MISSION LOG – SOL 418
It’s been a little while since my last entry, but I’ve been busy, what with hunting down electrical leaks in the Whinnybago, helping do pre-trip physicals, and doing other prep work. So I’ve got a lot of ground to cover to tell you how I got where I am now, which is back in the Hab after another attempt at Sirius 7.
It really helps that the skies are clear again- well, except for the fact that it’s now considerably colder in the Whinnybago at night. The RTG and the insulation in the habitat compartment help with that, but this morning we woke up in a cuddle-pile, and we definitely didn’t go to sleep that way. And getting up and suiting up in the chill was no fun at all, let me tell you. But it’s not really uncomfortable yet, so we’re dealing with it.
Over the past week I’ve been monitoring the noontime power output of the solar cells. On Sol 410, with the clouds still in full effect, the panel I tested put out 108 watts at high noon. Today, Sol 418, with the sky clear except for the normal pink haze, we got 122 watts. That’s excellent news. So long as we have this kind of weather, we’ll get maximum recharge out of the system.
Over the past week we went over the electrical system of the Whinnybago twice and Rover 2 once. We found four bare spots on the wiring and one outright break (in a nonfunctional system, obviously), not counting the four entire wiring harnesses we removed because nothing they led to still functioned. We didn’t throw them away, though; they got added to the scrap and tools in the back of Rover 2. There are so many potential uses for wire that I just don’t want to part with it unless I have to.
Between that inspection and double-checking that the remaining cut ends are both switched off and insulated, we’ve secured the circuits about as well as we can do without actually dismantling the pony ship. I mean, more than it already is. The thing already looks like it spent six months at a U-Pull-It parts wrecker yard.
And, finally, we performed the two tests for Sirius 7B. Yesterday we left the Hab on a full electrical charge, one hour before dawn, with the harness for the solar panels on the roof of the trailer disconnected, so that only the RTG was still putting power into the system. Everything else, of course, was pulling power out. We ran until the power readings read 10%, which means more or less 48,600 watt-hours consumed. Distance traveled: fifty-seven and one-ninth kilometers, for a consumption rate lowered to 850 watt-hours per kilometer, probably thanks to the power leaks we patched.
We reconnected the solar panels, spread out the spares from Rover 2, and spent the day more or less as before. We pre-cooked four days of potato rations before leaving, so each round of taters only required about four minutes to bring from freezing to edible. (Quick thought; if we bring in tomorrow’s potato rations from the saddlebags to thaw each day, we can cut even that in half.) In every other respect we acted just like before- playing with the computers, talking, reading, recharging suits, whatever. And this morning, when we woke up, the battery charge was within 1% of full.
Yeah! Go team! Protect those pirate-ninjas!
This led to today’s experiment; drive back the way we came, with the solar panels disconnected again- basically, run all the same conditions as before- with the motor clutches on the rear two wheels of Rover 2 disengaged.
Here’s the logic behind this. The wheel motor systems are designed to produce a relatively low speed but outrageous levels of torque. Bear in mind, Rover 2 by itself hauled the wreck of the pony ship- a weight two and a half times its own. (Okay, it didn’t do it entirely by itself. We had a unicorn and a dragon to help over the gullies. But if the ground had been as flat as it looks from orbit, it would have. And if the ponies had used larger wheels for their landing gear, we could have done it a lot quicker than the one kilometer per hour. Seriously, the Ares rovers are fucking beasts.)
Now, the logic is that electric motors have a flat efficiency curve, i. e. that so long as the load isn’t zero or too heavy for the motor to budge, it’s at or near peak efficiency, and thus pouring all the electricity to one engine or distributing it among four or eight makes no difference. Thing is, that’s not necessarily so. In fact, once the load on an electrical engine drops below fifty percent of its rated capacity, its efficiency drops off. Below twenty percent, it becomes outright shitty.
The reason is friction. Friction constantly steals a bit of any engine’s efficiency- the bearings rub against each other, they rub against the housings, etc. When you lower the load you lower the electricity needed to move it, yes... but you also raise the percentage of the electricity that’s being eaten by that constant friction drain.
