PCsat SUMMARY PCsat: PCsat is a student satellite project to give students hands-on practical experience in the design of spacecraft. It has been worked on by students over the last several years: 1997 Midn 1/c Goodhiew 1998 Midn 1/c Morgan 1999 Midn Erik Theodore Lundberg Midn Brian Everett Scrabeck Midn Carlos Eduardo Gomez Midn Lester Michael Melanson III Midn John Anton Kollar IV Midn Travis Anthony Mattera Midn George Apolonio Najar Ortiz Jr Midn David James Burroughs 2000 Midn Robert Bradford Schwenzer Midn Laura Elizabeth Nolan Midn Steven Charles Lawrence Midn Daniel Antoine Boutros 2001 Midn Daniel Sullivan Midn Alex Gutweiler Faculty and Staff: Assoc Prof Daryl G Boden LtCol USAF Billy R Smith Bob Bruninga (WB4APR) MISSION: The Mission of PCsat is to serve as a worldwide position/status reporting and message communications satellite for remote travelers using only Handheld or Mobile radios with Omni-directional whip antennas. It uses the APRS (Automatic Position Reporting System) protocols to permit hundreds of users per pass to access the satellite. To demonstrate this concept, PCsat will augment the existing worldwide terrestrial Amateur Radio APRS tracking system by providing links from the 90% of the earths surface not covered by the terrestrial network. It will be licensed as an Amateur Satellite in the Amateur Satellite Service. BACKGROUND: Today, 95% of the US amateur population is covered by the terrestrial APRS network, BUT only 30% of the surface area of the USA is, or will probably ever be, covered. Similarly in just the last year we have seen explosive growth in the European theater as well. But, distant travelers, boats at sea, and stations in the rest of the world are presently unable to use the APRS system as a travelers safety reporting system when on distant trips. An APRS payload on one or more satellites would make such reporting possible throughout the world. PCsat will be a proof of concept for this mission. Credibility to the popularity of this mode is demonstrated by the recent decision of the South African SUNSAT team to re-write their flight software to user their SUNSAT satellite to also provide APRS type satellite service. FREQUENCY CONSIDERATIONS: Two meters is the ideal band for this mission due to the requirement for user access using only a handheld radio. Two meters offers a 9 dB link advantage over UHF. To take advantage of this advantage, the HANDHELD uplinks will be on two meters and the downlink will also be on 2 meters. This assures the best reception by mobiles and handhelds both with only omnidirectional antennas. Higher power mobiles who have 10 dB greater uplink power will use UHF. This splits the contention on the uplink channels and doubles overall throughput. Two downlink frequencies are required: DOWNLINKS: VHF-A should be in the Satellite Subband for operation worldwide VHF-B can operate on 144.39 over the North American continent. UPLINKS: VHF-A is for handhelds and low power (5w) stations everywhere VHF-C is for special events/applications/and comand/control UHF-A is for 50 watt mobiles everywhere UHF-B is for command/control UNIVERSAL CONTINENT PAGING: Since ALL terrestrial APRS users monitor the North American Continent frequency of 144.39 and this frequency is coordinated by all coordinated bodies, there is an additional capability that can be performed by an APRS satelite. It can be used to send urgent messages to ANYONE. SUch use will be minimized to only priority applications since it does add a burden to the terrestrial network everywhwere. INTERNET LINKED GROUND STATIONS: APRS is unique in the way it combines all packets heard everywhere in the world into a single common internet feed channel. THus the infrastructure for distributing APRS traffic no matter where its source into all other stations already exists. So all we need is a few PCsat donwlink stations to feed in the packets heard from space. Even on the 144.39 downlink, this is not a problem! To any single ground station receiver, the channel is still 70% vacant. (The Optimum Aloha TDMA channel operates at less than 20% occupancy). Since only a few ground stations are needed to link the PCsat downlink into the internet, any local instantaneous QRM at one receive site would not be present at all others simultaneouslly. Thus with only 5 PCsat downlinks sites all feeding the APRServe internet system and experiencing say 30% channel QRM in their area, still gives a 0.3 to the 5th power chance of a lost packet. Or better than 99.8% probabiliy of SUCCESSFUL receipt! Thus 144.39 is a GOOD downlink in the USA and there are no frequency coordination issues. WB4APR, Bob