## What-If 0124: "Lunar Swimming"

What if there was a forum for discussing these?

Moderators: Moderators General, Prelates, Magistrates

SuperSteve
Posts: 28
Joined: Sun Mar 09, 2014 10:20 pm UTC

### Re: What-If 0124: "Lunar Swimming"

Water is liquid only in a fairly narrow temperature range, which is rarely found on the moon. According to coolcosmos.ipac.caltech.edu "The temperature on the Moon varies from -387 Fahrenheit (-233 Celsius), at night, to 253 Fahrenheit (123 Celsius) during the day." During the day, the water would boil and you wouldn't be able to swim in it. At night, the water would turn to ice almost instantly. It would be a strange place to learn to skate, because you would not get as hurt from the impact when you fell, but you'd die of frostbite if you didn't get up soon.

SuperSteve
Posts: 28
Joined: Sun Mar 09, 2014 10:20 pm UTC

### Re: What-If 0124: "Lunar Swimming"

Whizbang wrote:Do the hydrogen and oxygen atoms suddenly get more mass when they bond to form water? 'Cuz if not then bringing them separated and then bonding them there wouldn't make a bit of difference.

I think the proposal was to use atoms that are already on the moon, so you wouldn't be "bringing them", just bonding them.

But bringing them separate would make a big difference. The mass might be the same, but the volume would be greater, so your spacecraft would be larger and there would be more air resistance. A parachute and a small rock might have the same mass, but the rock gets through the air easier.

SuperSteve
Posts: 28
Joined: Sun Mar 09, 2014 10:20 pm UTC

### Re: What-If 0124: "Lunar Swimming"

NealCruco wrote:
squall_line wrote:So, it used to be "Tuesdays: New What If?s!", which then sorta morphed into What If? Wednesday... Are we up to "What If? Whenever" now? Maybe the book tour turned into a road tour?

I know, I shouldn't look a gift horse in the mouth, complain about free ice cream, etc., but it worries me that there's nothing mentioned in the blog about delays or other personal strife, and I worry that there's something going on that Randall isn't telling us. Not that I expect him to reveal his personal life to the world, but something addressing the significant and frequent delays of the What If?s, even something as simple as "I'm busy, What If?s will be delayed until ready every week, maybe as late as Friday or Saturday" would be appreciated.

I posted about this just a month ago. It didn't generate much discussion, but here's the post:

NealCruco wrote:I'm thinking that Randall is losing interest in what-if, especially since publishing his book. Last year each installment appeared as promptly as each new comic, every Tuesday morning. Some months ago, the "every Tuesday" tagline was removed. Now new entries have slid from Tuesday to Wednesday, Thursday, and even Friday. It's no longer something that I look forward to- I enjoy each article when they come out, but I have no confidence that there will be another.

On today's what-if...
Whizbang wrote:Do the hydrogen and oxygen atoms suddenly get more mass when they bond to form water? 'Cuz if not then bringing them separated and then bonding them there wouldn't make a bit of difference.

...No, they don't. More mass requires more matter, and matter cannot be created or destroyed. You're right that bringing pure H and O2, then combining them on the moon, would give the same result. I don't know if it would be a better option, though.

No, bringing them separate and combining them on the moon, would not give the same result.

The mass might be the same, but the volume would be greater, so your spacecraft would be larger and there would be more air resistance. A parachute and a small rock might have the same mass, but the rock gets through the air easier.

buddy431
Posts: 446
Joined: Mon Dec 06, 2010 5:21 pm UTC

### Re: What-If 0124: "Lunar Swimming"

You don't even need to make oxygen first, you can just directly reduce (some) moon rocks with hydrogen. Requires pretty high temperatures, but cutting out almost 90% of the mass you have to ship has to be worth it.
Gellert1984 wrote:Also, bomb president CIA al qaeda JFK twin towers jupiter moon martians [s]emtex.

Mikeski
Posts: 1023
Joined: Sun Jan 13, 2008 7:24 am UTC
Location: Minnesota, USA

### Re: What-If 0124: "Lunar Swimming"

keithl wrote:Water droplets in the air above a lunar pool would take at least 6 times as long to fall down. There would be a lot more water in the air near a lunar pool surface, perhaps 36 times as much if this behaves like a diffusion problem. Breathing without choking could be difficult; that is my main problem as an incompetent swimmer on Earth. Swimmers might need tall snorkels.

Snorkels only work up to a certain length, though, and they work progressively worse up to that length.

If the volume of the tube (including your own internal tubing) is greater than the effective volume of your lungs, you won't get much new air; you'll just keep re-inhaling the same air from the tube. The air at the far end of the tube will keep exchanging itself, but that doesn't help the swimmer much.

