Using heat to travel in space

Jun 14, 2022
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As I was repairing my convection oven, replacing the heating element, I thought, could this be used to travel in space? The fan (propeller) blowing heat out of the rear of a space craft? Would this work? I look forward to reading your replies
 

Catastrophe

"There never was a good war, or a bad peace."
In what medium would the heat be?

I ask because if it were in air, you would quickly run out of air.

This will apply to most media, except IR radiation. Then you would have to carry the weight of, and supply power to, the IR generator.

Someone may have a workaround.

Cat :)
 
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As I was repairing my convection oven, replacing the heating element, I thought, could this be used to travel in space? The fan (propeller) blowing heat out of the rear of a space craft? Would this work? I look forward to reading your replies
It could work and it does work! Asteroids gain or lose orbital speed based on heat emission. If they rotate prograde (same direction as their orbit) then the sunlight will heat the surface and as they rotate a greater amount of heat is emitted in the direction that pushes them a tiny bit forward. Of course, retrograde rotation will have the opposite effect and slow them down.

This is the Yarkovsky effect. Over billions of years, it does make a difference.

But the energy of heat emission (IR as Cat mentions) is very weak. If a photon drive is desired, the higher the frequency the more energy a photon has and the more momentum transfer will take place to push the rocket.

Sunlight photons not only impact light sails but they also bounce off giving each impact a double impact effect. So using photons is a real possibility for limited space travel.

Powerful lasers is another photon propulsion method that has been proposed for speeds up to about 0.2c.
 

Catastrophe

"There never was a good war, or a bad peace."
I am rather interested to recall OP opening question:

The fan (propeller) blowing heat out of the rear of a space craft? Would this work? I look forward to reading your replies
My emphasis.

OP asked if this would work and I asked what was being blown out.

So, please, ;) what is being blown out? . . . . . . and, do you think the Yarkovsky will get them to their destinations in their lifetimes? ;)

I did cover myself with "Someone may have a workaround."
I am not well up on lasers. What equipment and any consumables are needed?


Cat :)
 
Jun 14, 2022
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Thanks to all. I was thinking more along the lines of electricity heating the element and being recharged by the propellor? Can heat be used as an air substitute to push the vehicle along?
 
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Thanks to all. I was thinking more along the lines of electricity heating the element and being recharged by the propellor? Can heat be used as an air substitute to push the vehicle along?
Yes, anything that comes off a body floating in space will behave according to Newton's law that states for any action there is an equal and opposite reaction.

But the wimpy IR photons (heat) radiating from a spaceship will do incredibly little to give it any velocity. The more energy given to those photons the more powerful they will be. But even with UV light, you won't be able to compete with other means of thrust unless you could convert, say, fusion energy into a beam of light, perhaps.
 
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Helio, fair comment. I think you will have judged from my 'take' on the suggestion, that I am not overenthusiastic about the suggestion.
Yep, I was trying to address just the OP view.

It is interesting, though, that heat does play a role in motions in our solar system.

This Y-effect applies more to the smaller particles since mass decreases by the cube of its reduced radius, but the surface area that gets sunlight is only cut by the square of this radius reduction. Exactly what results is unclear to me, but the prograde rotations might migrate outward and should produce prograde planets, and opposite for the retrograde rotations. We happen to see this in our system, though major impacts make a difference too. :)
 
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Catastrophe

"There never was a good war, or a bad peace."
Using heat to travel in space

Coming back to the OQ.

I think that there are two cases of using heat/radiation.

1. Heat/radiation that hits you en route. This is caught by a mirror, and used to reflect back in a controlled directional way. Some heat (IR)/radiation may hit you but cannot be used productively like
wimpy IR photons (heat) radiating from a spaceship
. Likewise wimpy Yarkovsky heating (Thanks Helio ;) )

2. Heat/radiation precursors you have to take with you. E.g., heating appliance to emit heat en route. Be careful to ensure that any such items you take with you are worth their weight. If the heat/radiation originates externally, then, if you do not reflect them, you have to absorb them and add (albeit minimally) to your mass, or maybe need to expend energy for cooling.

Cat :)
 
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Fair enough, but do you see the Yarkovsky as a feasible means of controlling space travel?
I see that I said earlier that it could work, but I didn't mean to imply it could work for human space travel. I only meant it works in the realm of physics. This is more obvious by my info on solar sails.

