Final GOES-R Satellite Ready to Fly

NASA and NOAA are preparing to launch GOES-U, the last of the four GOES-R series geostationary weather satellites on June 25th, 2024 at 5:16PM, Eastern Time atop a SpaceX Falcon Heavy. GOES-R has been one of the most powerful and revolutionary weather satellite programs in history, but what is it, what makes it so powerful, and how does GOES-U fit in?

GOES stands for Geostationary Operational Environmental Satellite and is the name applied to all US civilian geostationary weather satellites since 1972. As of writing, 20 GOES satellites have been launched, with GOES-U set to be the 21st launch of the program and 19th successful spacecraft if commissioning goes as planned. GOES is used for monitoring fires, aerosols, volcanoes, hurricanes, severe storms, snow and ice accumulations, lightning, and more. Its measurements are used as inputs for the numerical weather prediction models that produce everyday forecasts as well as climatological records.

GOES-R is significantly more technologically advanced than the generation of satellites that preceded it. The Advanced Baseline Imager (ABI), the primary instrument, is a visible and infrared Earth imager at twice the resolution of the previous generation and 3-4 times faster. It also adds movable “mesoscale,” or medium-size, view regions. The mesoscale regions allow rapid-cadence observations of places of interest, such as cyclones, severe storms, hurricanes, fires, and volcanoes.

GOES-R also carries the first ever lightning mapper based in geostationary orbit, the Geostationary Lightning Mapper (GLM). Lightning activity is known to increase as an immediate precursor to tornadoes and general storm intensification, so GLM aids forecasters in increasing warning lead time and saving lives, which is integral to the mission of the program.

A complete GOES generation consists of 3-4 satellites, but only two are operational at once. The extra satellites serve a dual purpose: they act as on-orbit spares or backups in case one of the primary spacecraft suffers an anomaly or must be pulled from service. They also serve as replacements when the prime satellites begin to near their design life. Detectors and other onboard components degrade with age in the harsh environment of space, so having a younger “hot backup” on standby provides a relatively seamless way of maintaining product quality for much longer. 

The GOES-R series has already invoked the spare functionality. Two months after the launch of GOES-S (now GOES-17) in May 2018, initial checkouts and startup of the ABI identified problems with the cooling system that affected the majority of the channels by providing inadequate cooling. Eventually the affected channels were reduced to 9 and the effects contained to the time periods immediately before and after the spring and summer equinoxes, when the instrument is warmest. Design changes were made to the ABIs on GOES-T and GOES-U, and GOES-T (18) replaced GOES-17 as the western active satellite in March 2023 instead of being placed in storage. GOES-17 remains operational as a backup to GOES-18 that can be used in the case of anomalies or failures. 

GOES-U will be made operational after its launch and will replace GOES-16 as GOES-East. Original plans were for it to instead be placed in hibernation as a spare after becoming operational. This “two-step generation” architecture allows the development investment poured into a single generation to last much longer, potentially up to 20-25 years. This provides more schedule margin to develop the succeeding generation and to enable the later satellites of the current generation to serve as spares and backups until the next-generation spares are launched and available. GOES-U will unfortunately be the final GOES satellite, as the succeeding GeoXO system will not use the GOES naming.

The E in GOES stands for Environmental, which refers to more than just the land and air. The National Weather Service is charged with forecasting, monitoring, and warning against not just terrestrial weather, but space weather too. The Space Weather Prediction Center in Boulder, Colorado is charged with that duty, and uses a network of satellite observatories as one of its main data sources. For decades, GOES has been one of the primary components of this network, alongside NASA, NOAA, and ESA spacecraft, positioned at the Earth-Sun L1 point and in heliocentric orbit. As existing space weather assets age out, keeping the GOES system refreshed is critical.

GOES-U has five instruments dedicated to fulfilling its role as a space weather observatory. The Solar Ultraviolet Imager (SUVI) and Extreme Ultraviolet and X-ray irradiance Sensors (EXIS) monitor UV and X-ray light emissions from the sun and surface features such as active regions, flares, and coronal holes to aid in forecasts of radio blackouts, coronal mass ejections (CMEs), and flares. The magnetometer measures the intensity and direction of the magnetic fields far away from Earth, which can indicate the presence or approach of a geomagnetic storm or particle event. Particle and radiation storms are also warned by the Space Environment In-Situ Suite (SEISS), which tracks particle fluxes. 

New on GOES-U is the Compact Coronagraph (CCOR), which observes the sun’s corona to detect and characterize CMEs. Currently only two operational space weather missions carry coronagraphs: SOHO, a joint ESA/NASA project launched in 1995, and STEREO-A, a NASA mission launched in 2006. Both are well into their extended missions, and NOAA wants to avoid the possibility of a gap in data.

The importance of coronagraph data continuity cannot be understated. CMEs are among the most damaging and consequential types of solar activity, so careful monitoring and characterization is needed to predict their arrival and impact. Out of the five spacecraft currently at the Earth-Sun L1 point, three were launched in the mid-late 1990s and four are well into their extended missions. The solution is the Space Weather Follow-On (SWFO) program, which will replace the three NASA spacecraft with the SWFO-L1 mission and sun-facing instruments on NASA’s IMAP, both due to launch in 2025. SWFO also encompasses the addition of CCOR to GOES-U to provide earlier data and additional coronagraph in space. 

GOES-U is now at Cape Canaveral in the middle of pre-launch preparations. It aims to ensure continuity of GOES-R’s outstanding record of success and quality for the Continental US and Caribbean regions into the 2030s. It will additionally bring the same revolutionary resolution and cadence to coronal imaging with the CCOR instrument.  As NOAA begins to ramp up development on GOES-R’s successor satellites and future space weather programs, GOES-U is poised to become a crucial backstop and keystone to saving money, lives, and providing scientific insights. 

Glossary:

• GOES – Geostationary Operational Environmental Satellite
• NOAA – National Oceanic and Atmospheric Administration
• ABI – Advanced Baseline Imager
• GLM – Geostationary Lightning Mapper
• SUVI – Solar Ultraviolet Imager
• EXIS – Extreme Ultraviolet and X-ray Irradiance Sensors
• SEISS – Space Environment In-Situ Suite
• CCOR – Compact Coronagraph