Rover Project

Objectives

The goal of this project is to develop rover platforms of different sizes (a single unit version, abbreviated 1U, and a 2U version) with increasing set of capabilities. The rovers shall be remotely controlled and be able to solve some tasks autonomously. On top of that, the rover shall be designed according to space engineering concepts and use space communication protocols for internal and external communication.

The project status is tracked here.

Shown here is the structural prototype of the 2U rover.

The baseline scenario is shown below. For this project we mostly focus on the remote segment (the rover) with a simplified ground segment.

Operational objectives for the 1U rover:

  1. Let the rover run a pre-programed (hardcoded) movement.
  2. Receive period status telemetry from the rover, via CCSDS downlink communication protocol.
  3. Send telecommands to the rover to control its operation, via CCSDS uplink communication protocol.
  4. Exchange files with the rover, via CFDP protocol.
  5. Run onboard procedures on the rover for automated operations.

Additional operational objectives for the 2U rover:

  1. Prolong operation through self-charging of batteries with solar cell panels.
  2. Rover shall determine its own location using GNSS receiver.
  3. Integrate camera to take images and them download via file transfer.

System Architecture

The rover will consist of structural parts, electronic boards, and onboard software. Shown here is the board stack for the 2U rover:

The boards are interconnected through the common CubeSat 104-pin connector using the LibreCube Board Specification.

Below is a block diagram of the various components and boards and their interfacing.

The abbreviations are as follows:

  • OBC: On-Board Computer
  • PCDU: Power Distribution and Control Unit
  • COM: Communications Unit

There are three on-board busses to be used:

  • System bus: The OBC controls and monitors the other boards. It uses the SpaceCAN protocol.

  • Payload bus: The OBC interfaces with the camera via the payload bus. This bus is not used to control/monitor the camera but to transfer image data. OBC commands (via system bus) the transfer of image data, which would then be sent over this payload bus. As this bus is not so critical like the system bus, (limited) data loss can be accepted (ie. images can be re-requested if incomplete).

  • Coms bus: The COM board is used to send and receive data over the radio link to external system (mostly ground station). For this it modulates a bit stream (containing outgoing data, like telemetry) into RF signal. Likewise, it decodes a bit stream from incoming RF signal (which contains mostly commands from ground). The coms bus therefore transports bit streams between OBC and COM board.

The interface between ground station (GS) and rover shall be implemented as CCSDS stack. For demonstration purpose we will use UDP over WiFi instead of radio modulation, but will add the proper physical layer at later stage. The interface between ground station and mission operations center (MOC) shall be based on Space Link Extension (SLE) protocol, which itself encapsulates forward and return CCSDS frames and rides on internet protocol stack (TCP/IP).

Development Setup

Shown below is a recommended setup to support the rover electronics stack development. The pyboards were chosen in particular as they provide two integrated CAN modules, as needed for the redundant CAN bus. They need to be accomplemented with CAN transceiver skins.

The suggested components for the development setup are:

  • 4x pyboards
  • 4x CAN transceiver skins
  • 1x OpenMV H7 R1
  • 1x LC2201 (or a 5V power supply)
  • 1x Linx PCB-EVM-RM
  • 1x Pycom WiPy
  • 1x PCA9685 PWM module
  • 4x Parallax Standard Servo
  • 4x Parallax Continuous Rotation Servo
  • 1x Raspberry Pi
  • 1x RS485 CAN HAT for Raspberry Pi

Using LC3101 to help with development:

System Description

Structure

The 1U rover will use LC2101 for the main structure The 2U version will use LC2102.

Electrical Power System

For the power conditioning and control, the LC2201 will be used. The solar cell panel is to be developed, the prototype is here. Also, the 2U version shall use an additional battery pack, the prototype is here.

Communications

TO BE WRITTEN

Wheel Drive

TO BE WRITTEN

Attitude and Position

TO BE WRITTEN

Camera Board

TO BE WRITTEN

Onboard Computer

TO BE WRITTEN

This is the main processing unit of the rover. It will run all the heavy on-board software: CFDP, OBCP engine, CCSDS protocol stack and ECSS PUS protocol. The above applications may be implemented as docker containers and are developed in the frame of software work packages (see further below). At later stage, the OBC firmware design shall be oriented on the SAVOIR functional reference architecture.

Onboard Data Buses

Onboard Software

Procedure Execution

Onboard File Delivery

Application Services