Author: Kirk

The two critical problems faced by manned deep space exploration are radiation (discussed in a later post) and microgravity induced bone loss.  NASA has been studying bone loss in astronauts for 50 years and has learned enough about the biological mechanism to develop the successful ARED exercise device and nutrition protocols for the ISS.  These work well for motivated, fit astronauts, but compliance might be problematic for the larger and varied crew of a very long duration deep space mission.  The traditional hard science fiction solution is to use spin to generate centrifugal gravity.  One question is how much spin?  When (hopefully) we have Lunar, 1/6 G, and Martian, 3/8 G, permanent bases we will be able to do comparative bone loss studies.  A rat centrifuge on the ISS could produce additional data.  It is inconvenient to spin an entire spacecraft because of issues with navigation, antenna orientation, maneuvering, and frame stress.  Spinning part of a craft creates problems with seal integrity between the sections.  The internal wheel of the 2001: A Space Odyssey spacecraft was a rather elegant solution to these problems but still represents an unlikely level of technology for the foreseeable future.  It is likely any long duration manned space mission in the next 50 years will need to deal with the problem of microgravity.

The research that resulted in the ARED and also related rat research have shown that it is the lack of resistance to movement or lack of force supporting body weight stressing the long skeletal bones, rather than lack of the internal force of gravity on the bone matrix, that causes bone density loss.

Fully aquatic mammals such as whales, dolphins, and manatees spend their entire lives in a neutral buoyancy environment, effectively weightless.  While the deep dives of whales and the hunting acrobatics of dolphins may or may not give their skeletons astronaut levels of stress, manatees are the original couch potatoes.  In any case, all are fully adapted to their environment.  While none of these animals are remotely suitable for research, it is almost certain that we have DNA samples for all of them which could be sequenced.  We also have DNA for their land based relatives – hippopotami, elephants, and hyraxes – for comparison.

As NASA’s and others’ research into microgravity induced bone loss proceeds, the signaling and metabolic pathways involved along with their associated proteins will be identified.  It would be useful to compare these proteins to the aquatic equivalents to try to identify any adaptive changes.  This might suggest new paths for the pharmaceutical research already underway in rat studies.