Book Review: The Martian, by Andy Weir (Spoilers at bottom)

Construction of my ice dredging hut. No other human for 7 miles.

Construction of my ice dredging hut. No other human for 7 miles.

An excellent book for anyone that likes science-based fiction and space travel. Includes spoilers, far down the page. The Martian was a fun read. It was very realistic and everything was based in science or backed up by science and math. Except, as the author acknowledges in interviews, for the initial Mars weather event at the start of the book; but even that could be plausible. I enjoyed the technical details and the decision making processes used by our hero and the people trying to help save him.

I’m glad that this book is currently being made into a movie. Ridley Scott as director is an exciting choice and Matt Damon should be good as the main character.

Go read the book, then give it to a teen.

Spoilers below.
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Spoilers:

A few things in the book, although realistic and believable, were not how I would imagine the situation to play out. I don’t know if a Mars astronaut would have allowed the “Rich Purnell Maneuver” scenario. He could have told them not to do it, with the type of drive they were using, it could have been aborted within weeks of it being initiated. The Purnell Maneuver causes significant risk to his five crew mates, and postpones or cancels the next Mars manned mission. I believe that if I were in his situation, I would have not cooperated with such a move. Instead, the resupply direct to Mars could have succeeded. And even if it didn’t, the hero could have conducted extensive science before he ran out of food and died. He could have made the trek to the Ares 4 MAV with his collected and labeled samples; used his water to add fuel capacity to the MAV. His samples, his spare parts, and his body would be waiting there once the next crew arrived. They would bury his body and use the extra fuel to carry his samples to orbit after their 31 sol mission. And if the food-direct resupply mission did work, yay, he gets to go home.

In the future, I suspect Mars (etc) mission planners will read this and other similar books to influence their designs. For example, in the book it took two months for NASA to realize he was alive because public disclosure laws required the publication of all images within 24 hours of receipt and they didn’t want to show his body. This is a good policy, but there should be an exemption for images of macabre, saying they are not to be released for 20 years. I’m not sure how this would have helped, except that the rest of the crew would have stayed in orbit for a few more hours. And maybe sent down their extra food somehow.

Also, how hard is it to throw in some seeds of edible plants and freeze dried soil bacteria. A few dozen grams. Just for fun. Every mission should bring a mini seed bank, if for no other reason than to leave then in a time capsule on the surface. And maybe add 200 grams for a SSD with a cultural archive. In compressed SD format, modern storage devices could hold more than just one decade of TV and movies.

And what is the deal with sending astronauts up with laptop computers that cannot survive a rapid decompression? There are options besides LCD screens.

As for the RTG, I would not have bothered to put it back. It’s pretty safe, and is a good backup to have around within walking distance for heat and minimal power. He could have left it in the one uninsulated rover.

I know it was fairly unforeseeable, but why didn’t he have some potatoes growing in the rovers? He needed all growing the capacity he could get. This would have enabled him to recover from the hab explosion. I would have kept them in the rover with the RTG.

For the Rovers, I wonder if there was a better strategy than stopping to to recharge for the 13 hours of sunlight. Lets explore:

Solar power, he has 50 panels for the hab, each with a bracket to hold it up at a 14-degree inclination. Each panel is 2 square meters, 10% efficient, that area gets a solar insolation of over 500w/m^2, which comes to 100w per panel.

Battery capacity per rover: 9000whr, he has two rovers

  • Range for 1 Rover with both batteries: 80km/sol (225whr/km), needs 14 panels @13hours to recharge
  • Range for 2 Rovers Loaded on rough terrain: 50km/sol (360whr/km), needs 14 panels @13hours to recharge
  • Range for 2 Rovers Unloaded on easy terrain: 60km/sol (300whr/km), needs 14 panels @13hours to recharge
  • Limiting factor is battery capacity. Hab batteries are too big to fit without chopping up the rover.

Lets consider mounting the solar panels in useful configurations while driving. The author does not say the shape or size of the rover or the panels, just saying the panel area and that two fit on the roof of each rover, overhanging on each side. Later, he stores two panels per side of the rover, using brackets he added. Let us consider towing the second rover, this gives us double the surface area and requires only 33% more energy to pull, unloaded. Lets use the 100w RTG to power the rover headlights and internals.

