# [extropy-chat] MARS: Because it is hard

Spike spike66 at comcast.net
Thu Apr 15 04:47:10 UTC 2004

```> Alan Eliasen
> Subject: Re: [extropy-chat] MARS: Because it is hard
>
> >
> > Spike: how fast is ELLO? Surely 100KM is long enough to
> stay below 1G?
...
>
>    a = v^2 / r
>
...
>
>     v = sqrt[g r]
>
...
> g = G m / r^2
...
>    v = sqrt[G m / r]
>
>    Plugging these numbers into Frink...
>
>    v = sqrt[moonmass G / moonradius]
>
>    (Frink knows a lot about different planetary bodies.  "G",
>   "moongravity" and "moonradius" are defined units in its data file.

Alan I agree with your equations to here...

>    This gives a velocity of about 1680 m/s.

...but I still get about 1200 m/s here.  The 1680 m/s is
square root of 2 times the answer I got.  This is
perhaps coincidentally the escape velocity from the
lunar surface.

> accelerator will either have to be more than 144 km, or
> you'll need to brake harder.
>
>    You can use Frink to plug in your own numbers.
> --
>   Alan Eliasen

The factor of square root of 2 explains why your
answer for track length is twice mine.  Anyone
want to break the tie?

spike

```