Amateur Mission

In the ARICA-2 Amateur Mission, we aim to provide amateur radio operators around the world with the opportunity to communicate with ARICA-2 (callsign: JS1YSD).
Various operations will be conducted to support this goal.

During the mission, the following activities will be available:

Message exchange via ARICA-2
Downlink of image data captured by the satellite

These operation modes will be conducted periodically, with specific operation periods designated for each mode.
Details such as operation schedules and timeframes will be announced as they become available.

(Links to the operation schedule and related announcements on the official website and social media are currently being prepared.)

For details about each operation mode during the Amateur Mission, please refer to the sections below.

１．Message exchange via ARICA-2

Message Upload and Download

ARICA-2 provides 20 message slots, each capable of storing up to 7 bytes of data for 48 hours.

In addition to uploading and downloading messages, a dedicated command is available to downlink information about which station’s message is stored in each slot.

Message Echo

ARICA-2 can also echo back (downlink) a message exactly as it was uploaded.

This function is available even when all message slots are occupied.

２．Downlink of image data captured by the satellite

ARICA-2 captures images of the Earth using its onboard infrared sensors, optical sensors, and machine learning–based image processing.
The image data are downlinked using GMSK modulation and are divided into packets of 100 bytes each.

By specifying the packet ID via uplink, you can request the corresponding packet data to be downlinked.
Received data can be submitted through the ARICA-2 website, where the reconstructed image will be gradually updated as new data are uploaded by participants.

Through this collaborative effort, we aim to rebuild the images captured by the satellite using data collected from amateur operators around the world.

Communication Method

In the Amateur Mission, communication with ARICA-2 can be carried out using the settings shown below.

The uplink uses a satellite-specific format. For details, please refer to the section below titled “Uplink Format.”

Please uplink the data formatted according to the specification below via a TNC in KISS mode.

Uplink Format

Uplink to ARICA-2 shall be performed in the following format:

0x42 (ASCII: 'B') + satellite-specific frame + AX.25 FCS

The total uplink data length shall be fixed at 21 bytes.

in the amateur mission, the header and call sign fields are common across all operations.
The green-shaded section of the uplink frame corresponds to the "Message Exchange via ARICA-2" operation mode, while the pink-shaded section is used in the "Image Downlink" operation mode.

Each mode will be conducted in different operational periods, and both modes will not operate simultaneously.
For any unused bits within the 21-byte uplink command, fill the remaining bits arbitrarily according to the bit length of each command.

Example:
During the Message Exchange via ARICA-2 mode, since “Packet ID for downlink” is not used, this field should be set to "0000000000" in the uplink data.

Header

The gray area in the diagram represents the header of the uplink command, which determines how ARICA-2 interprets the received uplink data.

During the amateur mission, please configure the header exactly as shown in the diagram when transmitting uplink commands.

Mode

Specify the operation mode.
Set "0101" when operating in the Message Relay via ARICA-2 mode, and set "0110" when operating in the Image Downlink mode.

Call Sign

The call sign field can contain up to 6 ASCII characters (6 bytes).
SSID shall not be appended in the uplink data.

Type Field

The type field specifies the command type during the Message Exchange via ARICA-2 mode.

type = "00"

Message Download — Requests ARICA-2 to downlink the message stored in the specified message ID. If no message is stored under the specified ID, or if the ID is invalid, ARICA-2 will downlink a notification message.

type = "01"

Message Upload — Requests ARICA-2 to store a message sent from the ground station. If an available slot exists and no message from the same call sign is stored, the message will be saved for 48 hours. After 48 hours, the stored message is automatically deleted. Each call sign may use one slot. If a new upload is received from the same call sign before expiration, the old message will be overwritten without resetting the storage timer. ARICA-2 will downlink the slot ID and message contents if storage is successful, or an error message if it fails.

If 0x00 is inserted in the middle of a message, any data following it will not be stored.

For example, even if 0x41 0x41 0x41 0x00 0x42 0x42 is uploaded, only 0x41 0x41 0x41 will be stored.

type = "10"

Stored Message Information Inquiry — Requests ARICA-2 to downlink information about stored messages, including which slots (IDs) are occupied and by which call signs. Empty slots will not be reported. If the total size exceeds 100 bytes, the data will be split into multiple downlink packets. Each slot’s information occupies 10 bytes, and each packet consists of address + PID (16 bytes) plus message info, resulting in 26 bytes (1 slot) to 86 bytes (7 slots) per packet.

