DESCRIPTION OF THE 1995 FLIGHT OF SERTS
The SERTS imaging EUV spectrograph will be flown on May 15, 1995 at approximately 12:00 Noon local time (1800 GMT) from White Sands, NM.
OBJECTIVES
The primary objectives of this flight will be to
Measure the temperature of 'rays' in the northern polar coronal hole using line-ratios. This northern region is chosen because it is being probed by the Ulysses spacecraft.
Obtain high resolution spectra of both the quiet and active Sun corona.
To to this, we expect to orient the SERTS instrument so that the slit is aligned in roughly a North-South direction. The wide portion of the slit will be placed over a portion of the northern polar hole, with the narrow slit on the solar disk. SERTS will be re-pointed to a second position by pitching the instrument parallel to the slit. Image demonstrating how the SERTS aperture might be pointed.
These plans will be reviewed continuously during the weeks prior to the flight, and the final target(s) will be chosen to optimize the scientific return from the flight. Updates will be provided here on the SERTS home page.
INSTRUMENT DESCRIPTION
The Solar Extreme-ultraviolet Rocket Telescope and Spectrograph (SERTS) is a stigmatic (imaging) spectrograph operating in the EUV. It combines high spatial and spectral resolutions over the full wavelength range of 170-450 A. A description of the basic SERTS instrument is available.
The 1995 SERTS flight features a grating which is physically similar to the gratings flown in the past, but it has been coated with a multilayer tuned to the region around 195 A. This coating will enhance lines seen in second order (170-225 A), including prominent lines of Fe IX-XIV. These should provide excellent temperature diagnostics. At the same time, the strongest first order lines like FeXVI 284A, HeII 304, and FeXV 335 will also be seen.
COLLABORATIVE OBSERVATIONS
The following collaborative observations are planned:
Yohkoh SXT images of the targets will be obtained prior to and at the time of the SERTS flight.
Kitt Peak will obtain magnetograms and HeI 10830 images will be obtained by Harry Jones.
Red and Green line observations will be obtained from Sacramento Peak Observatory by Tom Moran.
VLA observation of the target areas will be obtained by S. White.
May 25, 1995 STATUS
The flight EUV film has been developed and shows beautiful imaged spectra at both pointing positions for a range of exposure times. Quick visual inspection indicates that spatial and spectral focus were excellent. The He II 303.78A and Si XI 303.32A lines are easily separated, for example. At the first pointing position, the limb appears sharp in He II 304A, and contrast between the general quiet sun and the northern polar coronal hole is clearly seen at that wavelength. Active region AR7870 is also well placed in these frames, showing considerable EUV structure which again demonstrates good optical focus. The second pointing position aimed for high resolution spectra of AR7870, and many lines appear throughout the full bandpass in these frames. In fact, one very pleasant surprise is the number of lines appearing between 235 and 300A. The new multilayer coated grating was designed to enhance efficiency in the range 170 - 220A; we were prepared to sacrifice some performance outside that band. But quite a few 'out of band' lines appear, even so. Next comes film microdensitometry, and quantitative analysis. Then the fun really begins!
May 15, 1995 (Post-Flight) STATUS
The SERTS experiment launched on time at 18:00UT, and had a gorgeous flight. All telemetry indications were positive. The EUV film advanced as planned and on schedule. The real-time slit-jaw video showed that both pointing positions were accurate, and extremely stable. Solar acquisition occurred more quickly than on any previous flight, and stability was maintained throughout the entire exposure sequence. Recovery was smooth, and the instrument seems to be in excellent condition. As far as we can tell at present, it was a near perfect flight. The instrument is now being cleaned and dismantled in order to remove the main film camera. The EUV film itself will be developed back at Goddard Space Flight Center next week, after we return home. The entire SERTS team would like to thank all of you who supplied supporting data, equipment, effort, or encouragement. It was great!
May 15, 1995 STATUS
Final target coordinates have been inserted, the payload is fully pumped down, and we are ready for launch. Target position 1 now places the center of our spectrometer slit at solar N28.0/W13.0 with an angle to the solar axis of 24.21 degree. Position 2 puts our slit center at N09.0/W20.0 without changing its roll angle. See the previous status report below for a description of the scientific objectives for these two observing targets.
