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First to the Moon

Chapter Text

“Had Mercury been larger to begin with, much of Gemini's capabilities could
have been incorporated from the beginning and/or as the program
progressed. For that matter, had Mercury been, say, halfway between
itself and Gemini in size, a resealable EVA hatch could have been
incorporated and the Astronaut would have had enough room to get in
and out without having to use a giant shoehorn. In addition, some of
the additional life support & science equipment could have been moved
to external adapters in the same way as Gemini, allowing for more room
for the pilot. Ergo, a larger Mercury would probably have rendered
Gemini unnecessary as a gap between Mercury and Gemini, and as a
result would have sent Gus Grissom directly to NAA for Apollo
development from Day One, resulting in a safer Apollo Block I but with
a lower overhead requiring that only short astronauts make Apollo
flights”

- sci.space.history poster ‘OM’

Chapter Text

When the Titan IIIC rocket lifted off from Cape Canaveral with its payload,almost nobody saw the beginnings of the final leg of the race to the Moon. The payload was the Lunar Orbiter,a little contraption that cost only $36 million. 

The spacecraft was placed in a cislunar trajectory and injected into an elliptical near-equatorial lunar orbit for data acquisition after a flight time of 85 hours . The initial orbit was 122 miles by 1,150 miles at an inclination of 11.8 degrees. The perilune was lowered to 56 miles five days later after 33 orbits.

Now the Orbiter began its primary mission of photographing potential Apollo landing sites. Its orbit was maintained through a period of thruster firings. 

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The spacecraft was composed of three decks supported by trusses and an arch. The equipment deck at the base of the craft held the battery, transponder, flight programmer, inertial reference unit (IRU), Canopus star tracker, command decoder, multiplex encoder, traveling wave tube amplifier (TWTA), and the photographic system. Four solar panels were mounted to extend out from this deck with a total span across of 12.2 ft. Also extending out from the base of the spacecraft were a high gain antenna on a 4 ft 4 in boom and a low-gain antenna on a 6 ft 10 in boom. Above the equipment deck, the middle deck held the velocity control engine, propellant, oxidizer, and pressurization tanks, Sun sensors, and micrometeoroid detectors. The third deck consisted of a heat shield to protect the spacecraft from the firing of the velocity control engine. The nozzle of the engine protruded through the center of the shield. Mounted on the perimeter of the top deck were four attitude control thrusters.

Power of 375 W was provided by the four solar arrays containing 10,856 n/p solar cells which would directly run the spacecraft and also charge the 12 A·h nickel-cadmium battery. The batteries were used during the brief periods of occultation when no solar power was available. Propulsion for major maneuvers was provided by the gimballed velocity control engine, a hypergolic 100 pound-force (445 N) thrust Marquardt Corp. rocket motor. Three axis stabilization and attitude control were provided by four one lb-force (four newton) nitrogen gas jets. Navigational knowledge was provided by five sun sensors, the Canopus star sensor, and the inertial navigation system. Communications were via a 10 W transmitter and the directional one meter diameter high-gain antenna for transmission of photographs, and a 0.5 W transmitter and omnidirectional low-gain antenna for other communications. Both transmitters operated in the S-band at about 2295 MHz. Thermal control was maintained by a multilayer aluminized Mylar and Dacron thermal blanket which enshrouded the main bus, special paint, insulation, and small heaters.