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Show Aviation Week & Space Technology October 23, 1967 The initial flight of the Boost Glide Re-entry Vehicle (BGRV) developed by McDonnell Douglas Corp. probably will take place this month on board a General Dynamics Atlas F ICBM booster from Vandenberg AFB, Calif. BGRV, formerly known as the Aball or 122M Aeroballistic missile, will be fired into a high ballistic path, then refired downward from a high altitude into the earth's atmosphere. It will make a short ascent, revert to a relatively-flat, decaying aerodynamic glide so that it can skip along to a target. It would be hidden by its low altitude flight path within the ground clutter of the defense radar. Gas jets on BGRV execute roll and steering maneuvers. The flight altitude of BGRV may be so low as to make terrain clearance radar mandatory. The advantage of such a system is that the pre-programed evasive maneuvering of the vehicle might preclude effective calculation of its trajectory by the defense forces. This would make intercept computation more difficult. Susceptibility Because the vehicle glides over greater distances within the earth's atmosphere, it is susceptible to action by defense forces for a relatively-long period. In addition, the longer, more-complicated flight path places greater strains on the vehicle's inertial guidance system, making accuracies comparable to those of conventional nuclear warheads on straight, non-maneuvering ballistic flights more difficult to achieve. This shortcoming might be overcome if any of the terminal ballistic missile guidance schemes now under study materialize. Air Force also is looking at a maneuver-for-accuracy concept which might sidestep the problem. Unlike BGRV, which begins its maneuver long before re-entry, the other maneuvering concepts envision maneuver at the start of re-entry. One of these, the General Electric Maneuvering Ballistic Re-entry Vehicle (MBRV), finally achieved a successful flight this summer after three failures due to power dropout, guidance difficulties and booster failure, in that order. In the MBRV concept, the vehicle might traverse a shorter-range ballistic trajectory, deceiving the enemy into anticipating assault at a given target. At a pre-determined altitude above the false target area, MBRV would go through a pre-programed pull-up, followed by another ballistic descent on a Athena rocket can boost a 400-lb. pay-load into a simulated ICBM trajectory. Over 80 have been fired from Green River. more-distant target. It might force the enemy to commit his weapons to defense of a given area prematurely, as it feinted toward unintended targets. The MBRV is believed to have complex hydraulic-driven moving surfaces. Perhaps $50-$ 100 million have been spent on the two efforts. A third approach, somewhat similar to MBRV in that it is ballistic rather than aerodynamic in nature, is under investigation by McDonnell Douglas. Known as the MARCAS concept, it calls for the injection of fluids into the slipstream and the use of reaction-control gas jets for roll control. Test flights down the inland range are planned. Critics of the maneuvering re-entry approach cite the great expense involved in these techniques, the extra cost of strengthening the missile boosters and the need for extra equipment such as hydraulics and gas generators that add undesirable weight. In addition, they point to the need for developing nuclear-hardened guidance systems for any maneuvering vehicles. Since the guidance system must be active and functioning for prolonged periods of time in what would be a nuclear-defense environment, it would have to be hardened against acoustic and nuclear effects. A conventional missile guidance system would be less susceptible because of its essential quiescence after re-entry and the shorter duration of its exposure in the hostile environment. Sabre System Air Force and the Massachusetts Institute of Technology's Instrumentation Laboratory have been developing a guidance system specifically designed to withstand high accelerations experienced by maneuvering vehicles and hardened against nuclear effects. The Self-Aligning Boost and Re-entry System (SABRE) might be applicable to other re-entry vehicles, but its expense and complexity may restrict it to maneuvering applications. Two aerospace contractors, General Motors AC Electronics and North American Auto-netics, are developing prototype inertial platforms to MIT design and Bendix prints (AW&ST Mar. 23, 1964, p. 82), while Sperry Rand Univac is building the hardened computer. In Operational Maneuvering Re-entry Vehicle (OMRV) studies, McDonnell and General Electric are looking at a maze of requirements for maneuvering re-entry. They are examining body shapes, the advantages of maneuvering against specific targets, the number of vehicles needed to knock out specific targets, the constraints maneuvering imposes on vehicle and guidance system design. Another technique for countering missile-defense radars using at least a rudimentary maneuverable re-entry vehicle is under investigation by TRW Systems Group, assisted by Raytheon Co. This program, known as Degradation of Radar Defense Systems (DRADS), began about three years ago, was cut back and then was resumed recently. DRADS would employ a separate reentry vehicle, possibly carried piggyback on a ballistic missile for release to radiate jamming signals or to home on hostile radar signals, and having suffi- 98 Aviation Week & Space Technology, October 23, 1967 |