|fahnen/11.jpg Spotlight On: The Microsats|
Spotlight On: The MicrosatsBy:John A. Magliacane, KD2BD
[This article originally appeared inThe AMSAT Journal, Volume 15 No. 4, September/October 1992]
AMSAT-OSCAR-16 Catalog Number: 20439
DOVE-OSCAR-17 Catalog Number: 20440
WEBERSAT-OSCAR-18 Catalog Number: 20441
LUSAT-OSCAR-19 Catalog Number: 20442
SPECS: Launch: 22 February, 1990 Period: 100.8 Minutes Orbit: Polar LEO (Low Earth Orbit) Altitude: 800 km (497 miles) Size: 23 cm square (9 inches) Weight: 9 Kg
Spacecraft HistoryOn January 22, 1990, six Amateur satellites were launched by the European Space Agency from a launch site in Kourou, French Guiana, along with a commercial French SPOT-2 Earth observation satellite. Not since December 17, 1981 when the Russians launched Radio Sputnik satellites RS-3 through RS-8 had Amateur Radio experienced a multiple satellite launch from a single launch vehicle.
The Amateur Satellites carried on this launch represented the birth of a new generation of OSCAR satellites. Of these six Amateur satellites, UoSAT-OSCAR-14 and UoSAT-OSCAR-15 were designed and built by the Spacecraft Engineering Research Unit at the University of Surrey in Guildford, Surrey. UO-14 was taken out of the Amateur satellite service shortly after launch of UO-22. UO-15 experienced an on-board electronics failure shortly after launch, and is not operational. The remaining four OSCARs are known as "Microsats".
All six satellites utilize the AX.25 packet radio communications protocol, and all have computer systems designed around the NEC V40 microprocessor, which is similar to the microprocessors contained in today's personal computers. This allows the same program development and debugging tools used for PC software development to be used for controlling satellite operations. The multi-tasking operating system in operation on the Microsats was donated by Quadron Service Corporation and appears similar to MS-DOS to each running application.
All four "microsatellites" launched with SPOT-2 are very much alike in appearance and design. All are remarkably small in size, being cube shaped approximately 23 cm on each side. Although similar in appearance and architecture, each satellite carries its own unique mission in space.
Let's look at each Microsat in detail:
Catalog Number: 20439 Connect Address: PACSAT-1 Transponder: Mode JD, Digital Uplinks: 145.900 MHz 145.920 MHz 145.940 MHz 145.960 MHz Downlinks: 437.051 MHz 437.026 MHz 2401.143 MHzBased on the success of UoSAT-OSCAR-11's Digital Communications Experiment, AMSAT-OSCAR-16 was designed to be a dedicated store-and-forward file server in space. Using 1200 bit per second Mode JD radio links, AMSAT-OSCAR-16 interacts with ground station terminal software to appear as a packet radio bulletin board system to the user. Anyone wishing to download files, personal mail from anywhere in the world, or news bulletins can request the information be "broadcast" to all under the footprint of the spacecraft, or directed specifically to that ground station. This broadcast protocol differs from terrestrial packet radio communications, but allows a greater number of ground stations access to the spacecraft's resources during the limited time of a pass.
A total of 10 megabytes of static RAM is used for message storage and a RAM disk. PACSAT communicates with ground stations through a single downlink channel and a total of four uplink channels. The multi-tasking operating system allows mailbox software and an AX.25 protocol driver to operate concurrently.
Only one 70-cm downlink transmitter is active at any one time. Due to performance degradation of the primary transmitter on 437.026 MHz, the secondary transmitter on 437.051 MHz is being used at the current time. All Microsats transmit using several watts of transmitter power making their signals easily received on the Earth below. AMSAT-OSCAR-16 accepts 1200 bps 3.5 KHz deviation Manchester encoded FSK on any of its uplink frequencies. It transmits using 1200 bps binary phase shift keying (BPSK), a very robust binary modulation scheme.
AO-16 uplinks are made with 2-Meter FM voice transmitters, while downlink reception requires a 70-cm SSB receiver or HF SSB receiver with a 70-cm converter. Several modem designs are available for Pacsat operation. These modems are also mode compatible with Fuji-OSCAR-20.
The uplink receivers are VERY sensitive. AX.25 connection to the spacecraft can be made with just a few watts of transmitter power and a modest antenna system. While testing a newly designed 1200 bps Pacsat modem, it was discovered that seven watts of transmitter power and an indoor antenna were all that was required to connect to oneself using AO-16 as a digipeater.
"Experimenter Days" are scheduled for PACSAT from time to time. During these periods, ground stations are encouraged to limit their uplink transmitter power to the minimum necessary to establish and maintain AX.25 connection with the digital transponder. Usually the transmitter power level is on the order of just a few watts.
Whole Orbit Data (WOD) collections are also performed by AO-16, and WOD files are available through the mailbox for all those who are interested in processing and analyzing spacecraft telemetry.
