Sunday, June 24, 2007



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Can interstellar radio signals go directly from sender to receiver?? Even on Earth with transmission distances far less than one Light Year (LY), this basic method needs considerable augmentation. 
CURRENT EXAMPLES include "store and forward" technologies as well as numerous nodes which regenerate data packets and reroute data streams.Some such nodes orbit Earth as communications satellites (COMSATs).  
However, vast distances to other stellar systems introduce prohibitive delays, given light speed limitations. An immediate radio reply to nearest stars would take years; however, most stars would require generations to just converse. Some scholars have made an excellent point: "If it takes generations to just talk with entities on other stars, why not send manned probes???"

·        1974, B.S. from Harvey Mudd College (dual major, physics and psychology)
·        1978, J.D. from University of Santa Clara School of Law. 
Work history includes:
·       Late 1970s and early 1980s, published several editions of Lobbying for Space, the first space program political advocacyhandbook.
·        Co-edited the 1980 NASA feasibility analysis of self-replicating space factories
·        1996, authored the first detailed technical design study of a medical nanorobot ever published in a peer-reviewed mainstream biomedical journal. 
· Three separate observational SETA/SETI programs.
·  Research Fellow and Study Editor, NASA/ASEE Summer Study Programs, including Advanced Automation for Space Missions
Co-founded the Nanofactory Collaboration (2000-now)
·        Senior Research Fellow, Institute for Molecular Manufacturing (IMM)
·        Member American Association for the Advancement of Science
·       Member, National Space Society
·      Research Scientist,  Zyvex Corporation
Thought Experiment's (TE's) Typical Interstellar Profile
ACCELERATION: G force propulsion for 1 year brings vessel to .6443 Lightspeed (c) and .38 Light Year (LY).
CRUISE:Ship turns off propulsion and spins for several years (as observed from Earth) until it reaches deceleration point.
DECELERATION: Once again, do G force propulsion for 1 year and .38LY to reduce vessel velocity to orbital speeds at destination stellar system.
Consistent Two Way Communications. Home base at Earth will want constant flow of scientific data gleaned from new vantage points far from our home star, Sol. Vessel occupants will want latest home news, latest developments in relevant fields of knowledge not to mention lessons learned from other interstellar missions. Also, they'll want as much entertainment as bandwidth will allow. 
Sadly, such huge data flows over such great distances (LYs) will likely prove problematic. 
How does an interstellar vessel consistently communicate with home base as well as established bases throughout other stellar systems?
We might insert beacons, interstellar communications capsules, in static positions between Sol and other stars. Deployed comm. capsules could regenerate signals much like repeaters in current Wide Area Networks (WANs).
Primary vessel (i.e., "mothership") could start deploying these comm capsules at selected points during cruise portion of flight. 
To maintain a constant position with respect to neighboring stellar systems, they must decelerate from cruise speed per the typical interstellar profile. 
EXAMPLE: In above diagram, planners arbitrarily decide to place comm. capsule at one LY from Sol.

