The third unmanned Apollo/Uprated Saturn I flight will be launched no earlier than Aug. 25. This will be the second flight test of the Apollo spacecraft command and service modules and the third flight test of the Saturn I rocket in preparation for manned missions orbiting the Earth.The 17,825-mile flight will carry the spacecraft three-quarters of the way around the Earth. Landing will be in the north central Pacific about 300 miles southeast of Wake Island.
The National Aeronautics and Space Administration will launch the space vehicle from Launch Complex 34, Kennedy Space Center, Fla., at 12:30 a.m. EDT to provide a long period of daylight for spacecraft recovery operations. The flight will take almost 93 minutes.
The mission is the second performance cheek of the Apollo command module ablative heat shield. The shield will be subjected to extended high heat loads -- about 23,000 BTU/per square foot -- resulting from a reentry path resembling a "roller coaster" ride on Earth.
On the first unmanned Apollo mission last February, the heat shield underwent high heating rates at a very steep angle. The reentry trajectory in this mission will be longer and shallower to produce very high heat loads.
The two types of trajectories represent reentry heating conditions encountered in manned Earth orbital missions. For lunar landing mission reentry, the spacecraft heat shield will be tested next year on Saturn V missions.
The Apollo/Uprated Saturn space vehicle stands 224 feet high (launch vehicle is 141 feet and spacecraft 83 feet). Total weight on the launch pad will be 1,326,400 pounds (launch vehicle is 1,269,500 pounds and spacecraft 56,900 pounds).
The Apollo command module, although unmanned, is a fully operational spacecraft except for crew couches and a few displays for pilots. The guidance and navigation system and fuel cell electrical power system will undergo their first flight test.
The Apollo Emergency Detection System will be tested in the automatic mode. It will automatically initiate firing of the spacecraft launch escape system and separation of the command module if two of the Saturn first stage engines fail, or if a guidance failure causes excessive pitch, yaw and roll during first-stage powered flight.
On manned missions, the emergency detection system can operate automatically or it will signal the crew to initiate firing of the escape system. Relay logic of the emergency detection system is located primarily in the Saturn vehicle instrument unit.
The first test of S-Band communications will be conducted on the mission, although it will not be the prime method of air-to-ground communications. The Apollo Unified S-Band system will be fully operational for Saturn V manned missions in 1968.
The 21,500 pound thrust service propulsion system engine will be fired four times in flight for a total of more than five minutes. On Apollo lunar landing missions, this engine will provide thrust for the spacecraft to correct velocities en route to the Moon, break into lunar orbit and return to Earth.
A structural test of the common bulkhead separating the Saturn second stage propellant tanks will be conducted after the stage separates from the spacecraft. Similar to the check on the second Uprated Saturn I mission, it is designed to determine the strength of the sandwich-like structure which insulates the liquid oxygen at minus-297 minutes degrees F. from supercold liquid hydrogen at minus-423 degrees F.
Ground tests and the previous flight test show that the bulkhead will withstand pressure differentials of about 34 pounds per square inch -- more than three times normal operating conditions. Maximum pressure is expected as the stage reenters the atmosphere over the Atlantic. Pressure differential reached will depend on the amount of liquid oxygen remaining in the tank. It is not known whether this will cause the stage to break up as it did in the previous Saturn flight last month. Six movie cameras and one television system will record data (See Cameras, Page 23 ). A total of 2,158 measurements will be recorded during the mission, 863 from the Apollo spacecraft and 1, 295 from the Saturn.
Copyright 1997, 1998 by John
Duncan |