{"id":3965,"date":"2021-07-22T19:50:53","date_gmt":"2021-07-22T19:50:53","guid":{"rendered":"https:\/\/www.s5lab.space\/?page_id=3965"},"modified":"2021-10-19T14:00:27","modified_gmt":"2021-10-19T14:00:27","slug":"decoding-ledsat","status":"publish","type":"page","link":"https:\/\/www.s5lab.space\/index.php\/decoding-ledsat\/","title":{"rendered":"Decoding LEDSAT"},"content":{"rendered":"

[et_pb_section fb_built=”1″ admin_label=”About Section” _builder_version=”4.9.0″ background_color=”#000000″ custom_padding=”0px||0px|”][et_pb_row _builder_version=”4.9.0″ _module_preset=”default” background_color=”#000000″ width=”100%”][et_pb_column type=”4_4″ _builder_version=”4.9.0″ _module_preset=”default”][et_pb_menu menu_id=”22″ menu_style=”centered” _builder_version=”4.9.4″ _module_preset=”default” menu_font=”Lato|700|||||||” menu_font_size=”22px” menu_letter_spacing=”1px” background_color=”#000000″ background_layout=”dark” menu_text_shadow_style=”preset1″][\/et_pb_menu][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”1_4,1_2,1_4″ use_custom_gutter=”on” gutter_width=”1″ make_equal=”on” admin_label=”About Area” module_class=” et_pb_row_fullwidth” _builder_version=”3.25″ background_color=”#999999″ width=”100%” width_tablet=”100%” width_phone=”” width_last_edited=”on|desktop” max_width=”100%” max_width_tablet=”100%” max_width_phone=”” max_width_last_edited=”on|desktop” custom_padding=”0px||0px|” make_fullwidth=”on”][et_pb_column type=”1_4″ module_id=”col1″ _builder_version=”3.25″ background_color=”#1e1d1c” custom_padding=”0%|0%|10%|0%” custom_css_main_element=”background: rgb(22,22,22);” custom_padding__hover=”|||”][et_pb_text admin_label=”LEDSAT Info” _builder_version=”4.9.4″ _module_preset=”default” global_module=”3992″ saved_tabs=”all”]<\/p>\n

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Participating in the European Space Agency Fly Your Satellite! Programme<\/span><\/strong><\/span><\/p>\n

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Latest Data<\/a><\/span><\/p>\n

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Decoding LEDSAT<\/h2>\n

LEDSAT transmits in UHF at frequency 435.190 MHz using GMSK modulation at 1200, 4800 or 9600 baud. At deployment, the baud rate will be 1200 but it will be upgraded to 9600 during the first operations. Any tool used for receiving 1KUNS-PF can be used to receive LEDSAT as well, since they use the same transceiver – the AX100 from GomSpace. This transceiver is common among CubeSats and several tools exist to receive and interpret the packets.<\/p>\n

Data Link Layer
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The data link layer uses an Attached Sync Marker (ASM) to determine the beginning of a packet. The marker is C9D08A7B (MSB).
\nThe next field after the ASM is the Golay-encoded length. This is a 3-byte length field with FEC provided by the Golay 24,12 code.
\nThe rest of the packet is scrambled with the typical G3RUH scrambler.<\/p>\n

Network Link Layer<\/h3>\n

The packet uses the Cubesat Space Protocol<\/a> (CSP). The header contains information on the source and destination of the packet; the end of the packet is composed of a CRC32, which provides a checksum of the data, and a Reed Solomon (223, 255) field.<\/p>\n

Tools to receive the satellite<\/h3>\n

GNURadio<\/h4>\n

The satellite can be received using a Software Defined Radio (SDR) and GNURadio. To aid in this, one can use the Out-Of-Tree module gr-satellites<\/a> developed by Daniel Estevez.
\nSeveral branches are made to support the different GNURadio versions. An example script that can receive the satellite with an SDR is shown here.<\/p>\n

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The team is working on an ad-hoc block to interpret the telemetry and the pictures, based on the one developed for 1KUNS-PF.<\/p>\n

UZ7HO SoundModem<\/h4>\n

SoundModem<\/a> is a popular tool to receive Packet Radio, developed by UZ7HO. A version of SoundModem, made to receive 1KUNS-PF, can also be used to receive LEDSAT.
\nThis version can be found in the other_versions.zip <\/em>file on the webpage of UZ7HO<\/p>\n

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Formats<\/h3>\n

Telemetry<\/h4>\n

The telemetry is sent either via a Beacon, which is sent periodically every 15 or 60 seconds, or by request from the ground station. The request can be of either the current status of the satelite, or of past telemetry.
\nThe telemetry packets are identified by CSP Destination Port 8 and have length of 140 bytes (data only, no CRC).<\/p>\n

Detailed information on the telemetry can be found in this spreadsheet<\/a>..
\nIn particular, each telemetry begins with two bytes indicating its ID, either 0x162A, 0x1629 or 0x1628. Any future update to the telemetry structure will alter this ID, making each telemetry format uniquely identified.<\/p>\n

The spreadsheet also contains a simple telemetry decoder with some examples.<\/p>\n

Pictures<\/h4>\n

The pictures are identified by CSP destination port 11 and have length of 130 bytes (data only).
\nThe pictures are encoded in JPEG and separated in multiple packets; the first two bytes of the data indicate the packet number.
\nThe receiver must assembled the picture using the correct order. Each image starts with FFD8 and ends with FFD9, as per the JPEG standard.<\/p>\n\n\n\n\n
Unsigned short (2 bytes)<\/td>\nUnsigned bytes (128 bytes)<\/td>\n<\/tr>\n
Packet number<\/td>\nJPEG Image Data<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Example image packets:<\/p>\n

First packet:
\n00 00 FF D8 FF FE 00 24 67 03 42 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 78 00 A0 00 1A 00 32 12 0B 51 04 51 04 00 00 FF DB 00 84 00 07 04 05 06 05 04 07 06 05 06 07 07 07 08 0A 10 0B 0A 09 09 0A 14 0E 0F 0C 10 18 15 19 18 17 15 17 16 1A 1D 25 20 1A 1C 23 1C 16 17 21 2C 21 23 27 28 2A 2A 2A 19 1F 2E 31 2E 29 31 25 29 2A 28 01 07 07 07 0A 09 0A 13 0B 0B 13 28 1B 17 1B 28 28 28 28<\/p>\n

Fourth packet:
\n00 03 F5 F6 F7 F8 F9 FA FF C4 00 1F 01 00 03 01 01 01 01 01 01 01 01 01 00 00 00 00 00 00 01 02 03 04 05 06 07 08 09 0A 0B FF C4 00 B5 11 00 02 01 02 04 04 03 04 07 05 04 04 00 01 02 77 00 01 02 03 11 04 05 21 31 06 12 41 51 07 61 71 13 22 32 81 08 14 42 91 A1 B1 C1 09 23 33 52 F0 15 62 72 D1 0A 16 24 34 E1 25 F1 17 18 19 1A 26 27 28 29 2A 35 36 37 38 39 3A 43 44 45 46 47 48 49 4A 53 54<\/p>\n

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Supported by:<\/h1>\n

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Participating Universities:<\/h1>\n

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Technical Supporters:<\/h1>\n

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