But one spacecraft, the European communications satellite OLYMPUS, could not take precautionary measures. OLYMPUS already had been dealt an unlucky blow by a sporadic meteoroid, which disabled one solar array's pointing system. So OLYMPUS was stuck facing the oncoming Perseid stream.
At its 1993 peak, rates for the Perseid meteor shower reached about 350 meteors per hour, or more than 3 times normal. One of those dust-size pieces of comet fluff struck OLYMPUS' jammed array.
You might imagine the meteor would put a hole in the solar panel and leave the rest of the satellite undamaged, and it is, indeed, true the meteor probably left a crater of some sort on the array surface. But, another effect, one engineers had not previously considered, caused the spacecraft's demise.
Spacecraft solar arrays generate electricity when exposed to sunlight, and so they have an electrical charge. The meteoroid vaporized when it struck the array, generating a small cloud of electrically charged gas. This plasma acted like a wire, allowing electrical charge on the array to move into the spacecraft's attitude control electronics.
OLYMPUS tumbled wildly. By the time operators regained control, the satellite's attitude-control fuel was exhausted, and its useful life was over. By month's end, the satellite was moved to a "graveyard orbit" and shut down. OLYMPUS had been "killed" by a Perseid.
Much to the relief of satellite operators, this year's Perseids will not outburst like in 1993. Although an increased activity was predicted earlier this year (and is reported in Astronomy
issue), more detailed calculations no longer show this component. Rates will be normal, peaking at about 100 meteors per hour around 11:54 P.M.
EDT on the night of August 11. This is just after the setting of the First Quarter Moon, so the best part of the shower will occur in a darkened sky.
Observers in England and western Europe are best placed for the maximum, as Perseus will be high in the pre-dawn sky. However, the shower will not disappoint skywatchers on the other side of the Atlantic, where observers may see as many as 80 meteors per hour between 4 and 6 A.M.
Go out after moonset, lie down on a comfortable lawn chair, sleeping bag, or blanket, and enjoy nature's fireworks.
And be grateful for the atmosphere's protection. Satellites — and future lunar explorers — will have to make do without it.