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U.S. Moves to Upgrade Missile Warning
 


Air Force, industry to focus on vulnerability of current satellite system improvements,
tracking quality and hardware design

By Barry Miller
Aviation Week & Space Technology - December 2, 1974

Los Angeles-U. S. is taking steps to reduce the vulnerability of its satellite based ballistic
missile early warning system to hostile action and to improve the quality of tracking data it
now gathers on foreign ballistic missile launches.

    The satellite warning system, or Defense Support Program (DSP) (AW&ST July 15,
 p.45), is an indispensable part of the early warning network that alerts North American
Aerospace Defense Command, Strategic Air Command and the National Military
Command System to enemy Intercontinental or Submarine- Launched ballistic missile
attack against the U.S.. (AW&ST May 14, 1973, p. 17; Sept. 20, 1971, p. l8).
    Air Force efforts to strengthen the system are essentially twofold:
    Improve the existing system and reduce its vulnerability to counteraction.
    Explore future satellite missile warning system design.
    To insure viability of the satellite warning system in the future, USAF's Space and
Missile Systems Organization (SAMSO) is expected to kick off a series of. parallel
industry studies shortly after the first of the year. These studies will investigate whether a
new satellite design is necessary or whether the existing design-which incorporates at
least decade-old technology-can be adapted to satisfy future needs. The studies also
are likely to explore the possibility of adding more missions, such as tracking objects in
space, to the system's basic mission of detecting and providing initial tracking information
on ballistic missile launches. Competitors for these studies are likely to include TRW
Systems, Lockheed Missiles & Space, Rockwell International, Hughes Aircraft and
Grumman Aerospace.
    SAMSO will soon initiate an effort in "proliferated ground stations" for the early
warning satellite system with selection of a contractor to develop a simplified processing
station (AW&.ST July 22, p. 17) over the next two years. The simplified processing
station will be a special-purpose transportable data readout center intended to enhance
satellite sys- tem survivability by reducing dependence on the system's two existing fixed-
site data receiving and processing centers. Small simplified processing station centers
could be deployed in airborne command display launch warning data transmitted directly
over two data links from the synchronously orbiting warning satellites. The data are
derived from the satellites' infrared, charged-particle and radiation sensors that detect
missile firings shortly after liftoff. At present, the information is data linked in real time
from the satellites to either of two similar ground facilities, one operated by SAMSO's
Detachment 2 near Woomera, Australia, and the other at SAMSO's Aerospace Data
Facility, Buckley Air\field (Air National Guard), CO., where data are processed and
correlated with other intelligence information by dual IBM 360-75J computer
processors.
    The small processing station will be comprised of two units--a satellite communications
module and a data
processing equipment unit. The communications module will receive data from the
satellites, route them to the processing unit before transmission in near real time to
dedicated users. Competitors for the development are two teams incorporating the four
existing early warning satellite associate contractors, TRW Systems, IBM Corp., Aerojet
Electrosystems and Philco-Ford. IBM is lead company in a team including TRW Systems
and Radiation, Inc. Aerojet heads a second team that includes Philco-Ford and Control
Data Corp.
    USAF's intent with a multiplicity of transportable centers is to make the critical ground
centers less vulnerable by having more of them and making them more elusive targets.
The centers would provide an airborne alternative in the event one of the ground  were
lost and could give USAF airborne command posts a capability roughly equivalent to
what is now at Buckley without having to operate through Norad. The proliferated sites
would enable the Navy to use data the Defense Support Program can give it to help
speed response to surface-to-surface missile threats. The transportable centers could
relieve dependence of command authorities on one or both of the existing ground
stations, particularly the politically controversial site in Australia (AW&ST Apr. 30,1973,
p. 67).
   
