MISSION LOG – SOL 522
We’re turning water into rocket fuel. It’s easier than you’d think.
Yesterday we finished the last bit of modifications on the exterior of the MAV, when I very carefully installed the pony thruster systems on top of the holes left by removing the secondary maneuvering thruster systems. The last bit of undesired interior equipment, the tertiary communications system, is getting removed by Dragonfly and Fireball today. After that all that’s left is installing the three remaining pony flight couches, then the two RTGs- and that last item won’t happen until the day before launch. We need the heat from at least one RTG for sleeping at night, and the MAV makes the Whinnybago look like a blimp hangar by comparison. So with the major work done, we’re moving on to secondary tasks like extra fuel.
All you need to separate oxygen and hydrogen from water is electricity and two electrodes. The problem lies in collecting the hydrogen. One early design for the MAV actually had an electrolysis plant included as part of the fuel plant. The MAV would launch with a fuckload of water to split apart to get hydrogen, which it could then use to make rocket fuel. It would get the carbon for the fuel from carbon dioxide, which is mostly what Mars’s athmosphere is made of. The oxygen would be stored as oxidizer for the fuel, with excess oxygen being vented into the Martian air.
Unfortunately for me, a clever boffin found a way to apply the oxygenator tech to replace the old system of converting water and carbon dioxide into fuel and oxygen. Instead the fuel plant splits apart carbon dioxide and takes stored hydrogen to make methane. The CO2 provides enough oxygen for the fuel oxidizer and no more, which means no wasted mass being sent to Mars. Even with the super-insulated storage bottle for the molecular hydrogen and the inevitable leaks and losses, the new system ended up less than half the mass of the old, simply because about 91% of the reactant weight at launch had been eliminated.
The upshot of all this is, the MAV fuel plant can’t accept water directly. It has no electrolysis unit and no ability to separate oxygen from hydrogen. All I can do is swap out empty hydrogen tanks with full ones, feed it electricity, and watch it work.
Fucking mass-conservation obsessed NASA engineers. How could they not have known that some dumb schmuck would be stranded for years on Mars and suddenly need to make enough fuel to top off the fuel tanks in order to make a lunatic lunge at an escape-velocity rendezvous with a rescue ship? It’s such an obvious scenario that could happen to anybody, after all. No excuse.
But since the fuel plant can’t isolate hydrogen for us, we have to do it the complicated way. Fortunately, we have a small air tank compressor built into Rover 2. It’s what vents the airlock when it cycles, so that we don’t waste precious oxygen and nitrogen on Mars, ungrateful world that it is. It’s a simple trick to get that pump to suck up the entire contents of Rover 2’s interior into its tank instead of just the airlock.
But doing that gets us a bunch of mixed gases. That’s no good. And since we have no equipment that can un-mix gases, naturally we turn to magic for the solution. In fact, we’re using almost the same spell that we used to purge the methane from the cave farm. (Except, of course, we’re being much more careful, since we can’t afford to rip this airlock out from its frame.)
Here’s how it works. We isolate Rover 2 from the trailer and depressurize it. Then we use that tanked air to return the rover interior to about a quarter of an atmosphere. We need some air pressure, or else the water will just boil off before we can electrolyze it. Then we take a plastic box full of water (filled from the pony life support spigot), drop a couple of electrodes in it, and let it run. At the end we have an atmosphere that’s roughly ten percent hydrogen by weight, most of the rest of it being molecular oxygen. We can read that on the rover’s atmospheric analyzer.
If you’re thinking that this basically turns the inside of Rover 2 into a bomb, you’re right. And if you’re wondering where Starlight Glimmer and I are standing for all this, well, wonder no more- we’re at Ground Zero. Then Starlight casts her little spell, creating a force field that isolates the atmosphere sensors from the rest of the rover. The force field stops anything as heavy as molecular nitrogen, but molecular hydrogen just flits right through. A little bit of force field flexing later, and the hydrogen just flows into the bubble. The analyzer tells us when we’ve got it going.
Once we have the bubble of 100% hydrogen started, Starlight moves it from the analyzer to the airlock, and we wait until the analyzer shows the hydrogen content of the air in the rest of the rover as less than 1%. Then I activate the airlock air compressor and pump our harvested hydrogen into the tank.
