Spotlight On: UoSAT-OSCAR-22

By: John A. Magliacane, KD2BD

[This article originally appeared in The AMSAT Journal, Volume 15 No. 3, May/June 1992]


Name:     UoSAT-OSCAR 22 
Object #  21575
Launch:   17 July 1991
Period:   100.24 Minutes
Orbit:    Polar LEO (Low Earth Orbit)
Altitude: 775 km (482 miles)
Height:   600 mm and 5 Meter Gravity Gradient Boo with 3 Kg tipmass
Width:    300 mm
Depth:    300 mm
Weight:   46 Kg
Modes:    9600 Baud FSK

UoSAT-OSCAR-22 is the most recent spacecraft in a series of Amateur Radio communications satellites designed and built by the Department of Electrical Engineering at the University of Surrey in Guildford, Surrey, England. UoSAT-OSCAR-22 was launched on July 17, 1991 on an Ariane rocket along with four "microsatellites", one of which is an amateur astronomy satellite called "SARA". UoSAT-OSCAR-22 is a multiple mission spacecraft designed to serve several audiences. One mission was to carry out experiments originally slated for UoSAT-OSCAR-15, whose on-board electronics failed shortly after the spacecraft reached Earth orbit . The primary purpose of UoSAT-OSCAR-22, however, was to provide non-amateur radio related store-and-forward digital communications for VITA and SatelLife, a non-profit, humanitarian organization. UoSAT-OSCAR-22's primary role in space has recently been modified when the satellite played a part in Amateur Radio's first "role reversal" with another spacecraft, UoSAT-OSCAR-14.

One of the most unique aspects of UoSAT-OSCAR-22 is its Earth Imaging System (EIS), designed by University of Surrey doctoral student Marc Fouquet. The Earth System was designed to capture Earth images from low-Earth orbit using a charge coupled device (CCD) camera, and broadcast those images to ground stations using amateur frequencies and the AX.25 packet radio "Pacsat Broadcast Protocol" when the spacecraft was not providing service to SatelLife. The monochrome CCD imager produces a CCIR video image having a resolution of 578x576 pixels with an aspect ratio of 4:3. Images taken by the CCD camera are first digitized using an 8-bit half-flash analog to digital converter, and then stored in RAM for later processing and transmission over the downlink transmitter. Received images can be captured and displayed using a personal computer with suitable graphics capability. The images can also be converted to popular GIF and JPEG formats and viewed in those forms if so desired.

[Here are several photos taken from UO-22 and converted to GIF format by Harold Price, NK6K. - N7HPR]

The Big Switch

While UoSAT-OSCAR-22 was serving the needs of SatelLife, UoSAT-OSCAR-14 was providing the Amateur Radio Service with its only 9600 baud packet radio store-and-forward communications satellite. In late December 1991, UoSAT spacecraft controllers introduced an enhanced broadcast server on UoSAT-OSCAR-14 which did a lot to reduce congestion on the satellite's single uplink frequency. However, since OSCAR-14 had only 256 kilobytes of memory, the spacecraft used a RAMDISK system which could only store 400 packet messages at a time. With uplink contention reduced, packet gateways on line, and more than 150 stations regularly active on OSCAR-14, the 400 message limit was often exceeded. When the satellite message space became full, new messages could not be uploaded and older messages had short lifetimes before being deleted automatically to make way for new messages.

After some initial use, it became clear that OSCAR-22's CCD imager success and the less than optimum conditions on OSCAR-14 required that some operating changes to both UoSAT-OSCAR-14 and UoSAT-OSCAR-22 be made. Amateur stations around the world were downloading CCD Earth images several times per week, with each image containing more than 300 kilobytes of data. Furthermore, it was discovered that OSCAR-22's high power amplifier which produced excellent output on amateur frequencies, did not work reliably on the non-amateur frequencies used by SatelLife operations.

Taking into account the resources available and the obligations to SatelLife, HealthNet and VITA, UoSAT controllers decided to swap the roles of UoSAT-OSCAR-14 and UoSAT-OSCAR-22 in a attempt to optimize the capabilities and resources of each spacecraft. On February 5, 1992, all non-amateur traffic, both SatelLife and VITA, moved fro OSCAR-22 to OSCAR-14, which no longer transmits on its amateur downlink frequency. All amateur traffic moved from OSCAR-14 to OSCAR-22, and OSCAR-22 now operates as a dedicated amateur radio satellite transmitting constantly on its amateur downlink frequency.

Now that UoSAT-OSCAR-22 is operating exclusively in the amateur satellite service, the spacecraft can dedicate its 512 kilobytes of memory for storing as many as 800 packet messages. Two 9600 baud uplink receivers are available on frequencies of 145.900 and 145.975 MHz, and the single downlink transmitter on 435.120 MHz is available on a non-interrupted basis. The only minor inconvenience occurs when some users access the satellite to download CCD images while others connect just to check their mail. Solutions to these problems are being investigated by UoSAT controllers, while more efficient spacecraft operating software is developed to maximize the efficiency of UoSAT-OSCAR-22 operations.

UO-22 Link Frequencies

UO-22's Digital Transponder Frequencies:
Mode JD Uplink #1 : 145.900 MHz, 9600 bps FSK
Mode JD Uplink #2 : 145.975 MHz, 9600 bps FSK

Mode JD Downlink : 435.120 MHz, 9600 bps FSK

UO-22 Ground Station Requirements

Hardware requirements for full access to OSCAR-22 include a 9600 baud packet radio modem, a pair of low-gain directional antennas for the satellite's Mode JD link frequencies, a 2-Meter FM uplink transmitter, and a 70-cm FM downlink receiver. Pacsat terminal software such as PB, PG, PHS, and PFHADD are used with OSCAR-22 just as they are with PACSAT-OSCAR-16 and LUSAT-OSCAR-19. Programs such as these, along with a KISS mode capable TNC allow ground stations to access the mailbox and file server available on the satellite, as well as capture CCD imager data from the spacecraft. Both text and executable binary files may be downloaded from the satellite or fed into a queue for broadcast to all stations within the footprint of the satellite using the Pacsat broadcast protocol. Pacsat terminal software is widely available for MS-DOS compatible computers as "freeware" on many dial-up BBS systems that carry Amateur Radio related software.

UoSAT-OSCAR-22 is currently the only 9600 baud store-and-forward packet radio satellite available for amateur radio use. [KO-23 and KO-25 have since joined the ranks of 9600 baud store-and-forward satellites - N7HPR] It is currently acting as a powerful gateway between widely spaced terrestrial ground stations, moving vast quantities of packet radio traffic around the globe in record speed. The 9600 baud packet link available on OSCAR-22 cannot be compared with the 300 baud "long haul" packet forwarding networks currently in use on the HF bands. OSCAR-22, and high baud rate packet radio satellites that follow in the lines of OSCAR-22, will go far in increasing the throughput and the reliability of the worldwide amateur packet radio (AMPR) network, especially in polar regions of the Earth where frequent auroral disturbances make HF operation unreliable.

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