ISS/APRS Satellite Frequently Asked Questions

Bob Bruninga, WB4APR, US Naval Academy Satellite Lab, Annapolis, MD

ARISS PACKET SYSTEM: ISS packet operation began with the Ericcson radio and an extrnal TNC and then used a Kenwood D700 installed in late December 2003. A decade later it reverted back to the Erriccsson and a replacement external TNC and later to a D710 radio. Now it is using a D710/G and all new power system. This packet system lets schools and students access/or use the packet transponder on ISS without dependence on the very busy schedule of the astronauts. In 2007 this ISS packet operation switched to the global APRS satellite channel on 145.825 to join the constellation of other AX.25 1200 baud packet digipeaters such as PCSAT-1, ANDE , RAFT and also at 9600 baud, GO32 . All of these have since de-orbited except for the long lived PCsat and the soon coming crop of additional APRS satelliltes:

PCsat-1 in orbit since 2001
ARISS on the ISS since 2003
Psat for launch May 2015
QIKcom-1Launched to ISS but SNAFU with FCC never allowed it to be turned on
QIKcom-2Lost its launch in 2018
PSAT-2 Launched in 2019. PSK31/SSTV operational but packet system died.

The ISS keeps the ISS Packet station on 145.825 when it is available. This lets the packet downlink from ISS operate with the other APRS satellites there and its downlink to be collected by the established global network of APRS Internet-Gateway stations feeding the data to the ARISS-APRS web page.

JOINT DIGIPEATER CONSTELLATIONS The first joint operations test (11-23 Oct 2002) was successful during which the ISS packet station joined the PCsat frequency so that both could operate as a joint constellation of two satellites, not only doubling the number of available pass times, but also allowing some dual-hop links. See report on PCsat web page. Since then this experiment has been conducted several other times, most recently early Dec 2005 between PCSAT2 and PCSAT-1 both operating on 145.825, the Satellite Digipeater frequency. . The longest dual dual hop packet observed is shown at right:

This page contains notes about AX.25 Packet radio operations via the ISS or other satellites. Introduced to the manned space programs in 1990 on the Shuttle and MIR, packet radio first became operational on the present ISS on 22 Feb 2001, and operated well for over a year until it became intermittant and was replaced with the new Kenwood D700. This new system, like PCsat, consists of a TNC which can operate in two modes:

  • UI/APRS Digipeater - Can be used by everyone at the same time (best multi-user mode)
  • Personal Messages - Only usable by one person at a time and extremely inefficient(not Recommended!)

    UI DIGIPEATER: This page addresses how to use the space based UI/APRS digipeaters for maximum enjoyment by everyone by using UI or APRS packets. Typically 50 to 100 stations per day use this system. With well over 3500 stations captured and archived by Steve Dimse's worldwide APRS file server at FINDU.COM. See LIST in 2002.

    ISS PMS SYSTEM: The PMS (Personal Message System) was a common packet function 2 decades ago on Earth but it is extremely inefficient on orbit. Just to communicate one line of text, can take over 5 packets, all exchanged in an extreemely congested channel. It simply makes no sense on orbit where one logon-attemp, can consume an entire pass with zero passed traffic.

    One hand clapping: Notice how coastal stations have far less congestion to deal with than central USA stations!

    The remainder of this page is dedicated to helping newcomers to understand how to use APRS via the ISS digipeater.

    WHAT IS APRS? . APRS was designed in the 1990 time frame as a digital equivalent to simple voice nets; anyone talks, everyone listens and takes notes. APRS was intended for local tactical real-time HUMAN exchange of brief digital information.

    WHAT IS APRS NOW? . APRS has evolved into a global digital simplex commmunications channel. You can send almost anything, anytime, anywhere, to anyone. Just make it fit in one packet. Think of it as HAM radio's RF INTERNET and the Kenwood and Yaesu radios as your wireless digital communicator.

    WHAT DOES THE RADIO DISPLAY? . See some example radio displays. See also how local info such as repeater frequenceis, net times and monthly meeting times can all fit into a single local beacon and on the radio frotn panel. without the need for a laptop or other device.

    HOW BIG IS APRS? . Basically, APRS is global. Zoom in anywhere in the world and look at the activity on the APRS.FI web page. Also, just tune your radio to 144.39 anywhere in North America or in Europe tune in 144.8.

    WHAT DOES THIS HAVE TO DO WITH ISS? . The packet relay capability on ISS allows a large number of people to share the channel for their 1 seocnd of fame. And since the downlink is captured and displayed on the web page it encourages today's kids to use their familiarity with the power and fun of the internet to explore ham radio. Further, since each school or station can fully participate with only a single one-second packet, it was thought this would let more schools participate on each pass with success.

    WHAT IF THE ISS IS NOT IN VIEW DURING MY CLASS? . You can see the live downlink from ISS at any time on the worldwide LIVE LIVE ISS Downlink Map. or the similar PCSAT/PSAT/QIKCOM/etc site.

    HOW DOES THIS LIVE GLOBAL MAP WORK? . Volunteer ground stations around the world simply leave their PC's connected to the internet running most APRS client software that includes a built-in IGATE function. Every IGATE you saw on the above site is feeding data into the network LIVE. Anyone running APRS and also on-line as an IGate can feed ISS packets automatically. With APRS activity in many countries already, we hope to see live feeds daily from the locations shown below: [See Permanent IGates (in 2001)].