Freitas authored Nanomedicine, a seminal, multi-volume, technical discussion of the potential medical applications of molecular nano-technology, published by Landes Bioscience. 
Home page has publication list of 617 items.
He has published 49 refereed journal publications and contributed book chapters, co-authored Kinematic Self-Replicating Machines (Landes Bioscience, 2004),
Professional Awards include:
·        2006 Guardian Award from Lifeboat Foundation. 
Extensive research interests include: 
·        nano-medicine
·        medical nano-robotics design
·        molecular machine systems
·        diamondoid mechano-synthesis (theory and experimental pathways)
·        molecular assemblers and nano-factories
·        atomically precise manufacturing
·        self-replicating machine and factory systems. 
Patents include first ever filed on diamondoid mechano-synthesis (awarded on 30 March 2010)
Serves on the Editorial Boards of 9 technical journals.
HABITATS will likely start small with larger versions to follow Perhaps first Earth orbiting habitat might be Dr. O'Neill's Island 1, a cylindrical structure with radius of 225 m and spin rate of 12°/sec to simulate Earth gravity for about 10,000 occupants  inside of outer hull. Humanity will eventually build much larger habitats such as Island 3, which might house a million humans.
Islands in Space
In his book, The High Frontier, Colonies in Space, Dr. Gerald O'Neill states that Earth orbiting "habitats" will someday host many humans (perhaps millions). Others extrapolate this habitat concept to orbits around other planets and throughout the Solar System. Most materials to construct and support these habitats can come from asteroids and comets throughout the Solar System especially in the Kuiper Belt and the further out Oort Cloud.
For Earth Orbiting Habitats: Dr. O'Neill further assumes 
1) energy via sunlight reflected from large co-located mirrors
For interstellar habitatsTE assumes energy needs will be augmented from other sources, perhaps Helium -3 mined from Solar System's gas giant planets.  
2) artificial gravity via carefully controlled spin about vessel's longitudinal axis. NOTEWould still work for interplanetary and interstellar habitats.
3) extensive agriculture for food, breathable air, and pleasant environments.NOTEWould still work for interplanetary and interstellar habitats.
For Interstellar Cruises, An Island 3 habitat could fill the Mothership role. It's reasonable to assume that many Island 1 habitats could be carried and/or constructed to fill the comm capsule role.
Earth Based RF or Physical Probes... nearby stars; which is better?
Bob Freitas expertly examines relevant issues 
(1) Do deployed probes cost more than an Earth bound radio frequency (RF) beacon? 
No! Cost for observable RF signals roughly equals probe cost over the duration of an entire exploration program.  Even better, if probe self-replicates, only one initial device need deploy for much less cost.
(2)Does interstellar probe flight take too much fuel? No! EXAMPLE: Probe might accelerate to 10%c; then, eventually decelerate back to zero. Such performance requires a mass-ratio (initial/final mass) of 5.0 for a fusion rocket, much less than ratio of 21 for the recent Space Shuttle.
(3) Is the Interstellar Probe way too expensive? No! Routine interstellar probes implies a highly advanced, well resourced society, e.g.,  Kardashev Type II society cost for interstellar, g-force vehicle compares to a current Saturn V orbital launch by us.(4) Should we divert probe launch resources for other societal uses?
If active cosmic exploration is a priority; then, we must spend accordingly.
(5) Are interstellar flights slower than radio signals? Of course they are; however, probes don't waste time for radio messages to cycle between the stars. (6) Is probe technology too difficult? No! While RF tech is simpler, interstellar probes, are more capable. NOTE: Probes will likely include RF tech.
Recall that Snowball from Oort can quickly deploy with following advantages over the Mothership Method.
1) 7G acceleration to about .87c takes only 100 days; 7G deceleration is same duration.
2) Quicker cruise speed.
3) Artificial Intelligence (AI) Controlled by autonomous robots; i.e. much less human error.
4) With no humans, no need for associated life support, certainly no need for in-flight entertainment.
5) Such a vessel can quickly establish comm. capsule ; it can also quickly resupply an established capsule.
                          To establish beacons at 1 LY intervals, ABOVE EXAMPLE shows:
  1. A group of "snowballs" (ice encased beacons) accelerate in tandem.
  2. After 291 days of joint cruise, one snowball decelerates.
  3. Remaining beacons cruise jointly for another 456 (100+356) days; 1 more beacon decelerates.
  4. This goes on until we run out of snowballs or Light Years.
More Snowballs  A series of beacons between Sol and any destination star would definitely help two way communications Given inevitable signal attenuation due to great interstellar distances, a repeater beacon could receive RF signals, regenerate them, amplify them; then, re-transmit them to the next beacon or perhaps the intended receiver. 
Operational considerations include:
a. Onboard Power. After deployment, these capsules will need continuous power supply.  Thus, subsequent snowballs could reprovision these waystations.
b. Positional Stability. Track both Sol and destination star to maintain constant position.
c. Minimize Hazards. To avoid inflight collisions, they must track subsequent vessels, likely traveling at .65c (or even faster).
d. Emergency Waystations. If these relay stations were big enough they could even be used as "way stations" for vessels that needed such things. (perhaps emergencies or scientific observatories). 
(7) Does each probe require a dedicated RF listening antenna? No! Only one radio antenna system can simultaneously collect signals from all the probes. NOTE:Redundancy is good; so; use back up systems.(8) Does Inevitable Obsolescence Obviate Interstellar Probes? No! Of course, interstellar flight's lengthy duration means probes must use very mature tech. However, old tech probes can remain very useful.
(9) Are probes reliable for long-term missions? Yes!!!
EXAMPLE: NASA's reliability of 99.99% for the Apollo Project. works out to a survival probability of 99.9% after 1000 years and 81.9% after 100,000 years.
(10) Is searching for probes a passive task?  No.  It would be passive to  just wait for visiting extraterrestrial probes to initiate contact; however, SETI now actively seeks both probes and RFs.
(11) Can we search all possible, physical artifact sites?  Of course not, but recall possible RF bin quantity is infinite. However, it makes most sense to focus our search on the more likely "magic frequencies"; likewise, the "magic orbits" are where probes are more likely (e.g., Icarus, 1980 [Ref]).(12) Are RF signals superior to probes with physical artifacts?
Clearly not!!! RF beacons are limited to only repeat same information for perhaps eons to gain nothing new. On the other hand, manned (and/or AI) probes can autonomously seek out evidence of life such as communications.
SUMMARY:  For interstellar communication,
physical AI probes are more capable than RF waves.
SOURCE DOCUMENT:  Freitas, Robert A. Jr. (July–August 1983).
Debunking the Myths of Interstellar Probes"AstroSearch 1: 8–9.
Sending physical vessels between stars may prove much more useful than just RF signals. While vessels are limited to speeds far below light-speed, information in a few tons of physical matter could easily exceed utility of data via practical RF bandwidth for the foreseeable futureRobert Freitas proposed physical space-probes for better interstellar communications than RF signals.


