|
MISSION
STATUS ARCHIVES:
Spacecraft, Instrument and Science Processing System
04-25-07 to 02.07.08
AIM Spacecraft Bus Status
Electrical Power System
The Electrical Power System (EPS) is operating
nominally, providing adequate power with healthy margins.
No issues have occurred with switches or shunt control.
Solar Array
The solar array deployment was nominal. The array is providing
approximately 23.5 Amps of peak current as measured by the
on-board current sensor. The received power provides healthy
margins for an extended mission. Full battery recharge is
achieved 23-25 minutes into the 61 minute sunlight portion
of the orbit. This illustrates more than enough margin such
that solar array degradation will not be a life-limiting factor.
Battery
Typical eclipse minimum state of charge is 73-76 %, and typical
peak state of charge is 97 %. This is within the expected
pre-launch range. Battery temperature is being maintained
between -4 C and +4 C, depending on location within the battery.
With these conditions, the battery will easily support the
mission for at least 5 years and more.
Attitude Control System
The Attitude Control System (ACS) performance is excellent
and meeting all pointing and knowledge requirements. Some
ACS software parameters were adjusted post-launch. In addition
to the expected updates for commissioning, the following updates
occurred: Contingency Mode parameters were updated to point
the solar arrays 30 degrees off of the sun in order to reduce
the array temperatures in this mode; ACS tables were updated
on May 2 and the Star Tracker RAM was patched on May 4 to
prevent loss of track with the Moon in the Star Tracker field
of view; and some related ACS table parameters were also subsequently
updated. Momentum dumping was disabled during Sun-Target mode
on June 21 in order to provide more stable pointing during
SOFIE observations. The last update occurred on June 28, 2007,
which adjusted the gyro-Star Tracker on-board alignment matrices.
No degradation or unexpected performance is being experienced
in the ACS. The only potential life limiting items are the
reaction wheels; however, the wheel control software is designed
to minimize zero crossings and will enable lifetime well beyond
5 years.
Thermal Subsystem
The Thermal Subsystem is operating nominally and has not shown
any sign of degradation. All heaters are functioning normally.
Bus temperatures have been very stable since the last thermally-significant
operation on June 5, 2007 (lowering the TCVR heater set points).
There has been a slight up-trend of ~ 3° C between the
summer solstice and early November, which was expected due
to the decreasing Sun distance over this period.
Temperatures are running slightly warmer than per pre-launch
plans, in particular at the TCVR and RW-Z. This is due to
the operational choice to leave the heaters for these two
components at higher set points than per the pre-launch plan,
in an attempt to prevent aggravation of the receiver subcarrier
lock issue. However, while the temperature has been higher
on the TCVR, there has been essentially no cycling of temperature
(< 2° C variation over the orbit). Temperatures should
not be a life limiting factor.
Command & Data Handling
Subsystem
The Command & Data Handling (C&DH) subsystem has been
performing nominally. No significant C&DH issues have
been noted. The mission performs occasional dumps of the EEPROM
contents in the APE and Uplink cards (which do not have their
own scrubbing), and there have been no EEPROM integrity issues.
On-board clock speed was calibrated after launch, and is currently
showing a drift of approximately 0.3 msec per day. Even without
further adjustment, if this drift rate holds, the clock will
be sufficient for bus activities for at least 10 years. On-board
memory scrub routines have encountered occasional single-bit
errors in the mass memory, which have often correlated to
the South Atlantic Anomaly. This is an expected artifact of
the radiation environment, and the Triple Modular Redundancy
(TMR) of the memory is handling these cases as intended.
Flight Software
The Flight Software (FSW) has been operating nominally. CPU
usage has been 38% on average, and maximum 55%. To date, two
patches to OBC RAM have been made on-orbit (OBC 6.3 and OBC
6.4), and both have gone smoothly.
RF downlink
Transmitter performance has been nominal, with no issues noted
since launch. The pre-launch plan was to leave the transmitter
off nominally, and only turn it on during GN/high rate passes.
Also, it was not planned to operate in TDRSS/low rate mode
except during exceptional circumstances. In contrast, actual
usage has been to leave the transmitter on continuously, and
to regularly return to TDRSS/low rate mode after every high
rate pass. This is being done so as to minimize temperature
variations in the receiver and to provide for maximum downlink
coverage.
RF uplink
The RF receiver has exhibited a significant anomaly in which
it sometimes will not lock onto the uplink subcarrier signal.
Approximately 3 ground network passes plus 7-10 TDRSS passes
are typically attempted per day, which allows for significant
statistical data to be collected on the receiver performance.
