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Damburger
2007-Aug-17, 04:22 PM
Assuming you are already in orbit, would it be possible to generate thrust using and ion engine running under human power? A bicycle (or equivalent device that can function in weightlessness) providess electricity, and the material by-products of the life support system (such as used CO2 scrubber material) provide reaction mass.

Granted you wouldn't get anywhere quickly, but could you get anywhere at all?

Doodler
2007-Aug-17, 04:37 PM
Why do I get the image of that old ESPN commercial where the power goes out in the building and the guy goes to the electrical closet where Lance Armstrong is taking a breather and gives him grief about stopping?

Probably not a bad idea, but is the weight of the generator equipment and rechargable batteries worth the return? I'm assuming the cyclist isn't going to be biking for demand loads on call, so whatever power he generates will likely be stored in batteries until needed. That can get mass costly depending on the batteries used.

Damburger
2007-Aug-17, 04:46 PM
Why do I get the image of that old ESPN commercial where the power goes out in the building and the guy goes to the electrical closet where Lance Armstrong is taking a breather and gives him grief about stopping?


Sounds funny, but we don't get ESPN in the UK. Whilst writing it I was thinking of the bit from Red Dwarf when they are low on power, and trying to fry an egg with a bicycle powered hair dryer.



Probably not a bad idea, but is the weight of the generator equipment and rechargable batteries worth the return? I'm assuming the cyclist isn't going to be biking for demand loads on call, so whatever power he generates will likely be stored in batteries until needed. That can get mass costly depending on the batteries used.

Even a small amount of thrust will get you *somewhere* when there's no friction to worry about. So the extra weight wouldn't necessarily stop such a vessel getting anywhere, just slow it down a great deal.

Certainly nobody is going to Mars like this, but it might be the sporting event of the future, along with orbital skydiving (http://www.theregister.co.uk/2007/06/27/cap_troopers_r_go/). :)

01101001
2007-Aug-17, 05:28 PM
Picturing the Gossamer Albatross (http://en.wikipedia.org/wiki/Gossamer_Albatross) in space... Might be a lot less wind resistance. And a lot less mass available to throw behind you.

If they could just harvest the normal heat output of a human -- what, about 100 watts? -- and apply it to throwing ions out the rear, you could probably get somewhere. Over time.

No doubt there are some engineering challenges there.

Name drop: I once did pizza and beer with Mort Grosser (Gossamer Odyssey: The Triumph of Human-Powered Flight. MBI Press, 2004).

Ronald Brak
2007-Aug-17, 05:44 PM
A hundred watts is about how much power a human could generate with light to moderate exercise. I suppose you could get somewhere with that, but space is big and that somewhere would be pretty much equivilant to nowhere.

If you really wanted you could grow plants using sunlight on your ship, then eat the plants and use the energy to power your ion drive. You would be doing extremely well to get half a percent efficiency out of that system. Much better to invest in some solar cells which can be made over 40% efficient.

01101001
2007-Aug-17, 05:53 PM
ScienceDaily: NASA's Dawn Mission: To Explore 'Dwarf Planet' Ceres And Massive Asteroid Vesta (http://www.sciencedaily.com/releases/2007/06/070626143015.htm)
At full throttle, the ion engine consumes 2,300 watts of electrical power and produces 1/50th of a pound of thrust -- about the same pressure as a sheet of paper resting on the palm of a hand, and far less thrust than is produced by even small chemical rockets. This engine, for a given amount of fuel, can gradually increase a spacecraft's velocity 10 times more than can a conventional rocket powered by liquid or solid fuel.

100 watts? Just be patient. Real patient.

