Thruster ICD

The purpose of this document is to describe the mechnaical, electrical, and data interfaces between the thruster subsystem and other satellite system.

Electrical Interface (UMS-0660)

The thruster subsystem interfaces electrically with the power subsystem through its Controller and Communication Assembly (CCA). The electrical connections for each component are shown in the figure below. All components are powered via onboard voltage regulators located on the thruster board, which operates from the spacecraft’s common power bus. Power is supplied from a distributed bus at an unregulated battery voltage, routed through load switches managed by the Power Module Controller.

The thruster control board receives power at the common bus voltage, typically ranges from approximately 6.5 to 7.2 Volts.
The solenoid driver receives 12 Vdc and 1.6 Vdc from the onboard voltage regulator.
The pressure transducer receives 5 Vdc± 10 mV from the onboard voltage regulator.
The MCU receives 3.3 Vdc from voltage regulator.

Figure 1- Thruster electrical interface

Data Interface(UMS-0660)

The figure below illustrates the data interfaces associated with the thruster components, as well as interfaces with other subsystems.

The Attitude and Orbit Determination and Control Subsystem (AODCS) communicates with the thruster control board via a UART interface, while the reaction wheel cluster connects to thruster board through the SPI bus. Power control is managed by CAN-Controlled Load Switches and Monitors (CCLSM) via the auxiliary CAN bus, operated by the power subsystem.

The solenoid valve driver primarily interfaces with the thruster board using a PWM signal. In addition to PWM, the driver requires a GPIO control signal that functions as an arm command. Both the PWM and GPIO signals must be active to actuate the solenoid valve. This dual-signal implementation ensures that the valve remains closed in the event of an unintended PWM activation.

The pressure and temperature transducers interface with the thruster board via analog inputs.

Figure 2- Thruster data Interfaces

Software Communication Protocol

This section defines the software-level communication protocol between thruster CCA and the AODCS. Communication is point-to-point over a UART link and uses byte-oriented packet protocol. It specifies message framing, command structures, byte ordering, acknowledgement rules, and error reporting. The interface enables the AODCS to command precise thrust levels for Collision Avoidance (COLA) maneuver .

Communication Overview

Parameter Specification

Physical layer UART

Baud rate 115200 bps (default)

Data format 8 data bits

Direction ADCS to CCA (commands), CCA to ADCS (ACK/NACK/Telemetry)

Integrity Check CRC-8 computed over CMD + VAL fields

The CCA accepts commands only from ADCS, validates them, performs CRC checks, and returns an acknowledgement.

Command Frame Format

All AODCS-originated commands follow the same 8-byte frame:

Byte index Field Size(bytes) Description

0 Start 1B Start of frame, fixed value 0x55*

1 CMD 1B Command identifier( 1 to 4)

2-5 Val 4B Command value(uint32_t )

6 CRC 1B CRC-8 over bytes 1–5

7 End 1B End-of-frame marker, fixed value 0xFE

*Only command frames use the 0x55 START byte

Command Set

1-AODCS_SET_Des_THT_CMD

This command is issued from the AODCS to the thruster. The data type is uint32_t, representing thrust in micro-newtons (µN). The valid thrust range is 0 to 10000 µN. If the requested thrust value falls outside the allowable range, the CCA shall reject the command and return a NACK.

2-AODCS_SET_Des_T_CMD

This command is issued from the AODCS to the thruster. The data type is uint32_t, representing thrust time in micro-second (µs). The valid thrust range is 2500 to 30000000 µs. If the requested time value falls outside the allowable range, the CCA shall reject the command and return a NACK.

3-AODCS_SET_ARM_SIGNAL_CMD

This command is issued from the AODCS to the thruster, representing arm signal activation.

4-AODCS_SET_DISARM_SIGNAL_CMD

This command is issued from the AODCS to the thruster, representing disarm signal.

Telemetry Set and Frames

The thruster control board shall transmit telemetry information to the AODCS. Telemetry frames use the standard command frame structure, starting with 0x55.

5-THRUSTER_SET_AVAILABLE_PPRESSURE_CMD

This command is issued from the thruster to AODCS. The data type is uint32_t, representing pressure in absolute atmosphere. The valid thrust range is 0 to 2.76 absolute atm.

6-THRUSTER_SET_CURRENT_PMWDC_CMD

This command is issued from the thruster to AODCS. The data type is uint32_t, representing duty cycle of PWM in percent. The valid thrust range is 1 to 100 percent.

