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Aviation History
2001
2001 - 0117.PDF
SPACEFLIGHT ESA ponders Huygens recovery TIM FURNISS/LONDON A EUROPEAN SPACE Agency X\(ESA) investigation board has identified 10 recovery options to overcome a communications error on the Huygens mission to Saturn. The fix is intended to ensure that all the Huygens probe's data trans missions from the vicinity of Saturn's moon Titan in 2004 can be collected by the receiver on the NASA Cassini mother ship, which will transmit the data to Earth. A decision on which option to take has to be made by May to enable NASA to change Cassini's mission. The board, established follow ing the discovery of the communi cations error during tests last February, has criticised the "entire structure" of the European Huygens project. During the tests it was discov ered that the Doppler shift - the change in the apparent frequency and the wavelength of sound, light and otherwaves due to the motion between the Huygens lander and Cassini - caused the data signal from Huygens to fall outside the bandwidth of a component in the Doppler shift is causing communications problems Cassini receiver. The Cassini receiver's bandwidth is too narrow to collect all of the data from Huygens, which will change its velocity during a planned 2.5h Titan descent. Huygens and Cassini were launched in October 1997. Cassini is due to enter an initial orbit of Saturn on 1 July 2004 for an extended orbital tour of the planet and some of its 28 known moons. Huygens will be released on 6 Nov ember 2004, with Cassini in a slightly higher orbit. Huy gens is scheduled to descend into Titan's atmosphere on 27 November, while Cassini flies past, collecting atmospheric and surface data from Huygens. Options include raising Cassini's final approach to Saturn to at least 50,000km (31,000 miles) instead of the planned 1,200km, which would "solve the entire probe receiver Doppler problem". However, this would hamper Cassini's multi-orbital "tour" of Saturn's rings and moons. Other options would not entire ly correct the error. One is to ensure that wind direction and velocity in Titan's atmosphere which might affect Huygens' speed and direction is known before the landing attempt, and that modifi cations are made to communica tions parameters. Other options are: altering the clock bias on Cassini's receiver; reducing the planned pendulum motion of the Huygens lander's descent under a parachute; reduc ing the communications distance between the two spacecraft and delaying the release of Huygens; performing the mission during one of the later orbits of Saturn; and redesigning the first Cassini orbits ofSaturn. The investigation board was unable to find any direct reference to Doppler shift in original mission specifications and the issue did not surface in any ESA, NASA or inde pendent project reviews, it says. "Had anyone on the receiver design team at Alenia, Alcatel, ESA or NASA's Jet Propulsion Laboratory asked about the effect of Doppler on the data stream, the problem would probably have been discovered in time," it says. • Isidis site selected for Beagle 2 Mars landing THE UK'S Beagle 2 spacecraft will land on Isidis Planita on Mars in December 2003, the European Space Agency (ESA) has announced. The $40 million Beagle 2, which is almost 50% funded by ESA, will be launched piggyback on the ESA Mars Express orbiter. Isidis Planita appears to be a sed imentary basin and the "best site given the landing constraints and scientific aims of Beagle 2", says John Bridges of London's Natural History Museum. Isidis lies between 5° and 20°N. The landing site is located close to 10°N, which will be warm enough in the Martian spring when Beagle is due to land, and without too many rocks to spoil the landing. The site, in an area about 500km (310 miles) long by 100km wide, was selected from high resolution images taken by NASA's Mars Global Surveyor orbiter. Other potential sights were eliminated because they would be too cold for the craft's instruments, too rocky or too steep. 4 • NASA has exercised a $68 million contract option with Boeing for the Delta II Jaunch of the second Mars Exploration Rover in June/July 2003. The Mars Expedition Rover 1 launch had already been assigned for another NASA 2003 Mars mission which was cancelled after a restructure of the agency's Mars programme. • •.^idlliiJMIL'WII^L'IH.l'id No Date Spacecraft 71 10 Nov GPS BlockllF 72 16 Nov PAS 1R+ 73 16 Nov Progress Ml-4 74 20 Nov QuickBird 1* 75 21 Nov E0-1+ 76 21 Nov Anik Fl 77 30 Nov Sirius 3 78 1 Dec Endeavour 79 5 Dec Eros Al 80 6 Dec NRO 81 19 Dec Astra 2D & GE 8 82 20 Dec Beidou ,I:MIM!IIII ii: Type Navsat Comsat Tanker Earth obs Earth obs Comsat Comsat ISS Rem sens Classified Comsats Navsat Launcher Delta 1 Ariane 5 Soyuz U Cosmos 3M Delta II Ariane 44L Proton K STS97 Start 1 Atlas 2AS Ariane 5 LM3A Country USA Europe Russia Russia USA Europe Russia USA Russia USA Europe China + Also carried STRV lc and d and Amsat 3D. * Quick Bird re-entered, classed as launch failure. Also carried SAC-A and Munin. Tsyklon 3. launched 27 December, failed to place six Strela satellites into orbit Last Satellite Launch Log: Right International, 21-27 November 2000 Launch site Canaveral Kourou Baikonur Plesetsk Vandenberg Kourou Baikonur KSC Svobodny Canaveral Kourou Xichang Atlantis ready for launch after cable check STS 98 Atlantis has been cleared for launch on 19 January after an extensive evaluation of the ord nance cables of the solid rocket booster (SRB) separation system. The checks followed the discov ery of cable damage in the ord nance system of the left hand SRB attachment system. Atlantis was rolled out to launch pad 39A on 2 January, but a crawler transporter fault necessitated a return to the Vehicle Assembly Building. The roll-out was reset for 3 January. • FLIGHT INTERNATIONAL 9 - 15 January 2001 23
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