Hacking On Mars In “The Martian”

It’s been 6 years since the hacker’s treat of a book, “The Martian” by Andy Weir, was self-published, and 2 years since the movie came out. We’ve talked about it briefly before, but enough time has passed that we can now write-up the book’s juicier hacks while being careful to not give away any plot spoilers. The book has more hacks than the movie so we’re using the book as the source.

For anyone unfamiliar with the story, Mark Watney is an astronaut who’s left for dead, by himself, on Mars. To survive, he has a habitat designed for six, called the Hab, two rovers, the Mars Descent Vehicle (MDV) they arrived in, and the bottom portion of the Mars Ascent Vehicle (MAV), the top portion of which was the rocket that his five crewmates departed in when they left him alone on the inhospitable desert planet. If you haven’t read it yet, it’s easy to finish over a long weekend. Do yourself a favor and pick it up after work today.

Making Water

Watney’s major concern is food. They sent up some potatoes with the mission which will sprout roots from their eyes. To grow potatoes he needs water.

One component of the precious H2O molecule is of course the O, oxygen. The bottom portion of the MAV doesn’t produce oxygen, but it does collect CO2 from the Martian atmosphere and stores it in liquid form. It does this as one step in producing rocket fuel used later to blast off from the surface.

For Watney to get the oxygen from this CO2 is easy. In the Hab is a device called the oxygenator whose purpose is to take in the CO2 exhaled by humans and extract the oxygen. Next he needs the H, in H2O, the hydrogen and that calls for a chemistry hack.

Hacking a Combustion System

Fueling the MESSENGER space probe with anhydrous hydrazine
Fueling the MESSENGER space probe with anhydrous hydrazine

During the crew’s landing in the MDV they hadn’t used up all the fuel, which includes hydrazine, N2H4. Separating the N2 (nitrogen) from the H4 is easy, he just runs it over an iridium catalyst, also available in the MDV. A side effect of the reaction is the release of some leftover ammonia, NH3, but this is mentioned in passing as a nuisance.

3 N2H4 → 4 NH3 + N2
N2H4 → N2 + 2 H2
4 NH3 + N2H4 → 3 N2 + 8 H2

The rest of the rig is neat. He creates a chimney from a space suit’s air hose and arranges it so that the hydrogen (hot from the reaction) rises up it. A flame in the chimney burns the rising H2, combusting with oxygen in the air and leaving water: H2O.

What it actually leaves is humid air which the Hab’s water reclaimer turns into liquid water. The flame itself comes from splinters of wood cut from a religious cross belonging to one of the departed astronauts. Watney ignites the splinter using an electrical spark in the presence of a little oxygen.

Tricking Life Support

His efforts don’t go off without mishap though. He fails to notice that some hydrogen gets past the flame in the chimney and accumulates in the air. On realizing this later he measures the air as 64% hydrogen, a very explosive amount in the presence of oxygen.

So he decides to reduce the oxygen to 1%, and then burn off the hydrogen a little at a time. The problem is that the Hab’s air regulator that decides how much oxygen is allowed in the air won’t let it go below 15%. To trick it, he tapes an oxygen filled bag to one of the regulator’s sensors, at which point it thinks there’s way more oxygen in the air than there is, and proceeds to allow the oxygen to get down to the desired 1%.

Cheating With Radioactivity

GPHS-RTG used in the Cassini probe
GPHS-RTG used in the Cassini probe

The MAV comes with a Radioisotope Thermoelectric Generator (RTG), a generator containing 2.6 kilograms (5.7 pounds) of plutonium-238. This gives off just shy of 1500 watts of heat which it then uses to produce 100 watts of electricity. And of course it contains abundant radiation shielding. Its purpose was to generate power for producing fuel for the return trip. Watney makes use of this easy energy source a few times. To use Watney’s own words, “As with most of life’s problems, this one can be solved by a box of pure radiation” (from log entry: sol 199).

