Space News Letter to Editor

victoriatangoman wrote:

"
You're correct about the variety of NEO material, and their delta-v
advantage, but the Hohmann orbit launch windows needed to realize
those advantageous delta-v orbits will be few and far between.
"

True enough. However, there's a nuance to which I'd like to draw
attention. It is not possible to get down to the surface of the Moon
with a xenon arc thruster, but it is possible to reach some NEOs with such
equipment. Electrical propulsion systems are more efficient than
chemical propulsion systems, and they may be safer too. One might be
willling to endure a higher delta-V requirement to reach a NEO than to
reach the surface of Luna because to reach the NEO one can utilize the
much more efficient propulsion system. Chemical propulsion systems seem
to explode with alarming frequency (e.g., recent problem with CONTOUR
probe).

It is not possible to utilize Hohmann transfer orbits with low-thrust
electrical propulsion systems, because Hohmann transfer requires large
impulse thrusts that are not achievable by electrical propulsion. Rather,
electrical propulsion systems utilize continuous-thrusting trajectories.

Of course, as many have pointed out before, getting to a NEO takes a lot
more time than getting to Luna, and that's certainly a huge disadvantage
to NEO development vis a vis Luna development.

Ron