PinkShinyRose
Posts: 832
Joined: Mon Nov 05, 2012 6:54 pm UTC
Location: the Netherlands

### Re: What-If 0124: "Lunar Swimming"

Mikeski wrote:
keithl wrote:Water droplets in the air above a lunar pool would take at least 6 times as long to fall down. There would be a lot more water in the air near a lunar pool surface, perhaps 36 times as much if this behaves like a diffusion problem. Breathing without choking could be difficult; that is my main problem as an incompetent swimmer on Earth. Swimmers might need tall snorkels.

Snorkels only work up to a certain length, though, and they work progressively worse up to that length.

If the volume of the tube (including your own internal tubing) is greater than the effective volume of your lungs, you won't get much new air; you'll just keep re-inhaling the same air from the tube. The air at the far end of the tube will keep exchanging itself, but that doesn't help the swimmer much.

You could fix this by using separate inlets and outlets with valves.

rmsgrey
Posts: 3413
Joined: Wed Nov 16, 2011 6:35 pm UTC

### Re: What-If 0124: "Lunar Swimming"

Didn't we land a probe on a large chunk of ice floating free in space not so long ago? Sure, the delivery times will be longer, but dropping comets on the moon is probably a more energy efficient way of getting water there...

ps.02
Posts: 378
Joined: Fri Apr 05, 2013 8:02 pm UTC

### Re: What-If 0124: "Lunar Swimming"

rmsgrey wrote:Didn't we land a probe on a large chunk of ice floating free in space not so long ago? Sure, the delivery times will be longer, but dropping comets on the moon is probably a more energy efficient way of getting water there...

Makes me think of Asimov's story "The Martian Way" about a mission of Martian settlers to solve their water shortage in a similar fashion. For political (not technical) reasons, it was easier to capture a ball of ice from Saturn's rings than to get more water from Earth. Whether all that would ever be practical, I have no idea. Part of the need for water was the use of steam-powered rockets (presumably fired not by coal but by nuclear power - I forget whether he specified).

Neil_Boekend
Posts: 3220
Joined: Fri Mar 01, 2013 6:35 am UTC
Location: Yes.

### Re: What-If 0124: "Lunar Swimming"

SuperSteve wrote:Water is liquid only in a fairly narrow temperature range, which is rarely found on the moon. According to coolcosmos.ipac.caltech.edu "The temperature on the Moon varies from -387 Fahrenheit (-233 Celsius), at night, to 253 Fahrenheit (123 Celsius) during the day." During the day, the water would boil and you wouldn't be able to swim in it. At night, the water would turn to ice almost instantly. It would be a strange place to learn to skate, because you would not get as hurt from the impact when you fell, but you'd die of frostbite if you didn't get up soon.

Any moon habitat is going to be well isolated. Thus the min and the max don't matter so much as the average temperature over the day, and even that will be corrected with heating/cooling if it is too far off. There is no way the internal parts of the moon habitat go down to -233°C. They'll stay nicely at a comfortable temperature.
Mikeski wrote:A "What If" update is never late. Nor is it early. It is posted precisely when it should be.

patzer's signature wrote:
flicky1991 wrote:I'm being quoted too much!

he/him/his

cellocgw
Posts: 1918
Joined: Sat Jun 21, 2008 7:40 pm UTC

### Re: What-If 0124: "Lunar Swimming"

NealCruco wrote:[
On today's what-if...
Whizbang wrote:Do the hydrogen and oxygen atoms suddenly get more mass when they bond to form water? 'Cuz if not then bringing them separated and then bonding them there wouldn't make a bit of difference.

...No, they don't. More mass requires more matter, and matter cannot be created or destroyed. You're right that bringing pure H and O2, then combining them on the moon, would give the same result. I don't know if it would be a better option, though.

Not strictly true. Due to good old E=mc^2, there is a change in the total rest mass when you do things like building atoms as well as IIRC molecules.
https://app.box.com/witthoftresume
Former OTTer
Vote cellocgw for President 2020. #ScienceintheWhiteHouse http://cellocgw.wordpress.com
"The Planck length is 3.81779e-33 picas." -- keithl
" Earth weighs almost exactly π milliJupiters" -- what-if #146, note 7

Nicias
Posts: 161
Joined: Tue Aug 13, 2013 4:22 pm UTC

### Re: What-If 0124: "Lunar Swimming"

True, but unless I've done my math wrong. The mass change from a 2 moles of H2 and 1 mole of O2 to 2 moles of H20 (about 32 grams) is about 5 nanograms. So, negligble.

mathmannix
Posts: 1410
Joined: Fri Jul 06, 2012 2:12 pm UTC
Location: Washington, DC

### Re: What-If 0124: "Lunar Swimming"

SuperSteve wrote:
NealCruco wrote:On today's what-if...
Whizbang wrote:Do the hydrogen and oxygen atoms suddenly get more mass when they bond to form water? 'Cuz if not then bringing them separated and then bonding them there wouldn't make a bit of difference.

