As a bit of something different here’s a requested article on the difficulties of landing on Mars. If you too have an idea for an article shoot me an email at comfyninja@gmail.com. I would love to research your questions, ideas, or random musings.
Reading through the science fiction of sixties and seventies few planets feature as prominently as Mars. In fact, as early as 1877 it had captured the public imagination, when Giovanni Schiaparelli decided to give the name “canali” to the linear features sketched across his map of the surface- and which English translations decided to render as “canal” rather than the more appropriate “
channel.” Suddenly the world was convinced of life on Mars, a conviction that was only intensified with the 1976 Viking 1 photograph of the
“face” on Mars.
It makes sense, then, that literature set in the future often treats colonization of Mars as foregone conclusion. But here we are, 113 years after Wells’
War of the Worlds and 48 years after Zelazny’s “A Rose for Ecclesiastes” without being any closer to having human settlements on our red neighbor. And while plans may be in the works for a potential 2030’s
human landing those plans are very much still up in the air.
It turns out that there are a couple really good reasons for that. The biggest is that we have no idea how to land safely on the surface.
But wait, someone out there is probably exclaiming, haven’t we landed multiple rovers on Mars just fine? While it is true that the recent Spirit and Opportunity missions have been successful the sad truth of the matter is that 26 of the 43 total missions to Mars have failed either partially or completely. That means that 60% of rovers or orbiters to Mars have gone disastrously wrong, to the extent that scientists still joke about a
galactic ghoul out in the darkness plaguing technology like some kind of space-dwelling gremlin (the WWII kind, not the don’t-feed-after-midnight kind).
And even ignoring the rather dismal mission statistics, which is partially due just to the difficulty of sending technology off to fend for itself for a long seven months, there are three very big differences between a rover mission and a manned one: manned missions are heavier, human beings are fragile, and we want our humans back in one piece.
It makes sense that a manned mission would be heavier, not only does the lander have to carry a person it also has to carry all of their gear, including food, water, air along with the basic scientific devices that would be included on a rover. And if we want to get our astronauts back in one piece they’ll also have to have enough fuel to allow themselves to break free of the planet’s gravity.
But every pound of extra weight added to the package brings us back to the problem discussed above: we have no idea how to land that much weight safely on the surface.
This problem lies in the nature of Mars’ atmosphere. It’s not much more than a thin, cold sheet of carbon dioxide, much less dense than Earth’s. Our own atmosphere is often described as “luxuriously thick” in comparison to Mars. Spaceships re-entering Earth can be slowed to subsonic speeds (below Mach 1) simply by using a heat shield and air resistance and they can reach those speeds while still 20 km above the surface- more than enough time to deploy parachutes or use drag or lift to glide home.
Parachutes can only really be utilized at subsonic speeds or, in the case of new supersonic designs, at Mach 2 at the most. (If you need a reminder of what exactly the speed of sound is or how the Mach measurements work an excellent refresher can be found
here).
But due to Mars’ thin atmosphere there’s something engineers call a “Supersonic Transition Problem.” Basically a heavy vehicle will enter Mars’ atmosphere at about Mach 5, moving much too quickly to deploy a parachute, and has only about ninety seconds before it impacts the surface. Somehow within that time frame the vehicle has to transition to speeds slow enough to not kill its passengers, a difficult proposition when parachutes can’t even be deployed until the vehicle has slowed to Mach 2.
This results in what scientists involved in Mars missions call the “six minutes of terror,” as their precious, expensive devices- to which they’ve devoted several years of their lives- approach the surface.
But while Mars doesn’t have enough atmosphere to allow astronauts to use the same techniques used on Earth, it has too much to allow for use of thrusters like the Lunar Lander used during the Apollo missions. With what atmosphere it does have the plumes thrown up by the rockets at supersonic speeds would cause a chaotic, unstable system of air that would result in forces that would likely destroy the entry vehicle.
To date, Mars landers have gotten around this problem by using airbags that inflate around the rover, bouncing it slowly to a stop. But scientists like Rob Manning, the Chief Engineer for the Mars Exploration Directorate, don’t think that the current airbag design can handle much more weight. Even if it could, a rover wrapped in airbags is still subjected to about 10-20 G’s of force. Much too much for us fragile humans.
But NASA and other space organizations are toying with other options. One such solution to the STP is aerocapture. Essentially an aerocapture maneuver gets the most work out of what atmosphere Mars does have by piloting the spacecraft through a deep dive that burns off speed. Of course, such a maneuver would require proper heat shielding on the spacecraft, but even more frightening is the fact that there isn’t a lot of room for error.
If the dive is too deep the spacecraft will either burn up or, even worse, simply impact the planet at speed. If the dive is too shallow not only will the spaceship not burn off enough speed it will also probably shootright out of orbit and sail off into space- a risky and fuel-wasteful error that, if not a deadly one, would probably at least be a mission-ending one.
To help with the aerocapture scientists are currently exploring new decelerators, including something marvelously deemed the “hypercone.” Reminiscent of a huge donut covered in a skin it would inflate to a cone that would hopefully slow the vehicle to Mach 1.
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| http://www.hdtglobal.com/services/logistics-support/space-recovery/hypercone-decelerators/ |
When combined with the issues of keeping a human alive for- at best- seven months in space (with all the cosmic radiation, kidney stone and zero gravity problems that that entails) it is truly amazing that there are even scientists who are willing to work on these problems and try to make a 2030 deadline.
But then again, that’s what scientists do, isn’t it? Set their hearts and minds on making the impossible possible, while the rest of us sit and whine about how long its taking.
For further reading check out Martian Outpost by Erik Seedhouse, of which google has a preview here.