May 13, 1995 STATUS
We have selected the following two pointing positions for our flight at 18:00UT on May 15. Position 1 places the center of our spectrometer slit at solar N30.0/W15.0 with an angle to the solar axis of 23.29 degree. This provides: a) high resolution EUV spectra of the quiet sun at mid-northern latitudes; b) spectroheliograms of the northern quiet sun, polar coronal hole, and coronal rays at the north pole out to a distance of more than 0.2 solar radii; and c) spectroheliograms of active region AR7870. Position 2 puts our slit center at N09.3/W21.9 without changing its roll angle. This provides a) EUV spectra of a cut perpendicular to the primary active region loop system in AR7870; b) spectroheliograms of the quiet sun regions from which spectra were obtained in the first pointing position; and c) spectroheliograms of AR7869 and the X-ray emitting loops that extend from that active region to the south-east. See the photo in GIF or (higher resolution) PostScript format which overlays our planned aperture positions on a rotated X-ray image from Yohkoh. These positions will be refined early on Monday from the latest ground-based and Yohkoh images, and frozen by 16:00UT, two hours prior to launch.
May 12, 1995 STATUS
SERTS is now almost ready for launch. The ballast ring was received yesterday afternoon and installed. After the payload passed its final vacuum-leak check, it was taken to the launch rail and mated to the Terrier - Black Brant rocket motors. A 'boom' test was carried out successfully, followed by another full-scale flight simulation run, which also went well. This weekend will be spent pumping on the instrument, and making final observing target selections.
May 9, 1995 STATUS
Preparations for a May 15 launch continue to go remarkably smoothly, as we passed the 'horizontal' simulation run in fine shape. The flight EUV film has now been loaded into the main data camera, the instrument has been thoroughly cleaned, and we are in process of pumping it down for final vacuum-leak checks. A ballast ring is being fabricated at Wallops to bring the payload's center of mass closer to optimum; it will be installed on Thursday. In addition to continued instrument pumping and yet more practice on flight control operations, focus will now shift to selection of observing targets, as the solar disk that will be visible during flight rotates into view.
May 6, 1995 STATUS
The optical alignment of our instrument after vibration is now better than we have ever been able to achieve at this stage on prior flights. Light-leak tests demonstrate that the present Aluminum filter is intact and without pinholes, so that there is no need to replace it. Exhaustive runs were carried out yesterday and today using the new ground link command system, practicing both the normal flight sequence, as well as contingency procedures to recover from a wide range of potential anomalies. The instrument is now being buttoned up to prepare for the full-scale 'horizontal' flight simulation scheduled for Monday morning. We then move it to the flight rail on Thursday. By coincidence, Dale Gary and Hal Zirin had previously planned to observe the north polar region at 8.5 & 15 GHz with the VLA on May 15, just at the time of our flight. These data should provide an excellent complement to our EUV measurements.
May 4, 1995 STATUS
The SERTS payload has now been through spin balance and full-level vibration testing in all three axes. The post-T&E flight simulations show that all systems are functioning well. In particular, the experiment sequencer started properly both from ground telemetry command and from the internal backup timer. Next will be measurements to verify optical alignments. Then we move to the heliostat, which presents visible sun-light onto the instrument. This allows tests of the slit-jaw video camera, and practice with the new joy-stick system for in-flight pointing corrections. Checks will also be made at this time to assure that the EUV spectrograph has no visible light leaks. Several spare filters are now on hand, should any problems arise.
April 28, 1995 STATUS
The initial flight simulation test yesterday showed that both internal timers and the telemetry system supplied by the rocket support team at White Sands did not function properly. Lockheed personnel worked through the night to find and fix these problems, and further tests today verified that all systems now operate as expected. Additional electrical tests will be performed on Monday, and T&E is scheduled for Tuesday thru Thursday.
April 26, 1995 STATUS
The SERTS instrument and crew have now arrived safely at White Sands Missile Range. Basic checks of electrical connectors and optical alignments show that the payload survived shipment in good condition. However, some damage occurred to the ground-support vacuum system, which was eventually repaired. Integration of the instrument with the rocket pointing-control and telemetry sub-systems is underway. The present SERTS crew consists of Principal Investigator: Joseph Davila, Co-Investigator: Roger Thomas, and Technicians: Dave Linard and Pat Haas.
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Responsible NASA Official: joseph.davila@gsfc.nasa.gov
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