Although the periods of high g force and free flight were short, the extremes were considerable, and the changes from one state to the next were rapid. In spite of this, the cardiovascular, hemodynamic, and electrocardiographic phenomena were remarkably well maintained. Apparently the animals were not in serious plight at any time. That psychological factors entered into the observed phenomena is clearly evident from the increase in cardiac rate associated with the noise of the engine prior to liftoff and also from the cinematographic record of facial expressions. Nevertheless, the integrated responses indicated that the animals' physiological states remained sufficiently normal to insure a safe flight.

LITTLE JOE FLIGHTS

The first step in an attempt at animal verification of the adequacy of the Mercury flight program was the development of two tests by NASA in collaboration with the U.S. Air Force School of Aviation Medicine in which there would be a biomedical evaluation of the accelerations experienced during the abort of a Mercury flight at and shortly after liftoff. These flights were launched at the NASA Wallops Station with a Little Joe solid-fuel launch vehicle.

Two Little Joe launches were made with activation of the escape rockets during the boost phase to secure maximum acceleration; only a brief period of weightlessness was attained. The first launch was on December 4, 1959, and the other on January 21, 1960. A 36 by 18-inch sealed, 125-pound, cylindrical capsule containing the subject, an 8-pound Macaca mulatta, the necessary life-support system, and associated instrumentation was flown in a "boilerplate" model of the Mercury spacecraft. The rhesus monkeys were named "Sam" and "Miss Sam."

The flight profile included maximum accelerations of about 10 to 12 g and periods of about 3 minutes at 0±0.02 g. The peak altitude obtained in the last ballistic flight was about 280 000 feet. The experimental capsule was pressurized at 1 atmosphere with 100 percent oxygen at the start of the experiment and fell to just below a half atmosphere of oxygen due to breathing during flight. The capsule temperature was kept between 10° and 20° C in both flights.

The measurements taken from the rhesus monkeys were the electrocardiogram, respiration, body temperature, eye movements, and bar pressing, but only partial results were obtained in the first flight. Oxygen tension, total pressure, capsule temperature, and relative humidity were recorded. Both animals were recovered alive and did not show pathologic alterations in their physiologic and psychological reactions.

MERCURY ANIMAL TEST FLIGHTS

In the Mercury animal test program a Redstone missile carried the chimpanzee Ham on a ballistic flight to a height of 155 miles to provide animal verification of the success with which the Mercury system could be applied to manned flight. The male chimpanzee was trained to perform a two-phased reaction task during the 16 minutes of flight. The chimpanzee Enos was put into orbit for 3 hours and 20 minutes. Results of the two flights gave the following information:

  1. Pulse and respiration rates during both the ballistic (MR-2) 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, both arterial and venous, were not significantly changed from preflight values during 3 hours of the weightless state.
  3. The 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 simulated acceleration, noise, and vibration of launch and reentry were able to maintain performance throughout an actual flight.

From the results of the MR-2 and MA-5 flights, the following conclusions were drawn: