posted 04-27-2006 02:53 PM
cSpace Historygram:: No Problems for Next Saturn-Apollo
Source: MISSILES AND ROCKETS (March, 14 1966)
Houston – Results of the first unmanned Apollo flight from Cape Kennedy aboard Saturn IB on Feb. 26 indicate that only minor “cleaning up” is needed prior to the Apollo-Saturn 202 mission this summer.
Preliminary analysis of telemetered data and on-board camera film, and inspection of the re-entry module after recovery has revealed that the Feb. 26 flight “met all test objectives,” NASA officials said here last week.
Dr. Joseph P. Shea, Apollo spacecraft program manager, reported that data stripped from on-board telemetry tapes collecting heat-shield measurements show that a surface temperature of 4,050 deg F was reached during maximum re-entry heating – 10% below what was expected. Maximum heat rate imposed on the spacecraft by its ballistic trajectory was 186 Btu/ft.2/sec., or 7% less then anticipated.
Chamber pressure drop—NASA officials have concluded that the slightly reduced re-entry speed of the Command Module—some 500 mph less then the programmed 18,500 mph—was caused by the drop in Service Propulsion System (SPS) engine chamber pressure during the two burns to accelerate the Command Module through the atmosphere for higher-then-normal orbital re-entry heating rates.
Chamber pressure, normally about 100 psi, began to decay gradually after the first 80 sec. of the 180-sec. burn, leveling out to “around 70 psi,” Shea said. Engine-mounted accelerometers indicated that the engine was burning smoothly.
Shea said telemetry showed a simultaneous decay in the oxidizer inlet pressure measured downstream of the tanks, but that the regulator for helium, which is used to pressurize the oxidizer, was at the nominal 195-psi pressure.
After shutdown of the first SPS burn, which was followed by a 10-sec. coasting period, the SPS engine was re-ignited and for the first 5 sec. burned “abnormally,” Shea continued.
“At about 5 sec., the chamber pressure dropped to a low of 10 psi-almost off-then recovered sharply and stabilized at 95 psi.”
Shea concluded that the “problem: apparently was not in the engine or the engine chamber but “in the bottom of the (oxidizer) tank” or where the oxidizer enters the engine.
Visual inspection of the Command Module showed that ablation was heavy on the aft portion of the heat shield, which was “expected.” Heavy charring was reported along the conical portion of the spacecraft “from 20 degs. around to 150 degs. (aft of the horizontal axis through the spacecraft).” VHF scimitar antennas which protrude on both the wind and lee sides of the Command Module during re-entry were not excessively charred, the NASA official reported.
One of two pyrotechnic cutting devices designed to sever the parachutes from the Command Module after splashdown failed to operate, and only one end of the bridle was severed, Shea said. However, Both the “pyro” and the sequencer were recovered for closer inspections.
Difficulties—Glynn S. Lunney, AS-201 flight director in Houston’s Mission Control Center, reported a few “plus-time” problems:
A temporary loss of power at Cape Kennedy knocked out the MCC’s impact predict computer for several minutes—long enough to lose its data. Flight controllers picked up the track from telemetry coming out of the Saturn guidance system directly into the MCC and several minutes later had a radar track on MCC impact point plotboards based on Bermuda tracking data.
A 17-deg. “drift” in an instrument gyro placed on board to monitor the SPS engine burn was noted during the “max Q” portion of powered flight. Lunney said they calibrated the deviation by cross-checking twith the launch vehicles’s platform and relayed the anomaly to flight controllers aboard the Rose Knot Victor tracking ship who would be monitoring the Service Module burn when the vehicle moved into range.
Impact occurred 43 n. mi. uprange at a point 8 deg., 11 min. south latitude and 11 deg., 9 min. west longitude. The “miss” was attributed to the re-entry module’s achieving slightly less lift then anticipated in L/D predictions, Lunney said. The command Module was retrieved from the sea about one minute before sundown by the aircraft carrier USS Boxer. Booster performance excellent—Col. William Teir, deputy manager for the Saturn IB launch vehicle at Marshall Space Flight Center, reported only minor deviations in the booster’s performance.
Velocity cutoff of the S-IB first-stage outboard engines was 26 fps faster then predicted but “within tolerance.” The inboard engines cut off at 141.4 sec., or 0.9 sec. late; outboard engines (by propellant depletion sensors) terminated by 146.9 ec., or 0.3 sec. after the predicted time.
The S-IVB stage ignited at 149.3 sec., in proper sequence with the first-stage cutoff. Separation was “clean.” Second-stage engine cutoff (SSECO) occurred at 602.9 sec. and the longer burning time of approximately 9.8 sec. was attributed to average engine thrust being 2% less then predicted calculations, Teir explained.
Velocity at SSECO was 21, 439 fps, or 1 fps less then predicted. The spacecraft separation signal was given at 843 sec., or 240.2 sec. after SSECO, Teir pointed out. Total velocity at spacecraft separation was 3.9 sec. faster then predicted. “We feel this is due to tail-off burn of the S-IVB stage with a slight additional thrust, probably from venting,” Teir said. Altitude at separation was 234.8 n. mi., or 0.6 n. mi. higher then predicted.
The S-IVB stage during its powered phase maintained unusually stable attitude, Teir revealed. In-flight stabilization is provided by main-engine gimbaling for pitch and yaw control and by two auxiliary propulsion system (APS) sets of thrusters for roll control. After S-IVB engine cutoff, the APS takes over pitch and yaw attitude control. Propellant consumption, Tier explained, was much lower then expected. The APS used only one-third of total propellant—50% less then anticipated.
Both on-board cameras located in the front of the S-IB stage to film the separation sequence ran into “parachute troubles,” Teir said, but one was recovered intact. On-board tape recorders operated without problems. “We lost only 12 pieces of data out of 1,2000-1,300 TM measurements.”
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Scott Schneeweis
URL http://www.SPACEAHOLIC.com/
[This message has been edited by LT Scott Schneeweis (edited April 28, 2006).]
posted 04-27-2006 02:53 PM
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