Each box full of water contains about fifty liters, weighing fifty kilograms. That water contains about five and a half kilograms of hydrogen. Each five and a half kilos of hydrogen, fed into the fuel plant, makes about seventy-two kilos of rocket fuel. If we do this for twenty-five sols, once per sol, we get a bit more than 1,400 kilograms of fuel.
Why are we bothering with this, you ask? Hasn’t the MAV fuel plant already filled its tanks? Well, as it happens, the answer is no.
The MAV fuel tanks, first and second stage combined, have a bit of excess volume for both fuel and oxidizer to compensate for the hydrogen the MAV might or might not lose to leaks from leaving Earth until the stored supply is exhausted. The MAV is rated to achieve normal orbit, with normal cargo, on about eighteen tons of fuel, and the fuel plant is calculated to make over nineteen tons to provide a safety margin… but an absolutely full load for the MAV would be twenty-one tons of fuel plus adequate oxidizer to go with it.
Thanks to the ponies, who are being very understanding about us drinking their planet dry, we have an infinite supply of water to electrolyze. With the solar cells on the Whinnybago, we have enough power to supercharge the fuel plant systems to make it run much faster than normal. Normally the fuel plant only makes about forty to forty-five kilos of fuel per day. Extra power lets us double that. We could go a lot higher without risking a burnout or accident, but we don’t need to. One electrolysis session gives us enough hydrogen for seventy-two kilos, and we have enough time for that to add up to all the remaining space in the tanks.
That’s our only safety margin. With all the stuff we’ve ripped off the MAV, almost anything that breaks from now on means we’re fucked. But we’ll have ten percent more delta-V (not counting the magic boosters) than we otherwise would, which means if we lose a rocket engine or magic booster, we can make up the difference with a longer burn.
In one way it’s a shame we have all the water we’d ever need. I could just as easily electrolyze urine, which is mostly water. Then, for the rest of my life, I could brag about being so tough I pissed rocket fuel. But then, I think my guests are just as happy we don’t have to do that. It smells bad enough in the Whinnybago as it is without adding the smell of boiled pee.
9205378 The point of the line is that changelings do better when they're the intended recipients of the love, not someone else. That's why "us" is a stress word.
One moon circles.
Im wondering how much research is going into the claim that graphene oxide sheet is totally impervious to molecular hydrogen, even though it seems to be at least totally nonexistant to water vapour.
Also, why ship water to Mars when your Hayabusa class impact rover drones can shotgun the surface and give an idea of subsurface ice distribution, from discoveries since the book?
Wonder how little reinforcing you would need to do to use a methane oxygen Verne cannon melted through the 250 metre thick ice layer in one place? At least for resources, not crew?
"We'll see if it makes a damn come Launch Day."
DUN DUN DUUUUUUUN.
T-minus 29 Sols
Okay. I went to the public library on Saturday and checked out the original book. In two days (about 8 hours of total reading time) I have fully inhaled all 369 pages of Andy Weir's novel. Which means I only have to wait for this to finish. Tomorrow can't come fast enough. Mission Day 687 can't come fast enough. Keep up the amazing work man and I hope you get better.
More fuel is good. As long as not fire balls there.
The one safety margin they have will be their undoing won't it
More seriously, Mars yet again is not quite hostile ENOUGH to solve your problems for you. If it was just a little colder you could rig something up for fractional distillation, separate out the liquid oxygen from the hydrogen. But no, it's too WARM outside for that. Just like Mars has just enough atmosphere to bleed heat by convection and make spaceships burn up on reentry, but not enough to actually help them slow down or let you fly.
"The only time you ever have too much fuel is when you're on fire."
9205402
Put another way, Dragonfly is talking about all changelings as a group in which she counts herself (us) as opposed to speaking only for herself (me).
I'm a little confused here. If they're able to completely fill up the MAV's fuel tanks, why do they need to strip it of excess weight at all?
With a full fuel load it can reach the Hermes normally with all its parts intact, six astronauts, and a half ton of rocks. Here they have an extra full fuel load. Even before adding the pony booster system that should be enough that they could have added a half ton of rocks. Why did they need to remove a couple tons of parts?
In the book he wasn't able to fill the fuel tanks due to lack of time, power, and water.
9205417
ST:TNG, I get that reference!
9205488 Was going to raise exactly this point.
Also, the pony crystal transfer system for water and air *should* be able to transfer pure hydrogen, if they make absolutely sure they use the right suit/faucet/etc.
