Gas is much more efficient than batteries. And as to the weight, we
are not going to see battery powered aircraft anytime soon. I think a
balloon would work even if you have to bring both components for
combustion. If we only need to heat some air to gain boyancy, the
amount a fuel necessary is minimal compared to powering a jet or a
rocket engine. Sending liquid oxygen into space is 40 years old proven
technology. A balloon is not as good as a rover, but great science is
done with weather balloons on earth all the time. A Titan balloon
which could map terrain for a few days would be a step up from
dropping a volkswagen on Titan for a couple of hours. I don't know how
long Cassini is expected to last, but Voyager is still sending data
from the heliopause and there is opportunity here to send another
mission to Titan in the next decade and use Cassini to relay the
messages. A rover is not going to happen, but something ambitious just
might.

Paul C


On Sun, 23 Jan 2005 22:03:05 GMT, "David Nakamoto"
wrote:

A rover had more control over where it goes, and can go short distances in a
controlled fashion. A balloon is great for surveying large swaths of land but
is lousy for in-situ measurements where precision of positioning is concerned.
Also debatable if there's enough methane in the atmosphere to collect and burn.
Carrying oxygen is a heavy proposition even in liquid form, while you always
need some form of battery if you're going to operate equipment.

A combined rover - balloon device, in case anyone is tempted to think along
these lines, is going to be so heavy and cumbersome to design and invent that it
won't be practical. Aside from the excessive complexity of such a beast is the
fact that no one has ever tried to fly such a beast. Lots of experimentation to
find out how to do it, and NASA isn't rolling in dough the last time I checked.

One thing people don't realize is that it's a totally different thing when a
human is there to pilot something than when a robot has to do it. You can't
control the thing remotely in real time - the round trip light time is over two
hours. And robots are less flexible than human beings at handling extreme or
difficult situations, and of getting themselves out of the slightest trouble.

This is another case of an idea inadequately thought out. Reminds me of one of
the lessons learned from professional writers when someone submits a rough idea
to them and asks them to write it up. As I personally know, the idea is 1% of
the work, and the actual write-up is the other 99%, hence the guy who came up
with the idea should only get 1% of the profit, but they never realize the work
involved, nor accept the fair payment. A little thought would have ferreted the
difficulties out, but then it's so much easier to do 1% of the work than the
full 100%.