GLO5 and GLO6  -  STS-85 

     The two GLO instruments have been interfaced to the IEH2 hitchhiker bridge for flight on STS-85, August 7, 1997.  The orbit will be inclined 57° with a launch window causing the orbiter to pass through the earth shadow in the southern hemisphere.  There are several reasons for flying the two nearly identical GLO instruments together.  The most important are probably:   1) to allow stereoscopic viewing of dayglow structures such as metal ion clouds and gravity waves, 2) to try and relate waves observed in the night sky emissions from orbit to orbit, and 3) we can maintain continuous surveillance of the airglow throughout the flight with one instrument while the second instrument is performing supporting experiments.

STS-85  GLO5, GLO6 Instrument Enhancement 

     One of the important advantages of the Shuttle as an observing platform is having time in space long enough to fully exercise the experiment, followed by the opportunity to improve and develop new techniques for the next flight opportunity.  The following adjustments have been made to the GLO instruments to adapt them to a developing scientific program and improve the performance.

Scan Platform Orientation 

     Both of the GLO scan platforms have been placed on a 15° wedge (see Figures).  This will ensure continuous monitoring of the airglow emissions throughout the mission.  For a considerable time during a shuttle flight, the orbiter is in a bay to earth attitude.  The 15° wedge tilts the slit 15° to the horizon instead of tangent as in the past.  At 15° the slit extends over 65 km in altitude at the limb, giving excellent data on both night airglow and day glow limbs.


    The UV spectrograph section of GLO (115 - 320 nm) has been using a solar blind intensifier (CsTe photocathode).  As the field of view approaches the bright dayglow limb, near a tangent height of 120 km, rayleigh scattering from the sunlit limb scatters into the spectrograph, compromising the observation.  For future flights, a second intensifier will be installed with a CsI photocathode having a long wavelength cutoff at ~ 180 nm.  This will allow us to scan down through the limb in the dayglow.  This will improve our capability to examine the dayglow limb chemistry as we extend the observations down from the thermosphere.


    The GLO observations of the airglow in past missions have lead to some significant conclusions about wave characteristics in the lower region of the thermosphere.  The monochromatic images of the O2(ATM), OH (Meinel) and [OI](5577) all show intensity enhancements along the orbit.  The period of the major enhancement is from 7000 km to 12000 km, and the changes in intensity are up to factors of 3-4.  However, the enhancements appear to be uncorrelated between the emissions.  Waves with much smaller amplitude were observed in the tracker image, that was a bare CCD with a wide bandpass.  These types of measurements have laid the foundation for the next flight opportunity to observe this global activity and expand our observational base to smaller structure.  We will also try to correlate with ground based programs where much smaller wave structure has been observed, also in an uncoupled fashion.

Wavelength (
FOV (deg) 
O2 (ATM) 
762 nm 
± 2.0 nm 
30 X 40 
OH (Meinel) 
762 nm (NOTCH) 
650 - 850 nm 
30 X 40 
OI (557.7) 
557.7 nm 
± 2.0 nm 
30 X 40 

    These imagers will be intensified CCDs.  Intensifiers are required to minimize the exposure to accommodate the Shuttle motion of 7.8 km/sec.  The imagers will be operated in several modes. 
     While imaging the limb in support of the spectrographs, we expect to be able to observe the orientation of long period and medium period waves recorded by the spectrographs.  The orientation of the wave is important since it will assist in identifying the wave on the next orbit. If we can identify the wave, we can estimate its velocity.  Or if we can track the wave, we can estimate its velocity. 
     The wide field imagers will allow us to see shorter period waves.  There is some smearing of limb data due to spacecraft motion.  However, we can stop the motion during an imager exposure by slewing the scan platform at a rate consistent with the rate of the target waves.  This technique is variable and can be adapted for viewing angle.  Nadir imaging can be done in a manner which will accommodate the shortest period waves. 


    We have not been successful in tracking the bright limb in the dayglow.  This has compromised the dayglow observations in the past, since the limit cycle motion carries the spectrograph field of view down into the rayleigh scattering region of the atmosphere and saturates the detectors. 
 We have changed the tracking imager to give a much larger dynamic range.  We will have a very fast lens for night sky work, but will be able to shorten the exposure and reduce the aperture for dayglow observations. 
 Several bright stars pass through the tracking field of view during airglow limb tracking.  These stars are easily identified and provide an instantaneous calibration of the scan platform azimuth and elevation position with respect to the accurately known orbiter position and attitude.  A sufficient number of stars are seen during any one night transit to verify the calibration several times.  The scan platform pointing calibration is validated by this technique regularly during the flight. 

o Last Updated: 6 May, 1997

This page is maintained by:
Jesus A. Ramirez