Mercury-Atlas 5

By November 1961, the Soviet Union had launched Yuri Gagarin and Gherman Titov into orbit during the Vostok 1 and Vostok 2 manned orbital flights while the United States had managed only suborbital ones. At that time NASA was still debating placing a chimpanzee in orbit as part of the Mercury-Atlas subprogram, with NASA headquarters questioning the wisdom of the Manned Spacecraft Center launching another unmanned Mercury mission.

The NASA Public Affairs Office issued a press release prior to the flight, stating "The men in charge of Project Mercury have insisted on orbiting the chimpanzee as a necessary preliminary checkout of the entire Mercury program before risking a human astronaut."[2]

Enos in his flight couch, being prepared for insertion into his Mercury capsule

The flight used Mercury capsule #9 and Atlas #93-D. On February 24, 1961, spacecraft # 9 arrived at Cape Canaveral. It took 40 weeks of preflight preparation. This was the longest preparation time in the Mercury program. The mission of spacecraft #9 kept changing. It was first configured for a suborbital instrumented flight, then for a suborbital chimpanzee flight, then a three-orbit instrumented mission, and finally for the orbital flight that Enos flew.

MA-4's successful flight in September had renewed confidence in the Atlas's reliability, and although an Atlas E test carrying a monkey was lost in a launch failure that November, NASA officials assured the public that it was a different model of booster than the Atlas D used for the Mercury program and that that accident had no relevance here. Although MA-4 had performed well, there was still some concern about high vibration levels during the first 20 seconds of liftoff, so the autopilot on MA-5's booster was modified slightly to correct this problem.

Atlas 93D arrived at CCAS on August 12 and was erected on LC-14 October 6. Prelaunch preparation proceeded relatively smoothly, with a number of minor repairs, including a potentially serious problem with the vernier engines not being bolted in place tightly, which could have resulted in damage to the airframe during launch.

The Range Safety system on Atlas 93D was modified so that a manual cutoff command could be sent to the sustainer engine. This was to prevent the capsule from being accidentally boosted into a higher than planned orbit if engine over-acceleration occurred.

A more compact all-solid state telemetry unit replaced the bulky vacuum tube-based package used previously.

Atlas 93D was the second D-series Atlas to contain the new SMRD (Spin Motor Rotation Detection System), designed to ensure proper gyroscope operation prior to launch.

MA-5 was planned as a close approximation of the upcoming MA-6 manned orbital mission. Mercury-Atlas 5 would be launched from Complex 14 at Cape Canaveral on a heading 72.51 degrees east of north. Orbital insertion of the Mercury spacecraft would occur 480 miles (770 km) from Cape Canaveral. The altitude would be 100 miles (160 km) and the speed would be 25,695 feet per second (7,832 m/s). Retrofire was planned to take place at 4 hours, 32 minutes, and 26 seconds after launch. The spacecraft would land 21 minutes and 49 seconds after retrofire. Reentry temperatures were expected to reach 3,000 °F (1,650 °C) on the heatshield, 2,000 °F (1,090 °C) on the antenna housing, 1,080 °F (582 °C) on the cylindrical section, and 1,260 °F (682 °C) on the conical section. The spent Atlas sustainer engine was expected to reenter the atmosphere after 9⅓ orbits.

Spacecraft #9 had originally been intended to fly on MA-4, but Spacecraft #8 was used instead after having been recycled from the failed MA-3 launch. #9 was the second of the "Mark II" Mercury capsules with a larger square window and explosive bolt hatch, while the older "Mark I" capsule had small port windows and a heavy locking mechanism. Gus Grissom's flight on MR-4 had used a Mark II capsule, but it was necessary to test it on a proper orbital mission to ensure that the large window could handle the much higher heat of reentry there.

On October 29, 1961, three chimps and 12 medical specialists moved into quarters at the Cape to prepare for the flight. The name given to Enos, the chimp selected to fly the MA-5 mission, in Hebrew means "man". Enos's backups were (in order of possible call-up) Duane, Jim, Rocky, and Ham (the Mercury-Redstone 2 veteran). Enos was from Cameroon, Africa (originally called Chimp # 81), and was purchased by the USAF on April 3, 1960. He was about 5 years old at the time of flight and weighed just under 40 pounds (18 kilograms).

On November 29, 1961, about five hours before launch, Enos and his spacesuit-couch were inserted in the spacecraft. During the countdown, various holds took 2 hours and 38 minutes. Liftoff came at 15:08 UTC. The Atlas launched the MA-5 spacecraft into an orbit of 99 by 147 miles (159 by 237 km). The modified autopilot apparently worked as vibration remained within comfortable levels and the boost phase was uneventful. All Atlas systems performed excellently and there were no performance deviations of any significance. BECO occurred at T+130 seconds and SECO/VECO at T+300 seconds, followed by capsule separation two seconds later.

The turnaround and damping maneuver consumed 6 pounds (2.7 kg) of the 61.5 pounds (27.9 kg) of control fuel aboard. The spacecraft used less fuel than the MA-4 did during the same maneuver. MA-5 assumed its planned 34-degree orbital attitude and after that, through the first orbit the thrusters used only 1.5 pounds (0.68 kg) of fuel to maintain a correct position.

At the end of the first orbit, ground controllers noticed the capsule clock was 18 seconds too fast. As it passed over Cape Canaveral a command was sent to update the clock to the correct time. The Mercury Control Center at Cape Canaveral received information that all spacecraft systems were in good condition.

As the MA-5 passed over the Atlantic tracking ship at the beginning of the second orbit, indications were received that inverter temperatures were rising. The environmental control system malfunction was also confirmed by Canary Island trackers. Abnormal heating had occurred on earlier flights; in such cases, inverters had continued working or had been switched to standby. There was no alarm at Mercury Control. When the spacecraft reached Muchea, Australia, high thruster signals and capsule motion excursions were detected. Other data indicated that the 34° orbit mode was being maintained. When the MA-5 crossed the tracking station at Woomera, Australia, attitude control problems were not detected, so earlier reports were discounted.

Mercury spacecraft # 9, used in the Mercury-Atlas 5 mission, on display at the Museum of Life and Science, in Durham, North Carolina.[3]

The spacecraft and Enos were both found to have survived the mission in good condition, although the chimp had removed all of the medical electrodes and the urine collection device from his body.

On November 4, 1962, Enos died of dysentery caused by shigellosis, which was resistant to antibiotics of the time. He had been under constant observation for two months before his death. Pathologists at Holloman reported that they found no symptom that could be attributed or related to his space flight a year before.

The Mercury spacecraft and Atlas booster had now been qualified to carry a human into orbit.

• Splashdown

 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.