Amateur Radio Satellites - Contacting The Mir Orbital Complex

By John A. Magliacane
Email address:magliaco@pilot.njin.net

Ever since its launch in February 1986, the Russian space station Mir has held special interest among space enthusiasts. Mir is the world's first permanently manned spacestation. Its high orbital inclination takes it over most populated regions of the globe, and its large size makes it easily visible in the early evening and early morning skies. Except for several brief periods of time, the Mir orbital complex has been occupied on a full-time basis by various crews for the past ten years. But just what do Mir cosmonauts do for recreation after their daily work is complete?

Since the installation of a VHF-FM amateur radio station on Mir in November 1988, a favorite recreational activity for every crew inhabiting the Mir orbital complex has been establishing amateur radio contacts with ham radio operators all over the world.

A Brief History

The majority of the amateur radio activity from Mir over the years has been centered on the use of one of several 2-meter FM voice transceivers. The first transceiver, a 2.5-watt Yaesu FT-290R, provided limited coverage of the 2-meter amateur band, but allowed many exciting voice contacts to be made with ground stations. A ground plane antenna was mounted outside the Mir spacecraft for use with this transceiver by cosmonauts Vladimir Titov and Musa Manarov in November 1988.

Three years later, a second transceiver, an ICOM 228A/H, was brought to Mir along with a PacComm "Handipacket" packet radio Terminal Node Controller (TNC) and an AT-class laptop computer to provide wireless electronic mail capabilities. The addition of the packet radio TNC allowed the operation of a Personal Message System (PMS) on Mir so hams on Earth could exchange e-mail messages with the cosmonauts whenever it was most convenient.

The Mir cosmonauts typically use 145.550 MHz as a simplex communications frequency with hams on the ground. The term "simplex" means that a single frequency, in this case 145.550 MHz, is used as both a downlink and as an uplink frequency to the Mir orbital complex. In an effort to dodge some of the interference on this popular frequency, Mir occasionally switches to unpublished frequencies, just as the SAREX experiments on the U.S. Space Shuttles do for special purposes. Last year, several voice contacts were made between school children and the cosmonauts on the Mir orbital complex using a pre-arranged schedule and an unpublished operating frequency. The success of these contacts brought great joy not only to the school children on the ground, but also to the cosmonauts in space.

How Much Power?

A frequently asked question is, "How much transmitter power is required to reach the Mir orbital complex?". Based on the slant range to Mir during a typical pass, the frequency and mode of operation, the antennas used, and the sensitivity of the receiver used on Mir, the transmitter power required is only several milliwatts.

Narrowband FM voice signals can be easily copied with a signal level that is only 10 dB above the sum total of all noise received or generated by the front-end of the receiver. With no interference, the transmitter power level required to achieve this signal level is remarkably low. Once the signal level exceeds the noise threshold of the receiver, the capture effect starts suppressing the receiver noise, causing the desired signal to be heard loud and clear.

What happens when multiple signals are received at similar signal levels on the same frequency? The capture effect still takes place, but it takes a signal level at least 10 dB above the sum total of ALL other signals on frequency to be heard. So, if ten stations, each with an effective radiated power (ERP) of 100-watts were competing with one another on Mir's uplink frequency, none would be heard. It would take a signal level of at least 10 dB above the sum total of all signals to be heard. In this case, that's 10 dB above 1000 watts, or an ERP of at least 10,000 watts to be heard on Mir -- a far cry from just a few milliwatts!

On packet radio, the situation is worse. Packet radio communications is a strong signal mode that is very suseptible to corruption by noise. It only takes one corrupt bit in a packet radio frame to destroy the integrity of the entire frame. A signal level that produces at least 25 dB of receiver quieting is required for acceptable packet radio communications performance.

If ten packet radio stations are competing with one another on Mir's uplink frequency as in the example above, the signal level required to get through the interference equates to over 300,000 watts! Since packet radio uses short transmission times, the probability of transmitters from all groundstations under the footprint of Mir firing simultaneously is remote. There is a much greater probability that packets can be successfully received by Mir if they are carefully timed to interleve between those of other groundstations, allowing contact even with low transmitter power levels.

Mir Operating Procedures

Communicating with the cosmonauts on the Mir orbital complex is a very simple matter, and success is not hard to come by provided some simple operating procedures are followed and common sense is used. As the above examples show, the effects of interference between a high volume of groundstations trying to contact Mir can be very damaging to everyone's effort. Interference between groundstations competing with one another to contact Mir, especially over populated areas of the world such as North America and Europe, is the cosmonauts biggest criticisms of groundstations. Lets look at some operating procedures that can help reduce interference between groundstations, and increase everyone's chance of successfully contacting Mir.

The first "common sense" rule for contacting the Mir orbital complex is to make orbital predictions very carefully using the latest available Keplerian orbital data for Mir, and listen very carefully to Mir's downlink frequency to determine what mode of communications is being used by Mir when it comes into range.

