MISSION LOG – SOL 409
There may be a problem.
We began Sirius 7 with the Whinnybago loaded as it would be, more or less, for the final trip:
ROVER 2 (empty, with extra hydrogen cells) – 3.7 tons
FRIENDSHIP TRAILER (empty) – 14.5 tons
FOOD (110 days supply) – 0.65 tons
BOOSTER SYSTEM (substitute equivalent weight of rocks) – 4.5 tons
SPARKLE DRIVE plus 7 batteries to power it – 0.5 tons
OTHER MAGIC BATTERIES – 0.84 tons
FRIENDSHIP THRUSTER PACKS – 0.12 tons
TOOLS, SCRAP, AIR TANKS FOR SPACE SUIT AND MAV, ETC. – 0.5 tons
CREW, SPACE SUITS, AND PERSONAL EFFECTS – 0.7 tons
14 SOLAR PANELS (NOT COUNTING THOSE INSTALLED ON TRAILER) – 0.1 TON
TOTAL ESTIMATED MASS: 26.11 TONS
To be specific, the trailer’s total loaded mass is a little more than seventeen tons, with Rover 2 carrying the balance.
This load was propelled on ten wheels, eight of which are powered, two of which have the clutch disengaged so they rotate freely. (All the rover wheels have their own built-in electrical motors, rated at roughly fifty watt-hours per kilometer of travel on a normal load. This is more than double the normal load rating, with Rover 2 almost at maximum emergency load and the trailer miles beyond that..) The two rover batteries plus four Hab hydrogen storage cells add up to fifty-four pirate-ninjas to power all of this.
Bear with me. I’m laying all of this out so I can think.
We got a bit of a late start, so the sun was already up before we began rolling. We drove for about three hours, until the battery readouts showed 10% power remaining. (The rover computer is smart and can detect the extra, unauthorized power storage and monitor its charge level. Which is good, for reasons which will become obvious in a moment.) This got us 69.66 kilometers away from the Hab. All well and good, right?
We stopped, unloaded the fourteen extra solar cells from their stacks on top of Rover 2, and set them out for recharging the system. With a clear sky each panel provides 120 watts at peak power. The ongoing cirrus cloud coverage knocked that back a little, but with forty-two out of the Hab’s fifty-four panels with us, we figured we had power to spare. Also, we have the 100 watts provided by the RTG, which isn’t much, but it’s 24/7.
So we retired to the trailer for the rest of the day, gathering in the habitat deck when the sun went down and it began to get uncomfortable in the bridge. I set the alarm for first light, about an hour before dawn, expecting to get up to find a full power system and an easy drive back the way we came to return to the Hab.
Nice theory. Too bad it didn’t quite pan out.
We got up when my alarm went off. I suited up, went outside, picked up the solar panels in the Martian pre-dawn, and got into Rover 2 for the drive home. And that’s when I discovered that the batteries were only recharged up to 70%.
Remember, it took 90% of the batteries to drive seventy kilometers yesterday. And since 70% is less than 90%, we definitely weren’t going to get seventy kilometers today. But, since this was a test, we pushed on anyway. 90% got us seventy klicks, so 60% should get us two-thirds as far, right? Forty-six and two-thirds kilometers, no problem, yeah?
Nope. Barely forty kilometers. And that’s where we are now, as I type this; thirty kilometers from the Hab, and temporarily out of contact with Earth.
I’ve got a lot of questions I need to find answers to. Where did my recharge go? Why is my driving performance fourteen percent less efficient on the second day? And, assuming I find answers, what can I do about it?
I do know one thing: forty kilometers a day is not going to do it. That’s over eighty days- more than half our safety margin for modifying the MAV gone.
So we’re cancelling today’s read-along. No D&D. All of us are doing math and brainstorming solutions to this issue. I’m keeping this log open and using it for, well, kind of the minutes of the meeting. If we come up with good ideas, this will help us remember.
Okay, going forward.
