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Aviation History
1962
1962 - 2282.PDF
FLIGHT International, 4 October 1962 one-half orbits the suit temperature indicated a steady decrease to a value between 64° and 67°. Cabin-air-temperature readings were slightly higher with the MA-6 flight. A maximum temperature of 108° was monitored by the Hawaii station near the end of the second orbit. This temperature decreased and tended to stabilize at about 100 during the remainder of this orbit and the first portion of the third orbit. •Over the Woomera site, the astronaut reported that he could tem porarily change the spacecraft attitude by moving his arms and body. The mission continued normally throughout the remainder of the second orbit. The astronaut was behind the flight-plan schedule by several items, and it was noted at California acquisition that the astronaut had used rather large amounts of manual fuel and was down to approximately 42 per cent as he began the third orbit. The low automatic and manual fuel quantities caused con siderable concern on the ground and resulted in a further request to the astronaut to conserve his fuel in both the automatic and manual systems. Site evaluation of telemetry recordings during the first and second orbits indicated considerable high thruster activity. These indications generally occurred while the astronaut was in the fly-by-wire mode, and it appeared that he was employing high thrusters excessively during attitude changes. . . . "The Mercury Control Center made a go decision for the beginning of the third orbit at 2hr 55min ground elapsed time. The astro naut was cautioned to conserve his fuel and it was suggested that he increase his water flow to the inverter cold plates. The inverters had indicated an increase in temperature similar to the previous MA-6 flight. This caused no major concern: however, the increased water flow reduced the rate of this temperature increase to an acceptable level. As a result of the request to conserve fuel, the astronaut entered a period of drifting flight at 3hr 9min g.e.t. while he was in contact with Cape Canaveral. Over Mercury Control Center during the third orbit, 45 per cent of the fuel in the automatic system and 42 per cent of the fuel in the manual system remained." Re-entry Sequence The retro-firing sequence and re-entry was described as follows in a discussion of pilot performance by Mr H. A. Kuehnel, Mr O. Armstrong, Mr J. J. van Bockel and Mr H. I. Johnson of the Manned Spacecraft Center's Flight Crew Operations Division. "It was intended to have the automatic control system maintain spacecraft attitude during the firing of the retro-rocket; however, the malfunction of the pitch horizon scanner circuit dictated that the pilot manually control the spacecraft attitudes during this event. Except for the late ignition of the retro-rockets, the pilot reported that he believed the manoeuvre had proceeded without serious misalignment of the spacecraft attitude. However, the spacecraft overshot the intended landing point by approximately 250 n.m. "The pilot backed up the automatic retro-fire system by pushing the manual retro-fire button when the event did not occur at the commanded time. Retro-fire occurred 3 to 4 seconds late which accounted for approximately 15 to 20 miles of the total overshoot error. "In an effort to explain the major cause of the overshoot error, a review of the events just prior to and during the retro-fire is presented. At approximately llmin prior to retro-fire, the pilot observed a possible source of the luminous particles previously reported by Astronaut Glenn during the MA-6 mission. This event, followed by photographing of these particles, delayed his completing the stowage of the onboard equipment as well as the accomplishment of the pre-retro-sequence checklist. "At approximately 6min prior to retro-fire the pilot enabled the manual proportional control system as a back-up to the automatic stabilization and control system, as specified for an automatic retro-fire manoeuvre. The pilot then engaged his automatic contiol system and almost immediately reported a discrepancy between the instruments and the external window references. In the 5min prior to retro-sequence (T-30sec), he attempted to analyse the automatic control-system problem, and rechecked his manual control systems in preparation for this event. "At 30sec before retro-fire, the pilot again checked his ASCS orientation mode upon ground request. While the pilot was making this check, the spacecraft attained excessive pitch-down attitude; therefore, the pilot quickly switched from ASCS to FBW modes and repositioned the spacecraft to retro-fire attitude using his Earth- through-window reference. It was during this period that gyro outputs indicated a significant excursion in yaw attitude. As a 573 result of switching to the FBW mode without cutting off die MP mode, the pilot inadvertently used double-authority control. Because of the horizon scanner malfunction the pilot cross-referen ced between the gyro indications and the external references for attitude information during the firing of the retro-rockets. . . . "Radar tracking data have indicated that the mean spacecraft pitch attitude during the retro-fire period was essentially correct. Thus the deviation in pitch attitude did not contribute to the overshooting error in landing. Some deviations are also shown in spacecraft roll attitude during retro-fire; however, roll errors of this magnitude have a negligible effect on landing-point dispersion. Thus, the error in landing position resulted primariK from a misalignment in spacecraft yaw attitude. Radar tracking data have shown that the spacecraft had an average yaw error of 27° during retro-fire." On the subject of fuel consumption, Mr J. H. Boynton and Mr E. N. Fields of the Center's Mercury Project Office stated: "Double- authority control was inadvertently employed at times during the flight, and the fly-by-wire high-thrust units were accidently actuated during certain manoeuvres, both of which contributed to the high usage rate of spacecraft fuel. In addition, operation of the ASCS mode while outside the required attitude limits resulted in unneces sary use of the high-thrust units. The manual system fuel was depleted at about the end of the retro-fire manoeuvre, and the automatic-system fuel was depleted at about halfway through the re-entry period. "Because of the early depletion of automatic-system fuel, attitude control during re-entry was not available for the required duration. As a result, attitude rates built up after the ASCS became inoperative because of the lack of fuel, and these rates were not sufficiently damped, as expected, by aerodynamic forces. These oscillations continued to diverge until the pilot chose to deploy the drogue parachute manually at an altitude of approximately 25,000ft to stabilize the spacecraft. "In order to prevent inadvertent use of the high-thrust jets when using FBW mode of control, the MA-8 and subsequent spacecrafts will contain a switch which will allow the pilot to disable and reactivate the high-thrust units at his discretion. An automatic override will reactivate these thrusters just prior to retro-fire. Additionally, a revision of fuel management and control training procedures has been instituted for the next mission." Gen Bernard A. Schriever, Commander of the US Air Force Systems Com mand, and USAF pilots selected to fly the X-20 Dyna-Soar "piloted research aerospacecraft,"are seen with a fullsize model of the craft on display recently at the Air Force Association Convention in Las Vegas. Among the background exhibits is a model of the recently announced Titan 3 space launcher
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