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TheSSETI
ExpressHandbook
AMSAT-UKSeptember
2005
The SSETI Express Handbook
Published by AMSAT-UK
Compiled edited & written by Richard.W.L. Limebear G3RWLFrom SSETI Express and Amsat-UK documentationFrench translation by Christophe Candebat F1MOJJapanese translation by Toyo Komatsu - JA0CQP
September 2005
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Contents
SSETI ExpressThe SSETI Concept and Amsat-UK 1SSETI Express Systems 3Construction 4Launch & Early Operations 4Payload Operations 6Spacecraft Modes of Operation 7Cubesats 7
The Amateur Radio PayloadGeneral 9Hardware 11Payload Modes of Operation 12Beacons 14Voice Operating 14
Telemetry and CommandingOn/Off Keying 15Nominal Beacon 15DTMF 16Downloading 16“Friendly” Commanding 17
How you can help SSETI Express 18Data Formats 20
Cover graphics: SSETI Express construction: before and after
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SSETI Express
The SSETI Concept and Amsat-UK
SSETI stands for the Student Space Exploration and Technology Initiative founded by the Education Department of the European Space Agency (ESA). The Education Department works to increase the interest and motivation of young Europeans in technology in general and space in particular. The initiative started in 2000 and plans exist, ultimately, to go on to a Lunar mission.
The first spacecraft built within this initiative is SSETI Express, a 62-kg spacecraft that will fly into Low Earth Orbit. The satellite should serve as a technological demonstration and as a test bed for some of the hardware that will be used for the second mission, ESEO.
SSETI Express uses active magnetorquers for attitude control as well as a passive magnet. Therefore the main spacecraft axis will be aligned with the Earth’s magnetic field.
The European Student Earth Orbiter (ESEO), the second SSETI spacecraft, should be launched directly into a geo-stationary transfer orbit using an Ariane 5 launch vehicle; this is planned for 2007/8. After this the third step will be the development of a Moon Orbiter followed by an actual Moon landing. This may even include a Moon Rover.
Participants come from over 25 different European universities and technical institutions. They each take responsibility their own financing, often working together with industries that act as sponsors for the project. (Sponsorship can be monetary as well as material, providing essential hardware, or even knowledge and expertise.)
ESA's involvement with SSETI concentrates on the role of management and system engineering, focusing on communication, meetings and workshops, as well as integration, verification and testing activities. They are also responsible for facilitating the launch and essential operations. For more information about the SSETI Programme and all the projects it encompasses, please visit the SSETI website at http://www.sseti.net
SSETI projects are, of course, primarily for students. The Amsat-UK involvement came because of a chance meeting at an international ARISS meeting at ESTEC in the Netherlands in May 2004 where AMSAT-UK representatives happened to bump into some of ESA's SSETI Express team. The project's S band team were experiencing difficulties resourcing their S band requirements, so Amsat-UK offered to assist.
At Amsat-UK’s Colloquium in July 2004 their Chairman, Professor Sir Martin Sweeting, G3YJO, announced a new amateur transponder project to be launched as part of the SSETI Express satellite. He said that Amsat-UK would provide, at very short notice, an S band (2.4GHz) transmitter. Amsat-UK is delighted to have been
Students building SSETI Express 0
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entrusted with such an important task and the team will have the organisation’s full support.
As well as providing the S Band hardware, Amsat-UK members have provided “mentoring” for the students about RF, orbital data, tracking and all the facets of satellite operations with which we have become familiar over the years.
With ESA headquarters located in France and dependent on French legislation, Amsat-France were the ideal organisation to manage all the administrative and licensing paperwork with the French administration. In fact the licence was issued personally to F6AGR and he is one of the command stations.
SSETI Express will downlink general telemetry at 9600 bps on 70cms and it will also be possible for radio amateurs to request specific downloads. In addition it is planned that the 38k4 bps telemetry transmitter on 2.4GHz will also be available for amateur voice operation as a Mode U/S transponder after initial tests on the satellite have been completed.
It is intended that the 2.4GHz downlink transmitter will transmit telemetry and data at a data rate of 38k4 before being switched over to voice transponder operation as part of the payload cycle. After main operations are completed it will be left in this mode for the remainder of the mission lifetime.
Because the main objectives of the mission can be completed within a couple of months, we suggested running an extra line from the U band uplink into the S band downlink - i.e. making a bent pipe FM transponder. Not only that, but even if the On-Board Computer fails, this bent pipe function is autonomous and so should still operate.
Another radio amateur, DF2FQ, provided the 437 MHz transceiver. These frequencies will enable the many amateurs who have Oscar 40 equipment to use it in an exciting new way.