The percentage of successful uplink contacts per day is plotted
in Figure 5.1.7-1 from launch through early January.
The pattern exhibits a general condition of about ~20% of
total uplink possibility. It is not known whether recent performance
is a reliable indicator of future performance. Other than
the intermittent ability to achieve subcarrier lock, the receiver
and all of its telemetry have been normal.
In order to maximize mission success in light of this receiver
anomaly, the following changes on the spacecraft bus have
been made:
• On-board command storage has been increased from 6
days to 24 days. This provides the ability to seamlessly collect
science data while experiencing an uplink outage of up to
20+ days. To date, the longest period without uplink capability
has been ~ 6 days.
• Bus flight software updates have been made which allow
for science collection in the event that no further commands
are received by the spacecraft. These updates include:
- an autonomous state vector update routine which uses eclipse
entry timing plus on-board static table data to achieve the
required on-board orbit knowledge,
- a simplified on-board ACS pointing sequence to continue
SOFIE and CIPS data collection, and
- automatic data dumping upon detection of uplink carrier.
Additionally, CIPS and SOFIE sequences are on board to control
their science data collection in the event of no further commanding.
In this scenario, CIPS and SOFIE will continue to collect
data, but there will be increasingly long periods in which
the common volume is not imaged by CIPS due to the simplified
ACS pointing sequence.
• On-board mission planning software has
been uploaded, which will provide reliable pointing of CIPS
at the common volume. This effectively removes the limitations
due to spacecraft pointing and significantly increases the
probability of adequate orbit knowledge so that all common
volume science data will can continue to be returned in the
case of an extended uplink outage.
The following bus changes are in development. Once loaded,
these updates will further increase the science collection
capability and mission robustness if the receiver were to
no longer accept uplink:
• Implementing on-board sequences in response to ground-controlled
RF ‘signaling’ patterns (a.k.a. Morse code commanding),
without relying on subcarrier lock. This will provide great
robustness as it will allow the ground to command resets and
recovery from transient anomalies. There is also the opportunity
for signaling changes in autonomous mission parameters, which
would allow for even further mission longevity in the absence
of subcarrier lock. This capability is currently in development
and is planned to be tested and uploaded to the spacecraft
prior to the 2008 northern hemisphere season.
The final stages of achieving spacecraft autonomy are nearly
complete and all software changes to do this have been uploaded.
In this condition, the mission can go on indefinitely with
no commanding. The only exception will be in the case of a
spacecraft safehold contingency situation, in which case,
command capability will be very important in order to diagnose
and fix any anomaly. The spacecraft autonomy capability has
been tested in a passive mode in orbit and after the current
southern hemisphere season is over, it will be tested actively,
implemented and made operative for the 2008 northern hemisphere
season. With the addition of Morse code commanding prior to
the 2008 northern hemisphere season, the spacecraft will be
even more robust due to commandability even in the event of
no uplink subcarrier lock. Consequently, the AIM spacecraft
is robust and will be capable of supporting an extended mission
and many more science seasons.
Software sequences have been put on board such that if science
data is no longer being collected (e.g. due to a new anomaly)
and there has been no uplink for an extended period, then
the spacecraft will perform various actions to attempt to
return the receiver to a functioning state. These actions
include, among other things, increasingly-wide temperature
cycles on the receiver, and cycling various electronics boxes.
This ensures that every possible attempt is made to regain
command capability should it become necessary.
AIM Instrument Status
SOFIE
SOFIE has been performing very well on orbit, providing 15
sunset measurements each day at latitudes from 65° - 85°S
and 15 sunrise measurements each day at latitudes from 65°
- 85°N. All products, except CO2 and NO, are now being
produced routinely and are already at a scientific high quality.
The CO2 retrievals require that the two CO2 channels (4.3
microns and 2.7 microns) be inter-calibrated to very high
accuracy, which requires lengthy in-orbit tests and calibration.
The NO measurements are delayed due to an unexpected sensitivity
to detector temperature. An ongoing development effort is
underway to produce accurate corrections using detector temperature
measurements and in-orbit characterization of detector heating
behavior.
SOFIE is performing at pointing, noise, and drift levels necessary
to achieve all measurement objectives, meeting or exceeding
all pre-launch requirements. On-orbit pointing stability is
typically 2-3 arcseconds during science measurements, easily
meeting requirements. The knowledge requirement for FOV position
on the solar image of < 1 arcsecond is determined by the
SOFIE sun sensor array (SSA) which is co-aligned with the
FOV. The measured solar image is currently tracking the solar
edges on the SSA to a precision of better than 0.2 arcseconds,
again easily meeting the requirement. Post processing is expected
to eventually reduce this even further to under 0.05 arcseconds.
