An Untold Story of NASA’s Gemini 76 Mission

As with much of history, it’s the old stories that are interesting and provide additional information about specific points in our past.

NASA’s Gemini program was the two-man capsule follow-up to Project Mercury (which launched the first American into space).

There were many differences between Project Mercury and Project Gemini, not the least of which were the propellants used for the onboard engines. The Mercury capsule’s propulsion system used hydrogen peroxide forced through a metal screen into the steam-producing engines that drove the capsule. The Gemini capsule used nitrogen tetraoxide and hydrazine, each of which was forced into the engine chamber. These two chemicals automatically ignite on contact (hypergolic) producing the force for the spacecraft’s steering and reentry engines.

These two chemicals were stored in Teflon bladders which, when pressurized with helium, “sprayed” the respective chemical into the engine chambers. In the early 1960s, much was unknown about Teflon, as with the two chemical propellants, and there was trial and error.

During verification of Gemini 6, the check valves (which were to prevent chemical vapors from migrating back into the common helium supply) were found to be open. No one knew why and it was of such magnitude that the subsequent release of Gemini 6 was scuppered by moving Gemini 7 to the next release slot.

I was working as a chemical specialist at the NASA Propulsion System Office at Cape Canaveral and felt that the stuck check valves were being caused by something to do with the chemical propellants. I suggested running a series of tests to find out if that was really the reason and, if so, to find a solution to the problem.

I ran a series of tests on a disused launch complex with the help of Joe Fitzsimmons (a NASA summer assistant). Helium was blown onto individual canisters of nitrous oxide and hydrazine and allowed to mix in a column outside the blockhouse in case of explosion.

Sure enough, a yellowish substance was deposited on the inner surfaces of the column. We had found the source of what was causing the check valves to stick. Now the question was how to get rid of it.
We found the solution: blow the yellowish substance with dry helium or nitrogen and the substance will “melt”. With this information we were able to fix the stuck valves on Gemini 6 allowing for the subsequent launch of Gemini 6 and the “head to head” meeting of the Gemini 7 and 6 capsule.

For this paper, Joe and I received large images (framed without glass) of a Gemini capsule on a Titan Launch vehicle at liftoff. I still have that photo today.

© September 2007 John D. Beeson