Dragonfly asks how much power each solar cell produces. On Earth, with its almost circular orbit, sunlight adds about 1400 watts of heat energy per square meter of surface. Mars is a lot farther out, and its orbit is a lot more elliptical. Raw solar energy ranges from 500 to 700 watts per square meter. The solar cells turn that energy into electricity we can use at a 10.2 efficiency rate. That means, on a clear, day, each 2 sq. m. solar panel should have a peak power of about 120 watts.
Of course, we aren’t having clear days lately. Cirrus clouds let in most of the sunlight, but not all of it. Also, the northern hemisphere’s summer corresponds almost perfectly with the Martian apisol- that means farthest point from the sun in orbit. Mars is gradually getting closer to the sun, but this hemisphere is tilting away from the sun as we approach the equinox, so it’s kind of a wash, energy-wise.
Fireball points out that estimates aren’t the same as actual testing. Okay, so thing to do: connect one of the power meters in my tool kit to a solar panel and monitor its performance. That will give us an exact measurement.
Starlight Glimmer does some math and works out that, assuming twelve hours of good sunlight, our forty-two solar panels ought to produce a total of 60,480 watt-hours, or more than enough to fill up the batteries without the RTG. Nice idea, except that fourteen of the solar panels aren’t producing while we’re driving. We can’t start driving until there’s at least enough twilight for the ponies to see beyond the range of their suit helmet lights, so some recharge time during the day will be lost to driving.
Fireball asks: doesn’t that mean that the batteries are charging from the twenty-eight solar panels on Friendship while we drive? Good point… come to think of it, damn good point. Let’s think about that for a moment.
It takes at least half an hour after sunrise for the sun to be high enough off the horizon for the solar cells to get a decent current going. Before then the angle is too low and the panels are catching more photons reflected from the atmosphere than direct from the sun. But after that, the current is close enough to peak as makes little difference. And yesterday- and in the prior power test, come to think of it- we started driving at or after that point. That means that, in addition to burning what was in the batteries, we were also using 100 watts from the RTG and as much as 3,360 watts from the solar cells every hour. In three hours, that comes up to maybe 10,380 watt-hours.
I think we just found that fourteen percent efficiency loss. We didn’t lose any efficiency. We were just burning more juice than we thought we were.
This morning we got rolling long before dawn and ran out of juice in a bit less than two hours of driving. The solar cells were putting out negligible amounts of current for about two-thirds of our drive time today, so we didn’t get the benefit of their juice.
Doing the math again. With a normal load, the rover wheel motors are rated for fifty watts per kilometer per wheel, or (with eight drive wheels running) four hundred watts per kilometer, total. But more weight requires more juice. Yesterday’s performance was (I thought) sixty-nine kilometers on 49.6 pirate-ninjas, or in round numbers about 720 watt-hours per kilometer. But it turns out we were probably closer to 60 pirate-ninjas, or roughly 870 watt-hours per kilometer.
More than twice as much energy consumption, for more than twice the rated load. There are a lot of reasons why this could have been different- lack of air resistance, rolling load, Mars gravity, all sorts of other shit- so I never bothered to run this calculation before. But…
… eight hundred seventy watt-hours per kilometer, at seventy kilometers, requires 60,900 watt-hours- call it sixty-one pirate-ninjas. We can only store fifty-four pirate-ninjas at a time, and an all-day recharge cycle gets us not more than 60.5 pirate-ninjas per sol. That’s not sustainable. Either we find a way to use less power in motion, or else we accept a maximum theoretical range of (fifty pirate-ninjas divided by 0.87 pirate-ninjas per klick) fifty-seven kilometers per day.
The obvious answer is to lighten the load. The problem is, that’s impossible. The ship is stripped down to the absolute minimum systems. We need all the magic batteries for emergencies, for magic rations to keep Dragonfly from crawling back into a cocoon, to top off the jumbo batteries for launch day, etc. We’ll have to think of something else.
Anyway, next time we do a dress rehearsal run, we drive without the solar cells plugged into the electrical system until we stop driving for the day. That’ll give a more accurate idea of what kind of daily driving range we can sustain without making changes.
