MESSENGER Launch Rescheduled

Why should mariner 10 in 1973 require 1 Venus flyby to set up 3 Mercury
flyby's and the 2004 Messenger mission require one Earth flyby, 2 Venus
flyby's and 3 Mercury flyby's before it actually goes into orbit in
2011?
Getting to Mercury is less energy intensive than getting to Jupiter.

Are you sure about that? I thought it was more intensive, since you
effectively have to lose all your momentum.

And going into orbit about a body is also more intensive then doing a
flyby.



You don't want to loose all your momentum, that puts you on a collision
course with old Sol himself, you just want to loose the difference in
orbital velocity for the Earth and Mercury, which is about the same energy
wise as a high asteroidal belt orbit or a Jupiter level orbit.

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.

Using
'energy saver' orbits is fine so long as you have all the time in the
world,
but NASA has developed the IMO bad habit of selecting the cheapest
orbits
no
matter what the time delay. To get people to vote and fund space
missions
you have to give them pretty pictures to look at. Maybe NASA is smarter
than I think because the way they are doing Messenger they will get a
nice
set of Earth pics and two sets of Venus pics to publish, but Venus and
Earth
are somewhat well known. Mercury is mostly still unknown territory so I
want the mission to get there and start Mercury science while I am still
alive and interested, not 7 years down the road when many things may
have
changed in both my life and the world at large.


True, and consider how the scientists whose jobs depend on this feel.

However, more than pretty pictures, people look at the bottom line and
appear to want cheaper rather than faster.


Bean counters are the same the world over, and if I hear one more time how
we can't afford more money on Space when SSI gets 100 times as much funding
with gross CPI raises every year I think I will puke.

Allen W.

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

"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.