SAMPEX Payload and Rocket

Mike McCants (mike@comshare.com)
Mon, 27 Feb 1995 12:50:12 -0600

I have "discovered" that the Scout rocket that launched the SAMPEX payload
in July, 1992 is tumbling.  In one sense it is surprising that no other
observers had noticed this.  In another sense it is not surprising.
because the explanation is that NORAD had the payload and rocket elements
switched from the time of launch until January, 1994.  So, a large number
of observers had noticed that the "payload" was tumbling and reported
a large number of observations of the object, 92 38A.  But these observations
were really observations of the Scout rocket.

The current monthly report says:

92- 38 A: to be observed again!

The last reports are:

93-08-15 BD   5.6   F, mag +7.0->
93-08-17 BD   5.76  F, mag +5.5->inv
94-01-02 KJ   0.7   I, var max

Since NORAD switched the elements to their proper identities in January, 1994,
subsequent observers have very likely been attempting to observe the wrong
object.  The real payload is normally faint and not tumbling and the orbit
is fairly low and the inclination is 90 degrees - so the chances every
six months only last for a little while.

At the end of 1993, NORAD stopped issuing elements on the object it
was calling 22013 for about a month:

Ted's file for Jan 8, 1994:

1 22012U 92038  A 94 03.91837350  .00002591  00000-0  22374-3 0  4534
2 22012  81.6726 343.6059 0117249 212.8243 146.5663 14.92042561 81830
1 22013U 92038  B 93336.63697153  .00000006  00000-0  55252-6 0  4394
2 22013  81.6757  18.1691 0119433 321.5055  37.7686 14.90709488 76990

Then in Ted's file for Jan 15, 1994, both elsets are the same:

1 22012U 92038  A 94 12.36833122  .00001892  00000-0  16305-3 0  4659
2 22012  81.6689 334.6747 0117708 185.3322 174.6668 14.92074532 83094
1 22013U 92038  B 94 12.36833093  .00001698  00000-0  14402-3 0  4578
2 22013  81.6680 334.6736 0117690 185.3498 174.6460 14.92074299 83098

Then the next week, the payload and the rocket have been switched.

1 22012U 92038  A 94 17.14654002  .00000316  00000-0  25660-4 0  4675
2 22012  81.6768 330.1645 0119652 171.8201 188.4914 14.90702236 83775
1 22013U 92038  B 94 20.88519258  .00001652  00000-0  14212-3 0  4599
2 22013  81.6724 325.6771 0118241 157.3099 203.3401 14.92102441 84362

I observed the payload in 1993 (as B) and didn't see anything unusual.
I observed the payload again in 1994 (as A) and wondered why everyone had
made such a fuss about how spectacular it was - I didn't see anything
interesting.  :-)

I have observed the Scout rocket twice in the last week and my observations
do not agree with each other.  However, my observation of Feb 24 was unusual.

                                 tot   acc cyc
yy-nnnaa yy-mm-dd hh:mm:ss.t nam sss.t s.t nnn ss.tht remarks
92- 38 B 95-02-20 01:26      MM  110.4 0.5  12  9.20
92- 38 B 95-02-24 01:56      MM  158.5 0.5  17  9.06  N=17.5, 7-inv, asym

I took a number of timings on Feb 24 and first analyzed them as follows:

2/24/95 - 92 38B

period =  9.067
predict = 9.067 * count

               1       2       3       4       5       6       7       8

count        .00    1.00    2.00    3.00    4.00    5.00    6.00    8.50
obs          .00    9.00   18.10   29.20   37.40   47.70   56.80   77.30
predict      .00    9.07   18.13   27.20   36.27   45.33   54.40   77.07
diff         .00    -.07    -.03    2.00    1.13    2.37    2.40     .23
pred count   .00     .99    2.00    3.22    4.13    5.26    6.26    8.53

               9      10      11      12      13

count      11.50   13.50   15.50   17.50   19.50
obs       103.90  121.90  140.70  158.50  177.80
predict   104.27  122.40  140.53  158.67  176.80
diff        -.37    -.50     .17    -.17    1.00
pred count 11.46   13.44   15.52   17.48   19.61

"count" is the assumed cycle count.
"obs" is the observed times.
"predict" is the predicted time = 9.067 * count.
"diff" is obs - predict.
"pred count" = obs / 9.067

I think the last obs really could have been 1 second late.

At the end, due to the asymmetry of the observed light curve, it was
obvious that the true period was approximately 18.1.

At the beginning, the two maxima were not all that different and the
period could have been called 9.1.

