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Comment by joering2 | Hacker News Reader

Has been fixed by now.

IF you have spare monitor going at your office/home, its fun to watch the ISS up to second tracking locations [1].

Fun fact I learned lately about ISS: at 400km above Earth's surface, the gravity is about 80% of a normal Earth gravity. The ISS is constantly falling down but because of Earth rotation it is falling "at the edge" so to speak so it never actually fell on the ground. Hope that make sense, I'm sure you read better explanation on Wiki.

[1] http://www.esa.int/Our_Activities/Human_Spaceflight/Internat...

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I prescribe you 20 hours of Kerbal Space Program as homework.

Ksp is a truly amazing game.

That is what orbits are, really. Just falling around a bend.

> so to speak so it never actually fell on the ground.

Well, that and the rocket motor the have onboard that allows them to periodically reboost[0] the entire station to a higher orbit.

[0]: https://www.youtube.com/watch?v=CsZUkrGGfuo

That’s the equivalence principle: https://en.wikipedia.org/wiki/Equivalence_principle

>Fun fact I learned lately about ISS: at 400km above Earth's surface, the gravity is about 80% of a normal Earth gravity.

That doesn't seem to match the movies of ISS shown, where there seems to be no (or very small) gravity. In 80% of normal earth gravity water wouldnt stay up in the air for example, and cosmonauts wouldn't be floating around in the station as we see in the videos...

The ISS is orbiting, it's falling sideways fast enough to miss the earth.

It's effectively in freefall, so although objects at 400km altitude are subject to 80% of the gravitational pull you experience on the ground, the astronauts don't notice it because they're falling sideways at the same speed as the ISS.

Edit: I just noticed that the post you were replying to included pretty much the exact same information I did, so I apologise if what I've said hasn't helped.

The gravity is there, thats what keeps the ISS in orbit. However the gravity acts on everything in the ISS the same, so there is no relative acceleration in the ISS. A cosmonaut who is not touching anything and not moving relative to the walls will thus stay not touching anything, yet at the same time will still be accelerating towards the earth.

This is why we should use the term "free-fall", instead of "zero-gravity".

There is no way known to remove gravity. At best, you can cause the room to fall at the same rate as the things inside the room, causing the contents to float around.

It's the same principle that allows specialized airplanes to create the sensation of weightlessness, while very-much in almost Earth-surface gravity.

>There is no way known to remove gravity

Well, you can go far away from large masses to effectively diminish e.g. earth's gravity though, no?

>It's the same principle that allows specialized airplanes to create the sensation of weightlessness, while very-much in almost Earth-surface gravity.

Yes, but I was confused because space offers also regular diminished gravity, and we also have the example of the astronauts on the moon, where gravity was much much smaller.

But I should have guessed that at the height ISS is it's too little to actually reduce gravity at any substantial way, and it's all the effect of the orbit/free fall.

cool, I hadn't seen that link before. thanks.

You welcome!

And you welcome to upvote me, since no matter what I say, a few of HN moderators will continue to be down-voting my postings.

Oh well...

Is that what is happening? I was struggling to see a possible reason for why your post was being voted down, and unless your original post was modified, there are not many other explanations (unless people don't understand how gravity/orbits work).

I would be very disappointed if members of the HN community are voting down your posts because of who you are, rather than the content. I'd like to think we're above that sort of petty behaviour. If it were were moderators abusing their positions...

Yeah I have no idea why your parent post got down voted. Why do you say HN mods downvote you?

Seriously? "Get the latest Flash player to view this content". Wow, just wow.

2018 is almost 3/4 done, and we still have sites with Flash.

I guess they're too busy building boring old space stations.

That's why you staff that stuff out.

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