Third Time is a Charm: Stardust-NExT Heading Home Once Again
After being placed in hibernation, the Stardust spacecraft has begun a new journey to resurvey comet Tempel 1. In preparation for the Feb. 14, 2011 encounter with comet Tempel 1, the spacecraft team is performing a few housekeeping activities. One of those activities is to take a series of images to calibrate the navigation camera’s performance.
Before taking the calibration images the Stardust-NExT team first needed to clean up the camera’s optical path. During the original Stardust mission, contamination was observed on the camera’s lens during a post-launch calibration test. The contamination was minimized by heating the camera’s optical path by maneuvering the spacecraft to place the sun on a radiator that is connected to the camera via a thermal strap. The spacecraft dwelled at this attitude for approximately 30 minutes and “baked” the camera, in anticipation of the encounter with comet Tempel 1, the Stardust-NExT team conducted a similar “bake” prior to the calibration images and is in the process of comparing it against the previous data set collected from 2003. Though not necessary at this point in the mission, the calibration images will allow scientists to be better prepared for images taken at encounter, allowing for better knowledge of the cameras performance and capabilities.
Another Tempel 1 preparation task is to image the moon at 55 hours before closest approach during the Earth flyby. These images will be taken both on and off the periscope. A concern exists that one of the two reflecting surfaces that make up the periscope may have suffered pitting due to dust during the Wild 2 encounter in 2004. If the surface is pitted, it may impact how to capture images during the Tempel 1 encounter. These images will confirm the usability of the periscope.
Getting Ready to Swing by Earth
|Artist rendering of Stardust-NExT spacecraft approaching Earth's gravitational pull, resulting in accelerating of spacecraft and bending of flight path. Credit: NASA|
On January 14, 2009, Stardust-NExT flew by Earth approximately 5713 miles (9200 kilometers) from the Earth’s surface at 19:40 UTC (12:40 pm PST) as it received a gravity assist from the planet. + See fly by animation
A gravity–assist works like this: when a spacecraft closely approaches a planet, the planet’s gravitational pull accelerates the spacecraft and bends the flight path. Mission designers account for this extra pull and use it to their advantage to boost spacecraft speed and direct interplanetary spacecraft to their targets. Like a windup before the pitch, the Earth gravity-assist slung Stardust-NExT into the right path to meet comet Tempel 1. Because of the spacecraft’s distance from the Moon, its gravity had essentially no influence on the spacecraft’s flight path.