SOFIE autonomy for prediction and execution of its own science
events is on-board and functioning nominally. The ability
to seed the SOFIE autonomy in the absence of receiver bitlock
has been added as part of the overall system robustness effort.
With this added autonomy and robustness, the SOFIE instrument
is well suited to an extended AIM mission.
CIPS
The CIPS instrument has performed flawlessly on-orbit. The
instrument is expected to continue operating well into an
extended mission as it currently shows no signs of performance
degradation.
CIPS is also well-suited for AIM autonomous operations. CIPS
has the ability to store internal instrument sequences for
both CIPS and CDE operations. This allows mission operators
to have a full month of operations loaded on CIPS in case
of delayed uplink communications. In addition, if communications
are lost for a longer period of time, CIPS will begin autonomous
operations which will allow it to continue taking science
data indefinitely, performing nominal science observations
based on orbit events (eclipse exit and entry). CIPS autonomy
also includes detection of the PMC science season (northern
vs southern hemisphere), allowing the instrument to take images
over the correct pole. Work is underway as part of the mission
autonomy efforts to ensure that the onboard sequences are
not lost should the instrument lose power. This will allow
for immediate beginning of CIPS and CDE science collection
upon repowering of the instruments, rather than to have to
wait for the sequences to be reloaded during available uplinks.
CIPS’s ability to take images of the common volume has
been preserved as part of the autonomy efforts such that the
s/c rolls as necessary to place the common volume in the CIPS
FOV utilizing beta angle prediction.
CDE
The CDE instrument continues to operate with nominal housekeeping
signatures. CDE has two performance issues that are being
successfully mitigated. First, the instrument registers more
science events than expected. CDE self-monitors science activities
and has 'autonomy' rules to change thresholds or pause science
collection on an individual channel to regulate downlink volume.
These parameters have been modified and are currently reset
daily to assure optimal performance. This is currently done
via the spacecraft ATS. If the ATS expires, the CIPS sequence
will take over this daily maintenance. Second, the instrument
periodically 'watchdogs' after detecting a stray 1 pps signal
or overflowing a tier during processing. This does not affect
the performance of the instrument, but if the count were to
reach ten watchdogs without a reset, the Flash memory would
be turned off and some data collection parameters would revert
to pre-flight modified values, decreasing the science data
return. In order to mitigate the issue, if the watchdog count
changes the instrument is reset to clear the count in an automated
process via a TMON.
Like CIPS, CDE is also well-suited for AIM autonomous operations.
CDE does not require commanding aside from the mitigations
described above. The monthly calibration activity is currently
done manually, but will become autonomous if CIPS falls into
its autonomy mode.
AIM Mission Operations Center Status
AIM was launched successfully on April 25, 2007 into a near-circular,
600 km sun-synchronous orbit at 97.79º inclination. Over
the next 37 days, a series of tests verified the on-orbit
performance of the satellite and instruments. A significant
problem with the receiver was encountered in which it often
does not achieve lock on the uplink/forward link sub-carrier,
thereby preventing any commanding activities from the ground.
Ground initiated commanding, and the loading of stored commands
has been limited to those contacts where “bit-lock”
is achieved, and additional SN support is now used to mitigate
this problem (also see the Spacecraft Bus Status section).
Instrument commissioning was completed without further incidence
and science operations commenced in early June, 2007. Several
flight software and table modifications have been implemented
to improve the robustness of the system and its ability to
collect science data with limited uplink opportunities (see
the AIM Spacecraft Bus Status section for details).
Current predictions indicate that AIM will stay above its
end-of-life orbit altitude of 450 KM until ~2017. Predictions
show that beta angle does not begin to exceed +/- 9° until
~2011, thus ensuring full common volume science through at
least that time period. Beyond that timeframe, each instrument
can continue to perform valuable science independently.
Three GN contacts and three SN events with AIM are scheduled
per day to facilitate the uplink of new command sequences
and the downlink of recorded telemetry. In addition, eight
to ten additional SN events are scheduled overnight to accumulate
bitlock statistics. Originally, three GN contacts per day
during PMC Season and five per week the rest of the year were
planned.
Standard NASA services are used to connect the MOC to the
primary ground stations located at Svalbard, Norway, Poker
Flats, Alaska and Wallops Flight Facility in Virginia, as
well as to the SN ground terminals at White Sands, New Mexico.
In the time since launch, an additional aperture at Poker
Flats, Alaska has been certified and certification of an additional
aperture at Svalbard, Norway is in progress. This added diversity
significantly increases the reliability of the AIM ground
network.
