Where you have a self contained world in space vacuum without weather,
grounding is not an issue. There is no wind static build up, no lightning
storms,etc. However, if you were to pass thru solar wind, there could be
issues of ions building up on surfaces exterior to the craft.
Antennas which are operated against sizeable ground planes, reflectors,
dishes or as dipoles are completely balanced and self contained as to
completion of the RF path.
The need no other ground reference, if they have these reference elements.
The confusion among hams is that a ground rod is needed with a vertical
antenna, a dipole, or a beam. The ground rod is for static discharge
dissipation, and AC safety grounding ONLY. It seldom can provide an
adequate RF ground, as it has no resonance nor sufficient area for RF
conduction at low impedance. The quarter wave or shorter vertical needs
radials, or ground plane, or screen, or counterpoise wire for optimum
efficiency and to complete the RF circuit.
The vertical Dipole is complete as it is a balanced antenna, as are
horizontal dipoles, beams, Vees, Loops, etc. The two elements in a driven
unit mean you do not need anything connected to earth to complete the RF
circuit for those types of radiators.
Thus, the spacecraft does not put out a ground rod; there is no ground. But
also, there is not static from atmosphere. However, at liftoff in the lower
atmosphere; there can be static buildup on the shell, and there are needs
for bonding all parts of the shell to avoid potential differences and
arc-over. The Skylab launch vehicle was struck by lightning causing a
glitch in onboard electronics. After that, transient protection was looked
at more closely in spacecraft.
Some earth grounds then, may help complete the RF path for certain shorter
antennas, (shorter in the sense of having only one element connected to the
feeder, and no element
to the shield or return feeder conductor.) But the earth rod is seldom an
adequate RF ground element alone.
All earth grounds provide a point to hopefully dissipate static charge build
up or even induced secondary currents of nearby lightning. In tall towers,
grounding should provide a path to dissipate and spread charge from each leg
of the tower into the earth to lessen difference of potential from direct or
indirect strikes. They also serve to bleed off charge buildup on adequately
bonded tall towers, and sometimes lessen chances of a strike.
AC grounds satisfy electrical code safety and fire issues, and are again a
last ditch protection for lightning faults.
But, if you had a dipole on a station sitting out on a rocky mountain top,
you would not need, nor could get, a ground rod connection; and, the station
would work RF just fine. Just do not have the antenna as the highest point
around during a storm!
Hope this helps clarify the grounds for a ground!
-Stuart
K5KVH
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