AS-101

• 1. Introduction

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  AS-101 launched from Cape Kennedy Air Force Station on the 28th of May 1964, carrying not an astronaut, not even a real spacecraft, but a hollow metal stand-in bolted to the top of a Saturn I rocket. Officially known as Apollo Saturn-101, it was also designated SA-6, the sixth time this launch vehicle had ever left the ground. The payload was something called BP-13, a boilerplate Apollo spacecraft that looked every inch like the real command and service module but weighed about five thousand pounds more than a flight-weight capsule would. What was NASA testing? Not the spacecraft itself, but the air it would punch through on the way up. The questions hanging over the mission were deceptively simple: would the shape of the Apollo capsule survive the aerodynamic forces of ascent? Would the launch escape tower, the device meant to yank astronauts away from an exploding rocket, work as designed? And lurking beneath all of that was the reliability of a new engine called the H-1, which had never been asked to carry anything quite like this before.

• 2. The Stand-In Spacecraft

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  BP-13 was not a spacecraft in any functional sense. It weighed 17,000 pounds and was built specifically to mimic the outer dimensions of the Apollo command and service module, with a dummy launch escape system tower riding on top. A real flight-weight command module came in around 12,000 pounds, making BP-13 substantially heavier, a deliberate choice so engineers could put maximum aerodynamic stress on the vehicle. What made BP-13 genuinely sophisticated was its interior: 116 sensors measuring strain, pressure, temperature, heat flux, and acceleration across the skin of the craft. Every shudder and push of the atmosphere on ascent would be recorded and transmitted back to the ground. The first five Saturn I flights had carried Jupiter nosecones, a proven design that let engineers concentrate on the rocket rather than worry about the payload. BP-13 represented a deliberate turn toward what the Saturn I was actually going to be asked to carry. Also mounted on the first stage were eight film cameras, pointed upward to observe the moment the two stages separated.

• 3. Three Attempts to Launch

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  Cape Kennedy Air Force Station Space Launch Complex 37B saw three separate launch attempts before AS-101 got off the ground. The first attempt ended when liquid oxygen damaged a wire mesh screen during pre-launch testing, contaminating the fuel supply and ending the day. The second attempt failed when the rocket's guidance system overheated after an air conditioning compressor quit working. On the third attempt, liquid oxygen vapors created an unexpected problem by drifting across an optical window in the instrument unit. A ground-based theodolite, a precision sighting instrument the countdown computer needed to confirm before allowing launch to proceed, could not get a clear line of sight through the vapor cloud. Engineers examined the requirement, determined the theodolite reading was not actually critical to the safety of the mission, and reprogrammed the computer to allow the launch to continue without it. The vehicle lifted off on the 28th of May 1964.

• 4. The Engine That Quit

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  At 116.9 seconds after liftoff, engine number eight shut down. This was not planned. On a previous Saturn I flight, SA-4, an engine shutdown had been deliberately triggered as a test of the rocket's ability to compensate, but AS-101 carried no such plan. The rocket's guidance system reacted automatically, burning the remaining seven engines for an extra 2.7 seconds to make up the lost thrust. The first stage separated cleanly. Ten seconds after that, the launch escape system was jettisoned on schedule, and the second stage ignited. The second stage cut off at 624.5 seconds after launch, 1.26 seconds earlier than predicted, with the vehicle and boilerplate spacecraft settling into an orbit of 182 kilometers by 227 kilometers. The spacecraft continued transmitting sensor data for four orbits before its batteries failed. Over the course of the mission, the vehicle completed 54 orbits in total before reentering the atmosphere east of Kanton Island and coming down in the Pacific Ocean on the 1st of June 1964.

• 5. What Stripped the Gear

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  Engineers traced the engine shutdown quickly after recovery. One of the gears inside the turbopump of engine number eight had its teeth stripped off, starving the engine of the flow it needed to keep burning. The finding could have been alarming, a mechanical failure on a flight carrying early Apollo hardware. But engineers had already identified the gear design as substandard before AS-101 ever launched and had planned to replace it for the next mission. The stripped gear confirmed a decision that was already made. This turned out to be the only H-1 engine failure recorded during an actual flight. AS-101 was followed by four more Saturn I flights designed to keep testing the aerodynamics of the Apollo command and service module and its escape system, the program methodically filling in its confidence before committing to a crewed vehicle.