IPAC

Notes to IPAC_ATT files released on March 6, 1996

1. The format of the files has been changed slightly because the previous releases did not quote the quality flags properly.

2. The reconstructions are still based on the previously described methods; each orbit is reconstructed in two segments as before.

3. We decided against forcing the orbit/segment reconstructions to be smoothly connected to adjacent orbits/segments. Had we done so, we would have caused the reconstructions to appear to have a rapid slewing between segments; we felt this was not a proper trade off. A proper smooth connection of orbits/segments will be addressed in future releases.

4. 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. (See Figures 1 and 2.)
5. A set of 116 detections by MIRS were used to verify external consistency. These data show that the relative positions of MIRS and STS are as expected. (See Figures 3 and 4.)

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

7. The reconstruction data indicated that the spacecraft appeared to undergo a systematic limit-cycle type of oscillation upon exit from the eclipse; this oscillation had a peak to peak range of 2' in the cross-scan direction, and a much smaller range in the in- scan direction. We have removed this periodic trend from the data. As a result, our internal reconstruction uncertainties have been reduced to 40" and 1' in the in-scan and cross-scan directions. (See Figures 1 and 2, 5 and 6.)

8. In this release, the quality flags should be consulted for determining periods of nominal behavior. The nominal reconstruction uncertainties for the STS have been set at 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 at 30'. When there is a g-angle change during a segment, the STS reconstruction uncertainties are set at 99'. When a segment is reconstructed by extrapolation from two adjacent segments, the STS reconstruction uncertainties are set at 10'. When an entire orbit is reconstructed from adjacent orbits the STS reconstruction uncertainties are set at 30'. In contiguous time periods longer than 800 seconds, when no JACT sources could be identified, the STS reconstruction uncertainties are set at 30'.

ipac_att Formats

The file header:

\ Reconstructed Attitude File (IPAC- Phase I)                                                                                                                         
\                                                                                                                                                                     
|date-time     |LAUNCHtime |ra_sts  |dec_sts |sigi|sigx|posang  |sigpa  |FPang   |sFPang |ra_bs   |dec_bs  |s1bs|s2bs|pa_bs   |spa_bs |packet |qflag          |spare |
|double        |double     |double  |double  |d   |d   |double  |double |double  |double |double  |double  |d   |d   |double  |double |char   |int            |char  |
|mmddhhmmss.sss|seconds    |deg     |deg     |amin|amin|deg     |deg    |deg     |deg    |deg     |deg     |amin|amin|deg     |deg    |       |               |      |

Format for reading the data:

        integer*4 month, day, hour, minute
        real*8 seconds
        real*8 time, ra_sts, dec_sts, sigin_sts, sigx_sts, pa_sts, 
        real*8 sig_pa_sts, fp_ang, sig_fp_ang, ra_bs, dec_bs, 
        real*8 sigin_bs, sigx_bs, pa_bs
        integer*4 numpacket, qflag(15)
        character*6 spare

        read("ipac_att_lan", 100) month, day, hour, minute, seconds, 
        time, ra_sts, dec_sts, sigin_sts, sigx_sts, pa_sts,
     &  sig_pa_sts, fp_ang, sig_fp_ang,
     &  ra_bs, dec_bs, sigin_bs, sigx_bs, pa_bs, sig_pa_bs, numpacket,
     &  qflag, spare 

100     format(1x, 4i2, f6.3, 
     &  f12.3, 2f9.4, 2f5.1, f9.4, 
     &  f8.4, f9.4, f8.4,
     &  2f9.4, 2f5.1, f9.4, f8.4, i8, 1x, 15i1, 1x, a6)

Definition of Variables

Figure Captions

• Figure 1. The plot of residuals of reference stars from the reconstructions, in the in- and cross-scan directions, before the periodic trend was removed from the boresight.

• Figure 2. The plot of residuals of reference stars from the reconstructions, in the in- and cross-scan directions, AFTER the periodic trend was removed from the boresight.

• Figure 3. The scatter of in- and cross-scan positional differences between MIRS detections relative to the C2 point of the STS.

• Figure 4. The histogram of the distribution seen in Figure 3 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.

• Figure 5. The histogram of residuals in Figure 1, in the in- and cross-scan directions.

• Figure 6. The histogram of residuals in Figure 2, in the in- and cross-scan directions.