Electromagnetic Propulsion

[joekgamer]

Currently, (unmanned) spaceflight is limited primarily by two factors: cost and fuel. While the first one is probably inevitable, there has been some promising research as of late into "solar sails" - large, thin sheets that catch light from, for instance, the sun, using that force to accelerate. However, solar sails are very large and fragile, tending to fail even before launch. This problem lead me to wonder if one could "reverse" the idea of a solar sail, and instead use some sort of electromagnetic radiator mounted to the craft itself as a thruster. All one would need to do to ensure sufficient fuel is to include a small battery and solar panel. However, despite the seemingly simple nature of the idea, I have been unable to find anything more closely related than this forum thread.

 

Anyway, what does everyone here think? Is the idea realistic? Unrealistic? Is there something wrong with the idea in a fundamental, theoretical level?

[CraigD]

This problem lead me to wonder if one could "reverse" the idea of a solar sail, and instead use some sort of electromagnetic radiator mounted to the craft itself as a thruster. All one would need to do to ensure sufficient fuel is to include a small battery and solar panel. However, despite the seemingly simple nature of the idea, I have been unable to find anything more closely related than this forum thread.

 

Anyway, what does everyone here think? Is the idea realistic? Unrealistic? Is there something wrong with the idea in a fundamental, theoretical level?

This is a well-known idea (by spacecraft enthusiast, at least) known as a photonic rocket.

 

The only thing I can see wrong with your post is the assertion/assumption that “All one would need to do to ensure sufficient fuel is to include a small battery and solar panel.” Like convention reaction-mass expelling rockets with a very high exhaust speed (photons are as fast as you can get, though not exactly comparable to ordinary reaction mass), photonic rockets have very high power/thrust ratios: for the simple radiator attached to the ship scheme you describe, 300,000,000 W/N. To produce 1 Newton of thrust (enough to accelerate 1 kg by 1 m/s/s, about 1/10th of a g), you’d need 300,000,000 W, about the output of 6 small (50 MW) naval nuclear reactors, far from a “small battery”. A nearly perfectly efficient solar panel at Earth’s distance from the Sun would need to be about 250,000 m², about a 500x500 m square, far from a small solar panel.

 

Given the mass requirements of a power source for a photonic rocket, given best current energy density technology (nuclear fusion), they’d have maximum accelerations of about 0.0001 m/s/s. This acceleration, sustained continuously, would travel 1 light-year in about 436 years.

 

A photonic rocket capable of much higher accelerations would need to have a much higher power/mass ratio than nuclear fission of fusion can provide. AFAIK, the only such possibility is antimatter fuel, which likely won’t be available for many decades.

 

We’ve had several discussions of this here at hypography. This google search finds several of them.

[belovelife]

i was thinking the same thing, like use a laser onboard to power it,

 

or multiple lasers, specifically tuned to allow for a thrust

 

i think i was told that it would wear away in time or something,

[7DSUSYstrings]

I'd gladly take a look at the link, but when I went to join at that site, they assumed I was some other member they'd banned, when I was just the same person as here, save for a different nick, and banned me immediately. Those our our "mainstream" physicists for you.

 

Beyond that, electromagnetic propulsion as you are suggesting might be possible, but doesn't it seem more effective to use an electromagnetic pulse generated at a frequency so high that it would deflect gravity itself?