Software that let children follow Santa's Christmas Eve trek last year may give satellite makers a heads up this fall when a major meteor shower is expected to hit.
The 3-D visualization tool developed by Analytical Graphics will allow users to create simulations of events in space, such as a meteor shower, to see how to best position their equipment to avoid any damage or outage. Companies, mindful of the Galaxy IV outage in May, are using the software to sort out how the coming Leonid meteor shower –- a celestial event that occurs every November -– might affect their orbiting satellites.
Using information gleaned from a simulation, a satellite maker could, for example, decide to turn sensitive instruments to point away from the direction of the storm, noted James Woodburn. "You'll know where your satellites are and where the meteors generally come from, so you can re-orient your craft to reduce the chances of a collision," said Woodburn, chief orbital scientist for Analytical Graphics.
Tracking the Leonid shower is one of a growing stable of commercial applications for the visualization tool. Before 1996, the software -– which has no real commercial name other than the Satellite Toolkit Family –- was used almost exclusively by the military. Over the last two years, the commercial sector has been knocking on Woodburn's door to see about using the software.
For example, when engineers for Hughes Global Services decided to retrieve a wayward communications satellite last spring, they used the visualization software to determine how to best orient the craft to take advantage of the moon's gravitational force to send it into a useful orbit. Their efforts were successful, but Woodburn doesn’t give all the credit to his software. "There are no guarantees," he said.
There will be no guarantees for avoiding collisions with meteors, either, Woodburn noted. That's because creating the simulation is much like solving an algebra problem, finding values for variables to determine a path. The values for a problem -- such as helping a satellite avert a collision with a meteor -- are mostly known. The satellite makers will know roughly where their satellites are at any given time, thanks to the cataloging by the North American Aerospace Defense Command (NORAD).
Meteor showers also provide values to plug into the equation. Meteor showers result from the break up of a comet as it travels around the sun. The part of the comet closest to the sun breaks off as a result of the energy from the sun, sending particles of dust and ice into space. The particles follow the general trajectory of the comet, with some bits straying ahead while others straggle behind. Scientists can estimate the direction of the shower because they know where the comet originated in space. In the case of the Leonid shower, the comet Tempel-Tuttle originates at the constellation Leo.
But one important value -- where the meteors are headed -- is missing. Because the particles are smaller, and therefore weigh less than the comet, they are more vulnerable to the gravitational energy from the sun and other celestial bodies. Such forces can send the meteors scattering in different directions.
The Leonid shower is significant because the orbit of comet Tempel-Tuttle passes close enough to Earth's orbit to be of worry or interest, said Donald Yeomans, senior research scientist at NASA's Jet Propulsion Laboratory (JPL).
One gauge of this interest is the fact that civilizations have recorded the Leonids for thousands of years. Yeomans, who is considered one of the top experts in the study of meteors and comets, has examined historical records dating back to 902 AD. Records kept by the Japanese, Chinese, and the Europeans contained notes dated at times corresponding to the Leonid time frame of November.
The notes would describe events where "stars fell like rain," Yeomans said. From the data, Yeomans said he could extrapolate the orbits of the comet. The closer the orbit, the greater the chance for a heavy meteor shower. And the greater the meteor shower, the greater the chances for a collision with a satellite or other spacecraft.
Woodburn said Analytical Graphics is using data from JPL to help the satellite makers.
The data will allow Yeomans to extrapolate more than the comet's orbits over time. He will also see the chain of events that trigger a large meteor shower. For example, roughly every 33 years, the comet Tempel-Tuttle returns to the inner solar system early in the year. Each time, the resulting meteor shower is very heavy, Yeomans said.
Astronomers are interested in the coming Leonid shower because comet Tempel-Tuttle returned to the inner solar system in February and again in March, signaling that there is likely to be a large shower. Typical meteor showers generate 15 to 20 meteors per hour. But the size of a large shower varies, depending upon the proximity of the orbits.
For example, the showers of 1931 and 1932 generated 200 meteors per hour. Thirty-five years later in 1966, the Leonid shower generated up to 150,000 meteors per hour. In the latter event, the orbits of the Earth and comet were separated by roughly 33,000 miles. This time, the Earth is three times farther from Tempel-Tuttle’s orbit.
It is with this perspective that Yeomans believes the coming shower isn't likely to cause collisions between satellites and meteors. "It's a bit of a non-issue," he explained. "That said, if you have a multimillion-dollar craft like Hubble, you'll want to take precautions."
Software such as the visualization tool from Analytical Graphics can help companies understand how they can take precautions, Yeomans noted, adding that NASA will back Hubble into the direction of the storm to protect its delicate optical instruments.
