Communication specification

Technical specification

Hardware

KRAKsat is equipped with two hardware redundant UHF transceivers - parts of SR-NANO-BUS platform.

Frequency

KRAKsat was assigned coordinated frequency for up- and downlink 435.500 MHz with emission designator 25K0D1D and EIRP 32 dBm. Downlink modulation is AFSK 1200bps and uplink is 2GFSK 9600bps. Satellite callsign is SR9KRA.

Downlink

KRAKsat downlink communication can be one of three types:

  • beacon - emitted every 15 minutes

  • commands responses - specific to uplink type

  • payload logs transmission - on request, encoded in Base91

SR-NANO-BUS downlink can be distinguished by their frames format. Data transceived by UHF1 is decoded as APRS message (with a hardcoded callsign), while data from UHF2 contains frame in APRS telemetry format (without a callsign).

Beacon

Beacon is emitted every 15 minutes by SR-NANO-BUS platform OBC. It consists of 8 frames, sent one by one from both radios. Beacon frames are ASCII strings, terminated by \0, containing information about the status of crucial components.

Beacon frame

Frame name

Frame value

1

Satellite status

M1;STS;[User Flags (32-bit value)]

2

Master status

M1;LOG;[Timestamp];[Boot nr];[CPU voltage];[CPU temperature]

3

UHF1 Status

U1;RL;[Timestamp],[CPU voltage];[Battery voltage];[CPU temperature];[Amplifier temperature]

4

UHF1 Modem Status

U1;MS;[Timestamp];[Current RSSI];[Latch RSSI];[Afc frequency offset]

5

UHF2 Status

U2;RL;[Timestamp],[CPU voltage];[Battery voltage];[CPU temperature];[Amplifier temperature]

6

UHF2 Modem Status

U2;MS;[Timestamp];[Current RSSI];[Latch RSSI];[Afc frequency offset]

7

ADCS Flags Status

A1;FLAGS;[Fault] [Flags1] [Flags2] [Accelerometer temperature] [Magnetometer temperature]

8

Payload status

PL;STATUS;[Payload status as decimal number]

Data from frames 1-7 of the beacon status are calculated in SR-NANO-BUS platform OBC. Frame 8 with payload status is prepared in the payload software and updated every minute.

Beacon's first line, master status (M1;STS) is not properly implemented in SR-NANO-BUS platform, so data from 32-bit flags aren't generated correctly.

Payload status

Parameter

Bits

Comment

MODE

0, 1, 2

NEXT MODE

3, 4, 5

µC VOLTAGE

6, 7

0 - correct

1 - too big > 3.7V

2 - too small < 3.0V

SATELLITE VOLTAGE

8, 9

0 - correct

1 - too big > 9.5V

2 - too small < 9.5V

GYROSCOPE

10

0 - correct

1 - error

MAGNETOMETER

11

0 - correct

1 - error

IMU TEMPERATURE

12

0 - correct

1 - error

EXPERIMENT TEMPERATURE

13

0 - correct

1 - error

UNUSED (2 zeros)

14, 15

Mode and Next mode values in beacon payload status were encoded as 3-bit numbers while having 9 possible values. This software error caused inability to properly distinguish the current payload state.

Commands responses

Every uplink command has a defined command response, based on which the operator knows if the request was successfully received.

Command

Action

Response

ADCS_LOGS_ASCII_GET

Get ADCS FLAGS

A1;FLAGS;[fault] [flags1] [flags2] [acc temperature] [mag temperature]

AOCS_ADCS_CONTROL_FLAGS_SET

Set ADCS control flags

BROADCAST_TIMESTAMP_SET

Set the current timestamp on the satellite modules

M1; TS; [number of platform's boot]; [timestamp set]; [set value]

BROADCAST_DEV_RESET

Reboot the satellite

MASTER_CLEAN_PLAN

Clear the planner

M1;TSK;CLEAN_PLAN

MASTER_CMD_DOWNLINK_S

Enable/disable downlink for chosen radio

M1;DWN;154;0;1.

