Important ROSAT Dates
Below are listed the more important dates associated with ROSAT operations:
- 2011 October 23
-
ROSAT re-entered the atmosphere sometime between 01:45 to 02:15 GMT Sunday, October 23, 2011
- 1999 February 12
-
ROSAT turned off
- 1998 December 8
-
PSPC-B put back into the focal plane of the XRT to use remaining gas
for observations.
- 1998 September 20
-
Spacecraft lost attitude control and the HRI was severely damaged during an
accidental slew near the sun.
- 1998 August 21
-
Nominal timeline was resumed with WFC star tracker in the attitude control
system.
- 1998 June 1
-
Eight-year anniversary of ROSAT's launch.
- 1998 April 28
-
Last XRD star tracker failed. Attempts are made to add the WFC
star tracker to the attitude control system.Timeline suspended
- 1997 June 1
-
Seven-year anniversary of ROSAT's launch.
- 1997 January 17
-
Routine reset of the spacecraft clock was initiated.
- 1996 December 19
-
ROSAT satellite entered a safe mode caused by an erroneous signal from
the star tracker. Normal timeline operation was resumed about 11 hours later.
- 1996 June 1
-
Six-year anniversary of ROSAT's launch.
- 1996 May 15
-
AO-7 proposals due.
- 1996 April 29
-
ROSAT long-term science mission plan session at San Diego HEAD meeting.
- 1995 December 2
-
First AMCS safe mode since 29 October 1994, Eight-hour duration.
- 1995 October 1
-
HRI hot spot reported.
- 1995 September 25-29
-
Wuerzburg Meeting: "Roentgenstrahlung from the Universe"
- 1995 July 3
-
New AMCS software tested for operating with fewer gyros.
- 1995 June 1
-
Five-year anniversary of ROSAT's launch.
- 1995 May 15
-
AO-6 proposals due.
- 1994 November 3
-
Safe mode triggered by solar eclipse. Timeline restarted the following
day.
- 1994 October 31
-
Release of the WGAcat ROSAT source catalog.
- 1994 October 26
-
Release of the MPE ROSAT source catalog.
- 1994 September 5-11
-
Final normal timeline operation of the PSPC.
- 1994 June 1
-
Four-year anniversary of ROSAT's launch.
- 1994 April 25-28
-
Pointing difficulties.
- 1994 March 31
-
AO-5 proposals due.
- 1994 February 27
-
New angular-momentum-stabilized operating mode for ROSAT to compensate
for lack of startracker and sunsensor information.
- 1994 Feb 2
- A reduced pointing observing program began, due to AMCS problems.
- Dec 1993-Jan 1994
- In December and early January there were a number of occasions during
which problems in ROSAT's attitude measurement and control system (AMCS)
caused the satellite to drift away from its nominal pointing direction.
This resulted in the safe mode being triggered.
It soon became clear that the problem was related to the new attitude
control strategy, which became active after the Z-gyro failure that occurred
in November 1993. For more information see rosat status report
#83. In December 1993 and January 1994 ROSAT, was only partially operational.
Observations actually carried out are listed in
dec93-feb94.obs.
- 1993 December 18
- ROSAT entered safemode again. During the days that followed, different attempts
to recover from the safemode were only partially successful and never for
more than one orbit. On December 22, the wobble was disabled, which seemed
to help avoid safe mode.
- 1993 November 26
- Timeline operations were resumed with a modified observing program,
constructed under the boundary conditions that slews occur only on the day
side and no observations be carried out with a sun cone angle between 85
and 95 degrees.
- 1993 November 18
- Z-axis gyro failed permanently, sending ROSAT into safe mode.
- 1993 September
- A roll angle error was found. The effect of this roll error was not included
in the current SASS processing. (It will be included in the "Rev1"
reprocessing of the entire dataset planned for the near future.)
- The error was small, being 0.185 degrees for the PSPC. This error corresponded to a
position error of 6 arcseconds at the radius of the support ring.
- 1993 September 22
- Survey Data made available for background estimations.
- 1993 August 10
- The Off-Axis Point Spread Function algorithm was released.
- 1993 August 1
- MPE and GSFC (in consultation with SAO) concluded, through independent
analysis of calibration and other data, that there was some temporal
variation of the PSPC gain that was not included in the gain correction
process currently applied to data in SASS.
- This effect showed up primarily as inconsistencies between calibration
spectra of N132D taken at different epochs across the ROSAT mission.
Another artifact of the problem was the highly significant residuals in number
of spectra compared to the expected model. These appeared as large negative
residuals below about 0.20 keV and large positive residuals between about
0.20 to 0.4 keV.
- 1993 June
- The HRI was moved into the focus on June 10 for the last time in AO-3.
The PSPC gas-flow rate was reduced the same day. The PSPC had time
until June 15th (the beginning of AO-4) to settle down at the new
equilibrium. Immediately after the switch-on on June 15th, an extended
radioactive source calibration was started, which was followed by one orbit
of filter-wheel-closed background measurements. This procedure was
repeated the next day. For the first week after the switch-on, the
radioactive calibrations were repeated once per day. Background
measurements are taken once per week for one orbit.