Amsat-UK and ESA hope that as many amateurs around the world as possible will be willing to download the telemetry, decode it, and forward it to the SSETI Mission Control Station Centre over the Internet. This opportunity to participate will enable us to show that the amateur satellite service’s groundstation network is a viable system for such short-term projects. This in turn will encourage ESA, SSETI and possibly other launch
S-Band unit mounted in the spacecraft 0
The S-Band Flight Unit 0
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agencies to actively consider incorporating amateur transponder equipment in future projects!
For detailed information on the SSETI Express mission please see the SSETI Express Mission Website at http://www.sseti.org/express
SSETI Express Systems
PCU (Power Control Unit): supplies power for the spacecraft, controls the spacecraft modes, and controls the battery charging and discharging.
UHF (Ultra-High Frequency): is the primary communications system. It contains a radio and TNC and is capable of 9600 bps up and downlink via a monopole antenna.
OBC (On-Board Computer): controls the spacecraft in nominal mode. It processes telecommands, collects housekeeping data, controls the payloads and collects payload data.
ACDS (Attitude Control and Determination System): controls the attitude of the spacecraft using a pair of magnetorquers and a passive magnet and determines the attitude of the spacecraft using a magnetometer and a pair of sun-sensors.
S-BAND: is the secondary communications system. It contains a radio and TNC and is capable of 38400 bps downlink, or it can transpond audio from UHF. It transmits via three patch antennas.
PROPULSION: This is a demonstration and characterisation payload capable of controlling the attitude of the spacecraft using cold-gas thrusters. It has a 6-litre nitrogen tank filled at 300 bar, and is controlled by the Propulsion Instrument Control unit (also known as “MAGIC”).
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CAMERA: This payload uses CMOS technology and is capable of taking full colour pictures in the optical range at a ground resolution of about 100m per pixel, with an image size of 1280x1024 pixels.
CUBESATS: SSETI Express will carry three small nano-satellites, in separate launch pods, into orbit as passengers. These will be ejected early in the mission, and will then undergo their own, separate, missions.
Construction
You don’t just build a satellite: you start off deciding what to do, how to do it, where to do it, and what and who to do it with.
The project began in December 2003 and started construction in January 2004. Parts and modules came from university-based teams all over Europe. The integration and testing phase mainly ran from August 2004 to March 2005 although various issues still needed attention right up to the time when the spacecraft left the cleanroom late in June 2005 to travel to the launch site, Plesetsk, for the original August launch window.
The integration process was logged in a VERY LARGE (about 30-megabyte) document that is available on the SSETI website. This is a no-holds-barred record, including mistakes and lessons learned. Well worth a read if you have the inclination to peruse its 600 or so pages.
Launch & Early Operations
The launch is shared with four other customers; the prime contractor for the launch is Surrey Satellite Technology Ltd. (SSTL). The primary launch payloads are spacecraft completing the Disaster Monitoring Constellation (DMC), therefore the launch is denoted as “DMC-3”. The launch orbit is designed for the DMC, and is a sun-synchronous orbit with an inclination of 98º and a Local Time of the Ascending Node of 10:30h at an orbit height of 680km. Launch is from Plesetsk in Russia on 27th September 2005 at approximately 06:52 UTC with the next day as a back up.
Before 1
After 0
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Another passenger on the flight will be a beacon-only payload from AATiS left on the launcher. It is called Rubin/Safir-S and uses 2401.90MHz as a downlink with 9k6 AX25 telemetry and a recorded FM voice message: callsign DP1AIS. A transmission cycle consists of 15-second FM-voice beacon transmission and short data packets every 15 seconds for a total cycle of 2-3 minutes. See http://www.aatis.de for more information.
The preliminary pre-launch Keplers are below; these are only provisional and may be refined nearer to the launch date. Amendments will be published to the regular Amsat places.
Satellite: SSETICatalog number: 288XXUEpoch time: 5273.28641000Element set: 1 Inclination: 98.1900 degRA of node: 170.3700 degEccentricity: 0.0001920Arg of perigee: 0.0000 degMean anomaly: 50.5000 degMean motion: 14.60850000 rev/dayDecay rate: -1E-08 rev/day^2Epoch rev: 1
SSETI1 288XXU 0503XC 05273.28641000 -.00000001 00000-0 10000-4 0 152 288XX 98.1900 170.3700 0001920 0.0000 50.5000 14.60850000 00012
In case of another launch delay, and assuming that start time, LTAN (local time of ascending node) and flight schedule (time after start and location of separation) remains the same, the date and RAAN need to be altered. Increase RAAN by 0.9856 degrees per extra day (and adjust the checksums in both lines of TLE's). [See http://www.celestrak.com for a good description.] In case of any problems (a program might check for numbers) the X’s can be replaced by zeros without any other change.
SSETI Express will coast for 74 minutes after orbital injection (to ensure a good separation between SSETI Express and the other passengers) and will then automatically deploy payload 1, all three Cubesats. At the same time it will enter safe mode and transmit simple beacons. One minute later, when the computer boots up, it will enter nominal mode, transmit nominal data beacons and start to de-tumble; this should be completed within about two orbits. The final attitude should be with the 70cm monopole on the downward face when in the Northern Hemisphere.
