Overview and Status of the SORCE
Gary Rottman
Laboratory for Atmospheric and Space Physics, University of Colorado
(303) 492-8324
gary.rottman@lasp.colorado.edu
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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The Earth's Radiation and Energy Balance
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Endorsement(s)
“SOLAR INFLUENCES ON GLOBAL CHANGE”
(1994 NATIONAL ACADEMY OF SCIENCES REPORT)
Primary Recommendation: “One activity ranks above all
others for determining solar influences on global change:
Monitor the total and spectral solar irradiance from an
uninterrupted
series
of
spacecraft
radiometers
employing in-flight sensitivity tracking.”
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Basic Radiometic Quantities
The total irradiance or radiant f lux density is
the radiant flux across a surface element, dA :
E = dΦ
dA
dΦ
{W / m 2}
dA
The spectral irradiance, E λ, is the radiant flux
density per unit wavelength interval:
2
Eλ = d Φ
dAdλ
{W / m 3}
[1368 W/m2]
NOTE: the Total Solar Irradiance, TSI, is the
integral over all wavelengths o f the Solar
Spectral Irradiance.
∞
E= ∫ Eλ dλ
λ =0
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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SORCE Science Objectives
• Establish a data set of Total Solar Irradiance (TSI)
– 5-year duration from December 2002 to November 2007
– Daily measurements with an absolute accuracy ‡ better than 300 ppm (3σ)
– Relative accuracy between measurements of 0.001% (10 ppm) per year
• Establish a data set of Solar Spectral Irradiance
– 5-year duration from December 2002 to November 2007
– Spectral coverage from 1 nm to 2 µm
– Daily measurements with an absolute accuracy of 2 to 5% in the
ultraviolet, and 0.1 % in the visible to near infrared
• Improve our understanding and generate new inquiry
– How does a variable solar irradiance affect our atmosphere and climate?
– How and why does variability occur at the Sun? — use this knowledge to
estimate past and future solar activity
‡
combined standard uncertainty
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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SORCE Spectral Coverage
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Why the Solar Irradiance Varies
• Changes in distance to the Sun
Periodicities to Consider:
• 27-day rotation period coupled
with a non-uniform distribution
of brightness
1 year
18000 year
23000 year
41000 year
100 Kyear
400 Kyear
• Intrinsic changes in the Sun —
magnetic activity, radius,
luminosity, temperature, flares,
etc.
27 day
11 year
22 year
88 year
208 year
SORCE Science Team
Steamboat, CO
Orbital
Solar
Gary Rottman
July 17, 2002
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Current Record of TSI Measurements
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Concept of Electrical Substitution Radiometers
• Based on the measurement of heat flux. Two
identical sensors, one active and the other used
as a reference, are connected so that they are in
the same environment and at the same
temperature.
• Joule heat is supplied to each sensor by an
“actively controlled” heater circuit.
• These sensors have high absorptance in order to
efficiently collect radiation. Photon energy is
completely converted to heat.
• A shutter opens and solar radiation is allowed to
fall on the active sensor — a corresponding
amount of Joule heat must therefore be removed
from the active sensor in order to maintain the
heat flux balance. The change of Joule heat to
the active sensor is equivalent to the amount of
radiation now incident upon it.
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Total Irradiance Monitor — TIM
Mass of 6.5 kg
3
13 x 13 x 26 cm
For redundancy there are two pairs of
cones — either can be the active
sensor, and each cone has its
independent shutter
Cones have a single point thermal
“ground”
l
They are thermally and
mechanically mounted at their
centers of gravity by stainless
steel spiders
l
Heaters and thermistors are
terminated at diamond standoffs —
these thermal shunts precisely
define nodes for characterization
l
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Spectral Irradiance Monitor — SIM
50 k? thermistors
100 k? thin
film resistor
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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SOLSTICE
SOlar Stellar Irradiance Comparison Experiment
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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XPS —XUV Photometer System
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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How SORCE Has Evolved
•
•
•
NASA AO-88-OSSA-1 — EOS SOLSTICE selected February 1989
Science Objectives:
– Make daily measurements of solar spectral irradiance between 1 nm and
2000 nm, achieve state-of-the-art precision and accuracy
– Continue the data base of solar ultraviolet irradiance (120 < λ < 300 nm)
first established by the UARS SOLSTICE (1991 to present)
NASA AO-97-MTPE-01 for TSIM — selected February 1999
Science Objectives:
– Extend the monitoring of Total Solar Irradiance (TSI) beyond that of
EOS/ACRIM, at or exceeding the absolute accuracy of 1000 ppm
– Spectral Irradiance measurements from 200 nm to 2 µm
Combined Mission — Letter of April 1999 from Ghassem Asrar, NASA
Associate Administrator For Earth Science —
“... new programmatic direction is being provided to combine the
SOLSTICE/SAVE and TSIM missions. The new combined mission will be
called the Solar Radiation and Climate Experiment (SORCE).”