But anyway, yesterday we had nine good hours of sunlight recharge with all solar panels. Let’s say the clouds knock ten percent off their peak performance- it shouldn’t be that much, but let’s say. That should have got us almost 41 pirate-ninjas back in the tank, plus the 5 pirate-ninjas in reserve. And during our sleep cycle, when even the computers are powered down, the RTG should add close to another pirate-ninja. We should have had 46,500 watt-hours in the system when I got up this morning. Instead we had 37,500.
There is an electricity thief somewhere on Mars, and it’s stolen nine pirate-ninjas from us already.
Cherry Berry beats me to my suggestion: make a list of everything, absolutely everything, that draws electricity.
Okay. First are the rover computer and the five Hab laptops, all of which we’re taking along for reasons of morale. If all six are running at the same time, they draw a total of ninety watts, more or less.
The rover life support, with air circulation fans and air sampler, draws an average of twenty watts.
Two Hab light strips for illumination in the ship; twenty watts each.
Rover radio system, about ten watts. It’s on to let us track the Hab beacon when we get within twenty-five kilometers of either the Hab or (at the end of our drive) the MAV. This was NASA’s idea, and it’s an excellent one. Schiaparelli is one of the largest craters on Mars, and the MAV isn’t all that large in geological terms.
Microwave. Or, as I shall henceforth call it, Slayer of Pirate-Ninjas. Twelve HUNDRED watts. We’ve been cooking our potatoes in it, and only three or four potatoes fit in it at a time. And microwaving a raw potato into what we laughingly call an edible condition takes a fucking long time compared to just heating up a pre-cooked meal pack. The three ponies and I ate a combined thirty potatoes yesterday cooked by the Slayer. I’m willing to guess that it ate two entire pirate-ninjas yesterday by itself.
Can anyone else think of anything? No. That’s it.
So tonight we’ll shut everything down except the life support and the rover computer. That’s roughly thirty-five watts, which means the RTG should be recharging the battery system at a rate of sixty-five watts per hour even in pitch black. If it’s anything different, we’ll know we missed something.
So, recap:
Tonight- turn things off, check for electricity thief.
Tomorrow- get back to Hab, reactivate Hab. (Everything’s shut down except for Pathfinder, because the Hab currently has only six solar panels left.) Tell NASA our results and plans.
Two sols after tomorrow- second dress rehearsal run. Drive without solar panels.
After that: fuck if I know.
Meeting adjourned.
You need MOORREEE POWWWEEERRR
9100646 Top Gear Mars: Ambitious but Rubbish... IN SPACE!
Eat raw potatoes, Mark. Problem solved.
Hydrogen fuel cells aren't 100% efficient. They aren't even close to 100% efficient. Is that already being accounted for?
Edit: One suggestion, if they do half of their driving at dawn and half at dusk, that would maximize the amount of driving they can do with enough light to see but not enough to get much from the panels. It all works out the same as far as drain/charge cycles.
Well, it works out the same for the machines. The inefficiently optimized organic units might object to working until it gets too dark to see and then getting up before dawn.
Maybe try to cobble together some sort of solar oven to slow cook the potatoes during the day so they don't have to use the microwave?
Man, after this, Mark should be an honourary part of Top Gear.
So, the homework we get from this chapter in a nutshell:
Why is the rover not performing as efficiently as is should be?
Mark's answer:
How edible are raw potatoes?
YES! PIRATE NINJAS ARE BACK!!!
Dust storm, a regular dust storm has somehow brewed up in the basin that they are in. That’s where the efficiency loss has come in and it explains why the solar panels aren’t charging as much because they aren’t getting as much sunlight.
You must construct additional pylons.
9100674
.... You know, your comment just gave me a stupid/brilliant idea:
THE POTATOES CAN WORK AS TINY BATTERIES
Just string up all the potatoes they're bringing along, and boom! A little bit of free electricity to offset power loss.
