The Orbiting Frog Otolith (OFO) was a NASA space program which sent two bullfrogs into orbit on November 9, 1970, for the study of weightlessness. The name, derived through common use, was a functional description of the biological experiment carried by the satellite. Otolith referred to the frog's inner ear balance mechanism. The Orbiting Frog Otolith Program was a part of the research program of NASA's Office of Advanced Research and Technology (OART). One of the goals of the OART was to study the vestibular system function in space and on Earth. The experiment was designed to study the adaptability of the otolith to sustained weightlessness, to provide information for human spaceflight. The otolith is a structure in the inner ear that is associated with equilibrium control: acceleration with respect to gravity as its primary sensory input. The Frog Otolith Experiment (FOE) was developed by Torquato Gualtierotti of the University of Milan, Italy, when he was assigned to the Ames Research Center as a resident Research Associate sponsored by the National Academy of Sciences. Originally planned in 1966 to be included on an early Apollo mission, the experiment was deferred when that mission was canceled. In late 1967 authorization was given to orbit the FOE when a supporting spacecraft could be designed. The project, part of NASA's Human Factor Systems program, was officially designated "OFO" in 1968. After a series of delays, OFO was launched into orbit on November 9, 1970. After the successful OFO-A mission in 1970, interest in the research continued. A project called Vestibular Function Research was initiated in 1975 to fly a vestibular experiment in an Earth-orbiting spacecraft. This flight project was eventually discontinued, but a number of ground studies were conducted. The research has given rise to several very useful offshoots, including the ground-based Vestibular Research Facility located at ARC. OFO should not be confused with similar acronyms describing the Orbiting Observatory series of spacecraft, such as Orbiting Geophysical Observatory (OGO), Orbiting Solar Observatory (OSO), and Orbiting Astronomical Observatory (OAO).
The OFO spacecraft
The OFO experiment was originally designed for flight within the Apollo Applications Program, which was established to make optimum use of hardware used in Apollo lunar missions. However, because the low acceleration levels needed for the experiment could not easily be maintained in a crewed Apollo spacecraft, an uncrewed satellite was later chosen as a more suitable vehicle. The satellite's design eliminated exposures to acceleration levels above 10−3g (10 mm/s²). This meant that the experimental specimens could experience an almost weightless state. The spacecraft had a diameter of approximately 30 in (760 mm) and a length of 47 in (1,200 mm). The octagonal lower section of the spacecraft housed the electronic apparatus. The upper section, which contained the experiment package, was shaped like a truncated cone. A heat shield covering this upper section protected the experiment during re-entry into the Earth's atmosphere. A yo-yo de-spin assembly was located around the girth of the spacecraft. Four booms, folded against the side of the spacecraft, were located radially around the satellite. After the spacecraft separated from the launch vehicle, the yo-yo despin subsystem slowed spacecraft rotation. The four booms were then released to extend from the side of the spacecraft. The extension of the booms increased the moment of inertia of the spacecraft, permitting the acceleration level to remain below 10−3g.
Orbiting Frog Otolith-A
The OFO-A mission was launched on November 9, 1970 (06:00 GMT) from Wallops Island launch site. 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 American bullfrogs (Rana catesbeiana) were used as experimental subjects in the flight experiment. The bullfrog was chosen for study because its inner ear 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. The frogs were sourced from the Louisiana Frog Company in Rayne, Louisiana. The town was the nation's top exporter of frogs through the early and mid-20th century and already known as the "Frog Capital of the World." Local Congressman (and future four-term governor) Edwin Edwards helped connect the agency with Rayne, six miles east of his hometown of Crowley. A total of 20 Rayne frogs were sent to NASA for evaluation, where they were narrowed to a group of four—two of which would go into orbit and two who would remain as a backup crew. The two space-bound specimens were named Pierre and Tee-Nom ("Little Name," roughly, in Louisiana French). Both flight frogs had electrocardiogram (ECG) electrodes implanted in their thoracic cavities and microelectrodes implanted in their vestibular nerves. The frogs were demotorized by cutting their limb nerves to prevent them from dislodging their implanted electrodes, and to reduce their metabolic rates. With this lowered metabolic activity, the frogs could survive 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.
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