NASA space ship

And why would you need to lift that much water out of a gravity well when you can mine it from other sources in space (Europa, asteroid belt etc) as soon you can establish the infrastructure for it?

Statement was that it didn´t matter taking it FROM EARTH. I even specifically mentioned that it was a different matter if it was taken from elsewhere.

Why would it cost 100x than filtering tap water since NTR's doesn't need potable water?

Riiiight, so you expect machinery, tubing and all to run ok with saltwater, or water with anything at all in it?
This is one of the reasons why steam engines fell out of use, because getting clean enough water to avoid clogging anything during operation was troublesome.
Why do you think it´s not advised to use tapwater in car engines?

And your reasoning that some people are cheapskates isn't relevant at all in this discussion.

Reality is not relevant? That´s news.

Tenshinai wrote:Why do you think it´s not advised to use tapwater in car engines?

Tap water is used on 100% of car engines. Anti freeze is only added to keep engine block from freezing and splitting. If freezing is not a problem, anti freeze is not generally added. Go visit anywhere it does not freeze. No one even bothers with anti freeze as no one wants to deal with the poisonous stuff when repairing their cars. Some add it as it raises the boiling temperature if they are having overheating problems on their engines. If you have an ancient car/radiator using steel, adding anti corrosion additives helps for a while but must be replaced often. In modern cars, anti corrosion additives(added to anti freeze generally) used to slow down galvanic corrosion to increase the wear life of the radiator. It is certainly not needed though.

gen info~~
Treatment of water purity required is entirely dependent on temperature and pressure it is used at. Of course this is only for initial water injection. Once a machine operates for a period of time, wear particles and corrosion also collect. That is why oxidizer filtration is used for anti corrosion in high temperature applications. If Temperature is low enough, one can also add anti surfactants. This decreases 1) the friction of the water equating to higher efficiency and 2) wear drastically reduces as well. To combat wear particles from being circulated creating lower efficiency and higher wear is also why turbidity traps are used for dense particles.

Any salts "ium" in the periodic table can deposit itself via water and pressure differentials, galvanic "grabbing, clogging the works. Same goes for copper, zinc, etc.

Really depends on how you designed the steam works and how long you wish it to operate without failure on a steam systems dependency for pure water. If you wish, there is no reason you could not use salt water if you had designed the systems to handle the salt load. Wear is going to be a problem depending on the velocities involved and same goes for salt "balls" running through if you do not have a turbidity trap or 3.

Of course not sure why anyone would, pulling salt or other particulate out of water is not that power intensive. A pain; yes. Difficulty; no.

Ok. Why am I getting flashbacks to reading the old Asimov story on "Wasters" in this drift in the topic.

Can't remember if it was a short story or a novel. But you folks are reminding me of it.

Thank you,
T2M

Why not do the numbers your self? The formulas were given above - for you information here they are again.

From basic physics: a = v^2/r. v = 2*pi*r*(rev) where rev is the rotation rate in rev/second.

So a = (2*pi*rev)^2*r. Assuming you want 1/2g as your gravity at the end of your tether, that's 4.9 m/sec^2. Substituting the numbers you get r*(rev)^2 = .12411. If you want 1 g, the later constant is .24822.

if you you want the formula for rev in terms of a given acceleration and radius (half the diameter) it is:
rev = sqrt(a/r)/(2*pi).[/quote]


1 Gravity at 5000 metres diameter
rev = sqrt of (9.8/2500) / 6.283...
Sqrt of (0.00392) / 6.283
0.06261 / 6.283
~0.01 revolutions per second or 36 revolutions per hour.
That is at 10 miles = 360 Mph 576 kph

that seems awful fast.

or perhaps that is

0.01metres per second and 36 metres per hour which is awful slow.

This reminds me of my Greek classes before I knew the greek alphabet.

as confusing as Nai which sounds like Nay but in Greek means yes and English no.

now I'm just confused again

Tap water is used on 100% of car engines.

Nope. CLEAN tap water is used. If you use tap water in the wrong place, you get clogging.

People unaware of this is a reason why some folks keep having their cars break down way more often than they should.

If you use straight tap water from where there´s a lot of calcium in the ground water(like where my dad lives for example), then you are asking for trouble.

To avoid trouble or more likely RISKS, you use destilled water.