I mean, it's electricial engineering for kids; should be right in Marks skill set to rig up a Potato Power Grid
9100681
Just set them on the RTG to bake. They're using it for heating anyways and the heat is still there even if it passes through a potato first.
9100696
As amusing as this would be, potato batteries take very specific materials. Also they produce less than a watt.
Could they use the RTG to boil water and cook the potatoes there? And I mean boil it directly by leaving the RTG in a water tube and let it heat up. Even if it doesn't come to a boil as long as it reaches some 70 to 80 degrees celcius it would soften and cook the potatoes, it would just take a while.
It would save a shitload of power AND help with heating.
9100674
Raw potatoes are not very nice. Not only that they end up not being very caloric (your body needs to spend a lot more energy to process a raw potatoe than a cooked one).
9100706
Copper and zinc, and some wire connectors, essentially. I guarantee you his electrical kit probably has a good deal of those parts.
If Mark can rig up a suit's camera to remotely record the power reading for a solar cell like he did in the book, he can easily make a potato battery.
Also, just because they produce less than a watt individually, if you wired them all together, their cumulative total would produce several hundred watts.
9100699
Some how I can't see 'cooking dinner on the box of death' as something that would fly with anyone involved.
9100679 The book treats the hydrogen cells as batteries- infinitely rechargable, lightweight, but bulky batteries.
Raw potatoes are "delish", just don't eat green potato skin. They are of the nightshade group after all, has that been brought up? What would have been nice would be to use a very large Fresnel lens to bake potatoes. I guess they don't have one? Etch gorilla glass screen protectors with magic?
Oh well.
9100706
IIRC, the potato facilitates the reaction between the dissimilar metals. Doesn’t that mean you’d be leaving metal ions in the food? And a Watt is generous- I’d guess closer to 10 mW.
No matter what we try, we just cant get the Command Module systems to power up again without tripping a breaker somewhere. We need just 1.5 more amps to get through the restart procedure until the consumption drops back to running level.
Faliure is not an option.
9100714
I'd be hesitant to put that thing into water. Especially water with any mineral content, air currents and any humidity would be bad enough to risk corrosion of seals.
9100742
Kris, I’ve figured out why the solar cells are suddenly producing less power. Something that has just screwed Mark and Company royally for making the Hermes on Sol 551. We got a Dust Storm brewing, a global monster something that in a few weeks will make the entire Martian surface look like this and the planet look like this from goddamned orbit!
In case your wondering, the first image came from this article: https://medium.com/@tanyaofmars/dusty-skies-for-opportunity-eff237e4d512
Bottomline, Mark and Company is fucked big time for the making it to the Hermes on Sol 551. Also when will Slephiner Two arrive?
Wrong units, I think...?
Why not cook a bunch of spuds before the drive? Is there some particularly compelling reason to take them raw and cook them just before eating them?
If it's just a matter of not wanting to eat cold cooked potato, then as a few others have suggested they could simply use the RTG as a food heater.
2 m² and 2 square meters are not the same thing.
9100782
Just make some Nothin' Stew.
Boil some potatoes, then add Nothin'
Oh shit, that IS a really big deal... Mark had better find a solution that involves precooking all those taters before he leaves, because if he can save that extra 2 pirate-ninjas/Sol then that'll be a really large step towards minimizing non-travel power draw and therefore maximizing distance traveled per Sol
Lots of good ideas in these comments.
Am I correct in understanding that, in the book/movie, Mark travels only at night and parks and charges during the day?
9100771 Again, going by the novel. Power is almost always measured in watts. Amps are mentioned only in the context of frying forty-year-old space probes.
9100782
Cooked taters don't have a great shelf life compared to raw, which can sit for literal months and still be edible. Cooking them and then packing them up, most of their nutrients will decay over time.
Cooked potatoes will usually stay good for 3 to 5 days in the refrigerator and 10 to 12 months in the freezer. Bacteria grow rapidly at temperatures between 40 °F and 140 °F; cooked potatoes should be discarded if left out for more than 2 hours at room temperature.
