IPAC

2. This final IPAC release of IRTS attitude data covers the post-flip period from orbit 346, the first after the STS-off interval, through the end-of-data at orbit 586:

    Packet         Orbits
   04092249:     346 -- 363
   04110242:     364 -- 378
   04120140:     378 -- 393
   04130040:     393 -- 409
   04140046:     409 -- 425
   04150222:     425 -- 438
   04152348:     438 -- 454
   04170049:     454 -- 470
   04180057:     470 -- 485
   04190035:     485 -- 500
   04200009:     500 -- 516
   04210105:     516 -- 531
   04220036:     531 -- 546
   04230012:     546 -- 561
   04232351:     561 -- 576
   04250016:     576 -- 586
   
   

3. Although this release contains the entire post-flip data, only eleven orbits have changed from their earlier values, due to improved solutions obtained since the previous release. These nine of the eleven orbits/segments, that were previously interpolated from neighboring orbits or segments, have now been fully reconstructed. For the other two (584 and 585 in the list below) improved solutions have been obtained. In addition, we have determined that the reconstructions for 49 orbits previously labeled as possibly problematic are OK. Comparing the old and new solutions, there are differences only in the following orbits/segments:

   363AB
   364AB
   364CC
   393CC
   394AB
   400AB
   400CC
   420AB
   420CC
   454AB
   454CC
   483CC
   584AB
   584CC
   585AB
   585CC
   586CC
   
   

4. We have also revised the positional uncertainties for all or part of a number of orbits. Specifically, for the first 500 seconds of all orbits we have increased STS positional uncertainties to 5'. This 500 s interval is a minimum, and may be increased further by the settling parameter in the Tgood file. Also, for orbit 569, the region affected by the G-angle change has been extended to the beginning of segment CC. The uncertainties assigned for other situations are summarized below.

5. In general, the methods of reconstruction have followed those previously used, which were described in README files accompanying the previous pre-flip releases of 1996 March, 1995 December, and 1995 November. In particular, each orbit is reconstructed in two segments as before.

6. The data have been checked for internal consistency by verifying that using the reconstructed boresight, the positions of sources detected by the STS coincide with the positions that are used to generate the parameters that determine the orbit reconstruction.

7. From the list of MIRS and NIRS sources that were available to us we have determined the relative locations of NIRS and MIRS with respect to point C2 of the STS, based on 115 MIRS (Figures 1 and 2) and 596 NIRS (Figures 3 and 4) detections. The nominal separation of MIRS center and point C2 is 65.7' and 64.5' in the in- and cross-scans respectively, these agree well with the observed values of 65.3' and 64.8' respectively.

   As has been previously noted, but for reasons which are not entirely clear, these data indicate small shifts with respect similar plots for the pre-flip data. We now recommend that the derived relative distances be used instead of pre-launch measurements for the MIRS and NIRS locations with respect to the STS. Since to understand the differences between these offsets and those found for the pre-flip data, a detailed analysis of all MIRS and NIRS observations in concert with STS observations will be required, this will need to be pursued, if desired, by Dr. Minoru Freund or other members of the IRTS teams with access to all IRTS data.

8. The reconstructed packets were also checked with the Tanaka-san IDL program; the differences seen in the plots from this program can be explained easily based on the assumptions used in the program.

9. As always, the quality flags must be consulted for determining periods of nominal behavior. In this release we have increased STS positional uncertainties to 5' for at least the first 500 seconds of all orbits. The nominal reconstruction uncertainties for the STS have been set to 1' and 2' in the in- and cross-scan directions respectively. A 1' uncertainty in the relative position of the STS and boresight has been assumed and convolved into the STS uncertainties to arrive at the boresight reconstruction uncertainties. During the periods of high gyroscope activity, the STS reconstruction uncertainties are set to 30'. When there is a g-angle change during a segment, the STS reconstruction uncertainties are set to 99'. When a segment is reconstructed by interpolation between two adjacent segments, the STS reconstruction uncertainties are set to 99'.

10. Finally, for a single orbit, number 420, there is evidence of a shift of about 20' in-scan, which we have not been able to understand, and which we tentatively attribute to a time stamp error of approximately 5 seconds.

Figure Captions:

2. The scatter of in- and cross-scan positional differences between MIRS detections relative to the C2 point of the STS.

3. The histogram of the distribution seen in Figure 1 in the in- and cross-scan directions. The nominal separation of MIRS center and point C2 is 65.7' and 64.5' in the in- and cross-scans respectively, these agree well with the observed values of 65.3' and 64.8' respectively.

4. The scatter of in- and cross-scan positional differences between NIRS detections relative to the C2 point of the STS.

5. The histogram of the distribution seen in Figure 3 in the in- and cross-scan directions.