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Comment by joering2 | Hacker News Reader

> I'm surprised they landed so close together.

this doesnt make sense to me. On the orbit they look like they gaining a distance between each other. Any distance on that altitude would be 150-fold back on earth. How come they landed less than 20m from each other, no idea. Anyone?

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The 150-fold figure might apply if they actually took divergent paths back to Earth by a degree or two, but that doesn't seem to be the case--they took very nearly parallel tracks, with a few meteres of random jostling one way or the other. I'm not sure how much effect the explosive detachment from the shuttle+main tank has though / which way those forces are directed.

Interesting reading here on the details of the booster rockets: http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/s...

Once they hit the atmosphere, their lateral motion (groundspeed) is probably greatly reduced by air resistance, while theory downward motion is maintained by gravity. So shortly after reentry, they probably mostly stop diverging.

Still, though, I feel like I would be hard-pressed to throw two objects from space and have them land within sight of each other.

Where do you get the figure of 150? I reason that if they are nearly identical pieces, and falling near each other, wind and other atmospheric forces would shift them about equivalently. Even if they veered hundreds of miles, it seems reasonable that they would do so together.

150 was a wild guess. I think there is so many variables when they orbit in space and drop to Earth, that I don't see it that simple to land one next to another. Its like taking two peppercorns and throwing them at the same time, very close to each other from the Empire State building.

well they are similar objects, undergoing the same forces, and they were released from nearly the same spot (from which they were both traveling in the same direction) the difference is mostly from the forces due to slight differences in tumbling motion when interacting with the atmosphere. just try thinking about conducting the same situation with out an atmosphere. the objects would follow the same trajectory from the moment they were released back to the ground. I'm sure nasa has to try to calculate the specifics/landing location, you dont want SRB's falling on property.

> just try thinking about conducting the same situation with out an atmosphere.

I can't since they DID travel through the atmosphere.

you can't imagine a simple physics problem? i understand that they DID travel through an atmosphere, but the basic mechanics involved can be understood just using projectile motion equation without taking the effects of air drag.

what are you talking about? in this example they were travelling through atmosphere.

I think you can see ships in the background of the video, presumably for recovery. So maybe they know pretty close to where they land, close enough that they don't have to worry about hitting the ships. That's impressive.

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