The WX Subsystem Weather Station was designed for use as part of the Weather Instrumentation (WX) Subsystem for the Constellation Program (CxP) to be implemented in the Launch Complex 39B at Kennedy Space Center. The weather stations need to be rugged, robust, and reliable. Although this equipment is not to be located in hazardous zones, it is still required to withstand harsh environmental conditions typical of the launch environment. Health management considerations are incorporated in the design so the user can be notified remotely when sensors, power supplies, dataloggers, etc. require service or maintenance.
The weather station measures, acquires, and transmits meteorological data descriptive of its surrounding environment (i.e. wind speed, wind direction, temperature, relative humidity, etc.). It is a modular system that can be set to operate according to the user's requirements. The use of commercial off-the-shelf (COTS) products in the design of the weather station adds versatility to the system since most components have been tested to operate in harsh environmental conditions. The station is accessed remotely in order to retrieve the collected data and verify the health of the processing unit. The auto-monitoring features of the station provide tools to automatically schedule service requests, allowing automation of maintenance efforts. Battery backup operation mode allows for local data acquisition and storing for limited periods of time during power outages in the station.
The station consists of a power supply unit, a data acquisition system, and a series of meteorological sensors. The data acquisition system is the processing unit of the weather station, and is in charge of acquiring, storing, and transmitting the data from the sensors. The power supply unit provides the power protection and signal conditioning needed to operate the meteorological instrumentation and related equipment. Both the power unit and the data acquisition system are housed inside separate weatherproof enclosures that provide protection against harsh outdoor environments and electromagnetic interference (EMI). The enclosure with the power unit is known as the Meteorological Power Box, whereas the enclosure containing the data acquisition system is the Meteorological Instrumentation Box.
The input of the Meteorological Power Box is a single-phase, 120-VAC signal. At the power unit, this signal is converted and conditioned to provide 12 VDC, 24 VDC, and an optional backed-up 12 VDC to the instrumentation box. A surge protective device (SPD) is used at the input of the unit to mitigate the effects of excessive system voltages and currents caused by electrical events such as lightning, load switching, and others.
Every measurement in the weather station is terminated inside the Meteorological Instrumentation Box at the data acquisition system, which is a COTS datalogger. The datalogger converts the acquired measurements to engineering units and stores the data in its internal memory. Data can be transferred from the datalogger to a remote workstation via serial communication protocol (RS-232), or through a TCP/IP network. An optional Ethernet media converter can be used to connect the datalogger to a remote workstation via fiber-optical link. Also, an Ethernet surge protective device is used for applications that require copper links (i.e. CAT 5 or CAT 5e) between the remote workstation and the datalogger. The datalogger and the meteorological sensors are powered up through terminal blocks that receive their power from the Meteorological Power Box.
The sensors connected to the datalogger describe the surrounding environment as well as the internal status of the Meteorological Instrumentation and the Power Boxes. The meteorological measurements acquired by the Meteorological Instrumentation Box are wind speed, wind direction, relative humidity, temperature, and rain precipitation. These measurements are acquired by sensors containing non-moving parts, which allows extended operating time. This translates into longer calibration cycles and less maintenance. The datalogger also acquires the temperature and relative humidity inside both enclosures, and monitors the output voltage of the sealed lead acid battery and the status of the AC-to-DC converters inside the Meteorological Power Box.