Generic Aocs Test Bench

Author(s):
Antonio Ayuso - Sener Ingenieria y Sistemas

Industry:
Aerospace/Avionics

Products:
LabVIEW, PXI/CompactPCI

The Challenge:
Attitude and Orbit Control Subsystems (AOCS) Test Benches for current Space Missions are predominantly designed from scratch for every Spacecraft. The Generic AOCS Test Bench objective is to be an adaptable, reusable, modular and expandable system capable to test –with minor modifications– any upcoming AOCS Client.

The Solution:
Usage of NI and European Space Agency (ESA) solutions into a PC based system that controls a PXI rack where all interchanged signals with the real or emulated On Board Computer are simulated –into the PXI controller– and interfaced –with the corresponding I/O boards

Introduction

Every Space Mission requires test benches to validate and verify different Spacecraft Subsystems. Such test benches are predominantly designed from scratch for every Space Program. New trends –driven by cost criteria– are obviously evolving towards designs capable to deserve words like reusable, modular and expandable.

The Generic AOCS Test Bench (GATB) is an adaptable and scalable system that enhances SENER with the capability to successfully participate in any upcoming opportunity related to Verification and Validation activities in the field of the AOCS.

System Implementation

There are four main elements in the GATB architecture (see Figure 1):

§     Matlab/LabVIEW host. It is a PC running Windows XP devoted to develop and to manage the software –hereafter referred to as Simulation Software– whose mission is to simulate the conditions around the AOCS SW under test. The software models –Spacecraft Dynamics, Kinematics and Environment plus Sensors and Actuators– are translated into code targeted for NI real time systems using the Simulation Interface Toolkit.

§     SCOS 2000 host. It is a PC running Linux dedicated to host the ESA SCOS 2000 command and monitoring tool from which the communication with the Spacecraft –in this case the emulated or real On Board Computer– is performed. Usage of such tool for the execution of the test scripts ensures the compatibility with the later flight operations.

§     PXI rack. This element hosts the PXI controller together with the I/O boards devoted to interface with the AOCS SW. The PXI controller executes the Simulation Software. The I/O boards generate the analog and digital signals and manage the data bus communications.

§     VME rack. This rack contains the ERC32 flight processor –radiation hardened processor typically used in European space programs– board. It interfaces with the PXI rack via a VME-MXI-2 board.

§     Note that NI solutions participates in three of the four above mentioned elements, namely:

§  Matlab/LabVIEW host:

• LabVIEW Developer Suite.
• Simulation Interface Toolkit.
• I/O NI boards drivers.

§  PXI rack:

• NI-PXI 1045 (18 slots chassis).
• NI-PXI 8187 (PXI controller running LabVIEW RTOS).
• Input/Output boards:

o    NI-PXI 6723 (Analogue outputs).

o    NI-PXI 6704 (Current outputs).

o    NI-PXI 8320 (PXI – VME bridge).

o    NI-PXI 6511 (Digital outputs).

o    NI-PXI 6512 (Digital inputs).

o    NI-PXI 8464/2 (CAN bus interface).

§  VME rack.

• NI VME-MXI-2 bridge to PXI board.

Staggered Approach

Testing an AOCS is a major complex task. Thanks to the GATB staggered approach, the AOCS Verification and Validation can take place starting from communication principles running in real time, up to open and close loop tests that may include both the On Board Computer and/or the Unit Models –Sensors and Actuators– in the loop.

The ad hoc selected simulation parameters are available during test execution in the Simulation Software Front Panel (see Figure 2) and the Spacecraft Telecommand and Telemetry can be followed in the SCOS 2000 Desktop Panel (see Figure 3).

The following are the four testing steps offered by the GATB:

§     Step A. The AOCS SW and the Simulation Software run together in real time in the processor of the PXI Controller.

§     Step B. The AOCS SW runs in real time in a flight representative on board processor –ERC32 or LEON–, whilst the Simulation Software runs also in real time in the PXI rack. Communication between both racks is performed using the MXI-2 bus.

§     Step C. The AOCS SW runs in real time in the On Board Computer, while the Simulation Software runs in real time in the PXI rack. Interface between both devices is performed via the I/O boards (analog and digital) plus the data bus boards (MIL1553, CAN, etc.). Communication with the AOCS SW –Telecommand and Telemetry– is performed using the ESA tool.

§     Step D. Same as Step C but additional flight hardware –Sensors and/or Actuators– may be included in the loop.

Author Information:
For more information on this Case Study, contact:
Antonio Ayuso
Sener Ingenieria y Sistemas

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