So, to be clear, a heat engine would be very, very impractical as a space engine, as far as I can see.
 
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Nov 19, 2021
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Here are formulas telling how far an oven would travel in one year resulting from a given number of watts in a propulsion system using only heat (not expelled air) as thrust. Assume the oven has 1000 watts of power and weighs ten kilograms.

Force in newtons (1 newton equals about 100 grams) = number of watts divided by the speed of light (in meters per second) squared

The force will then result in a certain acceleration:
Acceleration = force in newtons divided by mass in kilograms

The velocity attained over a certain time, say one year, follows as:
V = Acceleration times time in seconds

The distance travelled:
Distance =1/2 times acceleration times time squared

For example: A 1000 watt microwave oven weighing ten kilograms allowed to go on for one year

Force = 1000 watts divided by (3e8)^2 = 1e-14 newtons
Acceleration = 1e-14 divided by 10 = 1e-15 meters per second squared
Velocity after one year = 1e-15 times 3e7 = 3.3e-8 meters per second
Distance after one year = 1/2 times 1e-15 times (3e7) squared = .45 meter

The oven would travel about half a meter.
 
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Here are formulas telling how far an oven would travel in one year resulting from a given number of watts in a propulsion system using only heat (not expelled air) as thrust. Assume the oven has 1000 watts of power and weighs ten kilograms.

Force in newtons (1 newton equals about 100 grams) = number of watts divided by the speed of light (in meters per second) squared

The force will then result in a certain acceleration:
Acceleration = force in newtons divided by mass in kilograms

The velocity attained over a certain time, say one year, follows as:
V = Acceleration times time in seconds

The distance travelled:
Distance =1/2 times acceleration times time squared

For example: A 1000 watt microwave oven weighing ten kilograms allowed to go on for one year

Force = 1000 watts divided by (3e8)^2 = 1e-14 newtons
Acceleration = 1e-14 divided by 10 = 1e-15 meters per second squared
Velocity after one year = 1e-15 times 3e7 = 3.3e-8 meters per second
Distance after one year = 1/2 times 1e-15 times (3e7) squared = .45 meter

The oven would travel about half a meter.
I will guess sunlight pressure would move it outward by about 25x farther.
 
Nov 19, 2021
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Well, I suppose sunlight pressure would be equivalent to its strength in watts which is 1300 per square meter, so it would probably be about the same, don't you think?
 
Well, I suppose sunlight pressure would be equivalent to its strength in watts which is 1300 per square meter, so it would probably be about the same, don't you think?
If the photons are about 3x — I somehow thought 10x — the energy of IR photons, and you get double action in momentum (absorbed plus emitted), and at ~ 1370 watts/m at 1AU, then I crudely am now guessing a net of about 8x. But I’m goofing-off on this iPhone while visiting others.
 
Nov 19, 2021
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Yes, must double the force due to reflection. Yes, heat oven photons are very weak but there are more of them to the watt. Counting watts causes photon energy to drop out.
 
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Using heat to travel in space

Are we agreed that this is not going to be a practical solution?
Yes, but it is more an extremely poor propulsion method. Heat is often considered waste energy. [I know, of course, you know this as an engineer/scientist, but others might not.] If combustion engines could effectively use more of it, they would. Instead, they simply dump it out the exhaust.
 
Nov 19, 2021
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Granted, light beam propulsion has very low forces but it has a big advantage in that it does not require mass be tossed out the back of the ship.
Perhaps we might start off from the Earth's surface with chemical propulsion, very large forces available to escape the Solar System but at the cost of very high weight.
Then we might transition to ion propulsion, lower in force but frugal with the weight.
At a high enough speed, and once our fuel has run out, we then might transition to a light beam. Very low forces but the effective exhaust velocity is c, allowing for very high final velocities. Power source would probably need to be fusion or antimatter.
 

Catastrophe

"There never was a good war, or a bad peace."
Just a thought: "be tossed out the back of the ship" - it is not going to leave of its own accord. We have to toss it out, so we need to expend energy to gain any propulsion. Taking this into account, is there any net gain in doing this?

Cat :)
 

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