APRS Via The ISS – A Quick Tutorial - FARS

APRS via the ISS – A Quick TutorialInternational Space StationPhoto credit: NASAAF6DSCopyleft 2008 Peter ChowAll Wrongs Preserved March 10, 2008 – Rev. 41

Sending APRS Packets via the ISSConcept: To have the International Space Station“digipeat” digitally repeat your transmittedAPRS packet(s) to any ground-basedInternet-linked station (called SGate) Verify that your ISS digipeated message wasrecorded by APRS tracking websitesPurpose: For fun – and possibly for sending emergencymessages out-of-area (although unreliable)AF6DS2

What is APRS ? Automatic Packet Reporting System A digital (non-voice) method of transmittingmessages, status, and position – usingspecially formatted AX.25 packet messagesTNC (Terminal Node Controller), similar to acomputer dial-up modem, transmits packetsand APRS data over the airwavesAPRS is normally operated terrestrially – for2m VHF in USA: 144.390 Mhz FM simplexCreated by, and is a registered trademark of,Bob Bruninga WB4APR (www.aprs.org)AF6DS3

Packet Digipeating Concept Digitally repeating anAX.25 packet onsimplex frequencyusing a store-andforward method,e.g. like a children'sTelephone Game(Chinese Whisper)Allows packets totravel farther usingintermediate hopsAF6DSIGateor BBSInternetforwardout ofreachstore4

APRS – Terrestrial vs. SatelliteTerrestrial APRSOperationISS144.390 MhzIGateSGateInternetDigipeatingvia ISSISS145.825MhzSatellite APRSOperation -IGateSGateInternetAF6DS5

ISS Pass Opportunity Window of opportunity for transmitting to ISS––– Each ISS orbit period is about 90 minutes5 to 10 minute window per orbit passGroups of consecutive passes about twice a day,roughly 12 hours apartNumber of usable consecutive passesDepends on your latitude, e.g.– 1 pass near equatorial latitudes– Up to 7 passes near the 50 latitude– But typically at other latitudes: 1 to 2 usable passes within an 1 ½ hour periodRarely: 3 usable passes in a 3 hour periodAF6DS6

ISS Pass Prediction Pass prediction websites–––– e3d iss.htmlhttp://www.n2yo.com/?s Pass prediction computer ftware.php–Windows: –SatScapeOrbitronWXtrackUnix: predict with gsatgpredictktrackclientAF6DS7

ISS Station Operation ISS universal callsign alias: ARISS– Other callsigns: NA1ISS, RS0ISS, DP0ISS, etc.Kenwood TM-D700, etc. on-board the ISSPacket digipeating operations–145.825 Mhz simplex FMsince September 2007 – hopefully it will be permanent– ISS digipeater callsign: ARISSISS beacon message:RS0ISS-4 CQ,SGATE: ARISS - International Space Station (BBS/APRS on) More details adio/http://www.rac.ca/ariss/oindex.htmAF6DS8

Ground Station Equipment Required Any Tech / Gen / Extra class amateur license2 meter VHF transceiver––– No PL tone required (i.e. old equipment OK)5 watt power with Log-Periodic or Yagi antenna10 to 25 watt power with ground-plane antenna1200 baud packet TNC and/or software – plustransceiver model-specific TNC cableAntenna: beam, ground-plane, eggbeaterComputer with serial port and Internet accessSatellite / ISS tracking software or websiteOrientation / compass, and local / UTC clockAF6DS9

Ground Station Equipment Setupantennacomputercable / DSL / wireless(if available)serial TNCxcvrInternetInternet access might be unavailable indisaster and remote areas or mobile opsNo transceiver pre-amp normally requiredTransceiver mic and speaker connections arededicated to the TNC – voice ops unavailableSome TNCs accept a GPS connection forAPRS beacon operation (don't use with ISS)AF6DS10

Typical Interfaces for TNC HardwareKantronics KPC-1AF6DS11

Ground-Plane Antenna No aiming required––– Unity gain (¼ wave)–– OmnidirectionalStationaryWorks indoors too More transmit powerrequired than LogPeriodic or Yagi10 to 25 watts (to ISS)Radiation pattern––Low takeoff angleNull at zenithArrow GP146-440on PVC pipeAF6DS12