As soon as possible after the command station in Aalborg has acquisition of the spacecraft they will start platform checkout; payload commissioning (to check the infrastructure) will follow this and then payload operations will commence. Payloads 2 and 3 are the propulsion and camera systems. Their website will include a webcam of the mission and ground control room during the pre and post launch operations phase at http://www.express.space.aau.dk
Cosmos
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The SSETI community are happy to receive all the help they can during this phase, and you are welcome to help with the initial acquisition of the spacecraft. If you receive any of the beacons from SSETI Express before they do then the main groundstation in Aalborg would be very happy to hear from you. Submit your data, from the SSETI Express Radio Amateur Communications Client, SERACC, (if the spacecraft is in nominal mode), and then contact them at [email protected] or telephone +45 2219 6094 (first two days after launch) or +31 648 561 261 (more than two days after launch).
Payload Operations
The purpose of this flight, after the educational aspects, is to demonstrate and characterise several of the sub-subsystems for future SSETI missions, the main one being the cold-gas attitude control propulsion system. There is also a camera for taking pictures of the Earth. Everything else, including the amateur radio payload, is secondary.
The Propulsion System (a nitrogen a cold-gas attitude control system) will be operated until the gas runs out. Two clusters of two thrusters each are used. Each thruster contains a solenoid valve and a conical nozzle. The thrust is expected to be of the order of a few tenths of a Newton.
The Camera System is based on a colour CMOS sensor and an instrument control unit. It needs in-orbit calibration to adjust the brightness. In addition, the camera contains a one-axis accelerometer for use by the ADCS. The camera payload is adapted from the AAUSAT-1 Pico-satellite mission.
The optical part of the camera consists of a specially manufactured lens and a colour CMOS chip with a resolution of 1280 by 1024 pixels. The chip is masked with a Bayer RGB colour pattern. The instrument control unit controls the optics. It supports full size images (approx 1.3 megabytes) and thumbnail image downloads in two smaller sizes.
The camera provides a resolution of 1280 by 1024 colour pixels with 24 Bits per pixel. The image is compressed in a proprietary format in the camera. The ground resolution in a 700km orbit is expected to be 100 x 100 meters per pixel.
Images can be downloaded in three quality levels:• Small Thumbnail: 160 by 128 pixels, 20kB• Large Thumbnail: 320 by 256 pixels, 80kB• Full Size: 1280 by 1024 pixels, 1.3MB
A Thruster 0
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NCube-2
Spacecraft Modes of Operation
SSETI Express has several modes of operation:
Safe mode: Only the PCU and UHF units are turned on while the solar panels charge the battery. Every 30 seconds a simple on/off carrier beacon is transmitted. Once the battery reaches 24.4V the spacecraft moves into recovery mode.
Recovery mode: The PCU attempts to power up the computer. The S-Band unit is turned on, and transponding and DTMF telemetry are possible (but disabled by default). Every 2 minutes the simple on/off beacon is transmitted on UHF. Once the computer has booted up successfully the spacecraft moves into nominal mode.
Nominal mode: The on-board computer is running and collecting housekeeping data. The S-Band unit is configurable in either data or voice mode and DTMF telemetry is possible. Every 18 seconds a packet beacon is transmitted on UHF, and the same is also transmitted every 36 seconds on S-Band if it is configured for data. Propulsion and camera operations are possible in this mode. The spacecraft will return to recovery mode if the PCU loses communication with the computer. The spacecraft will return to safe mode if the battery voltage ever drops below 22.4V.
Cubesats
Ncube-2 http://128.39.102.180/index.html The Norwegian student satellite, Ncube-2 [NCUBE], is an experimental spacecraft that was developed and built by students from four Norwegian universities. The project was initiated by the Norwegian Space Centre with support from Andöya Rocket Range, Norway. Data transmissions and digipeater use 1200 and 9600 bps.
The main mission of the satellite is to demonstrate ship traffic surveillance from a LEO satellite using the maritime Automatic Identification System (AIS) recently introduced by the International Maritime Organisation (IMO). The mission objectives for NCube-2 are:
Receive, store and retransmit at least one ship’s AIS message, Demonstrate reindeer herd monitoring from space by equipping a reindeer with an
AIS transponder during a limited experimental period, Maintain communications and digipeater operations using amateur frequencies, Demonstrate efficient attitude control using a combination of passive gravity
gradient stabilisation and active magnetic coils.