And as I said, the engines in each rover wheel are monsters. NASA wanted energy-efficient rovers, but they wanted a vehicle that would be able to climb over bad terrain and get its crew home a hell of a lot more. And the same idiots who gave us safety-glass helmet faceplates and one-use disposable CO2 filters said, “Well, there’s no kill like overkill,” so they gave us motors which could pull England across the Channel and connect it to France, nearly.
I exaggerate a bit, but the key point is that the rover motors are overpowered. That’s a good thing for getting a twenty-six ton load started, but once it’s moving it only takes a little juice to keep it moving. The apparent load drops off a cliff, and friction- aggravated by the excess weight of the Whinnybago- starts going all om nom nom on the efficiency. And telling the computer to cut all power to those motors doesn’t help, because if you do that the motors immediately become dynamos, producing a massive drag on the other engines that more than eats up any power they produce.
Now, of course deactivating two wheels out of eight is not going to give us a twenty-five percent efficiency boost. First, when we’re getting up to speed, all that torque is welcome. As beefy as these engines are, twenty-six tons from a dead start on six motors is a bit above one hundred percent of rated load, so the efficiency takes a hit until we’re up to speed. Also, every time we brake the connected motors regain a bit of the electricity we’ve lost, but the wheels with the clutches disconnected don’t do that. Free-wheeling wheels don’t turn dynamos. So with the six-wheel configuration we lose efficiency both starting and stopping.
And then there’s up-slopes. The six-wheel configuration does not like anything above a one in four upgrade. I actually had to get out four times today and re-engage the two wheel clutches long enough to get us out of gullies we had to cross, because we couldn’t find any banks less steep than a thirty degree angle. When we make the trip for real, that represents lost time, which means lost recharge, which means shorter legs of the trip. It also means wasted energy stopping and then accelerating again.
NASA tried the experiment on the streets of JSC (and that must have been a thing for the tourists to see, though I feel sorry for the engineers who had to move their cars out of their on-street parking). They got an efficiency gain of twelve percent in Earth gravity on perfectly flat streets with no obstacles and little braking or accelerating.
So what did we get? Well, yesterday we got 57.11 kilometers on 48,600 watt-hours. Today we got… drum roll… 60.53. That’s a 5.5% efficiency improvement, 805 or so watt-hours per kilometer instead of 850. After that we recharged for a couple hours and drove the short distance back to the Hab, which we had to drive past before. And here we are.
Five point five percent helps, but not one hell of a lot, especially when you consider there’s going to be a lot of terrain where we won’t be able to move without those two extra wheels. And critically, we drove more or less in our own tracks going back to the Hab in that second test, so at least a bit of that efficiency improvement is down to not having to slow down to pick a way around obstacles. (And there’s going to be a lot more of those where we’re going than there are in Acidalia.)
In short, we can only disconnect two motors if we can count on a really long, mostly level stretch where we can just barrel on through. Otherwise it’s not worth the hassle.
Now, to be fair, the issue isn’t really power consumption so much as power generation. You can put up with shitty efficiency so long as you have fuel to throw at the problem. And we do have an advantage in that right now Mars is getting rapidly closer to the sun, and will continue to get closer during the trip. To make things better, Schiaparelli is almost on the equator- 3 degrees south latitude. That means, if anything, we’ll get a slight gain in power from the solar panels as the trip progresses.
But that’s not enough. We don’t know what Mars will throw at us next. We might break down for days for some reason. We might find an obstacle NASA hasn’t spotted from space that makes us detour. We might have more dust storms- autumn is the beginning of the main dust storm season, as the southern hemisphere warms up and gets really active. We really need that seventy kilometers a day.
So let’s look at current ideal, best-case recharge rates. With eleven good hours of recharge time in a sol, if we use them all we’re guaranteed of a full battery. But my math says there’s very little margin. If we lose more than half an hour of prime recharge time, we don’t start the next day on a full battery.