The satellites, which are identified as code 647, are highly vulnerable to attack, lacking
even the simple self-protective measures of decoy dispensing and orbital change that
SAMSO is in the early stages of investigating for future satellites. USAF does plan to
protect the 647 satellite's sensitive optics from probing laser beams that an enemy could
direct at them. Martin Marietta is developing for USAF a passive warning device,
probably a silicon detector located within the satellites' giant Schmitt telescope. The
warning detector either could alert USAF or trigger a protective shutter when laser
energy penetrates into the 3-ft.-dia. telescope. Unprotected Unprotected optical
mechanisms are especially sensitive to detection, identification and even damage when
illuminated by optical energy in the technique known as retro-reflection.
   The Air Force also will flight test a simple impact alerting device, built by Westinghouse for the 647 satellites, which gives USAF an independent alarm when the satellite is struck by foreign bodies.
   USAF is pleased with the performance and capability of its 647 satellites, despite nagging software problems that have swelled program costs. Commenting on the program, Air Force Secretary John L. McLucas observed: "We have developed satellites which can detect and track intercontinental ballistic missiles and submarine-launched ballistic missiles, almost from the moment they are fired. In addition these warning satellites have the capability to detect nuclear explosions above the ground and ultimately will replace current satellites [Vela satellites] which monitor the atmospheric nuclear  testban  treaty" (AW&ST Feb.18,p.. 9).
   More than 1,000 ballistic missile launches by the Soviet Union, China, France and the U.S. have been observed by 647 satellites since the first one was orbited in 1971. These include firings of the Sovet SSX-18 and SSX-19 ballistic missile, and the submarine-launched SS-N-8 missile. The satellites' launch observation have corrected mistaken intelligence estimates of the performance of ceruin Soviet weapon systems.
   Tle ability of the satellites to provide even coarse tracking information and to predict the missile's impact area was a surprise fallout from the program, since the spacecraft were designed and optimized for detection, not tracking. The satellite's infrared sensor detects energy emited by a missile's booster during the early powered stages of flight, typically spotting a Soviet missile launch within 90 seconds liftoff. USAF has taken two steps to avoid the relatively high probability of false alarms created by the sensor erro neously identifyng forest fires, blast furnaces or natural phenomena as missile launches. It can command the threshold levels of each of the hundreds of infrared detectors in the satellite sensor to be triggered above minimum levels and has configured logic in an onboard processor to respect as spurious events phenomena of low interest. In addition, the sensor must make a series of "detections" on successive scans to confirm a missile launch, the only discriminating a genuine missile trajectory from a comparatively static hot spot like the large California brush fire a 647 satellite observed in the summer of 1974, or a spurious phenomenon like reflections of solar energy off cloud edges. The multiple hits effectively define a velocity vector that supplies an immediate indication of the corridor through which the missile will travel and forecasts the target area.
   As the missile speeds toward its target after burnout, the intensity of the .infrared energy emitted in the short wavelengths monitored by the satellite declines sharply, causing the satellite to lose missile track in midcourse, but be- fore any decoys are dispensed. The Air Force is relying on other tracking sensors, such as airborne and ground tracking radars, like its three BMEWS sites and eight sea-launched missile detection sites, to pick up missile targets after handoff from track data supplied by the 647 .
  Studies were conducted by TRW Systems and Philco-Ford several years ago on a low earth orbit midcourse satellite surveillance system using long wavelength infrared detectors, like mercury cadmium telluride, to track missiles after burnout for high confidence trajectory information to be fed into ballistic missile defenses. Long wavelength infrared detectors can detect relatively cold bodies, such as a burned out booster or reentry vehicles, against cold sky back-grounds at long ranges because of the relatively high intensity of energy emitted over the 8 to 14 micron band. But these efforts have been stalled because long wavelength detectors require cryogenic cooling at low temperatures (77K) and complicated plumbing that lacks sufficient assurance of long-term, trouble- free operation demanded by reliable military satellite operations.
   Now USAF is going to take another look at midcourse surveillance in its space track augmentation activity to determine whether it can more effectively hand off 647 information. A USAF West Coast study group has recommended new efforts in this direction. Visible light sensors may prove to be one of the more attractive alternatives for midcourse tracking, but they are cloud limited.



  Observers attribute successful 647 operation in large measure to the choice in such a complex system design of simple, proved technology wherever possible. For infrared detectors, for example, Aerojet Electrosystems resorted to lead sulfide cells.. one of the oldest and better known infrared detector materials. These detectors provide good sensitivity at comparatively elevated temperature of 193K, which permitted Aerojet, designer of the satellite's optical telescope, to rely on passive, space radioactive cooling. This avoided the expense and mechanical pit- falls of active cooling. Aerojet has earned substantial incentive fees from the Air Force over a three-year period for the performance of the infrared telescope in orbit. Similarly, TRW Systems, the spacecraft designer and fabricator, also has received incentive awards for its performance.
   The 647 satellite consists of a 10-ft-long, 9-ft-dia. cylinder section supporting an infrared telescope. Weight of the satellite, which is orbited by a Titan 3C booster, is over 2,000 lb. In its equatorial orbit, the spacecraft is oriented so the telescope points toward the earth. The vehicle spins about its cylindrical axis at a rate of about 5-7 rpm. The telescope line of sight is offset from the satellite's spin axis so that the telescope field of view turnabout the satellite spin axis, generating a constant conical scanning of the infrared detector array and effectively enlarge the telescope field of view. A 400-ft.-lb Sperry Flight Systems momentum wheel. About 24 inches in dia., housed in the supporting cylindrical section, spins at a constant speed counter to the spin direction of the satellite to remove any momentum accumulated during the satellite spin A pair of visual star sensors helps maintain proper satellite orientation.


