The Maretian

by Kris Overstreet

Chapter 125: Sol 217

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Venkat's brain still sensed the world through a blanket of jet lag, compounded with the exhaustion of traveling halfway around the world. But the job of Project Ares director didn't stop. Thus, only sixteen hours after he had been poured into his bed by a wife he really didn’t deserve, he stood in the doorway to his office, ready to catch up on the work that hadn’t been able to follow him to China.

And he continued to stand there, staring at the five people- three men and two women- who had beat him into his own office. That, and the neat stack of paper next to them on his desk that looked like three or four reams of office paper, unwrapped and piled together. ”Let me guess,” he said. “You’ve discovered another Rich Purnell.”

“Nope.” The voice triggered recognition; the woman speaking was the one who’d taken charge of the Project Sirius tiger team discussions. “Rich Purnell was one guy. This,” she slapped the top of the stack of paper, “took over a hundred people to develop.”

“That’s nice,” said Venkat, for whom a tall venti hadn’t been nearly enough caffeine this morning. “What is it?”

“This,” the woman said, “is what Mark Watney and the aliens have to do to get to Schiaparelli. In detail. Step by step. Complete with suggested alternatives and workarounds if our assumptions of the alien ship turn out to be inaccurate.”

“And the sooner we send all of this to him,” one of the male engineers added, “the better.”

Venkat sighed. It took a motion of his hand to get them to step aside so he could get behind his desk. He dropped his briefcase, slumped into his chair, and said, “Okay, walk me- no.” He powered his computer on, and while waiting for the boot-up process to complete itself, he said, “We’re only three hours ahead of Mars time today. You can walk Watney and his friends through the process yourselves.”


[07:24] JPL: Good morning, everybody! This is Venkat Kapoor, back from China. The Chinese people send you their love and good wishes. How is everybody?

[07:52] WATNEY: Mostly good. Cherry, Spitfire and Fireball are preparing to go to the cave. Hay harvest is in a couple of days, with the potato harvest a few sols later. Starlight and Dragonfly are helping me with Hab maintenance, with the main task being reconditioning the water reclaimer wastewater holding tank. Nobody’s risked injury or death in, oh, whole days now. How’s by you?

[08:18] JPL: Tired from the flight back from China, but working hard on your problems. With that in mind, Mark, I’m handing this computer over to some very smart people who have worked out the details for building what you called the “Whinnybago”. They’re going to give you broad outlines. After that we’re sending you the actual procedures. It should tell you how much work they’ve gone through that the procedures document will likely eat up all available bandwidth for the rest of the day and possibly into tomorrow.

[08:22] JPL: Good morning, Mark. I’m Jennifer Laurence. I’m a senior systems engineer in the Engineering Directorate at JSC. With me are personnel from Astroresources, the EVA office, and Flight Operations. I’ve been chosen as spokesperson for the Sirius Tiger Team.

[08:25] JPL: We’ve spent weeks working on the best way to modify your rovers and the alien ship to get you across Arabia Terra to Schiaparelli Crater. What follows isn’t what we want to tell you; it’s what we have to tell you. This is the best solution we could find out of a lot of rather bad ones. So please be understanding about what you’re about to read.

[8:34] JPL: The main point we worked with is that the cabin space of both rovers isn’t sufficient to carry the six of you and the food you would need for up to 150 days away from the Hab and up to seven in the MAV. And that’s leaving aside the materials, tools, Sparkle Drive, and whatever else you need to make the MAV into something that can get you off Mars and to safety.

So from the beginning we’ve worked on the assumption that we would convert Rover 1 into a trailer with the Rover 1 pressure chamber removed and the forward half of the alien ship mounted onto the chassis in its place. In order to make this work the ship will have to be mounted backwards, with what you call the habitat section facing Rover 2 and the nose section hanging off the back. You’ll need to mount both spare rover wheels on the alien forward landing gear to support the weight. Dr. Kapoor told you this when we began.

The main problem is, our best estimate shows that the trailer, empty and trimmed, weighs not less than twenty tons. We can’t make it any lighter than that using the mock-ups here. One rover could just barely tow a dead load of that weight on a paved highway with not worse than a five degree grade, conditions which exist precisely nowhere on Mars. That means all eight wheels on the two rover chassis will have to be powered. We think we can get away with releasing the clutches on the wheels you put on the landing gear and leaving them unpowered, but that's the only power savings to be had for wheels.

The good news is the heating system you improvised for the Pathfinder trip is just about enough to substitute for all heating systems, which would give a normal unloaded rover tandem system, all eight wheels under power, a range of about seventy kilometers on the flat. But our tests here on Earth show you get only about forty kilometers before the rover batteries run out of juice. Mind you, that’s with the batteries running nothing but the motors, the interior lights, air circulation, controls and computer. (Martian gravity might be less, but the inertia of moving a load from a standing start is the same on any planet.)

