Personnel from the Space Task Group involved in the study of reentry methods visited the Air Force Wright Air Development Center, Dayton, Ohio, for the purpose of preparing test specimens. Along with individuals from the center and the Air Force Ballistic Missile Division, the group then met at the Chicago Midway Laboratories, Chicago, Illinois, to investigate various ablation methods of reentry. Concurrently, these same methods were being investigated at high-temperature test facilities at Langley.
A meeting was held at the National Aeronautics and Space Administration Headquarters to discuss the method for spacecraft heat protection. Two plans were considered: beryllium heat sink and ablation. Based on this meeting a decision was made to modify the spacecraft structure in order to accomodate interchangeably ablation heat shields and beryllium heat sinks , and orders were placed for 12 and 6, respectively. The material chosen for the ablation heat was Fiberglas bonded with a modified phenolic resin. This material was found to have good structural properties even after being subjected to reentry heating.
During a meeting of the Space Task Group, it was decided to negotiate with McDonnell for design of spacecraft that could be fitted with either a beryllium heat sink or an ablation heat shield. Robert R. Gilruth, the project director, considered that for safety purposes, both should be used. He also felt that the recovery landing bag should be replaced by a honeycombed crushable structure. At this same meeting, a tentative decision was also made that design, development, and contract responsibilities for the Mercury tracking network would be assigned to the Langley Research Center.
Between June 28 and July 11, 1959, 12 heat-transfer tests were made in the Preflight Jet Test facility at Wallops Island on several ablation materials being considered for use on the spacecraft afterbody (not heat shield) for the Little Joe flights. Test conditions simulated those of actual Little Joe trajectories. Of the materials used, triester polymer and thermolag demonstrated the capability to protect the spacecraft against expected heat loads.
The first phase of the program in which boilerplate spacecraft with impact skirts were dropped by helicopters on water and land surfaces was completed. These tests were performed to investigate spacecraft dynamics, effects of parachute restraint and release time on spacecraft dynamics, and to determine maximum landing decelerations. During the drops into the water spacecraft water stability was shown to be unacceptable, because a portion of the spacecraft cylindrical section remained under water. McDonnell immediately investigated this problem and performed such experiments as redistribution of weight to obtain center-of-gravity positions which were acceptable but yet provided satisfactory flotation characteristics. Space Task Group was investigating the possibility of extending the heat shield from the remainder of the spacecraft and thereby creating a greater stabilizing moment. Results from the drops on land appeared to be acceptable because of the relatively low decelerations and the overall low probability of a landing on land.
Because of poor tower separation of the production spacecraft in the off-the-beach abort test at Wallops Island, NASA personnel at Langley started a series of jettison rocket tests. It was found that rocket performance had been only about 42 percent of the desired level, and experiments were started to raise thrust effectiveness. Measures taken included canting the motor, adding a cone to the blast shield, and, in one instance, deleting the blast shield. Space Task Group personnel advised McDonnell that plans were made to test a redesigned jettison rocket nozzle, consisting of three nozzles spaced 120 degrees apart and canted at a 30 degree angle to the rocket centerline. The three-nozzle effect, which produced the desired results, was another NASA engineering contribution.
Primary objectives of the drops were to study further the spacecraft suitability and flotation capability after water impact. Six drops were made, but later (April 24-28, 1961) the tests were extended for two additional drops to monitor hard-surface landing effects. In the water phase of the program, spacecraft components under particular scrutiny were the lower pressure bulkhead and its capability to withstanding heat shield recontact without impairing flotation capability. Helicopters were used to make the drops.
The Manned Spacecraft Center requested that the Langley Research Center participate in acoustic tests of ablation materials on Mercury flight tests. Langley was to prepare several material specimens which would be tested for possible application in providing lightweight afterbody heat protection for Apollo class vehicles. Langley reported the results of its test preparation activities on September 21, 1962.