On Tue, 05 Feb 2008 16:27:07 -0600, Michael Ash <mike@[EMAIL PROTECTED]
> wrote:
>Robert Martinu <invalid@[EMAIL PROTECTED]
> wrote:
>>> Another option is to use a bigger rocket, of course, if
>>> available.
>>
>> That collides with the "within a decade"-statement as Cassini already
>> used the biggest laucher available.
>
>A quick trawl through wikipedia reveals that this is not entirely true,
>although it was quite big. I found three launch systems with greater
>payloads than Cassini's Titan IV, the Delta IV, the Proton, and the
>Shuttle. Of these three, the Proton is barely any higher, and the Delta
IV
>has about 20% greater payload to LEO. I believe you could also increase
>the payload further by the simple expedient of launching from a more
>equatorial launch site (Cassinia was launched from Florida). Adapting the
>launcher and the facilities in Guiana is probably non-trivial, but this
>can be carried out in parallel with the probe development, and I would
>hope would not take many years.
>
>I have no real idea how much an equatorial launch would help or how much
>the extra payload capacity would reduce the travel time, but it must make
>some difference.
I get about a 1.5% gain in payload to LEO, 2.0% to Earth escape. And
judging by the Franco-Russian experience in launching the Soyuz from
Kouru, that's going to take rather more than three years to set up.
Kouru was chosen specifically for launches to Geostationary orbit, which
is by definition equatorial. You lose a lot of payload if you have to
do a plane-change maneuver anywhere near Earth. For interplanetary
missions, you don't have to do that - just pick the right launch window,
and those come twice a day. The gains due to just the extra rotational
velocity, aren't all that impressive - Kennedy is already 87.9% of the
way to the Equator.
Also, you can't really do probe *development* in parallel with launch
preparation, as each launch is different and the launcher people need
to know a lot of the technical details before they start making plans
and bending metal. There's a nominal 24-month lead time on Delta IV
launches, and the Heavy version you're talking about is proving to be
somewhat of a hangar queen compared to the stock DIVM. Proton claims
it can handle a new spacecraft on 18 months' notice, so that may be a
better bet.
Since a Hohmann transfer to Saturn takes about six years, that gives you
two and a half years to assemble your team and design your spacecraft.
Or you can hope the launcher people can beat their advertised schedule,
but based on past performance that's not a very safe bet.
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