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How effecient would the heat (calories) from the human body be in propelling a spacecraft? Our bodies can boil water in the vacuum of space. All we need for fuel is food.
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How exactly would your biothermal engine work? I am not sure about what the efficiency would be, but it would probably not be able to generate enough heat to get a decent isp.
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An interesting idea but the problem is that humans actually use very little power. The average human goes through about as much power as a 100W light bulb. This energy is also at a low temperature. The Isp that people talk about is roughly related to the temperature of the exhaust. For things like ions engines, this doesn't really apply but for heating up a propellant and having it expand out the back, the hotter, the better.
The amount of thrust you can get from human crew is very low in power and very low performance. You might be able to run some tiny electronic gadget with the waste heat from the crew but that's about it. Spacecraft propulsion requires huge amounts of energy if you want to get to your destination in any reasonable amount of time.
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I bet a humming birds is much much more.
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The basal metabolic rate for a hummingbird is greater than for a human but not by that much. Perhaps a factor of 10 at the most. So then you'd need thousands of hummingbirds. Hummingbirds have to eat half of their own body mass every day. That adds up to a tremendous amount of weight in food. The ernergy you get is still very low in temperature and will give very poor performance. You'd be better off taking all that food and stuffing it into a rocket engine and setting it one fire.
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If this idea is to work at all, it would almost certainly require the boilogical components to be genetically engineered in order to meet the power and temperature requirements.
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And if you had the flu it would help since your body temperature would be higher. How high of a temperature would the shuttles skin reach in the sunlight if it was painted black?
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Black paint gets to a few hundred degrees in direct sunlight in space. The idea you are thinking of now is called a solar thermal rocket. It's a well established idea. The performance is mediocre at best but it is an alternative to nuclear thermal rockets.
As for even biologically engineered organisms, the maximum temperature you can hit is very low. The most thermotolerant organism ever found tops out at 121 C. Even with advanced bioengineering, that's not going to go up much. And what's the point? Nuclear reactor driven drives can get to thousands of degrees with no problem. No matter how good your organic heat generation mechanism, standard propulsion methods will always be superior.
If there were a way to get useful work out of the waste heat coming out of the crew, then it might be useful. However, the thrust you could gnereate from this is pretty much zero. Adding thousands of sick hummingbirds as a spacecraft drive is about the silliest thing I've ever heard of. It weighs more and has lower performance than any other drive mechanism in existence!
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Considering the tiny thrust and large mirrors needed for solar thermal, I would equate it more with solar ion in practice, if not in theory.
For thermal rockets of all types, for comparison between engines using the same fuel, temperature is everything. The efficency of hydrogen fuel increases an order of magnetude between NERVA-NTR and VASIMR RF/Plasma rockets.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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How about a combination of both solar thermal, and solar power in each panel?
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Those are two mutually incompatible concepts... solar pannels want to absorb light, while solar thermal wants to reflect it. You can't do both.
Also, the solar/ion option uses an ion engine fueled by Xenon usually, but solar/thermal uses liquid hydrogen. You would need two different kinds of engines and two different fuels, which is silly since solar/ion and solar/thermal have similar performance.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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On a chemical note...
The fundimental chemicals bonds that keep molecules of living beings held together are not able to withstand high temperatures, a few hundred degrees is usually sufficent to break most of them, and practical operating temperatures are quite low. I don't see how its possible to make a practical engine that would provide more than stationkeeping thrust, and even then a nonliving thruster would be much more weight efficent. Also, you can turn machines on and off, but a biological system you can't simply flip off a switch.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Lets see, is the shuttle painted white so it will reflect the sun light? If it was black I bet it would get awfully hot inside.As the solar panel absorbs the light how much heat is generated in it? How hot does it get?
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Yes, the Shuttle is painted white largely to prevent excessive heat absorbtion. In fact, the inside of the cargo doors are giant radiators to help to get rid of extra heat.
When looking at solar energy, the best way to calculate things is to look at where the power goes. At the Earth's distance from the sun, one square meter of material gets about 1500 Watts of power or enough to power a small toaster. Some of that light is reflected and doesn't heat the material. Shiny surfaces, not suprisingly, reflect more light than dull or black surfaces. This light does give some momentum to the material but the force is very small - less than a thousandth of a pound.
The rest of the light is absorbed. This light is either turned into heat or electricity in the case of solar cells. A 100% efficient solar cell wouldn't heat up in the sun at all or recieve any thrust at all. A 10% efficient solar cell doesn't exist, though. The best we can do is about 25%. In theory, we might be able to get up to maybe 30-40% percent but that's about the limit. Therefore, the solar cell will heat up and will get pushed around a bit by the sunlight. The thrust it gets from the sunlight will only be half of what you get from a reflective surface.
So, if you want something that is going to get pushed by the light, you want a shiny surface. If you want the surface to heat up, you want it to be black. If you want the surface to make electricity, you make a photocell which reduces the ability to either make heat or generate thrust. You've only got 1500 Watts to work with and you can pick what that power does. But no matter what you do, you can't get the energy to do more than one thing for you.
Presently, the best use of the power is to use photovoltaic cell to make electricity which powers an ion engine. If we were able to make a material that was about 5 times lighter than what we can make now, solar sails would be the most efficient way to move spacecraft.
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If you want the surface to heat up, you want it to be black. No way to run water through the non vital areas of a solar panel to take advantage of the surface area to boil water off in the vacuum of space? This should add to the crafts total acceleration.
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You mean to use the excess heat on solar arrays because of <100% absortion in order to heat a propellant of some kind in a thermal engine?
This would increase the total amount of useful energy from the solar pannels per-area, but they simply don't get extremely hot, and water is an awfully heavy propellant, it would not be very efficent. Low temperatures and high molar mass means low efficency. In the end, it would beyond any doubt only weigh your spacecraft down and make it worse.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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You mean to use the excess heat on solar arrays because of <100% absortion in order to heat a propellant of some kind in a thermal engine?
Yep!
What about h2 or he?
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That would work but every part of the solar panel you reserve for generating heat would take away from the electrical generation capacity. You have to make a choice about what you want your surface to do. If you want force, power or electricity, you have to choose which one you want. For an effective rocket drive, electricity or force are your best bets. Heat energy will let you generate thrust but not very well.
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The solar pannels simply won't get hot enough to produce thrust efficently with any propellant. SBird is ultimatly correct, that you have to optimize the solar collectors of whatever type to do only one thing. You can make it do multiple things, but the sum total of all of those things is less than doing any one well. As the saying goes, Jack of all trades and master of none.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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