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Laboratory for Atmospheric and Space Physics


MAY 1, 1999

Three papers describing initial results from the SNOE mission were published in Geophysical Research Letters. These papers are available as Portable Document Format (PDF) files from the Publications page.

February 28, 1999

SNOE completed its first year of operations on February 26. The spacecraft continues to perform well, and scentific results have exceeded expectations. We look forward to another successful year, and once again thank the individuals and institutions who made this mission possible.

January 31, 1999

January was a routine month, excepting only some minor ground station configuration anomalies. Solar activity has continued to increase, with the F10.7 index reaching 184 in late December and 178 in late January. Solar soft X-rays in the 2-10 nm range have shown variations by a factor of 4.5 since the start of the mission.

December 31, 1998

Four papers analyzing SNOE data were presented at the fall meeting of the American Geophysical Union in a special session, “Odd Nitrogen in the Upper Atmosphere”. Relationships between low-latitude nitric oxide and the solar X-ray flux and between high-latitude nitric oxide and auroral activity were shown. Theoretical results given in the SNOE papers and in other papers at the session quantified the photochemistry and auroral processes responsible for the observed relationships. Good agreement was found between SNOE results and other measurements.

November 30, 1998

November saw the solar beta angle (the angle between the sun and the orbit plane) reach a minimum of 15 degrees on Nov. 20. This was at the limit of the protection zone for the Earth-viewing instruments, but not harmful. The beta angle is now increasing and will remain at safe values through September 1999, but the long-term trend is a drift toward the solar plane which could necessitate attitude adjustments in October-November 1999. Another non-event was the Leonid meteor shower on November 17, which caused much concern in the space flight operations community but had no effect on SNOE. There was a spurious computer reset on Nov. 29, the first in 83 days.

October 31, 1998

Operations were routine during October. The hardware command occurence rate has diminished, with only a non-essential-bus off command executed on October 3, which was recovered in real time.

September 30, 1998

Other than a spurious computer reset to EEPROM on Sept. 6 that lost 8 hours of science data, operations and data analysis continue to be routine. The period Sept. 21-26 had slightly anomalous spin axis pointing due to an axial torque rod command timing error. Late September also saw another period of enhanced solar and geomagnetic activity as solar cycle 23 continues to ramp up.

August 31, 1998

An increase in solar activity and another series of intense auroral storms during late August caused high levels of nitric oxide production. Four abstracts describing scientific results from SNOE were submitted to special session SA01, “Odd Nitrogen in the Upper Atmosphere”, of the fall 1998 American Geophysical Union meeting.

August 15, 1998

Routine operations continue after the reset problems in late July and early August. The hardware command reset occurence rate has been about 2 per month over the course of the mission, with typical loss of about a half-day of data each, so we are losing about 3% of the otherwise continuous data. Recoveries have been quick, however, usually occuring in real time during the course of the pass, and there have been no apparent engineering problems related to this annoyance. There have also been a few spurious non-essential-bus-off hardware command accepts, but those are generally recovered immediately with minimal loss of data. The spurious commands mostly occur during acquisition of signal at the start of a pass, which tends to validate the theory that they are caused by the minimum hardware command decoder response to random noise in the signal received by the spacecraft.

August 5, 1998

A spurious computer reset to UVPROM lost 20 hours of science data.

July 26, 1998

A spurious computer reset to EEPROM lost 5 hours of science data.

July 24, 1998

A spurious computer reset to EEPROM lost 14 hours of science data.

July 17, 1998

Attitude control has been improved using a revised computation of torque rod activation sequence positioning. The small per-orbit circle around orbit normal has been tightened up to about half a degree in radius. Operations continue to be uneventful with near-continuous instrument data being received.

July 5, 1998

Routine operations continue. Data from four solar rotations with moderate ultraviolet and X-ray modulation have been obtained.

June 23, 1998

A spurious computer reset to EEPROM at acquisition of signal occured during a pass over Wallops Island, resulting in the loss of 24 hours of science data.

June 17, 1998

Operations and data analysis continue with good results. The TOTS ground station at Poker Flat, Alaska has started to experiment with automated/unattended operations for SNOE. So far, this has gone well.