I say eleven hours, but that’s not precisely true. There’s almost twelve hours of good charging daylight each day. The problem is, I use an hour of it each day for driving, in addition to the pre-dawn drive. If I reconnect the solar cells and drive with constant recharging, I get about 3.6 pirate-ninjas in that hour, or about enough power for three and a half kilometers more. The less efficient charging right at dawn would probably stretch that to four, which requires maybe an extra nine minutes of driving. Push it any farther, and it becomes unsustainable.
I can’t throw more solar panels at this. We only have six spares, and anyway with the saddlebags and roof storage already accounted for there’s no place to put them.
Maybe Starlight Glimmer could stick those solar power catchers she made for the cave farm on top of the panels. Not the same ones, of course. The solar panels are lightweight and can’t stand to have a big fucking slab of quartz sitting on top. But maybe a thin layer of glass…
Maybe I see a way out of this. Yeah. Time to talk to the man with the plan… or the unicorn with the horn… or something.
"Protect those pirate-ninjas!" words to live by.
“Deploy robot-zombie brigade on my mark! Mark!”
“OW! OW! OW! OW! OW! OW! OW! OW! OW! MY SPLEEN!”
“Not on that Mark!”
Watt-hours per kilometer
oh, that made me think of an old commercial, i think it was for Ford trucks, where someone appeared to PULL THE MOON DOWN with a pickup truck!
9106559
It's been so long, I've almost forgotten what that means.
Mark does not want to drive in the dark because headlights eat pirate-ninjas, could there be a magic lighting solution so they can use the full sunlight available for recharge?
Given theres a kilowatt or so body heat inside at night, thats a lot of hull that couldve done with half an inch of insulation, because in space cooling is the problem?
I just get this image of someone going, but they had 14 miles or wire, couldnt they use that for the first few miles extension lead from the Hab, and someone having to go all out on them with The Dilbert Manual to demonstrate just how dumb an idea that is. Apart from the wrong wiring loom?
9106855 No, Mark was saying that the Apollo command module had fourteen miles of wire in it. (And it did. Just in the capsule alone. Not including the LM or the service module.)
Just use the RTG to cook already. Save that power.
9106904
Which is just a fraction of the amount of wire in a Space Shuttle—230 miles!
I can’t remember what the Pirate-Ninja stands for, could I get a re-up?
9106996 Technically, one kilowatt-hour per sol (as in, a fixed and limited energy budget), though Mark is being fast and loose with terminology and using it interchangably with one kilowatt-hour, period.
Pirate-ninjas are kilowatt hours per sol, not kilowatt hours. I think you did that last chapter too.
9106996
Kilowatt hours per sol
9106712
Basically they used geared down Tesla motors, because those things aren't complete overkill for a road car already.
9107094 Doing it deliberately.
9106952
Easier said than done; the RTG tosses out heat via radiator fins spaced evenly around the outside of the main casing; so it makes a decent space heater, but focusing that heat output into a contained area to cook with would be tricky at best, and would require them to mess around with the sealed cylinder of radioactive death. The casing itself may be fairly robust, but if the radiator fins get damaged or broken off, the device would begin to overheat, and potentially suffer a mini meltdown.
9107207
No need to mess with the RTG unit itself. Just put it in a bag, dunk it in a pot of water and let the heat bring it to a boil or a very high temperature. Then use the hot water to boil the potatoes or steam them.
Pretty sure you don't get electric engines, just motors. :)
BTW, the whole chapter appears to be one paragraph if you select it. Maybe due to the italics tags.
My brain is saying that the term for the type of graphed line describing engine efficiency (or any system that experiences marked increases and decreases at the ends) is an "esoteric curve".
I'm pretty sure my brain is wrong.
I do know that the closer that you get to using 0% or 100% of an engine's power, the sharper the decline in efficiency, though the top end decline is much sharper due to how close to 100% you have to get. Which is funky.
Ooh! If they could get crystals to capture light and help concentrate it on the solar panels... No, that's basically just another panel... Hmmm
9107394
Yeah, but it's a panel they can create.
