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Gemini Space Program - Development and Decisions

written by: •edited by: RC Davison•updated: 1/10/2010

Developing the Gemini spacecraft proceeded relatively smoothly wiith the Mercury experience to build on. But there were challenges and controversies. There were questions of what the craft was to accomplish, how it was to be recovered, and what vehicle would lift it into orbit.

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    Design Controversies

    With the President’s orders to land a man on the moon in ten years, NASA began to look for ways to do that. The arguments quickly shook out into three concepts:

    • Direct ascent

    • Earth orbit rendezvous

    • Lunar orbit rendezvous

    Direct ascent seemed at first glance the simplest. A huge launch vehicle would boost a spacecraft directly to the moon for a landing. But the booster would indeed have to be gigantic, because the lunar spacecraft would have to carry fuel for the landing and takeoff.

    It didn’t take much discussion for some form of rendezvous to win the day. So Mercury’s successor would have to develop the techniques to rendezvous and dock with another spacecraft.

    This meant the new spacecraft would have to have a propulsion system of its own, not just the attitude control system of Mercury. The propulsion system would be housed in an equipment module behind the spacecraft. It would contain eight 25-lb thrust engines and the fuel tanks for them. Between the equipment module and the spacecraft was the retro module, which contained the solid rockets used to slow the craft for reentry. Orbital attitude maneuvering jets (OAMS) were contained in the craft’s fuselage.Cutaway view of the new spacecraft 

    While the design of the new spacecraft proceeded with relative smoothness, there were disputes among the engineers as to the best way to go on several fronts. One of those was the recovery system. No one was happy with Mercury’s parachute landing in the ocean. The Liberty Bell 7 had been lost, and a couple of astronauts became seasick waiting on pickup as their capsule rolled and pitched in the waves.

    NASA wanted a landing on land. An engineer named Francis Rogallo at Langley Research Center had developed a flexible wing called a paraglider. He and his colleagues were convinced this concept could return a spacecraft to a smooth land touchdown. The concept piqued NASA’s interest, and Rogallo and his team were given the go ahead to develop the system.The paraglider landing concept 

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    Booster Bummers

    Meanwhile, engineers were looking at launch vehicles. The Atlas, used for Mercury, was not quite powerful enough for the heavier—8500 lb--, two man spacecraft. The Von Braun team, which had rushed the Redstone to the rescue for the Explorer satellite and Mercury suborbital flights, were now a part of NASA at the Marshall Spaceflight Center (MSC) in Huntsville, AL. They were working on a family of vehicles that were to lead to the moon rocket booster called Saturn. The first in the series was a gangly erector-set booster called the Saturn 1. It was to produce 1.5 million pounds of thrust, more than enough to boost the new spacecraft into orbit.Saturn 1 

    But there was no assurance Saturn 1 would be ready in time, so the rocket scientists looked back to Air Force ICBMs for their vehicle. By now, the Atlas, as the Strategic Air Command’s main missile deterrent, had been replaced by the Titan II. This was a two stage vehicle that used storable, hypergolic fuels. Hypergolic fuels are fuels that ignite when they come in contact with each other. Titan II Titan II used hydrazine and nitrogen tetroxide in both stages. This meant there was no question the second stage would ignite. The first stage’s two engines produced 430,000 lbs of thrust, almost 60,000 lbs more than Atlas and enough to boost the new spacecraft into orbit.

    The storability of the fuels was also a plus for NASA. The vehicle could be fueled and not have to be unloaded and refueled through extended holds as with cryogenic (liquefied gas) fuels like liquid oxygen.

    But the rocket scientists were still getting their on the job training. Flight testing of the Titan II did not proceed as desired. Flight tests by the Air Force revealed a unique and worrisome phenomenon for NASA—the POGO effect. Combustion deviations in the booster engines caused compression waves to travel through the vehicle. It was like the rocket was pulsing through its length. This was not a good situation for manned flight.

    On top of that, the second stage engine showed instability on startup in ground tests. This had never happened in flight, but it was enough to concern NASA. MSC was put on the case.

    The Huntsville team located a number of parts in the booster that had to be redesigned. Their main fix however was to add standpipes on the oxidizer lines and accumulators on the fuel lines to reduce the POGO effect.

    Aerojet General, the engine manufacturer, meanwhile solved the instability problem. On Nov. 1, 1963, a Titan II with all the fixes lifted off from Cape Canaveral and posted a perfect flight. After that Titan II achieved a string of 11 flawless flights.

    Meanwhile, NASA was completing the design of the new spacecraft, giving it a name, and tapping new astronauts to fly it.

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    Sources

    Gemini cutaway: NASA

    Paraglider concept: McDonald Douglas Co.

    Saturn 1: NASA

    Titan II: NASA

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    Sample contents.

Rendezvous in Space--The Gemini Program

With President John Kennedy's challenge to land a man on the moon by the end of the decade, NASA had to develop and prove the techniques of rendezvous and docking two spacecraft in orbit. That was Gemini's mission. Along the way, five astronauts would take a stroll in space.
  1. Gemini Space Program - Development and Decisions
  2. Gemini Space Program--Final Design, a Name, and More Astronauts
  3. Gemini Space Program--The Initial Flights
  4. Gemini Space Program--Rendezvous at Last
  5. Gemini Space Program--Finally, Success