60 years ago: Enos in orbit in Mercury test

Enos the astrochimp geared to go aboard Mercury Atlas – 5.


OK, this is it.  This is November 29, 1961.  This is Mercury Atlas (MA) -5, the dress rehearsal for the first U.S. manned orbital flight.  This is the flight of Enos (“man”), a 39-lb. chimpanzee on a three-orbit mission, delayed from October to Nov. 7 to Nov. 14 to today due to leaks in the hydrogen peroxide system that fuels the capsule’s thrusters.  This is capsule #9, of the modified design flown suborbitally by Gus Grissiom in July, with the large trapezoid “picture window,” quick-jettison explosive hatch, and other modifications.  This will be its first orbital flight. Three orbits, as planned for the first manned mission.  Although for now, two will do.  Even one.

If this flight goes well, NASA still has hopes, although faint ones, meeting its unofficial target of placing an astronaut in orbit in 1961, as had the Soviet Union.  That flight might be possible on December 28.

Launch of 93-ft.-tall Atlas/Mercury is set for 7:30 a.m. EST from Pad 14.  Enos, a rambunctious, to say the least, even willfully wild, astrochimp, rides inside his enclosed seat, a pressurized aluminum container placed inside the capsule 5 hrs. before launch.  He may be wired on the wild side, but none of the other astrochimps can run through the flight tasks as nimbly as he can.  He has a full program of tasks to check his reaction time, such as depressing  a lever on his right every 20 sec. when a red light comes on, or a lever on his left when a blue light comes on, and other more complicated sequences of lights and symbols.   In some tasks, he receives a reward for a correct response, such as a banana pellet.  But for some, he receives “negative reinforcement,” a “mild” electrical shock on the sole of his foot.

Like for so many launches, we must wait through long delays.  A hold for installation of hatch  insulation that had been overlooked.   For reopening the hatch to change a switch position.  For problems with data and computer links with several tracking stations.  In all, 2 hrs. 38 min. of holds.

And then finally, at 10:08 a.m. EST:  we reach T – zero.  The modified Atlas missile come alive in fire and steam, its three main engines providing 376,000 lbs. of thrust to lift a weight of 260,000 lbs. off the pad.  The engines fire for 131 sec. and then, altitude 39 mi., the two outer (booster) engines are jettisoned, leaving the center, sustainer engine to push for orbit.  The red escape tower atop the capsule is jettisoned 23 sec. later.  Enos experiences 7.6 g’s before sustainer cutoff, 5 min. 4 sec. after launch.  He is jolted into weightlessness — while continuing to pull levers without missing nearly a beat.   Alas, he’s in for a  jolt of another kind.  Due to a malfunction, he receives a electrical shock even when he completes a task successfully.  Eventually he becomes so enraged, he pulls out electro leads and even his catheter line.  

As far as the network of ground stations can tell, all is proceeding well.  The capsule has entered an orbit with a high point of 147 mi. and a low point of 99 mi.  It looks perfect, the capsule using less fuel than expected to maintain orbital attitude, heat shield forward, canted down 34 degrees.  That is, until the second orbit.  As the capsule passe over the Muchea, Australia, tracking station, telemetry indicates that a roll jet has failed. Because of the failure, capsule sways out of the desired orientation by about 30 degrees, then the automatic control system fires to align it.  Then the cycle begins again, wasting fuel.  After the flight, NASA will determine that a metal chip blocked the flow of fuel to the roll jet.  If an astronaut had been onboard, he could have taken manual control and bypassed the problem.

Mission Control is dealing with two problems.  In addition to the roll jet, the cabin temperature rises.  Enos is overheating.  Then temperatures stabilizes.  The chimp is in no danger.   

That leaves the roll problem, with more data from Woomera, Australia, and Hawaii tracking stations not quite conclusive.  Final confirmation arrives with telemetry from the Canton Island station.  Nine times the fuel-depleting cycle repeats itself during the second orbit.  Now the question is, does the capsule have enough fuel left for a third orbit?

Coming into range of the station at  Pt. Arguello, California, where astronaut Gordon Cooper is on duty.  This is the station that will send the signal to fire the retrorockets and bring Enos home.  If the capsule is to be brought down after two orbits, the decision has to be made here.   And quickly — only seconds remain before Enos will be committed to a third orbit.

Flight Director Christopher C. Kraft at Mercury Control queries his controllers.  They hesitate.  

What’s the word?  We need a decision now.   

It’s too risky to continue — bring the capsule down.

The command is sent.  The three retros fire at 1:08 p.m. EST.  The fires of reentry come quickly on a steep ballistic path toward the Atlantic Ocean.  Just 20 min. after retrofire, MA-5 carrying Enos splashes down 242 mi. south of Bermuda after a flight of 3 hr. 20 min. 59 sec.   Enos’s ordeal is not over — he must wait in his capsule within a capsule nearly 1.5 hr. before retrieval by the destroyer USS Stormes.  He is healthy — and retains a healthy rage about his experience of 181 minutes of weightlessness.  He’d bite your head off if he could.  Yet on the carrier he accepts two oranges and two apples.

Robert R. Gilruth, Director of the Manned Spacecraft Center, calls the flight “a superb success,” saying that nothing was lost by shortening it by an orbit.  Indeed, it proved that the worldwide tracking network was able to detect, analyze and deal with problems in flight.

So we’re next, one of the seven astronauts — specifically John Glenn.   NASA reveals he has been chosen as pilot for the Mercury Atlas – 6 mission.  However, hope of an orbital flight in 1961 ends on December 4.  NASA decides not to rush ground crews preparing the vehicle.  Launch is set for January 16, with a possibility it could be moved up by a week.  

Welcome to 1962.

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