We now know the fate of OceanGate Expeditions’ Titan submersible, which, it seems, suffered a catastrophic failure while descending to the wreck of the Titanic. It’s a tragic outcome that space scientists are taking every effort to avoid on a long-duration mission to Mars.
A trip to the bottom of the deep ocean shares some important characteristics with a trip to space. The vehicle is small and must provide protection, air and supplies for the crew in an extremely hostile environment that is very hard to reach.
Before the U.S. Coast Guard revealed that debris from the Titan had been found and declared the crew lost at sea, it was thought the passengers might just be trapped in a malfunctioning vehicle.
Two key factors in mounting a rescue operation to the submersible were time — with only 96 hours’ worth of oxygen on board — and distance. The site of the Titanic is 600 kilometres from land and nearly four kilometres below the surface of the ocean, making any rescue mission to the ocean floor next to impossible.
Astronauts on a 480 million-kilometre trip to Mars will take about seven months just to get there, which means if something goes wrong, a rescue mission would take just as long. In an emergency, a Mars crew is entirely on their own.
However, there is one saving grace on a space mission that can bring them back home naturally: using the laws of gravity.
The technique is called free return, where the gravity of a planet or moon will swing the spacecraft around its far side and slingshot it back toward Earth without any action by the crew.
We saw free return used in 1970 when an explosion disabled the the Apollo 13 spacecraft on the way to the moon. The craft was aimed on a precision course that brought it very close to the moon, then followed a natural curve under the moon’s gravitational pull and looped back toward Earth.
Thanks to the survival capabilities of the crew and innovative support from the ground, the astronauts were able to survive the increasingly cold and uncomfortable conditions of the failing spacecraft during their three-day return home.
Early Apollo missions were intentionally sent on free return flight paths. In case something did go wrong, the spacecraft would naturally return to Earth like a boomerang returning to the thrower.
A spacecraft on a Mars mission will be quite large, with enough air, food, water and medicine to supply the crew for years. Assuming a similar free return mission plan, even if the spacecraft loses its propulsion, as long as the life support remains functioning, the crew could survive the seven-month return trip home.
A version of the Mars free return trajectory was portrayed in the 2015 movie The Martian. While on its way back to Earth, the mothership’s crew, led by Commander Wilson (Jessica Chastain), used the planet’s gravity to swing the ship back out to Mars and rescue their crew mate (Matt Damon) — about 15 months after they left him behind.
In his book Mission to Mars, astronaut Buzz Aldrin — who along with Neil Armstrong made the first landing on the moon — suggests permanent spacecraft he calls cyclers that would use the free return boomerang method to continuously cycle the spacecraft between Mars and Earth, acting like commuter trains between the planets.
As we have seen, the risks of traveling to the deep ocean are high. So is a trip to deep space. One reason the technology for a trip to Mars and living on the surface is being carried out first on the moon is because rescue is only a matter of days away rather than months.
Perhaps lessons learned from the Titan tragedy will reduce the risk for future travellers in the deep ocean and deep space where there is always the risk that things can go very, very wrong.
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