After 7 years of continuous activity, the Mir Space Station PMS has become the most popular Amateur Radio Satellite in the world. When Mir is retired, a suitable replacement will need to be found. This proposal will attempt to improve on what has proven to work very well. And will address some of the existing limitation of the Mir PMS system. This proposal does not cover all of the exact hardware/software details of the equipment implementation.

Details:

1. The new ISS-PMS will need to be accessible by as many people around the world as possible.

Any ground station currently capable of accessing the Mir PMS, should continue to be able to access the ISS-PMS. The reliability of the packet link can be easily increase, with should result in fewer bit-errors.

The Mir PMS is the easiest and least expensive satellite in the world to operate. The ground station requirements can be easily built or purchased. Expanding the capabilities of the ISS-PMS, will allow easier access and improved data through-put. The new ISS-PMS MUST continue to support 1200 baud AX.25 Packet, in the FM mono-band mode. Ground station requirements will be similar to the existing Mir PMS, including:

- Antenna 0 dBd Gain Omni or small Yagi,
- Radio, standard FM mobile 25 watt transceiver or better
- Terminal Node Controller (TNC) supporting AX.25 packet protocol

Top

2. The new ISS-PMS, receiver specification:

As most of us agree, it is a good idea to keep the 2-meter Mono band radio station active on Mir, and in the future on the International Space Station. This radio will be used for both FM voice and FM AX.25 Packet.
But the choice of the radio equipment is important, so as not to limit access by ground stations. The 3.5k Doppler shift is not a serious problem on 2-meters, however the ISS radio receiver my need to be modified to accommodate a wider receiver.
Ground stations may not need to shift their transmit frequency during a ISS-PMS Pass. It is true that adjusting your uplink will improve the bit-error rate on packet, but most beginners are "Channel Locked".
A channel locked station is not able to make the fine tuning adjustments required to compensate for Doppler.

Goals of the Ideal 2-Meter receiver:

1. Perform as well as the existing Mir 2-meter station.
2. Improved Adjacent channel interference
3. Improved ability to copy off frequency stations (up to 3.5 kHz, with AFC)
4. Direct connect AX.25 Packet (volume control independent)
5. Remote control of TNC settings from ground.

Sample Radio Selectivity values:

Radio            -6 dB       -60 dB
ICOM 228         15 kHz      30 kHz   (Mir station 1993- June 1996)
Kenwood TM-733   15 kHz      28 kHz   (Existing Mir Station)
Yeasu 736        12 kHz      25 kHz
Yeasu 2400       12 kHz      30 kHz
Ideal Mir        18 kHz      24 kHz   (attempted Goal)

The Ideal radio should have a wide front end at the -6dB Selectivity points. This will allow the radio to better receive the incoming signals when the signal is shifted 3.5k by Doppler.

Example:

Ground Station Transmits on:  145.550.0
Doppler Shift induced         3.5k (Mir heading Towards the Ground Station)
Frequency heard at Mir        145.553.5

With the old Icom radio, less than 20% of the signal would fall out side of the -6dB receiver Selectivity point.
With the Ideal radio, less than 1% of the signal would fall out side of the -6dB receiver Selectivity point.

At the same time we need to widen the -6dB point, and tighten the -60dB point to help reduce Adjacent channel interference. With this filter configuration, the ISS station would be in better position to tolerate stations operating 20kHz on either side of the ISS channel. However, I would still recommend that all ground stations to stay at least 25 kHz from ISS Uplink/down link frequencies.

If we use existing off the shelf radio equipment, we should be able to meet most of the goals. The receiver modifications could be done with a minimal expense.

Suggested Transceiver:

Top

3. The new ISS-PMS, should be able to take advantage of improved antenna designs.

Which should result in stronger signals for both Transmit and Receive.

The existing Mir station is using an externally mounted dual band antenna. The gain values are unknown.
The transmitter on Mir is running approximately 5-25 watts. The current power levels on Mir have proven to be sufficient for most ground stations. There are however deep signals fades caused by polarity shifts in the received signal.
A new circular polarized mono band antenna should be installed on the ISS. The circular polarization should help ground stations running linear polarized antennas by reducing signal fading.
An antenna on the ISS, with a gain figure of 3-9 dBic should be possible.
The Antenna will then be place on the Nadir (Earth facing) side of the Space Station.

At the present time MIREX does not have the resources to provide an antenna solution. The MAREX team will need to find a stable antenna solution.

Top

4. The new ISS-PMS, should be able to support multiple users.

The first release of this PMS will only support 1 user. The multi user version will not be read until late 1999.
There are existing Pac-Sats in use, which have proven the ability of a Pac-sat to support multiple users.
The big difference with the ISS-PMS and the Pac-sats, will be the mode (FM) and the frequency.

To keep the costs low for ground station operators, the ISS-PMS MUST stay a Mono-band system, in the 2-meter band. The initial system will be able to support 1 users.

