re: Cassini/Huygens Saturn probe flyby

Philip Chien (
Wed, 3 Feb 1999 09:12:20 -0500

"Bryan & Jane Carney" <> asked:

>    I have read that Cassini Saturn probe will make a speed gathering flyby
>of earth in August (having all ready done the same with Venus) .The pass
>will be at a distance of  1000km.
>    - Will the probe be visable ? ( I assume its speed will be pretty fast

Recall that Cassini doesn't have solar arrays or other highly reflective
surfaces.  And nuclear RTGs are relatively small and non-reflective.
Neverthless it is *LARGE*.  I saw it in its cleanroom before launch - this
is a TWO STORY high spacecraft.

>    - If so ,will it be possible to generate an Elset for it ?

Objects in orbit around the sun (as opposed to around the Earth) need solar
keplerian elements.  There are several sky chart programs which permit you
to enter the elements for asteroids.  Of course few asteroids are coming
close enough to the Earth for a gravitational assist ...  In theory you
could use one set of solar keps for the incoming trajectory and another set
for the outgoing and assume that there's an instantaneous change in
velocity at the point of closest approach.  Maybe JPL's public outreach
program could make those elements available.

The other challenge would be to determine when Cassini's in sunlight while
you're in darkness.

Minor details like ensuring that you're on the correct side of the Earth
and ensuring that the weather cooperate are left as exercises for the
reader.  ;-)

The Galileo probe flew by the Earth in December 1990.  By coincidence the
shuttle was in orbit on the STS-35 ASTRO-1 mission.  Mission Control
radioed up viewing angles and Jeff Hoffman and Mike Lounge looked but
didn't see anything.

Philip Chien, KC4YER
Earth News
world (in)famous writer, science fiction fan, ham radio operator,
all-around nice guy, etc.