  1. Freitas, Robert A. Jr. (1980). "Interstellar Probes: A New Approach To SETI". Journal of the British Interplanetary Society 33: 95–100. Bibcode:1980JBIS...33...95F.
  2. Freitas, Robert A. Jr. (July–August 1983). "Debunking the Myths of Interstellar Probes". AstroSearch 1: 8–9.
  3. Freitas, Robert A. Jr. (November 1983). "The Case for Interstellar Probes". Journal of the British Interplanetary Society 36: 490–495. Bibcode:1983JBIS...36..490F.
  4. Freitas, Robert A. Jr.; Francisco Valdes (1980). "A Search for Natural or Artificial Objects Located at the Earth-Moon Libration Points". Icarus 42 (3): 442–447. Bibcode:1980Icar...42..442F. doi:10.1016/0019-1035(80)90106-2.
  5. Valdes, Francisco; Robert A. Freitas Jr. (1983). "A Search for Objects near the Earth-Moon Lagrangian Points". Icarus 53 (3): 453–457. Bibcode:1983Icar...53..453V. doi:10.1016/0019-1035(83)90209-9.
CONCLUSION:  For several decades, the Search for Extra-Terrestrial Intelligence (SETI) project has  searched for signals from other stellar systems.  So far, no success; 
HOWEVER,  Earth will eventually receive interstellar signals from our descendants traveling to neighboring stars. Two way interstellar communications will undergo considerable attenuation due to intervening LYs; thus, it might be necessary to deploy RF repeater beacons at static interstellar positions.
1G Acceleration for 1 year.
7G Acceleration for 100 days.
7G Deceleration for 48¼ days.
1G Deceleration for 1 year.


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