The advantage of an ion thruster
for a spaceship is a higher "specific
", which means that, for a given mass of motor and
propellant, it will push the spaceship farther or faster than a
conventional chemical motor.
The downside is that current ion thrusters exert a very weak force;
you wouldn't even notice their push if you were onboard. But they
exert that push for years in a row, which makes the difference. This
is OK for military satellites in low orbit or for space probes like
Deep Space 1
But it will not allow to get astronauts to Mars in two months.
Ion thrusters with high throughput are being developed. Now, I was
wondering if a solution wouldn't be to use the spaceship itself as
the ion thruster. This is, the hull of the spaceship, or the solar
panels structure, or a Mylar balloon. It would be electrically
charged to a high positive tension. The ionized propellant gas would
just "deposited" or injected at low speed outside the hull and the
huge electric field created by the hull would repel the propellant,
creating the thrust.
A 10 meters radius sphere of Mylar charged to 1 million Volts, would
repel atoms of ionized Xenon to a speed of about 3,000 km/s. And it
can probably do that for a lot of ions at a time. Ionized
nanoparticles can already be a good enough propellant.
This system implies that an electron canon must also be used, to
keep the hull positively charged. It is this canon, that will drain
the massive amount of electric power needed by the system. In order
to be shot away from the spaceship and never come back, the
electrons must be imparted a much higher velocity than the positive
ions. But an electron canon is simpler and lighter than an ion
A variant would be to separate the spaceship in two distant hulls
linked by an electric wire. That wire can possibly be a structure
with solar panels that creates the electric potential difference
between the two hulls/spheres, each meter of structure adding its
own contribution to the electric potential difference (highly
redundant...). One hull would expel positive ions and the other hull
would expel negative ions. A version with no link between the two
hulls would have one shooting electrons at he other.
Maybe the fluxes of ions or electrons, or the field between the two
spheres, can be used to shield the spaceship from solar flares.
Conversely, electrons or ions falling back to the spaceship could be
Eric Brasseur - December 29 2015