  • Roof: 2 panels each, 2 roofs = 4 panels @ ok angle => 400w
  • Side: 2 panels each, 4 sides = 8 panels @ poor angle =>400w to 600w
  • So 12 panels is 800w to 1000w, @300w/km = 2.6kph to 3.3kph, for 13 hour sunlight = 34km to 43km per sol
  • Or 20 panels (stack 2 deep on all 4 sides, plug in exposed panel) takes 18,000whr/(20*100w) = 9 hours to charge, 60km/sol plus 4 hours of sunlight driving at 2.6kph to 3.3kph, adds 10km to 13km for a total of 70km/sol. Still less than the 80km/sol he got in the book.

Lets assume he can make a roof rack out of the panel frames, the rover benches, and struts from the MDV and MAV. These roof mounts are large enough that each panel overhangs the sides a little more than half way.

  • Roof: 4 panels each, 2 roofs = 8 panels @ ok angle => 800w
  • Side: 2 panels each, 4 sides = 8 panels @ shadowed, poor angle =>200w to 600w
  • So 16 panels is 1000w to 1600w, @300w/km = 3.3kph to 4.5kph, for 13 hours = 43km to 58km per sol
  • Or 24 panels (stack 2 deep on all 4 sides) takes 18000whr/(24*100w) = 7.5 hours to charge, 60km/sol plus 5.5 hours of sunlight driving at 3.3kph to 4.5kph, adds 18km to 24km for a total of 78 to 84km/sol. About the same as the 80km/sol he got in the book with one rover.

Looks like one key is to minimize the stationary recharge time by increasing the number of panels. This also increases the setup and take down time, only half can be done in the dark, in order to maximize solar powered sunlight driving. The other key is to maximize solar capacity while in motion.

Lets make the roof racks bigger, 2×3 per roof, overhanging off both sides and both ends. We can drive slower for safety.

  • Roof: 6 panels each, 2 roofs = 12 panels @ ok angle => 1200w
  • Side: 2 panels each, 4 sides = 8 panels @ shadowed, poor angle =>300w
  • So 20 panels is 1500w, @300w/km = 5kph, for 13 hours = 65km per sol
  • Or 28 panels (stack 2 deep on all 4 sides) takes 18000whr/(28*100w) = 6.5 hours to charge, 60km/sol plus 6.5 hours of sunlight driving at 5kph, adds 32km for a total of 92km/sol. Now we are making progress.

I don’t think it’s feasible to mount more than 6 panels to the roof. It could be, I just don’t know the shapes we are dealing with. Driving at half the 25kph battery speed, makes for 4.8 hours of night driving per sol.

Lets work the problem backwards to find out how many panels we would need to mount on the rover to drive the whole 13 hours of sunlight without stopping to setup panels. Overnight RTG power charges batteries enough for the internal functions for the whole sol.

  • For 80km/sol @300whr/km & 13 hours => 6.2kph, 1850w (18 panels), 3×3 per roof, still too many unless we know the dimensions.
  • For 90km/sol @300whr/km & 13 hours => 7kph, 2100w (20 panels with RTG since we don’t need headlights). That’s 40 square meters of panels.
  • For 108km/sol @300whr/km & 13 hours => 8.3kph, 2500w (24 panels+RTG), 3×4 per roof. Now I’m just being silly. With that much overhang, turning may be an issue, depending on the gap between the rovers. Although, if he had a couple masts placed on the centerline of the roof, one towards the front and one towards the back, then lines going out to the roof rack for support, maybe he could pull off this many watts of power. Especially if he placed two panels back to back, vertically against each mast.

Ok, lets say that in addition to the 6 panels per roof, he can store the panels on the sides two wide and three deep. They were designed to stack and so that should be fine. This allows stationary charging with 36 panels, leaving 14 with the hab. He can charge the batteries in 18000whr/(36*100w)=5 hours. Assuming he sets up in the dark and needs 1/2 hour of sunlight to pack them away, this leaves 7.5 hours for sunlight driving. In driving configuration, the panels provide 1500w. At 300w/km = 5kph, for 7.5 hours this is 37km per sol. Plus the night battery driving of 60km is a total of over 97km/sol. Now this is enough to shave some time off the trips. Of course the Pathfinder would take up the space of one roof panel, so it would only be 93km/sol.

Solar powered driving would have also saved him from backtracking to determine the direction of the dust storm, because he would have been able to read the panel output in real time, at several select times a day for a couple days. Also, the slow driving would have reduced the chance and severity of his crash. Although longer driving time and fatigue could have increased this risk.