9205443
So... Keep the dragon away from the fuel plant?
9205488 9205498 The MAV can get to an ORBITING Hermes with a normal fuel load and no modifications.
Hermes is not going to orbit. Hermes is doing a fly-by much too fast to be captured by Mars's gravity well.
The MAV is getting stripped down AND extra fuel AND the magic boosters to make damn sure that the MAV can reach escape velocity and rendezvous with Hermes. Lighter ship plus more delta-V equals higher final velocity, and unused fuel means margin for pilot error or breakdowns.
Remember that, in the book, Mark was launched to space in a vehicle that was one short step away from being nothing more than a lawn chair bolted to a really big firecracker. That's how much stuff was ripped off the ship. They didn't get that radical this time because they wanted to preserve a backup option of using the MAV as a Sparkle Drive deep-space ship for a direct run to Earth. The delta-V lost to a heavier ship gets offset by the magical boosters... if they work.
9205498 9205488
The Hermes is in a Solar orbit and doing a fly-by of Mars higher than the parking orbit it would be in on a normal mission. The MAV needs to go past it's designed end point in order to rendezvous with the Hermes.
9205514
how high is the save roll for the boosters and is it one roll for all or is each one a roll?
9205514
If it works? Well that's ominous
9205514 So they're launching the MAV with an *intact* and fueled (semi-kinda) descent stage with their magic repulsor first stage boost. Then they fire the descent stage at altitude to provide additional boost (at the point the repulsorlift is dropping off newtons of thrust), then drop it when empty (and the heavy discharged magic batteries used in the "up" part of the repulsorlift booster) in order to fire the *normal* ascent stage already at altitude and making a good velocity, so that when it burns out, they're in a captureable position with regard to the Hermes, with or without the Sparkle drive. (checks calculator) Hm. I'm guessing from the Nasa website that the MAV is designed for a 667 second boost to orbit. (11 minutes) Add 5 minutes of combined repulsor/descent stage thrust... About right?
(Edit) Calculating a 6 km/sec end velocity using an online calculator, with 960 seconds of acceleration at 6.25 m/s-sq. Mars gravity is 3.7 m/s-sq, so add that and you get an average of really close to 1G (9.8 m/s-sq), so it's not *nuts* to use those vague numbers. (Yes, I know the real numbers will be much different, because initial launch G-forces will be as high as possible in order to maximize the repulsorlift booster plus all kinds of air friction/orbital mechanics/High Math that I'm hopeless at)
Did... did you just IMPROVE upon the original story? I mean, granted ponies are already an improvement, and this whole solution necessitates magic, but still. Pokin’ holes in the original content. Noice!
It would boil until vapor pressure is brought to what it should be at that temperature. Which (for partial pressure) it would do in any case during electrolysis.
They'll also need some stainless steel and something like NaOH. And low-voltage supply (or multiple cells in series)
Well, if we generously assume 10m3 of volume inside the rover and they bring partial pressure of H2 to 1bar, then it would be ~400 moles of ~800 grams of H2 and they need to do their thing 7 times for 5.5kg. And then all that times 25 hoping each time not to trigger it with accidental 20 microjoules. I suspect that even Starlight may be not insane enough for that
BTW, where MAV and hydrogen tank gets power for it's cryocoolers?
For RTG's output of couple kWh per day that looks really a lot.
9205458
Oxygen should be solid at liquid hydrogen temperatures (although it may be well-dissolvable in H2, I don't know for sure).
On the other hand, good old stoichiometric gas 2H2/O2 mixture already detonates at a few km/s, so in case of seeing liquid/solid H2 and O2 together I personally would probably run.
9205678
I just meant cool things down so the oxygen turns to liquid, then bottle the hydrogen that remains. Let the oxygen evaporate, pump into a different bottle, repeat.
9205458
Well, the first parts are still true enough, but the last?
Mars Helicopter to Fly on NASA’s Next Red Planet Rover Mission
9205498 9205488
I don't recall off the top of my head if Weir ever explicitly stated how fast Hermes' flyby of Mars during the Rich Purnell maneuver was, which is the velocity the MAV needed to match to make Watney's rescue possible. We can make some assumptions, though. First, Mars Global Surveyor circled the planet at an altitude of 450 km at a velocity of about 3.4 km/s in its final science orbit, and so makes a good reference for a nominal MAV launch under normal conditions. However, Mars escape velocity is just a tad over 5 km/s, and Hermes came screaming by above that, so even 6 km/s isn't an unreasonable assumption.
