Re: Uncertainties about Lunar Prospector TLE

Bjoern Gimle (b_gimle@algonet.se)
Tue, 6 Jan 1998 17:07:04 +0100 

>I have questions about the data provided on the Lunar Prospector
>Launch:
>
>Typically. MET or Mission Elapsed Time, starts at launch.  The UT and
>MET times does not agree for a 0131 UT luanch on 6 Jan 98.
>
>Furthermore, it appears that a one minute burn starting at 02:27:37 UT
>on 6 Jan moves the spacecraft out to 24143.0763 km.   That seems very
>unlikely.
>
>Can anyone shed light on exact times based upon a 0131UT launch for 
>the various orbits and exactly when the lunar transfer orbit starts?
>
>I am not a rocket scientist so I need a little hand holding to try to
>generate an elset to try to find this satellite before it gets too far
>from earth.
>
>Ron Lee
>
>Lunar Prospector (From Ron Lee-questionable elset)
>1 88888U 98-xxx A 98006.10251157  .00000670  00000-0  00000-0 0    10
>2 88888  29.1520 303.7500 0025480 192.2960 121.2530 16.37615000    11
>
>>LUNAR PROSPECTOR NOMINAL ORBITS
>>
>>                                    LUNAR PROSPECTOR LUNAR PROSPECTOR
>>EPOCH (D/HH:MM:SS.SSS):             006/02:27:37.000 006/02:28:37.000
...
>>START ORBIT TIME (HHH:MM:SS.SSS)MET:000:56:37.000    000:56:38.000
...
>>HEIGHT (KM):                          179.3983       24143.0763
...
>>INJECTION TIME (D/HH:MM:SS.SSS):    006/02:27:37.000 006/02:28:37.000
>
The injection times given match the epochs, and are 0:56:37 and 0:57:37
MET (after 01:31 launch), so 0:56:38 is possibly a typo.

We do not necessarily have to assume that the spacecraft orbit is the
result of a one minute burn from the previous orbit - the epochs could
be unrelated, or (near) the end of the final spacecraft burn.

Ron's orbit does indeed pass at 02:27:37 close (118.99) to the
20.71S, 118.31E injection point given.
Lunar Prospector 01:31 launch (From Ron Lee-ques)189 x 155
1 88888U 98-xxx B 98006.10251157  .00000670  00000-0  00000-0 0    10
2 88888  29.1520 303.7500 0025480 192.2960 121.2530 16.37615000    11
and at 02:27 its orbit plane is close (11.5W) to the 3.798S, 16.914W
injection point given for the A object. 

Using the given values, and Kepler and other elliptic motion equations,
the 0.7 degree MA is 15.7 degrees EA, and 94.2 degrees True Anomaly.
The orbital radius at that point is 0.0686 * semi-major axis.
But 94.2 deg after perigee=318.5 deg is 52.7 deg after Ascending Node,
well into the northern hemisphere.

If this were a classical orbit from a LEO parking orbit, it could mean
a perigee radius of 6500 km, apogee radius of 395156 km (a=200828 km),
period = 248.8 hours (?)
This would make the current radius only 13783 km (height=7405 km)

Lunar Prospector 01:31 launch (From Bjoern G.)388778 x 122
1 88889U 98-xxx A 98006.10320602  .00000001  00000-0  00000-0 0    11
2 88889  29.1560 303.0690 9676340 318.5690 000.700 00.096464360    10

According to Track16, this orbit takes it within 0.5 degrees SE of the
injection point at 02:29 UT, 3.8S, 16.9W, at a height of 23400 km,
decreasing ! This is strange, but almost consistent with the AOP=318.569
degrees, TA=-130.7548, but gives R=6378+28347 km, EA=-31.2675	deg,
MA= -2.4915 deg, and this would give perigee pass at about 04:11 UT.
However, Track16 gives an earlier perigee, at 1500 km below the surface,
and SkyMap gives very different time, and I can't see what is wrong
in the elset, or my uses of it.

Track16 gives the range near 364000 km on Jan.9 noon, at RA 5:22
decl.+19.7 deg. Moon is 4:43, +15.7 at that time, but of course Lunar
Prospector is also accelerated towards the Moon.
 
To produce a radius of 24143+6378 km at MA=+0.7, a must be 444715 km !


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