The two chimpanzee flights in Project Mercury were to reveal significant medical data. The suborbital flight of Ham was without complications, but it was considerably less complex than Enos’ orbital flight.

In the Mercury-Atlas 5 (MA-5) orbital flight, Enos performed a complex multiple operant task as lie twice orbited the earth. The 42-pound subject, whose age was estimated to be 63 months, had been exposed to simulated launch accelerations on the centrifuge at the University of California. He had also served as a subject for a laboratory model of a 14-day flight. Over a 16-month period he had received a total of approximately 1,263 hours of training, of which 343 hours were accomplished under restraint conditions in a model of the actual couch used in flight.⁶
 
According to Henry, the results of the two animal flights (Ham and Enos) showed that:

(1) Pulse and respiration rates, during both the ballistic (AIRS) and the orbital (MA-5) flights, remained within normal limits throughout the weightless state. Effectiveness of heart action, as evaluated from the electrocardiograms and pressure records, was also unaffected by the flights.

(2) Blood pressures, in both the systemic arterial tree and the low-pressure system, were not significantly changed from preflight values during 3 hours of the weightless state.

(3) Performance of a series of tasks Involving continuous and discrete avoidance, fixed ratio responses for food reward, delayed response for a fluid reward, and solution of a simple oddity problem, was unaffected by the weightless state.

(4) Animals trained in the laboratory to perform during the simulated acceleration, noise, and vibration of launch and reentry were able to maintain performance throughout an actual flight.

(1) The numerous objectives of the Mercury animal test program were met. The MR-2 and MA-5 tests preceded the first ballistic and orbital manned flights, respectively, and provided valuable training in countdown procedures and range monitoring and recovery techniques. The bioinstrumentation was effectively tested and the adequacy of the environmental control system was demonstrated.

(2) A 7-minute (MR-2) and a 3-hour (MA-5) exposure to the weightless state were experienced by the subjects in the context of an experimental design which left visual and tactile references unimpaired. There was no significant change in the animal's physiological state or performance as measured during a series of tasks of graded motivation and difficulty.

(3) The results met program objectives by answering questions concerning the physical and mental demands that the astronauts would encounter during space flight and by showing that these demands would not be excessive.

(4) An incidental gain from the program was the demonstration that the young chimpanzee can be trained to be a highly reliable subject for space-flight studies.⁷
 

6.  Frederick H. Rohles, Jr., Marvin E. Grunzke, and Herbert H. Reynolds, "Performance Aspects of the MA-5 Flight," ch. 9 in Results of the Project Mercury Ballistic and Orbital Chimpanzee Flights, NASA SP-39, 1963.

7.  James P. Henry, "Synopsis of the Results of the MR-2 and MA-5 Flights," ch. 1 in Results of the Project Mercury Ballistic and Orbital Chimpanzee Flights, NASA SP-39, 1963.