Forensic Sleuthing Ties Ring Ripples to Impacts-NASA's Information

scientists working with data from NASA's Cassini, Galileo and New Horizons missions have traced telltale ripples in the rings of Saturn and Jupiter back to collisions with cometary fragments dating back more than 10 years ago. The ripple-producing culprit, in the case of Jupiter, was comet Shoemaker-Levy 9, whose debris cloud hurtled through the thin Jupiter ring system during a kamikaze course into the planet in July 1994. Scientists attribute Saturn's ripples to a similar object – likely another cloud of comet debris -- plunging through the inner rings in the second half of 1983. The findings are detailed in a pair of papers published online today in the journal Science.

"What's cool is we're finding evidence that a planet's rings can be affected by specific, traceable events that happened in the last 30 years, rather than a hundred million years ago," said Matthew Hedman, a Cassini imaging team associate, lead author of one of the papers, and a research associate at Cornell University, Ithaca, N.Y. "The solar system is a much more dynamic place than we gave it credit for." From Galileo's visit to Jupiter, scientists have known since the late 1990s about patchy patterns in the Jovian ring. But the Galileo images were a little fuzzy, and scientists didn't understand why such patterns would occur. The trail was cold until Cassini entered orbit around Saturn in 2004 and started sending back thousands of images. A 2007 paper by Hedman and colleagues first noted corrugations in Saturn's innermost ring, dubbed the D ring.

When is an Asteroid Not an Asteroid?

German astronomer Heinrich Wilhelm Olbers spotted Vesta as a pinprick of light in the sky. Two hundred and four years later, as NASA's Dawn spacecraft prepares to begin orbiting this intriguing world, scientists now know how special this world is, even if there has been some debate on how to classify it. Vesta is most commonly called an asteroid because it lies in the orbiting rubble patch known as the main asteroid belt between Mars and Jupiter. But the vast majority of objects in the main belt are lightweights, 100-kilometers-wide (about 60-miles wide) or smaller, compared with Vesta, which is about 530 kilometers (330 miles) across on average. In fact, numerous bits of Vesta ejected by collisions with other objects have been identified in the main belt.

"I don't think Vesta should be called an asteroid," said Tom McCord, a Dawn co-investigator based at the Bear Fight Institute, Winthrop, Wash. "Not only is Vesta so much larger, but it's an evolved object, unlike most things we call asteroids." The layered structure of Vesta is the key trait that makes Vesta more like planets such as Earth, Venus and Mars than the other asteroids, McCord said. Like the planets, Vesta had sufficient radioactive material inside when it coalesced, releasing heat that melted rock and enabled lighter layers to float to the outside. Scientists call this process differentiation.

Work Stopped on Alternative Cameras for Mars Rover

NASA rover to be launched to Mars this year will carry the Mast Camera instrument already on the vehicle, providing the capability to meet the mission's science goals. Work has stopped on an alternative version of the instrument, with a pair of zoom-lens cameras, which would have provided additional capabilities for improved three-dimensional video. The installed Mastcam on the Mars Science Laboratory mission's Curiosity rover uses two fixed-focal-length cameras: a telephoto for one eye and wider angle for the other. Malin Space Science Systems, San Diego, built the Mastcam and was funded by NASA last year to see whether a zoom version could be developed in time for testing on Curiosity.

"With the Mastcam that was installed last year and the rover's other instruments, Curiosity can accomplish its ambitious research goals," said Mars Science Laboratory Project Scientist John Grotzinger, of the California Institute of Technology, Pasadena. "Malin Space Science Systems has provided excellent, unprecedented science cameras for this mission. The possibility for a zoom-camera upgrade was very much worth pursuing, but time became too short for the levels of testing that would be needed for them to confidently replace the existing cameras. We applaud Malin Space Science Systems for their tremendous effort to deliver the zooms, and also the Mars Science Laboratory Project's investment in supporting this effort." Malin Space Science Systems has also provided the Mars Hand Lens Imager and the Mars Descent Imager instruments on Curiosity. The company will continue to pursue development of the zoom system, both to prove out the design and to make the hardware available for possible use on future missions.

NASA Stardust Spacecraft Officially Ends Operations

NASA's Stardust spacecraft sent its last transmission to Earth at 4:33 p.m. PDT (7:33 p.m. EDT) Thursday, March 24, shortly after depleting fuel and ceasing operations. During a 12-year period, the venerable spacecraft collected and returned comet material to Earth and was reused after the end of its prime mission in 2006 to observe and study another comet during February 2011.

The Stardust team performed the burn to depletion because the comet hunter was literally running on fumes. The depletion maneuver command was sent from the Stardust-NExT mission control area at Lockheed Martin Space Systems in Denver. The operation was designed to fire Stardust's rockets until no fuel remained in the tank or fuel lines. The spacecraft sent acknowledgment of its last command from approximately 312 million kilometers (194 million miles) away in space. "This is the end of the spacecraft's operations, but really just the beginnings of what this spacecraft's accomplishments will give to planetary science," said Lindley Johnson, Stardust-NExT and Discovery program executive at NASA Headquarters in Washington. "The treasure-trove of science data and engineering information collected and returned by Stardust is invaluable for planning future deep space planetary missions."

After completion of the burn, mission personnel began comparing the computed amount of fuel consumed during the engine firing with the anticipated amount based on consumption models. The models are required to track fuel levels, because there are no fully reliable fuel gauges for spacecraft in the weightless environment of space. Mission planners use approximate fuel usage by reviewing the history of the vehicle's flight, how many times and how long its rocket motors fired.