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The communication system of Ncube-2 is as follows: Direction Frequency EiRP Antenna [MHz] [W]Uplink (AIS) 161.975 MonopoleUplink 145.980 MonopoleDownlink 437.305 1,5W Monopole
The first transmissions will be 20 minutes after separation from SSETI Express. The message: "DE LA1CUB NCUBE2 FF LA1CUB" will be sent in morse at 26 words per minute using a 2400Hz tone; FF is a hex number indicating battery voltage [00 = 3.0V, FF = 4.5V]. If the battery voltage is above 3.8V, transmissions will be every 2 minutes; if the battery voltage is below 3.8V, transmissions will be every 5 minutes.
At the end of the message an unnumbered AX.25 packet is sent containing the string: DE LA1CUB NCUBE2 NORWEGIAN CUBESAT – WWW.NCUBE.NO . The AX.25 header will include Callsign: NCUBE, and Destination: EARTH. Reports can be sent to [email protected] or telephoned to +47 76 14 44 00
UWE-1 http://www7.informatik.uni-wuerzburg.de/cubesat The UWE-1 spacecraft is a registered Pico-satellite of Julius-Maximilians Universitaet Wuerzburg, Germany and stands for ”University Wuerzburg’s Experimental satellite 1”.
UWE-1 was designed and manufactured by students at the University of Wuerzburg, Department of Computer Science VII. Its research aim is to test IP based telecommunications protocols in space, in order to derive robust variants in the range between UDP and TCP. It will also be used for educational demonstration purposes.
The communication system of UWE-1 is as follows: (full details have not been published)
Direction Frequency EiRP Antenna [MHz] [W]Uplink 435Uplink 145Downlink 437.505 1.0 Monopole
First transmission will occur after the antenna is deployed, ~6 minutes after separation from SSETI Express. The communication protocol is AX25. The satellite will transmit for about 1 sec every 1 minute. The radio-amateur community can contact them at [email protected]
XI-V http://www.space.t.u-tokyo.ac.jp/gs/satinfo-e.html#xi5 The XI-V satellite is a Pico-satellite of the University of Tokyo, Intelligent Space Systems Laboratory (ISSL). It will be used for educational demonstration purposes.
UWE-
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The objectives of XI-V are: Test new solar cell technology Test and verify commercial-off-the-shelf (COTS) components Take pictures of the earth Transmit health information via a beacon
The communication system of XI-V is as follows: Direction Frequency EiRP Antenna Modulation [MHz] [W]Downlink (telemetry) 437.345 0.8 λ/2 dipole AFSK AX.25, 1200bpsDownlink (beacon) 437.465 0.08 λ/2 dipole CW
First transmissions will be made 30 minutes after separation from SSETI Express. Most transmissions will be CW repeated about every 30 seconds; this is always ON and its format can be seen at the website above. Packets will not be transmitted unless enabled by the command station. The XI-V team would appreciate reports on the signal and you can send received data via email to: [email protected] or upload via the http://www.space.t.u-tokyo.ac.jp/cubesat/upload/xi5report-e.aspx web page. General information is available from [email protected]
The Amateur Radio Payload
General
UHF S-BandFrequency 437.250 MHz (half-duplex) 2401.835 MHzAntennas Monopole whip 3 x patch antennas facing ±x and +zPower Approx 3W Approx, 0.7W ± x and 1.5W +zModulation FSK FSKProtocol Unnumbered AX25 Unnumbered AX25Baud rate 9600 bps 38400 bpsPolarisation Linear Right-hand circular
It is intended that, during the main mission, the 2.4GHz-downlink transmitter will be mainly used to transmit picture data at rate of 38k4. However, it will be switched over to single channel FM U/S voice transponder operation occasionally as part of the payload cycle, and then left in this configuration after the onboard experiments have been completed. This frequency usage will enable the many amateurs who already have Oscar 40 equipment to use it in an exciting new way.
For the SSETI Express project, ESA and SSETI are very keen to have as many amateurs contributing received downlinked telemetry on 437MHz and 2.4GHz to a central database. They recognise that our worldwide network is a unique facility that is not otherwise available to them.
XI-V
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A new website giving full details of the telemetry, how to decode it and how to forward it to the SSETI database can be found at http://www.sseti.org/express complete with several free custom-designed software applications for this purpose.
Anyone with the appropriate equipment is welcome to download data from SSETI Express on both the UHF and S-Band channels. The telemetry format is made transparent for your own analysis, and you can also submit it. Software for data collection and basic decoding is provided on the SSETI Express mission website.
At appropriate times in the mission, “friendly telecommands” will be activated on the spacecraft computer so that suitably equipped amateurs may use the UHF uplink to request telemetry downloads on the UHF system or, alternatively, downlinks on the S-Band channel of pictures taken with the on-board camera. Such telemetry downloads may include housekeeping data, alarm data and payload data from the propulsion system. Software for sending commands and for data collection is provided on the SSETI website http://www.sseti.org/express
At certain times in the mission the S-Band unit will be configured to emit bursts of telemetry encoded in DTMF tones. Software to decode this telemetry is provided on the SSETI website.
