Sky & Telescope July 1985 [antikvár]

Spacelab 2: A PreviewKarl G. Henize, NASA-Johnson Space Center, Houston, TexasEighteen flights of the Space Shuttle have taken place over the last four years. The 19th Spacelab 2 is the first dedicated primarily to astronomy. It carries an outstanding payload, including telescopes for deep-space observation, telescopes for solar studies, and instruments for probing the Earth's ionosphere. But before we delve into the scientific details, there are some peculiarities about this astronomy mission that deserve explanation.Strange as it may seem, Spacelab 2 is actually the third mission to be flown in this series. It was originally scheduled to fly in mid-1984, but the redesign of a major piece of equipment caused the mission to slip past Spacelab 3, which flew in May. Now our launch aboard the shuttle Challenger, pending last-minute delays, is set for July 12th.Another peculiarity is that the shuttle will not be carrying the pressurized module that most people identify with Spacelab missions. Instead, Challenger's cargo bay has been filled with instruments that are operated via computers from within the shuttle cabin. However, the payload com-puters, the pallets on which the telescopes are mounted, the instrument-pointing system, and the accompanying electrical system are all standard components of the Spacelab system, as designed and built by the European Space Agency (ESA). In return for supplying this equipment, the Europeans became full partners in the first Spacelab mission, which took place in December, 1983 {ST: July, 1984, page 18). However, except for the two British telescopes aboard, Spacelab 2 is strictly an American mission.July's payload includes four telescopes for studying the Sun, a dual X-ray telescope for studying clusters of galaxies, and a helium-cooled infrared telescope for studying interstellar clouds and other extended sources. Also included is a gargantuan cosmic-ray detector, the largest ever used in space. Three experiments will probe the Earth's ionosphere and the shuttle's interaction with it.There are also two life-science packages aboard: one to examine the vitamin D chemistry of human blood under zero-g conditions, and another to study how pineseedlings sense gravity and respond to it. A 13th experiment (if you've been keeping count) is to study the physical properties of superfluid helium, a key substance for scientific work both on Earth and in space, that exists only within 2° Kelvin of absolute zero (-455° Fahrenheit).One of the more intriguing of Spacelab's experiments is a solar telescope that combines the ability to make very detailed images with a sophisticated, tunable narrowband filter. It will be used to map magnetic and Doppler-induced velocity fields over small areas of the Sun in visible light, then create and display these maps to the crew within a few seconds. This optical system is the first to view the Sun in greater detail than that possible with earth-bound telescopes. Its main objective is to determine how minuscule solar features are related to magnetic fields, thus shedding light on how the magnetic field at the Sun's surface originates and is controlled. The high-resolution, computer-generated maps give the rather exciting possibility of letting us make real-time discoveries through simple visual observation aCosmic-ray detectorSpacelab 2 PayloadHard X.ray imaging instrumentSolar magnetic- and velocity-field measurement systemHelium-cooled IR telescopeSuperfluid.tielium experimentPlasma diagnostics packageCoronal helium abundance experimentVerification flight InstrumentationSolar UV high.resolutlon telescope/spectrograph Solar UV spectral Irradiance monitorUnlike the previous missions in the series, Spacelab 2 does not involve a pressurized crew module. Instead, die Arbiter's payload bay contains a tram of modularized pallets on which various experiments are mounted. NASA-Marshall diagram.