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The OFO-A mission was launched on November 9, 1970. The satellite carrying the OFO-A experiment remained in orbit for almost seven days. Recovery of the spacecraft was not planned. The payload was the Frog Otolith Experiment Package (FOEP).
The objective of the experiment was to investigate the effect of microgravity on the otolith, a sensory organ that responds to changes in an animal's orientation within the Earth's gravitational field.
Two bullfrogs (Rana catesbeiana) were used as experimental subjects in the flight experiment. The bullfrog was chosen for study because its labyrinth is very similar to that of humans. Since it is an amphibian, preflight surgery could be performed above water, but it could be kept in water during the flight. The water medium served to cushion the vibration and acceleration of launch, and to facilitate gas exchange with the organisms.
Both flight frogs had electrocardiogram (ECG) electrodes implanted in their thoracic cavities and microelectrodes implanted in their vestibular nerves. The frogs were demotorized to prevent them from dislodging their implanted electrodes, and to reduce their metabolic rates. With this lowered metabolic activity, the frogs could survive in good health without being fed for as long as one month. Immersion in water allowed the frogs to breathe through their skin. The water medium also helped to move carbon dioxide and heat away from the animals.
The flight hardware unit, the FOEP, was a pressure-tight canister containing a water-filled centrifuge that housed the two frogs. The centrifuge was a cylindrical structure that rotated the frogs' heads at scheduled intervals. The FOEP also contained a life support system which could maintain a regulated environment for the frogs. This system consisted of two closed loops, one containing liquid and the other containing gas. The interface between the two loops was a selectively permeable silicone rubber that acted as an artificial lung. Oxygen passed through the membrane from the gas to the liquid side, and carbon dioxide from the liquid to the gas side. The frogs were immersed in the liquid loop. A pump circulated oxygen through the gas-containing loop. Carbon dioxide entering the gas loop was removed by an absorbant and the purified oxygen returned to the ump for recirculation. A water evaporator and an electric heater maintained the water temperature at about 60šF. An amplifier system in the FOEP increased voltage output from the microelectrodes implanted in the animals to the level required by the telemetry apparatus.
Surgical preparation of the flight frogs was completed about 12 hours before launch, and the animals were sealed inside the FOEP. A backup FOEP was also prepared with similar specimens. The flight FOEP was installed in the satellite about three hours before launch. The flight hardware unit, the FOEP, was a pressure-tight canister containing a water-filled centrifuge that housed the two frogs. The centrifuge was a cylindrical structure that rotated the frogs' heads at scheduled intervals. The FOEP also contained a life support system which could maintain a regulated environment for the frogs. This system consisted of two closed loops, one containing liquid and the other containing gas. The interface between the two loops was a selectively permeable silicone rubber membrane that acted as an artificial lung. Oxygen passed through the membrane from the gas to the liquid side, and carbon dioxide from the liquid to the gas side. The frogs were immersed in the liquid loop. A pump circulated oxygen through the gas-containing loop. Carbon dioxide entering the gas loop was removed by an absorbant and the purified oxygen returned to the pump for recirculation. A water evaporator and an electric heater maintained the water temperature at about 60°F. An amplifier system in the FOEP increased voltage output from the microelectrodes implanted in the animals to the level required by the telemetry apparatus.
The centrifuge was activated as soon as possible once the satellite was in orbit and stabilized at 10-3 g. The centrifuge applied gravity stimuli in cycles. Each cycle lasted about 8 minutes, and consisted of the following: a 1-minute period without acceleration, an 8-second period when rotation slowly began, 14 seconds of constant 0.6 g,an 8-second period when rotation slowly stopped, and a 6-minute period when aftereffects of rotation could be measured. Cycles were performed every 30 minutes during the initial 3 hours in orbit,and less frequently during the rest of the flight.
The OFO experiment continued until the seventh day in orbit, at which time the onboard battery failed. Recovery of the OFO spacecraft and FOEP hardware were not required.
The experiment was successful. ECG indices showed the flight frogs to be in good health during the entire flight. Vestibular recordings were made as expected. Two equipment malfunctions occurred during the flight: pressure in the canister increased to 11 psi, and the temperature decreased to 55°F for nine hours. However, control experiments performed on the ground showed that these malfunctions had little effect on the outcome of the flight experiment.
Several vestibular response changes were noted during the early period in weightlessness. All of the observed changes reverted to normal during the last 10 to 20 hours of the flight, suggest adaptation.
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Anonymous. OFO-A Conclusive Report. Istituto di Fisilogia Umana II, Milan, Italy, unpublished report, May 1977.
Gualtierotti, T. The Orbiting Frog Otolith Experiment. AGARD CP-61-70, September 1970.
Gualtierotti, T. and F. Bracchi. OFO Experimental Techniques and Preliminary Conclusions: Is Artificial Gravity Needed During Prolonged Weightlessness? Life Sciences and Space Research X, Proceedings of the 14th Plenary Meeting of COSPAR, Seattle, Wa., June 21-July 2, 1971, Akademie-Verlag, Berlin, 1972, pp. 121-132.
Gualtierotti, T., F. Bracchi, and E. Rocca. Orbiting Frog Otolith Experiment (OFO-A): Data Reduction and Control Experimentation, Final Report. NASA CR-62084, January 1972.
NASA. Orbiting Frog Otolith/ OFO-Project Press Kit. NASA News Release No. 70-132, 1970.
Space General Company. Orbiting Frog Otolith (OFO) Satellite Mission Performance Report. NASA CR-62083, December 1970.