terrawatt years

robertjford80

This comes from Robert Zurin's the Case for Mars

While Mars may have super-oxides in its regolith or nitrates that can be heated to release oxygen and nitrogen gas. the process would require enormous amounts of energy, about 2,200 TW-years for every millibar produced

What is a Terrawatt year? Is that 1 terrawatt produced in one year? I don't see why it's measured in terrawatts. Why not just terrawatts?

Further down he says

By combining the efforts of such biological systems with perhaps 90 TW of space-based reflectors and 10 TW of installed power on the surface (terrestrial civilization today uses about 15 TW) the required 120 millibars of oxygen needed to support humans and other advanced animals in the open could be produced in about nine hundred years

That's more understandable.

Tell me if this calculation is correct. To get 120 millibars of oxygen you need to multiply 2200 by 120 since 2200 TW are needed for 1 millibar of oxygen.

2200 * 120 = 264,000 terrawatts

It looks like he thinks you can produce 100 TW a year with 90 coming from reflectors and 10 coming from factories. If that's 100 TW a year that would take 2640 years, so there is something that I'm not understanding.

But I should also point out that I don't really trust this guy. He has an agenda, going to Mars and quick, so he's motivated to minimize all the obstacles and make everything seem easier than it is.

256bits

Terrawatt-year is a unit of energy. His 2200 terawatt-years is expressing how much energy would be needed to produce 1 millibar of oxygen. So if you could produce 2200 terawatts of power it would take 1 year, or if you could produce 1 terawatt of power it would take 2200 years to obtain that 1 millibar.
It is the same as your electrical company charges you - they charge for energy usage as kw-hour.
Just stating a power level is insufficient - you have to know the length of time that power level would be sustained.

He says "By combining the efforts of such biological systems with perhaps 90 TW of space-based reflectors and 10 TW of installed power on the surface ... " I believe he includes some biological organizisms helping out to produce the oxygen to get his figure of about 900 years.
What he does say previous to the quote may be the clue you are looking for in the diecspancy of your result versus his.

robertjford80

Let me just go ahead and quote the whole thing. Remember I'm trying to figure out how he got the 900 year figure.

The most technologically challenging aspect of terraforming Mars will be the creation of sufficient oxygen in the planets atmosphere to support animal life. While bacteria and primitive plants can survive in an atmosphere without oxygen, advanced plants require at least 1 mbar and humans need 120 mbar. {
While Mars may have super-oxides in its regolith or nitrates that can be heated to release oxygen and nitrogen gas. the process would require enormous amounts of energy, about 2,200 TW-years for every millibar produced. Similar amounts of energy-are required for plants to release oxygen from carbon dioxide} Plants, however, offer the advantage that once established they can propagate themselves. The production of an oxygen atmosphere on Mars thus breaks down into two phases In the first phase, brute-force engineering techniques supplemented by pioneering cyanobactena and primitive plants are employed to produce sufficient oxygen (about 1 millibar) to allow advanced plants to propagate across Mars. Assuming three 125-kilometer radius space mirrors active in supporting such a program and sufficient supplies of suitable target material on the ground, such a goal could be achieved in about twenty-five years. Alternatively, {
a 1 millibar oxygen content could be added to the atmosphere in about a century through the action of photosynthciic bacteria} Either way.
once an initial supply of oxygen is available, and with a temperate climate, a thickened carbon dioxide atmosphere to supply pressure and greatly reduce the space radiation dose, and a good deal of water in circulation, plants that have been genetically engineered to tolerate Martian regoliths and to perform photosynthesis at high efficiency could be released together with their bacterial symbiotes. {
Assuming that global coverage could be achieved in a few decades and that such plants could be engineered to be 1 percent efficient (rather high, but not unheard of among terrestrial plants) then they would represent an equivalent oxygen-producing power source of about 200 TW. By combining the efforts of such biological systems with perhaps 90 TW of space-based reflectors and 10 TW of installed power on the surface (terrestrial civilization today uses about 15 TW) the required 120 millibars of oxygen needed to support humans and other advanced animals in the open could be produced in about nine hundred years

I'm sure there is some chart out there that shows how much energy humans are able to produce per human over the course of the last 200 years in, say, UK and USA, most likely it grows at a very steady tick, just as computing power doubles every 18 months. I think someone should track that chart down and come up with a reasonable extrapolation of how much energy we'll be able to produce in the next 500 years. I know they have charts of worker productivity. Also France is building a fusion generator which is supposed to be up and running in 2018. If it works we'll be able to get 10 units of energy for every unit we put in.

mfb

I found this graph here, which gives a factor of 10^4 in ~300 years or (conservative) a factor of 10 per 100 years.
I would not trust any extrapolation over 500 years, but if you like to do this, you could add 5 orders of magnitude and try to add a "mars factor", as mars is more remote than conventional power plant locations. 5 orders of magnitude are the difference between 1 GW (usual power plant size) and 100TW. However, keep in mind that conventional power plants need cooling water, which is tricky at mars.

256bits

There is your answer - 200 TW from plants and 100 TW from humans.

robertjford80

ok, good, 264,000/300 = 880 years, that's reasonable.

haruspex

Fwiw, the word is terawatt, one 'r'. It has nothing to do with terra = earth (Latin), but much to do with tera = monster (Greek). I do hate searches failing because technological terms are misspelt. Or misspelled if you prefer.

D H

Quote by robertjford80

What is a Terrawatt year? Is that 1 terrawatt produced in one year? I don't see why it's measured in terrawatts. Why not just terrawatts?

Terawatts are units of power. The power output of the world's most powerful laser is measured in petawatts, or 1000 terawatts. However, the energy output was only 680 joules because the laser fired for less than a trillionth of a second. Energy is power times time.

A terawatt-year is a huge amount of energy. The total electrical power generated by all of the electrical power generators in the US during 2009 was 0.44 terawatt-years. Another way to look at it: That 2,200 terawatt-years figure is equal to 5,000 times the total electrical power output for all of the US for all of 2009.

Yet another way to look at it: It's pure science fiction.

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256bits	There is your answer - 200 TW from plants and 100 TW from humans.

robertjford80	ok, good, 264,000/300 = 880 years, that's reasonable.

haruspex Recognitions: Homework Help Science Advisor	Fwiw, the word is terawatt, one 'r'. It has nothing to do with terra = earth (Latin), but much to do with tera = monster (Greek). I do hate searches failing because technological terms are misspelt. Or misspelled if you prefer.