7-THRUSTER_SET_CURRENT_TEMPERATURE_CMD

This command is issued from the thruster to AODCS. The data type is uint32_t, representing temperature of thruster tank. The valid thrust range is -60 to 60 Celsius.

8-THRUSTER_SET_CURRENT_THRUSTTime_CMD

This command is issued from the thruster to AODCS. The data type is uint32_t, representing the thrust time achievable. The valid thrust range is 2500 to 30000000 second .

9-THRUSTER_SET_AVAILABLE_FULLMASS_CMD

This command is issued from the thruster to AODCS. The data type is uint32_t, representing the remained mass of fuel. The valid thrust range is 0 to 4000 mg .

Acknowledgements and Error Handling

The CCA send an acknowledgement frame after processing each received command. Unlike standard command frames, ACK and NACK frames do not use the 0x55 START byte. Instead, the first byte directly encodes the acknowledgement type:

ACK frames begin with 0x44 (Command Accepted)
NACK frames begin with 0x11 (Command Rejected)

The END marker (0xFF) is still retained.

The ACK frame format (Command Accepted ) is as follows:

Byte index Field Description

0 0x44 Start of frame, ACK indicator

1 CMD Echo Command ID that is being acknowledged ( 1 to 4)

2-5 Reserved 0x00

6 CRC CRC-8 over bytes 1–5

7 End End-of-frame marker, fixed value 0xFE

The NACK frame format (Command Rejected) is as follows:

Byte index Field Description

0 0x11 Start of frame, NAC indicator

1 CMD Echo Command ID that is being acknowledged ( 1 to 4)

2 Error code See error table below

3-5 Reserved 0x00

6 CRC CRC-8 over bytes 1–5

7 End End-of-frame marker, fixed value 0xFE

Error codes:

Code Meaning

0x01 Value out of valid range

0x02 CRC mismatch

0x03 Unsupported command

0x04 Internal CCA error

Mechanical Interface

The following drawings shows the mechanical interface of the thruster.

Fuel Storage Tank (UMS-0656)

The fuel storage system consists of ten off-the-shelf CO₂ cartridges(UMS-0873) mounted to a machined block manifold (UMS-0870).

Material: The manifold is made from aluminum alloy 6061-T6, while the CO₂ cartridges are composed of carbon steel.
Connection: The cartridges are threaded directly into the block manifold. The entire assembly is secured using a support bracket fastened to the manifold with M3 × 0.5 screws. Finally, the complete assembly is mounted to the base plate, which is securely attached to the satellite’s structural shell using M3 × 0.5 hex drive screws.

Solenoid Valve (UMS-0658)

Material: 316 Stainless steel
Connections: The solenoid valve inlet is connected to the storage tank outlet using a Swagelok fitting (UMS-0781). The valve outlet is connected to a compression fitting that routes the flow from the solenoid valve to the nozzle inlet. The solenoid valve is securely mounted to the manifold using a bracket fastened with M3 × 0.5 mm thread hex screws.

Pressure Sensor (UMS-0743)

Material: 17-4PH Stainless Steel
Connection: Directly threaded into the outlet port of the storage tank .

Fill and Drain Valve (UMS-0657)

Material: stainless steel
Connected to the storage tank outlet via a fitting (UMS-0877). The valve is mounted to one of the CubeSat’s external faces using a bracket (UMS-0967), secured with M3 × 0.5 mm thread hex screws.

Nozzle (UMS-0659)

Material: Stainless steel
Connections: The nozzle is connected to the solenoid valve outlet via a compression fitting. It is mounted to the CubeSat structure using a bracket (UMS-0966) and secured with M3 × 0.5 mm thread hex screws, ensuring mechanical stability during operation.

Nozzle Orientation

The nozzle is mounted along the central rail and exits from the face of the satellite, aligned with the X direction. Its orientation is slightly offset from the satellite’s center of mass, by 15 mm in the Z direction and 9 mm in the Y direction. This offset introduces a small disturbance torque, estimated at approximately 0.150 mN.m in the Y direction and -0.090 mN.m in the Z direction. These torques are expected to be within the control authority of the reaction wheels. Figure 3 illustrates the nozzle vector configuration and its orientation within the LISSA satellite layout.

Figure 3- Nozzle orientation