Purpose of the flight and payload description

LEE is an instrument which measures the energy spectrum of comic ray electrons. In the picture at left we can see a scheme of it (click to enlarge). It detects incoming electrons with 3 plastic scintillators (T1, T3 and G in the drawing) the last one for anticoincidence and a gas Cherenkov detector (T2). It measures the electron energy in a cesium iodide (T4) and leadglass (T5) calorimeter. Another Scintillator (T6) also assists in particle identification and energy determination by counting the number of particles that escape the calorimeter.

The LEE instrument was developed in the late 60's at the University of Chicago and made his first flight in 1968. Over the years, regular ballon flights have been made from Northern Canada yearly during the years 1968 to 1975 and approximately bi-annually until 1979. Then, the experiment was transfered to the University of Delaware, wich now operates it.

The observations from LEE provide one of the few more precise measurements of the electron spectrum over an extended period of time.

Details of the balloon flight

Balloon launched on: 8/25/2002 at 1:05 utc
Launch site: Lynn Lake Airport, Manitoba, Canada  
Balloon launched by: National Scientific Balloon Facility (NSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon Raven Big 60 - 1.700.000 m3 - SF4-59.84-.4/.52/.52-NAR
Balloon serial number: R59.84-2-01
Flight identification number: 508N
End of flight (L for landing time, W for last contact, otherwise termination time): 8/26/2002 at 22:31 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 22 h 15 m
Landing site: 8 miles SSW of Anzac, Alberta, Canada
Payload weight: 1546 lbs

The balloon was launched by dynamic method assisted by a launch crane on August 25th.

After a nominal ascent phase the balloon reached the float altitude of 49.4 km and started a flight path due to the west as can be seen in the map at left (click to enlarge).

During the flight the balloon mantained a flight level of ~ 49 km until after near 23 hours of flight it was terminated.

The payload landed near the city of Fort McMurray, in Alberta, Canada.

Besides the LEE instrument, this flight was mainly focused on testing a new balloon of a kind known as Ultra-High Altitude Balloon (UHAB). These vehicles allow to take payloads approaching 900-1,000 kg to altitudes in excess of 45 km using traditional zero-pressure designs.

In addition to providing unprecedented altitudes from which to make scientific observations, the UHAB also opens new avenues for long duration ballooning at mid-latitudes. With altitude excursions of 10-12 km, these balloons will be able to execute long duration flights without the need for large quantities of ballast. If augmented by a small superpressure anchor balloon, the altitude excursions could be kept to a minimum. While not as capable as the ULDB in carrying large payloads, the UHAB would add another capability for scientists with relatively light payloads who desire to maximize mission time and altitude.

The development started in March, 2002, when NASA requested that Raven Industries perform a study on a series of ultra-high altitude zero pressure balloon platforms. After analyzing several load-altitude targets, NASA chose a 1.7 million cubic meter (60 million cubic feet) design with an ultimate payload capacity of 750 kg. While the balloon was designed using traditional zero-pressure techniques, the shell and cap material was chosen to be Stratofilm-430 (which was based upon the Stratofilm-420 developed for the ULDB program) a three-layer co-extruded film using the same resins as Stratofilm-420. The total film thickness is 10.2µ for the shell and 13.2µ for each of the two cap layers. Compared to traditional zeropressure balloon film, the Stratofilm-430 has higher strength and ductility at normal surface temperatures, making the shell better able to withstand dynamic launch loads.

Production of the balloon, unofficially christened the ''Big 60", required some minor rearrangement of production space to accommodate the almost 230 meter gore length. Fabrication of the balloon was relatively straightforward and uneventful due to its similarity to standard zeropressure designs. Because of the delicate film, special considerations were made for the processes of expelling excess air and loading the balloon.

The first test conducted during the summer 2002 campaign at Lynn Lake was uneventfull. After a successfull launch the balloon climbed to a peak altitude of 49.4 km, and was terminated normally after approximately 23 hours of flight time.

This was the largest balloon ever successfully flown, setting a new world record that remained unbeated from 1975.

External references

Images of the mission

Hang test of the LEE payload The gigantic balloon ready to be launched Distant view of the flight line    

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