4 ms·

It doesn't drop vertically back down the elevator cable! It performs a Hohmann transfer from GSO to LEO. The delta-v to transfer from GSO to an LEO at 400km is

It doesn't drop vertically back down the elevator cable! It performs a Hohmann transfer from GSO to LEO. The delta-v to transfer from GSO to an LEO at 400km is 4km/s, whilst to go from ground level is about 7km/s. That's a significant fuel reduction, _and_ that fuel doesn't have to go up all at once: you can keep fuel tankers at the GSO station and fuel up a rocket from there. https://en.wikipedia.org/wiki/Hohmann_transfer_orbit https://en.wikipedia.org/wiki/Hohmann_transfer_orbit

johngalt 11y ago
I believe you are overestimating the cost of a transfer from GEO to LEO and underestimating the costs from ground to LEO. Specifically you haven't accounted for the earth's atmosphere. The earths atmosphere adds to the cost of ground launch (drag) and subtracts from the cost of GEO->LEO transfer (aerobrake). Instead of 4km/s transfer vs 7km/s direct, it should be 2km/s vs 9km/s.
sandworm101 11y ago
4k/s is still a huge number. This will still involve a rocket 1/4 to 1/8th the power of a ground launch. AND, pieces or not, that thing has to be hauled up the elevator. So my point still stands. The space elevator will only provide ready access to geostationary orbit. Journeys to more useful low orbits will benefit marginally at best.
- JupiterMoon 11y ago
  LEO is useful for current satellites. But not that useful for moving human influence beyond Earth's surface.
- CapitalistCartr 11y ago
  Only if you release it from GSO, but that's not ideal. Release it from a higher altitude than LEO, but far less than GSO and it takes vastly less fuel.
  - parenthephobia 11y ago
    Ah yes. There's a lower point on the cable where you're already in an elliptical orbit with the perigee at the altitude you want. For a target orbit of 400km, that happens at about 23.8Mm, 57% of the way up the cable. At that point you just have to let go of the cable and you'll only need a circularizing burn when you reach 400km: Δv of ~2,137m/s. This is not taking into account the further savings from aerobraking as I don't know how to calculate that.

johngalt 11y ago

I believe you are overestimating the cost of a transfer from GEO to LEO and underestimating the costs from ground to LEO. Specifically you haven't accounted for the earth's atmosphere. The earths atmosphere adds to the cost of ground launch (drag) and subtracts from the cost of GEO->LEO transfer (aerobrake). Instead of 4km/s transfer vs 7km/s direct, it should be 2km/s vs 9km/s.

sandworm101 11y ago

4k/s is still a huge number. This will still involve a rocket 1/4 to 1/8th the power of a ground launch. AND, pieces or not, that thing has to be hauled up the elevator. So my point still stands. The space elevator will only provide ready access to geostationary orbit. Journeys to more useful low orbits will benefit marginally at best.

JupiterMoon 11y ago
LEO is useful for current satellites. But not that useful for moving human influence beyond Earth's surface.
CapitalistCartr 11y ago
Only if you release it from GSO, but that's not ideal. Release it from a higher altitude than LEO, but far less than GSO and it takes vastly less fuel.
- parenthephobia 11y ago
  Ah yes. There's a lower point on the cable where you're already in an elliptical orbit with the perigee at the altitude you want. For a target orbit of 400km, that happens at about 23.8Mm, 57% of the way up the cable. At that point you just have to let go of the cable and you'll only need a circularizing burn when you reach 400km: Δv of ~2,137m/s. This is not taking into account the further savings from aerobraking as I don't know how to calculate that.