June 10, 1998

A spurious computer reset to UVPROM at acquisition of signal resulted in the loss of 14 hours of data.

June 4, 1998

SNOE has now operated for twelve weeks past the two-week early orbit campaign. The mission has obtained data from all instruments for three solar rotations.

May 29, 1998

Some preliminary results from SNOE were presented in a paper at the American Geophysical Union spring meeting in Boston, Massachusetts.

May 19, 1998

Routine operations continue with all systems performing well. We now have over two months of nearly continuous nitric oxide data, with significant solar and geomagnetic variation during that time.

May 14, 1998

A spurious computer reset to UVPROM at carrier up resulted in the loss of 14 hours of data.

May 7, 1998

A period of disturbed solar/geomagnetic conditions during May 2-6 was observed, including including two X-class flares, a coronal mass ejection, and elevated levels of auroral activity. Although several other spacecraft were affected by these events, no damage to SNOE occured.

May 1, 1998

A procedure was instituted to turn off the high voltage supply to the Auroral Photometer photomultiplier tubes during the sunlit portion of each orbit. This was done to conserve the photomultiplier tubes for their primary ojecteive, measurement of the aurora during night.

April 29, 1998

A spurious computer reset to EEPROM at carrier up resulted in the loss of 11 hours of data.

April 21, 1998

The mission continues to operate smoothly. Some GPS data have been analyzed at JPL, and we hope to soon have agreement between the orbital ephemeris determined by GSFC/FDF, by JPL, and by NORAD.

April 14, 1998

Solar activity continues to increase as cycle 23 ramps up. The latest rotation reached peak values of F10.7 = 141 and Sunspot Number = 131 on April 8, the highest values observed so far during cycle 23. Preliminary results from the SXP show clear changes in X-ray levels as solar activity declined during late March and then increased during early April.

April 11, 1998

A spurious computer reset to EEPROM at carrier up resulted in the loss of 8 hours of data.

April 7, 1998

SNOE has now taken scientific data with all instruments in their nominal modes for four weeks past the early orbit campaign. This meets the mission minimum success criteria.

Mar. 26, 1998

A spurious flight computer reset to UVPROM while the spacecraft was over Canberra caused the loss of about 10 hours of scientific data. There were no problems with the engineering systems, however, and the spacecraft was quickly restored to its operational mode.

Mar. 23, 1998

All Spacecraft subsystems continue to function well. Preliminary analysis of SXP data shows an increasing trend in X-rays during the last solar rotation. A solar flare, with X-rays significantly above background levels, was detected in data from Mar. 15, 1998.

Mar. 16, 1998

SNOE engineering health continues to be excellent. Science data continues to be of high quality. Calibration and analysis activities are in progress.

Mar. 12, 1998

The early orbit campaign was brought to a successful conclusion, and regular science operations have commenced. All spacecraft subsystems and instruments continue to perform well. Ground contacts will continue at 2-4 per day for a few weeks and then phase back to twice per day from Poker Flat.

Mar. 10, 1998

Automatic on-board roll correction for the UVS data cycle was turned on, and the instrument put into its nominal, high-resolution mode. Roll correction is working well and after one adjustment the limb scan was centered to cover the range from 0 – 200 km altitude. The SXP is in its nominal mode, opening its door every forth orbit, or about four times per day.

Mar. 9, 1998

A spurious hardware command accept at acquision of signal resulted in a computer reset to EEPROM. Recovery was accomplished during the remainder of the pass, but some data were lost.

Mar. 8, 1998

UVS on-board spin correction is working well. The spacecraft attitude continues to be excellent, with the spin rate held between 4.9 and 5.1 rpm. An axial adjustment was made to bring the spin axis declination into alignment with orbit normal. Right ascension precession of the spin axis continues to closely follow orbit normal.

Mar. 6, 1998

Instrument operations continue in a routine early orbit campaign mode. All three have been on continuously since activation. The UVS is taking low resolution limb scan data from about 0 to 400 km altitude. Automatic on-board spin correction for the UVS data cycle was turned on. The SXP continues to open its door once per day. The AP is in its nominal mode, taking data in a 60 degree scan centered on nadir.

