2014.B.3.1 Test System for Payload-OBC interface in PiSat

Author(s)

Dhananjay V Kumar (1)
R Adarsh (1)
B M Dayanand (1)
Nayak M Mahendra (1)
Dr Vinod Kumar Agrawal (1)

PES Institute of Technology, Bangalore, India

Session

B.3

Keywords

OBC,Test System,Payload,CSP,Simulation

Abstract

PISAT is a pico-satellite being designed and developed by students at PES Institute of Technology, Bangalore. It is 3 Axis controlled by using Magnetometers and magnetic torquer rods as actuators along three axes. PISAT is based on a 32 bit Atmega AVR microcontroller-AT32UC3A0512. The PISAT carries an imaging payload, Gomspace NanoCam C1U. To facilitate testing of OBC and payload, a test system that simulates payload and Onboard computer (OBC) is developed. The simulated OBC helps in testing payload and payload simulation helps in testing OBC without actually interfacing OBC to the payload. The payload test system is proposed to be used in bench and environmental testing of the satellite. This paper provides insights into the test system design and how the testing of the payload and OBC is proposed to be carried out on ground.
The NanoCam uses CSP enabled I2C Serial Communication Protocol in multi-master mode to communicate with the OBC for command and data transfer. The OBC uses four commands while communicating with the NanoCam. The commands follow the CubeSat Space Protocol or CSP. The OBC is in master mode when it send the command to the NanoCam. The Nanocam is in master mode when it responds to the OBC forcing the OBC to slave mode. Hence the test system needs to be designed in multi-master mode.
A. Testing Of OBC(Paylaod Simulation)
In response to commands from OBC on I2C bus the payload simulator responds like real payload to OBC. The front end application on the PC displays the operations between OBC & Payload, Whenever a download command is received by the simulator the picture stored in the PC is loaded onto the payload in blocks since Uno board does not have enough onboard memory. But the test system ensures that the data transfer from simulator to payload is identical to real payload.
B. Testing Of Payload(OBC Simulation)
While testing the Payload the OBC must be simulated. An Arduino UNO board is used to simulate the functions of the OBC. The appropriate commands are sent and the replies from the NanoCam are read. The User can choose to send the necessary commands from the Front End Application on the System.
This paper presents the design of of test system and the test results. Also the detailed step by step procedure to validate the operation of the payload and its interface to OBC is shared as part of this paper.