Unfortunately kinetic energy is a function of the square of velocity, so an unmodified MAV would have required over four times the amount of fuel a normal launch would once you ran the numbers through the rocket equation. Hence the need for Watney (or Watney + Equestrians) to strip the MAV down to an absolute minimum dry mass in order for it to have any shot at accelerating to beyond Mars escape velocity with propellant tanks sized to merely insert the MAV into low Mars orbit.
I choose to interpret that Watney's comments (in the movie, at least) about being "...launched faster than any human in the history of spaceflight..." refer to his acceleration (peaking at roughly 12g) rather than velocity, because otherwise the MAV has to exceed 11.2 km/s (Earth escape velocity). At that point we're talking about a MAV the size of a Falcon Heavy, Delta IV Heavy, or Saturn V!
Well, this is interesting but i felt like making hydrogen required more than a 9 volt battery and some wires stuck in an air tight water bucket and some method of unmixing the gases.
Also, I'm wondering just what people are thinking now that dragonfly has kind of admitted to being a low key war criminal with vague allusions to said warcrimes being related to something she ate...
Colorful horse logic says she stole candy from a baby and ate it but edgy human suspicion would be more like she stole a baby from a someone and ate them.
On the note of warcrimes, fun fact:. There are statues in china honoring a nazi liason who regularly went around breaking up gang rapes during the rape of nanking. Kinda says how dark a situation is when a Nazi officer ends up being the hero of an occupied enemy force.
9205498
AIUI, every remote life support unit in use by CSP and ESA (Amicitas, Concordia, the joint space station, whatever other spacecraft may be in service at the time, and all the suit life support units) draw from the same set of master transmission crystals in Baltimare. This means switching the air supply to molecular hydrogen (or anything other than the expected Equus-standard atmosphere) would have unwanted side effects for everypony in Equus orbit.
Granted, it’s just a matter of logistics to enchant a new batch of source crystals and distribute replacement daughter sets among the ships and suits, leaving the original crystals exclusively for sending to Mars, but whether Twilight “Must do everything herself” Sparkle considered the notion, much less thought to delegate this task to, say, Moondancer or some other reasonably talented unicorn on the ESA payroll is something only Kris can answer.
Hydrogen has another nasty habit that makes it a poor choice. As the hydrogen escapes through materials, it weakens them as well.
9205425
I'm counting the seconds.
And I bet they are too!
Is Mark an American? Boffin is generally a Commonwealth slang term for scientist. Given the international feel of the team, it's possible that it slipped into common parlance or Mark's an anglophile or I'm entirely off base but Americans generally use egghead or the like. And since my physics level is firmly at high school and I can't chime in on the in depth conversation above, I thought I'd put that out there.
What stops magical aliens from Horseland simply pumping in hydrogen instead of oxygen through their life support?
9205743
It doesn't. Oh well, almost. Takes a spoon of salt per tub to make the water conduct electricity. And unless you use some platinum electrodes or similar, new electrode per batch, as you're getting monoatomic oxygen alongside with the hydrogen, and that stuff oxidizes your positive electrode like crazy.
OTOH, as for separation, you're getting oxygen (with a little chlorine from salt) on the + electrode, hydrogen on the negative electrode (sodium immediately reacts with water). You're getting the mix only if you apply AC.
9205844
In the book, he is an American. However the author of this story are most likely from UK
9205936
The same thing that keeps them from pumping methane from the cave back to Equestria without the system shutting itself down. (And which keeps Pinkie from sending cupcakes through the same type of system.)
"no ability to separate water from oxygen" Did you mean "no ability to separate oxygen from water"?
9205402
For some reason, I never got an e-mail for this reply. The next time I record, I'll re-do this one line. Also, I noticed I accidentally had one line of Beth's on Dragonfly's track, and incorrectly applied the changeling vocal effect to her. I'll fix that, too.
9205844
I noticed that too. Canadian English is a little too Americanized for boffin to be in use here, despite Canada being a commonwealth country.
9205964
I dunno, I have a tolkien dwarf-looking american native friend, who lived whole life in Virginia and uses boffin often.