Mar. 5, 1998

The Auroral Photometer was turned on and is working well. Preliminary science data look good. For some plots of very raw data from all three instruments, see the preliminary science data page.

Mar. 4, 1998

Operations contine to be nominal. Another spin-up maneuver was performed overnight, and the UVS data mode changed by stored command to adjust. The UVS is taking limb scan data and the nitric oxide gamma band fluorescence and Rayleigh-scattered sunlight limb features have been identified. The SXP is opening its door to take X-ray data once per day. The spin rate was increased to 5.0 rpm. Spacecraft attitude is settling down, with the spin axis oscillation about the orbit normal now 0.5 degrees in radius. With the axial torque rod residual magnetism in the “minus” state, the spin axis precession rate in right ascension is within 0.1 degree/day of the orbit normal precession rate.

Mar. 3, 1998

The Ultraviolet Spectrometer (UVS) was turned on. Health and safety checks show that it is working properly. Preliminary science data look good.

Mar. 2, 1998

Solar X-ray data with the door open and closed were compared, and good X-ray signals were obtained in all channels. A test spin-up maneuver was performed that brought the spin rate up to 4.7 rpm. An additional axial maneuver was performed that brought the spin axis to orbit normal, to adjust for the difference between spin axis and orbital precession rates. The oscillation about the orbit normal vector described by the spin axis has grown to about 1.25 degrees in radius. There have been no further spurious hardware commands executed since the computer reset early on Feb. 28. Power and thermal data continue to show nominal performance.

Mar. 1, 1998

The SXP door was opened and closed, and a solar X-ray measurement obtained. The instrument is functioning well and the X-ray data are being analyzed. Attitude data from the first maneuver were analyzed. The spin axis is nearly aligned with orbit normal. Its motion during the course of an orbit describes a circle about the orbit normal vector that is 0.4 degrees in radius. The spin rate has slowed to 4.5 rpm, so the next maneuver will be a spin-up. For a look at some engineering data, see the early orbit campaign page.

Feb. 28, 1998

The first attitude control sequence was uplinked for execution by stored command. The sequence activates the axial torque rod to move the spin axis a degree toward orbit normal. The commands were executed just before a pass at Wallops, and the ADCS status verified during that pass. The next pass at Poker was missed due to a computer reset caused by a spurious hardware command during acquisition. The spacecraft was re-acquired and restored to its nominal configuration during the next pass. Central plate and battery temperatures remain acceptable at near 20 C. Power generation remains strong with 3 array string circuits on. The computer has seen 13 single-bit memory errors in the first 2 days, which is about 1E-7 errors per bit per day, well within acceptable limits. There have been no non-correctable errors. The 1.2-day watchdog timer was tested and it properly reset the computer.

Feb. 27, 1998

SNOE is in good shape. Aside from its surprising tendency to generate too much power from its solar arrays, everything is working as expected. Due to this power surplus, S/C temperatures are running a little high, but well within acceptable limits. The power is being managed by turning off unneeded array string circuits; experience from the first day of operations indicates that it will probably run at 75% power (3 array string circuits on, 1 off) for some time. A known problem from test is that a hardware command can inadvertantly execute during acquisition when the received signal is noisy. This happened during the blind acquisition at Wallops late on Feb. 26th, turning off the non-essential bus. The solution during routine operations will be to assure that transmitter-on sequences are programmed in advance to avoid having to do blind acquisitions. Other than that, the early orbit campaign has procceded very well. Attitude data show that the spin axis is within a degree of orbit normal, and that the small amount of nutation present at launch has damped out. Spin rate is 4.8 rpm. The SXP is on (with the door closed) and the data look good.

