Re: Location, Location, Location!

Henry Spencer wrote:

In article <joe-35C36D.10573427122006@xxxxxxxxxxxxxxxxxxxxxxxx>,
Joe Strout <joe@xxxxxxxxxx> wrote:

...But is it possible, with enough finesse, to toss things to one of the Lagrange points and have them stay there (or arrive so close to staying there that they could be caught with relatively little energy)?


There was some work, a number of years ago, on "achromatic" trajectories,
lobbing from a carefully-chosen location on the lunar surface to lunar L2. With the right location, there is a focusing effect, and even trajectories
with small errors end up passing through L2, although perhaps in slightly
different directions or with slightly different transit times. And the
arrival velocities are low, so a catcher system could be positioned there.

With patience and cleverness, you can get almost anywhere high up in the
Earth-Moon system from L2 at quite small cost. So although the catcher
probably needs to be there, the colonies could easily be elsewhere.


This is one of the topics James Nicoll likes to throw out in his blog.

It may be possible to go a long ways with just a little delta vee, but trip times are very long. It doesn't seem practical to me.



HEOs tend to be either substantially more expensive to enter and leave

Aren't the least expensive orbits to enter or leave HEEOs (highly elliptical earth orbits)?

Dipping the perigee a tad can shed velocity a little at a time as the perigee passes through the upper atmosphere. I believe MRO did this.
http://www.astro.uio.no/ita/artikler/tema/MRO/images/aerobraking_med.jpg

A burn at perigee gets a lot of bang for the buck from the Oberth effect and the fact that an HEEO is going nearly escape velocity at perigee.

It wouldn't take much delta vee to snag incoming asteroidal material to an HEEO.

Hop
.

Relevant Pages

  • Re: Ballistic entry into circular orbit?
    ... mass, perigee at the gun 4,000 miles out. ... to do so when the satellite is at apogee. ... velocity, and is under no accelerations other than gravity. ...
    (sci.physics)
  • Re: Ballistic entry into circular orbit?
    ... mass, perigee at the gun 4,000 miles out. ... to do so when the satellite is at apogee. ... velocity, and is under no accelerations other than gravity. ...
    (sci.physics)
  • Re: Ballistic entry into circular orbit?
    ... basic orbital mechanics says the orbit intersects ... | mass, perigee at the gun 4,000 miles out. ... | to do so when the satellite is at apogee. ... | velocity, and is under no accelerations other than gravity. ...
    (sci.physics)
  • Re: Ballistic entry into circular orbit?
    ... radial velocity to get out of the draggy atmosphere, ... mass, perigee at the gun 4,000 miles out. ... to do so when the satellite is at apogee. ...
    (sci.physics)