Features of the KPC-9612 Plus

Hardware
128K byte RAM (expandable to 512K), battery backed to save all parameters and PBBS messages
Real-time, battery-backed clock
Low power: 5.5-25 Vdc at <45 mA
Four digital output lines enable remote control of attached devices
Two analog inputs which can be monitored with the ANALOG command
Eight front panel LEDs provide operational information
Measures only 0.8" x 6.7" x 6.9" (2 cm x 17 cm x 17.5 cm)
Weighs only 18 oz (0.5 kg)
RS-232 serial port (cable not included)
Expansion header allows connection of future modems (third port) or other additional hardware

1200 Baud Port
Connects to mic jack
Internal, external, or software carrier detect
AFSK output (1mV-4V P-P) adjustable from the keyboard with digital potentiometer
Can be configured for 300, 400, 600, or 1200 baud

9600 Baud Port
Connects to high-speed-capable radio
Can be configured for 4800, 9600, 19200 or 38400 baud and is G3RUH compatible
Internal or external carrier detect
GMSK output (2mV-4V P-P) adjustable from the keyboard with digital internal potentiometer

Firmware
Change all KPC-9612 Plus parameters from another packet station using remote sysop access
Can connect to one radio and still operate at two speeds, automatically
Command sets for both new and experienced users; on-line help messages for each command

Top

5. Limitations and restrictions will be added to enhance message traffic and reduce interference.

The new ISS-PMS will have most features commonly available to terrestrial PMS users. One specific feature the PMS will need is an Idle-User-Timer. This timer will force a user off the ISS-PMS, after a sysop-selectable time has expired (the initial value of 2 minutes is suggested).

This is a limitation we have with the current Mir PMS system. Idle-User-Timer is hard coded into the TNC for 7 minutes and cannot be changed by the Mir crew. This limitation has proven to be a serious problem. When a connected ground station goes out of range, the new stations coming in range cannot log into Mir for 7 more minutes. This waist valuable time and causes lots of frustration to the calling ground stations.

The Digital-Repeater option will be tuned off. All Unproto, APRS and Two-way connects will be blocked from this ISS-PMS. We have seen from the past 7 years of using the Digital-Repeater option on Mir, that excessive Unproto traffic lowers the message traffic and reduces reliability significantly. If there is a need to Unproto and APRS traffic, then a separate Digital-Repeater could be installed using different frequencies on a different band.

Call Sign Date base:
This option could be used to assist in blocking illegal Amateur Radio Calls. In the USA, we have several stations using the call sign "NOCALL". The ISS-PMS can then automatically reject illegal call signs.
An extended data base look-up table, could offer even more protection from illegal use of the ISS BBS.

Top

6. Hardware, this design may require some custom hardware and software development.

It may be possible to build this system by using off the shelf equipment.
Further investigation is needed to determine the exact amount and weight of the ISS-PMS.
The incorporation of an AFC circuit may nessicate custom designed hardware.

Top

7. Mono Band operations verses Dual Band operations:

The two-meter band is ideally suited for the satellite operation for beginners. The equipment for the two-meter band is easy to build and or inexpensive to purchase. Most new Amateur Radio Stations first radio is a two-meter FM transceiver. This make the two-meter band the primary candidate to introduce new users to satellites.

The Two-meter packet band is not plagued with the problems of the 70 cm band, packet or voice.
The Doppler shift on two-meter band is somewhat negligible, and station power necessary to provide reliable communication is easily available.
The equipment and procedures are not so highly technical, but just a solid understanding of all the fundamentals of satellite communications is necessary.
The two meter band has the fastest growing user base of any of the amateur radio bands in the world.
Almost all newly licensed USA technicians without code will start with the two meter band (voice) and then add two meter packet. This large growing base of users, will undoubtedly lead new users to the better, but much more highly advanced and expensive forms of satellite communication.
This in turn should bring a wide new influx of abilities and ideas into satellite communications leading to development of cheaper, better equipment and methods.

Top

8. Remote control from authorized Amateur radio ground control stations.

Authorized Amateur radio station on the ground should be able to remotely control the following functions:

1. All TNC Parameters
2. PL Tones
3. Down Load system telemetry
4. To be defined

Top

9. Project Duration:

This project is expect to be the first Amateur Radio Experiment enabled on the ISS. The First experiment must always be the experiment which reaches the most users around the world. It is expected the single user PMS system, will be in use from 1998 until the year 2000. After this date, the Multiple user PMS should have built and ready to fly.

The proposed 2-meter Mono band Packet system does have limited functionality in that the initial version will only support 1 packet user. Plans are currently in development to expand the capabilities of the PMS system to support multiple users via multiple 2-meter channels.
The hardware for the Multiple user system has not been funded and as a result Mirex will only be able to fund a single user PMS system in time for the first module launch.

The long term goals for 2-meter packet for ISS, are to keep a 2-meter Mono band project in place for beginners around the world for the next 10 years.

Mirex encourages other more sophisticated experiments to be installed on ISS, just as long as they do not interfere with the operations of the beginners 2-meter mono band PMS station.

Top

10. Skill Level

Mirex has designed this experiment for Amateur Radio Stations with a Skill level of (1).

Skill Level 1: Entry Level

Newly licensed Amateur Radio stations with Minimal technical and practical experience.

Stations who have never operated through Amateur Radio Satellites.

Limited funds: Since these are beginners, the amount of time and money invested into the Amateur Radio hobby is limited, their ability to work sophisticated satellites is limited.

Access: Satellites designed for Skill Level 1, will have the greatest access to the largest number of stations around the world. Even stations in Third-World-Countries should not have difficulty in operating satellites designed for Skill level 1.

Top

Summary: