Control Groups

Space biology experiments make extensive use of control groups in part because limited flight opportunities may not allow for replication of a given experiment. Employing control groups is essential to increase the statistical validity of the results of an experiment with a relatively small number of subjects in the experiment group. Control groups help researchers isolate the effects of microgravity and the vibration, acceleration, and noise of spacecraft launch and landing from the effects of other conditions that research subjects may encounter inflight, such as altered environmental conditions, and the stress that can be associated with confinement, isolation, implantation of sensors, and biosampling procedures.

Several types of control groups are often employed in space biology experiments. The synchronous control consists of organisms that are identical in type and number to those flown on board the spacecraft. They are housed in identical habitats and kept within a simulated spacecraft environment in a ground laboratory. Conditions within the simulated spacecraft environment, such as humidity and temperature, are set to levels expected to occur within the actual spacecraft during flight. The synchronous control procedures last for a period identical to that of the flight. This control is used to determine whether the effects that may be seen in the flight organisms are the result of anomalous environmental conditions, such as increased temperature, that may have occurred during the flight. Due to time or resource constraints, the synchronous control may be delayed in time compared to the actual spaceflight. This asynchronous control is then similar to the synchronous control except that procedures begin several hours or days after the flight. For the asynchronous and delayed synchronous controls, conditions within the simulated spacecraft environment are identical to those that prevailed within the actual spacecraft throughout the flight.

A vivarium control is usually conducted to determine whether effects that may be seen in the flight organisms could be due to the stress of being confined or isolated or of being housed in flight hardware units. In this control, a group of organisms similar to the flight group is housed in standard laboratory conditions for duration identical to the length of the flight.

Important inflight controls include the use of onboard 1-g centrifuges. Some experimental set-ups also include an on-ground control centrifuge. Scientists have indeed observed some differences between samples on an inflight centrifuge and non-rotated specimens (Schmitt et al. 1996). Although these differences might be resulting from launch effects, cosmic radiation or a pre-exposure of inflight centrifuge samples to microgravity, it is also possible that centrifuge inertial shear artifacts might have caused these differences (see this Chapter, Section 1.2.2). The relative role of the inertial shear forces can be evaluated by comparing the results between the inflight 1-g and the on-ground (1.41-g) centrifuges since, due to Earth's gravity, the on-ground centrifuge generated higher shear accelerations compared to the inflight centrifuge.

Additional controls may be conducted as indicated by specific research concerns. For instance, when the flight research subjects are mammals implanted with biosensors, a control group of similar animals without implanted sensors may be studied to determine whether any effects observed could be the result of the implants.

Figure 3-10. Cosmonaut Salizhan S. Sharipov, Expedition-10 flight, prepares to set up the European-built "Kubik" biological incubator in the Zvezda Service Module of the International Space Station. Photo courtesy of NASA.
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