Feb. 26, 1998

First contact at Poker Flat, Alaska was successful. Voltages and temperatures were nominal. The non-essential bus was turned on and a communications sequence uploaded. Second contact with the DSN station at Madrid, Spain, was also successful. The attitude determination control system was turned on and tested. The power profile is excellent. Communications links exceed expectations. The command and data handling system is functioning properly. Third contact at Poker Flat was nominal. The Solar X-ray Photometer (SXP) was turned on breifly to verify that the door is closed. During the fourth contact, also at Poker Flat, one of the solar array string circuits was turned off, since the spacecraft was generating too much power. On the fifth contact, at Wallops Island, Virginia, full flight software was loaded from programmable read-only memory. The sixth and seventh contacts at Poker were also nominal. On the eighth pass, the SXP was turned on. Data from the SXP (with the door closed) look good. An additional array string circuit was turned off on the ninth pass. The next two passes were missed due to a station configuration problem at Canberra. On the next pass at Wallops the spacecraft was re-acquired blind, but the non-essential bus inadvertantly turned itself off, which automatically turns on all 4 array string circuits. The non-essential bus was turned back on during a subsequent pass at Poker, and the array string circuits returned to the 3-on, 1-off configuration.

Feb. 25, 1998

SNOE final arming was completed on schedule at 19:00 PST. The launch checklist proceeded with no significant anomalies. L1011 engines were started at 21:30 and wheels up was at 22:10. Pegasus drop occured at 23:05 and SNOE was turned on at 23:14. Separation was at 23:15 PST. SNOE was launched into a 580 km x 550 km orbit at 97.75 degrees inclination. The inclination and apogee were exactly as targeted, while perigee was 30 km low but well within the targeted range.

Feb. 24, 1998

The VAFB Launch Readiness Review was held. The SNOE/BATSAT Pegasus mission is green for launch.

Feb. 23, 1998

The “delta” NASA Flight Readiness Review was passed, and the Combined Systems Test completed.

Feb. 21, 1998

Pegasus was transported to the hotpad and mated to the L1011.

Feb. 20, 1998

The SNOE GSE was moved to the hotpad in preparation for rollout. Minuteman launched but was cut down 5 minutes into flight due to a range tracking problem.

Feb. 18, 1998

A SNOE short-form functional test was performed and batteries were charged. A GSE problem with data frame rejects was resolved by swapping out the shift register box. Delta/Iridium launched, and Pegasus/SNOE/BATSAT is back on the range schedule with rollout on Feb. 21 or 22 and launch on Feb. 25.

Feb. 17, 1998

The Pegasus/SNOE/BATSAT launch date is uncertain at this time. Delta/Iridium has the range for Feb. 18 and probably until they launch. Minuteman is penciled in for the 20th. The next Pegasus opportunity is the 25th. Orbital performed an end-to-end test of the FTS and charged its batteries. The L-1011 arrived and pre-mate electrical tests were done. Rick, Pete, and Gail arrived at Vandenberg AFB.

Feb. 16, 1998

Delta/Iridium did not launch due to winds aloft. With Delta and Minuteman both trying to launch this week, there is are further range schedule threats to Pegasus. Nevertheless, rollout is planned for Wednesday, Feb. 18. Jim Westfall returned to Boulder.

Feb. 15, 1998

The Pegasus fairing was re-installed.

Feb. 14, 1998

The new FTS receivers were tested and installed.

Feb. 13, 1998

New FTS receivers arrived. Range safety has decided not to require that they be from different lots.

Feb. 12, 1998

FTS batteries were re-installed.

Feb. 11, 1998

Range Safety is now asking for FTS receivers from different lots to minimize the risk of systematic errors impacting the redundancy. Sean Ryan and Steve Steg returned to Boulder.

Feb. 10, 1998

A problem was found with the Pegasus FTS receivers for the TRACE mission, so the SNOE/BATSAT receivers will have to be removed and replaced. New receivers are expected to arrive on Feb. 13. Taurus/GFO launched successfully at 05:20 PST. Jim Westfall arrived at Vandenberg.

Feb. 9, 1998

FTS batteries were removed for inspection and conditioning.

Feb. 8, 1998

The original launch site team (Rick Kohnert, Pete Withnell, and Gail Tate) returned to Boulder.