I wonder if they could wire the clutch switch to disconnect it from inside the rover.
9107618 It's not a switch. It's a lug. The only reason NASA thought of to disconnect it under any circumstances was if something broke the engine but left the wheel able to turn freely, so it was engineered to be declutched only from outside.
9106737
They have to save as much magic as they can on the trip because they will need it for the launch. It doesn't help that non-magic environment eats at the charge on the batteries.
whuhh… Are these permanent-magnet DC motors? You'd think NASA would have splashed out for AC induction motors on something like this.
How about just driving faster on the flatlands? instead of slowing down and disabling 2 wheels.
That should get the wheels back into the efficiency curve.
9107176 Yes, but they were mainly local/internal conflicts or wars over old bordering enemies. There were no large international conflicts going on.
And the fear-mongering over Reagan nuking everything was just typical left-wing paranoia, when in fact his policies were what led to the end of the Cold War. In fact, they used the same exact tactic with both Bushes and now Trump. It's getting old and boring because they can't come up with a novel fantasy.
The left gets pissy when their methods utterly fail and it starts to look like their political enemies are going to succeed.
I remember the duck and cover silliness in 81. I was 5, but even by then I thought it all ridiculous. I knew the Soviet Union was dying, because I had paid attention since I was 2. It was the first time I defeated the mainstream media's narrative, and it was hardly the last!
9108007 25 km/h is apparently a locked-in top speed, for what reason I don't know.
Every little bit helps, but some bits are too little to be worth the trouble. Still, the more they know before setting out for real, the better.
9108041
I am surprised the "right" stands behind Trump as much as it does.
That aside, as someone without any political motivation, I think I can let you know a little secret. Nuclear deterrence only works if people believe that the guy in charge would push the button. The more likely he seems to push that button, the more powerful that tool. Instead of complaining about it, thank the "left" for doing its job.
9108509 I recall the media's portrayal. It had nothing to do with 'helping' anyone other than themselves. It was a fear-mongering tactic meant to scare voters. They used the exact same tactic on Barry Goldwater too. It's lame, it's played-out. It's pathetic.
The fact is, the closest we ever came to a full-on nuclear war was under JFK. Had the blockade been breached, the missiles would have started flying immediately.
North Korea is essentially a pest. Pakistan is a far greater threat, since they sponsor terrorism and could at any time let slip a few warheads. Fortunately, they are confronted with India, who will not hesitate to strike if they're attacked.
9108535
Did you expect the media to go: #Our president is a stable, capable leader. Only wants the best for everyone, Is obsessed with pushing buttons, Will kill everyone on the planet at the earliest opportunity.#
My memory if those events is rather spotty, having lived in the wrong continent and at the wrong time.
Besides that, it's important that the job got done, cant speak for the diverse motivations for the individuals doing that job.
9108535 The Soviet Union spent Reagan's first five years in office on 24-7 instant readiness nuclear alert. They were absolutely convinced that Reagan WOULD launch a first strike, based on his rhetoric and his abandonment of disarmament talks. On three different occasions during that period- one incident involving a flock of geese- only the restraint of certain front-line Soviet launch officers saved us from global nuclear war. It is a miracle that we're all alive here now to celebrate ponies who forgive past the point of sanity and always seek to turn the most intractable enemy into a friend.
It wasn't just the liberal media. That's what Reagan looked like to EVERYBODY except his supporters. And it damn near got us all killed on ACCIDENT.
9108650 At the moment it's history. I'm letting it slide because I lived through that history and remember just how scared most of us kids were, despite being in deeply pro-Reagan territory. Spent basically the first fifteen years of my life convinced that the world was about to end- like, tomorrow. So I have really strong feelings about the subject. But I don't intend to go on indefinitely.
A couple of questions
Are they traveling east or west on this trip?
How wide is a time zone on mars?
What’s the range of the sunlight spell? And how small could they be made?