- The PSPC performance at reduced flow rate looked good. The
gain dropped slightly, from channel 103 before to 100 after the
switchover.
- Attitude error: two cases were found where the AMCS after a slew locked on to a wrong star
pattern-due to the reduced accuracy of the onboard
gyro system. In both cases, only two stars were available in the
startracker field of view and the commanded star pattern (essentially
star separation and the magnitudes) were fulfilled also by a nearby
star pattern, about two degrees off from the commanded position. Both the
on-board and the ground system attitude software system therefore assumed
a correct pointing and could not recognize the error.
- 1993 May
- The malfunction of STC 1 was traced to a failure in the
conventional RAM area. This failure was similar to the
cause of the complete loss of STC 2 in autumn 1990, when a much
more vital memory cell was lost, rendering STC 2 unusable. The
STC 1 anomaly has stabilized at a rather lower failure rate than observed
in January/February, corresponding on average to a 5-10 percent loss of
observing time.
- 1993 Jan 10
- Problems with startracker 1. In about
30 percent of the slews to a new target position, the mapping period of the
startracker at the end of the slew takes more time (from 1 up to 20
minutes) for the tracker to enter the pointing mode. This lead to a
minor shortening of some of the observations, while a few targets were
lost.
- German and UK data entered the US archive later the same month.
- 1993 Feb 24
- 1000 days in orbit celebration
- 1993 Jan 12
- A new PSPC response matrix was released
- 1992 Nov 1
- The US ROSAT Public Data Archive (USRPDA), located at the Goddard Space
Flight Center in Greenbelt, MD, officially opened.
- 1992 March
- The MPE/GSFC/SAO ROSAT calibration team found that the HRI point-spread
function had an unexpected component, which redistributes roughly 10 percent
of point-source photons beyond a central core (radius ~ 10 arcsec) and
into a region that extends out to about 5 arcmin, an effect that is
relatively independent of energy.
- 1992 Feb 06-24
- A large transient in the ROSAT Z-gyro current occurred late on Feb 06,
reminiscent of that which immediately preceded the loss of the Y-gyro in
1991 May 12. The s/c was put into safe mode at that time and
observations were suspended.
- The Z-gyro, although continuously with too high a current, was still
giving meaningful readings of angular velocities. However, its output signal
seemed to be scaled wrongly, indicating speeds slower by a factor of three or four than
the spacecraft actually was performing.
- Evaluation
of the Z-gyro malfunction proved that the measurement outputs of
the Z-gyro were still valid, however, the scale factor had changed by a
constant factor of 2.8. The most convincing explanation of the available
data implied that one of three phases of the gyro motor failed, and consequently
the motor current had increased.
- To compensate for the decreased Z-gyro output, a new change of the onboard
software was developed and tested on the GSOC simulator over Feb 18-19.
This software patch contained the change of the Z-gyro scale factor by
280 percent.
- This software update meant that the scale factors of the other gyros
cannot be commanded anymore, which fortunately has little impact on mission
operations.
- The software patch was successfully up-linked on Feb 20 and passed a
first test in the form of a slew to the north ecliptic pole on the same
day. After the slew, the attitude was correct and reference stars were
identified.
- ROSAT went back on the Mission Timeline on 1992 Feb 24
and the first three slews were successfully performed. This success indicated
that the new gyro scale factor was correctly determined and appeared to be
quite stable.
- 1991 Nov 04
- The new AMCS onboard software allowed a successful resumption of normal
pointing operations, marking the end of the reduced pointing
phase (which followed the loss of the Y-gyro on May 12)
and the start of AO-2.
More than two hundred pointings were carried
out in the reduced pointing phase, most of them lasted one day
(and were selected from AO-1 targets with approved times
approximately great 10^4~s).
The scheduling
constraints varied quite frequently and required rapid adjustments by both
MPE and GSOC mission planning staff.
- 1991 Oct 14
- During October, the PSPC-B developed a slightly higher background rate
extending over the whole sensitive area of the detector, but confined to the
lowest pulse height channels. A hot spot near the edge of the field of view
also was observed. Investigations revealed that the hot-spot count rate had
increased from about 0.001 to about 0.01 cts s^{-1} over the
preceeding approximately six-month period. Purging of the detector gas and
switching the gas supply from tank B to tank A (to exclude the possibility of
different gas composition) reduced the hot-spot count rate and the count rate
in the lowest pulse height channels by a factor of approximately two. Although
no immediate danger for the detector operation could be identified, the high
voltage of the detector was lowered from 3060 to 3000 volts on October 14 . As
a consequence, the PSPC-B gas gain dropped by approximately 30 percent, and
thus the lower energy range limit of the detector was raised from about 70 to
about 100 eV. Calibrations at the reduced voltage have shown that there is
no change in the spectral resolution of the detector
- 1991 July 05-08
- After a long slew on Jul 05, ROSAT became lost due to Earth-block
and lack of guide stars. Consequently, the s/c went into safe mode due to
operating too long without reference stars. Successful
recovery procedures were carried out over the weekend of Jul 06-07.
