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Comment by tomc1985 | Hacker News Reader

tomc1985

Could an astronaut grab a smaller satellite and simply chuck it towards the sun? Would it have enough velocity break out of earth orbit or would it just get stuck in some really large, wide, graveyard orbit?

If not the sun then maybe the earth?

That would be a fun spacewalk.

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To fall into the sun you would have to negate most of Earth's orbital speed which is about 29.8 kilometers per second. To escape the solar system you need about 42.1 km/s of speed. It actually takes less energy to yeet yourself out of the solar system from Earth than to fall down into the sun. If you threw an object from Earth's orbit along Earth's orbital path an extra 12.3km/s that object would be going 42.1 km/s and eventually but barely leave our solar system.

Unfortunately throwing things at kilometers per second by hand is not possible, 1 km/s is just under 2237 mph.

Of course with atmospheric drag for most low orbit satellites things will come down eventually, in which case throwing something the right way could add or subtract from the time it will stay in orbit, but that would be highly dependent on where you started. And LEO is already like 7.2 km/s or about 16,000 mph. Standing on a massive enough satellite using a large stick or like a sling staff would certainly help you get more speed in your throw though. A 100 mph baseball throw really wouldn't be that significant though.

It takes a "huge" amount of energy to get something to the sun.

Something in earth orbit is also orbiting the Sun. The Earth is traveling ~30km/second around the Sun. If you want to fall into the sun, you have to cancel out all that sideways speed.

Another fun thing I didn't really understand all that clearly until I spent time playing KSP: Why it's theoretically easier to get to the Sun from Pluto than it is to do so from here.

Related: my mind was blown when I realize how easy it is to fall down to Earth (well, Kerbin) if you're in high enough orbit. I've had cases where my orbital velocity was on the order of 200 m/s, which means that at apoapsis you can just fart, and have the satellite crash into the ground a day later.

(I've also had my fair share of high-orbit missions where in the middle of the launch I realized I'm aiming for a prograde orbit, where the contract specified retrograde. Instead of reloading game from launchpad, I just carried on, put my apoapsis at target altitude, and once reaching it, burned off couple hundred m/s of Δv to reverse the orbit's direction.)

The point isn't really for it to fall into the sun, just to push it to some kind of orbit that is irrelevant to the space junk problem.

Orbits are periodical. Anything you throw at the sun will come back up to the same height soon enough.

(Ignoring smaller effects)

It would be difficult for an astronaut to chuck an object with over 32,000m/s of delta-v.

For comparison, the fastest bullets go like ~1,500m/s, and they are very very very small.

I think the goal would be to first accelerate the astronaut to that level of velocity and then relatively adjusting its trajectory isn't so difficult. But, that is just my understanding that speed is relative (especially in space with no drag)

Speed is also extremely expensive due to the rocket equation- changing your velocity, that is.

It would surely be easier to accelerate space trash into the sun than it would be to accelerate both the astronaut and space trash into the sun.

I don't think we should do either of those, but less mass is always easier to speed up.

If I chuck a baseball out of an airplane I don't have to worry about accelerating the baseball to the airplane's speed, as I am also traveling at that speed.

Similarly, if a satellite is light enough in low-G to grab and manipulate from a craft that has straddled up along side it, would a single astronaut have enough strength to use his arms to put a satellite on a path that is effectively out of the way? Or could they just chuck it back at the earth so it can burn up on reentry?

edit: it's 24k, not 32k, I had the wrong number initially

edit2: actually now I'm not so sure, I might have had the right number initially. It's either 24k or 32k. Either way it's impractical.

24,000m/s is the difference in speed that the astronaut is already traveling with the speed necessary to get to the sun

Getting to the sun is really hard.

Chucking it back into the atmosphere is much easier, but GP was asking about throwing things into the sun.

> If I chuck a baseball out of an airplane I don't have to worry about accelerating the baseball to the airplane's speed, as I am also traveling at that speed.

But the speed of the baseball you just thrown out will be (ignoring air friction) that of the airplane +/- 40 m/s, assuming you're some super strong thrower.

> if a satellite is light enough in low-G

Microgravity doesn't mean the satellite is light now. It still has the same mass, it's just that you're both in free fall, so it doesn't pull away from you. For the purpose of throwing it, the satellite is just as hard to throw as it would be on the surface of Earth.

But even assuming it weighs as much as a fastball, when you throw it super hard, you'll change its velocity by... 40 m/s at best. Compare that with the orbital speed, which is many kilometers per second (e.g. about 7.6 km/s if you're on ISS). So e.g. instead of going 7.6 km/s, the thrown satellite now goes... 7.56 km/s. Which translates to one end of the orbit dropping by a couple hundred meters. So instead of 408km, it'll now go as low as... 407.5km, or something in that ballpark.

That's the limit of what you can achieve by just tossing things with muscle power.

The ∆v to escape Earth orbit is generally quite large, and it's far, far greater still to collide with the Sun (though this wouldn't normally be considered necessary).

In comparison, a deorbit burn is usually relatively inexpensive.

From low Earth orbit, delta-v to Earth and to escape the solar system are about the same. Delta-v to fall into the sun is two orders of magnitude bigger.

Directly. Not if you take it the long way - near escape to reduce orbital speed, a little push to cancel the rest, and you will fall directly into the Sun (with a high velocity).

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