4. PROGRAMS, MISSIONS, AND PAYLOADS

Skylab 3

MISSION PROFILE: Skylab 3

Mission Duration: 59 days

Date: July 28-September 25, 1973

Life Sciences Research Objectives
To study circadian periodicities during space flight.

Life Sciences Investigations
Regulatory Physiology ( CPE-1, 2)

Organisms Studied
Perognathus longimembris (pocket mouse)
Drosophila melanogaster (fruit fly) pupae

Flight Hardware
Circadian Periodicity Experiment Package
Pocket Mouse Housing Unit

The Skylab 3 mission began on July 28, 1973 when a three-man crew arrived at the Skylab station in a modified Apollo spacecraft. During their 59-day stay onboard the space station, the crew members conducted several experiments, including two life sciences investigations developed by ARC.

Life Sciences Objectives

The objective of the first experiment was to study the stability of the circadian rhythm of a mammalian system during space flight. The other experiment was designed to study the phenomenon of temperature compensation in an insect's circadian rhythm. Because the objectives of the two experiments were similar, they were packaged together as an integrated unit, which remained attached to Skylab for the duration of the mission. The unit was installed in the Apollo command service module.

Life Sciences Payload

     Organisms

     The first experiment used the pocket mouse (Perognathus longimembris) as the experiment subject. This species was chosen for study for several reasons. First, it is easy to maintain in caged conditions. Since it is a natural hoarder, food can be provided freely. It produces water metabolically from its food, and so does not require a supply of drinking water. As a result, feces are produced in small, concentrated amounts. Second, it is well suited for studies of circadian periodicities because it shows remarkable precision in the timing of daily periods of lowered body temperature, or torpor. Third, its small size allows a larger number of subjects to be used in the experiment. Six mice were used in the flight experiment. All were implanted with biotelemeters for monitoring body temperature and activity.

     The other experiment used 180 pupae of fruit fly (Drosophila melanogaster). They were divided into four groups. Flashes of light were to be delivered to the pupae to stimulate emergence of adult flies at different times during the flight. The objective was to determine whether the daily rhythm was disturbed in microgravity.

     Hardware

     Pocket mice were kept in individual circular cages that were placed in a common enclosure. Each cage was lined with porous polyethylene and contained 50 grams of dried seeds. A small fiberglass tube at the center of each cage contained the receiving antennas for the implanted biotelemetry unit. A thermistor monitored the ambient temperature in each cage. An environmental control system maintained cage air pressure at about 700 mm of mercury and the relative humidity at about 20 percent.

     The data system consisted of a data processor, memory, and power supply. It collected data on biological, environmental, and engineering parameters for both experiments. One accumulated activity count and one body temperature reading was recorded every 10 minutes from each pocket mouse for the duration of the experiment. Ambient temperature recordings were made every 10 minutes. Engineering parameters were recorded every 40 minutes.

     Fruit flies were housed in four sealed enclosures. Each enclosure contained a pupa plate that could be warmed to induce hatching, a temperature control system, a programmable stimulus lamp, and a photodetector for counting hatchings. A relative humidity of about 62 percent was maintained at the surface of the pupa plates. The data system was designed to collect data on lamp status, population count and temperature of the housing enclosure and pupa plates.

Operations

Collection of preflight baseline data from the flight and control mice began about 40 days before the mission. The flight mice were placed in flight hardware in dark conditions six days before launch. The hardware was loaded into the command service module two days later.

     The mouse holding unit operated perfectly for the first 30 hours after launch. The fruit fly experiment was initiated, temperatures in the pupa plates were raised to 20°C, and the stimulus lights came on at the appointed time. Unfortunately, about 30 hours after launch a power failure occurred and resulted in the loss of both experiments. The ground controls were operated for about a month after the loss of the flight experiment. The control data was expected to be useful in the event that the function of the flight hardware could be restored, or, in the case that the flight experiment was re-flown, on a later mission.

     The data from the flight mice and the ground control data obtained during the 30 hours prior to the hardware malfunction were analyzed.

Results

     Mice

     The investigators concluded that meaningful results could have been obtained if the animal holding unit had continued to function because the telemeters were able to provide reliable data.

     Fruit flies

     No useful scientific data were obtained because of the power failure.

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Additional Reading

Compton, D.W. and C.D. Benson. Living and Working in Space: A History of Skylab. NASA SP-4208, 1983.

Lindberg, R.G. and P. Hayden. Research on the Properties of Circadian Systems Amenable to Study in Space. NASA CR-137523, June 1974.

NASA. Spaceflight: The First 30 Years. NASA NP-150, December 1991.

Newkirk, R.W., I.D. Ertel, and C.G. Brooks. Skylab: A Chrono- logy. NASA SP-4011, 1977.

Rycroft, M., ed. The Cambridge Encyclopedia of Space. Cambridge University Press, 1990.