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The Cape, Chapter 3, Section 8

Medium and Light Military Space Operations


The first two military ATLAS II/CENTAUR missions were launched from Pad 36A during 1992. We will look at those flights presently, but a few comments concerning the launch vehicles and flight sequences are appropriate at this point. The ATLAS II/CENTAUR vehicle was an improved version of the ATLAS G/CENTAUR. The ATLAS II's performance was increased over the old design, and the ATLAS' fuel tank was lengthened nine feet (e.g., from 73 feet to 82 feet). The ATLAS II's uprated Rocketdyne MA-5A booster and sustainer engines gave the ATLAS II 484,000 pounds of thrust at sea level, and the ATLAS I's vernier engines were replaced with a hydrazine roll control system. The new CENTAUR's tank was three feet longer than the ATLAS G's tank, but the two Pratt & Whitney RL10A-3-3A engines used on both vehicles provided about 16,500 pounds of thrust apiece. Vehicle differences aside, certain flight sequences were common to all ATLAS/CENTAUR flights. Following lift-off, the booster, vernier/hydrazine roll and sustainer engines combined to thrust the vehicle on its way. Between 153 and 171 seconds into the flight, the section containing the two booster engines was jettisoned, but the sustainer engine continued to thrust for approximately two more minutes until that stage's fuel was depleted. The payload fairing was jettisoned during the sustainer burn. Two seconds after sustainer engine cutoff, the CENTAUR separated from the ATLAS/ATLAS II, and the CENTAUR's first main engine burn started about 10 to 12 seconds later. Typically, the first burn placed the CENTAUR and its payload into an elliptical parking orbit anywhere from 80 x 282 nautical miles to 80 x 1239 nautical miles above Earth. The CENTAUR's axial thrusters were brought into play for propellant settling, venting and prestart purposes during a coasting period ranging from 13 to 16 minutes of flight time. The CENTAUR's second burn occurred approximately 24 to 26 minutes into the mission, and it accelerated the CENTAUR and its payload into a highly elliptical transfer orbit from which the spacecraft could be sent into final orbit. Following spacecraft separation, the CENTAUR coasted, turned 90 degrees, and fired its reaction control system to carry itself out of the spacecraft's orbit. A final fuel depletion "blowdown" ended the CENTAUR's fiery performance.47

Figure 121: Blockhouse scene-ATLAS II Wet Dress Rehearsal
October 1991
Figure 122: ATLAS II/CENTAUR launch
11 February 1992
Figure 123: DSCS III Satellite
Figure 124: ATLAS II/CENTAUR erection on Pad 36A
Figure 125: CENTAUR Hoist Operations
Figure 126: Preparation for Tower rollback at Pad 36A
Figure 127: ATLAS II/CENTAUR Pretest

Now we turn to the missions themselves. Following two unsuccessful launch attempts on 6 and 8 February 1992, the first military ATLAS II/CENTAUR mission was launched successfully from Pad 36A on 11 February 1992. The countdown on February 10th was eventful, and two extensions in the launch checklist's built-in holds were required to: 1) repair an environmental control regulator and 2) deal with payload fairing temperature anomalies. The extensions added approximately 70 minutes to the countdown, so the checklist continued through the scheduled 2330Z lift-off on the 10th to the ATLAS II/CENTAUR's actual lift-off at 0041:02Z on February 11th. The mission marked the first launch of a fully operational DSCS III spacecraft aboard an ATLAS II/CENTAUR vehicle. The CENTAUR's first burn placed the CENTAUR and its payload into an 80 x 282-nautical mile parking orbit, and its second burn accelerated the spacecraft into a highly elliptical 94 x 19,282-nautical-mile transfer orbit. Though ATLAS and CENTAUR yaw maneuvers contributed to the proper placement of the spacecraft, the first production model Integrated Apogee Boost Subsystem (IABS) was introduced on this mission to change the spacecraft's orbital plane a whopping 26.5 degrees. The spacecraft separated from the CENTAUR approximately three minutes after the CENTAUR's second burn. Two IABS burns were planned, but some fuel migrated after the first burn, and it caused the payload to shift approximately 25 degrees from its spin axis. This made the remaining IABS fuel inaccessible, and the second IABS burn was cancelled. The spacecraft's reaction control thrusters had to be fired over the next several weeks to place the satellite in its proper final orbit. To avoid a reoccurrence of the problem, the second IABS burn was deleted from later DSCS mission profiles, and one full-duration IABS burn was substituted.48

Figure 128: Second ATLAS II/CENTAUR launch from Pad 36A
2 July 1992

Figure 129: 3rd Space Launch Squadron Emblem

The next military ATLAS II/CENTAUR mission was also a fully operational DSCS III flight. It suffered six launch scrubs in May and June 1992, and the countdown on 2 July 1992 seemed equally unpromising. There were unscheduled holds for weather, a hydrazine leak indication and a Command Message Encoder/Verifier failure, but the launch vehicle lifted off Pad 36A at 2154:01Z as scheduled. The launch was very important to the Air Force's medium launch operations at the Cape. As the second successful military ATLAS II/CENTAUR operation, the mission cleared the way for the activation of the 3rd Space Launch Squadron on 2 July 1992. The activation, in turn, was a highly visible symbol of the Air Force's confidence in the ATLAS II/CENTAUR as an operational launch system. The 3rd Space Launch Squadron looked forward to working with General Dynamics on medium military launch operations at the Cape for many years to come.49

The Cape: Miltary Space Operations 1971-1992
by Mark C. Cleary, Chief Historian
45 Space Wing Office of History
1201 Minuteman Ave, Patrick AFB, FL 32925

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