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Planetary News: SMART-1 (2006)SMART-1 Prepares for Lunar Crash-Landing -- and You Might Be Able To See Itby Melanie Melton Knocke
Plan to take a look at the Moon this coming Saturday night (September 2-3, 2006). Depending on where you live (and the topology of the Moon's southern hemisphere) you might be able to see first-hand the climactic crash of the European Space Agency's (ESA) highly successful, first-ever mission to the Moon. What you may (or may not) see during SMART-1's demise will depend largely on the lunar landscape. And, while this small spacecraft has proven to be an unqualified success, there is still much we don't know about the Moon -- in particular, if there are any high peaks in the southwestern sector of the Earth-facing side of the Moon. SMART-1 is about to find out. What We Do KnowSMART-1 (which is the first in ESA's Small Missions for Advanced Research in Technology program) will impact the Moon sometime during the late evening or early morning hours of September 2-3, 2006. The primary impact opportunity will occur at 10:41 pm PDT on September 2, 2006 (1:41 am EDT, 5:41 UT on September 3). However, there are other factors that might affect this time -- more about that in a moment. This is to be a controlled, intentional crash. The spacecraft's mission (which lasted a year longer than originally planned) is complete and its fuel is gone. Since its decaying orbit was going to crash the spacecraft into the Moon anyway, scientists decided to use SMART-1's final moments to see what they could learn about the lunar surface by observing the impact and analyzing any resulting debris. Impact is scheduled to occur in the region of the Moon known as Lacus Excellentiae (Lake of Excellence). When looking at the Moon from Earth, this small, irregular patch of dark lava is located on the lower left-hand side of the Moon's disk, just to the left and up a bit from the bright, rayed crater Tycho. However, knowing what the Lake of Excellence looks like won't help you the night of impact. Even though the Moon will be in its waxing gibbous phase, with just over 70% of its surface visible, SMART-1 will impact the surface just across the terminator on the night-time side of the Moon. The lunar darkness will provide scientists with a better opportunity to see any explosion caused by the impact. Coming In For a "Landing"
As SMART-1 approaches the Moon, it will be traveling at a very shallow angle with respect to the lunar surface. In fact, if everything goes as planned and the ground beneath the spacecraft is smooth and flat, SMART-1 will drop only about 15 meters in the last kilometer (one half mile) before impact. At such an orientation, the spacecraft will be traveling about 70 kilometer (40 miles) per hour relative to the ground when it hits, much slower than an average meteor (which travel at speeds of 10-70 kilometers (6-40 miles) per second. If the above scenario plays out, ESA scientists predict that SMART-1 will plow a shallow crater 3-10 meters wide and 1 meter deep into the Lake of Excellence at 10:41 pm PDT September 2, 2006 (01:41 pm EDT, or 05:41 UT September 3). Impact should occur at the lunar coordinates of 36.44 degrees South and 46.25 degrees West. Alternate SceneriosIf the plains of Lacus Excellentiae aren't as smooth as thought, if there are rocks or peaks rising from the ground along the flight path, if there is a pile of rubble in the wrong place, the SMART-1 mission could end sooner than scientists predict. In fact, knowledge of the terrain elevation is so uncertain that scientists are providing a second time and location for the crash, one that takes place an orbit earlier. The alternate crash site is still located within Lacus Excellentiae, at lunar coordinates 36.4 degrees South and 43.5 degrees West. The impact itself, however, would take place much earlier, at 5:36 pm PDT on September 2 (8:36 pm EDT, September 2 or 00:36 UT, September 3). If the flight path takes the low-flying SMART-1 over some high peaks before it reaches Lacus Excellentiae, the spacecraft may crash even before that. Or, if the Lake of Excellence landing site is lower in elevation that predicted, it may go an additional orbit before impacting. It just depends on what the Moon has to offer. ESA's SMART-1 website should have up-to-date mission briefings throughout the day. What Will You See -- If AnythingWill you be able to see the SMART-1 impact with the naked eye? Probably not. But that is part of the fun of observational astronomy. You never know.
If SMART-1 impacts at the primary crash site, there is a chance that Earth-bound viewers in the western hemisphere will see an impact explosion. Binoculars or a telescope (the bigger the better) will dramatically improve your chances of seeing something. Try not to include any of the bright gibbous Moon in your field of view, it could easily drown out any brief flash. If enough debris is lifted during the impact, the plume might rise high enough for sunlight to illuminate it. If so, the Sun-lit debris cloud has the potential of being even brighter than the initial explosion. SMART-1 scientists are asking observers around the world to be a part of their lunar impact observing team. Visit SMART-1's Call for Ground Based Observers website for more information. Brief HistorySMART-1 was launched on September 27, 2003 from French Guiana. Its primary mission was to test new technologies, including an ion engine and a suite of miniaturized scientific instruments. The slow but super-efficient ion engine got the small spacecraft into lunar orbit on November 15, 2004. After adjusting its orbit, the spacecraft began collecting data in March 2005. When its primary mission was completed in six months, engineers used the remaining fuel onboard the spacecraft to boost its orbit and extended the mission another year. Now, the only thing left to do is wait and watch. Will SMART-1 go out with a flash, or will its radio signal simply stop? Stay tuned. |
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