National Aeronautics and Space Administration

The NIGHTGLOW instrument consists of three Newtonian telescopes (each has a 14" diameter mirror and a 19" focal length - an f/1.4 design) instrumented with two photomultiplier tubes (PMTs). The PMTs are the Phillips XP3062, 39mm hexagonal design, identical to those used on the Fly's Eye Experiment. A bandpass filter is used to limit the signal to wavelengths between 300 - 400 nm. The electronics consist of a PC104 format 386 microprocessor, comm port card, digital and analog I/O, and a fast digitizer (5 Mhz) for the LIDAR system. The LIDAR is designed for measuring cloud reflectivities down to an optical depth of approx. 0.1. The LIDAR uses a Laser Science, Inc. laser, at 335 nm, pulsed, with a pulse width of _____ nsec.

In addition to the LIDAR, there are three on-board IR sensors which operate between 8 and 15 microns. They measure the cloud and/or surface temperatures below the payload.

Telemetry is provided through the TDRSS system, with a throughput of order 3 kbits per second. The data are telemetered to an NSBF ground station in Palestine, Texas, where a remote GSE is located. An on-board GPS unit keeps track of the current payload position, the UT, and the time until sunrise and sunset. Data taking is disabled during the day, but not at night, even if there is a moon.

One of the three main telescopes is nadir-viewing and fixed in position. The other two rotate in a plane, from 45 degrees away from zenith through the nadir position, and back up to 315 degrees. The zenith cone (half angle of 45 degrees) is blocked by the balloon. At the time when the rotating telescopes are pointing down, a calibration cycle is performed on all three telescopes, and the LIDAR system is triggered to identify cloud cover. The stepper motor and mechanism (with a 50:1 gear reduction) that rotate the telescopes are shown here. The rotating telescopes view the horizon and the UV glow at high altitudes (above 90 km). The PMT output is fed directly into a DC integrator, which is gated on for approximately 120 msec (programable). The high altitude nightglow comes from the molecular oxygen Herzberg (I and II) and Chamberlain bands. (See science page.)