3 ms·

But you don't need to hit the sails with 100GW to get a few grams of weight up to relativistic speeds right? 1 gram at 0.2c has 1030MWh of energy. So at 1Mw of

by rocqua 2y ago

But you don't need to hit the sails with 100GW to get a few grams of weight up to relativistic speeds right? 1 gram at 0.2c has 1030MWh of energy. So at 1Mw of received power it would take 1030 hours or about 60 days to accelerate 2g to 0.2c. I believe most plans call for much more than 60 days of acceleration. So less than 1Mw of power needs to be delivered to the solar sail. Realistically the mass will be more than 2g. Lets say they roughly cancel out. At 99.99% efficiency that would be 100w to dissapate. Seems like a lot, but could be doable.

ben_w 2y ago
> 1 gram at 0.2c has 1030MWh of energy. So at 1Mw of received power it would take 1030 hours or about 60 days to accelerate 2g to 0.2c. If only we could perfectly convert laser light into kinetic energy, this kind of thing would be much easier. Light has momentum: 1 GW/c is ~3.336 N, but that's when absorbed, by reflecting it (and because of conservation of momentum) you can double that. 6.672 N / 2 grams = 3336 m/s^2 => 5 hours 1 MW/c makes that 60 weeks: https://www.wolframalpha.com/input?i=0.2c+%2F+%28%281+MW%2Fc%29+%2F+2+grams%29 https://www.wolframalpha.com/input?i=0.2c+%2F+%28%281+MW%2Fc... (I assume the researchers have done all the relevant details or it wouldn't have gotten this far).
bufferoverflow 2y ago
You obviously forgot to calculate how far your accelerators would have to be spaced out if you're accelerating that slow. At 2g and 60 days, your system would have to span 263,632,527,360 km. That's more than 10 times further than Voyager 1, which is tiny space probe that has been traveling for 47 years. And that also assumes that your light to speed conversion is 100% efficient and that you can hit the 1-gram target perfectly over 263 billion km. Sorry, it doesn't work no matter how you slice it.

3 ms·

But you don't need to hit the sails with 100GW to get a few grams of weight up to relativistic speeds right? 1 gram at 0.2c has 1030MWh of energy. So at 1Mw of

by rocqua 2y ago

ben_w 2y ago
> 1 gram at 0.2c has 1030MWh of energy. So at 1Mw of received power it would take 1030 hours or about 60 days to accelerate 2g to 0.2c. If only we could perfectly convert laser light into kinetic energy, this kind of thing would be much easier. Light has momentum: 1 GW/c is ~3.336 N, but that's when absorbed, by reflecting it (and because of conservation of momentum) you can double that. 6.672 N / 2 grams = 3336 m/s^2 => 5 hours 1 MW/c makes that 60 weeks: https://www.wolframalpha.com/input?i=0.2c+%2F+%28%281+MW%2Fc%29+%2F+2+grams%29 https://www.wolframalpha.com/input?i=0.2c+%2F+%28%281+MW%2Fc... (I assume the researchers have done all the relevant details or it wouldn't have gotten this far).
bufferoverflow 2y ago
You obviously forgot to calculate how far your accelerators would have to be spaced out if you're accelerating that slow. At 2g and 60 days, your system would have to span 263,632,527,360 km. That's more than 10 times further than Voyager 1, which is tiny space probe that has been traveling for 47 years. And that also assumes that your light to speed conversion is 100% efficient and that you can hit the 1-gram target perfectly over 263 billion km. Sorry, it doesn't work no matter how you slice it.