Data of the stratospheric balloon launched on 6/12/2005
For BLAST (Balloon-borne Large Aperture Sub-millimeter Telescope)
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Data of the stratospheric balloon launched on 6/12/2005For BLAST (Balloon-borne Large Aperture Sub-millimeter Telescope)
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Details of the balloon and launch operations
Launch site:European Space Range, Kiruna, Sweden Launch team: National Scientific Balloon Facility (NSBF) Balloon: Open balloon (zero pressure) Volume: Raven W 39.570.000 cuft - (0.8 mil) Serial number: W39.57-2-25 Flight identification number: 545N Campaign: - Payload weight: 3835 lbs Gondola weight: - Overall weight: 6000 lbs This flight was the first transatlantic launch in the frame of the agrrement signed between NASA and the SSC to use the Kiruna base to launch such missions by the american agency. The balloon was launched after various delays by bad weather on June 12th at 1:09 utc, by dynamic method using a launch vehicle called "Hercules". After a nominal ascent phase the float altitude of 128.000 ft was achieved. Then the balloon started a slow west drift over the Atlantic Ocean towards Northamerica. Althought the flight was scheduled to fly for 5-9 day, at the fourth day of travel was decided to end the flight when flying over Northern Canada because the balloon experienced a higher speed than anticipated. Had the flight continued, BLAST would have been carried across the Arctic Ocean so the Victoria Island was selected as the "point of no return" because the island is so large, that was the best place available to land the payload. The cutdown command was sent by satellite from the NSBF's Operations Center in Palestine, Texas, at 5:30 utc on June 16th. The gondola impacted ground at 6:15 utc on Victoria Island, 170 miles NW of Cambridge Bay (71º 9' - 110º 49'). The payload tipped over on impact but did not drag. Both onboard NSBF Iridium transceivers continue to transmit NSBF housekeeping data. The recovery of the gondola was achieved using a heavy lift helicopter. |
ImagesClick to enlarge.      © BLAST team, Swedish Space Corporation |
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Description of the payload or experiment
BLAST (Balloon-borne Large Aperture Sub-millimeter Telescope) Responsable institution: University of Pennsylvania Principal Investigator: Dr. Mark Devlin The BLAST instrument is composed by a telescope with a primary mirror near two meters in diameter and a 50 cm diameter correcting secondary mirror, mounted in a rigid support structure for the secondary. This secondary has been designed to give diffraction limited performance over a 14' x 7' field of view at the Cassegrain focus. The image detected by the telescope or better the radiation detected by the telescope pass through a vacuum window made of polypropylene near the Cassegrain focus and enters in the cryostat. The cryostat makes possible the radiation detected to be re-imaged onto the three detector arrays (bolometers) using a pair of mirrors arranged in a "Gaussian beam telescope" configuration, which corrects for aberrations in the main telescope, and provides a flat focal plane. The longer expected duration of flight demands that the cryostat operate for at least 14 days with the detectors at very low temperature so it requires 37 liters of liquid helium for cooling purposes, along with a separate miniature pumped Helium pot, and a Helium recycling refrigerator. The BLAST focal plane (detectors) consists of three bolometer arrays with 149, 88 and 43 detectors each at 250, 350, and 500 µm respectively. They are read out with an differential circuit and data is collected using a high-speed, flexible, 18-bit data acquisition system. All the instrument's parts are mounted in a structure formed by a precision-pointed inner frame (containing the primary mirror, secondary mirror, near-field baffle, and cryostat) supported by an external gondola. The outer frame will be pointed in azimuth by a flywheel and an active pivot. The inner frame has an elevation mount and is driven by motors relative to the outer frame. Balance of the inner frame will be achieved using actively positioned weights for differential buoyancy and cryogen blow-off. The cable-suspended gondola design is lightweight, with a high tensile strength and a high resonant frequency. By providing the first sensitive large-area submillimeter surveys at these wavelengths, BLAST looks to address some of the most important cosmological and Galactic questions regarding the formation and evolution of stars, galaxies and clusters. The main science goals include to measure photometric redshifts, rest-frame FIR luminosities and star formation rates of high-redshift starburst galaxies, thereby constraining the evolutionary history of those galaxies that produce the FIR/submillimeter background, also to measure cold pre-stellar sources associated with the earliest stages of star and planet formation and to make high-resolution maps of diffuse galactic emission over a wide range of galactic latitudes. A final goal is to observe solar system objects including planets, large asteroids, and trans-Neptunian objects. | ||||||||||||||||||||||||||||||||||||
Performance in flight and data obtainedThis was the first scientific flight of the instrument. After launch the ascent was rather slow, which was initially a problem since the instrument got really cold when going through the tropopause, freezing some of the electronics onboard. After some time at float, however, staring at the sun, things seems to have thawed out, and started working again. The other thing of note during ascent was the remaining charge in the flight batteries. Since was spent so long on the flightline before launch, the batteries got depleted more than anticipated so the ground team started pointing in azimuth significantly before got to float, in an attempt to keep the solar panels pointed at the sun. Later it turned out a very wise action so the instrument was able to recharge the batteries. The first hours while the balloon was in direct connection with the Kiruna base have been spent trying to characterise the telescope and made some quick sky maps. Others problems arose first when the internet connection in Kiruna died (it was vital to establish connection with the CSBF Texas site wich would be the only link with the gondola after loss the line of sight link) and also an electrical storm wich occured in Palestine, which brought the link to the gondola down for some time. At middle of the flight the ground team managed to obtain the first maps from the line-of-sight data, but they showed the sensitivity was lower than initially expected. That meant that they need to control the telescope manually from the ground rather than just letting it run automatically, something specially complicated due to the network link instability. Once over Canada the speed of the balloon remained high than expected forcing to cutting down the payload from balloon a day earlier than hoped and thus reducing the amount of data obtained. Once the balloon flown over Victoria Island the speed dropped dramatically, and the operation team in Palestine, Texas decided to delay termination allowing to find more fields to scan, but soon the groud team in Kiruna received a phone call from Texas asking for a shut down of BLAST for termination as quickly as they could: the balloon had taken an unexpected turn to the south, into an area of the island full of lakes, instead of the more northerly plateau oroginally planned for landing. The instument was turned off at once, locked and separated immediately from the balloon. |
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External references and bibliographical sources
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| If you detected mistakes in the information presented here, please tell me (Updated on 17-Aug-2007 - 03:27:11pm) | ||||||||||||||||||||||||||||||||||||
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