As with much of history, it’s the untold stories that are interesting and provide additional insight into specific points in our past.

The Gemini program of NASA was the two man capsule follow-on to Project Mercury (which launched the first American into space).

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

These two chemicals were stored in Teflon bladders which when pressurized with helium “squirted” the respective chemical into the engine chambers. In the early 1960s a lot about Teflon, as with the two chemical propellants, which was unknown and there were trials and errors.

During the checkout of Gemini 6 it was discovered that the check valves (which were to keep the chemical vapors from migrating back into the common helium supply) were sticking open. No one knew why and it was of such a magnitude that the subsequent launch of Gemini 6 was, scrubbed moving Gemini 7 into the next launch slot.

I was working as a chemical specialist in the NASA Propulsion System Office at Cape Canaveral and felt that the sticking check valves were being caused by something having to do with the chemical propellants. I suggested that a series of tests be conducted to find out if this was in fact the reason and if it were, to find a solution to the problem.

I conducted a series of tests at an unused launch complex with the assistance of Joe Fitzsimmons (a NASA summer aide). Helium was blown over individual canisters of nitrogen tetra oxide and hydrazine and allowed to mix in a column outside the block house in case of an explosion.

Sure enough a yellowish substance deposited onto 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 across the yellowish substance with dry helium or nitrogen and the substance “melted” away. With this information, we were able to fix the sticking valves of Gemini 6 allowing the subsequent launch of Gemini 6 and the “face-to-face” meeting of Gemini capsule 7 and 6.


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