NASA identifies what hobbled Hubble.NASA NASA: see National Aeronautics and Space Administration.
in full National Aeronautics and Space Administration
Independent U.S. identifies what hobbled Hubble
Two errors -- one human, one mechanical -- worked in tandem Adv. 1. in tandem - one behind the other; "ride tandem on a bicycle built for two"; "riding horses down the path in tandem"
tandem to cripple crip·ple
One that is partially disabled or unable to use a limb or limbs.
To cause to lose the use of a limb or limbs. the Hubble Space Telescope's primary mirror, a NASA-appointed investigative team announced last month. But in contrast to the human goof -- upside-down insertion of a precision measuring tool into an optical system that guided mirror grinding -- the flawed construction of that measuring tool alone would have likely resulted in a defective primary mirror, says Roger Angel, a panel member and a telescope-mirror designer at the University of Arizona (body, education) University of Arizona - The University was founded in 1885 as a Land Grant institution with a three-fold mission of teaching, research and public service. in Tucson.
Hubble's mirror makers used laser light and the precision measuring tool -- called a metering rod -- to determine how far apart to space two components of the grinding guide, a device known as the reflective null corrector (SN: 7/21/90, p.39). Measuring distances this way should have provided far greater precision than using a micrometer micrometer (mīkrŏm`ətər, mī`krōmē'tər).
1 Instrument used for measuring extremely small distances. . However, the technique required passing a laser beam through a tiny hole in a nonreflecting sleeve capping one end of the precision metering rod, so that the beam would bounce off the rod and not its sleeve. And in cutting the millimeter-sized hole in that sleeve, technicians accidentally chipped the cap's nonreflecting coat. This caused the laser beam to erroneously bounce off both the sleeve and the rod. The extra signal returning from the sleeve confused scientists, and inadvertently led them to improperly position the null corrector's components.
Human error appears to have confounded the spacing error, the panel notes. Accidentally inverting the metering rod before capping it -- so that the sleeve loosely covered the opposite, more poorly machined end -- caused scientists to place the test lens and small mirror in the null corrector 1.3 millimeters farther apart than intended, Angel says. Those errors, the panel says, led to the spherical aberration spherical aberration: see aberration, in optics. that today renders Hubble's primary mirror virtually useless -- without corrective lenses -- for resolving faint, distant objects in the universe.
As the NASA panel prepares its final report, due next month, it will examine how the measuring error escaped detection. Several clues that were dismissed or ignored hinted something might be awry a·wry
1. In a position that is turned or twisted toward one side; askew.
2. Away from the correct course; amiss. See Synonyms at amiss. , Angel told SCIENCE NEWS. Examples he cited include a test of the reflective null corrector that spotted what appeared to be errors in its assembly, and measurements taken with a second type of null corrector indicating that the primary mirror was indeed misshapen mis·shape
tr.v. mis·shaped, mis·shaped or mis·shap·en , mis·shap·ing, mis·shapes
To shape badly; deform.