DESCRIPTION OF THE 1999 FLIGHT OF SERTS
Successful Flight: 1999 June 24 at 17:00 UT
July 29
Although decompression of our science data is still in progress, we now have processed enough to assure that their quality are excellent. The focus was good, the wavelength range was as planned, the exposures times were just right, and the pointing was on target. Spectral data were not affected after all by the cracking of the entrance aperture late in the flight. The EUV spectrum shown below is a composite of two flight frames taken on target 2; the portion between 333 - 338 A is from a 2s exposure, while the rest is from a 90s exposure. Even without dark-image correction or flat-fielding, numerous spectral lines are clearly seen from a solar area co-observed by both CDS and EIT, so that our goal of cross-calibration with SOHO can indeed be achieved.
Tue. July 27
An initial co-alignment has been made between SERTS-99 EUV images and those taken simultaneously by the EIT and CDS instruments onboard SOHO.
This EIT image in the Helium II line at 304 Angstroms shows the CDS (black) and SERTS (white) fields of view. Each of the three SERTS pointing positions are shown with differing line styles. In pointing positions 2 and 3, the SERTS slit fell well within the CDS field of view, while position 1 observed in a relatively quiet area of the Sun.
Fri. June 25 (T + 1)
Post-flight optical alignment checks and packing are the tasks for today. Now we can look forward to getting back home at last, after a grueling, but exciting few weeks in the field. Then there is all that wonderful new EUV spectral data to analyse from what would have to be called a very successful SERTS-99 flight!!!
Thu. June 24 (T + 100 Min.)
Rocket recovery is proceeding - all nine exposures have been received and they are being decompressed.
This is a raw SERTS-99 flight image - the first 2-second exposure. The 2-second exposure is the shortest SERTS exposure. The 'lobe'-emission on the left is from He II 304A, that towards the right is from Fe XIV 334A and Fe XVI 335A.
The rocket was recovered and initial checks indicate that the experiment survived the flight.
Thu. June 24 (T + 20 Min.)
Operations during the SERTS flight proceeded nominally. A crack appeared to form at the corner of the slit during the final few seconds of the last exposure; this should not seriously affect the data on this one image, but its cause will need to be investigated further. Targetting was successful and preliminary evidence indicates that the science experiment was successful. Recovery will proceed shortly and we are awaiting science telemetry data.
Thu. June 24 (T - 1 hour)
SERTS is GO for launch! Rocket motors are being armed and we will proceed at 1700 UT!
Wed. June 23 (T - 1)
The final "vertical" test proceeded without any problems. We are doing final checks of the cooling system, but we are "go" for launch. The pointing for the observation targets has been chosen: (-450,300) arcsec from Sun center, which corresponds to 20 degrees North and 30 degrees East heliocentric location.
Tue. June 22 (T - 2)
The instrument is on the launch-rail attached to the rocket motors, and is being pumped down to vacuum in preparation for the flight. All the needed electrical and cooling lines have been connected and checked out between the blockhouse and payload; we are just about ready to go. Now the focus turns to solar target selection. Our present plan is to observe with our slit oriented in roughly an east-west direction the area centered near N23E23 (x=-340,y=+340 arcsec); this would allow us to get data on an extensive complex of active regions there, as well as coverage in one lobe of the corona above the limb. These coordinates will be refined tomorrow morning based on the latest images from SOHO.
Mon. June 21 (T - 3)
With lots of sunshine at last, we were able to complete all needed instrument tests requiring the heliostat, such as checks for detector light-leaks and validation of slit-jaw camera operation and alignment. The new detector cooling system has been installed at the rail and checked out before being attached to the payload. Another potential target has appeared at the sun's east limb, AR8594, which will be located near N14E35 at the time of our flight.
The Mission Readiness Review (MRR) proceeded without incident. A few minor things must still be resolved before launch, but otherwise it was agreed that everything is nominal. A final end-to-end test will be done before we ship the payload to the launch rail.
Sun. June 20 (T - 4)
Constant rain and heavy overcast sky forced us to postpone the heliostat tests yet again. We will just have to hope that Monday morning is better, because the next step is to move the payload to the launch rail for mating with the rocket motors; no further optical testing will be possible after that. Solar active region AR8592 has appeared on the east limb, and is now our baseline target for planning purposes at this early date; its projected position at the time of launch will be fairly near disk center at N23E10.
Fri. June 18 (T - 6)
The instrument and its supporting systems were completely assembled in their final flight configuration. Unfortunately, clouds yesterday and today are preventing us from doing the needed post-vibration optical tests in sunlight from the heliostat; these will have to be done over the weekend. The bit-sync error was found to be a hardware problem that somehow adds extra bits to the data stream after it is transmitted from the rocket; since no data are actually lost, this can easily be fixed either in software or by changing out some ground-receiver equipment. A new control function to allow cycling of power to the detector's vac-ion pumps during flight if necessary was wired into the instrument and checked through the ground Command Link. The full-up formal 'horizontal' flight simulation was run, which tests every part of the payload's mission profile that can be done at this point. In particular, we verified that the new flight-support sequence and science-exposure program worked exactly as expected, as did all ground-command functions. A minor misalignment in roll between the instrument and the pointing control nozzles was corrected, and the instrument was then moved into the heliostat room to await some sunshine.
