Planets and Moons  ID: 3453

LRO Ground Track - One Sidereal Month

A satellite's ground track shows the path of its orbit on the surface of the parent body. Lunar Reconnaissance Orbiter will be placed in a nearly circular polar orbit about 50 kilometers (31 miles) above the surface of the Moon, completing each orbit in a little less than two hours. The orientation of this orbit remains fixed in space, relative to the stars, while the Moon slowly rotates beneath it as they travel together around the Earth, allowing LRO to scan the entire surface of the Moon every two weeks.
The animation depicts LRO's ground track over a period of 27.3 days (348 orbits) or one sidereal month, the amount of time it takes the Moon to turn once on its axis, relative to the stars. This is two days shorter than the synodic month, the period of the Moon's phases. The difference arises from the motion of the Earth. While the Moon is orbiting the Earth, the Earth is carrying them both around the Sun, changing the Sun's direction relative to the stars.
Each LRO orbit is separated from the previous one by about one degree of longitude. On the Moon's surface near the equator, this corresponds to a spacing of 30 kilometers (19 miles), but the orbits converge near the poles; at 84 degrees N or S latitude, the ground distance is only 10% of the distance at the equator. At all latitudes, later LRO orbits will fill in the gaps left by earlier ones. Orbits in the latter half of the month depicted in this animation are seen to form a cross-hatch pattern that begins to fill in the gaps left during the first half of the month.
The points at which the orbits cross provide an opportunity to refine our knowledge of LRO's precise position. LOLA, the LRO instrument that maps the lunar terrain by measuring surface elevation, should get the same reading for these crossing points each time it passes over them. If it doesn't, then LRO might not really be at a crossing point, meaning that its actual position differs slightly from its predicted position.
The elevation map comprises low-resolution data from a number of sources, including the Clementine and JAXA/SELENE spacecraft, combined with high-resolution insets for the regions near the poles. The surface color is derived from photographs taken by Clementine.


Visualization Credits

Ernie Wright (UMBC): Lead Animator
Marte Newcombe (GST): Animator
Andrew Freeberg (NASA/GSFC): Producer
John Keller (NASA/GSFC): Scientist
Please give credit for this item to:
NASA/Goddard Space Flight Center Scientific Visualization Studio. Some elevation data provided by JAXA/SELENE.

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Data Used:
KAGUYA/Laser Altimeter (LALT)/DEM
Unified Lunar Control Network 2005
Note: While we identify the data sets used in these visualizations, we do not store any further details nor the data sets themselves on our site.

This item is part of these series:
The Moon
LRO Pre-launch

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