Since Mir is capable of several different operating modes, it would be foolish to attempt a packet radio contact with Mir if the cosmonauts are engaged in a voice contact. Only if a cosmonaut is heard calling CQ is it wise to call Mir on voice. Keeping the call short and waiting a few seconds before transmitting will increase the chance of being heard by Mir as this will tend to intersperse the transmissions made by groundstations.

Also keep in mind that most cosmonauts speak Russian and are only confortable in their native language. Use standard phonetics where appropriate to make it easier for the cosmonauts to understand what is being said. Also, keep in mind that in space it's hard to tell whether a groundstation that has "disappeared" has gone out of range of Mir, or is simply being "covered up" by interference from other groundstations. Be patient, and avoid the temptation of picking up the microphone and calling Mir if you find the cosmonaut is losing contact with a groundstation. Follow the directions of the cosmonauts whenever possible.

Packet Radio On Mir

There are basically three different types of packet radio communications that can take place via the amateur radio station on Mir. Groundstations may access the Personal Message System (BBS mailbox) on Mir, they may establish a live keyboard "chat" with one of the cosmonauts, or they may use the Mir packet radio station as a digital repeater to establish live contacts with other groundstations too distant to allow a direct contact by way of groundwave propagation. Although these features exist, the packet radio station on Mir should only be used to exchange short electronic mail messages with the cosmonauts, and nothing else.

There are some very important reasons for limiting packet radio activity to cosmonaut e-mail only. The Personal Message System on Mir has a very limited storage capacity of only 22 kilobytes. This is adequate for several brief messages, but not much more. The Mir PMS should not be used to exchange messages between groundstations. Digital store-and-forward communication satellites called "Pacsats" have been designed, built, and are available for this purpose and should be used instead. Messages on the Mir PMS should also be deleted once they are read to free-up storage space on the PMS.

The Mir PMS should not be used as a digipeater, since the efficiency of Mir as a digipeater has been shown to be low, and digipeating off Mir only causes interference with the groundstation who is connected to the PMS. Again, Pacsat satellites can be used for this purpose, if needed.

The Mir PMS is very limited in that it is a single-user electronic message system. Only one groundstation may connect to the PMS at a time. All others must wait their turn. Attempts to contact the Mir PMS while it is in use will only cause interference with the current PMS user and result in a signal from Mir.

Careful monitoring of Mir's downlink packets can show if the PMS is actually connected to a groundstation. Groundstations MCOM TNC parameter should be turned ON. This will allow the monitoring of all packet frames coming from Mir, including connect and disconnect packets.

The packet radio station on Mir uses callsigns with two different secondary station identifiers (SSID). The PMS uses an SSID of `1', while the keyboard port uses an SSID of '0' (SSIDs of 0 are not normally displayed by terminal node controllers). Connections with the keyboard port should be avoided, unless it is obvious that a cosmonaut is at the keyboard and is looking to make a contact with a groundstation.

The proper procedure for contacting the Mir PMS is to wait until the current user disconnects from the PMS, and then initiate a connect request with the Mir PMS. Of all the groundstations attempting connections with Mir, only one will be successful. All others will receive a signal.

LOS

These restrictions may sound less than pleasant, but it is important to realize that the packet radio station on Mir is a single user system and is not designed for operation from an orbital complex. It works well and is a great asset to the cosmonauts, but only if proper operating procedures are closely followed.


Table 1: Commands for Mir's Personal Message System (PMS).

B(ye) B [CR] disconnects you from PMS.
H(elp) H [CR] or ? [CR] displays this help file
J(log) J [CR] displays a list of callsigns heard (optional date/time)
K(ill) K n [CR] deletes message number n (only to/from your callsign)
KM(ine) KM [CR] deletes all READ messages addressed to your callsign
L(ist) L [CR] lists the 10 latest messages
M(ine) M [CR] lists the 10 latest messages to/from your callsign
R(ead) R n [CR] reads message number n
S(end) S (callsign) [CR] begins a message addressed to (callsign)
Subject: max 28 characters ending with [CR]
Text: End each line with [CR]
End message by typing /ex [CR] or CTRL-Z [CR] at the beginning of a new line.
SR(eply) SR n [CR] Sends a reply to message n prompting only for text
V(ersion) [CR] displays the software version of the PMS system


Table 2: Mir QSL information for all regions of the world
Please send a business-sized SASE along with your QSL

Sergej Samburov, RV3DR
P.O. Box 73
Kaliningrad-10 City
Moscow Area, 141070, Russia
Russia only

Amateur Radio Station DF0VR at GSOC Control Center
Oberpfaffenhofen, Munich, Germany

Thomas Kieselbach, DL2MDE
Joerg Hahn, DL3LUM
DLR Amateurfunkstation Oberpfaffenhofen
P.O. Box 1116
82230 Wessling, Germany
All of Europe except Russia
Contact with Thomas Reiter [DP0MIR]

Dave Larsen, N6JLH
P.O. BOX 1501
Pine Grove, California 95665
USA
All of USA, Cananda, Australia, New Zealand & South America




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