QUESTION: Please tell me about the materials used to make the heat shield and parachute. They must be able to stand extreme conditions. How were they designed and tested on earth? ANSWER from Mike Izidi on December 29, 1995: The following information briefly discusses how we designed and tested the heatshield and parachute. The heatshield design was a combined effort between NASA-ARC, NASA Langley and the Hughes Aircraft Company's. Subcontractor- General Electric Reentry Systems Division. The testing was done at a material part level and again was a combined effort between GE-RSD and NASA-ARC. The forward heat shield is made of carbon phenolic and is a little over six inches thick at the tip of the nose. The aft cover is made of phenolic nylon. The materials testing were accomplished by using laser arc-jets designed at NASA-ARC similar devices cases at GE-RSD. Special attention was paid to lop joints which transition the chapped molded carbon phenolic nose section to the freestreem or aft section of the 45 degree cone. Also special attention was paid to the aft cover pilot chute aft area. This area was exposed to the heat input using lasers at GE-RSD and then functioned using an actual pyrotechnic pressure cartridge in order to determine that the pilot chute would deploy following entry heating. All of these tests indicated that we have a satisfactory design with ample margin and the forward and aft heatshields were exposed to all the standard tests that an entry vehicle must undergo such as launch vibration, space cruise thermal vacuum, and entry high GUs deceleration tests. Additionally, the heatsheild went through a comprehensive static load test which included a structual model of the Hughes built descent model and simulated the joint entry loads, This test was designated as the JELT or joint entry load test. A similar test was performed to simulate the main Parachute operational load test referred to in the chute industry as the "snatch" load. This test was called the POLT or parachute operating load test. The parachutes (pilot & main) were designed to the loads and temperatures expected for the mission based upon ground based and previous mission flight data of the Jupiter atmosphere. The materials are similar to design Hughes and GE used for the Pioneer Venus large probe. Many ground tests were conducted on the parachutes such as structural tests of the materials and materials joints. Static ground deployments, active deployment in entry elevation shafts etc. The most exciting were as follows: The chutes were fired from a canon mounted to a fighter plane in a high speed dive. This was performed at the NAVAL Air Station at China Lake in South Eastern California. The purpose was to determine the structural capabilities of the dynamic load conditions of chute deployment. All of these test had successful chute performance with ample margin. The next test was a complete chute and separation system test using a special probe test vehicle with instrumentation and properly weighted to simulate Jupiter, tethered to a giant helium balloon. The balloon was raised to 95,000 feet and at this altitude the probe was released such that it went through the complete chute release sequence. The first chute indicated (via the on board cameras) that the main chute did not deployed cleanly. After a painstaking analysis the experts determined that the main chute was to close to the descent module and was in dirty or turbulent air. The risers were lengthened and the test repeated. The results indicated absolutely nominal performance. By-the-way, we rebuilt and replaced the main and pilot chutes as a result of the shuttle accident launch delay. The experts, nation-wide, had a lot of aging data on nylon chutes but little or none on Dacron. Every one thought we would be OK, but suggested if we had time we should replace them. Consequently new chutes were built tested packed and installed on the flight Probe. ADDITIONAL ANSWER from Charlie Sobeck on January 5, 1996: The Galileo Probe heat shield was made of a composite material called carbon phenolic. This material was developed by the Department of Defense for ballistic missile heat shields. It is a laminated composite material (just as plywood is) consisting of about 30 layers of carbon cloth per inch, held together by a phenolic plastic resin (glue). To test the heat shield on the ground, a special facility was built at Ames Research Center, called the Giant Planet Facility. This facility was a supersonic wind tunnel that used a high power electric arc to heat the air. But even this enormous facility, operating at more than 70 megawatts (that's a LOT of power) couldn't heat up the heat shield as much as Jupiter will! So the heat shield was also tested by firing a powerful laser at it, and the results of the test were combined by the scientists. The heat shield, all by itself, slows the Probe down from 106,000 mph to about 2,000 mph. At 2,000 mph the parachute is deployed to slow the Probe down even more and to keep it from falling through the interesting parts of the atmosphere too quickly. The parachute is made of Dacron, a material much like you'd find in a windbreaker. The parachute was tested by taking a model of the Probe and dropping it from a weather balloon at a special test site in New Mexico. ADDITIONAL REFERENCES from Dan Carlock on January 10, 1996: http://ccf.arc.nasa.gov:80/dx/basket/storiesetc/GalBkgd.html#Probe spacecraft http://ccf.arc.nasa.gov/galileo_probe/htmls/probe_spacecraft.html http://kauai.arc.nasa.gov/stmhome.html