| Description: | Item donated to BBML: meteorological equipment retrieved from the 1991 Ballooning Over Everest expedition: Vaisala RS80 lightweight radiosonde balloon transmitter
This very compact and lightweight RS80 radiosonde has already been flown around extensively in 1991-not underneath its helium-filled latex balloon, but by airliner from London to Kathmandu, then by a DH Twin Otter to Lukla, and then on the back of a yak all the way up the valleys of the Khumbu to Martin Harris' weather station established in 1991 in the hamlet of Gokyo at 15,000 ft. amsl. in the Everest National Park, to support the hot air balloon flights by pilots Chris Dewhirst and Andy Elson directly over the summit of Mount Everest, to land afterwards in the Tibetan plateau. The 1991 film of "Ballooning Over Everest", available on YouTube, retells some aspects of this extraordinary ballooning expedition's story, and includes a few seconds on the launch of one of these RS80 radiosondes, for which this one was a spare, tested and ready for flight, but not launched.
Gokyo was chosen as a likely good take-off point for the two hot air balloons because in autumn it is sometimes directly upwind of the summit of Mount Everest, but knowing when that happy coincidence of an upper wind from that precise direction will occur is of critical importance, and furthermore, a wind fast enough to carry the hot air balloons far beyond the highest mountains for a safe landing in Tibet before their propane fuel would run out. The wind data sent back by the radiosondes was vital. The pilots' flight plan involved a fast climb out of the valley, where local valley winds might otherwise pull the hot air balloons away from their ideal trajectory, to enter airflow heading directly towards the summit of Everest at around 30,000 ft. amsl., and then to climb to around 32,000-33,000 ft. amsl, to provide what was considered to be a safe enough altitude separation from the turbulent lee vortex which is known to develop over the eastern steep lee slopes of the mountain in strong winds from the west.
To be reasonably certain of the wind direction and wind speed over the summit prior to the take off of the two piloted hot air balloons, the meteorological support plan was to send up one of these RS80 radiosondes to about 40,000 ft.amsl. twice each day when the balloon pilots were ready on standby and waiting for suitable weather, with one of these radiosonde ascents made soon after dawn, so that a decision could be taken early on for the hot air balloon team to either begin their preliminary preparations, for a take-off for Everest early on the next day, or if the wind data received from the radiosonde was far outside the desired values for the hot air balloon flights, to stand everyone down and relax, at least until data from another radiosonde ascent later on had either confirmed or conflicted with the early data. The radiosonde's initial reported positioning data was also checked visually. This tiny RS80 unit contains a Geographical Positioning System, using US communications satellites, which reported its 3-dimensionsl position to the expedition base station in Gokyo by radio at very frequent intervals, so that it was possible not only to know the general wind direction as it ascends through each altitude level, but also if there is any directional shear or turbulence between any of these layers. The radiosonde base radio station inside a little hut in Gokyo, was the most advanced available, borrowed from the military, and it ran off a Honda generator, received the GPS data, and then output data as an observed vertical profile of wind speed and direction, and it also cleverly generated a coded signal which Martin could then send, using a borrowed Inmarsat radio facsimile machine, to the UK Met. Office in Bracknell, where it generated enormous interest as no one had ever before sent radiosondes over the summit of Mount Everest. To save the full data set sent back by the RS80 before it disappeared over the top of Everest, its signals were also recorded on tape cassettes using a high-end Nakamichi professional tape recorder, borrowed from Oxford Scientific Services. All this equipment survived its long bumpy journey on a yak to Gokyo!
This particular RS80 was tested ready to fly, and it is complete, except for the battery which is normally inserted and connected to the power leads inside shortly before launch to test the radio link. It is a fine example of miniaturisation, with a minute temperature sensor and a very rudimentary but effective wire antenna, with one thin copper filament also wound into the nylon line which is used to suspend this sensing package a long way below the helium balloon to give it a smoother ride. However, the use of punched paper tape, still in the package here, with important calibration data for each individual radiosonde, for inputting this data into the computer in base station receiver, is a sign that this early 20th century data transfer system was still in use even in 1991. Nevertheless, the interpretation of the data from these RS80 radiosondes, coupled with the interpretation of the satellite cloud pictures received from overflying US weather satellites, was fundamental to making the first ever manned balloon flights over Everest successful so that everyone was able to walk away afterwards . Specification sheet here. |
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