undefined | Better HN

0 pointsbisby5mo ago0 comments

A space elevator doesnt just take you to the karman line (like in the OP website), to get to orbit, you'd need to get up to geostationary height. That's 22,000 miles.

What's the best way to pull yourself directly vertical along a cable for 22,000 miles?

What's the best way to descend 22,000 miles quickly, but also with a braking mechanism that isn't going to require a heat shield?

Some sort of slow cable car going at 10mph even is going to take 2200 hours... 1000mph is going to take 22 hours still. That's a full day to orbit even going REALLY fast. And getting up to 1000mph vertically, for a sustained 22 hours... that's not an easy feat.

And if the goal is just to get up past the karman line and use the elevator as a stage 1 for a rocket launch and detaching from the elevator while suborbital is fine, then it's a one way trip, and still need to re-enter the old fashion way.

The scale of space makes all of the problems far more complicated (edit: not just the cable strength issue, but traversing the cable)

0 comments

notahacker5mo ago

Unless we're using it for humans the transit time isn't that big a deal; "last mile" orbital transfer times are often measured in days anyway.

That "last mile" bit is going to entail independent propulsion anyway. Getting to the altitude if the ISS is a mere 10 hour trip at a sedately 40kph which isn't unpleasant even for humans, but the ISS orbits at nearly 29000kph (as will you if you let go of the space elevator at that altitude) and the velocities are only half as scary at the far end, so your rendezvous anywhere other than one specific point in geo is going to be complicated. But you've saved the fuel costs of escaping the earth's atmosphere that's rather significantly more than the fuel costs of other bits of your satellite mission, including reentry. (At least until the costs of building and maintaining and protecting the elevator are factored in, but who knows what unobtanium costs?)

gizmo6865mo ago

> as will you if you let go of the space elevator at that altitude)

Doesn't the teather have a constant (24 hour) rotational period at every elevation? That is significantly slower than the ISS

notahacker5mo ago

fair point, you'd need to be orbiting at that speed to stay in that orbit, but you'd need propulsion to get the delta v to get there after letting go of the tether, but a lot less than to launch from ground level through the atmosphere. Or you could figure out the point higher up the tether to release where your orbital decay would intersect the IS orbits, but given the precision involved in that rendezvous you'd still want propulsion. You'd want propulsion for the last mile bit for pretty much anything other than building a station attached to the tether was kind of my whole point :)

oofbey5mo ago

You don’t need to get to geostationary to get to orbit. The reason elevators need to get that high is because that’s the lowest place you could “anchor” the top of the elevator to something fixed relative to the earth.

j / k navigate · click thread line to collapse

0 pointsbisby5mo ago0 comments

A space elevator doesnt just take you to the karman line (like in the OP website), to get to orbit, you'd need to get up to geostationary height. That's 22,000 miles.

What's the best way to pull yourself directly vertical along a cable for 22,000 miles?

What's the best way to descend 22,000 miles quickly, but also with a braking mechanism that isn't going to require a heat shield?

The scale of space makes all of the problems far more complicated (edit: not just the cable strength issue, but traversing the cable)

0 comments

notahacker5mo ago

Unless we're using it for humans the transit time isn't that big a deal; "last mile" orbital transfer times are often measured in days anyway.

gizmo6865mo ago

> as will you if you let go of the space elevator at that altitude)

Doesn't the teather have a constant (24 hour) rotational period at every elevation? That is significantly slower than the ISS

notahacker5mo ago

oofbey5mo ago

j / k navigate · click thread line to collapse