In article ,
Steve Harris wrote:
Here's my own related question: why the devil didn't we take advantage
of economies of multiple production, to make more than one
Cassini-style probe when we're doing the first one?

Mostly because it was already too expensive the first time. There *was*
going to be a similar (not identical, but similar) spacecraft built for
the CRAF comet-rendezvous mission. But CRAF was canceled to save money,
and Cassini itself was cut back in certain areas. Cassini owes its
survival to Huygens, pure and simple -- Cassini too would probably have
died, had there not been a major international commitment involved.

(And alas, Huygens is really quite specialized to Titan. There's no
comparable target at any of the other outer planets.)

...You know they have to gear up to
make at least 2 (the one to launch, plus a backup for Earth simulation).

Actually, no, it has been decades since such major missions built a
complete backup spacecraft. Subassemblies, yes, but not a complete spare.
There was no Galileo or Mars Observer backup, never mind a Cassini backup.

A lot of people thought there should have been a Galileo-Saturn mission;
there were minor provisions made for it in some of the development work.
Didn't get funded.

So what's the bill to simply make a couple more?

Making them wouldn't be that expensive, with the exception of the RTGs.
Launching them (on Titan IV) costs maybe three hundred million each.
Between spacecraft, RTGs, launch, and a decade or two of operations, it's
still probably the better part of a billion each. Not as expensive as
another start from scratch... but there isn't going to *be* another start
from scratch on that scale. In some ways, Cassini was the last gasp of
the Cold War.

...And the big
differences in arrival time would let the data teams still do both
planets in sequence, with plenty of time between.

Kind of, maybe. Note that the travel time isn't wasted -- much of the
detailed post-arrival planning for such missions is routinely left until
after launch, to help smooth out the operations load.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |