Monday, January 29, 2007


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Can interplanetary radio signals go directly from sender to receiver throughout the inner Solar System?? Even on Earth with transmission distances far less than one Astronomical Unit (AU), the attenuation is considerable; thus, interplanetary communication will likely need considerable augmentation.
RELEVANT TECHNOLOGIES now include "store and forward" capabilities as well as numerous nodes to regenerate data packets and reroute data streams. Some nodes now orbit Earth as communications satellites (COMSATs). Perhaps, we could deploy many specialized vessels in various orbits about the Sun as well as planets and moons.  These vessels would have considerable memory and storage, long term power systems, and high tech antennas; we could populate them with Artificial Intelligence (AI) entities instead of humans.  We could call such vessels, communicators.

Given interplanetary distances and inevitable signal attenuation, specialized vessels can greatly improve two way communications throughout the Solar System. Such vessels could receive RF signals, regenerate them, amplify them; then, re-transmit them to the next communicator or  the intended receiver.
Operational considerations include:
a. Store and forward capability would ensure all data stored on board until next communicator acknowledges receipt and safe storage.
b. Power. These vessels will need continuous power supply likely based on collecting sunlight
c. Networking:  Communication vessels must inter-operate.
In his book, The High Frontier, Colonies in Space, Dr. Gerald O'Neill predicts orbiting "habitats" will someday host millions of humans in orbits around Earth and other planets. Most materials to construct and support these habitats can come from asteroids and comets throughout the Solar System. Thus, an Island 3 habitat could construct countless Island 1 habitats; refashion them as communicators; then, deploy them.

Like other habitats, communicators could satisfy their power needs via collected sunlight.
Unlike the Island 3 habitats, communicators would not be populated by humans, but mostly by AI entities such as large robots and millions of nanobots.
Thus, communicators don't need artificial gravity via centrifugal force which Islands gain by carefully controlled spin about vessel's longitudinal axis.
With no permanent human population, they won't need Island's extensive agriculture for food, breathable air, and pleasant environments.
Consistent Two Way Communications. 
Home base at Earth will want constant flow of scientific data gleaned from new vantage points.

Vessel occupants will want latest home news, latest developments in relevant fields of knowledge as well as lessons learned from other missions. Also, they'll want as much entertainment as bandwidth will allow. Sadly, such huge data flows over such great distances (AUs) will likely prove problematic.

How does a vessel consistently communicate with home base as well as other habitats?

We might insert communicators, habitats refashioned as interplanetary communications capsules, in orbital positions throughout the Solar System. Communicators could regenerate and forward signals much like repeaters in modern Wide Area Networks (WANs).
Semi-major axis (a)
is the basic building block for orbits.
For near circular orbits (such as for Earth and Mars),
'a' value closely approximates 'r', the radius.

Assume following values for this example:
Previous figure (Day 0) shows all three objects aligned.
During the 90 days since "Day 0",
all three objects have strayed far from alignment.
Period (P)
is duration of a completed orbit.
Compute P per Kepler's 3rd Law:
Square of Period, P, equals cube of semi-major axis, a.
P2 = a3
P = a3/2
Assume following values:
After 180 days, objects disperse even further,
but Communicator's position still enables it
to provide some useful relay service.
Mean Motion (n)
helps approximate angular distance.
n = 360°/P
Assume following values for this example:
By Day 270, Earth and Mars are in conjunction with Sol;
they can both see the communicator,
but the Sun blocks direct path between them.
Perhaps the communicator might relay their signals around Sol.
Leveraging above tables
determine angular distances
as shown below:

After 360 days, Earth almost returns to Day 0 position.
By now, all objects are completely dispersed,
and one lone communicator is not in a useful position.
Perhaps a system of communicators might work better!!!
Instead of putting a communicator in its own orbit, place a few nodes on same orbit.
EXAMPLE: The Martian Team might deploy communicators A and B into Mars orbit to lead by 60⁰ and 30⁰; also, nodes C and D might lag Mars by 30⁰ and 60⁰ as shown.
ADVANTAGES of this configuration include:
Persistent Position: Communicator can easily maintain same relative orbital position; i.e., once 30⁰ ahead; always 30⁰ ahead.
Redundancy: If Communicator B has a problem, A takes over. Likewise, D backs up C.
Operational Simplicity: Much like current internet user does not worry about how signal reaches destination, habitat does not worry about signal’s complete path. It just hands off signal to either B or C; then, each communicator relays signal until received.
SCENARIOS: Sometimes, signal to the habitat is blocked by the very planet it orbits.
Scenario-1: If planet blocks Habitat’s signal to communicator C (as shown); then, Habitat sends signal to either B or A.
Scenario-2: If planet blocks C’s signal to Habitat, C can send message to either A or B for subsequent relay to Habitat, or it can hold message till path is clear.
In Earth’s Solar orbit, assume two Island-3 Habitats, Alpha (α) and Omega (Ω), which lead and lag Earth by 60°. Perhaps the millions of humans who populate α and Ω will do a considerable business manufacturing and supporting other habitats including Communicators. 

Furthermore, assume a network of communicators such that Earth, Habitat α and Habitat Ω, always have a primary and a backup communicator available. For example, Habitat α can always send/receive signals from either Communicator W or X. Similarly, Earth can always use either X or Y, and so on.

Finally, all communicators could service signals from any entity; we just assume that the nearest node will start the shortest path and most likely the optimum signal routing solution.
Optimum signal path is always the direct path between sender and receiver. Unfortunately, direct path between Mars and Earth will be blocked by Sol much of the time (not to mention degraded by Solar flares and other cosmic disturbances).

However, placing a few communicators in both Martian and Terran orbits greatly enlarges the performance window.

Diagram shows worst case scenario when Mars and Terra (i.e., Earth) are on opposite sides of Sol. Fortunately, Communicator A (on Martian orbit) has a short, clear path to Z (on Terran orbit). Communications is delayed only by light speed (about 500 sec/AU) and slight processing at each relay node.

More communicators are better!!!!


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