It’s January 31, 1961, exactly three years since the United States launched its first satellite, Explorer 1, just 6 ft. 8 in. long and weighing 30.8 lbs. If all goes well this day, NASA will launch a Mercury capsule weighing 2,667 lbs. on a suborbital flight lasting 15 minutes down the Atlantic Missile Range.
This is Mercury-Redstone 2. No mere repeat of the first MR mission in December 1960, this flight will carry the first primate in space. As the human astronauts are tired of hearing, a monkey is going to make the first flight. That is, a 3.5-year-old chimpanzee weighing 37 lbs. will be aboard Mercury capsule #5.
Originally named Chang, one of six “astro-chimps” trained at Holloman Air Force Base to fly in space, he’s been renamed Ham for the mission — for Holloman Aerospace Medical. He will ride into space in a special sealed couch, a capsule within the capsule, that serves as his spacesuit. The enclosure is equipped with two lights and levers and he his trained to pull the levers in response to the lights — with a reward of banana pellets — or if he doesn’t respond in a set time, a “mild” shock to the bottoms of his feet. The reaction times of chimpanzees are comparable to that of a human — so the tasks seek insight into a human’s ability to function during spaceflight.
The flight profile for the second Mercury has been modified from the first flight. The trajectory will be a flatter curve, to a peak altitude of 115 mi. compared to 130 mi., and extending downrange 289 mi. instead of the 239 mi. of MR-1. This will be the first flight with a complete attitude control system, retrorockets and environmental control system. Capsule #5 is the first with a landing bag: Before splashdown, the heatshield drops down, an airbag deploying between it and the capsule to cushion the shock of landing.
Astronaut Alan Shepard, above all others, holds an interest in the flight. Although not publicly announced, he has just been chosen to pilot the next flight, MR-3, launch date already set for March 24. If all goes well with this flight, he will become the first human in space.
After 7 a.m. (EST), Ham is sealed in the Mercury capsule, launch aimed for 9:30 a.m. Just after, a hold is called — an electrical inverter inside the spacecraft has overheated, must be shutdown as it cools. The count resumes at 10:45 a.m. But then another hold is called when an elevator in the gantry becomes stuck. Then checks of the environmental control system take 20 min. longer than planned. And flaps over the tail plugs of the Redstone booster jam. And then the inverter overheats again.
Ham has been sealed in the capsule for nearly 5 hrs. But appears to be doing well. Finally the count resumes at 11:40 a.m., fifteen minutes to go.
The Redstone’s engine ignites at 11:54:51 a.m., and the rocket leaps off the pad. Everything proceeds OK for the first minute. Then tracking detects that the vehicle is lofting — the flightpath is too steep. She’s running “hot” — a propellant pump is injecting too much liquid oxygen into the engine, creating an over-thrust. And depleting the liquid oxygen supply faster than planned. The Redstone runs out of it and the engine shuts down a bit early, at 2 min. 17.5 sec. into the flight. The automatic abort system, sensing the thrust decay, activates the solid-fueled escape tower above the capsule. The tower pulls the capsule away, giving poor Ham a jolt that causes him to pause in his tasks.
In addition, as soon as the tower fires, pressure drops within the capsule, from 5.5 to 1 psi. Ham’s sealed couch does its job — just like a spacesuit — and maintains pressure within. The a valve in capsule’s air inlet snorkel, intended to open as the capsule descends on its parachute, has opened. It’s later determine that vibrations at launch caused a locking pin to come off.
With the added kick from the escape rocket, the capsule reaches a speed of 5,840 mph, rather than the planned 4,411 mph. And that means that at the top of it’s arc, it hits an altitude of 157 miles, 42 miles higher than planned. Instead of the planned 4 min. 54 sec. of weightlessness, Ham experiences zero-g for 6 min. 27 seconds. Worse is ahead, as gravity pulls the capsule down. Ham experiences 14.7 Gs, that’s three 3 Gs higher than planned. Through it all, he continues to work his levers with excellent reaction times, an indication that a human can function in such extremes.
The capsule’s parachute system works perfectly, and the heatshield drops to inflate the airbag. Splashdown occurs 423 mi. downrange, a 130-mi. overshoot. Ham’s ordeal is not over. The heatshield rebounds and punches two small holes in the aft pressure bulkhead. Water leaks into the capsule which lists over, allowing more water to enter the open snorkel. The capsule rides lower in the water. Finally rescue helicopters locate it and 2.5 hours after splashdown, at 2:52 p.m., hoists it out of the water. The spacecraft had taken on 800 lbs. of water — but Ham is safe within his couch enclosure. On the recovery ship, after being taken from the capsule, he calmly accepts an apple.
A human could have survived the flight. Yet so much had gone awry, NASA officials are extremely nervous about committing Alan Shepard to flight on March 24.
And of course no one would dream that ten years later on January 31, 1971, a much larger rocket would send Shepard and two others towards the moon.