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Overview of the LASP Approach to SORCE
LASP manages the entire SORCE program including:
–
1
LASP has built and delivered four instruments —
TIM — the Total Irradiance Monitor
- Measures TSI
- A new development that incorporates the modern, state-of-the-art technologies
of the Electrical Substitution Radiometer (ESR)
- It takes full advantage of the best heritage of previous radiometers
2 SIM — the Spectral Irradiance Monitor
- Measures spectral irradiance 200 nm to 2000 nm
- A new development using prism as the dispersing element
- Also using an ESR (miniaturized)
3 SOLSTICE — the Solar Stellar Irradiance Comparison Experiment
- Measures spectral irradiance — 120 to 320 nm
- An evolution and refinement of our UARS SOLSTICE
- Observes bright, blue stars as a long term calibration standard
4 XPS — XUV Photometer System
- Measures broadband spectral irradiance — 1 to 30 nm
- An instrument of “identical” design to the XPS operates on the TIMED Program
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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LASP Approach to SORCE (cont.)
–
has provide a highly capable, and low-risk
spacecraft
– We will launch SORCE in November 2002 on a
Pegasus XL
– We will operate the SORCE for a period of five
years
– We will process, analyze, validate and distribute all
irradiance data
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Key SORCE Personnel
(It takes a village to launch SORCE)
Gary Rottman (LASP)
Tom Sparn (LASP)
Tom Woods (LASP) ‡
George Lawrence (LASP) ‡
Jerry Harder (LASP) ‡
Greg Kopp (LASP) ‡
Bill McClintock (LASP) ‡
Rick Kohnert (LASP)
Mike Anfinson (LASP)
Tim Holden (LASP)
Principal Investigator
Program Manager
Project Scientist
Instrument Scientist
Instrument Scientist
Instrument Scientist
Instrument Scientist
System Engineer
Instrument Manager
Spacecraft Manager
Bill Ochs (GSFC)
Debbie Dodson (GSFC)
Bob Cahalan (GSFC)
Doug Rabin (GSFC)
SORCE Project Manager
Resource Manager
Project Scientist
Deputy Project Scientist
Don Anderson (NASA HQ)
Program Scientist
Additional Co-Investigators:
Dominique Crommelynck
Peter Fox
Claus Fröhlich
Judith Lean
Julie London
Peter Pilewskie
Ray Roble
Paul Simon
Dick White
‡ SORCE Co-Investigator
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Shipment to Orbital Dulles Facility
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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Instrument Module at Orbital
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Steamboat, CO
Gary Rottman
July 17, 2002
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Testing at Orbital
EMI/EMC
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Steamboat, CO
Solar Array Deployment
Gary Rottman
July 17, 2002
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SORCE (Launch November, 2002)
SORCE motor at WTR
in December 2001
HESSI at KSC
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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The Future
•
•
•
•
•
UARS will more than likely end in October of this year
ACRIMSAT, SOHO, and ERBS will likely continue (?)
SORCE will launch in November and has a goal to operate until 2007
NPOESS will carry TIM and SIM instruments beginning in 2012
There will likely be a 5 year gap between SORCE and NPOESS —
NASA intends to fill the GAP with the SIGF ‡ Mission, but there are no
$’s in 2003 for a new start
Remember:
Primary Recommendation: “One activity ranks above all others for
determining solar influences on global change: Monitor the total and
spectral solar irradiance from an uninterrupted series of spacecraft
radiometers employing in-flight sensitivity tracking.”
This message keeps getting lost
‡ Solar Irradiance Gap Filler
SORCE Science Team
Steamboat, CO
Gary Rottman
July 17, 2002
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