Uncontrolled tumbling of a spacecraft may result from collision, malfunction or other disabling event associated with the application of a large disturbing torque or breakup of a vehicle. Since there is no preferred axis of rotation associated with such motion, a hazardous environment for in-orbit rendezvous and docking is created for such missions as debris removal and crew rescue operations.

One example scenario might be the collision of a large debris object with the International Space Station (ISS). In such an instance the station would very likely break up, but hopefully, leave the crew in a pressurized segment of the station.

Since attitude control of individual station segments is not designed into the ISS, the dynamical nature of this type of event would almost certainly leave the crew in a tumbling state of motion. This kind of motion was depicted in the film, Gravity.

The expected response by a rescue team would be to rendezvous and dock with the segment containing the crew and evacuate the astronauts. However, no one has ever tried this with a truly tumbling object.

Clearly, the crew compartment would have to be stabilized before a rescue could take place. This scenario may sound far-fetched, but large debris objects frequently pass the ISS within a few miles. Many of these objects are discarded whole and partial upper stages that were once used for the geostationary transfer of communications satellites.

Any attempt to perform a hard docking by a rescue vehicle would certainly be very dangerous, because the ability to execute the required approach maneuvers does not yet exist. The only reasonable approach to achieving a successful rescue will require active detumbling prior to crew extraction. Thus, the stranded crew or rescue vehicle must first eliminate the tumbling motion or transform it into simple spin motion.

To be clear, a collision event of the type assumed here could result in very dramatic tumbling, i.e., high rates of rotation about all three spacecraft axes. The internal dynamic environment of the crew compartment would be violent and the crew would have to be restrained by harnesses.

Any sizable loose objects could become potential lethal weapons as they flew around the crew compartment. This potential scenario is one of the reasons for the ISS crew to evacuate the station and secure themselves in the Soyuz rescue capsules for those occasions when large objects are predicted to pass nearby.

Not every large debris object that passes near the ISS is detected in time to respond. Clearly, any collision between the ISS and a medium-to-large size debris object could easily be catastrophic. However, the assumed scenario here is one in which the crew survives the encounter event, but results in a tumbling crew compartment. Even though a rescue craft cannot stabilize the motion, all may not be lost. Detumbling can be accomplished by transforming the motion into simple spin about one axis.

The use of attitude control jets would be the simplest and most effective approach, but individual pressurized crew compartments do not have these. Another, more logical approach is one that makes use of momentum-exchange devices such as properly oriented spinning rotors or momentum wheels.

However, these are unlikely to be available in our assumed situation. Passive energy dissipation devices are reliable and simple, but they may require long periods of time to absorb enough kinetic energy to stabilize the compartment.

Based on the complexity of the situation and the lack of a workable solution, it appears that one option would be the addition of a yet-to-be-developed autonomous internal system which uses an active movable-mass-with-energy-dissipater to quickly stabilize motion about a single compartment axis. Such a system could be activated upon initiation of tumble and would greatly facilitate crew evacuation after complete despinning is accomplished by a rescue vehicle.

Understanding the dynamics and control of spacecraft is a fundamental requirement for designing space vehicles and operating them. Launchspace offers a course, Spacecraft Dynamics and Attitude Control, that precisely addresses these topics.