NEA trajectory / relative velocity

andy-nimmo wrote:

> Hi John,
>
> You say, "Quite the contrary: Its orbit is very like ours (definition
> of NEA). Similar mean distance from the Sun necessarily means that its
> velocity around the Sun is similar to ours around the Sun. Hence, low
> Delta-V requirement." This is simply untrue. For its velocity to be
> similar to ours in a similar orbit it would have to have similar mass
> to us, and none of these do.

What matters is the ratio between the mass of the Sun and the object
orbiting about it. If the masses are reasonably similar they each orbit
about.in between them. As long as the sun's mass is sufficiently
dominant, the satellite effectively orbits around the center of the sun
regardless of its mass.

The equation is: GmM/r^2. So if m <<<< M variations in m don't matter
much.

> --

Al Globus
aglobus@..., (650) 604-4404
http://www.nas.nasa.gov/~globus/home.html

The dinosaurs weren't spacefaring. We are. I don't think that's an
accident.
Maybe we are life's taxi to the stars.

I think we should:

1. Devote half of NASA's budget ($7 billion) to reaching NASA's 2020
goal of
reducing launch costs to Low-Earth-Orbit to $220/kg with a 0.01% failure
rate.
This should enable space tourism. The resulting orbital hotels will need
to
develop efficient orbital life support and other necessary technologies.

2. Build orbital space colonies. The materials in the largest asteroid
are
sufficient for orbital colonies with a combined surface area about 500
times
greater than Earth's. Eros alone could make over ten thousand space
colonies,
each with about about 10 square kilometers of 1g living area.

3. After a few generations of orbital living, people won't need their
colony
to be near Sol. Then small groups of colonies with populations in the
tens-of-thousands can set out on multi-decade journeys to nearby stars.

Except the launch goals, none of this is even a little bit official.