Also in May, but repeated in September, we have tracked bright sources with a TEL configuration that did not include the track model. The resulting pointing errors ought then to be comparable with what we would expect from our preferred track model. The differences between the two might reveal deficiencies in our assumptions and algorithms. Tracking of planets was performed without a track model as follows :
Date Source HST az,el seeing adopted 950518 Mars 17:30 - 23:00 143,83 - 276,28 1" - 0.4" 1" 950913 Mars 16:20 - 18:20 210,52 - 240,30 2" - 1" 1.5" 950913 Uranus 18:30 - 19:20 139,37 - 152,44 2" - 1" 1.5" 950914 Mars 16:20 - 18:30 219,48 - 241,29 4" - 2" not analysed 950914 Jupiter 18:40 - 20:20 208,44 - 230,28 < 0.5" 0.5"The first dataset was taken with a track model of resolution 1
and the others with the latest mixed-resolution model, with greatest
resolution around the track joints of 0.2
. The azimuths of the logged
pointing measurements are corrected for the effect of the delay in logging,
az
- 0.5*(az
-az
),
to 1
) is
typically larger
than that of predicted corrections (0.35
) so the predicted
corrections
may be considered the independent variable in the relationship.
Thus we solve for m in
O = m * P + const
where m = 1/n. Secondly an analysis of the variances is made :
= (VAR(P) - VAR(I)) / (VAR(O) - VAR(S))
of
a joint (j) and those not (nj). All rms's are all w.r.t. the nj means.
The results are presented below.
Str line fits : ------- daz ------ ------- del ------
N m +- s.d. n m +- s.d. n
950518 Mars all 176 0.91 0.03 1.2 1.10 1.19 0.03 1.0 0.84
nj 106 1.05 0.04 0.9 0.95 1.20 0.04 0.8 0.83
j 70 0.84 0.05 1.4 1.18 1.22 0.04 1.1 0.82
950913 Mars all 61 1.09 0.12 1.2 0.92 0.80 0.04 0.9 1.25
nj 44 1.10 0.22 1.3 0.91 0.78 0.05 0.9 1.28
j 21 1.05 0.16 1.0 0.95 0.78 0.06 0.7 1.28
950913 Uranus all 30 1.03 0.09 1.8 0.97 1.01 0.10 1.4 0.99
nj 14 1.12 0.09 1.0 0.89 1.17 0.10 0.9 0.85
j 16 1.00 0.14 2.3 1.00 0.87 0.16 1.6 1.15
950914 Jupiter all 61 0.90 0.08 1.2 1.11 1.14 0.14 0.8 0.88
nj 40 0.80 0.11 1.1 1.25 1.23 0.04 0.8 0.81
j 21 0.94 0.12 1.4 1.06 0.99 0.05 0.7 1.01
Weighted Means : all 0.93 1.03 1.05 0.99
nj 1.04 1.00 1.11 0.94
j 0.88 1.05 1.05 1.07
typical +- .04 .10 .10 .18
VARIANCE analysis
data N daz del
rms(O) rms(P) n rms(O) rms(P) n
950518 all 176 2.61 2.57 1.06 3.11 2.49 0.84
Mars nj 106 2.25 1.97 0.97 2.54 2.00 0.85
j 70 3.08 3.27 1.12 3.84 3.15 0.85
950913 all 61 1.91 1.34 1.10 2.41 2.80 1.48
Mars nj 44 1.60 0.89 1.50 2.26 2.66 1.56
j 17 2.60 2.12 0.99 2.87 3.17 1.29
950913 all 30 4.19 3.67 0.93 2.86 2.50 1.02
Uranus nj 14 3.59 3.08 0.94 3.02 2.47 0.94
j 16 4.69 4.24 0.95 2.70 2.74 1.21
950914 all 61 2.15 1.96 0.93 3.58 3.06 0.86
Jupiter nj 40 1.63 1.51 0.95 3.71 2.95 0.80
j 21 2.94 2.62 0.90 3.39 3.31 0.98
all 1.01 +- 0.09 1.05 +- 0.30
Means nj 1.09 +- 0.27 1.04 +- 0.35
j 0.99 +- 0.09 1.08 +- 0.20
In summary, there is no compelling evidence to suggest that m, and hence n,
which = 1/m, is systematically different from 1.0 for az or el, joints or
non-joints.
The agreement between the two methods for each night, and the internal errors
for each night, are better than the deviations between nights, indicating that
the validity of the track model varies, perhaps with elevation, temperature,
azimuth range, or perhaps with a general evolution of the track. Recent
experience following a central bearing adjustment was that the track model
derived from inclinometry had become inapplicable after maybe as little as a
week.