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The Maretian

by Kris Overstreet

Chapter 109: Sol 193

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MISSION LOG – SOL 193

Went out to the cave farm today. It’s actually warm there now- only a few degrees cooler Centigrade than in the Hab. Apparently sealing the cave properly also insulated it more efficiently. I’ve turned down the remaining space heater. I considered uninstalling it, but even if it is springtime on Acidalia Planitia, outdoor temperatures still hit nearly -80 C at night. We might need that heater in here, and the ones we already pulled out too. Better safe than sorry.

We’re a little more than halfway to the next harvest. The alfalfa is recovering beautifully from the cutting a month ago. The potato plants are prospering, and a few are even flowering. Of course that’s a waste, since we don’t need potato seeds- I’ve kept a few spuds safe from freezing in the Hab just in case, so we can start over. If anything I’d like to see the alfalfa blooming, since we only have about a third of the original seed remaining. I would love to get replacement seed, because the ponies absolutely, positively need alfalfa for continued survival. But no, no signs of flower buds.

Oh, and Cherry Berry’s saplings are bifurcating with amazing speed. They look like they’re a year old, maybe two, already. I could almost believe we might get a harvest out of them before we have to abandon this place. (Not that I’m mentioning that to Cherry Berry, since she spends almost as long with the trees as she does with the hay, never mind that there’s five hundred square meters of alfalfa and only one row of saplings. Whatever keeps her sane and focused is fine by me, and I don’t want to fuck it up.)

After we got back to the Hab I discovered we had some homework from the new team at JSC, who have accepted my suggested name of Project Sirius. Go me! My first step on the ladder of bureaucratic achievement! In five years they’ll be painting my name on Teddy Sanders’ door! Well, no, not likely, since the only things I’ve administered are plants, some Eritrean farmers, and five adorable but unpredictable aliens. But a man can dream.

Anyway, the rest of today was about math and engineering. A lot of the math depends on the procedures NASA sent us for testing the power of Friendship’s engines and maneuvering thrusters. And, of course, all the engineering is about how to actually carry those procedures out.

Here’s how that’s going to work. First we have to dismount all three of the ship’s main engines, complete with the replacement engine bells the ponies stole from the MAV landing stage. I then get to take the three remaining intact landing struts off the MDV and use some scrap metal to make a holding cradle for the engines.

Now, according to the rough unit conversions Dragonfly and I whipped up, each of those engines weighs about one and a half tons, conservative estimate. The large rock sample scale maxes out at 500 kilograms. It’s calibrated to Mars gravity, so the readout will show its mass accurately. We put the scale under one foot of the cradle and, in theory, it will show one-third of the weight of the engine plus the cradle.

In order for that to work, of course, the cradle will have to be perfectly symmetrical and the engine perfectly centered inside it. That means precision craftsmanship. The hammer will have to stay at home and read a book for this one. And then, of course, the cradle will have to be absolutely level after the scale is stuck under the foot, because tipping it will change the center of gravity and throw off the results.

That’s a lot of work, and the numbers will still be fuzzy, but not as fuzzy as they are now. More to the point, this method also gives us the best shot at an accurate measurement of the power of those engines. We’ll have the engine hooked up to a couple of Starlight’s magic batteries and controls from Friendship. We kick the engine on at minimum power and, very gradually, we ramp up the power until the scale reads one-quarter its starting load. We don’t want to go farther than that, because the last thing in the world we want is a liftoff of an engine connected to loose things by long cables.

Once we have a reading of what percentage of full power takes away three-quarters of the weight of the whole, we can extrapolate the maximum power from there. Also, we can monitor the power readout of the batteries and get a good idea of how quickly the power drains out. When that’s done, we power down as slowly as we can before the batteries run out, because we don’t want all that weight coming back onto the scale at once. We can’t fix or replace that scale, and if we fuck it up, our only backup plan is to cobble together a sled, pile rocks on it, and test Friendship to see how good it would do at a tractor pull.

The math as we currently have it is like this: one of Starlight’s batteries will run one of the main engines for about four point four seconds if it doesn’t recharge itself. In the pony universe this wasn’t really a problem. The batteries are also passive energy collectors, and in Pony-land space magic energy is literally everywhere. The thing is, each battery weighs about seventy kilos, so in order to power all three engines for one minute at full throttle, you need forty-one batteries. That’s not quite three tons, or about two-thirds the estimated weight of the engines themselves.

Now, that’s not terrible compared to the weight of a liquid-fueled rocket at takeoff- on the contrary. But the problem is, with a liquid-fueled rocket the ship’s weight decreases the longer you fly, so what’s left becomes more effective. But with magic battery powered flight, the weight remains constant. You’re dragging every ounce the whole flight, and the rocket never gets any more efficient.

