CLARREO Pathfinder: Mission Overview

The CLARREO Pathfinder mission officially began in 2016 with the directive to achieve two primary mission goals: 1) measure Earth-reflected sunlight with an unparalleled accuracy of 0.3%-0.6% (k=1) – a 5-10x improvement over existing reflected solar (RS) sensors and 2) serve as an on-orbit inter-calibration reference to other orbiting sensors.

CLARREO Pathfinder's unprecedented accuracy traceable to international standards and its high spatial and spectral resolution also ideally position CLARREO Pathfinder to serve as an on-orbit calibration reference to other RS instruments. This is essential because most reflected solar instruments experience on-orbit degradation with extended exposure to the extreme space environment. Alternatively, CLARREO Pathfinder has been designed to be resilient to such on-orbit degradation with frequent on-orbit calibration measurements.

A major element of the CLARREO Pathfinder payload is a Reflected Solar (RS) spectrometer called HySICS, developed by the Laboratory for Atmospheric and Space Physics (LASP). The CLARREO Pathfinder payload will be hosted on the International Space Station (ISS).

CLARREO Pathfinder: Achieving Unparalleled Accuracy

The CLARREO Pathfinder instrument is designed to be calibrated regularly on orbit primarily by positioning the entire instrument to take direct measurements of the Sun, a very well-known and long-monitored calibration target. These calibration measurements and the rigorous pre-flight ground characterization enable HySICS to maintain its high accuracy throughout its lifetime. CLARREO Pathfinder's high accuracy measurements can then be used to transfer its high accuracy to other RS instruments. In this way, CLARREO Pathfinder can demonstrate its ability to serve as a calibration reference for other instruments orbiting Earth at the same time. The 2017 Earth Science Decadal Survey recommended continuation of the CLARREO Pathfinder mission and identified radiance inter-calibration as a high priority.

CLARREO Pathfinder Team and Partners

Primary Organizations

Organization	Contributions and Responsibilities
NASA Langley Research Center (LaRC	• Lead NASA Implementing Center • Production of science data demonstrating inter-calibration between CLARREO Pathfinder and CERES/VIIRS • Distribution of CLARREO Pathfinder data products from the NASA Atmospheric Science Data Center
Laboratory for Atmospheric and Space Physics (LASP)	• CLARREO Pathfinder payload development, integration, test, and delivery for flight on ISS • Payload operations, instrument science, calibration, and production Earth reflectance measurements
NASA Johnson Space Center (JSC) / International Space Station (ISS)	• Launch and accommodations of CLARREO Pathfinder payload on ISS
NASA Goddard Space Flight Center (GSFC)	• Independent calibration of CLARREO Pathfinder instrument
NASA Kennedy Space Center (KSC)	• Launch site services and launch to International Space Station

Major Component Suppliers and Other Participants

Organization	Contributions and Responsibilities
NASA Marshall Space Flight Center (MSFC)	• CLARREO Pathfinder payload command and data routing to and from International Space Station
National Institute for Standards and Technology (NIST)	• Technical consultation and peer reviews for measurement and inter-calibration uncertainty propagation
United States Geological Survey (USGS)	• Technical consultation and leadership for  lunar inter-calibration measurements and analysis
Teledyne Scientific Imaging, Inc.	• Provider of CLARREO Pathfinder instrument focal plane array and focal plane electronics design
Zeiss, Inc.	• Provider of CLARREO Pathfinder instrument spectrometer grating
Moog, Inc.	• Provider of pointing system actuators
Northrop Grumman Aerospace Systems	• Provider of CLARREO Pathfinder instrument cryocooler
Iris Technology, Inc.	• Provider of cryocooler control electronics
Technical University of Denmark (DTU)	• Provider of pointing system star tracker