...No, they don't. More mass requires more matter, and matter cannot be created or destroyed. You're right that bringing pure H and O2, then combining them on the moon, would give the same result. I don't know if it would be a better option, though.

No, bringing them separate and combining them on the moon, would not give the same result.

The mass might be the same, but the volume would be greater, so your spacecraft would be larger and there would be more air resistance. A parachute and a small rock might have the same mass, but the rock gets through the air easier.

Wait... air resistance? That wouldn't apply for most of the trip to Mars - in SPACE. (Just the beginning bit (and to a lesser extent the end bit, but there it would help slow you down.) There's no friction in space, IIRC. (More volume = bigger target for asteroids, but space isn't really a thicket of them.)) The fuel necessary is based on mass, not volume.
I hear velociraptor tastes like chicken.

Klear
Posts: 1965
Joined: Sun Jun 13, 2010 8:43 am UTC
Location: Prague

### Re: What-If 0124: "Lunar Swimming"

mathmannix wrote:Wait... air resistance? That wouldn't apply for most of the trip to Mars - in SPACE. (Just the beginning bit (and to a lesser extent the end bit, but there it would help slow you down.) There's no friction in space, IIRC. (More volume = bigger target for asteroids, but space isn't really a thicket of them.)) The fuel necessary is based on mass, not volume.

But isn't the atmospheric part of space flights the most fuel consuming?

gmalivuk
GNU Terry Pratchett
Posts: 26443
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

### Re: What-If 0124: "Lunar Swimming"

Yes, though part of that is due to gravity drag rather than atmospheric drag, which happens to occur at the same time.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

Boson Collider
Posts: 13
Joined: Wed Oct 29, 2014 6:20 pm UTC

### Re: What-If 0124: "Lunar Swimming"

I think the best way to get enough water would be with oxygen ISRU. Something like the LUNOX proposal by NASA in the 90s.

When you can make oxygen from lunar soil, you only need to ship liquid hydrogen to the surface. If you were building a moon base, you'd probably want to have the infrastructure to do that anyway for ascent fuel so that reusable landers can lift off from the surface.

With this, I get ~11.2 tonnes of hydrogen for a 5m x 10 m x 2m pool of water that could fit inside a Bigelow BA-330 module. In other words, if Bigelow does build his private lunar hotel, he HAS to include a swimming pool.

Posts: 5654
Joined: Wed Jun 11, 2008 11:03 am UTC
Location: The Netherlands

### Re: What-If 0124: "Lunar Swimming"

cellocgw wrote:Not strictly true. Due to good old E=mc^2, there is a change in the total rest mass when you do things like building atoms as well as IIRC molecules.

Nicias wrote:True, but unless I've done my math wrong. The mass change from a 2 moles of H2 and 1 mole of O2 to 2 moles of H20 (about 32 grams) is about 5 nanograms. So, negligble.

Actually gravity works on energy, not just mass. Mass just happens to completely dominate other forms of energy under ordinary circumstances. Lifting the equivalent of 1 kg of matter in another form of energy out of earth's gravity well would be exactly as hard as lifting 1 kg of matter would be.
It's one of those irregular verbs, isn't it? I have an independent mind, you are an eccentric, he is round the twist
- Bernard Woolley in Yes, Prime Minister

Neil_Boekend
Posts: 3220
Joined: Fri Mar 01, 2013 6:35 am UTC
Location: Yes.

### Re: What-If 0124: "Lunar Swimming"

Of course it would be possible to burn the hydrogen along the way, powering a thermoelectric powerplant wich in turn powers an ion engine. With that ion engine the capsule can increase it's orbit size to the moon's orbit size. That way the resulting water can be captured.

Note: this may turn out to be heavier than just sending the water and sufficient rocket fuel to get to the moon the ordinary way.
Mikeski wrote:A "What If" update is never late. Nor is it early. It is posted precisely when it should be.

patzer's signature wrote:
flicky1991 wrote:I'm being quoted too much!

he/him/his

DanMcQueen
Posts: 9
Joined: Tue Aug 31, 2010 12:22 pm UTC

### Re: What-If 0124: "Lunar Swimming"

Nicias wrote:True, but unless I've done my math wrong. The mass change from a 2 moles of H2 and 1 mole of O2 to 2 moles of H20 (about 32 grams) is about 5 nanograms. So, negligble.