The Status Schedule on the Radio Amateur Connection page of the SSETI Express website shows which functions are available at which times. This should be used as a regular reference for all participating radio amateurs.
Later on in the mission (and maybe, occasionally, earlier) the single-channel U/S audio transponder will be activated and will be freely available to all suitably equipped amateurs. However, this will only be possible with the spacecraft properly controlled from Aalborg, so please DO NOT transmit to SSETI Express if you can see it is being used by the SSETI team during the passes over the main control station.
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Hardware
The 2.4GHz downlink exciter, switched mode power supply, and control interfaces were developed by an AMSAT-UK team comprising of Sam Jewell, G4DDK, David Bowman, G0MRF, Jason Flynn, G7OCD, and Howard Long, G6LVB, with Graham Shirville, G3VZV, assisting.
The 3 watt 2.4GHz power amplifier was provided by Charles Suckling, G3WDG; this unit is already space qualified as it is identical to the one flying in the recently launched Oscar 51 spacecraft. Tests performed on the flight model transmitter indicate that the total power output on 2401.835 MHz should be just under the intended 3 watts.
All the other modules were built using, as far as possible, COTS components that are suitable for the space environment.
The three S band patch antennas being used on SSETI Express have been developed by the SSETI team based at Wroclaw University in Poland. The patches are manufactured from specialist microwave laminates capable of withstanding the cold and vacuum of space and the heat from the sun. The reverse sides of the patches have metal backplates to prevent radiation into the spacecraft.
The S Band RF output is applied to a 3-way splitter that divides it into one output of 1500mW (-3dB) and two outputs of 750mW (-6dB); each output feeds a patch antenna.
Each patch has a nominal gain of 7.8dBic and a beamwidth of about 70°. The main antenna is mounted on the +Z facet of the satellite and receives power from the –3dB output from the splitter in the S Band unit. The passive magnetic stabilisation means that this antenna is earth facing over the Northern Hemisphere.
To supplement the signal from the main S Band antenna, there are two identical patches mounted on the +X and –X facets. These antennas use the two 750mW (or -6dB) outputs from the power splitter. The signals radiated from these antennas will ensure usable signals when the satellite is seen at lower elevation angles (below 30°) and will provide the main output for groundstations located in the Southern Hemisphere. Overall, the design of the antenna system should minimise spin fading of the 2401.835MHz
S-band RF deck with 3- way power splitter
An S-Band Patch Antenna
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output, allowing uninterrupted reception of the 38k4 data and U/S transponder signals.
Similar antennas are presently under construction by the same team for eventual incorporation onto the outer micrometeorite protection panels of the Columbus module on the International Space Station. This module which is being constructed for ESA is expected to be delivered to the ISS towards the end of 2007 and it is anticipated that it will operate on 1.3GHz and 2.3GHz and possibly on 435MHz.
Holger Eckardt, DF2FQ, generously provided the single-channel UHF transceiver system for SSETI Express. It is a single channel 3W transceiver on 437.250 MHz. Provisionally the bandwidth is 15kHz and the receiver sensitivity is 0.28µV on packet and 0.20µV for 20dB SINAD on voice. The antenna is a simple inclined quarter-wave monopole antenna derived from an ESA Meteosat antenna. The transceiver module also contains a 9600bps FSK modulator and a G3RUH-compatible TNC that will use standard un-numbered AX25 encoding. A UHF FM voice uplink will be downlinked on S band when the transponder mode is operational. In the picture, the radio is in the right compartment, the audio interface and power supply in the middle, and the TNC is on the left.
Payload Modes of Operation
Friendly TC S Carrier S Mode DTMF TM PictureOFF
Amateurs may not request additional downloads
AS REQThe carrier comes up only when
needed
DATAData may be
transmitted by the unit
OFF The spacecraft
will not transmit DTMF
telemetry
THUMB1/2A small/large thumbnail is
ready for download
ONAmateurs may
request additional downloads
ONThe carrier is up constantly
VOICEAmateurs may
use the transponder
ONThe spacecraft will transmit
DTMF telemetry every
2 minutes
FULLA full picture is ready for download
Whenever there is radio amateur functionality activated on the spacecraft (such as friendly telecommands, DTMF telemetry, and voice transponding), you are free to use it in whatever way interests you. The scheduled periods of voice transponding and friendly telecommands will gradually increase during the mission as the other
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objectives are achieved, and will be available right until the end-of-life of the spacecraft.
Users must refrain from sending requests to the spacecraft when friendly telecommands are not enabled. Such requests will not be successful, and will only serve to waste on-board power and interfere with commands from the main control station. If users receive an “Encryption Failure” message from the spacecraft, then the request was denied and should not be repeated until the next permissible pass.
The S-Band transmitter is required to operate in two different configurations. Both configurations will be able to be activated with either the carrier transmitting continuously or only on demand. This will be controlled from the ground and will depend upon the state of the battery charge, thermal considerations, and power budget after launch.