However, obs 8 to 13 are "off" 1/2 of a 9.067 cycle compared to obs 1 to 3.

And it looks like obs 4, 6, 7 are off a quarter cycle.

Obs 5 is probably just wrong.

I did not realize at the time I was making the observations that they
were not going to "line up" properly.  But I did realize that the
observed light curve had changed quite a bit as the observation
(over a 3 minute span) had progressed.  I "ignored" secondary flashes
that occurred in between what I considered to be the primary maxima.

Of course it is possible (likely?) that A) the rotation axis is not
90 degrees from the cylinder axis, and B) the rotation axis had a
"special" orientation during this pass that caused the appearance
to change during the observation.  (See articles in Flash 89,
Jan. 95, and Flash 90, Feb. 95)

Let me also put in a disclaimer:  The two observations are only
4 days apart and the period determined seems to be significantly
different.  So it is certainly possible that one of the two is
incorrect.  I did not note any unusualy behavior on the Feb 20
observation.

Two parts of the Feb 24 observation can be fit with a 9.20 second period:

count        .00    1.00    2.00    4.00    8.50
obs          .00    9.00   18.10   37.40   77.30
predict     -.20    9.00   18.20   36.60   78.00
diff         .20     .00    -.10     .80    -.70

Here the "predict" value is: 9.20 * count - 0.20

count      11.50   13.50   15.50   17.50   19.50
obs       103.90  121.90  140.70  158.50  177.80
predict   103.80  122.20  140.60  159.00  177.40
diff         .10    -.30     .10    -.50     .40

Here the "predict" value is: 9.20 * count - 2.00
(and the count has an extra 0.50 cycle in it.)

The "offset" between these two series is thus 0.30 cycle.

These two can be combined into a single solution if it is assumed that
the first series and the last differ by 1/4 of a 9.24 second cycle:

period  9.24
predict = 9.24 * count - 0.50

count        .00    1.00    2.00    3.25    4.25    5.25    6.25    8.25
obs          .00    9.00   18.10   29.20   37.40   47.70   56.80   77.30
predict     -.50    8.74   17.98   29.53   38.77   48.01   57.25   75.73
diff         .50     .26     .12    -.33   -1.37    -.31    -.45    1.57

count      11.25   13.25   15.25   17.25   19.25
obs       103.90  121.90  140.70  158.50  177.80
predict   103.45  121.93  140.41  158.89  177.37
diff         .45    -.03     .29    -.39     .43

So, the questions are: 1) Is the current half period 9.067, 9.20, or 9.24?
And B) did I observe an unusual series because the axis of rotation had
a special orientation for that pass?

Here is SeeSat 4.0 output for the 3 minutes of this pass:

SEESAT (SGP4) 1992 Jan 4 by Paul Hirose
lat 30.3153 lon -97.8663 height .28
Sampex r
1 22013U 92038  B 95 55.05225504  .00001176  00000-0  96863-4 0  6074
2 22013  81.6674 263.3937 0114288 292.0251  66.8842 14.93270450143917
start 1995 feb 24 0156:20 stop feb 24 0159:20 step 0:10
Sampex r         1995 FEB 24
 time   alt azi    R.A.    dec  range   hgt sun
0156:20  43 250   2 39.6   7.39   566   405  10
0156:30  42 245   2 46.6   3.20   576   405  10
0156:40  40 239   2 53.1  -0.86   589   405  10
0156:50  39 234   2 59.3  -4.74   605   404  10
0157:00  37 230   3  5.0  -8.42   624   404   9
0157:10  35 226   3 10.5 -11.90   645   404   9
0157:20  33 222   3 15.6 -15.16   669   403   9
0157:30  31 219   3 20.4 -18.22   694   403   9
0157:40  30 216   3 25.0 -21.06   721   403   9
0157:50  28 214   3 29.2 -23.72   750   402   9
0158:00  26 211   3 33.3 -26.19   780   402   9
0158:10  25 209   3 37.1 -28.49   812   402   9
0158:20  23 207   3 40.8 -30.64   844   401   9
0158:30  22 206   3 44.2 -32.64   878   401   9
0158:40  20 204   3 47.5 -34.52   912   401   9
0158:50  19 203   3 50.6 -36.27   947   400   9
0159:00  18 202   3 53.6 -37.92   983   400   9
0159:10  16 201   3 56.5 -39.46  1020   400   9
0159:20  15 200   3 59.2 -40.92  1057   399   9
RA and dec are 1950 and range, hgt are in miles.
This observation was made while using my 8 inch telescope.

Mike