Bob B.
2007-Aug-17, 06:09 PM
A healthy human can sustain only about 0.1 horsepower, or 75 watts, for a period of about 8 hours. Higher power levels can be produced but for shorter periods of time before exhaustion sets in. Ion engines are very fuel efficient but they require much electrical power to operate. 75 watts of power is enough to produce only about 3 milli-Newtons of thrust. Suppose we have a small spacecraft not much bigger than a Mercury capsule, letís say 1,500 kg. The acceleration is then 0.000002 m/s^2. A full 8 hours of work will therefore produce a velocity change of only 0.0576 m/s.

tlbs101
2007-Aug-17, 06:14 PM
...At full throttle, the ion engine consumes 2,300 watts of electrical power and produces 1/50th of a pound of thrust ...

I can personally maintain about 200-230 Watts on a stationary bicycle for an hour, so if you get 6 astronauts on 6 bicycles all pedalling at the same time, you could conceivably generate enough power for 1/2 of one of those ion engines. Furthermore, astronauts are in better physical condition than the 'average' human, so they would be able to sustain this level of power for longer than 1 hour if necessary.

I'd call that significant, as to the amount of propulsion they *could* provide.

.

Doodler
2007-Aug-17, 06:25 PM
Last time I checked, the guys who crunched the numbers for navigation and whatnot liked their thrust rates nice and constant. It seems to me that asking a human to generate a consistent amount of energy, as opposed to simply continuous energy, is asking a bit...

So you can pedal for 8 solid hours, can you also guarantee your watts per hour will be absolutely consistent during the entire ride? Bet not.

Bob B.
2007-Aug-17, 06:28 PM
I can personally maintain about 200-230 Watts on a stationary bicycle for an hour...

A person can generally do more work before reaching exhaustion when performing at a slow steady pace sustained for a long period of time than they can at a high power for a short period of time. 230 watts on a bicycle for one hour is 230 watt-hours. On the other hand, 75 watts sustained over 8 hours is 600 watt-hours. If converted to ion propulsion, the later will generate more impulse.

Bob B.
2007-Aug-17, 06:38 PM
So you can pedal for 8 solid hours, can you also guarantee your watts per hour will be absolutely consistent during the entire ride? Bet not.

The ion engine could run off a battery and then and the astronaut's pedaling could recharge the battery. For instance, if the ion engine ran 24-7 drawing 25 watts, that would be 600 W-h per day. The astronaut could then replace this throughout the day at irregular intervals.

danscope
2007-Aug-17, 06:56 PM
Technicalities are interesting, although acedemic.
I had a question onetime concerning the raising of a 3000 ton submarine.
The boat is on the bottom....ledge, no mud....in perfect equilibrium, absolute
neutral bouyancy. You cannot blow any tank, and you cannot pump any trim or drain tank to sea. Yet it "is" possible to surface the boat.
*********** How? ....................
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Got an idea.......yet?
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Well......it centers on displacement........
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Yes! You raise the periscope ! If you raise the scope 15 feet......
you have actually 'displaced' something close to 150 pounds. And....
yes, eventualy , with 150 pounds of displacement bouying the boat, it will
surface. Academic exercise builds character. :)
Best regards, Dan

Swift
2007-Aug-17, 08:52 PM
A healthy human can sustain only about 0.1 horsepower, or 75 watts, for a period of about 8 hours. Higher power levels can be produced but for shorter periods of time before exhaustion sets in. Ion engines are very fuel efficient but they require much electrical power to operate. 75 watts of power is enough to produce only about 3 milli-Newtons of thrust. Suppose we have a small spacecraft not much bigger than a Mercury capsule, letís say 1,500 kg. The acceleration is then 0.000002 m/s^2. A full 8 hours of work will therefore produce a velocity change of only 0.0576 m/s.
But I have to imagine that an astronaut peddling away to power the engine is going to use more oxygen, require more CO2 scrubbing, and eat more food, than an astronaut just sitting. Ok, the food you could just lift to orbit (but you could have also lifted more fuel for an ordinary rocket engine). But I have to imagine the extra strain on the life support system requires power. I suspect that there would be no net gain - you're better off letting things like fuel and solar cells power your engine, than the physical labor of your crew.