Data configurationIn this state the transmitter will downlink telemetry and other data collected from the on board experiments. This data will vary depending on the current operating mode of the satellite itself. Callsign is SSETI1.
Voice configurationIn this state the transmitter will act as a voice transponder for radio amateurs. The transponder will operate on NBFM and will relay the uplink audio received by the UHF transceiver. In this configuration it will be possible for mission control to select telemetry data bursts every two minutes (which will over-ride transponded audio). This telemetry will indicate output power, amplifier temperature and uplink signal strength. Software to decode this telemetry is available on the SSETI website.
The Amsat-UK Team:G0MRF G3VZV G4DDK G7OCD G6LVB
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Beacons
There are four different beacon signals that may be transmitted by the spacecraft:
Safe Mode Beacon:A digital signal sent periodically containing information about the battery voltage. This is repeated every 30 seconds. It toggles the PTT line to on/off key the carrier and give information about the EPS (Electrical Power System) and the spacecraft mode. See the Telemetry section for more information.
Recovery Mode Beacon:This is the same signal as the safe mode beacon but repeated at a lower repetition rate. This is repeated every 120 seconds. It carries the same information as the safe-mode beacon. See the Telemetry section for more information.
Nominal Mode Beacon:An AX25 packet radio signal that contains housekeeping telemetry. This is repeated every 18 seconds. It carries housekeeping telemetry. Software to decode this beacon, and any other AX25 data from the spacecraft, is provided on the SSETI website http://www.sseti.org/express
DTMF beacon:When configured for “voice” the S-Band unit may also be set up to transmit encoded bursts of DTMF tones to give telemetry about the unit. Software to decode this beacon, written by Howard Long G6LVB, is also provided on the SSETI website.
Voice Operating
At appropriate times in the mission the single-channel U/S transponder will be activated and will be freely available to all suitably equipped Amateurs. A CTCSS tone of 67 Hz is required on the uplink. The uplink receiver has no AFC so adjustment for uplink Doppler shift may be prudent (but as the receiver is designed for 9600bps it probably has a fairly wide filter so for FM voice it might not need too much Doppler correction on the ground).
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While transponded audio requires an access tone to open the squelch, the transponder will transmit a 5-second unsquelched tail so that any uplink QRM can be observed.
The footprint from the predicted altitude (680km) is about 2800km making QSOs just possible between Western Europe and the Eastern seaboard of the USA, or fully transcontinental QSOs possible throughout the USA.
Telemetry and Commanding
Telemetry is stored on-board and dumped to the command stations during their communication windows; all telemetry processing and exploitation is then performed on the ground.
On/Off Beacon
When the spacecraft is in safe mode or recovery mode it will transmit a simple cw pulse beacon by toggling the push-to-talk on the UHF radio (with no modulating tone). The pulses are each 100ms long and the complete beacon represents 16 “bits”, where the values are “1” when the carrier is on and “0” when the carrier is off.
Bit 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Value 1 1 0 X X X X X X X X X X X X YItem Start Battery voltage Mode
Start: The beacon always starts with the carrier UP, UP, DOWN, to mark the beginning of the cycle.
Battery voltage: The next 12 bits are a binary number, X, with the most significant digit first and the least significant last, representing the measured voltage of the battery. This number can be converted to the battery voltage as follows:Battery voltage = X * 0.006053
Mode status: The last bit, Y, is simply “0” when the spacecraft is in Safe Mode, and “1” when the spacecraft is in Recovery Mode.
Or use the Pulse Beacon Decoder available on the SSETI Express website.
Nominal Beacon: To receive and decode this beacon you need the SSETI Express Radio Amateur Communications Client (SERACC), which can be downloaded from the SSETI Express website.
Screen-Grab from SERACC
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When the spacecraft is in nominal mode it will transmit a single-packet beacon on 70cm every 18 seconds. Packet header will be SSETI1>UI followed by data and below is a typical data field as seen in SERACC:
Callsign: SSETI1Header: www.sseti.net * SSETI-ExpressSubsystem: BEACONOn-board time: 2005-06-24 18:31:45EPS battery voltage: 23.61 VOBC temperature: 22.4 °COBC boot attempts: 42ACDS magnetometer: [-1599 275 7903] nTACDS field rate: [-9 1 51] nT/s
DTMF telemetry: At appropriate times in the mission the S-Band unit will be configured to emit bursts of telemetry encoded in DTMF tones. DTMFFFT decoding software is provided at the SSETI Express website http://www.sseti.org/express
When the voice transponder is enabled the DTMF telemetry may also be turned on. This will emit a burst of DTMF tones every two minutes that can be decoded to obtain information about the status of the S-band unit. The tones will probably override any transponded audio. Each DTMF tone pair represents a telemetry parameter and the burst carries just three sequential parameters. Pair 1 is
the PA Temperature, pair 2 is the PA power at the -3dB port, and pair 3 represents the receiver signal strength indicator (RSSI).