The first time, he uses it is to help heat Rover 2 during an expedition to find Pathfinder, a NASA Mars lander whose mission ended in 1997, the one that contained the first bug on Mars. Using the RTG as a heater turns out to be almost as simple as just sitting it in the rover. However, it makes too much heat, and so Watney uses a hammer to remove plastic sections and solid foam insulation from the rover’s walls, allowing some heat to escape.

RTG heating return cold air
RTG heating return cold air

As story progresses, Watney needs to make a much longer journey to Schiaparelli crater, again in Rover 2 and to have enough breathable air ne must take the air regulator form the Hab along for the ride. As mentioned above, the air regulator analyses the air and controls the amount of O2 and CO2 present. To do that it first does spectroscopy and then separates the gases by supercooling them. Luckily Mars is often cold enough that much of this cooling can be done by simply running the gas to a compartment located outdoors. The problem is that the cold air then has to be reheated so that it can be breathed. And for his long journey in the rover, that would take too much power.

Enter the RTG, that seemingly infinite heat source. Watney runs the regulator’s cold air output hose down into a plastic box where he coils it up and pokes small holes in it. He then fills the box with water and submerges the RTG in the water. The RTG heats the water while the cold air enters via the hose. It then leaves the hose through the small holes, bubbling up through the water, and being heated up at the same time.

Mapping A Dust Storm with Solar Panels

Mapping the dust storm
Mapping the dust storm

During the journey in Rover 2 to Schiaparelli crater, Watney encounters a dust storm in his path. He needs to figure out in which direction the storm is moving and the shape of the storm, so that he doesn’t drive into it where it’s getting thicker.

Since he gets his power from solar panels he immediately looks at the previous day’s power generation and see’s that it was 97% of optimal. Solar power is generated from sunlight and the dust obviously blocks the sun. That gives him an idea of how to figure out the storm’s shape. He’ll make simultaneous solar power generation measurements at different locations in the storm.

For that he’ll drop off a solar panel, drive south 40 kilometers and drop off another one, and then go south another 40 to drop off one more. The amount of power each generates over the same period of time will tell him where the storm is thicker (higher efficiency loss) and thinner (lower efficiency loss).

To do the measurements simultaneously he carefully strips cameras from an extra EVA space suit he’d brought along. His electronics kit includes plenty of power meters, so each camera would film one of those. The cameras insert a time stamp into the lower left corner of each image. That all goes in a sealed container, and to keep it all warm during the Martian night, he has some of the power go through resistors, which heat up. All of this is powered by the solar panels and some backup batteries, also taken from the EVA suit.

Preparing all that takes time, after which he measures how much power his regular solar panels have generated. Power generated had dropped from the previous reading’s 97% to 92.5% of optimal. That tells him the direction the storm is moving, west.

Making his 40 kilometer steps to drop off the panels and then retracing his steps to get them back, he finds the northernmost one recorded a 12.3% efficiency loss, the middle one 9.5%, and the southernmost 6.4%. That means the shape of the storm is such that the thickest part is north of him. He therefore drives south, then continues east as he was doing before.

Sixteenth-Century Global Positioning

A sextant in use
A sextant in use

During Watney’s long journey in the rover, he has to figure out his latitude and longitude without landmarks. Mars’ axis points at the star Deneb. Knowing this, Watney figures out his latitude using a sextant made of a hollow tube for looking through, a string, a weight, and something with degree marks on it.

Longitude, however, has historically been a harder task, having required the invention of an accurate time piece, no mean feat if you want one that works on a rocking ship on an ocean. Fortunately Watney has abundant computers all giving him the current time, and he has the moon Phobos, which orbits Mars in under a Martian day. To get longitude he simply observes when Phobos dips below the horizon and plugs the time into a complex formula he worked out.

Leaving Mars

Perhaps my favorite hack from the book was the ingenious use of solar panels to measure the thickness of the dust in the dust storm. Not that we haven’t seen clever uses for solar cells before, this ball balancing wheel is one such example. What hack struck you as the most clever, or perhaps one that you’ve done yourself, from either the book or the movie? Maybe it was one that we missed? Let us know in the comments and please try to keep the comments spoiler-free or at least give a warning first.

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