Bob B.
2007-Aug-17, 09:02 PM
But I have to imagine that an astronaut peddling away to power the engine is going to use more oxygen, require more CO2 scrubbing, and eat more food, than an astronaut just sitting. Ok, the food you could just lift to orbit (but you could have also lifted more fuel for an ordinary rocket engine). But I have to imagine the extra strain on the life support system requires power. I suspect that there would be no net gain - you're better off letting things like fuel and solar cells power your engine, than the physical labor of your crew.

I agree; I believe there will likely be a net loss. Increased metabolic activity comes at a price; there are surely more efficient means to get the needed power output.

Van Rijn
2007-Aug-17, 09:23 PM
There was a story by (I think) Charles Sheffield about an (at least partly) human powered space race. Sheffield was very good with technical details, so I'm sure he would have run through the numbers. I'll see if I can find the collection, but I'm not sure if I have it handy.

I don't remember too much about it, but I remember that the contestants had highly efficient spacesuits, and the spacecraft were as open to space as a bicycle. I think there were specific mass limits placed on their vehicles. The hero did have a foot pedal generator/ion drive combo, but as I recall, there were other options. The trick to the game was that gravity assists and small velocity differences could cause a substantial difference in the time they reached the finish "line." There was never any assumption that this was useful outside of the sport. They even had pacer spacecraft to monitor the race and pick up anyone in trouble.

novaderrik
2007-Aug-17, 11:07 PM
well, they are going to have an exercise bike up there anyways, so why not hook it up to a generator and get some sort of energy return out of it?

Ronald Brak
2007-Aug-17, 11:56 PM
well, they are going to have an exercise bike up there anyways, so why not hook it up to a generator and get some sort of energy return out of it?

Weight of solar cells (or maybe uranium) versus weight of dynamo.

mugaliens
2007-Aug-18, 03:50 AM
A hundred watts is about how much power a human could generate with light to moderate exercise.[/quote\

Actually, when I ride, I'm generating an average of around 450 watts. Of course I don't ride "light to moderate," but the point is that humans are capable of far more than 100 watts.

If you ride bikes, you can determine how much energy you generate, here (http://www.kreuzotter.de/english/espeed.htm).

[quote]Much better to invest in some solar cells which can be made over 40% efficient.

There you go! :)

publiusr
2007-Aug-18, 08:09 PM
Or just give ISS a big shove with both feet.

Ronald Brak
2007-Aug-18, 08:51 PM
Or just give ISS a big shove with both feet.

Or we could write a story about a ship on it's way to mars that due to a leak doesn't have enough fuel to make mars orbit. To deliver their cargo the crew use themselves as reation mass by leaping out of the ship and the eventually crewless ship makes it to mars orbit and delivers its cargo of baseballs.

loglo
2007-Aug-19, 03:42 PM
It might be better to connect the bike to a generator which feeds an electrodynamic tether which could reboost the station's orbit . It might cut down on the number of resupply ships needed to deliver fuel. :)

Zachary
2007-Aug-21, 07:19 PM
It might be better to connect the bike to a generator which feeds an electrodynamic tether which could reboost the station's orbit . It might cut down on the number of resupply ships needed to deliver fuel. :)

But then you'd have to supply more food and food is much less energy dense than fuel. So you'd need more resupply ships for the extra food the astronaughts would need.

BigDon
2007-Aug-23, 01:12 AM
Still, a hard working man can get by on 6000 calories a day easy. That isn't hard to meet. I was body building and moving furniture at the same time and that kept me stabile at 235 pounds. You can reduce that if the individual has excess fat and muscle to burn. But 6000 calories? That's what, two cheeseburgers and a shot of whiskey? If you can't afford that in your weight budget you shouldn't be going.

Damburger
2007-Aug-23, 07:32 AM
Still, a hard working man can get by on 6000 calories a day easy. That isn't hard to meet. I was body building and moving furniture at the same time and that kept me stabile at 235 pounds. You can reduce that if the individual has excess fat and muscle to burn. But 6000 calories? That's what, two cheeseburgers and a shot of whiskey? If you can't afford that in your weight budget you shouldn't be going.