MASTER_FLASH_BLOCK_ERASE

Erase sector (64kB) of FLASH data from the given address (independent of buffers)

FLASH BLOCK ERASE STATUS;[address];[status]

MASTER_FLASH_SECTOR_ERASE

Erase the sector (4kB) of FLASH data from the given address (independent of buffers)

FLASH SECTOR ERASE STATUS;[address];[status]

MASTER_GET_NR_OF_TASKS

Return the current number of tasks in the planner

M1;TSK;LEN;[amount of tasks]

MASTER_GET_PLAN_G

Return information about the Mission Planner status

M1; TSK; [task number]; [time of planned execution]; [destination module]; [command]

MASTER_LOG_G

Get timestamp, boot number, CPU voltage and temperature

M1;LOG;[TS];[Boot nr];[CPU voltage];[CPU temperature]

MASTER_LOGGER_INFO

Information about the normal buffer

FL; [full buffer]; [amount of used space]; [start of data address]; [end of data address]

MASTER_LOGGER_POP

Remove a given amount of data from the normal buffer, along with the offset of the data origin address

FL; [full buffer]; [amount of used space]; [start of data address]; [end of data address]

MASTER_PAYLOAD_STATUS

Return the last received payload status

PL;STATUS;[payload status]

MASTER_PL_ADCS_COIL_X_VAL

Set PWM duty for X magnetorquer in manual mode

MASTER_PL_ADCS_COIL_Y_VAL

Set PWM duty for Y magnetorquer in manual mode

MASTER_PL_ADCS_COIL_Z_VAL

Set PWM duty for Z magnetorquer in manual mode

MASTER_PL_ADCS_COILS_ALL

Set PWM duty for all magnetorquers in manual mode

MASTER_PL_ADCS_CONFIG_K_X

Set the gain for detumbling the X axis

MASTER_PL_ADCS_CONFIG_K_Y

Set the gain for detumbling the Y axis

MASTER_PL_ADCS_CONFIG_K_Z

Set the gain for detumbling the Z axis

MASTER_PL_ADCS_MAX_DUTY_ALL

Set max PWM duty for all magnetorquers

MASTER_PL_ADCS_MAX_DUTY_X

Set max PWM duty for X magnetorquer

MASTER_PL_ADCS_MAX_DUTY_Y

Set max PWM duty for Y magnetorquer

MASTER_PL_ADCS_MAX_DUTY_Z

Set max PWM duty for Z magnetorquer

MASTER_PL_CALIBRATION_CONFIG

Set configuration param - config param ID - config param

MASTER_PL_DISABLE

Turn off the payload power supply

MASTER_PL_ENABLE

Turn on the payload power supply

MASTER_PL_EXP_ACC_TIME

Set experiment acceleration time

MASTER_PL_EXP_END_PERIOD

Set experiment end period

MASTER_PL_EXP_MODE

Set experiment parameters: -experiment mode -experiment duty

MASTER_PL_EXP_PARAMS1

Set experiment parameters: - Experiment mode - Experiment duty - Experiment period - Experiment PWM frequency - Experiment PWM duty

MASTER_PL_EXP_PARAMS2

Set experiment parameters: - Experiment starting period - Experiment end period - Experiment acceleration time

MASTER_PL_EXP_PERIOD

Set experiment period

MASTER_PL_EXP_PWM

Set experiment parameters: - experiment PWN frequency -experiment PWM duty

MASTER_PL_EXP_START_PERIOD

Set experiment starting period

MASTER_PL_FRW_LIST_ARG

Set experiment add list element

MASTER_PL_FRW_MAX_DUTY

Set the max PWM duty for FRW electromagnets

MASTER_PL_GO_IDLE

Set payload to IDLE mode

MASTER_PL_LOG1MIN_CONFIG _ADD_REG

Provide address of registers that are assigned to the log with a period of 1 min (add)

MASTER_PL_LOG1MIN_CONFIG _DELETE_REG

Provide address of registers that are no more assigned to the log with a period of 1 min (delete)

