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A Disco Ball in Space

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A Disco Ball in Space


Marshall Space Flight Center





"Starshine 3 is on a mission to explore the outer reaches of Earth`s atmosphere and to discover what happens to satellites there," explains Prof. Gil Moore, the director of Project Starshine -- a unique program that combines cutting edge research with educational outreach.

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Starshine 3 is falling because the atmosphere is dragging it down.


Even though the thermosphere is practically vacuum-thin, it`s still dense enough to sap orbital energy from satellites by means of aerodynamic drag. Soon after the Kodiak Star disgorged it, Starshine 3 began to lose altitude -- dropping a few meters during each 90 minute orbit around our planet. The same thing happens to the ISS, which requires periodic re-boosts.

see caption beginning 'Starshine 1'

Above: Starshine 1, a beachball-sized cousin of Starshine 3, vaporized in Earth`s atmosphere last year. These data, courtesy of NRL`s Judith Lean, show how the satellite fell slowly at first, then with greater rapidity as it descended into lower (and denser) layers of Earth`s atmosphere.



see caption beginning 'magnetic fields loop'No one knows exactly when or where Starshine 3 will return because the thermosphere is unpredictable. Earth`s uppermost atmosphere "breathes" in and out in response to changing solar activity. During years (like 2000 and 2001) around the peak of the 11-year sunspot cycle, our star is a powerful and sometimes fitful source of extreme ultraviolet (EUV) radiation. Waves of EUV heat the thermosphere and cause it to "puff up," hastening the descent of falling satellites. Exploring the cause and effect relationship between solar activity and orbit decay is a primary goal of the mission.

Right: Magnetic fields loop above a sunspot group where hot gas glows brightly at extreme ultraviolet wavelengths. Such radiation heats our planet`s thermosphere and increases its drag on Earth-orbiting satellites. Credit: TRACE.

"We have very few direct measurements of the density of the upper atmosphere. That`s why Starshine 3 is so important," explains solar physicist Judith Lean of the Naval Research Laboratory (NRL) in Washington, D.C. "The satellite`s well-defined spherical geometry allows us to estimate its ballistic coefficient with a reasonable degree of certainty. As a result, by monitoring Starshine`s orbit and studying how that decays we can calculate the density of the gas that`s dragging it down."

Lean and her colleagues, led by NRL`s Mike Picone, are already using data from an earlier mission (Starshine 1, which orbited Earth for 8 months before it disintegrated in February, 2000) to predict the decaying trajectories of satellites and bits of orbiting space debris. Their calculations are of keen interest to ISS mission planners and shuttle pilots who fly through the swarm of Earth-orbiting objects. "We`re hoping that Starshine 3 will improve those predictions even more," says Gil Moore.

see captionBefore that can happen, though, someone must track the glittering satellite. Moore and his colleagues need to record about 800 sightings per day to define Starshine 3`s changing path.

It`s the perfect job for a legion of young scientists.

"We need students, teachers -- sky watchers of all kinds -- to go outside and spot Starshine 3 among the stars," says Moore. "The procedures for recording and reporting the data are straightforward. Anyone can do it. It`s a great science project and we hope many classrooms will sign up to participate."



"It`s beautiful," says Sharon Simon, a teacher at the Davis Creek Elementary School who saw the satellite glide over her town in West Virginia on October 2nd. "The flashes came in three quick segments that were clearly visible. [Each flash] was about as bright as Mars." (Visit to find out when Starshine 3 will glide over your town, suggests Moore.)

see captionSimon`s students helped polish Starshine 3`s mirrors, and their handwritten signatures are orbiting Earth on board the satellite. Indeed, the signature of every student who worked on the mirrors is up there -- all 40,000 of them laboriously digitized by Moore`s wife Phyllis. "That was hard work for Phyllis," recalls Moore. "But these youngsters are important to us -- they are a crucial part of what we`re doing."




Web Links

see caption beginning 'Layers of the Earths atmosphere'Project Starshine - Home Page -- this website to find out when Starshine 3 will glide over your town.

NASA`s J-Pass -- Another online resource to help you spot Starshine 3 from your own back yard.

Protecting Starshine -- All of Starshine 3`s student-polished mirrors were coated with a layer of silicon dioxide. "The silicon dioxide coating adds no reflectivity," says Vince Huegele, "but it does protect the mirrors from corrosion by atomic oxygen [a chemical constituent of the thermosphere]." Huegele works at the Marshall Space Flight Center`s Space Optics Manufacturing Technology Center where the essential coating was applied.

Solar S`Mores -- (Science@NASA) As a result of the solar maximum, Earth`s atmosphere is "puffed up" like a marshmallow over a campfire leading to extra drag on Earth-orbiting satellites.

Right:Layers of the Earth`s atmosphere. The troposphere is the first layer above Earth`s surface; it contains half of our planet`s atmosphere. Weather occurs in the troposphere. Many jet aircraft fly in the stratosphere because it is very stable. The stratosphere contains the ozone layer. Meteors burn up in the mesosphere. Auroras glow in the lower thermosphere; satellites like Starshine 3 and spacecraft like the Space Shuttle orbit in the upper thermosphere.

Starshine Returns to Cinder - (Science@NASA) Last year, Starshine 1, a beachball-sized cousin of Starshine 3, vaporized in Earth`s atmosphere after a successful 8-month mission exploring the thermosphere.


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