Free The Martian by Andy Weir Page B

motion (minus a negligible amount for computer, life support, etc.)
    According to my boring math, moving the rover eats 200Wh of juice to go 1km, so using the full 18,000Wh gets me 90km of travel. Now we’re talkin’.
    I’ll never actually get 90km on a single charge. I’ll have hills to deal with, and rough terrain, sand, etc. But it’s a good ballpark. It tells me that it would take at least 35 days of travel to get to Ares 4. It’ll probably be more like 50. But that’s plausible, at least.
     At the rover’s blazing 25kph top speed, it’ll take me 3½ hours before I run the battery down. I’d like to charge the battery up during the rest of the day. I can drive in twilight, and save the sunny part of the day for charging. This time of year I get about 13 hours of light. How many solar cells will I have to pilfer from the Hab’s farm?
    Thanks to the fine taxpayers of America, I have over 100 of square meters of the most expensive solar paneling ever made. It has an astounding 10.2% efficiency, which is good because Mars doesn’t get as much sunlight as Earth. Only 500 to 700 watts per square meter (Compared to the 1400 those spoiled Earthlings get).
    Long story short: I need to bring 28 square meters of solar cell. That’s 14 panels.
    I can put two stacks of 7 on the roof. They’ll stick out over the edges, but as long as they’re secure I’m happy. Every day, after driving, I’ll spread them out then… wait all day. Man it’ll be dull.
    Well it’s a start. Tomorrow’s mission: transfer Rover 1’s battery to Rover 2.
     
     
    LOG ENTRY: SOL 64
     
    Sometimes things are easy, and sometimes they’re not. Getting the battery out of Rover 1 was easy. I removed two clamps on the undercarriage and it dropped right out. The cabling is easy to detach, too. It’s just a couple of complicated plugs.
    Attaching it to Rover 2, however, is another story. There’s nowhere to put it!
    The things is huge . I was barely able to drag it. And that’s in Mars gravity.
    It’s just too big. There’s no room in the undercarriage for a second one. There’s no room on the roof, either. That’s where the solar cells will go. There’s no room inside the cabin, and it wouldn’t fit through the airlock anyway.
    But fear not, I found a solution.
    For emergencies completely unrelated to this one, NASA provided 6 square meters of Hab canvas, and some really impressive resin. The same kind of resin, in fact, that saved my life on Sol 6 (the patch kit I used on the hole in my suit).
     In the event of a Hab breach, everyone would run to the airlocks. Procedure was to let it pop rather than die trying to prevent it. Then, we’d suit up and assess the damage. Once we found the breach, we’d seal it with the spare Hab canvas and resin. Then re-inflate and we’re good as new.
    The 6 square meters of spare canvas was a convenient 1x6 meters. I cut 10cm wide strips, then used them to make a sort of harness.
    I used the resin and straps to make two 10m circumference loops. Then I put a big patch of canvas on each end. I now had poor-man’s saddlebags for my rover.
    This is getting more and more “Wagon Train” every day.
    The resin sets almost instantly. But it gets stronger if you wait an hour. So I did. Then I suited up and headed out to the rover.
    I dragged the battery to the side of the rover and looped one end of the harness around it. Then I threw the other end over the roof. On the other side, I filled it with rocks. When the two weights were roughly equal, I was able to pull the rocks down and bring the battery up.
    Yay!
    Unplugging Rover 2’s battery, I plugged in Rover 1’s. Then I went through the airlock to the rover and checked all systems. Everything was a-ok.
    I drove the rover around a bit to make sure the harness was secure. I found a few large-ish rocks to drive over, just to shake things up. The harness held. Hell yeah.
    For a short time, I wondered how to splice the second battery’s leads into the main