MASTER_PL_LOG1S_CONFIG _ADD_REG

Provide address of registers that are assigned to log with a period of 1000 ms (add)

MASTER_PL_LOG1S_CONFIG _DELETE_REG

Provide address of registers that are no more assigned to the log with a period of 1000 ms (delete)

MASTER_PL_LOG200MS_CONFIG _ADD_REG

Provide address of registers that are assigned to the log with a period of 200 ms (add)

MASTER_PL_LOG200MS_CONFIG _DELETE_REG

Provide address of registers that are no more assigned to the log with a period of 200ms (delete)

MASTER_PL_MODE_CONFIG

Set payload mode with parameters: -current mode -next mode -time for mode

MASTER_PL_WAKE_UP

Wake up payload from IDLE mode

MASTER_SPECIAL_LOGGER_INFO

Information about the special buffer

FSL; [full buffer]; [amount of used space]; [start of data address]; [end of data address]

MASTER_SPECIAL_LOGGER_POP

Remove a given amount of data from the special buffer, along with the offset of the data origin address

FSL; [full buffer]; [amount of used space]; [start of data address]; [end of data address]

MASTER_TIMESTAMP_GET

Get current timestamp from the satellite

M1;TG;[platforms boot amount]; [timestamp get]

MASTER_TRANS_END_FAIL

End of transaction - failure (no indicator shift)

PL;FINISH;sent = [address of the indicator];transaction FAIL

MASTER_TRANS_END_SUCCESS

End of transaction - success (indicator moved by the amount of data transferred)

PL; FINISH; sent = [address of the indicator], transaction SUCCESS

MASTER_TRANS_GET_CURRENT_ADDR

Information about the address of the indicator for the current transaction

PL; CURRENT ADDR = [address of the indicator]

MASTER_TRANS_SEND_1KB_LOG

Launch of a 1kB downlink

PL; [number 1kB part]; [chunk number]; [number of chunks]; [data] PL; INFO; WAITING FOR RETRANSMISSION REQUESTS PL; INFO; NO TRANSACTION IN PROGRESS

MASTER_TRANS_SEND_1KB_RETRY

Start the retransmission of a given data range within a part (1kB)

PL; R; [part number]; [chunk number]; [data] PL; RET; [part number]; [number of chunks]; 1kB retransmission done PL; INFO; NO TRANSACTION IN PROGRESS

MASTER_TRANS_SEND_NUM_PARTS

Initialization of a new transaction

PL;NOP;[timestamp];[number of parts in the transaction]

MASTER_TRANS_SET_ADDR

Set the address of the indicator for the current transaction

PL; TRANS START ADDR = [address of the indicator]

MASTER_TRANS_SET_CHUNKSIZE

Set the size of a single data chunk in the current transaction

MASTER_TRANS_SET_DATASIZE

Set the amount of data to be sent in the current transaction

MASTER_TRANS_SET_DEFAULT

Set the default transaction parameters

MASTER_TRANS_SET_NORMAL_DATA _START_ADDR

Set the normal transaction rate to the beginning address of the data in the normal buffer

MASTER_TRANS_SET_PARTSIZE

Set the size of a single piece of data in the current transaction

MASTER_TRANS_SET_SPECIAL_DATA _START_ADDR

Set the special transaction rate to the beginning address of the data in the special buffer

UHF_CHANNEL_RX_G

Get current frequency

U1;CH;[timestamp];[current channel]

UHF_CHANNEL_TX_G

Get current frequency

U1;CH;[timestamp];[current channel]

UHF_FEC_G

Read FEC flag

U1;FEC;[fec flag]

UHF_FEC_S

Set FEC flag (valid only for binary data sent through UHF)

U1;FEC;[fec flag]

UHF_LOG_G

Get battery voltage

[U1;RL;[timestamp],[3V3 bus voltage];[12V bus voltage];[RF amp temp];[MCU temp] ]

UHF_MODEM_STAT_G

Get radio data

[U1;MS;[timestamp];[current RSSI];[latched RSSI];[automatic frequency control offset] ]

UHF1_ECHO

Send an echo

48byte ASCII STRING

UHF2_ECHO

Send an echo

48byte ASCII STRING

SR-NANO-BUS platform contains IMU sensors for ADCS (gyroscope and magnetometer) but because of a software bug, IMU data can't be transmitted. It's connected with the fact that instead of being sent as ASCII, frames with IMU data are binary. '\0' sign that is used in APRS as the end of line can be anywhere in ADCS data, so if it's somewhere at the beginning, all the data behind won't be copied to AX.25 frame and transmitted.

