Hacker News Reader

Hacker News

Comment by nickalaso | Hacker News Reader

Parent Full thread

nickalaso

It would be a pretty good idea if it didn't require such an insane amount of delta-v to deorbit a payload into the sun.

View on HN

We just need to lift it there with a space elevator and then nudge it into the sun.

And then in a few thousand years we will be kicking ourselves for incinerating incredibly valuable resources.

It is less delta-V to launch something out of the solar system than it is to drop it into the sun.

Assuming you're not worried about nuclear waste leaving our solar system and becoming a problem for others, it makes absolutely no sense to launch it into the sun.

> becoming a problem for others

That seems a bit optimistic of a problem to have. Space is incredibly huge. For someone to accidentaly bump into it would have odds so huge I don't even know how to aproximate it.

There's no such thing as 'nudging' it into the sun. If you don't push hard enough, it will enter an orbit that coincides with earth's. And to push it hard enough you basically have to get it going away from earth at the speed earth orbits around the sun, which is quite fast.

Anything less, and it will be in an orbit that floats close to the sun then floats back up towards earth, more or less forever.

I think that we're going to need a bigger space elevator, then.

It's just being converted to solar :)

wouldn't you only need to deorbit if you "missed"? it's not like we're trying to safely land on the surface of the sun. we don't need it slow down at all, just aim straight for the middle and accelerate in.

As Earth is in orbit around the sun, everything launched from Earth automatically is also in orbit around the sun. To go into the sun, you need to deorbit from that orbit. Earth's orbit around the Sun has an orbital speed of about 30 km/s, so you need to cancel that to drop into the sun.

It doesn't have to get there fast. So what would the effect of putting up solar sails to create some drag to slow down? Wouldn't need heavy fuel to generate delta-v. Would the expense of a system to deploy/unfurl a solar sail cost more than fuel powered thrust?

Aside from the practical concerns with solar sails, there's a fundamental problem with using them to get to the Sun. To lower your orbit, you need to exert thrust in the retrograde direction (directly opposite to the direction you're going). However, that's perpendicular to the direction of the sunlight you receive, so a solar sail cannot generate any thrust in that direction!

once you've negated the delta-v, reel in the sails or detach them or whatever. at that point, Sol's gravity should do the rest. i'm sure some smart people with slide rules could determine when to do it to not be influenced by Venus/Mercury on the way in.

> once you've negated the delta-v

My point is that you can't cancel out the velocity of your orbit around the sun using solar sails.

So if you had the sail at a 45 degree angle to the sun, bouncing the photons forward to your orbit, wouldn't that eventually slow you down? Or do you get pushed outward into a slower orbit at the same time and cancel it out?

It's all a moot point anyway since solar sails are so ridiculously impractical that this would basically never work in real life regardless.

What about using mass drivers instead of chemical rockets?

Theoretically, sure. Practically we've entered science fiction territory here.

Yeah, I figured we did once we started talking about solar sails and space elevators.

Up next is just let the thing hang out in orbit around the sun at 1AU waiting for one of these "near miss" asteroids to come wizzing by so we can "catch" it with a net and let it drag our trash to the inner reaches of the solar system.

Reply on news.ycombinator.com