Considering they have been seeing temps above freezing, storing the taters in sealed containers in the airlock or in the saddlebags would not guarantee their lifespan. And if they could be cooked and then frozen long enough to last the journey, then you would have to deal with unthawing them before eating them anyways, which would also be a huge draw on the ninja-pirates.
9100726
I was going to say something like what 9100750 said first and better.
9100863
Yeah but "Watts per kilometer" indicates that the rate of energy consumption increases with distance, which I don't think is what you meant. You'd want "Watt-hours" (or something), a unit of energy.
So... Um...
A 2x2 panel will product FOUR times the energy as a 1x1 panel.
Because, you know, geometry.
9100841
Which I never really understood, really; he wouldn't waste power on headlights, and Mars' moons are too small and move too fast to provide adequate moonlight. I don't know how much light a field of stars generates, but I still think it'd be dangerous as hell to travel across an unknown terrain in near total darkness.
If they wind up making a superstring of potato batteries, Mark needs to sing Still Alive until they threaten to fix that.
Then start singing Want You Gone.
9100880
Well, the potatoes used for the batteries can be Fireball's share, then. If he can eat gems, then surely his physiology can handle zinc and copper ions.
Watt-hours I guess?
Watts.
Watt-hours.
Guess they're going to diversify their diet with RTG-fried and RTG-boiled potatoes.
Sixty-five watt-hours per hour (which is just watts )
9100891
The headlights use considerably less power than the panels generate, so driving for an hour with headlights to have the panels out for an extra hour is a net gain.
Also, RTG cooking seems like a decent idea.
Can... Can someone please link to the chapter in which pirate-ninjas were first defined? I'm afraid I don't have quite the late-night brainpower to make the dive myself; this story has amassed a LOT of chapters...
9100755
In the book Mark seals the RTG inside a large sample bag in the surface of Mars and brings it inside, resulting in a vaccum wrapped RTG. He could do the same here and it would keep all the elements out except for the heat.
Just a wild off-the-cuff guess, without any knowledge or experience to back it up...
If the solar panels are hooked up, in the absence of light they might drain small amounts of power.
They would essentially be large diodes. And if I remember correctly, diodes do have a reverse leakage current.
9100727
9100699
9100867
Yeah. Its one of those, "Its theoretically safe....BUT"
People worry about radioactive decay...its a paranoia you cannot shake. And add in Dragonfly's feelings on the subject and no one is eatting anything cooked by that box unless they have no other choice.
9100714
Is this still true though? I mean one thing we have established is most of the bacteria on Earth isn't here. Not none obviously, as humans carry some with them where ever we go, and some will be on the Potato skins and stuff....but we work very hard not to contaminate other planets with Earth Lifeforms.
Will the lack of bacteria and molds in the air make a significant difference to shelf life?
9100897
9100706
9100750
9100880
While true....their is a question of if this is even remotely worth it. Lets look at what the research said.
A Potato battery, if sliced, layered and boiled, according to this article and this article (can't find the original source paper) could power LED lights in a room for 40 days and also be used for simple medical equiptment or a low powered computer. Assuming that the lights for the Rover are just as energy efficient as current lighting, this should be worth it.
We have 2 problems though.
1) The Potatoes need to be kept wet. Soft boiled potatos lower resistance enough for them to be worth it, but if they dry out it stops being the case. On Earth, this is possible....on Mars...its more difficult. ESPECIALLY with limited water.
Secondly, the process destroys the metal that is between the layers of sliced Potatoes. That could be a major problem.
Regardless, its somewhat akin to turning Potatoes into D batteries.
Could be a bad ground somewhere. Actual Winnebagos can have this thing happen where the outer shell gets energized when hooked up to house current.
9100742
Actually, hydrogen battery is a fuel cell and electrolyzer with H2O and H2&O2 tanks. If you rig them, then you could increase their capacity by adding more tanks. Valves are automatic, so while you can tune the safety out to increase peak power output, this will do nothing if they are not on peak power (and they are not, Sirius TR is low-power, after all).
9100646
ye cannae change the laws of physics jim!
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