So electricity and weight are our two biggest obstacles.

[8:41] JPL: Our limitations for electricity are simple: how much storage capacity can you carry, and how much recharge capacity? Your limiting factor is going to be sunlight. By the time you travel it’ll be autumn, with about eleven hours per day of usable sunlight for solar cells.

On the other hand, we want to reduce your weight. Aside from trimming everything possible from your rovers and the alien ship, the only thing we can do in that department is shorten your travel time and save on food.

Straight-line distance is about 3200 kilometers, and a more reasonable actual driving distance would be 3500. At forty kilometers per day that would take you eighty-eight sols, which is less than our initial 100-sol estimate but still far too long. Our goal is seventy kilometers per day, for fifty days of transit. Based on our initial travel time estimate of 100 days, seventy kilometers per day saves you over half a ton of food, which is important considering how very heavy your total load is.

So that’s where we are- looking for the dead minimum load that can travel seventy kilometers per day and recharge appropriately. That’s what we’ve spent weeks experimenting with to make happen.

[08:44] WATNEY: Hello, very smart people! What have you got for me? I hope you don’t mind if I work while you talk, but the message turnaround is fifty minutes.

[08:45] JPL: With that in mind, we abandoned all thoughts of taking the life support systems from the Hab. The equipment weighs over a third of a ton not counting tanks and expendables, and the energy consumption for six people is simply too high for a mobile platform to sustain. You’ll have to rely on the alien life support systems. It’s absolutely vital that you preserve that system from harm at all costs.

But with that system plus the alien space suits, the Sirius tandem (we voted againt “Whinnybago” here, so we’re calling it Sirius tandem rover) will have air, water, and heat at zero energy cost. That means we can budget ninety percent of the electrical power to movement. and ten percent for everything else.

[08:47] WATNEY: Sure, lay it on me. I’ll wait until you’re done.

[08:51] JPL: Under that budget, the normal two rover batteries and their 18 kilowatt hours per sol would only be good enough for thirty-six kilometers per day. (Our road tests didn’t take into account overnight power costs.) We need to double that. That means stealing three of the remaining hydrogen fuel cells from the Hab. To make that work, the on-board alien ship batteries, which you described as “right out of a U-boat”, need to be removed, as will the passenger bench from Rover 2. Depending on the size and shape of the alien batteries (which are probably heavier than a fuel cell and definitely provide less storage), you can put the odd battery in either place.

That provides 45 kilowatt hours per sol of storage and over eighty kilometers on flat ground of travel range. That amount of power requires the same or greater recharge capacity. Based on your Pathfinder trip, fourteen solar panels was enough to provide 18 kilowatt hours per sol of recharge in twelve hours, counting dusk. Each Hab solar farm panel provides, mid-range, 120 watts per hour during good daylight conditions, for an estimated total 1.3 kilowatt hours per sol. That requires thirty-five solar panels total.

The good news is, even after cutting down the alien ship, our measurements show it to be wide enough to accommodate two rows of solar panels up to the front of the pressure chamber and one row along the nose, all mounted permanently to the roof. The removal of the ship’s outer skin provides ample mounting points and hardware to secure them properly, and the same adapter you’ve used to connect the ship to Hab power can be used to wire the panels directly into the Sirius tandem rover electrical system. Based on that, we estimate you can carry twenty-eight solar panels on the finished trailer alone. The remaining panels, plus whatever surplus you think you can accommodate, will be used as you used them on the Pathfinder trip, carried on the roof in a single stack next to Pathfinder. Procedures on mounting both are in the final report.

[08:56] JPL: That solves the power problem. The other problem is weight. The trailer is already excessively heavy, so we want to limit what else goes into it. Balancing the load between the two chassis will increase efficiency. It should be used for habitat, storage of things that can’t withstand vacuum, the Sparkle Drive core, and as little else as possible. Everything else will have to be stuffed into or onto the rover. That means you’ll have to recycle one of the emergency pop-tents to use its canvas to expand and strengthen your saddlebag arrangement so the extra weight of food, tools, etc. is spread more evenly around the rover’s pressure vessel to prevent its collapsing.

The heaviest things are the alien engines. Those will have to be mounted on the sides of the rover, along with a basket to hold alien batteries and thruster packs. We have a procedure for that as well. It’s ugly, but it won’t touch the pressure vessel- it’ll mount to the chassis as close as possible.

[09:01] JPL: One final note: the Sirius tandem will be tall with a high center of mass, especially in the trailer. To be blunt, it’s tippy as hell. Also, the rover suspension is being stressed past its rating, especially on dynamic loads. At a rough estimate, the total weight of your rig, loaded, with food and passengers, will be thirty-eight tons, twenty-four of which will be the trailer. The manufacturer of the rovers absolutely refuses to sign off on this load. And do I even need to talk about the brakes?

