by neufer » Fri Jan 25, 2019 3:52 pm
https://www.nasa.gov/centers/marshall/news/lunar/overview.html wrote:
About Lunar Impact Monitoring
Mission statement: Use Earth-based observations of the dark portion of the Moon to establish the rates and sizes of large meteoroids (greater than a few ounces in mass) striking the lunar surface. Observations are taken between New and 1st Quarter Moon and between Last Quarter and New Moon, when the solar illumination is between 10 and 55 percent. These conditions yield 10-12 observing nights per month.
Observing facility: Observations are conducted at NASA Marshall Space Flight Center in Huntsville, Alabama at the Automated Lunar and Meteor Observatory (ALaMO). The facility consists of two observatory domes, a 15 meter tower with a roll-off roof, and an operations center with laboratory space. A second observatory in Chickamauga, Georgia (Walker County) was operational from September 15, 2007 to June 2011. The facility consists of a ground level building with a roll-off roof. This observatory was run remotely from Marshall Space Flight Center. A fourth 14 inch telescope was operated at New Mexico Skies Observatory from October 2011 to September 2012.
Meteor showers: It is well known that the Earth experiences meteor showers when it encounters the debris left behind by comets; so too does the Moon, though perhaps at not exactly the same time. On Earth these showers are capable of producing spectacular celestial fireworks displays, delighting the public. On the airless Moon, however, these showers are swarms of high energy projectiles, producing fireworks only when they strike the surface with tremendous force. During such times, the rate of shower meteoroids can greatly exceed that of the sporadic background rate and may pose a hazard to spacecraft. Looking for meteor shower impacts on the Moon at about the same time as they occur here on Earth will yield important data that can be fed into meteor shower forecasting models, which can then be used to predict times of greater meteoroid hazard in near-Earth space.
In designing a system to look for these impact flashes, we need to take into account two important considerations. First, we want to see as faint as possible, and secondly we want to see as much of the lunar dark side as we can. The first is important because faint flashes are generally produced by smaller meteoroids, and the smaller the meteoroid, the more there are of them. More meteoroids mean more flashes and hence better statistics on which to base improved models. We can also get more flashes by monitoring as much of the lunar surface as possible, as the number of observed hits is going to be directly proportional to the amount of area seen by our instrument. That’s why the second point is important. It turns out that a modestly-wide field optical system (one with a fast focal ratio) meets both of these criteria nicely. So we perform simultaneous observations of the Moon using two 14” telescopes.
We attach a Watec Ultimate H2 camera to each of our telescopes, and route the camera output into a Sony tape deck or Canopus video digitizer, which converts the video signal into a digital format that is stored on a hard disk. After an observing session, we look for flashes in the data. Our first impact was found by someone simply looking through a couple of hours of video. This can be quite tedious, however, and tired humans can easily miss a short impact flash, so custom computer software was developed to look for the flashes. If one is found, additional software is then used to extract detailed information on the flash -- its brightness as a function of time (light curve), where it was seen on the Moon, if it was due to a meteor shower, and so forth. Using this information, we can estimate the mass or size of the meteoroid. If it is a sporadic meteoroid, all we can do is put limits on the size, as its speed can range from 20 km/sec all the way up to 70 km/sec. If it is a shower meteoroid, then things are better because every member of a meteor shower moves with the same, known speed. This allows us to calculate a single, less uncertain size estimate..>>
[quote=" https://www.nasa.gov/centers/marshall/news/lunar/overview.html"]
[float=right][img3=""]https://www.nasa.gov/sites/default/files/styles/full_width/public/thumbnails/image/simple_flash_table435_400x917.jpg?itok=SKYFiSqh[/img3][/float]
[size=150]About Lunar Impact Monitoring[/size]
Mission statement: Use Earth-based observations of the dark portion of the Moon to establish the rates and sizes of large meteoroids (greater than a few ounces in mass) striking the lunar surface. Observations are taken between New and 1st Quarter Moon and between Last Quarter and New Moon, when the solar illumination is between 10 and 55 percent. These conditions yield 10-12 observing nights per month.
Observing facility: Observations are conducted at NASA Marshall Space Flight Center in Huntsville, Alabama at the Automated Lunar and Meteor Observatory (ALaMO). The facility consists of two observatory domes, a 15 meter tower with a roll-off roof, and an operations center with laboratory space. A second observatory in Chickamauga, Georgia (Walker County) was operational from September 15, 2007 to June 2011. The facility consists of a ground level building with a roll-off roof. This observatory was run remotely from Marshall Space Flight Center. A fourth 14 inch telescope was operated at New Mexico Skies Observatory from October 2011 to September 2012.
[b][color=#0000FF]Meteor showers: It is well known that the Earth experiences meteor showers when it encounters the debris left behind by comets; so too does the Moon, though perhaps at not exactly the same time. On Earth these showers are capable of producing spectacular celestial fireworks displays, delighting the public. On the airless Moon, however, these showers are swarms of high energy projectiles, producing fireworks only when they strike the surface with tremendous force. [u]During such times, the rate of shower meteoroids can greatly exceed that of the sporadic background rate and may pose a hazard to spacecraft.[/u] Looking for meteor shower impacts on the Moon at about the same time as they occur here on Earth will yield important data that can be fed into meteor shower forecasting models, which can then be used to predict times of greater meteoroid hazard in near-Earth space.[/color][/b]
In designing a system to look for these impact flashes, we need to take into account two important considerations. First, we want to see as faint as possible, and secondly we want to see as much of the lunar dark side as we can. The first is important because faint flashes are generally produced by smaller meteoroids, and the smaller the meteoroid, the more there are of them. More meteoroids mean more flashes and hence better statistics on which to base improved models. We can also get more flashes by monitoring as much of the lunar surface as possible, as the number of observed hits is going to be directly proportional to the amount of area seen by our instrument. That’s why the second point is important. It turns out that a modestly-wide field optical system (one with a fast focal ratio) meets both of these criteria nicely. So we perform simultaneous observations of the Moon using two 14” telescopes.
We attach a Watec Ultimate H2 camera to each of our telescopes, and route the camera output into a Sony tape deck or Canopus video digitizer, which converts the video signal into a digital format that is stored on a hard disk. After an observing session, we look for flashes in the data. Our first impact was found by someone simply looking through a couple of hours of video. This can be quite tedious, however, and tired humans can easily miss a short impact flash, so custom computer software was developed to look for the flashes. If one is found, additional software is then used to extract detailed information on the flash -- its brightness as a function of time (light curve), where it was seen on the Moon, if it was due to a meteor shower, and so forth. Using this information, we can estimate the mass or size of the meteoroid. If it is a sporadic meteoroid, all we can do is put limits on the size, as its speed can range from 20 km/sec all the way up to 70 km/sec. If it is a shower meteoroid, then things are better because every member of a meteor shower moves with the same, known speed. This allows us to calculate a single, less uncertain size estimate..>>[/quote]