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SetOrbitalElements, TwoLineElementsOrbitTrackPlot

7.2 The GetLocation Function

GetLocation computes the location of an object in a coordinate system similar to that used by SetLocation.

Computing an object's position in geographic coordinates.

Consider, for example, the Mir Space Station. Once an object representing Mir has been added, you can use BestView to determine the times when Mir is making a visible transit pass overhead. Then use GetLocation to determine the location of Mir at that transit visible time. The location returned will be very close to the current site location, because Mir is traveling overhead. It is only visible for a minute or so on either side of the transit visible time; as mentioned earlier, the window for viewing a low-orbit satellite is always very narrow.

This adds the new object Mir, with elements appropriate for its orbit in late January 1995.

In[11]:=SetOrbitalElements[Mir,
"1 16609U 86017A 95025.53583445 .00005100 00000-0 71581-4 0 9062",
"2 16609 51.6458 152.6933 0001412 164.2374 195.8663 15.58639897510653"];

The next transit visible pass after January 20 is on January 30.

In[12]:=BestView[Mir, {1995,1,20}]

Out[12]=

At 21:49 on 1995 February 1, it is possible to see Mir from the current location.

In[13]:=BestView[Mir, {1995,1,31}]

Out[13]=

This gives the geographic location of Mir during the transit visible pass overhead.

In[14]:=GetLocation[Mir, {1995,2,1,21,49,0}]

Out[14]=

Mir is 70.4 degrees above the horizon, and thus very high in the sky, traveling overhead at the given time.

In[15]:=HorizonCoordinates[Mir, {1995,2,1,21,49,0},
ViewPoint -> TopoCentric]

Out[15]=

If you are tracking a satellite with radio equipment, visibility is not so important since all you need to know is approximately when the object is overhead. Culmination gives you the time when an object is next highest in the sky, and you can apply Ephemeris to determine the circumstances of the pass.

Culmination gives the time when Mir is next highest in the sky overhead.

In[16]:=Culmination[Mir, {1995,2,1,15,0,0}]

Out[16]=

GetLocation can, of course, be applied to other objects and not simply low-orbit Earth satellites. For example, use GetLocation to determine the part of the Earth that has the Moon directly overhead at any given time.

On the given date, the Moon is directly over the point with longitude -29 degrees and latitude -21 degrees, which is a location off the east coast of Brazil.

In[17]:=GetLocation[Moon, {1993,11,17,3,20,0}]

Out[17]=

SetOrbitalElements, TwoLineElementsOrbitTrackPlot



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