Other Antennas for Satellite UseBeam: Yagi / LogPeriodic– No aiming required Directional radiation–High gain ––Aiming required –EggBeaterLess transmit powerrequired than groundplane antenna5 watts sufficientBetter suited foroutdoor use withhandheld operation,weather permittingUnity gain – AF6DSMore transmit powerrequired than LogPeriodic or YagiRadiation pattern –OmnidirectionalStationaryCircular polarizationNo null at zenithExpensive to buy,cheaper to build13

Ground Station Operation Overview Setup–––– Verify your setup with terrestrial APRS operationPre-program transceiver with Doppler frequenciesSet TNC parameters (in TNC Command mode)Update TLE, track & predict ISS orbit passoverOperation–––––Check websites for recent ISS packet activityAdjust transceiver for Doppler shift, if necessaryTransmit APRS packet (in TNC Convers mode)If ISS digipeated packet is not received by yourTNC, then check at APRS tracking websitesIf nothing logged, retry transmission in 1 minuteAF6DS14

Compensating for Doppler Effect Doppler Effect frequency shift is a factor whenthe ISS is approaching and receding––––ISS travels roughly 214 statue miles (344 Km)above the earth @ 17,500 mph (28,000 Kph)Ground station transceiver should frequencycompensate when the ISS is near AOS1 and LOS2Only compensate on high elevation passesCompensation might not be required on 2m VHF,since Doppler shift is less than 3 Khz1AOS – Acquisition of Signal, i.e. ISS rising above the horizon2LOS – Loss of Signal, i.e. ISS dropping below the horizonAF6DS15

Transceiver Setup for Doppler ShiftISSCompensating onhigh elevation passTCAAOS LOSTx-, Rx Simplex @ 145.825 MhzTx , Rx-ApproachingTraversingRecedingPre-program AOS and LOS shift frequenciesinto the transceiver – using odd-split offsets–Most 2m transceivers have 5 Khz step minimumAOS: Tx 145.820 Mhz, Rx 145.830 Mhz FMLOS: Tx 145.830 Mhz, Rx 145.820 Mhz FMTCA: 145.825 Mhz FM simplex (Tx Rx)TCA - Time of Closest Approach, i.e. maximum elevationAF6DS16

AOS / TCA / LOS Frequency AdjusthorizonAOS (approaching)Tx 145.820 MhzRx 145.830 MhzLOSTCAISS60ºAOS30ºTCA (traversing)145.825 Mhz simplex(Tx Rx)you are here(zenith view)LOS (receding)Azimuth / Elevation chart forISS orbit pass (in light blue)annotated predict / gsat chartTx 145.830 MhzRx 145.820 MhzAF6DS17

TNC Settings (via terminal session) TNC has two modes: Command and ConversRecommended settings in Command mode:mycall your callsign-ssid passall on, monitor on, mcon on, flow on,paclen 70axdelay plus txdelay 3then set the unproto path string to:unproto aprs via arisswhereas for terrestrial operation the unproto path stringwould be something like: unproto aprs via wide2-1and turn beacon(ing) off Switch into Convers mode by typing:k or conversAF6DS18

APRS Type / Syntax (Convers mode) There are 3 main APRS types: message,status, position (designated by the firstcharacter of the Convers mode string)In TNC Convers mode, these types can bespecified as follows (maximum 64 bytes):Position[GG##gg].message.where GG##gg is the Maidenhead grid square, e.g. cm87xiStatus ( ) .comments. GG##gg/-.comments.Message (:): 9character TOCALL :.message.AF6DS19

APRS Position Type – Lat / LongAn example of specifying an APRS positiontype with latitude / longitude coordinates!3720.00N/12205.00Wx/A 000100/Happy trails ISS !!no timestamp, no APRS messaging capability3720.00N 37.2000º N latitude/symbol table to use for displaying map icon12205.00W 122.0500º W longitudexdisplay a X Windows icon on the APRS map/A 000100 altitude @ 100 feet (optional field)/comment delimiterAPRS map symbol / icon info:http://eng.usna.navy.mil/ .mil/ bruninga/aprs/symbolsX.txtAF6DS20

Orbital Description of Satellites A satellite's orbit can be mathematicallydescribed by Keplerian Elements – encodedin a format called Two-Line Element (TLE)TLE format:ISS1 25544U 98067A2 25544 51.6401 Satellite tracking software accepts TLE data– 08022.20136510 .00020651 00000-0 12618-3 0 763454.3302 0005382 315.0141 127.5080 15.77334577525339Make sure the orbital data is up-to-date, since theISS orbit may be boosted by visiting US SpaceShuttle or Russian Progress spacecraftObtain the latest TLE data ons.txtAF6DS21