- 1991 May 18 - Nov 04
- Reduced-Pointing mode, whereby slews and target acquisition were
tightly constrained due to the use of the X-gyro in the control loop.
Slews were reduced to one direction and constrained to be
short, guide stars needed to be available when the satellite was over
Weilheim (i.e. target declinations were constrained to be > +20 degrees), a
reduced sun cone angle was enforced (90 +/-5 degrees),
only one target was observed per day,
and only PSPC observations were allowed.
- Also during this period, an increased level of solar activity led to high
levels of radiation, causing the detector to safe itself several times.
These conditions resulted in a yield of about 30,000 seconds of ROSAT
data for each approximately one-day observation.
New AMCS on-board software enabled a successful resumption of normal pointing operations on 1991 Nov 04.
- 1991 May 12-18
- It became clear that WFC count rates were systematically less than expected
based on the WFC survey. A calibration observation of RE1629+781 confirmed
the gain loss, and showed that a new operating voltage was required. The
WFC count rates were determined to be sim 20 percent of the expected values
and the backup detector degradation was even more severe than that suffered
by the primary.
- The Y-axis gyro on ROSAT failed, sending the satellite into safe mode.
The Z- and S-gyros functioned normally, but the X-gyro is problematic (and was removed from the control loop during the All-Sky Survey after
its drift rate exceeded specifications).
Attitude control was successfully regained on May 18.
There appears to be no hope of retrieving use of the Y-gyro.
- 1991 Apr 26-30
- Difficulties were encountered with the uplinking of new software patches
developed to address the problems of maintaining known attitude, resulting
in the satellite switching to safe mode. By Apr 30 the problems were
resolved.
- 1991 Apr 06-10 and Apr 21
- ROSAT suffered a loss of attitude on Apr 06, and subsequently
ended up in safe mode as a result of the extra safety procedures implemented after the loss of PSPC-C.
Observations scheduled for 1991 April 06-10 were lost.
A further attitude loss occurred on Apr 21 resulting in the loss of an
additional day of data before normal operations were restored.
- 1991 Mar 25-27
- Solar flare activity in 1991 much enlarged the radiation belts and
increased the PSPC-B background, causing a loss of
observations due to the PSPC-B count rate exceeded the danger threshold.
Adjustments to the tolerances led to resumed operations, with 80 percent of the
pre-flare efficiency.
- 1991 Feb 08
- AO-1 pointed observations were begun using (the reserve) PSPC-B.
Some survey observations were made to make up for some losses of July 1990.
- 1991 Jan 25
- With all but the last week of the six-month all-sky survey completed,
an onboard computer glitch caused the ROSAT spacecraft to tumble out of
control for approximately 15 hours.
Housekeeping data taken during the tumbling showed that the
satellite scanned across the sun,
burning a hole (and hence destroying) in the window of PSPC-C
and damaging the S2a filter in use on the WFC.
During the subsequent contact cycle, the status of the spacecraft was
recognized and the proper safemode reached.
The (final) one-week (approximately) strip of the sky that went unobserved during this
time was surveyed later between 1991 August 03-13, thus
completing the All-Sky Survey.
- 1991 Jan 15-18
- At 07:10 UT, the survey rate was increased to 1.2678 degrees per day.
- 1990 Dec 22-26
- Gyro malfunction and subsequent loss of telescope attitude.
- 1990 September 08
- The ROSAT AMCS star tracker STC-2 stopped working
continuously during the scan mode and has since failed completely.
STC-1 remains fully operational, and there is only a minor decrease in
expected attitude accuracy.
- 1990 August 17-19
- Valve which regulates the flow of gas into the PSPC-C failed on Aug 17.
The gas pressure dropped to a point where the high voltage was automatically
switched off.
No PSPC data were taken between 1990 Aug 17 14:00 UT and Aug 19 00:00 UT,
but a backup value was switched on.
Since no area of the sky went totally unobserved, the decision was made not
to alter the offset angle and to proceed with the survey timeline as
planned.
WFC survey observations continued as planned during this period.
- 1990 July 30
- ROSAT all-sky survey begins (using PSPC-C in the focal plane)
- 1990 July 16-29
- PVC phase pointed observations using the PSPC (Jul 16-23)
and HRI (Jul 24-29).
- 1990 July 11-15
- As part of the PVC phase, the ROSAT `mini-survey' was performed.
- 1990 July 01
- One of the two WFC background monitoring instruments (GM tubes)
malfunctioned, causing WFC operational difficulties.
- 1990 July 01
- XRT/HRI First Light Observation of Cyg X-2.
- 1990 June 17
- WFC First Light Observation
- 1990 June 16
- Start of scientific observations with the First Light
Observation of the XRT/PSPC-C pointing at the LMC.
- 1990 June 01
- Launch of ROSAT spacecraft on a Delta II from Cape
Canaveral, USA, and in-orbit deployment.
Initial switch-on and on-board engineering tests were performed
without any indications of hardware or software problems.
Curator:
Michael Arida (ADNET);
arida@milkyway.gsfc.nasa.gov
HEASARC Guest Observer Facility
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