The net binding energy released per mole of water produced is 469kJ. A mole of water weight approx 18g (not 32g). Considering it takes 210 moles of water to make 1 gallon of water, carrying that much water up to the moon would require an extra 98.5MJ of energy per gallon, if the H2 and O2 are carried separately. The average adult would need 180-200 gallons of drinking water per year, which would require 19.7 GJ of energy to carry, or about the average annual energy consumption of Latvia. And this is just for making enough water to last 1 astronaut for 1 year.

In short, it would require a ludicrous amount of energy to send a long-term supply of water-making components to the moon. Much better idea would be to just mine and produce it locally.

tups
Posts: 20
Joined: Mon Mar 28, 2011 10:37 pm UTC

### Re: What-If 0124: "Lunar Swimming"

DanMcQueen wrote:
Nicias wrote:True, but unless I've done my math wrong. The mass change from a 2 moles of H2 and 1 mole of O2 to 2 moles of H20 (about 32 grams) is about 5 nanograms. So, negligble.

The net binding energy released per mole of water produced is 469kJ. A mole of water weight approx 18g (not 32g). Considering it takes 210 moles of water to make 1 gallon of water, carrying that much water up to the moon would require an extra 98.5MJ of energy per gallon, if the H2 and O2 are carried separately. The average adult would need 180-200 gallons of drinking water per year, which would require 19.7 GJ of energy to carry, or about the average annual energy consumption of Latvia. And this is just for making enough water to last 1 astronaut for 1 year.

In short, it would require a ludicrous amount of energy to send a long-term supply of water-making components to the moon. Much better idea would be to just mine and produce it locally.

Excuse my french, but you seem to be throwing around some numbers without much understanding of what is really going on, and without making much of a point.

You calculate, more or less correctly, the binding energy for a mole of water, except that you use the wrong number - the enthalpy of formation of one mole of liquid water is 285 kJ. This energy is not required, but produced when reacting hydrogen and oxygen. So one does not "require" it, you are already transporting it to the moon in the form of reactive hydrogen and oxygen. This transport would cost you the same amount of energy as transporting 200 gallons of water to the moon.
19.7 GJ is not the average annual energy consumption of Latvia. The annual *electricity* consumption of Latvia was 517 million kWh (in 2013), or around 2 PetaJoules, a factor 100.000 larger, and that is just the electricity. Energy requirements for domestic heating in a cold place such as Latvia will be about 10-fold higher, but I'm too lazy to look up the numbers.
20GJ is about the annual electricity consumption of two households in Belgium. You could make good use of this energy on the moon, while turning the hydrogen and oxygen into water and working at creating your 200 gallon pool. Which, by the way is the only reason for transporting 200 gallons of water up to the moon. One would suspect that waste water is recycled, and in a closed system one could do with much less than this amount per person, especially since we metabolize carbohydrates (which would need to be imported) into water and CO2 as well

jewish_scientist
Posts: 903
Joined: Fri Feb 07, 2014 3:15 pm UTC

### Re: What-If 0124: "Lunar Swimming"

Someone contact NASA; they will want to read this.

You probable read that and laughed, but I am serious. NASA has a list of 181 things they want to do on the Moon*. My favorite is turning the entire Moon into a Strange Matter detector, but that is not relevant. What is relevant is mEOR3 and mEOR6. These goals are:

Extend awareness of space activities to diverse, non-traditional communities, utilizing non-traditional means, to enhance public engagement.

Carry out a mission for pure public engagement to generate public excitement about exploration.

A pool on the Moon inherently meets both of these goals. It is also very likely that it will meet all of mC, a lot of mCO, all of mGP, mEOR1.1, mEOR1.2 mEOR1.4 through mEOR1.6, and mEOR7.

Congress cancelled NASA's space program because they are idiots who can't figure out how to get the richest country on the planet to pay back its loans. Perhaps the best part of a lunar pool is that NASA could make money, allowing the space program to continue despite political stupidity. Think about it; how much do you think Pepsi would pay to sponsor America's Aquatic High Jump Olympic Team. Also, if you freeze the water and lay some turf down, you have got yourself a field people could play sports on. No matter how you look at it, this is an investment NASA cannot afford to pass on.

*http://www.nasa.gov/pdf/163560main_LunarExplorationObjectives.pdf
There is a whole section based on observing the Earth, which sounds a little weird. 'We can't get any good pictures of the things 0 centimeters away; so lets send a camera 382,500 kilometers away and then try taking pictures!'
"You are not running off with Cow-Skull Man Dracula Skeletor!"
-Socrates

schapel
Posts: 244
Joined: Fri Jun 13, 2014 1:33 am UTC