Payload logs transmission on request

Payload logs are saved in the flash memory, part of SR-NANO-BUS platform. There is no special way of handling data e.g. filesystem - every new binary frame is just put into the first free memory address, depending on the payload mode (as described in logging logic).

Flash memory

Special

Normal

INFO

0x0

0x1000

CAPACITY

6MB - 16KB

2MB - 16KB

START

0x 20 00

0x60 00 00

END

0x 5F E0 00

0x 7F C0 00

Payload log frame

Every log frame contains 6 bytes of information - relative timestamp, register address (key) and register value. Its available parameters and logging interval are specific to the current payload mode. All log frames are prepared in the payload software and transmitted to the OBC as described in Logging logic chapter.

Log frame info

Size

Relative timestamp

2B

Register address

2B

Register value

2B

Payload log frames downlink

Log frames downlink is accomplished in form of a transaction. First, the transaction has to be initialized and a chosen address set. After that, 1 KB of logs can be downloaded. A part of data consists of chunks (typically 35-38 of them), numbered and encoded in Base91. Base91 algorithm used by SR-NANO-BUS platform is so-called rlyeh's modification.

Although UHF1 and UHF2 from SR-NANO-BUS are hardware redundant, their software has some differences. The biggest difference manifests itself in the fact that logs transmission can be provided only using UHF1. UHF2 can never transmit log frames.

Example of payload logs (1 kB)

