Tom Woods, participated
in the Living With a Star Workshop, GSFC, Greenbelt, MD, January
Brian Boyle and Bill Ochs, SORCE Mission Manager, attended the Alenia
Tranceiver CDR at Dulles, MD, February 7-8, 2001
The SORCE IV &V planning meeting was held at GSFC February 21, 2001.
The March SORCE Monthly Review will be held March 22, 2001 at LASP.
The Chandler Rocket review will be held in Chandler, Arizona, April
The SORCE Mission Operations Review will be held at LASP, Boulder, CO
April 23-24, 2001.
SORCE is planning a Science Team Meeting July 9, 10, 11 2001 at the
Laboratory for Atmospheric and Space Physics, University of Colorado,
SORCE February 2001 Project Summary
The EOS SORCE Mission
is on schedule and within budget. Launch is scheduled for July 2002.
No mission descopes are required at the present, but TIM Hitchhiker
will likely not be manifest on shuttle until 2002-2003 and therefore
build been lowered in priority to accomodate SORCE scheduling. SORCE
continues to closely monitor and adjust all schedules to meet program
needs. Instrument build is well underway and problems discovered through
test are addressed immediately. Ongoing program concerns are diminishing
slack, additional procurement costs, IFOG manufacture and reliability,
orbit trajectory, and late delivery of the transceiver and the spacecraft
bench. All of these issues are "front burner" and solutions
and fixes are developing.
A Science position will be offered in the near future to replace Tony
Canas, who left the SORCE program in early January. SORCE is planning
to hold two science meetings per year in the future, one summer and
one winter. The summer 2001 meeting will concentrate on the results
of SORCE instrument calibration and characterization. The winter 2001
meeting, to be held after the delivery of the SORCE observatory to Orbital
Sciences Corporation, will be of a broader science context, and may
be held in conjunction with the Fall AGU meeting.
TIM Nears Completion
The SORCE Total
Irradiance Monitor (TIM) is nearly assembled . This instrument is designed
to measure the total solar irradiance (TSI) to an absolute accuracy
of 100 parts per million (ppm), reporting four such TSI measurements
per day. Previous spaceborne TSI instruments, such as those currently
flying on ACRIMSat and SOHO, have established a 22-year record of solar
irradiance, recording the small fluctuations
to solar activity about an average 1367 W/m2. The SORCE's TIM will be
continuing these measurements through its goal 5-year mission life.
The TIM uses four electrical substitution radiometers (ESRs), each behind
a precision aperture, to measure solar irradiance. A shutter modulates
incident sunlight to a selected active ESR, while electrical heater power
maintains a balanced ESR temperature with a reference sensor. Phasesensitive
detection of the electrical power supplied to the active ESR at the shutter
frequency measures TSI and reduces sensitivity to thermal drifts and noise.
A digital signal processor (DSP) controls the instrument by timing shutter
positions, maintaining the ESR temperatures via heater power cycling,
and formatting instrument science and housekeeping data for telemetry
downlink. These components are currently being assembled and tested at
TIM characterizations are complete. NIST measured the 0.5 cm2 precision
apertures to stated accuracies of 25 ppm. LASP measured the ESR reflectances
at several wavelengths spanning the visible and near infrared, and selected
the flight ESRs based on their low (~100 ppm) and stable reflectances.
SORCE has recorded the resistances of all ESR electrical leads to the
needed accuracy level . The TIM flight instrument is currently undergoing
electrical and DSP functionality tests.
Over the next couple months SORCE will continue characterizations and
tests of TIM. "First Light" on the completed instrument assembly
will be in early March, along with tuning of the thermal control circuitry.
Thermal vacuum and shake tests will (hopefully!) verify instrument robustness.
LASP is installing a heliostat that will facilitate end-to-end tests of
the instrument and measure intra-instrument consistency by (nearly) equally
illuminating adjacent TIM ESRs. TIM and the other three SORCE instruments
are scheduled to be installed on the spacecraft optical bench in late
spring, followed by co-alignment and functional tests. During integration
and test on the spacecraft, we will finalize the preflight TIM measurement
equation parameters, getting the science data analysis software ready
for the SORCE July 2002 launch and subsequent TIM TSI measurements.
Significant progress has been made on the SIM Féry prism drive,
CCD electronics and DSP code development. One flight CCD experienced a
failure anomaly and the piece is at Goddard for analysis. CCD build will
resume when this analysis is complete. Additional progress had been made
in the focal plane, calibrator system and the sunshade and baffling design.
The SIM case is assembled for vacuum test. Slit calibration has begun.
The SIM thermal design was reviewed and resulted in only 3 minor RFA's
(requests for action).