Catalog Number: 20440 Transponder: None Beacon 1: 145.824 MHz Beacon 2: 145.825 MHz 2401.221 MHzAmong the other packet radio Microsats launched with AO-16 was DOVE, an OSCAR sponsored by AMSAT Brazil, and dedicated to education and classroom demonstrations. DOVE, an acronym for Digital Orbiting Voice Encoder, carries hardware capable of reproducing digitized speech, or controlling a Votrax speech synthesizer. However, due to hardware failures that have occurred since launch, the primary mission of providing voice messages of world peace from DOVE has not been fully realized.
DOVE operates sporadically on a downlink frequency of 145.825 MHz FM, transmitting AX.25 protocol packet radio telemetry. Using 1200 bps Bell 202 style AFSK emission, DOVE-OSCAR-17 can be copied on packet radio equipment currently in wide use on VHF. DO-17 contains no general-use uplink receivers and does not support any mailbox operations.
Regardless of the hardware malfunctions that have made voice software uploads difficult for spacecraft controllers, many educators and OSCAR enthusiasts have successfully captured spacecraft telemetry frames and have analyzed trends in that data and determined the spin rate of the satellite. These experiences, as well as AO-16 WOD analysis bringing real-world sciences directly into the hands of those involved and are an invaluable teaching resource that is free for the asking.
Catalog Number: 20441 Transponder: Mode JD, Digital - Not yet in operation Beacon 1: 437.102 MHz Beacon 2: 437.075 MHzSporting a full-color CCD camera, WEBERSAT-OSCAR-18 digitizes Earth images and downlinks them as a AX.25 serial data stream. WEBERSAT-OSCAR-18 also carries packet radio mailbox facilities, such as those on AO-16, however those capabilities will not be implemented until the primary mission of recording Earth images is fully exhausted.
WEBERSAT-OSCAR-18 is a product of the efforts of The Center for Aerospace Technology (CAST) at Weber State University in Ogden, Utah. WO-18's CCD camera has a resolution of 700 pixels by 400 lines, and can be viewed with Weberware software running on a personal computer having adequate graphics display capability. Digitized NTSC video from the camera is assembled into packets that are sent as unnumbered information UI frames. Ground stations must receive this data over several passes to capture a complete image. Each image contains about 200 kilobytes of data. An on-board 1265 MHz ATV uplink receiver allows ground stations to load WEBERSAT's memory using a groundbased video camera for later transmission by the spacecraft. WO-18 can also transmit CCD images on 70-cm using an analog "turbo" mode that is much faster than using the AX.25 packet downlink. However, no interference protection is afforded by the analog transmission mode since information received in this form does contain a checksum.
Ground station hardware requirements for WO-18 are similar to those of AO-16, except that a 2-Meter uplink transmitter is not required for reception of the CCD Earth images.
Catalog Number: 20442 Connect Address: LUSAT-1 Transponder: Mode JD, Digital Uplinks: 145.840 MHz 145.860 MHz 145.880 MHz 145.900 MHz Downlinks: 437.153 MHz 437.125 MHz CW Beacon: 437.127 MHzLUSAT-OSCAR-19 was coordinated by AMSAT Argentina, and is a packet radio store-and-forward spacecraft much the same as AMSAT-OSCAR-16. The only difference between the two satellites is that AO-16 supports an S-Band beacon in addition to the mailbox, while LO-19 has 70-cm CW beacon.
The LUSAT CW beacon transmits slightly modified CW on a frequency of 437.127 MHz with about 750 mW of power. CW is sent at 12 words per minute and consists of telemetry information allowing simple spacecraft telemetry analysis with a minimum of ground station radio equipment. The Morse telegraphy sent by the CW beacon is modified in such a way that multiple dashes in numeric data is sent as a single dash (1 = .-, 2 = ..-, etc.).
Being essentially identical to PACSAT, LUSAT is often used as test bed for updated on-board computer software before AO-16 is re-loaded. If all goes well with the update on AO-16, then LUSAT is re-loaded with the new operating software.
Microsat operating schedules are frequently made known through unnumbered information UI packet frames transmitted by the microsats. These short beacon announcements are usually written by one or more of the spacecraft controllers and are used to inform microsat users of the latest images on WEBERSAT, the status of LUSAT's CW beacon, when low-power "Experimenter Days" are scheduled for PACSAT, or when speech software is being uploaded on DOVE.
"Pacsat-class" Amateur satellites are revolutionizing Amateur Radio communications as we head through the "information age". Store-and-forward satellites along with automated Pacsat gateways are improving terrestrial packet radio throughput immensely, and are reducing the workload on the HF packet networks.
The success of the Microsats has influenced the future and the direction of OSCAR satellites leading us into the future through pathways we never thought were possible just a few years ago. At the present time, several new Microsats are in the making. Finland Amateurs are busy completing "HutSat", Italians are preparing "ITAmsat", and Israel is expected to launch its first OSCAR known as "TechSat" in the not too distant future.
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