If 1–7 slots are occupied → 1 downlink packet

If 8–14 slots are occupied → 2 downlink packets

If 15–20 slots are occupied → 3 downlink packets

If no messages are stored → ARICA-2 downlinks "ARICA-2 has no message..."

type = "11"

Echo Message — Requests ARICA-2 to immediately downlink the same message as received (echo test). This command does not access message storage slots, allowing message-based communication even when all slots are occupied.

If 0x00 is inserted in the middle of a message, any data following it cannot be received.

For example, even if 0x41 0x41 0x41 0x00 0x42 0x42 is uploaded, only 0x41 0x41 0x41 will be received, and 0x41 0x41 0x41 will be returned.

Message ID for Downlink

Used only when type = "00" to specify which stored message should be downlinked.
For other types, fill this field with arbitrary bits.

Upload Message

Used when type = "01" (message upload) or type = "11" (echo message).
Message length must be fixed to 7 bytes.
Unused bytes or bits must be filled with zeros.

Packet ID for Downlink

This command is used for the Image Downlink operation. You can specify the packet IDs to be downlinked in binary format. "0000000" corresponds to packet IDs 1 to 25, and "0001100" corresponds to packet IDs 301 to 325.

Not Used

Bits marked as not used are reserved and may be filled with arbitrary values.

Uplink Command Examples

When transmitting commands, send the hexadecimal data below through a TNC in KISS mode.
Values in parentheses represent FCS (Frame Check Sequence).

Example :

・Upload "AAA" (ASCII: 41 41 41 00 00 00 00) from JS1YSE during Message Exchange via ARICA-2

42 F8 BD 40 00 4A 53 31 59 53 45 41 41 41 00 00 00 00 00 (9D 44)

・Request message download (ID = 5) from JS1YSE

42 F8 BD 42 80 4A 53 31 59 53 45 00 00 00 00 00 00 00 00 (BE D5)

・Request image downlink (Packet ID = 1 ~ 25) from JS1YSE during Image Downlink operation

42 F8 BD 40 80 4A 53 31 59 53 45 00 00 00 00 00 00 00 00 (8F C1)

Uplink Data Generation

Uplink data can be generated by specifying information according to the format below.
[Currently under preparation]

Downlink Format

Message Exchange via ARICA-2

The downlink format complies with the AX.25 protocol.

In the downlink frame, the address field is left-shifted by one bit.
The entire data stream is NRZI-encoded, with bit stuffing (zero insertion), flag bytes (0x7E), and scrambling applied by the UHF transceiver onboard ARICA-2 before being downlinked.

Example:
When the Aoyama Gakuin ground station (callsign: JS1YSE) uploads a message "AAA" to be stored,
and the uplink succeeds, the following data will be downlinked from ARICA-2(as seen after demodulation in KISS format):

・If storage is successful (downlink message : saved 'AAA' at box: 1)

C0 00 94 A6 62 B2 A6 8A 60 94 A6 62 B2 A6 88 E1 03 F0 73 61 76 65 64 20 27 41 41 41 27 20 61 74 20 62 6F 78 78 3A 20 31 C0

・If storage fails (downlink message : message_box is full now)

C0 00 94 A6 62 B2 A6 8A 60 94 A6 62 B2 A6 88 E1 03 F0 6D 65 73 73 61 67 65 5F 62 6F 78 20 69 73 20 66 75 6C 6C 20 6E 6F 77 C0

Image Downlink

The specified packet data are downlinked in the following custom format,
followed by the AX.25 FCS.

By submitting the binary data as displayed in KISS mode,
the image on the ARICA-2 website will be progressively updated.
(The submission page and the details for header are currently under preparation.)

・Command ID

This field shows the command ID of the most recent command sent by the ARICA-2 team.

During camera operations, the command IDs that are downlinked will be published as they become available.

・Packet ID

This field indicates the packet number to be downlinked.

Camera image data are divided into packets of 97 bytes each and downlinked with packet IDs numbered from 1 to 325.

If you have any questions, please feel free to contact us.

E-mail : arica2-ama(at)phys.aoyama.ac.jp

(change (at) to @)

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