Prediction SW – gpredict (Linux) World mapYour locationSatellites &orbitsAz / El chartFuture passprediction– AF6DSTime to AOSDoppler shiftfrequenciesTLE updates22

Prediction SW – predict / gsatAF6DS23

Prediction Website – issfanclub.comClick on select your cityfor pass prediction infoClick on read more.for activity reportsAF6DS24

Sending the ISS Digipeated PacketWhat you type in TNC Convers mode to send, e.g.:[cm87xi]Happy trails ISS ! Enter What your TNC transmits (and what you see):AF6DS APRS,ARISS:[cm87xi]Happy trails ISS !What the ISS digipeats (and what you might see):AF6DS APRS,RS0ISS-4*:[cm87xi]Happy trails ISS ! ARISSdigipeated as RS0ISS-4Note: you will see your callsign instead of AF6DSDigipeating station inserts an asterisk (*) afterits own callsign in the packet stringPackets with an asterisk (*) marked ISScallsigns are logged by SGate stationsAF6DS25

ISS APRS Tracking Confirmationstationnear topof listclick onlink tosee data(see nextslide)AF6DS26

ISS APRS Tracking Confirmation(see next slide)AF6DS27

Anatomy of an ISS Digipeated PacketRaw packet: AF6DS APRS,RS0ISS-4*,qAO,KK5MV-12:[cm87xi]Happy trails ISS ! Silicon Valley,California ISSMidland,Texas January 25, 2008 04:07 UTCKK5MV (w/SSID of 12)is the SGate for thispacket – QTH in TexasFrom Silicon Valley ISS Midland, Texas Internet !1200 mile city-to-citysingle-hop digipeatThanks ISS and SGatestations like KK5MV !AF6DS28

Emergency Welfare Message via ISS During a major disaster (or for remote areaoperation), digipeat your APRS messagesoutside the region (via the ISS)––– Infrastructure outage: power, phones, Internet,repeaters, or HF operation is unavailable / busyYour operation needs to be totally self-sufficientDigipeating 1000 miles is possible via the ISSUnreliable! - no means to verify if yourmessage reached APRS tracking websitesPre-arrange with concerned parties where tolook for your status when a disaster occursAF6DS29

Improving Your Chances for Success Verify packet / TNC setup terrestrially firstCheck for recent packet activity:––– http://www.ariss.nethttp://www.issfanclub.comISS digipeating available 24 hours/day, but mightbe off during: docking, EVA (spacewalks), etc.Check for and use the latest orbital http://www.issfanclub.com– website tracking orbitaldata may get out-of-date occasionallyDistant ground or ISS packet collisions areoften not detected by your TNC – so retryAF6DS30

Other Things to Note Cost:––– TNC: 200 USDAntenna: GP 35 USD, Eggbeater 300 USDSoftware: freeware / open source availableTurn off Rx Save (power management) modein HTs, to allow proper decoding of receivedpackets by the TNC – quicker battery drain!APRS CQ and ISS packet BBS usage alsopossible, but maybe difficult in heavy trafficAF6DS31

GlossaryAOS – Acquisition of Signal (rise above horizon)APRS – Automatic Packet Reporting SystemAX.25 – X.25 packet protocol for Amateur radioDigipeat(ing) – Digitally repeating packetsIGate / SGate – Internet / satellite gatewayISS – International Space StationKeplerian Elements / TLE – orbital descriptionLog-Periodic / Yagi – directional beam antennaLOS – Loss of Signal (drop below horizon)Packet – digital form of data transmissionTNC – Terminal Node ControllerAF6DS32

Tracking Websites and DataSatellite tp://space.cweb.nl/space3d iss.htmlhttp://www.n2yo.com or http://www.n2yo.com/?s 25544http://www.heavens–above.comKeplerian AF6DS33

APRS Tracking and Map SymbolsAPRS Trackinghttp://map.findu.com/ your callsign-ssid http://map.findu.com/ your callsign *http://aprs.fi/info/ your callsign //wx.findu.com/ your callsign APRS Map Symbols and Iconshttp://eng.usna.navy.mil/ .mil/ RS symbols.htmhttp://wa8lmf.net/aprs/APRS symbols.htmAF6DS34

freqshttp://web.usna.navy.mil/ bruninga/iss-faq.htmlhttp://web.usna.navy.mil/ aqs/Intro t/ alan/ham/aprs/aprs.pdfAF6DS35