There is a readme.txt file available at: http://www.g6lvb.com/Articles/SSETI%20Express%20DTMF%20Telemetry/images/readme.txt
Downloading
Get the SSETI Express Radio Amateur Communications Client (SERACC). This application and its associated manual are free to download from http://www.sseti.org/express - it has the following features:
Allows anyone with suitable equipment to decode the nominal mode beacon from SSETI Express and collect telemetry and payload data.
Allows radio amateurs to send “friendly” telecommands to SSETI Express to request particular downlink data.
Screen Grab from DTMFFFT 0
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Saves downlinked SSETI Express camera data to a local RAW file format viewable in many graphics packages (such as the freeware IrfanView at http://www.irfanview.com )
Enables hole filling in downlinked picture data from SSETI Express. Allows logging of all up- and downlinking. Allows submission of collected telemetry to the
SSETI Express Telemetry Database, therefore allowing entry in the “Data Collection” competition.
Runs on a standard Windows PC, connecting to a KISS TNC over any standard COMM port at any standard baud rate.
The SSETI Express Pulse Beacon Decoder to decode the SSETI Express Pulse Beacon can be downloaded from http://www.sseti.org/express
The SSETI Express DTMF Decoder can be downloaded from www.sseti.org/express
Photographs taken using the on-board camera can be downlinked by radio amateurs either during passive downlink sessions scheduled in the news at the top of the Radio Amateur Connection web page, or by specific request using the SERACC software whenever friendly telecommands are enabled.
This functionality has four states. "THUMB 1" denotes that there is a small thumbnail on-board ready for downlink. "THUMB 2" denotes that there is a large thumbnail on-board ready for downlink. "FULL" denotes that there is a full picture on-board ready for downlink. Finally, "NONE" denotes that no picture is currently available. Please note that the SERACC software includes storage and re-request routines allowing multi-pass downlinks and error-control, as well as real-time colour previews of the images during downlink.
This feature will be available shortly after the project team has commissioned the camera.
“Friendly” Commanding
At suitable times in the mission, “friendly telecommands” will be activated on the spacecraft computer so that appropriately equipped radio amateurs may use the UHF uplink to request telemetry downlinks on the UHF, or picture downlinks on the S-Band channel. Such downlinks may include housekeeping data, alarm data and payload data from the propulsion system. Software for sending commands and for data collection is provided in the SSETI Express Radio Amateur Communications Client (see above) which allows radio amateurs to send “friendly telecommands” to SSETI Express to request particular downlinks. The SERACC software uses a simple and user-friendly graphical interface to cover all the options available to you.
The UK from space
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How you can help SSETI Express
Prizes:
Data Collection: The Education Office of ESA, the European Space Agency, have announced the prize that will be offered to the amateur radio community for downloading telemetry from the SSETI Express satellite. The prize will be given to the amateur who submits the largest amount of valid telemetry and payload data packets regardless of which band they are received on.
Radio amateurs around the world are encouraged to download the necessary software from the www.sset.net/express website (after approximately 12th September) and to use the SERACC system to forward the telemetry to SSETI Express Mission Control. Your submissions will be automatically recorded and a leader-board will be shown on the website.
The winner will be offered the opportunity to visit the STEC06 Conference and Exhibition in Germany in spring 2006. STEC, the Student Technology Education Conference, follows previous events in 2004 in Lausanne in Switzerland and in April 2005 in Aalborg in Denmark.
The three-day event is similar to the AMSAT-NA Symposium and the AMSAT-UK Colloquium but with more breakout technical sessions in addition to the Keynote Speeches. The meetings are always interesting and thought provoking and great enthusiasm and passion is shown by all attendees. The post-meeting attitude adjustment sessions have also proven to be exciting. The winner will also be encouraged to present a paper on how he/she achieved their success - but this is not mandatory!
In addition to attending the STEC 06 Conference, the winner will be invited to visit ESA's Mission Operations Centre - ESOC - near Darmstadt in Germany where they will be given a private escorted tour of the facilities. ESOC currently controls the many exciting orbital and deep space ESA missions. For more information check http://www.stec2005.space.aau.dk/ to see what this year's event included, and check http://www.esa.int/SPECIALS/ESOC/ for details of the ESOC facility.
The winner will be the amateur at the top of the leader-board at 00:00 on Jan 1st 2006. The prize will include economy class worldwide travel from your home location, accommodation during the trip, and a “small” daily subsistence allowance.
AMSAT-UK wishes to congratulate and thank ESA for their generous prize, a first in the field, and is confident that it will add to the great enthusiasm for the SSETI Express project which already exists within the amateur radio community. It will be a great opportunity for us to demonstrate that the amateur radio groundstation “network” is a valuable resource for satellite projects which are able include useful amateur radio payloads.
