Zee Media Bureau\Philaso G Kaping
Pasadena, California: NASA has released a schedule which will be implemented by Dawn spacecraft when it approaches the dwarf planet Ceres in late January 2015.
Not surprisingly, the time-table is packed with activities the space probe has to cover to fulfil its mission of studying the two biggest objects of the asteroid belt, the other being Vesta.
Dawn was launched in 2007 and reached the orbit of Vesta in July 16, 2011. After taking close-up images of the protoplanet, it broke free of Vesta’s gravity on September 5, 2012, and changed its course towards Ceres.
Bob Mase, Dawn`s project manager at NASA`s Jet Propulsion Laboratory, said the flight plan will be choreographed similar to the strategy that was successfully used around Vesta.
"This approach will build on that and enable scientists to make direct comparisons between these two giants of the asteroid belt."
Dawn will be captured by Ceres` gravity, possibly in late March or the beginning of April 2015, after which it will begin its study.
"We are expecting changes when we get to Ceres and, fortunately, we have built a very capable spacecraft and developed flexible plans to accommodate the unknowns," said Dawn`s chief engineer and mission director Marc Rayman. "There`s great excitement in the unexpected – that`s part of the thrill of exploration."
Here is NASA’s schedule for Dawn in 2015:
Dawn will make its first full characterisation of Ceres later in April, at an altitude of about 8,400 miles (13,500 kilometers) above the icy surface. Then, it will spiral down to an altitude of about 2,750 miles (4,430 kilometers), and obtain more science data in its survey science orbit. This phase will last for 22 days, and is designed to obtain a global view of Ceres with Dawn`s framing camera, and global maps with the Visible and Infrared Spectrometer (VIR).
Dawn will then continue to spiral its way down to an altitude of about 920 miles (1,480 kilometers), and in August 2015 will begin a two-month phase known as the high-altitude mapping orbit. During this phase, the spacecraft will continue to acquire near-global maps with the VIR and framing camera at higher resolution than in the survey phase. The spacecraft will also image in “stereo” to resolve the surface in 3-D.
Then, after spiraling down for two months, Dawn will begin its closest orbit around Ceres in late November, at a distance of about 233 miles (375 kilometers). The dance at low-altitude mapping orbit will be a long waltz -- three months -- and is specifically designed to acquire data with Dawn`s gamma ray and neutron detector (GRaND) and gravity investigation. GRaND will reveal the signatures of the elements on and near the surface. The gravity experiment will measure the tug of the dwarf planet, as monitored by changes in the high-precision radio link to NASA`s Deep Space Network on Earth.
At this low-altitude mapping orbit, Dawn will begin using a method of pointing control that engineers have dubbed "hybrid" mode because it utilizes a combination of reaction wheels and thrusters to point the spacecraft. Up until this final mission phase, Dawn will have used just the small thruster jets, which use a fuel called hydrazine, to control its orientation and pointing. While it is possible to explore Ceres completely using only these jets, mission managers want to conserve precious fuel. At this lowest orbit, using two of the reaction wheels to help with pointing will provide the biggest hydrazine savings. So Dawn will be spinning up two of the gyroscope-like devices to aid the thrusters.