Feb. 7, 1998

The fairing was removed and the motors and payloads inspected. There was no moisture inside the fairing, and both spacecraft appear to be in good shape. New CU/LASP personnel (Sean Ryan and Steve Steg) arrived at Vandenberg to relieve the launch site team.

Feb. 6, 1998

The Pegasus was de-mated from the L1011 and returned to the east bay at Building 1555.

Feb. 5, 1998

Launch has been postponed until Feb. 20, 1998 due to more bad weather. There are three other launches ahead of us now waiting for a break in the weather, including Taurus/GFO on Feb. 9-10, Delta/Irridium on Feb. 11-12, and a Minuteman launch on Feb. 17-18. The weather outlook is still poor.

Feb. 4, 1998

Vandenberg AFB re-opened and they are cleaning up the mess. The launch vehicle and payloads survived the storm and are in good shape.

Feb. 3, 1998

SNOE/BATSAT launch was scrubbed for 2/4/98 due to the weather situation. Vandenberg AFB was closed due to severe storms and flooding.

Feb. 2, 1998

The L1011/Pegasus Combined Systems Test was performed, and a launch dress rehearsal held.

Feb. 1, 1998

The Mission Director table-top meeting was held. Final redlines to the mission constraints and flight rules were made. The weather is bad and is likely to get worse, but the outlook for Wednesday 2/4/98 is mixed.

Jan. 31, 1998

The SNOE/BATSAT Pegasus mission was transported to the hotpad and mated to the L1011. The Launch Readiness Review was held. All parties pronounced the mission ready to go.

Jan. 30, 1998

Pegasus was transferred to the transport trailer. SNOE batteries were charged in prepartion for the move to the hotpad. The L1011 carrier aircraft “Stargazer” arrived at VAFB.

Jan. 29, 1998

Fairing installation and final closeouts were completed.

Jan. 28, 1998

The Auroral Photometer cover was removed and the port side fairing was installed.

Jan. 27, 1998

Solar array covers were removed, Ultraviolet Spectrometer and HCI covers were removed, and the starboard side fairing was installed.

Jan. 26, 1998

One kilogram of ballast was added to the avionics section to correct a discrepancy in the third stage motor weight.

Jan. 25, 1998

Broncos 31, Packers 24.

Jan. 24, 1998

BATSAT close outs and the INS drift test were completed.

Jan. 23, 1998

Data from flight simulation 4 were evaluated. The only anomaly was that BATSAT didn’t receive the orbit state vector from the launch vehicle until 154 seconds into flight. It’s not clear whether this is a problem, since the state vector was in the telemetry stream to the ground, and BATSAT doesn’t require it.

Jan. 22, 1998

Flight simulation 4 was performed. Preliminary data look good all around. The spacecraft received the turn-on command on schedule and activation was nominal.

Jan. 21, 1998

The telemetry problem was identified as a termination problem. It was resolved by adding termination resistors to the data and clock lines using a shorting plug in the avionics access connector.

Jan. 20, 1998

Flight simulation 4 was postponed due to a vehicle telemetry problem.

Jan. 19, 1998

Repaired pyro driver units and revised flight software were delivered to Vandenberg, and the SNOE launch site team returned to the field. Batteries were charged and the spacecraft prepped for flight simulation 4. The pyro driver units were installed on the launch vehicle.

Jan. 15, 1998

The SNOE launch site team flew back to Boulder.

Jan. 14, 1998

SNOE mechanical mate was finished, and a short-form functional run. The Pegasus – BATSAT – adapter cone – SNOE stack is complete. The pyro driver units (electronics boxes that trigger the separation between Pegasus stages and between the third stage and the payloads) have been sent back to Chandler for re-work. Some capacitors in the power supply section need to be made more rugged so that they don’t come loose during launch. This will take several days, so the SNOE launch site operations are on hold until preparations for flight simulation 4.

Jan. 13, 1998

BATSAT and the avionics section were re-integrated. Mechanical mate of the SNOE adapter cone to BATSAT was begun. However, due to a potential problem discovered with Pegasus pyro driver units, launch has been slipped to February 3.

