Drag Primer, current elsets, OBS

Walter Nissen (dk058@cleveland.Freenet.Edu)
Mon, 23 Mar 1998 11:10:44 -0500 (EST)

With the sunspot cycle on the rise again, the atmosphere of Earth is 
expanding and atmospheric drag on LEOs is increasing.  Thus, they are 
dropping faster into lower orbits.  These lower orbits are faster orbits 
and cause the satellites to arrive early compared to calculations based on 
smaller drag factors.  Thus, old elsets can give misleading results and 
the error will be late, i.e., you will tend to look up after the object 
has already passed, giving you no chance to see it. 
 
Thus, for the next few years, it will be more important to have current 
elsets than it has been for the past few years.  No longer will drag tend 
to decrease, energizing people to look up early. 
 
A program like QuickSat, which gives a specific value which estimates the 
likely error in time along the track, is very helpful in alerting you to 
objects for which you need to obtain fresh elsets.  Those of you who have 
attempted to see objects just before re-entry already appreciate the great 
value of the extrapolated elsets posted in advance here on SeeSat-L by 
Alan Pickup and others.  Generally speaking, the lower the perigee of the 
orbit, the more rapidly elsets will age and become useless. 
 
For objects like Mir and the shuttles, which can be maneuvered, fresh 
elsets are nearly essential, and are essential in the event of 
unanticipated maneuvers, which can occur for a number of different 
reasons.  I'm sorry to say the space agencies have a generally poor record 
of providing anticipated elsets far enough in advance to be generally 
useful.  Jonathan Weaver at JSC has made a couple of steps in the right 
direction.  Re-boosts of Mir will presumably become more frequent as the 
drag increases. 
 
At times, I have found it useful to cobble together parts of two elsets. 
E.g., in this elset, the v's point to the drag factors I glommed from an 
earlier elset and inserted bodily into a current elset from OIG with 
smaller, i.e., late, drag factors: 
 
Mir mine                         vvvvvvvvvv          vvvvvvvv 
1 16609U 86017A   98082.20658036  .00021972  00000-0  24943-3 0  356x 
2 16609  51.6560 121.4816 0005127 141.6712 218.4648 15.62970046690601 
 
The inserted drag factors can be unrealistically large.  That is good. 
Within limits.  At least I am early and am able to see her go by, a bit 
after I look up.  QuickSat makes it fairly easy to compare results from 
different elsets. 
 
Last night I saw good performances from Mir and these: 
Secor 1 r 
1 00727U 64001A   98069.19573696  .00000015  00000-0  51591-4 0  5509 
2 00727  69.9008 111.5248 0014343 323.6962  36.3164 13.94281561737413 
NOAA 11 
1 19531U 88089A   98070.93756798  .00000042  00000-0  47415-4 0  3119 
2 19531  99.1217 114.5161 0010934 264.2055  95.7870 14.13171116487810 
2228 
1 22286U 92094A   98068.65173755  .00000328  00000-0  46445-4 0  2032 
2 22286  82.5251 112.7288 0024477 245.7673 114.0979 14.73908513279776 
2347 
1 25088U 97079A   98081.77959197  .00004918  00000-0  85547-4 0  1453 
2 25088  65.0277 232.5327 0010057 274.2798  85.7343 15.52059273 16060 
Irdm 45          3.0  0.0  0.0  6.0 d            780 x 776 km 
1 25104U 97082A   98079.59709903 -.00000348  00000-0 -13133-3 0   715 
2 25104  86.3959 312.3477 0002695  44.0629 316.0787 14.34215720 12956 
Gblstr 1 r 
1 25166U 98008E   98082.20871949  .00127636  10347-4  96234-3 0   343 
2 25166  52.7215 110.1651 0677874 342.4839  15.3638 14.50088273  5303 
 
C* 2228 was pretty irregular.  Timings are encouraged.  Iridium 45 
apparently disappeared into the shadow of Earth while glinting to mag 
1(?).  NOAA 11 was steady, disappointing hopes for a bright glint, not to 
mention a double glint as previously observed from the NOAAs.  Also was 
fortunate enough to catch bright Mercury, Saturn and Mars, in that order, 
in twilight. 
 
Cheers. 
 
Walter Nissen                   dk058@cleveland.freenet.edu 
-81.8637, 41.3735, 256m elevation 
 
--- 
 
If you are a little late, you won't see it;
If you are a little early, you will see it.