"Brian Gaff" <bria...@blueyonder.co.uk> wrote in message

news:nQ9Ej.25552$XI.20777@text.news.virginmedia.com...

Well, the main thing though is ot to run out of the gas you want to
ionise
and accelerate as your propellant. I see no reason why you cannot make it
as
small as you like, but there must come a point where its really not worth
doing when added to the weight and complexity of the craft you are using
it
on.

But you'd only be adding the propellant, tank and engine; the power source
(the main reason ion thrusters form such a major part of the overall mass of
a probe) is already on the vehicle. It might only add a few percent to a
probe like New Horizon or Galileo, but the use of the 'unused' power from
the RTGs would reduce travel time, increasing the length of the mission by
several years and possibly even decades.

Imagine Voyager or Pioneer 10/11 fitted with an ion engine - small thrust in
the order of a few newtons; but over the life of the vehicle, the would
already have passed through the heliosphere and be in true 'deep' space with
all the fantastic scientific data that could reap. As it is, the Voyagers
are on their last legs and the Pioneers are gone for good.

So, maybe this group will become sci.space.propulsion in 2 years. Anyway,
what's the least powerful ion engine possible? Could one be built (and
what
thrust would it have) that would run on, say, 200 watts? This would work
for outer-planet probes like New Horizon where most of the instruments are
turned off for the 'cruise' phaze of the journey; so the electricity from
the RTG's would be available for an ion engine.

Well, the main thing though is ot to run out of the gas you want to
ionise
and accelerate as your propellant. I see no reason why you cannot make it
as
small as you like, but there must come a point where its really not worth
doing when added to the weight and complexity of the craft you are using
it
on.

But you'd only be adding the propellant, tank and engine; the power source
(the main reason ion thrusters form such a major part of the overall mass of
a probe) is already on the vehicle. It might only add a few percent to a
probe like New Horizon or Galileo, but the use of the 'unused' power from
the RTGs would reduce travel time, increasing the length of the mission by
several years and possibly even decades.

Imagine Voyager or Pioneer 10/11 fitted with an ion engine - small thrust in
the order of a few newtons; but over the life of the vehicle, the would
already have passed through the heliosphere and be in true 'deep' space with
all the fantastic scientific data that could reap. As it is, the Voyagers
are on their last legs and the Pioneers are gone for good.

"Alan Erskine" <alan.erskine@bigpond.com> wrote:

On all three, are in the condition they are in because the RTG's are
dying (or dead in Pioneer's case). With or without an ion engine,
they die on the same date as they did/do in real life.

"Derek Lyons" <fairwater@gmail.com> wrote in message
news:47e39c3a.2012959156@news.supernews.com...
"Alan Erskine" <alan.erskine@bigpond.com> wrote:

On all three, are in the condition they are in because the RTG's are
dying (or dead in Pioneer's case). With or without an ion engine,
they die on the same date as they did/do in real life.

Yes, but the journey would have taken less time - greater distance covered
in the same amount of time due to a constant thrust (well, 20,000 hours or
so anyway) would be a substantial boost even with a very low-power
thruster.

"Derek Lyons" <fairwater@gmail.com> wrote in message
news:47e39c3a.2012959156@news.supernews.com...
"Alan Erskine" <alan.erskine@bigpond.com> wrote:

On all three, are in the condition they are in because the RTG's are
dying (or dead in Pioneer's case). With or without an ion engine,
they die on the same date as they did/do in real life.

Yes, but the journey would have taken less time - greater distance covered
in the same amount of time due to a constant thrust (well, 20,000 hours or
so anyway) would be a substantial boost even with a very low-power
thruster.

Problem is, you don't want to flyby faster, you want to fly by slower.