What the hell kind of cheeseburgers do you get in california!?

BigDon
2007-Aug-23, 08:15 AM
Dam, two quarter pound patties, cooked on an iron or steel grill with cheese on each one, lettuce, pickles and mustard on a sesame seed roll. That's about 2 grand IIRC. (And I don't eat like that normally, I was making a point)

Has to be cooked on iron because the heme in the meat chemically reacts with it to form that tasty crust you can't get with aluminum or coated pans. I have a cast iron frying pan just for burgers and searing beef.

I try to offset the early death factors in these meals by taking in large amounts of fish oil and avoiding transfats. That and a little bit of exercise.

Damburger
2007-Aug-23, 09:05 AM
Dam, two quarter pound patties, cooked on an iron or steel grill with cheese on each one, lettuce, pickles and mustard on a sesame seed roll. That's about 2 grand IIRC. (And I don't eat like that normally, I was making a point)

Has to be cooked on iron because the heme in the meat chemically reacts with it to form that tasty crust you can't get with aluminum or coated pans. I have a cast iron frying pan just for burgers and searing beef.

I try to offset the early death factors in these meals by taking in large amounts of fish oil and avoiding transfats. That and a little bit of exercise.

2000 calories? In ONE burger? Thats insane. I won't even go into the fact it appears to contain metal as well. The recommended calorie intake for a male of normal weight is 2000 calories. Somehow I think getting all this in one uberburger might be a bad thing.

Maybe you've got the number wrong. I can't see how you can get that much chemical energy in one burger without deep frying it in petrol (please please tell me you don't do that?)

Ronald Brak
2007-Aug-23, 08:41 PM
The recommended calorie intake for a male of normal weight is 2000 calories.

8,400 kilojoules? Man, I can get through 13,000 of those things a day without putting on weight.

BigDon
2007-Aug-23, 11:27 PM
2000 calories? In ONE burger? Thats insane. I won't even go into the fact it appears to contain metal as well. The recommended calorie intake for a male of normal weight is 2000 calories. Somehow I think getting all this in one uberburger might be a bad thing.

Maybe you've got the number wrong. I can't see how you can get that much chemical energy in one burger without deep frying it in petrol (please please tell me you don't do that?)

Okay, okay I was exagerating. It's what I do. Most burgers run 800 to 1200 calories. Ya pinned me down.

You do know that movers in the peak of the summer moving season will often have to move 100,000 pounds of furniture in a week? Sometimes for weeks on end? Often up multiple flights of stairs in the case of San Francisco Bay area movers? I've had to move 10,000 pounds up a single flight of 83 stairs near Koit tower once. I can do gruelling work. Its a challenge I'm proud of because I know few people can do it well, especially at my age. I'll be 50 in 3 years. (None of the above paragragh was exagerated)

Van Rijn
2007-Aug-24, 01:11 AM
2000 calories? In ONE burger? Thats insane. I won't even go into the fact it appears to contain metal as well.


I did a search, the Burger King Double Whopper with Cheese (at the top of their range) is 1020 Calories. So make it two big burgers. Of course, there are specialty burger places that put those to shame. Personally, though, I don't eat those, though I've occasionally made a dinner out of a big Carl's Junior burger, and then usually when I haven't eaten much during the day.

By the way, what's wrong with a little iron in the meal?

Ronald Brak
2007-Aug-24, 01:19 AM
By the way, what's wrong with a little iron in the meal?

Iron in a form easily absorbed by your body such as that found in health supplements will kill you if you take too much. But eating ordinary rust isn't so bad.

BigDon
2007-Aug-24, 01:22 AM
Yeah, iron is right up there with calcium as something the body scours out of most food sources. And unless you have a certain genetic defect you'll excrete any excess in your feces via the liver.

I'm getting embarrased at the amount of highjacking here.

BigDon
2007-Aug-24, 01:23 AM
Ron snuck one in on me