[meteorite-list] Starshine 2 Return

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:50:29 2004
Message-ID: <200204252341.QAA24952_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2002/25apr_starshine2.htm

Starshine 2 Return
NASA Science News

A glittering satellite named Starshine 2 will disintegrate in Earth's
atmosphere on April 26th.

April 25, 2002: For some months now sky watchers have occasionally looked up
and seen a curious flashing light in the sky. Pulsing as brightly as a first
magnitude star, it would appear, race across the heavens, and be gone in a
matter of moments. A high-powered telescope -- if one could be made to track
the fast-moving thing -- would reveal a half-meter wide sphere, spinning and
studded with sunlight-reflecting mirrors. A disco ball in space.

In fact, it's a satellite. Scientists and the students who helped them build
it call the orb "Starshine 2." It was carried to Earth-orbit by NASA's space
shuttle Endeavour in Dec. 2001. But now, only five months later, Starshine 2
is falling back to Earth. Experts say it will disintegrate in the atmosphere
like a vivid meteor on April 26th.

"I'm thrilled," says Gil Moore, the director of Project Starshine. "This is
exactly what Starshine 2 is supposed to do."

Project Starshine is a consortium of volunteers supported by the US Naval
Research Laboratory, the Space Grant Program, and NASA. Together, they work
to involve school-age kids in cutting-edge research. Starshine 2 is one of
their many successes.

The satellite, which is dotted with mirrors ground by thousands of students,
is on a mission to explore the outermost reaches of our planet -- a
super-thin layer of the atmosphere called the thermosphere. The thermosphere
is so thin (1012 times less dense than air at sea level) it seems more like
a part of space than a part of Earth. Indeed, many Earth-orbiting satellites
are inside it.

"There's a lot we don't about the thermosphere -- particularly how it
responds to solar activity," says Moore. "Starshine 2 is helping us
understand that by falling back to Earth."

He explains: "As satellites skim through the upper atmosphere, sparse
molecules of air nip away at their kinetic energy little by little." This
"aerodynamic friction" causes all spacecraft in low-Earth orbit to fall.
Even the International Space Station sinks, albeit slowly, and must
occasionally be reboosted to counteract the drag.

If the thermosphere were steady, figuring out the decay rates of
Earth-orbiting spacecraft would be easy. But it's not. The thermosphere
expands and contracts in response to solar activity.

Last week, for example, explosions on the Sun hurled three coronal mass
ejections (or "CMEs") into space and toward Earth. When the electrified
clouds swept past our planet they warmed the thermosphere and caused it to
expand. (They also triggered beautiful Northern Lights.) The puffed-up
atmosphere exerted more drag than usual on Earth-orbiting satellites.

"By monitoring the orbit of Starshine 2, we can see how the thermosphere
responds to such events," says Moore.

When Starshine 2 was launched, Moore and colleagues expected it to return to
Earth in June. It's returning early because the Sun has been extra-active
during the first months of 2002. "The ongoing solar maximum is
double-peaked," explains Moore. "The first peak happened in 2000. The second
peak, which no one expected, coincided more or less with the launch of
Starshine 2 -- it was perfect timing!"

On April 26th Starshine 2 will sink below the stratosphere and disintegrate.
"The end will be spectacular," predicts Moore. If re-entry happens at night,
sky watchers will see a brilliant fireball -- much like a bright Leonid
meteor, only slower moving. No one will know exactly where the fireball will
appear until a few hours before the end; orbital decay is that
unpredictable. Click here for the latest re-entry predictions.

There's no danger to anyone on the ground, Moore assures. "We designed the
satellite so that it will be 100% consumed about 80 km up." Except for a few
small steel screws, the body of the spacecraft (including the mirrors) is
made entirely of aluminum -- a substance that will vaporize during the fiery
descent. "We had no choice," quips Moore. "Otherwise I was going to have to
buy a 100 million dollar insurance policy with a $50,000 premium." The
aluminum was cheaper.

The end of Starshine 2, welcomed as it is by researchers, might seem a sad
occasion for the many school kids who helped grind and polish its glittering
mirrors and who have tracked it faithfully for months. But it's not the end
of Project Starshine. Indeed, Starshine 2's larger cousin Starshine 3
(launched aboard a Kodiak Star rocket in Sept. 2001) remains in orbit around
our planet. It won't likely descend until October or November 2002.
Meanwhile, Starshine 4 and Starshine 5 are slated to launch on board a NASA
shuttle early next year.

The truth is, many kids, including kids-at-heart like Gil Moore, love the
idea that they helped make a fireball. They'll gladly do it again and again
(indeed, Moore has plans for Starshine 6 and beyond). And if scientists can
learn something by it, so much the better.
Received on Thu 25 Apr 2002 07:41:24 PM PDT