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- When the Dawn spacecraft reaches Vesta it will orbit the asteroid every 68 hours. During that one orbit Vesta will rotate 13 times. During a second orbit position Dawn will complete one orbit in 12 hours. In a third orbit position Vesta well complete only 3/4ths of an one rotation during one orbit.
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- Vesta is one of the brightest asteroids ( Magnitude +5.4) you can easily see with binoculars. It is 360 miles in diameter, potato shaped, 3.63 years to orbit the Sun at a distance of 2.57 to 2.15 A. U. It contains a range of minerals with an iron core 136 miles in diameter. Dawn took 4,700 pictures of Vesta. ( See Review #1572 for more info on Vesta)
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- Doppler shifts of Dawn's radio signals will be constantly monitored. Shifts in the wavelengths will occur with gravity perturbations as the orbit progresses. A gravity map will be created of the mass concentrations on the asteroid.
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---------------- The radio wavelengths, “w”, are 103 meters.
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--------------- The frequency, ”f”, is from 104 to 108 cycles per second.
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---------------- wavelength * frequency = the speed of light ,”c”, = 300,000,000 meters per second.
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----------------------------- w * f = c
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- The spacecraft's main antenna is 5 feet in diameter. The earth-based antennas are 112 feet and 230 feet in diameter.
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- Dawn is scheduled to arrive at this second asteroid ,Ceres, in April, 2015.
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- Ceres is large enough to be classified as a Dwarf Planet, the same as Pluto. These are what science calls "proto-planets". Studying them will help us learn how our solar system formed and evolved into what we see today.
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- Ceres is likely icy compared to Vesta that was a dry asteroid. It is 590 miles in diameter and perfectly spherical. It is the largest asteroid in the Asteroid Belt, 4% the mass of the Moon. Ceres has an icy mantle that is 37 t0 75 miles thick containing more fresh water than all the fresh water on Earth. Its “year” is 4.6 years orbiting at 2.77 A.U.
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----------------------- The square of the period = the cube of the radius
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----------------------- 4.6^2 = 2.76^3 = 21.2
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- When Dawn arrives in April 2015 it will be captured by Ceres’ gravity and orbit at an altitude of 8,400 miles. Once in stable orbit Dawn will begin to spiral down to 2,750 miles altitude.
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- 22 days later it will spiral down to 920 miles altitude. Each orbit is mapping the surface and using infrared spectrometry to identify the elements. In late November, 2015 it will spiral down to 233 miles altitude.
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- Fluctuations in the spacecraft's radio wave frequencies received on Earth are used to calculate the gravity map and mass of the asteroid. Mapping the residual Doppler shifts measures gravity perturbations. Any change in the mass concentration on the surface will exert an extra gravitational force on the spacecraft causing changes in the centripetal acceleration of spacecraft. These changes are only measured in line-of-sight velocities. Computers will calculate a complete map of the asteroid's mass distribution, density, and composition from this and the spectroscopy data.
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-- Doppler shifts of wavelengths will occur during orbit in a continuous cycle, shifting towards the blue end of the spectrum when it is coming towards us ( shorter wavelengths) and towards the red end of the spectrum when it is moving away from us ( longer wavelengths ).
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- These the radio noise created by the solar wind are removed from the data. Fluctuations as small as 1/10 of the millimeter per second remain. These residual Doppler shifts measure the gravity perturbations during orbit. Gravity highs occur when it is over mountains ; gravity lows occur when it is over valleys.
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- Mass concentrations on or beneath the surface are mapped with the spatial distribution. The total mass of the asteroid is measured as a function of the acceleration of the spacecraft in orbit.
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---------------------- F = m* a
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---------------------Gravity Force = mass * acceleration
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- Remember these asteroids are 4,500,000,000 years old, so, be gentle. An announcement will be made in the year 2015, stay tuned
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- See Review #1572 for more info on Vesta
- Review #847 to learn more about “Ceres our 5th Planet”
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RSVP, with comments, suggestions and corrections. An index of all reviews is available. Some reviews are at: -------------------- http://jdetrick.blogspot.com
,or: email request for copies to: ------- jamesdetrick@comcast.net
or: ---- https://plus.google.com/u/0/ ,or, “Jim Detrick” ------- www.facebook.com,
------ www.twitter.com or cell: 707-536-3272 ------ Wednesday, December 11, 2013
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