So the I.O.M.proposed that residents be required to get five continuous hours of rest for every sixteen hours on duty.

VOA: special.2009.06.02

So the Institute of Medicine proposed that residents be required to get five continuous hours of rest for every sixteen hours on duty.

VOA: special.2010.07.13

The apparatus which recycles human waste and turns "yesterday's coffee into into tomorrow's coffee needs frequent maintenance and would likely not survive years of continuous duty on Mars", he says.

BBC: Applicants wanted for a one-way ticket to Mars