Astronauts in microgravity for extended periods experience a number of maladaptations, including bone loss, muscle atrophy and muscle mass loss, redistribution of fluids, and reduction in immune function. Many proposals have been put forward to use centripetal acceleration to simulate gravity in long duration flights, thereby reducing the astronauts' physical deterioration. Most of these proposals are built around the assumption of simulating 1g, earth surface gravity. The resulting designs are heavy and large enough to eliminate them from serious contention for near-term human spaceflight.
This thinking seems oversimplified to me. Why a full 1.0g? My intuition tells me there may be a step function involved. i.e., bone loss is minimal from 1g down to a threshold value, below which some mal-adaptation trigger point is reached and bone loss jumps up to the high levels we see from 0g.
My question is two-fold.
1) Do we have any data (I'm thinking from mice on a centrifuge in space) correlating mal-adaptation versus artificial gravity in values below 1.0g?
2) How could we most cheaply collect this data, if it does not exist?
Expanding on my second question, my first thought is to put mice into a centrifuge at 0.5g and monitor their urine for calcium. Are there protein biomarkers for space mal-adaptation? Could you collect a sample of urine or blood from a mouse and tell quickly if that mouse is losing bone, losing muscle mass, redistributing fluids, or suffering a loss of immune function? I would love to see a "cheap" research mission with sealed cages of mice arranged along a long rotating tether like a string of pearls, the habitats closest to the counterweight experiencing the least artificial gravity but all other parameters identical, with their collected urine telling a story of how much gravity it takes to keep them healthy. Or have these questions been answered already to our satisfaction?