PACE

PACE [NASA]

The PACE (Plankton, Aerosol, Cloud and ocean Ecosystem) satellite is a planned mission developed by NASA's Goddard Space Flight Center (GSFC) to make global ocean color measurements to provide extended data records on ocean ecology and global biogeochemistry (e.g., carbon cycle) along with polarimetry measurements to provide extended data records on clouds and aerosols. Understanding of impacts and feedbacks of the Earth system to climate are critical importance.

PACE's advanced technologies will provide unprecedented insight into Earth's ocean and atmosphere, which impact our everyday lives by regulating climate and making our planet habitable. Our oceans teem with life, supporting many of Earth's economies. New discoveries in Earth's living ocean will be revealed with PACE's global observations, such as the diversity of organisms fueling marine food webs and how ecosystems respond to environmental change. PACE will observe our atmosphere to study clouds along with the tiny airborne particles known as aerosols. Looking at the ocean, clouds, and aerosols together will improve our knowledge of the roles each plays in our changing planet.

PACE's data will reveal interactions between the ocean and atmosphere, including how they exchange carbon dioxide and how atmospheric aerosols might fuel phytoplankton growth in the surface ocean. Novel uses of PACE data – from identifying the extent and duration of harmful algal blooms to improving our understanding of air quality – will result in direct economic and societal benefits.

GSFC is responsible for the principal mission elements, including the design and fabrication of the spacecraft, development of scientific instrumentation.

The two primary science instruments planned for PACE are the Ocean Color Instrument (OCI), which is being built at GSFC, and a multi-angle polarimeter that will be procured from an industry partner.

The primary science instrument planned for PACE is the Ocean Color Instrument (OCI) which will be capable of measuring the color of the ocean from ultraviolet to shortwave infrared. OCI is being built at GSFC. It is a highly advanced optical spectrometer that will be used to measure properties of light over portions of the electromagnetic spectrum. It will enable continuous measurement of light at finer wavelength resolution than previous NASA satellite sensors, extending key system ocean color data records for climate studies. OCI consists of a cross-track rotating telescope, thermal radiators, along with half-angle mirror and solar calibration mechanisms. It is based on the heritage of earlier instruments like SeaWiFS, which was flown on OrbView 2 (SeaStar).

PACE will also include two polarimeters. Such instruments are used to measure how the oscillation of sunlight within a geometric plane - known as its polarization - is changed by passing through clouds, aerosols, and the ocean.

The polarimeters onboard the PACE observatory are the Spectro-polarimeter for Planetary Exploration (SPEXone) and the Hyper Angular Research Polarimeter (HARP2). They will be contributed by a consortium based in the Netherlands and University of Maryland Baltimore County, respectively.

SPEXone is a multi-angle polarimeter. It measures the intensity, Degree of Linear Polarization (DoLP) and Angle of Linear Polarization (AoLP) of sunlight reflected back from Earth's atmosphere, land surface, and ocean. The focus of the SPEXone development is to achieve a very high accuracy of DoLP measurements, which facilitates accurate characterization of aerosols in the atmosphere. It is based on airborne and groundbased instruments and the Tropomi instrument from ESA's Sentinel 5p.

HARP2 (Hyper-Angular Rainbow Polarimeter #2) is a wide angle imaging polarimeter designed to measure aerosol particles and clouds, as well as properties of land and water surfaces. The amount and type of particles in suspension in the atmosphere are relevant to applications pertaining to health effects, cloud life cycle and precipitation, climate, etc. HARP2 will combine data from multiple along track viewing angles (up to 60), four spectral bands in the visible and near infrared ranges, and three angles of linear polarization to measure the microphysical properties of the atmospheric particles including their size distribution, amount, refractive indices and particle shape.. This instrument is based on an earlier airborne instrument called AirHARP and the HARP cubesat.

Together, SPEXone and HARP2 will meet the PACE mission's needs by providing complementary spectral and angular sampling, polarimetric accuracy, and spatial coverage (see table below). They will provide opportunities for improved OCI atmospheric correction, as well as a comprehensive range of aerosol and cloud science data products beyond what could be accomplished by the OCI alone. Thus, the synergistic payload of the OCI, SPEXone, and HARP2 will be poised to make significant breakthroughs in aerosol-cloud-ocean research.

PACE is being implemented as a NASA Class C mission with a notional launch date in the 2022-2023 timeframe and a minimum mission duration of three years, with orbit maintenance capabilities for 10 years.

In July 2017, passed the key decission point B, but has been cancelled in the Trump administration's 2018 NASA budget proposal only to be reinstated later. In the FY2019 budget, the cancellation again was proposed. In February 2020, a launch contract with SpaceX for a launch on a Falcon-9 v1.2 (Block 5) in December 2022 was signed. The Trump administration's 2021 NASA budget proposal again tried to cancel the mission.