From: "Anthony Van Herrewege" <anthony_v_h@yahoo.com>
Sent: Friday, November 12, 2004 9:13 AM


>> g =3D G*M/(r+h)=B2

Actually, this is supposed to be Newton's Law of Universal Gravitation, s=
o M
as stated above is the product of the mass of the earth and the mass of t=
he
spacecraft.  That makes your value for M below a little wrong.  Luckily, =
you
don't need it or big G because they are constants for the system we're
dealing with.  This is in reality a ratio question.

let g1 be g at earth's surface and g2 be g 71 kilmoters up.  Then:

g1/g2 =3D [(G * M)/r^2] / [(G * M)/(r+71)^2]
g1/g2 =3D [(r+71)/r]^2
using your values for r and g1 from below:
g2 =3D 9.745616


> G =3D 6.67300 =D7 10-11 m3 kg-1 s-2
> M =3D 5.9742 =D7 1024 kilograms
> r (=3D earth radius) =3D 6378137 meters
> h =3D 71 miles =3D 114263.424 meters

> so: g =3D 9.457803517 at 71 miles above sea level
> if you take h =3D 0 you get g =3D 9.799709356 with these constants (whi=
ch I
got from Google), so there isn't a lot of difference between the two.


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