    WHY MAPS? . Since HAMS communicate without wires, phone numbers or addresses over distances of between one to thousands of miles, usually the first thing of interest is where the other guy is. Thus one packet from each station usually contains a position report.

    DO I NEED GPS? . No... Only if you are lost...

    HOW DO I INPUT MY POSITION WITHOUT A GPS? . Just enter your LAT/LONG coordinates or grid square. On your APRS map, just move your cursor to where you are and CLICK, or hit ENTER, etc... it knows the LAT/LONG of your cursor.

    I DON'T HAVE APRS? . You don't need it. Here's how! Just enter your Grid Square, position, status or message in your packets. Any PACKET radio program can send UI packets. Just set the path to CQ VIA ARISS and put the TNC in converse mode and then everything you type will be transmitted in UI mode. If you want APRSdos, you can download it (now obsolete) or get other APRS clients for just about any platform or operating system.

    APRS IS COMPLEX? . There are only 4 types of packets. All packets stand alone and are complete in themselves. Position, Status, Messages and Other. By definition, everyone has only ONE position and only ONE status at any one time. They may send multiple individual messages but usually messages are only one line. Here's how!

    HOW OFTEN DO I TRANSMIT? . Your objective should be to share the channel with as many other like souls as possible and indicate your participation with one successful packet. See TIMING or the complete rules of UtIquette via ISS or peek at the Real Answer.

    CAN I SEND EMAIL? . Yes! Just use an APRS formatted message to "EMAIL" and the first word of your message as the EMAIL address, and the packet will be delivered via conventional Email (assuming it gets digipeated by ISS into the APRS infractstructure somewhere). Here's how!

    WHAT PATH DO I USE? . All APRS satellites and the ISS support the generic paths of ARISS or APRSAT. Since all of these satellites supports the same generic paths (when properly configured), this means you can operate either ISS or PCsat or PSAT without reconfiguring your TNC! Just set your UNPROTO path to APRS VIA ARISS and it should work with all APRS birds.

    HAS IT BEEN USED IN SPACE BEFORE? . Yes. See ASTARS for all the details on APRS in Space.

    WHAT ELSE CAN WE DO WITH ISS/APRS? . Since ISS Digipeater is NOT conjested over 70% of the earths surface, it makes an ideal HAM radio Space Communications Link for stations in remote areas or on the high seas. The Afloat Tracking Areas map below shows where a HAM with a simple 5W APRS HT can periodically report his position, and status and also send Email messages via ISS and the worldwide linked APRS system (as long as we have IGates in the areas shown. Hawaii, Canary Islands, SOuth Africa, New Zealand, Australia, Brazil).

    WHATS WRONG? WHY CAN'T I GET IN? . A station that works "OK" for your local BBS 5 miles away, may be operating 10 to 20 dB below its potential due to a variety of factors. See ISS DIFFERENCES.

    The remainder of this page details one of the first APRS experiments via SAREX back in the 1990's

    APRS Position/Status reporting via SAREX was authorized on the last several SAREX missions. Using the Shuttle as a digipeater allowed schools and stations to communicate amongst each other while seeing all other stations participating in the event.

    During June/July 1996, mission STS-78 offered 15 days of SAREX activity, on 75% of all passes with 20 voice, 25 packet and 11 school passes. APRS experiments were authorized and 18 stations successfully relayed their positions via SAREX as shown below. Two others relayed their STATUS but without their position.

    A total of 65 APRS packets were received here in Maryland. While 39 stations reported trying APRS, only 10 APRS stations reported making a serious effort, trying every pass. The conventional SAREX robot recorded over 1300 successful packet contacts for 561 different stations with 146 successful two-way contacts. We believe that APRS makes a good real-time display for schools involved in SAREX activity with the shuttle as shown below.

    As noted above, APRS is available for most platforms and systems. The original was APRSdos that ran on ANY old PC even without windows. download it (now obsolete).

    What should we do next?
    Here are my suggestions for an external ISS amateur radio kitchen sink payload that will have muiltiple uplinks and multiple downlinks. One assumes we will use the 2m band as the primary DONWLINK band (for maximum visibility by low-tech users)

    OLD IDEAS IN THE 2001/2002 time frame: These links are preserved here for historical purposes since they reflected the concepts we were promoting back then. There was a lot more going on with PCSAT2 on ISS in the 2006 time frame and then with the Kenwood D700 the went full time on ISS in the 2007 time frame(?). So read these with a grain-of-salt!

  • Proposal for use of Packet on ISS. See Power Point presentation. (historical)
  • Proposal for future Extertnal COMM payload on ISS. See Power Point presentation. (historical)
  • Possible External Payload power and command/control system:

    Other (Historical) ISS Proposals:

  • Proposed Cross-band Voice repeater operations from ISS.
  • Proposed PSK-31 Transponder operations on ISS
  • Proposed mode-B Planning for operations from ISS
  • Proposed ISS Mode-B downlinks
  • Proposed BAND PLAN for ISS

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