Click here to view photos from the horizontal test.Thur. June 17 (T - 7)
Analysis of yesterday's data shows that a bit-sync error first seen before vibration is still causing some telemetered science data to be garbled; though this is being fixed, we are glad to now have an on-board data recorder as backup in case of any such telemetry problems during flight. Another new feature for this flight is a system to cool our detector while on the launch rail right up to the moment of lift-off; we began installing it today. Final trajectory predictions just became available; with these and the results of the latest flight-simulation tests, we have negotiated final timings for all support events, such as power on/off, door open/close, etc., which are now being programmed into the on-board flight controller. The science-exposure sequence was also optimized for the new trajectory predicts; a new camera controller was fabricated, installed, and checked through our own Ground Support Equipment. Post-vibration alignment measurements were made between the telescope and sun-sensor so that appropriate corrections can be applied for accurate solar targeting.
Wed. June 16 (T - 8)
We are arranging to have a webcast showing the SERTS-99 rocket launch and images from its on-board slit-jaw camera in realtime, as well as providing audio of the operations-communication channel; information on how to hear & view these will be posted soon. Detailed plans are being negotiated for coordinated observing programs with various spacecraft and ground-based observatories; the latest information about these can be found on our Coordinated Observations page. Timings of some functions in the flight profile were adjusted to fix two instances of interference noted in yesterday's tests. Full-level vibration of the assembled payload in all three axes was carried out this morning. Afterward, extensive flight-simulation testing showed that all essential systems continue to operate properly, although some additional adjustment was indicated for the exact timing of a few functions. This was our first chance at WSMR to stimulate the EUV monitor supplied by USC, and it also seems to be working fine.
Tues. June 15 (T - 9)
The instrument was reconnected to the rocket support systems, and the flight simulation sequences of last Friday were run again, with some modifications to the exact timing of certain activities due to a more accurate prediction of the flight trajectory. The detector showed no sign of vacuum leaks during any of these runs. A few minor discrepancies were noted in the timing or operation of some functions, which should be easily fixed. The payload was then moved to the Vertical Assembly Building for spin balancing, bend testing, and final determination of weight, moments of inertia, and center of mass.
Mon. June 14 (T - 10)
A slight misalignment of the slit-jaw viewing camera was corrected, and the instrument reassembly was completed. This included installation of the student package provided by three classes at D.C.'s Bunker Hill Elementary School as a part of our Educational Outreach program. One effect of the leak seen on Friday was that a built-in safety circuit turned off the vac-ion pumps; a new command option is being wired into the payload so that we can override this if it should occur in flight. The total payload was then pumped down to allow another leak test late in the day. To the delight of all, that test showed that the leak we had seen earlier is now gone, which means that we can once again plan for a full observing sequence on the scheduled launch date.
Sun. June 13 (T - 11)
Careful examination of the detector by-pass valve and its operation did not reveal any obvious cause for leaks. We did find an unintended blob of epoxy on one of the gears that drive the valve, and that was thoroughly cleaned off. The instrument was then partially reassembled and the detector is being pumped down for further testing tomorrow to see if the leak is still there. An alternate observing sequence was developed, if needed, which would give additional exposure to the vacuum of space before turning on the science camera. This would allow us to operate the intensified CCD-detector safely even if its housing continues to leak, so that we can still keep to our planned launch schedule.
Sat. June 12 (T - 12)
The instrument was dismantled, and the Aluminum foil window of the detector housing was visually examined for flaws, but it showed no obvious indication of tearing or failure. Other tests are now underway on the detector by-pass valve, which was the other main suspect in causing the leaks that we saw yesterday.
Fri. June 11 (T - 13)
Because the guidance sensors had to be re-mounted yesterday, they were re-aligned today to the optical axis of the instrument. Then the integration of the instrument to the rocket support sub-systems was continued. "All-fire" tests were run to verify that all these systems were working properly. These runs also gave us the first opportunity at WSMR to open our detector door in vacuum, at which point we discovered a fairly substantial leak in the detector housing. Arrangements were made to ship from GSFC a replacement thin-Aluminum foil window and other spare parts for components that might be the cause. We will attempt to find the source of the leak and fix it over the weekend. Test measurements of the detector itself showed that it was not damaged in any way by the incident, so we hope to stay on schedule with some extra work.
Thur. June 10 (T - 14)
The instrument was moved to the heliostat, where we checked out the H-alpha slit-jaw camera and got some practice with the joy-stick system for in-flight pointing corrections. Here a problem was discovered with the mount for the two guidance sensors. By the end of the day, Dave Linard designed and built from scratch a sturdy extension that solved the problem beautifully, a truly impressive feat.
Wed. June 09 (T - 15)
Optical measurements showed that the alignment of the telescope, spectrograph, and guidance sensor are well within specs. The instrument was electrically connected with the rocket pointing-control and telemetry sub-systems. Initial flight simulations were run to check each of the two redundant on-board command timers and the flight telemetry system, as well as the built-in instrument observing sequence, all of which performed just as expected.
Tues. June 08 (T - 16)
The payload arrived intact at White Sands Missile Range (WSMR), where electrical checks showed that it survived shipment in good condition. At the Range Project Initiation Meeting, we learned that our launch window of 30 minutes starting at 1700UT on June 24 has been officially approved, but that there is no definite backup date available. So it looks like we just need to make sure we launch on schedule! This launch time is important, since it was chosen to get observations within 2 hours of local solar noon at WSMR, with Yohkoh in daylight and with TRACE in a clean part of its orbit.
Wed. June 02 (T - 22)
The SERTS team is preparing to ship the experiment to White Sands, NM, for its 9th flight, now scheduled for 1999 June 24 at 1700UT. The experiment will leave for White Sands on June 6, with the team departing a day later. Information on how to participate in the observations can be found on the SERTS-99 Coordinated Observations page. This flight will feature our first use of a Ritchey-Chretien normal-incidence telescope. News on the development of this telescope is also available.
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Responsible NASA Official: joseph.davila@gsfc.nasa.gov
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