A small piece of quartz paired up with a large collector in the next time zone could be a light weight and reliable flashlight or headlight allowing the crew to travel an extra hour in the morning or evening, wothout drawing on electricity.
They could also place the Hab lights over or near them, running off the solar panels they have to leave behind.
9108689 Nobody seems to complain about JFK, and us nearly ending up in a nuclear war on purpose in a deliberate stand-off.
And that too seemed to be a 'miraculous' salvation. But JFK = A-OK, I know the game. Such as somehow in this modern era blaming conservatives for Vietnam when it was JFK and Johnson who entered the conflict to help France maintain an imperial hold on a nation they were very clearly abusing the heck out of, it and Nixon who ended it and also began to make peace with China.
But I understand. That's the partisan game.
The fact is, both JFK and Reagan played a close game, and both somehow won. But college professors only celebrate JFK, despite Reagan's success going so far as to see the fall of the Soviet Union in its entirety.
9109142 That would be because JFK didn't initiate the standoff. That would have been Kruschev with the nukes in Cuba (which we didn't know at the time were already armed and operational, or that Castro was screaming his head off demanding a first strike). And JFK turned a deaf ear to every general he had, all of whom were ALSO demanding a first strike, and opened up a back channel to negotiate an exchange: no nukes in Cuba for no nukes in Turkey and a promise to leave Cuba alone. In short, JFK defused a situation; Reagan escalated one.
As for LBJ and Nixon in Vietnam, as candidate Nixon directly sabotaged LBJ's efforts, almost complete, to extract the US from active fighting without loss of face. Four years later, he got more or less the same deal LBJ almost had, after bombing Cambodia and Laos and opening the door for the Khmer Rouge to take over the former country. Nixon was no peacemaker; he was an opportunist who saw and did everything solely for personal power and the advancement of his party. LBJ abused power and had no sense when it came to foreign policy, but Nixon was no better- because neither man was strong enough to dare to look weak.
9109211
So, hooray pacifists for not destroying our life as we know it?
9108041
wait wait wait, you were 5 years old in 1981?
You sure that isnt a typo?
9110669
How is that difficult to comprehend?
9110669 I am very old, young one.
I don't look my age because... reasons.
Delightful, advantageous reasons which are going to be very VERY useful to me in 100 years more.
9107401
Yup! Concentrated Photo-Voltaics is a thing, just need to watch out for heat (increases electrical resistance, but it's not too much of an issue on mars)
There might be diminishing returns after a certain point if there is some sort of current saturation in the solar cell, but I'm not an expert.
Hmmmmmm.
In an earlier chapter SG talks about enchantments needing a medium with a regular atomic structure, making crystals ideal.
Well silicon solar cells are crystalline. You can even see the domains in a poly-crystalline cell with your eye.
So are perovskite cells.
Point being that they might take a light receiving/concentrating enchantment directly, without needing extra slabs of quartz.
If they are thin-film, or dye-based, or some novel future architecture though, then I guess not.
ok i have a question and i did this in kerbal on a rover i made why do they just not mount a small thruster to the underside of the whinnybago and use its thrust to lift weight off the wheels... think armaggedon flying drill rover
9114010
Because that would probably kill them. Kerbals and their equipment are ridiculously durable, far more so than most current space capable stuff. I think so anyway.
9121775
Lawn chair, parachute, Kerbal, = perfectly effective re-entry vehicle.
I don't see the problem...
There is nothing wrong about cuddling with cute ponies, right?
Especially of you HugTheBug at the same time.
9121775
Kerbal in a spacesuit = Perfectly capable reentry vehicle.
9114010
Power drain. If it's a human thruster, there's not only electricity but fuel to take into consideration. If it's a pony thruster, that's even worse because it means draining magic, which is going to be in extremely limited supply. That's assuming the TWR of the system is anywhere above 1, and you're proposing they do it in essentially giant leaps. In which case they risk destroying the suspension on landing. Shock loads and stuff. It's even worse if the TWR is less than one, because then the power drain is gonna be constant. I just don't see any way that sort of setup has a positive cost-benefit ratio.