European Space Operations Centre, Darmstadt(Image copyright © ESA)
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Other generous prizes are:
“I heard it first”: A truly unique “I heard it first” SSETI Express T-shirt will be awarded to the first person to receive and decode a transmission from the spacecraft.
Runners-up: Various runners up prizes of SSETI Express mission patches and mission DVD’s will be awarded to leading individuals in the above two categories.
Please check http://www.sseti.org/express for updated details of these competitions.
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Data Formats
The on-board time format is 32-bit unsigned standard Unix epoch time (since 1970-01-01 01:00:00) at a resolution of 1 second. The real time clock will be synchronised on each contact with the main ground station.
AX.25 Telemetry format: ____________________________________/______/______/______/_______/______/|| sid | mid | len | data | time || -> 7-71 bytes|__8___|__8___|__8___|_0-512_|__32__/
sid (8 bit): System IDmid (8 bit): Measurement IDlen (8 bit): Length of data in _bytes_data (nn bit): Up to 64 bytes of telemetry datatime (32 bit): Time of sampling
Subsystem identifiers (sid):hex - binary subsystem0x00 - 00000000 OBC0x02 - 00000010 EPS0x04 - 00000100 UHF0x06 - 00000110 MAGIC0x08 - 00001000 CAM0x0a - 00001010 ADCS0x0c - 00001100 S-BAND0x0f - 00001111 TEST/DEBUG0x1A - 00011010 A/D-CONV0x3A - 00111010 TCS0x2a - 101010 BEACON
OBC TM - telemetry (mid codes):Mnemonic Mid Code Data Description
OBC_TIME_SYNCED 0xff (4)Time diff Replies to TIME_SYNC w/ time diffOBC_FP_FLUSHED 0xfe (4)TCs left FP queue flushedOBC_HK_FLUSHED 0xfd (4)HKs left HK queue flushedOBC_AL_FLUSHED 0xfc (4)ALs left AL queue flushedOBC_PIC_FLUSHED 0xfb - PICTURE flushedOBC_THUMB1_FLUSHED 0xfa - SMALL THUMB flushedOBC_STACK_END 0xf9 - OBC_GET_"queue" end reached OBC_TC_ACK 0xf8 (1)TC-seq, (4)TC-time Ack: TC received with seq and timeOBC_TC_NACK 0xf7 (1)TC-seq, (4)TC-time NOT Ack: TC, DENIEDOBC_THUMB2_FLUSHED 0xf6 - LARGE THUMB flushedOBC_PICTURE 0xf5 (64)data Picture data (!)OBC_THUMB1 0xf4 (6'4)data Small thumbnail data (!)OBC_THUMB2 0xf3 (64)data Large thumbnail data (!)OBC_ACCEL 0xf2 (64)data Accelerometer data (%)OBC_ACCEL_FLUSHED 0xf1 - Accel. data flushedOBC_TEMP 0x7bOBC_MEM_INFO 0xf0 (44)data malinfo structOBC_FLASH_CHECK 0xef (4)true, false Flash integrity check resultOBC_OBC_UPTIME 0xee (4)time Number of seconds since last bootOBC_TC_CRYPT_ERROR 0x40 (9)tc Wrong crypt returns telecommand OBC_FILELIST 0x50 (9)fat entry Entry from onboard file table
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DTMF Format
Each sequential tone pair represents a number from 0 to 255, that in turn can be converted into the actual values using a straight line approximation, i.e. y=mx+c. The DTMFFFT software requires the 'm' and ‘c’ straight line parameters to be keyed in prior to use. The current values for the DTMFFFT software are:
Parameter 1Name: (S Band) PA tempOffset: 72.73292Multiplier: -0.31056Units: deg C
Parameter 2Name: PA power (at –3dB port)Offset: -0.690Multiplier: 0.02753Units: W
Parameter 3Name: RSSI (UHF uplink)Offset: -143.667Multiplier: 0.392157Units: dBm
Parameters 4 and 5 are not used.
Initial calibration tests provided the following parameters for SSETI Express:
Parameter 1: PA temp; Offset = 72.73292; Multiplier = -0.31056; Units = deg C
Parameter 2: PA power; Offset = -0.690; Multiplier = 0.02753; Units = W
Parameter 3: RSSI; Offset = -143.667; Multiplier = 0.392157; Units = dBm
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Amsat-UK
Prospective new members can find out quite a lot about Amsat-UK by visiting our web site at http://www.uk.amsat.org where they can find out about the aims of the organisation, check on the committee and Oscar News, and download a membership form.
AMSAT-UK, "Badgers", Letton Close, Blandford, Dorset DT11 7SSPhone: (+44) (0)1258 453959; Fax (+44) (0)1258 453959
E-mail: Jim Heck, G3WGM, [email protected]
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