NASA's Venerable Comet Hunter Wraps up Mission

At 33 minutes after 4 p.m. PDT on 24-3-2011, NASA's Stardust spacecraft finished its last transmission to Earth. The transmission came on the heels of the venerable spacecraft's final rocket burn, which was designed to provide insight into how much fuel remained aboard after its encounter with comet Tempel 1 in February. "Stardust has been teaching us about our solar system since it was launched in 1999," said Stardust-NExT project manager Tim Larson from NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It makes sense that its very last moments would be providing us with data we can use to plan deep space mission operations in the future."

The burn to depletion maneuver was designed to fire Stardust's rockets until insufficient fuel remains to continue, all the while downlinking data on the burn to Earth some 312 million kilometers (194 million miles) away. Mission personnel will compare the amount of fuel consumed in the burn with the amount they anticipated would be burned based on their fuel consumption models. Fuel consumption models are necessary because no one has invented a reliable fuel gauge for spacecraft when in the weightless environment of space flight. Until that day arrives, mission planners can approximate fuel usage by looking at the history of the vehicle's flight and how many times and for how long its rocket motors have fired. Mission personnel watched the final data from the burn come down at JPL's Space Flight Operations Facility and at the Stardust-NExT mission support center at Lockheed Martin Space Systems in Denver.

NASA's Stardust: Good to the Last Drop

On Thursday, March 24 at about 4 p.m. PDT (7 p.m. EDT), NASA's Stardust spacecraft will perform a final burn with its main engines.

At first glance, the burn is something of an insignificant event. After all, the venerable spacecraft has executed 40 major flight path maneuvers since its 1999 launch, and between these main engines and the reaction control system, its rocket motors have collectively fired more than 2 million times. But the March 24 burn will be different from all others. This burn will effectively end the life of NASA's most traveled comet hunter.

"We call it a 'burn to depletion,' and that is pretty much what we're doing – firing our rockets until there is nothing left in the tank," said Stardust-NExT project manager Tim Larson of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's a unique way for an interplanetary spacecraft to go out. Essentially, Stardust will be providing us useful information to the very end."

Burn to depletion will answer the question about how much fuel Stardust had left in its tank. "We'll take those data and compare them to what our estimates told us was left," said Allan Cheuvront, Lockheed Martin Space Systems program manager for Stardust-NExT. "That will give us a better idea how valid our fuel consumption models are and make our predictions even more accurate for future missions."

Next Mars Rover Gets a Test Taste of Mars Conditions

A space-simulation chamber at NASA's Jet Propulsion Laboratory, Pasadena, Calif., is temporary home this month for the Curiosity rover, which will land on Mars next year.
Tests inside the 25-foot-diameter chamber (7.6-meters) are putting the rover through various sequences in environmental conditions resembling Martian surface conditions. After the chamber's large door was sealed last week, air was pumped out to near-vacuum pressure, liquid nitrogen in the walls dropped the temperature to minus 130 degrees Celsius (minus 202 degrees Fahrenheit), and a bank of powerful lamps simulated the intensity of sunshine on Mars.

Other portions of NASA's Mars Science Laboratory spacecraft, including the cruise stage, descent stage and backshell, remain in JPL's Spacecraft Assembly Facility, where Curiosity was assembled and where the rover will return after the simulation-chamber tests. In coming months, those flight system components and the rover will be shipped to NASA's Kennedy Space Center in Florida for final preparations before the launch period of Nov. 25 to Dec. 18, 2011.




The mission will use Curiosity to study one of the most intriguing places on Mars -- still to be selected from among four finalist landing-site candidates. It will study whether a selected area of Mars has offered environmental conditions favorable for microbial life and for preserving evidence about whether Martian life has existed.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Science Laboratory mission for the NASA Science Mission Directorate, Washington.

MESSENGER Begins Historic Orbit Around Mercury

NASA’s MESSENGER spacecraft successfully achieved orbit around Mercury at approximately 9 p.m. EDT Thursday. This marks the first time a spacecraft has accomplished this engineering and scientific milestone at our solar system's innermost planet.

For the next several weeks, APL engineers will be focused on ensuring the spacecraft’s systems are all working well in Mercury’s harsh thermal environment. Starting on March 23, the instruments will be turned on and checked out, and on April 4 the mission's primary science phase will begin.

Prolific NASA Orbiter Reaches Five-Year Mark

NASA's versatile Mars Reconnaissance Orbiter, which began orbiting Mars five years ago on March 10, has radically expanded our knowledge of the Red Planet and is now working overtime.

The mission has provided copious information about ancient environments, ice-age-scale climate cycles and present-day changes on Mars.

The orbiter observes Mars' surface, subsurface and atmosphere in unprecedented detail. The spacecraft's large solar panels and dish antenna have enabled it to transmit more data to Earth -- 131 terabits and counting, including more than 70,000 images -- than all other interplanetary missions combined. Yet many things had to go well for the mission to achieve these milestones.

After a seven-month journey from Earth, the spacecraft fired its six main engines for nearly 27 minutes as it approached Mars on March 10, 2006. Mars could not capture it into orbit without this critically timed maneuver to slow the spacecraft. The orbiter's intended path took it behind Mars, out of communication, during most of the engine burn.