Jan. 12, 1998

BATSAT and the Pegasus avionics section were deintegrated and weighed. Due to changes in third stage mass properties and to the BATSAT receiver state during launch, final Pegasus flight software will not be delivered until Jan. 15.

Jan. 10, 1998

Flight simulation 3 was run. There were no problems with the SNOE spacecraft. The turn-on pulse was received on schedule, and spacecraft activation was confirmed by talkback. Data from the launch vehicle side are being evaluated.

Jan. 9, 1998

Electrical interface testing between BATSAT and the Pegasus third stage and between the SNOE adapter cone and BATSAT was completed.

Jan. 8, 1998

The BATSAT harness was hand-carried back to Vandenberg AFB. An electrical interface test between BATSAT and the Pegasus third stage was started. Due to the lost time, the projected launch date was slipped a day to Jan. 23.

Jan. 7, 1998

A problem was found with a connector on the BATSAT harness – a bit of epoxy in a socket. Orbital returned it to the Chandler facility where it was repaired.

Jan. 6, 1998

Electrical interface testing between SNOE and the adapter cone was concluded, and the spacecraft was mated to the marmon clamp / adapter cone assembly.

Jan. 5, 1998

SNOE was removed from its shipping container and set up in the clean tent. A short-form functional was run to verify that it’s still in good shape. Electrical interface testing between the spacecraft and the adapter cone resumed. Orbital switched two pins in a connector on the adapter cone harness to correct an interface polarity discrepancy.

Jan. 4, 1998

The launch operations team arrived at Vandenberg.

Dec. 23, 1997

The SNOE launch operations team returned to Colorado for the holidays. Launch operations will resume when Orbital re-opens its Vandenberg facility on January 5.

Dec. 23, 1997

The ORBCOMM-1 mission was successfully launched by a Pegasus XL. This brings the SNOE/BATSAT mission to the top of the Pegasus queue, next in line for launch.

Dec. 22, 1997

A fit check between the spacecraft and adapter cone was performed. The spacecraft was returned to its shipping container for storage over the holidays.

Dec. 21, 1997

An electrical interface test between the spacecraft and the adapter cone was performed.

Dec. 20, 1997

SNOE was moved to Building 1555. The spacecraft was unpacked and set up in a clean tent. A short-form functional test was run out of UVPROM. There were no problems.

Dec. 18, 1997

The SNOE spacecraft was returned to its shipping container in preparation for the move from Building 836 (the NASA payload processing facility) to Building 1555 (the Orbital vehicle assembly building).

Dec. 17, 1997

RF tests were performed, with the GSE plugs out and the spacecraft running on internal power. A short-form functional test out of UVPROM was run successfully. This completes the SNOE range stand-alone testing.

Dec. 16, 1997

Batteries were fully charged, and a long-form functional test was run out of EEPROM. There were no anomalies.

Dec. 15, 1997

SNOE arrived at Vandenberg AFB, and was moved into the cleanroom at Building 836, the NASA facility on the South Base. The spacecraft was unpacked, set up, and turned on. No problems were found.

Dec. 13-14, 1997

The Spacecraft was shipped by truck to Vandenberg Air Force Base.

Dec. 9, 1997

All functional testing and mission simulations were completed.

Dec. 5, 1997

Battery charging and final flight close-outs were completed.

Nov. 25, 1997

The evaluation of the SNOE transceiver was completed. The command lock-out was clearly identified as a subcarrier frequency shift in the receiver, which occurs less than 1% of the time at startup. The decision was made to fly the spacecraft as is. If the frequency shift occurs on orbit, the ground station will adjust the uplink data rate from 2.0 kbps to 2.2 kbps to compensate.

Nov. 19, 1997

The SNOE Mission Readiness Review was held at the Orbital facility in Dulles. The spacecraft and launch vehicle were cleared for flight with the exception of a few minor action items on the launch vehicle side and the single remaining SNOE anomaly. LASP was directed to solve the command lock-out problem as soon as possible.

Nov. 14, 1997

The SNOE Pre-ship Review was held at LASP. All items were closed and the spacecraft was approved for shipment, with the exception of the “command lock-out” anomaly.