Summary

Six months before the explosion of the shuttle, more precisely  July 17, 1985, erosion problems with o-ring seals were described in an internal NASA¹ memorandum.
On July 23, 1985, a second NASA²  memorandum was very explicit about the risks associated with a failure of the sealing joints. Following the Presidential  Commissions's inquiry on the Challenger tragedy, many newspapers³ published information about what really happened.
Wayne Biddle mentioned that «The immediate cause of the tragedy was probably the failure of the o-ring seals but the real reasons were that under economic and political pressure, NASA sacrificed  the safety standards ». In the magazine «Asbestos Abatement» of June/July 1986, it was sated «It was a minor component of the formulation, but asbestos played a key role in the technology of the 0-ring seals. Could a substitute product with known weaknesses have contributed to the explosion?»

The Presidential Commission which was mandated to discover what happened in this tragedy found that abnormally cold temperatures⁴ during the night preceding the fateful launch  reduced the capacity of the substitute mastic to prevent erosion of the o-ring seals.

The presence of holes in the substitute mastic reduced it's efficiency as a thermal shield. Hot combustion grases escaping from the rocket rapidly increased the temperature of the fuel, liquid hydrogen, in the lateral fuel tank. 73 seconds after the launch of the shuttle, it exploded, which resulted  in the death of 7 young astronauts, cost billions of  dollars of high tech materials, and delayed the space program of the world's most powerful country. What a shame!

It required nearly three years of arduous work for thousands of  engineers, technicians and scientists to change the shuttle design.
For the propulsive rockets only this required 145 changes. On September 19, 1988, in a C & EN magazine article, Mr Richard J. Sultzer⁵ reported that renewing the propulsive rockets and other systems of the shuttle were part of nine recommendations made by the Presidential Commission studying the causes of the Challenger shuttle accident.
He describes the new seal design containing asbestos in this way: «The preceding form a bond between the metal frame and the NBR (synthetic nitrile and butadiene based rubber) insulation which is then applied by the crew to the interior of the cylinders. The NBR is filled with asbestos and silica to improve its efficiency in protecting the frame from gases heated to 5700 degrees. The NBR is then vulcanized in place. Then comes the sheath, an electrometric material in liquid form. Its principal components are butadiene with carboxy endings with small quantities of tertiary amines, an epoxy resin, asbestos and mineral filler (silica). These components of the sheath polymerize together during filling of the tank with fuel».

We presume that the use of a reliable  material, with known and valued insulating properties like the original mastic used during the first 8 missions, would have permitted the avoidance of this tragedy. The money spent to test a substitute, the Randolph mastic, could have been spent on other technologies like an escape module. NASA evaluated the cost of certification of an asbestos free substitute mastic at$50 million in case the Randolph mastic was no longer available as was the case of the Fuller O'Brien mastic (testimony of Richard C. Cook, Resource analyst, Comptroller's Office, NASA, http://history.nasa.gov/rogersrep/v4part4.htm .

Chrysotile asbestos is a natural substance with fantastic and largely proven mechanical, chemical and thermal properties. Let us avoid new tragedies and the shameful waste of money!

References

• ¹ NASA (National Aeronautics Space Administration, July 17, 1985), Memorandum to the associate administrator for space flight. Subject : «Case to case and nozzle to case «O» ring seal erosion».
• ² NASA (National Aeronautics and Space Administration), (February 10, 1986), Presentation to the Presidential Commission on the space shuttle Challenger accident of a memorandum from R. Cook to M. Mann, subject : «Problem with SRB seals» dated July 23, 1985
• ³ Biddle, Wayne, What Destroyed Challenger (April 1986), Discover, pp 40-47
• ⁴ BENNETT, Michael J., Challenger : The accident that was waiting to happen (June/July 1986), Asbestos Abatement, pp 14-22
• ⁵ FISHMAN, Charles, Key NASA official blames faulty shuttle booster joint (March 20, 1985) Washington Post
• ⁶ SELTZER, Richard J., Space shuttle passes final tests, is ready for return to space (September 19, 1988) C & EN Washington, USA, pp 7-13