  The satellite's Schmidt telescope combines the simplicity, ease of alignment and mounting of a spherical reflector with diffraction limited performance and good image quality of a parabolic reflector. Energy is collected through an a spherical corrector lens located at the center of curvature of a spherical mirror, or reflector at the base of the telescope.
  Infared energy is reflected from the mirror into a spherically shaped detector array at the focal surface of the assembly, midway between the reflector and the correct optics. Each of the many lead sulfide detector cells, covered by a narrow-band spectral filter that peaks response at 2.7 microns, subtends an angle corresponding to an area on earth from this altitude of less than 2 naut. mi. square. The two-dimensional detector array is supplied by Electronics Corp. of America, Cambridge, Mass. Santa Barbara Research Center is the second source.
   Electrical outputs from each cell are signal ~(Jnditioned, amplified and digitized {:! transmission over data link to ground terminals. The spacecraft's electroni::!. IfJcated behind the reflector. compress  supplied by the infrared detector c:.l:lnels and several hundred chaJJ.rf::;s of data from other spacecraft SVSteI;li and sensors to mote eifectivelv

use available communications band- width. The infrared sensor data transmitted to earth include identification of the individual detector, and a digital volt- age corresponding to infrared intensity and time/frame number. The airborne processor is supplied by Radiation, Inc., Melbourne, Fla.
   The satellite's nuclear radiation detectors include proton counters and X-ray gauges mounted on two of the four solar cell pedals that generate additional power to supplement that of body-mounted solar cells on the main cylinder section. Several radiation detectors view the earth from locations next to the infrared telescope and parallel to the spin axis.
  A complete operational 647 satellite system is comprised of three satellites. One would be situated, as it now is, over the Indian Ocean area from which it can monitor Soviet and Chinese launch activity .Two are stationed over the Western Hemisphere to warn of submarine- launched ballistic missiles fired against the continental U. S. Two are necessary in the event one is blinded by solar phenomena. Natural interference with satellite operations is not as debilitating over the Eurasian land mass because U. S. warning capability from that quarter is supplemented by other warning sensors.
  Data from the satellites are processed on earth in near real time, generating warning times measured in minutes. Data also are stored on magnetic tape and subsequently sent to Aerojet in AZusa. Calif., where a vast library of information on missile launch and reentry phenomenology has now accumulated.
  Aerospace Carp., a major participant in the Defense Support Program, indicates it has assisted the Air Force from program inception, contributing to system conceptual design, and performing the general, systems engineering associated with the development, fabrication, installation and operation of the system."
   Besides its infrared payload role, Aero- jet had overall software responsibility for the first center in Australia, with IBM assisting it and supplying the preprocessor for its dual computers. IBM later got main responsibility for writing and implementing software for the second center at Buckley. System Development Corp., Santa Monica, Calif., works directly for USAF with responsibility for software management and consolidation of software documentation.
  Defense Support Program officials have advised the Navy, which is seeking ways of enhancing task force survivability, that the 647 satellites can provide essential warning data on Soviet surface-to-surface missile threats.
  Successful performance of the initial group of 647 satellites appears to be making it difficult for organizations working on the program to sustain their continuing early warning efforts. A backlog of completed satellites, perhaps three or four in number, has been accumulated and will be held in reserve as replenishments for satellites now in orbit for a longer period than had originally been planned because of unexpectedly lengthy mean mission-duration times. USAF has ordered a total of 13 647 satellites. The consequent stretch in launch schedule and diminution in inventory planning is being felt by TRW Systems, Aerojet and other groups on the program.
  USAF has launched a total of four 647 satellites, the first of which failed to achieve the desired orbit. The most recent 647 satellite was orbited on board a Titan 3C booster from the Eastern Test Range last year (AW&ST June 18, 1973, p. 17).
  For the current fiscal year, Air Force had requested $77.1 million for the Defense Support Program. "The major portion of this request, " Lt. Gen. William john Evans, USAF's deputy chief of staff for research and development, told the House Armed Services committee," will be used to procure a DSP the 13th satellite, to provide continued technical support, and to complete the survivability retrofit of three satellites.
  In addition to its concern about improving midcourse tracking of ICBMs, USAF would like to acquire positive mis- sile launch warning information earlier. One way of doing this would be to shorten the present time needed to initially detect a missile launch to well be- low the 90 sec. or less now required. Such a move would impose a heavy burden on system processing and may begin to push against the natural limitations of infrared technology to detect phenomena partially or  wholly obscured by atmospheric moisture.