors aboard two widely separated satellites in geosynchronous orbits, by the Lincoln Laboratory Firepond telescope facility on Millstone Hill in Westford, Massachusetts, and by airborne sensors dispatched for that purpose, in operations all coordinated by Aerospace. Thus, a valuable collection of data was obtained, despite the degradation of the infrared sensor aboard Delta Star. In particular, the infrared spectra collected by a spectrometer aboard the Air Force Research Laboratory's aircraft elucidated the chemical reactions between the propellant vapor and the upper atmosphere. The infrared intensities reported by the satellites in high orbits provided the means for assessing the scattering of sunlight by condensed particles in the cloud.

Resident Space Objects

The modeling of satellites and other objects deployed in space—resident space objects (RSO)—in support of systems for space-based space surveillance has been an important area of research at Aerospace. The Delta 183 program provided a good opportunity to collect relevant data from a space platform as opposed to the usual studies conducted at ground observatories such as AMOS, the Air Force Research Laboratory atop Mt. Haleakala on Maui, Hawaii. The data from Delta Star could monitor RSOs at much closer range and with more appropriate viewing aspects, providing data directly relevant to the development of a space-based space surveillance system. Delta Star proved valuable for analytical comparisons with a theoretical model developed at Aerospace.

Data from a resident space object viewed by the Delta Star long-wave infrared sensor as opposed to the Aerospace model. The self-emission depends on the size, configuration, and surface properties of the space object as well as the viewing aspect. The self-emission varies between the side- and end-viewing aspects approximately with the sine of the angle. Specular reflections of sunlight vary mostly with the orientation of the solar panels.

Infrared Backgrounds

The character of the infrared backgrounds against which targets must be observed in Earth-viewing defense systems is another subject of continuing interest (see Crosslink, Winter 2000–2001). Delta Star collected data in a spectral bandpass considered as a candidate for a space-based surveillance system, several years prior to a Ballistic Missile Defense Organization (BMDO) space experiment dedicated to that sole purpose (MSTI-3). Aerospace analyzed a number of scenes with various clouds, terrain, and solar illumination to determine statistical properties used in sensor design. The Delta Star data analysis was especially useful in developing the analytical tools Aerospace later applied to the more complete MSTI-3 data.

Shortwave infrared image of a typical background scene viewed by Delta Star analyzed for the statistical properties of the radiance patterns.

Background observations that proved very useful in another way were those collected in overpasses when the shortwave infrared sensor stared at specific points on the ground while the line of sight varied from horizon to horizon. Those collections were used to assess theoretical models for the variation of the cloud-free line of sight for various cloud patterns. Aerospace analysis interpreted the signal variations in terms of the probabilities of cloud-free lines of sight as a function of the incident angle for comparison with theoretical models.

Power spectral densities are seen to be directional, as might be expected for a scene with a striated cloud pattern. Power spectral density is a statistical property derived from analysis of the radiance variations in the background. The wave number is related to the frequencies of the fluctuations as the radiance structure is scanned in the two directions, arbitrarily designated horizontal and vertical.

Atmospheric Properties in Dispersing Laser Light

In an Aerospace experiment, Delta Star was illuminated by a laser beam directed by a telescope located at the U.S. Air Force Malabar facility at Cape Canaveral. The purpose of the experiment was to study the value of ground-based lasers for absolute intensity calibrations of infrared sensors in orbit. (McDonnell Douglas conducted a similar experiment, the Laser Illumination Detection System, to assess the vulnerability of space-based optical systems to interference from low-power ground-based lasers.) The Aerospace experiment involved the response of the long-wave infrared imager to illumination by a carbon-dioxide laser during an overpass in which the path from the ground to space varied by a large factor. This experiment yielded significant information on the properties of the atmosphere in dispersing laser light.

Image of a ground-based laser recorded by the long-wave infrared sensor aboard Delta Star. The grid denotes the pixels created by the scanning of the linear detector array; the third dimension denotes intensities. Without atmospheric dispersion, only a few pixels near the central peak would respond because of the blur of the sensor.

Conclusion

The Delta 183 program was notably successful, especially considering the constraints in time and budget. Certainly, in hindsight, some things might have been done differently. In particular, state-of-the-art sensors specifically designed for their purposes and other better equipment (especially the onboard data recorder) would have made the program much more productive at only a moderate incremental cost in time and money. Nevertheless, the experiments were singularly fruitful, especially for providing unique multispectral data on space launch vehicles viewed from space. The experiments also yielded valuable data about closed-loop tracking of such launch vehicles, booster contrails, characteristics of frozen particles in a liquid-propellant-induced cloud, RSOs, infrared backgrounds, and properties of the atmosphere in dispersing laser light.

Repeating orbit of Delta Star. The curved line represents the ground trace of every fifth orbit.

The United States and Russia have cooperated in a number of space ventures since the U.S.S.R. declined President Reagan's offer of joint work on a ballistic missile defense in 1983. After the dissolution of the Soviet Union in the early 1990s, the activities of the Mir space station assumed a more international character. Specifically, the United States assisted in the attachment of additional modules to the 1989 configuration. In all, NASA made nine shuttle flights to Mir, installing U.S. experiments and transporting astronauts for extended stays as "guest" residents. Mir reentered Earth's atmosphere March 23, 2001, more than 10 years beyond its intended five-year mission. The two countries continue to work together on the International Space Station. Another less publicized effort, the Russian American Observation Satellites (RAMOS) experiment, a program sponsored by BMDO, is currently in design review.

Acknowledgments

The successes of Delta Star were made possible by the dedicated efforts of many individuals in a number of organizations. SDIO planned and implemented Delta 183, which was conceived and initiated by SDIO director Lt. Gen. James Abrahamson and managed by Col. Michael Rendine and Michael Griffin. William Frederick chaired the Delta Star Science Working Group, which planned the experiments. Foremost among the several contractors that contributed to the program was McDonnell Douglas, which designed and built the launch vehicle and spacecraft and managed the flight operations. Peter Bythrow, Robert Gold, and Thomas Coughlin of APL coordinated the efforts of a number of contractors to supply instrumentation; integrated the sensors in the spacecraft; conducted experiments; and managed the ground site at APL for the retrieval, processing, and dissemination of the data from all experiments.

Aerospace personnel played major roles in planning several experiments and analyzing data. Frederick Simmons, a member of the Delta Star Science Working Group, guided Aerospace activities and oversaw analyses of launch observations. Thomas Hayhurst was instrumental in planning and executing the fuel release experiments, Richard Dickinson and David Glackin analyzed background collections, Bernard Klem planned and analyzed the RSO observations, and Frank Vernon and Henry Montes conducted the laser illumination experiments.

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