TORONTO: A NASA-backed study is exploring the feasibility of lowering the cost of a human expedition to Mars by putting the astronauts in deep sleep.The deep sleep, called torpor, would reduce astronauts' metabolic functions with existing medical procedures."Therapeutic torpor has been around in theory since the 1980s and really since 2003 has been a staple for critical care trauma patients in hospitals," said aerospace engineer Mark Schaffer, with SpaceWorks Enterprises in Atlanta, earlier this week at the International Astronomical Congress here.So far, the duration of a patient's time in torpor state has been limited to about one week.Coupled with intravenous feeding, a crew could be put in hibernation for the transit time to Mars, which under the best-case scenario would take 180 days one-way, 'Discovery News' reported."We haven't had the need to keep someone in (therapeutic torpor) for longer than seven days. For human Mars missions, we need to push that to 90 days, 180 days," Schaffer said.This will allow crews to live inside smaller ships with fewer amenities like galleys, exercise gear, water, food and clothing.The SpaceWorks study, funded by NASA , shows a five-fold reduction in the amount of pressurised volume need for a hibernating crew and a three-fold reduction in the total amount of mass required, including consumables like food and water.The study looked at a two-part system for putting Mars-bound astronauts in stasis and bringing them out.The cooling would be done through an internasal system, which Schaffer admitted is "not very comfortable," but inhaling a coolant has several advantages over reducing body temperatures with external cooling pads.Cooled from the outside, the body is more susceptible to shivering and possible tissue damage, Schaffer notes.Simply stopping the flow of coolant will bring a person out of stasis, though the study included rewarming pads as a backup and to speed up the waking process in case of an emergency.An alternative to having the whole crew in stasis is to have one person awake for two to three days, then hibernate for 14 days.By staggering the shifts, no one person would be in stasis for more than 14 days at a time and one crew member would be awake to monitor the ship, conduct science experiments and handle maintenance chores.More research is needed to assure prolonged stasis is safe, but initial results are promising, Schaffer added.