Careful driving is mission critical. Hitting a hole or rock at speed could roll the tandem rover or cause a suspension component to shear. We recommend, if the aliens are willing, that they EVA well ahead of the rover and clear the path of rocks between 20 centimeters and 60 centimeters in height. Boulders taller than 60 centimeters should be avoided whenever possible. Otherwise, we recommend a maximum of two crew in Rover 2, with the remainder either on scout duty or in the trailer.

Those are the high points. Do you have any questions?

[09:29] WATNEY: Thirty-six tons, huh? Well, at least I won’t be pulled over by the Martian Department of Public Safety for an overweight load.

“Kilowatt hours per sol” sounds clumsy. Doesn’t that unit have a name of some kind?

How do I link the life support systems of the alien ship and the rovers? Ditto the electrical systems?

Did you say carry the food outside the rover, in the saddlebags? I just want to be clear on that, that you’re proposing we turn the rover into a rolling food truck for all those snooty foodie hipster Martians out there. Do the procedures include a sign for “Watney and Company’s Home-Grown Taters and Sprouts”?

And finally, “Whinnybago” is a fine name. “Tandem rover” is boring. Next you’ll be calling the Astros the Houston People Who Mostly Fail at Hitting a Piece of Leather and Twine with a Stick.

[09:58] JPL: If the Martian fuzz pull you over, we’ll pay the ticket.

Kilowatt hours per sol sounds fine to us. If you don’t like it, suggest a better name.

Check with the alien engineer and verify that the charging port on the exterior is robust enough to handle the full load of a 45 kilowatt system. It should be. If so, run cables from the tow-hook of the Rover 1 chassis up to the port. Cannibalizing the Rover 1 pressure vessel, plus use of solar farm cables, will provide what you need. Connecting air will be a bit trickier, but it boils down to drilling two holes in the alien pressure vessel, sealing the air cross-feed lines into it, and connecting the air circulation system from Rover 1’s environmental systems to the other side.

The Sirius tandem rover is not licensed for retail sales in any Martian jurisdiction, so no sign is necessary. We do advise you watch out for Martian bears, particularly if they wear hats and/or ties.

And I don’t concern myself with sportsball matters. What other people call the Astros is their problem. But we’re calling what you’re building the Sirius tandem rover.

[10:23] WATNEY: A female engineer with a sense of humor. Marry me.

[10:48] JPL: I’m twelve years older than you are. Talk to me when the aliens give you a time machine. But beware of my ex-husband.

[10:50] JPL: Venkat here. I think we can go ahead with sending the procedure now. Looking forward to hearing about the harvest, Mark. Good luck.

Author's Notes:

This chapter (and the next) is me mostly nailing down the order of things.

If you've seen the movie but not read the book, having NASA give chapter and verse on how to mod the rover seems perfectly natural to you. But in the book Mark loses Pathfinder to an electrical accident on Sol 197 and has to work out very nearly all the procedures for making a two-rover rig that will sustain him for a hundred sols by himself. It's not the liveliest section of the book (which might explain why, after Hermes gets resupplied, Andy Weir has a 150-sol timeskip), but it has some clever moments.

Alas, one of those is not likely to surface here. Since NASA is doing the number crunching, and since the oxygenator, atmospheric regulator, and water reclaimer are all staying in the Hab, Mark has no real inclination to coin the electrical engineering term "pirateninja".

Anyway, this chapter marks a shift in the focus of events. We're now moving away from survival and towards actual rescue, and the time has come for our heroes to begin the preparations for that event. I'll try to make this interesting, but beyond a certain point I'll be skipping sols again for lack of anything interesting happening.

Jennifer Laurence is an original character, not in the novel. Weir really tended to mish-mash how NASA is organized to minimize the number of named characters. JPL, for example, would not be the sole place that all Mars probes were built in a real Ares program. I'm trying to correct that a little, but not so much that it bogs down the narrative.

By the way, when Jennifer says "on the flat" she's not kidding. JSC is about ten to twelve feet above mean sea level, if that, and the land is flat like a pancake for many, many miles. JSC does have a small rock-climbing hill that it used to test smaller rovers, but nothing of a size to test a tandem vehicle over twenty meters long.

Anyone inclined to complain that the electrical expenditure for travel for this weight is far too optimistic: I'm not interested. Looking at various numbers in the book, I'm pretty sure Weir just juggled numbers to turn them from "can't make it" to "can make it". I'm doing the same, because saying, "If you carry the whole damn Hab solar farm you still won't make it in time," isn't going to make for a fun story. This is one of those times when engineering must give way to storytelling.

I either have one standard-length chapter or two short ones in the buffer. I may try to stretch the second one a bit tomorrow, or I may move on.

Next Chapter: Sol 218 Estimated time remaining: 16 Hours, 32 Minutes
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