For AIM, the FOT is responsible for planning and scheduling
the observatory activities each day to support the collection
of science data. Besides planning, the FOT conducts real-time
operations and post pass analysis of the housekeeping data
from the satellite bus and the instruments. Plots are posted
to the website after every contact for FC review, and plots
are checked daily. The Level 0 data products are made available
to the SOFIE POC, and Level 1 data products are then made
available to the CIPS and CDE scientists and engineers for
the generation of higher level data products. Routine science
processing activities run unattended, with personnel regularly
monitoring data processing activities and data quality. Over
99% of the data collected on board has been successfully captured
on the ground and delivered to the science team.
To support the extended mission, a few updates to the AIM
ground system will be needed which would include, for instance,
increased disk-space.
AIM Science Data Center Status
SOFIE Science Data Center
The SOFIE Science Data Center is now fully operational with
Level 0 through Level 2 data being produced on a routine basis
and recorded in the SOFIE database. SOFIE is collecting 30
occultation events each day, and processing of these events
is being carried out at the Science Data Center. The collection
rate (fractional amount of data collected vs. data potentially
available) of for data since May 2007 is 99%.
Verification and validation of the SOFIE data is underway.
Once the validation is completed, data metafiles will be provided
to the Project Data Center at Hampton University. All Level
2 data will also be available through the SOFIE Science Data
Center at GATS.
The data access and management software on the SOFIE web site
is in place and ready for production processing, and currently
provides quick-look plots and ASCII data files on an event-by-event
basis. Software is in place to automatically generate NetCDF
science data product files. The process for routinely producing
these data product files has been tested, and will commence
upon authorization of the instrument and mission PIs. Current
data processing and storage resource requirements are within
the project estimates and readily handled by the GATS computing
infrastructure.
CIPS Science Data Center
The CIPS Science Data Center is fully operational and all
planned data products are being produced by the system in
a routine fashion. Our Level-4 analysis product, Cloud Properties,
identifies cloud albedo and particle sizes, as planned.
The biggest challenge for the CIPS Science Data Center has
been the receiver bitlock issue and resulting changes in the
mission and instrument operation approach. In this operations
mode, CIPS continues to send data to the ground between cloud
seasons, which has increased our needs for data storage beyond
what was originally expected. This has resulted in twice the
planned amount of data to process, manage, and archive. Since
the system was originally scaled to support a two-year mission,
we will continue to be able to absorb these needs through
the first year of operations. After the first year of operations,
the CIPS Science Data Center will require modest additional
funding for storage and data management.
CIPS data products are currently being archived at the CIPS
Science Data Center at LASP and will be made available to
the public beginning in February 2008 via the AIM Project
Data Center at Hampton University. All interfaces for CIPS
and CDE data have been tested and associated data products
are ready for delivery.
To support the proposed plan for an extended AIM mission,
the CIPS Science Data Center will require one FTE to manage
calibration updates, software updates, reprocessing, data
distribution, and continued archival activities. Additionally,
one-half FTE will be needed for algorithm development to support
new products that would provide insight into global ozone
density and gravity wave characteristics. We will also need
to purchase additional computer hardware to accommodate the
increased needs for data storage.
CDE Science Data Center
Preparation of CDE data products has been challenged by elevated
noise in the raw CDE data. Data products are being regularly
produced by the science processing software, but the higher-level
products need additional work to characterize and remove the
noise before those products will be scientifically usable.
This effort is the current focus of the CDE team and is expected
to be completed before the start of the extended mission.
For the extended mission, one full-time graduate student is
required in order to maintain calibration updates, processing,
and data archiving activities.
Project Data Center
The AIM Project Data Center hosts the AIM website, serves
as the public interface for finding and retrieving data from
the instrument data centers, and acts as host for the common
volume data. The basic operational capacity for each is in
place and operational. Ongoing development is currently proceeding
to increase the ease with which the public can access the
AIM data.
The AIM website, http://aim.hamptonu.edu, is
fully operational and contains general information about AIM,
updated news releases, links to more in depth information
on the design and performance of the
spacecraft and instrument. Information about AIM's orbit is
available along with a web based tool for predicting ground
overpasses. A form to receive automated weekly predictions
of overpasses is available to the public.
The Project Data Center is receiving meta-data
from the instrument Data Centers and is making this data available
to the public. The user interface to access the data is functional,
but work on improving the usability is continuing. Work to
integrate the AIM data search with the Virtual ITM Observatory
(VITMO) will begin shortly.
The common volume data is created from the overlapping
subset of the CIPS and SOFIE data products. Software for creating
the necessary subsets has been developed. Production and availability
of the common volume data will begin shortly.
|
