 |
 |
||
 |
|
||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
||||||||
 |
Space Topics: Lunar Reconnaissance Orbiter (LRO)LRO and LCROSS Enter their Respective Orbitsby Ken Kremer, June 26, 2009
On June 23, 2009, NASA successfully returned to Earth’s nearest neighbor with a pair of cutting edge robots. Four and a half days after blasting off from Cape Canaveral, both LRO and LCROSS arrived at the Moon within just a few hours of one another. It was all very reminiscent of the glorious days of the Apollo Moon landings far too long ago. LRO ignited its main engine to slow itself down, entering into polar orbit around the Moon. LCROSS, meanwhile, swooped past and around the Moon, traveling south to north along its far-side and entering into a polar Earth orbit, nearly perpendicular to the Moon’s orbit about Earth. Thanks to the success of these critical maneuvers, LRO and LCROSS will now proceed on entirely different trajectories for the crucial next steps of their science journey. LRO and LCROSS are designed to scout out the Moon's early history, create an atlas of current resources, and search for water. It is an unprecedented effort to pave the way for an eventual revisit by human explorers to the lunar surface by 2020. LRO entered lunar orbit after firing its breaking rocket for 40 minutes starting at 5:47 am EDT. The critical burn ended as planned at 6:27 AM. LRO was captured by the Moon and entered a highly elongated elliptical orbit. "All thrusters have stopped. All stations, this is flight. Congratulations on a successful LOI. LRO has returned NASA to the Moon", announced Flight Director Rick Saylor at NASA Goddard Spaceflight Center in Greenbelt, Md. The happy Mission Operations team at Goddard team broke out in a round of clapping, handshakes and hugs. The LRO Project manager at Goddard, Craig Tooley, said, “We have been captured by the Moon and we are ready to stay. We are in a 220 km x 3100 km polar lunar orbit. The tracking shows we're essentially where we planned to be. It went like clockwork. With a mission like this, we spent literally years practicing for every possible contingency to be ready for this. In the end, it went exactly as planned”. A sequence of 4 additional rocket burns were scheduled for the following four days to gradually lower the spacecraft and place it into its “commissioning orbit” of 30 km (18.5 mi) above the south pole and 216 km (134 mi) above the north pole for the next two months. Thereafter LRO will fire its engines once again, reduce its orbital eccentricity and entering into a near-circular polar for its one year primary mission. LRO's orbital altitude of around 50 km (31 mile) will be the lowest ever of any lunar spacecraft. LRO will make measurements to study the Moon in unprecedented detail with 7 science instruments. The spacecraft will map the Moon by collecting high resolution imagery to identify safe landing sites with smooth landing areas, use a laser altimeter to carefully measure topography, assemble a vast atlas of resources, and measure the temperature and radiation environment that could pose a hazard for future astronauts. “We already have two science instruments turned on, LEND and CRaTER, which measure radiation" Tooley said. "They were switched on during our transit out to the Moon. They are working well. The others will begin to be switched on in about a week in a methodical process to bring them on line and doing calibrations in orbit. Then we’ll begin observations over the next week." The team hopes to have the cameras operating in the next couple of weeks. Rich Vondrak, LRO project scientist said, “As soon as we get some images we will make them available to the public”. The cameras were not yet calibrated and operational during LOI. Both missions have an “extensive educational and public outreach campaign”. LRO carries a microchip with the names of 1.6 million people (including all Planetary Society members) as part of a public outreach program to “Send Your Name to the Moon”.
Meanwhile shortly after LRO entered lunar orbit, the Lunar Crater Observation and Sensing Satellite (LCROSS) was following closely behind to begin its gravity-assisted swing-by of the Moon. The maneuver was designed to radically alter the spacecraft's orbit and simultaneously calibrate its science instruments, cameras, and spectrometers. The swing-by put LCROSS into a long looping polar orbit around the Earth called Lunar Gravity-Assist, Lunar Return Orbit (LGALRO). Each orbit is roughly 80 degrees from the ecliptic plane, perpendicular to the Moon's orbit around Earth, and takes about 37 days to complete. LCROSS will make approximately three orbits before its planned impact in a lunar crater. The extended Earth orbit will also allow LRO several months to collect science data on the Moon's polar regions, to assist in targeting LCROSS. At its closest approach to the Moon (periselene) around 6:30 AM EDT, LCROSS was only 1998 miles (3,200 km) above the surface and dramatic pictures were expected, the first from either spacecraft on this dual mission. An automated sequence reoriented the spacecraft to look at the Moon and turn the antennas towards Earth. Live streaming coverage of the swing-by began at 8:20 AM EDT a few hours after closest approach as LCROSS was about 8000 km above the Moon. The two simultaneous streams consisted of a live video stream from the visible light camera at one frame per second and a real-time telemetry-based animation. The streams were provided by NASA Ames Research Center at Moffett Field, Ca, where LCROSS was designed and is controlled.
The science instruments were turned on for about 1 hour during the fly-by as LCROSS monitored 3 craters and the lunar limb. The first target was the Mendeleev region on the far-side of the Moon which is a large, ancient impact basin with relatively uniform floor deposits, thus providing a good calibration target for the down-looking LCROSS instruments. Goddard C was the second target and is a worn iron-rich crater with mare basalt flows mixed with rugged highlands-type material. The final target was Giordano Bruno, a relatively young crater (350 million years old) at the center of a system of bright rays. LCROSS then conducted two limb crossings which aid in alignments by steering the spacecraft three degrees above and three degrees below the limb. Today’s fly-by set LCROSS and its currently attached Centaur upper stage exactly on the course required for both to collide with the Moon at approximately 7:30 AM EDT on October 9. A debris plume of ejecta will be flung up perhaps 10 km and be analyzed for the presence of water ice or water vapor, hydrocarbons and hydrated materials. The purpose is to search for water ice in a permanently shadowed crater at the Moon’s south pole. Minutes after the Centaur impact the spacecraft will follow in its path, passing through the debris plume before it too will crash inside the dark crater, creating a second plume just a few km away from the first. LCROSS Principal Investigator Anthony Colaprete said, “We just successfully completed our lunar swing-by and we operated all of our instruments, our cameras and spectrometers for calibration. They all performed very well. We are very excited to dig into the data and get ready for impact. These data will ensure we are as prepared as possible for monitoring and interpreting data we receive during impact."
Did you like this story? Send
it to a friend or share it at:
Slashdot - Digg this - Reddit - Del.icio.us - Newsvine - NowPublic |
||||||||
 |
 |
||||||||
[ what is this? ]