Purpose of the flight and payload description

The objective of the flight was to use an INFRARED SPECTROGRAPH carried by a balloon to 102,000 feet to record the near infrared solar spectrum as a function of altitude and determine the amounts of water vapor, carbon dioxide, and other absorbing constituents at each atmospheric level. This was the first successful flight of such an instrument to these extreme altitudes. The Spectrograph was developed by the University of Denver with research sponsored by the Geophysics Research Division of the Air Force Cambridge Research Center. The Hi-Altitude Instrument Company of Denver manufactured the biaxial pointing control system.

The experimental apparatus which can be seen in the image at left consisted of a Littrow-type infrared spectrometer that used a 60-degree quartz prism and employed a lead sulfide (PbS) cell detector. All components including mirror mounts and enclosing boxes were constructed of duraluminum, except for the spectrograph base plate and film cassettes which were made of steel. The collimating mirror was spherical with a 3-inch diameter and 11-inch focal length, while the entrance and exit slits maintained fixed widths. The spectrum was swept across the exit slit in approximately 6 seconds once each minute through rotation of the Littrow mirror.

The detection system incorporated a chopper blade that interrupted solar radiation entering the spectrograph at 400 cycles per second. The amplified 400-cps signal from the PbS cell drove an oscillographic bifilar, oil-filled galvanometer whose window, functioning as a lens with 160-mm focal length, focused an image of the source onto 35-mm film. The light source consisted of two lamps connected in parallel with an automatic relay system ensuring continuous operation if one lamp failed. A slit positioned immediately ahead of the film defined the width of the trace on the film itself. The system used 100 feet of Tri-X 35-mm film to record the light traces, providing capacity for nearly 200 records since each record occupied about 6 inches of film.

The power systems included a 26-volt supply for motors consisting of 24 Mallory mercury cells connected in series, drawing approximately 0.5 amp during the six seconds of operation once each minute. Additional power came from a 130-volt supply for the amplifier and a 90-volt supply for the PbS cell, delivered from Eveready batteries in the power pack. The entire system also included telemetering equipment for monitoring pressure and the performance of elevation and azimuth drives, plus a barograph for altitude determination.

The biaxial pointing control system -that maintained an image of the sun fixed on the spectrometer entrance slit with an accuracy of approximately one-quarter degree of arc- consisted of elevation and azimuth drives where a tower holding the spherical mirror was mounted on ball bearings and turned in azimuth, while a plane mirror mounted at the base of the tower turned in elevation. The pointing control operated in two modes: a coarse mode that caused oscillation with about a 2-second period in elevation and a 10-second period in azimuth when off the sun, and a fine mode that engaged when the coarse control brought the mirror within 3 degrees of the sun. Two separate photocell systems operated the fine control, with solar radiation illuminating photocells equally when pointed squarely at the sun but unequally when pointed at an angle, creating differential currents that excited magnetic clutches operating in opposition to restore proper alignment.

Details of the balloon flight

Balloon launched on: 6/22/1955 at 5:59 local
Launch site: Holloman Air Force Base, Alamogordo, New Mexico, US  
Balloon launched by: Balloon Branch, Holloman Air Force Base (HAFB)
Balloon manufacturer/size/composition: Zero Pressure Balloon  
End of flight (L for landing time, W for last contact, otherwise termination time): 6/22/1955 at 8:54 local
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 2 h 55 m
Campaign:    

The balloon was launched at 5:59 MST on June 22, 1955, from Holloman Air Force Base in New Mexico. The balloon had a one million cubic foot capacity, measured 135 feet in diameter, and lifted 205 pounds of equipment to the ceiling altitude of 103,000 feet. The balloon rose at approximately 500 feet per minute initially, then maintained roughly 800 feet per minute throughout the ascent, reaching the ceiling altitude in 2 hours. It remained at the ceiling altitude for 55 minutes before command cut-down was given, and the equipment returned to earth by parachute. The spectrograph continued operating when the recovery crew reached the site around 10:30 AM, and the pointing control remained undamaged throughout the entire flight.

During the ascent, the infrared spectrograph automatically scanned the spectrum once each minute, though successful records required the pointing control to simultaneously fix an image of the sun on the spectrograph entrance slit. Due to the low intensity of the early morning sun, which was partly obscured by clouds, the pointing control operated sporadically up to about 13,500 feet altitude. The first usable record was obtained at 6:12 AM during the 25th cycle of the spectrograph, with 13 minutes having been consumed on the ground before useful data collection began.

The experiment successfully recorded the near infrared solar spectrum from the visible range to 2.5 microns, exhibiting water vapor and carbon dioxide absorptions that varied systematically with altitude. The data showed the near infrared spectrum of the sun as observed through Earth's atmosphere was indented by telluric absorptions due to H2O, HDO, CO, CO2, N2O, CH4, and O3. The researchers obtained complete records at various altitudes including 13,500 feet, 22,500 feet, 32,400 feet, 42,000 feet, 61,000 feet, 74,500 feet, and 89,000 feet, each differing by approximately 800 feet of altitude since records were taken once per minute during the steady ascent rate.

External references

If you consider this website interesting or useful, you can help me to keep it up and running with a small donation to cover the operational costs. Just the equivalent of the price of a cup of coffee helps a lot.



12972