And cars are still far more robust in general than anything you can play around with in space within a century or two.

If you wish, there is no reason you could not use salt water if you had designed the systems to handle the salt load. Wear is going to be a problem depending on the velocities involved and same goes for salt "balls" running through if you do not have a turbidity trap or 3.

How many steam engines through history do you know about that ran on saltwater?

Of course not sure why anyone would, pulling salt or other particulate out of water is not that power intensive. A pain; yes. Difficulty; no.

As i said, to get it clean to the point where you KNOW that there isn´t anything left in the water that MIGHT cause problems, you end up having to do it far more thoroughly than what you do for tap water, and doing this for large quantities while still relatively cheap, is vastly more expensive than basic tap water treatment.

If you pre boil the water you make the steam which can both get rid of the salt and be used as steam. You then have salt.

Of course if you just want an engine that runs without problems heat combustion etc.... you could just use a Compressed Air engine. It requires very little heat and gives off very little negative pollutants if any at all.

http://www.mdi.lu/

Lord Skimper wrote:If you pre boil the water you make the steam which can both get rid of the salt and be used as steam. You then have salt.

Of course if you just want an engine that runs without problems heat combustion etc.... you could just use a Compressed Air engine. It requires very little heat and gives off very little negative pollutants if any at all.

http://www.mdi.lu/

And where are you going to get the compressed air from? And desalinization via boiling is hideously expensive in terms of fuel.

Totally agree. Desalination plants use reverse osmosis which is much cheaper than distillation, but still expensive.

A compressed air engine doesn't produce energy just uses it after it is produced elsewhere. Unfortunately the only place you will find perpetual motion machines is the Honorverse.

fallsfromtrees wrote:

Lord Skimper wrote:If you pre boil the water you make the steam which can both get rid of the salt and be used as steam. You then have salt.

Of course if you just want an engine that runs without problems heat combustion etc.... you could just use a Compressed Air engine. It requires very little heat and gives off very little negative pollutants if any at all.

http://www.mdi.lu/

And where are you going to get the compressed air from? And desalinization via boiling is hideously expensive in terms of fuel.

fallsfromtrees wrote:

Lord Skimper wrote:If you pre boil the water you make the steam which can both get rid of the salt and be used as steam. You then have salt.

Of course if you just want an engine that runs without problems heat combustion etc.... you could just use a Compressed Air engine. It requires very little heat and gives off very little negative pollutants if any at all.

http://www.mdi.lu/

And where are you going to get the compressed air from? And desalinization via boiling is hideously expensive in terms of fuel.

Daryl wrote:Totally agree. Desalination plants use reverse osmosis which is much cheaper than distillation, but still expensive.

A compressed air engine doesn't produce energy just uses it after it is produced elsewhere. Unfortunately the only place you will find perpetual motion machines is the Honorverse.

You can also do it by boiling, but instead of raising the temperature, you produce a vacuum over the water, lowing the boiling point to the current temperature of the water. I believe that the Saudis have a couple of desalinization plants that work this way. Still takes a hideous amount of energy.

Since we are talking about using a NTR as a rocket engine and water as remass, the sources of energy and vacuum for desalinating the water seem pretty self evident. I hardly think a nuclear engineer is going to use straight water from the asteroid without at least some filtration, if only to keep grit from destroying the turbo pumps.

So for space prospecting, colonization and general transport, where cheap and rugged are the key operating principles, then a source of water in space (asteroid, old comet nucleus, Jovian moons) is key. Water is pretty cheap and common, and filtering and desalinating it seem to be pretty straight forward operations, which are still far cheaper and less resource intensive than turning water into LH2 and LOX.

Finally, if you really want to combine the "oomph" of a NTR with "dirty" water, I would simply inject the water into the reaction stream of a dusty fission fragment reactor. The stream of nuclear particles is moving out of the reaction chamber at about 1% of the speed of light, and carries considerable kinetic and thermal energy. Water injected into the stream would flash into vapour and provide a considerable amount of momentum, increasing the thrust at the cost of a much lower ISP (lower than the 1,000,000 seconds that you get from straight nuclear exhaust). Since the Dusty Fission Fragment reactor is pretty small and efficient (being a non Carnot machine, efficiencies of up to 90% are predicted), spraying water into the exhaust provides a much greater range of thrust and ISP for the ship which uses such a system.