First published Summer 2011, Crosslink® magazine.


In Defense of the Planet

Earth has been struck by asteroids numerous times in its history—sometimes with devastating effects. Is another major collision overdue? The International Academy of Astronautics held a conference in May 2011 to explore the potential of an asteroid collision and the prospects for avoiding such disasters. William Ailor, principal scientist in the Vehicle Systems Division, cochaired the conference.

The good news: observers find no near-term future threats of a one-kilometer or larger “planet killer.” However, smaller asteroids do pose a threat. “A small asteroid roughly 30 meters in size is big enough to take out a large city,” said Ailor. “There is a growing realization that we need to increase our efforts to find these small asteroids well before they might impact. But they are hard to see until they are fairly close to Earth, so the warning time may be very short.”

The world community is considering ways to prevent such collisions. One option would be to crash something into an asteroid, changing its velocity. This could be accomplished by a nuclear explosion, or by hitting the asteroid with a fast moving “bullet.” Another approach would use the tiny gravitational attraction between an asteroid and a spacecraft parked nearby to slowly pull the asteroid into a nonthreatening orbit.

The 2011 Planetary Defense conference was held in Bucharest, Romania. Aerospace has chaired or cochaired this conference since its inception in 2004, and this year’s was the fourth in the series. For more on potential collision risks, visit NASA’s Near Earth Object Program at http://neo.jpl.nasa.gov/risk/.



End of an Era

Space shuttle Discovery’s final launch from Cape Canaveral.

Space shuttle Discovery’s final launch from Cape Canaveral. Courtesy of NASA.

Space shuttle Discovery launched for the final time (STS-133) from Kennedy Space Center on February 24, 2011. The NASA shuttle and its six-person crew traveled to the International Space Station to deliver a new storage module, an equipment platform, and the first humanlike robot in space. Aerospace supported this last scheduled launch of Discovery.

“We performed studies to assess the risk of damage to the orbiter from foam debris, which became a potential issue when a seven-inch crack on the surface of the external tank was discovered during its first launch attempt. Our findings were used to quantify the risk to the shuttle, and helped clear it for flight to conduct its mission safely,” said Randall Williams, systems director, Civil and Commercial Launch Projects.

This launch marked the 39th flight for Discovery, which first flew in 1984. During its service life, Discovery made two return-to-flight missions and several satellite repair missions and launched the Hubble Space Telescope and Ulysses solar probe. It visited the International Space Station 13 times and spent 365 days in space. Discovery landed at Kennedy Space Center on March 9, 2011. Now retired, it will be displayed at the Smithsonian Institution in Washington, DC. NASA has announced where the other two shuttles will retire: Endeavour will go to the California Science Center, Los Angeles, and Atlantis to Kennedy Space Center, Florida.



Aerospace Nanosatellite Launched on Atlantis

The latest in a series of nanosatellites built by Aerospace was integrated onto the space shuttle Atlantis for the STS-135 mission which launched in July. David Hinkley of the Mechanics Research Department is the project manager. The Miniature Tracking Vehicle (MTV) is designed to serve as an orbiting reference for ground tracking systems. It will “demonstrate three-axis attitude control, solid rocket propulsion for orbit modification, adaptive communications, active solar-cell performance monitoring, and radio-occultation tomography in a nanosatellite platform,” said Siegfried Janson, senior scientist, Mechanics Research Department. MTV weighs just 4 kilograms and measures 5 × 5 × 10 inches; it was ejected shortly before shuttle reentry into a 340-kilometer orbit with an expected orbital lifetime of three to nine months, depending on solar activity, said Janson.

The nanosatellite will be controlled using a primary ground station at Aerospace and an Internet-based ground station network consisting of two additional antennas in U.S. territories. Two onboard GPS receivers will provide accurate time and position information to facilitate analyses of tracking errors. Multiple megapixel cameras took pictures of Atlantis as MTV left, thus supplying the last on-orbit photos of NASA’s workhorse space transportation system. MTV is the 12th Aerospace miniature spacecraft launched.



REBR Records Rocket Reentry

Ailor shows REBR

William Ailor shows the REBR instrument package nestled within its protective heat shield.

When the Japanese launch vehicle HTV2 reentered Earth’s atmosphere on March 29, 2011, it managed to send detailed information about its temperature, accelerations, and rotational rates as it disintegrated and burned up. That is because it carried a small device known as a reentry breakup recorder (REBR) designed and built by Aerospace. According to William Ailor, principal scientist in the Vehicle Systems Division and director of Aerospace’s Center for Orbital and Reentry Debris Studies, this event marked the first time that such data was collected during the planned breakup of a space object. “Prior to REBRs, there was no data to determine how spacecraft behave during reentry breakup,” said Ailor. “Now we will be able to predict more accurately which parts of the satellite will impact the surface as well as hazards posed by the surviving debris.” The data can aid in the design of space hardware that poses less of a hazard on reentry, he explained.

The HTV2 rocket launched in January 2011, and made its way to the International Space Station. It carried two REBRs; one remained attached to the HTV2, while the second was attached to the ATV2, a European spacecraft. As HTV2 reentered Earth’s atmosphere, the REBR attached to it broke away as designed, and at approximately 60,000 feet, transmitted data to receiving stations before crashing into the southern Pacific Ocean. The recorder was not designed to survive impact, but contained a GPS device to alert scientists to its location. Analysis of the data was expected to take six to eight weeks. The REBR launch and reentry test was coordinated by the Department of Defense’s Space Test Program.



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