So why bother? Because so long as the thrust-weight ratio of the ship these things get attached to is higher than 1, they’re worth having along. It’s positive delta-V, and we’re going to need every bit of delta-V we can cobble together to get off this rock. We estimate that these three engines, at full throttle, could just about allow Friendship as it currently is to hover- an estimated forty-five tons. The three engines plus the batteries for one minute of flight add up to a lot less than forty-five tons, which means all that excess thrust goes into pushing up the rest of the craft- which already has engines with a greater-than-1 thrust-weight ratio.

But, again, that’s seven point four tons, give or take two hundred kilograms, of extra mass on the ship that’s only useful for one minute. After that it’s dead weight. And, of course, adding more batteries for a longer flight also adds more weight, which makes the engines less useful. And, finally, there’s a simple matter of space; all this crap is going to have to be bolted, strapped, or glued to the outside of the MAV, and there’s only so much room for that.

Nobody at NASA has said so out loud yet, but it’s pretty obvious that the only way this works is if we re-use the landing stage. The landing stage engines have a thrust-weight ratio of about 1.1, just enough to land the thing after aerobraking and parachutes have done all they can do. With all tanks full, the landing stage has about three minutes of full power flight. Between the hydrazine monopropellant still in the Ares IV MAV’s tanks, the leftovers in the MAV and MDV here, and maybe a little pony magic, we should be able to get one minute of flight out of it and then activate the first stage ascent engines.

I grant you, one minute of 1.1 plus whatever the pony engines contribute isn’t going to be a hell of a lot of actual speed. But it’s speed we otherwise wouldn’t get.

And the whole point of this rigamarole is this: we need to know exactly, or as close as we can get, how much more speed this will be, so that JPL or JSC or whoever can plan the flight profile of the rest of the launch. We need to know how fast we can expect the MAV to be going when the first ascent stage lights and the landing stage gets dumped. All the other modifications to the MAV- lightening the load, adding fuel, whatever- depend on that information being accurate. Get it too badly wrong either way, and we miss our date with Hermes.

So Dragonfly, Starlight, Fireball and I tiger-teamed that for a while, figuring out how we’re going to build the cradle, dismount the engines and control systems, and so forth. Then I sat down to do some more math, and this is a bit more critical.

Based on the first harvest, the next hay harvest should provide enough to extend the ponies an alfalfa-only diet through Sol 520, taking into account the potatoes they’ve been eating so far to stretch the harvests. We already have more than enough potatoes to carry us through to launch day, even if all the food packs got stolen by Murphy. For food purposes alone, in about three weeks both the cave farm and the Hab farm become superfluous.

But that’s not the only thing we need. The cave provides faster magic recharge now than the Hab, so we store most of the new batteries there until we need them. If we lose the cave, we lose a lot of our magic production. That’s important, because we need roughly five times the batteries we currently have to make the Rich Purnell plan work.

Follow me here. The Rich Purnell plan has the five hundred kilo rock sample bay filled with a new Sparkle Drive. Six batteries is four hundred and twenty kilos, leaving eighty kilos for the Drive itself. Forty-one batteries for one minute’s use of the pony ship’s engines at liftoff. And one battery for emergencies, because God knows Mars isn’t going to stop fucking with us even after we leave.

Forty-eight batteries.

We currently have nine.

And even with the cave, the recharge time from zero to full for those batteries is seventeen sols- and we need at least two full batteries to make up to two new batteries. And sealing the cave a few days ago zeroed out the batteries we have, so it’s going to be another twelve sols before any batteries get built at all- and that’s if we didn’t use any magic at all in the meantime. But we have to use magic, because these tests, dismantling the ship, etc.

Argh.

Sometimes I get the feeling that I’m not really alive. I’m just an animated sprite in a resource-management video game. Balance your magic reserves, food stocks, and sanity level, and see how long you can keep Mark Watney alive! Buy now and get the Pastel Colored Aliens DLC for only $4.99!

If I am a video game character, I wish the user would go online and download the fan-made Dejah Thoris mod. Just sayin’.

Author's Notes:

I have to go back into town tomorrow for blood work. Which is going to be so much fun, considering that I'm phobic of needles.

I think today's Watney infodump is clear enough to not require explanation.

I just got the commissioned artwork of the castaways back from TexasUberAlles aka Jason Meador. I'll post it soon, but not today and likely not tomorrow.

Next Chapter: Sol 194 Estimated time remaining: 18 Hours, 49 Minutes
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