MESSENGER Launch Rescheduled

"Derek Lyons" wrote in message

"Allen W. McDonnell" wrote:

Going into orbit is a lot tougher than just doing a flyby, but we have
done
it many times with Venus and Mars and we have suceeded in doing it with
Jupiter once, with Galelio.

Which sounds bad until you realize we have only tried it once - with
Galileo.

D.

Heh. It's this kind of technique I've seen used _intentionally_ in op/eds
here and there with regard to the new space policy, and accidentally (?) in
various news reports. Like saying: "We've only had a single successful
manned lunar program". It's almost "Easterbrook-ish".

Jon

Heh. It's this kind of technique I've seen used _intentionally_ in op/eds
here and there with regard to the new space policy, and accidentally (?)
in
various news reports. Like saying: "We've only had a single successful
manned lunar program". It's almost "Easterbrook-ish".

Jon



That certainly was not MY intention, I was trying to say that if we can do
it at Jupiter we can do it at Mercury for about the same system cost.

Allen W.

On Sun, 28 Mar 2004 08:23:42 -0500, "Allen W. McDonnell"
wrote:


That certainly was not MY intention, I was trying to say that if we can do
it at Jupiter we can do it at Mercury for about the same system cost.

That's exactly the problem. Missions of the same "system cost" as
Galileo and Cassini are few and far between. MESSENGER exists only
because it is relatively cheap, compared to Galileo and Cassini.

Brian

"Allen W. McDonnell" wrote:

Heh. It's this kind of technique I've seen used _intentionally_ in op/eds
here and there with regard to the new space policy, and accidentally (?)
in various news reports. Like saying: "We've only had a single successful
manned lunar program". It's almost "Easterbrook-ish".


That certainly was not MY intention, I was trying to say that if we can do
it at Jupiter we can do it at Mercury for about the same system cost.

All I was pointing out is that your choice of phrasing was somewhat
poor.

D.
--
Touch-twice life. Eat. Drink. Laugh.

"Allen W. McDonnell" wrote in
:

That certainly was not MY intention, I was trying to say that if we
can do it at Jupiter we can do it at Mercury for about the same system
cost.

Allen W.

Getting to Mercury needs about 2km/sec more delta-v than getting to
jupiter. But once there, entering orbit around Jupiter is LOTS easier than
orbiting Mercury. Having a nice deep gravity well in your path is very
convenient, if you intend to enter orbit around it. Mercury's feeble
gravity is virtually useless in this respect. As is, Messenger will make
three flyby's of Mercury, each helping it slow down, before it will be able
to enter orbit under its own power.