9205735
> because otherwise the MAV has to exceed 11.2 km/s (Earth escape velocity). At that point we're talking about a MAV the size of a Falcon Heavy, Delta IV Heavy, or Saturn V!
Not necessarily. Martian gravity means lesser losses, so less thrust, better specific impulse. I'm surprised they get accelerations as high as they do as MAV could do with much lower launch TWR and still come ahead of huge rockets in terms of dV/mass. And definitely not Saturn V. It had 8km/s of LEO + 3km/s Moon transfer + 1km/s Moon low orbit + 2km/s for landing/ascent + 1km/s return burn = ~15km/s total across various parts. And all the electronics was much, much heavier than nowadays.
...and don't forget the magic booster. That stays on the ground, doesn't add to launch mass, and gives them a good couple km/s kick.
9205686
Wouldn't be bad idea - essentially distillation of the atmosphere - except you really don't want liquid oxygen in contact with anything that wasn't meant to come in contact with liquid oxygen. Temperatures aside, it's insanely corrosive.
9206171
Well, only if you insist on planets. On Titan the human could survive a couple minutes. (obviously loss of consciousness in under 30s, and death by poisoning, hypothermia, and suffocation simultaneously... but near-liquid methane kills slightly slower than near-vacuum.)
9205377 Poirot is my favorite because he's perfect.
Like me.
9205844 I prefer boffin to egghead when using it as a non-perjorative.
9205964 Kris is from Texas (first answer in the author interview), and half the author's notes are about him driving back and forth across the state for his job...
Daily sessions in the bomb closet? I see no way this could possibly go wrong.
And Mark's comment reminded me of something I've been wondering about for some time. Just how many liters of air and water did the crew pull off of Equus? Almost certainly not enough to matter in the long run, but it's probably still a staggering amount.
This is obviously not sarcasm.
Mark, you mustn't let short-term setbacks get in the way of long-term rewards!
Hooray for Hilbert's paradox!
9206046
That’s the heart of the problem really, the GM can’t win. They’re not a player, they’re a storyteller.
9206398
As someone that's gone full Killer GM in the past, I can say that you don't wake up one day and say "I'd like to kill the entire party" entirely out of the blue. There's an impetuous, and it's rarely just being burned out.
For me, I got frustrated with the party being incredibly cheesy minmaxers that had micro'd their build down to a T... while still being Leeroy Jenkins in gameplay. So I started to play things a little more lethal, not much, but just a little more. And then the first character died, and it felt pretty satisfying.
A couple months later we all agreed it was turning into rocket tag since half the group was showing up with backup sheets every session, and I bowed out as GM.
More recently, I played with a GM who didn't know how to balance encounters at all. We'd started in at level 4, and the first encounter was against a band of 8 CR 4 bandits. After the lone survivor finished off the last of the bandits we all had a long, silent moment before I told the GM that he needed to learn how the CR system worked. He's gotten better since, but yeah.
Point is, there's never one single instant where your humble friendly gm goes from "I just want to have fun" to "BLOOD FOR THE BLOOD GOD, SKULLS FOR THE SKULL THRONE". Some GMs are right bastards with an eye toward unpleasantness from day one, some are angry at the party and venting in a 'harmless' way, and some are just honestly bad at building encounters. You even rarely get one who is entirely burned out on DMing. So be kind to your Gms and try to understand where they are coming from; it's a surprisingly high stress spot and it's easy to slip.
9206512
I know, I'm a GM far more often than a player. I wasn't being accusatory, just saying that it's an easy attitude mistake to make.
9206524
Honestly, the whole 'us vs them' and 'who wins' thing always struck me as odd.
Winning isn't the goal of the game for either the players or the GM. As a whole group, the goal should be a fun and engaging story with, typically, piles of deadly monsters and maniacal villains along the way.
The only way anyone wins is if either: The whole group is having a blast, or if someone is secretly Charlie Sheen.
If only Fireball worked like Ringworld dragons.
9207178
I think you meant Discworld.
He would probably need a bigger supply of magic if he did. See, there's two types of Discworld dragons: the kind that need little to no magic and have horribly complicated digestion systems that roll to explode every day, and the big type that needs a considerable chunk of magic, and which demand sacrifices.
Bah! They should just build hydrogen storage tanks out of impermium, the super metal which lets NOTHING pass through it!
(When in doubt, invent BS elements until it works!)