Customer SolutionsJohns Hopkins University Applied Physics Laboratory Uses NI LabVIEW and PXI to Simulate Spacecraft Solar Arrays
Author(s):Bill Brandenburg, Johns Hopkins University Applied Physics Laboratory
Industry:Aerospace/Avionics, University/Education
Product:Data Acquisition, GPIB & Instrument Control, LabVIEW, PXI/CompactPCI
The Challenge:Developing a ground-based system to accurately simulate the operational conditions of spacecraft solar arrays and automate that process using National Instruments LabVIEW while simulating spacecraft orbital profiles from a missions operation center (MOC).
The Solution:Using NI LabVIEW, PXI-1000B DC chassis, PXI-6713 analog output module, and PCMCIA-GPIB interface to control power supplies, integrate to existing GPIB systems, and automate the entire process with a single programming language to fulfill our requirements for automated solar array simulation (SAS) with remote communications.
Solar Panel Operation Simulation Importance The Johns Hopkins University Applied Physics Laboratory Space Department is a key member of the aerospace community. From conception to launch, the laboratory creates innovative and technically challenging hardware for satellites. As an integral part of that process, engineers must conduct spacecraft solar panel operation simulation to fully test satellite power system components. Using LabVIEW and PXI, we created systems to completely fulfill our requirements for automated SAS with remote communications. Satellite Operation Test and Validation To properly test and validate satellite operations on earth, engineers must accurately simulate the power created by solar panels. While the batteries store the excess spacecraft power, the solar arrays serve as the primary power source. Engineers use the SAS to replicate this power for ground testing. They design the SAS by wiring a power supply group to simulate individual or entire solar array power strings. The system controls each power supply in such a way as to accurately create the operational conditions needed for testing. In the past, because engineers set the SAS settings for the open circuit voltage (Voc) and short circuit current (Isc) of each power supply, they could operate only in fixed operating modes. However, for some spacecraft, the frequency in the changes of the Voc and Isc values requires a SAS design with the flexibility to control the Voc and Isc setting via preprogrammed data. By incorporating LabVIEW into our design, we programmed the SAS power supplies to perform not only fixed-mode simulations but also dynamic orbital simulations. Also, by using LabVIEW Web technology, we operated autonomously from a remote location. For the contour nucleus tour (CONTOUR) spacecraft, we increased the SAS power supply control rate to adequately simulate the solar array power dynamics. CONTOUR was a spinner spacecraft with six solar array panels hard mounted to the spacecraft’s hexagon-shaped body. For this SAS design, we used LabVIEW to program four NI PXI-6713 analog output modules with large arrays of simulated data that directly controlled the SAS power supplies, simulating in two-degree increments the rapid solar array power dynamic variations during spacecraft spin-mode operations. The system simulated each individual solar array string to account for the cyclical solar array power panel shadowing caused by various protruding optics and antennae as the spacecraft spun at its 60 revolutions-per-minute rate. We never had used this level of fidelity at the Applied Physics Laboratory previously, and it was a big improvement over past designs. The designs for both the MESSENGER and STEREO spacecraft also required orbital simulations. In these cases, we used LabVIEW to retrieve orbital data from files our power system engineers designed that would establish the dynamic values for Voc and Isc as each spacecraft traveled through space. We created similar data files to simulate the fluctuating solar array power that occurs just after launch during the spacecraft detumble phase. Using LabVIEW, we were able to null errors produced by the hardware. Due to biasing circuitry in the Isc design, the Isc actual value exhibited a small variation due to the Voc value. With the LabVIEW formula node function, we autonomously corrected this variation. We incorporated multiple correction curves based on Y=Mx+B into the LabVIEW VI file while making small adjustments to the Isc values as Voc varied. As a final requirement, each SAS system not only had to be manually and locally controlled but also had to be remotely controlled. Using LabVIEW Web capabilities and a dedicated Ethernet connection, we designed each SAS so we could control it remotely from a MOC. With this additional functionality, the engineers and technicians gained flexibility as well as the safety benefit of not always having to be on station in the field during integration and launch operations. Satisfaction, Capabilities, and Accuracy LabVIEW and PXI improved our SAS design options when testing our satellite power systems. We now easily simulate operation modes, such as orbital simulation and spacecraft tumble, which we previously had difficulty implementing. In addition, the ability to have personnel, who are spread over great distances, control our systems remotely and accurately is not only a reality but the norm. For more information, contact: Bill Brandenburg Associate Engineer Space Department 11100 Johns Hopkins Road Laurel, MD 20723 Tel: (443) 778-5380 Fax: (443) 778-0497 E-mail: bill.brandenburg@jhuapl.edu
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