19/07/18:00/12/23:SR9KRA-6:=PL;   0; 0;37;AABtWAAAAAOmUEAAC'WAAAAAOmUE5FAA5A
19/07/18:00/12/24:SR9KRA-6:=PL;   0; 1;37;BAUA^XHnZ4AA,'pB@AoI~+OtCAv|&DDHAA
19/07/18:00/12/25:SR9KRA-6:=PL;   0; 2;37;3+`AKAg@u^McAA`wyB@ArPP&LtCA2OfbDH
19/07/18:00/12/26:SR9KRA-6:=PL;   0; 3;37;uWGXFCoA\20^uWBAyE&MvDAAFAC'CAzDAA
19/07/18:00/12/27:SR9KRA-6:=PL;   0; 4;37;vDuWKAAAKA)_bWMcBtjtrB*B@Q/LRAFAv|
19/07/18:00/12/28:SR9KRA-6:=PL;   0; 5;37;^ADHC'yemAKAR`kpMcC'v~sAoAiay9wWBA
19/07/18:00/12/29:SR9KRA-6:=PL;   0; 6;37;tNiKvDN/YcxAKA?zpVMcBtNuUD*BBtCAC'
19/07/18:00/12/30:SR9KRA-6:=PL;   0; 7;37;CA,BAAvDXLFAC'HAj|1mJVuW#W(A8A5*~t
19/07/18:00/12/31:SR9KRA-6:=PL;   0; 8;37;,\BAk~dBZFBtpJHAPAR`pqSqC'`,QCdBrP
19/07/18:00/12/32:SR9KRA-6:=PL;   0; 9;37;m=LtHA&qEDJVuWGXICdB#TJ:OtHAJJkYJV
19/07/18:00/12/33:SR9KRA-6:=PL;   0;10;37;AAKAAAPALHAAJVBtUAAAoAr?xcuWD'jtrB
19/07/18:00/12/34:SR9KRA-6:=PL;   0;11;37;vD@QcebAKAv|9CMcAAZg#AoAg@^_uWBAr\
19/07/18:00/12/35:SR9KRA-6:=PL;   0;12;37;mA*BrPOVJAFAtx^UGOY4x4GB@Ao.J=BtCA
19/07/18:00/12/36:SR9KRA-6:=PL;   0;13;37;ZCtGDHC'CAAAFA,BAADHXLFAC'MAtZ~nPj
19/07/18:00/12/37:SR9KRA-6:=PL;   0;14;37;uW#W(AJBVx8xyWGA+}\B1RC';7XAZAR`'n
19/07/18:00/12/38:SR9KRA-6:=PL;   0;15;37;e+C'QmRBSCrPwPKtMAgw)RPjuWGXPCSC#T
19/07/18:00/12/39:SR9KRA-6:=PL;   0;16;37;ReBtMAJJZZPjAAKAAAZALHAAPjBtUAAA8A
19/07/18:00/12/40:SR9KRA-6:=PL;   0;17;37;|L$/,\D'jtpBZF@Qg\WAPAv|}BSqAAjyVA
19/07/18:00/12/41:SR9KRA-6:=PL;   0;18;37;8Ag@/]+\BACZKCZF{eFfSAPAV%!fSquWGX
19/07/18:00/12/42:SR9KRA-6:=PL;   0;19;37;OC6C#T-lD'HAyE&MJVAAFAAAPAzDAAJVuW
19/07/18:00/12/43:SR9KRA-6:=PL;   0;20;37;KAAAjA)_FLoICtjtrBOG@Q~(U'RAv|nEVx
19/07/18:00/12/44:SR9KRA-6:=PL;   0;21;37;AAH2.A+Ag@@=@QCAp0WDOG{eFfT'RAs-pT
19/07/18:00/12/45:SR9KRA-6:=PL;   0;22;37;VxuWGXVCHD#TJKKtRAJJ!aVxAAKAAAjALH
19/07/18:00/12/46:SR9KRA-6:=PL;   0;23;37;AAVxBtUAAA@A}4..CtE'jtrBDH@QK0JAUA
19/07/18:00/12/47:SR9KRA-6:=PL;   0;24;37;v||EY4AAtk8A@Ag@1\BtCAGNODDH{eFfRA
19/07/18:00/12/48:SR9KRA-6:=PL;   0;25;37;UA37XsY4uWGXaCvD#T-1EAKAyE3NMcAAFA
19/07/18:00/12/49:SR9KRA-6:=PL;   0;26;37;AAUAzDAAMcuWKAAAtA(n$,0kCtjtrB^H@Q
19/07/18:00/12/50:SR9KRA-6:=PL;   0;27;37;GUD'bAiqInh=uW#W(AmCVx5#2(NA+}bC!m
19/07/18:00/12/51:SR9KRA-6:=PL;   0;28;37;C'd1gA3AR`#o$$D'hD`B-ErP9}JtbA&q8I
19/07/18:00/12/52:SR9KRA-6:=PL;   0;29;37;h=uWGXSC-E#Tq|EtbAJJJZh=AAKAAA3ALH
19/07/18:00/12/53:SR9KRA-6:=PL;   0;30;37;AAh=BtUAAAdB_)FyEtHA,'rByK@QXpCAeA
19/07/18:00/12/54:SR9KRA-6:=PL;   0;31;37;v|&Dk_AAEvgAdB!+z)CtHA=H5KJV[9JRkA
19/07/18:00/12/55:SR9KRA-6:=PL;   0;32;37;8A`ROh+\CtMugEyKjn17CAeAJJUYk_AAKA
19/07/18:00/12/56:SR9KRA-6:=PL;   0;33;37;AA8ALHAAk_BtUAAAnB^X@|aLIA,'rBnL@Q
19/07/18:00/12/57:SR9KRA-6:=PL;   0;34;37;r=L'gAv|yDlBBAX+`AnB!+`!YLIASouD\W
19/07/18:00/12/58:SR9KRA-6:=PL;   0;35;37;[94_iA%A{!^m:CDtMuqEnLjn0WX'gAJJZZ
19/07/18:00/12/59:SR9KRA-6:=PL;   0;36;37;lBBAK

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