Intro
On March 1st, 2022 the latest in a long line of weather satellites launched. The satellite is named GOES-T, and it launched on United Launch Alliance's Atlas V rocket from Florida. It is not a remarkable satellite, is not the first in a series; it is not the first to use a new technology. But it is nonetheless important.
For decades the United States has maintained a system of weather satellites that have provided comprehensive information about the Western Hemisphere. The Geostationary Operational Environmental Satellite (GOES) series has provided weather data for over 50% of the world for over 50 years.
How is weather data collected? What makes the latest series of GOES satellites unique? How has the design of GOES satellites changed over the decades? Why are these missions even that important? The answers to all of these questions are in this article.
The GOES Program
The Geostationary Operational Environmental Satellite (GOES) program is one of the longest lasting and most useful NASA programs ever. The program is a collaboration between NOAA (National Oceanic and Atmospheric Administration) and NASA (National Aeronautic and Space Administration), two agencies of the US government. NASA pays for the construction and launch of the satellites, while NOAA operates the satellites, and distributes GOES data. GOES satellites provide high-quality images of Earth, data about Earth's magnetosphere, and information about space weather. All of this information is useful to meteorologists and climate scientists.
Satellites in the GOES program operate in a geostationary orbit (GEO). A satellite in GEO takes 24 hours to orbit the Earth, which allows the spacecraft to stay above the same part of the Earth permanently. GOES satellites are stationed at one of two places, East (75.2°W) and West (137.2°W). The East slot, which is currently occupied by GOES-16, can view almost all of the Americas and most of the Atlantic Ocean. GOES-17, which currently occupies the West spot, can view the western United States and most of the Pacific Ocean. Together, two satellites can provide detailed coverage of America and help meteorologists all over the world predict the weather.
GOES satellites are given a letter designation, such as GOES-T, during development and construction. Once it launches and reaches geostationary orbit it is given a numbered name. GOES-T arrived in geostationary orbit on March 14th, and was renamed GOES-18, for simplicity I will refer to it as GOES-T for the rest of this article.
The GOES program began in the 1970’s after the two experimental Synchronous Meteorological Satellites (SMS) proved that geostationary weather satellites were useful to meteorologists. The first GOES satellite, GOES A, launched on October 16th, 1975. It was renamed GOES-1 shortly after it launched. GOES-1 and followed by GOES-2 and GOES-3, which launched in 1977 and 1978 respectively.
These early satellites were very similar to their SMS predecessors, and were much simpler than modern weather satellites. They were cylindrical and had three scientific instruments. An optical and infrared imager, a space environment monitoring system, and a weather data relay system.
Over the decades, new generations of the satellites have been developed by NASA and operated by the NOAA. The imagers have been combined with sounders, which can measure the height of clouds. Magnetometers and more advanced space environment instruments have improved data about space weather.
These satellites have culminated in the latest generation of GOES satellites, GOES-R.
The GOES-R series is a total redesign of the spacecraft with a new advanced collection of instruments. GOES-T is the third of the four planned GOES-R satellites. When all of the satellites are launched, two will become GOES East and West, while the other two will serve as backup satellites in case either one has issues. GOES-R (GOES-16) launched in 2016 and GOES-S (GOES-17) launched in 2018. GOES-T will be followed by GOES-U in 2024.
GOES-17, the current GOES-West, has a flaw with the radiator that connects to ABI, which prevents it from imaging in infrared part of the time. Which is why GOES-T is going to replace it once it completes on-orbit testing.
Spin-Stabilized and Three-Axis Stabilized
A major change in the GOES satellites is how they have been stabilized. The first seven GOES satellites were all spin-stabilized. Spin-stabilization is one of two common ways that spacecraft are kept stable. Since things that spin are more stable, spinning a spacecraft is a simple way to control where a spacecraft points and how it moves. However, it doesn't allow for precise pointing and can limit the scientific data that can be collected. The first GOES satellites could only image the Earth ten percent of the time.
Beginning with GOES-8 (GOES-I) all of the GOES satellites are three-axis stabilized. Three-axis stabilized spacecraft do not spin, but use reaction wheels, which are small rotating wheels, to change the orientation of the spacecraft. This allows for a spacecraft to stay pointed at a target and precisely control its momentum.
This switch to three-axis stabilization required more complicated technology, but revolutionized the data that could be collected. It allowed for constant Earth imaging, for the magnetometer to be placed on a boom that separated it from the spacecraft, and for the solar panels to always face the Sun.
Data Collection System (DCS)
Not only do GOES satellites collect weather data but they also relay weather data. All GOES satellites have been fitted with multiple antennas that pick up signals from isolated weather stations across the Americas and Atlantic and Pacific Oceans. These isolated stations are on mountain peaks, deep within forests, and on floating ocean platforms. They collect data about rainfall, earthquakes, tides, and winds and send them to GOES satellites via radio waves. GOES satellites then relay it to ground stations in Virginia and Maryland. This system allows for small weather stations to send data using only a simple antenna, and not require expensive communication cables to be built.
Because of the many antennas that are on GOES satellites some have been repurposed as communication satellites after retirement from meteorological duties. After GOES-3's meteorological instruments failed it was converted to a communication satellite. For 21 years it relayed data from the Amundsen-Scott South Pole Station in Antarctica. Most satellites in GEO can't communicate with the South Pole because they orbit in an equatorial orbit, but GOES-3 drifted into a more inclined orbit and was able to communicate with scientists living in isolation for a few hours out of each day.
Search-and-Rescue Assistance
Beginning with GOES-7 (GOES-H) all GOES satellites have been part of the SARSAT program. The SARSAT program is an international program that fits satellites in a variety of orbits with antennas that can pick up messages from 406 transponders. 406 transponders transmit the location of people in distress, such as plane crash or shipwreck survivors, or people who are lost in a forest. GOES satellites can pick up these signals and relay them to search-and-rescue groups. GPS, Galileo, GLONASS, and dozens of other satellites owned by governments around the world are part of this program, which has saved the lives of thousands of people.
Images
The most important scientific instrument on all GOES satellites has been the imager. All of the GOES satellites have had a camera that is capable of viewing the Earth in both visible and infrared light. The camera can be used to observe hurricanes, clouds, and volcanic eruptions. The infrared bands can determine temperature. This data is crucial to meteorologists and is fundamental in predicting weather. This is why NASA continues to make more advanced cameras for GOES satellites.
Beginning with GOES-4 (GOES-D) the image data has been combined with data from a sounder. A sounder uses visible and infrared light to determine the temperature and height of clouds. This allows for 3D pictures of the Earth to be created. GOES-R series satellites are not equipped with a sounder, and I think, but haven't confirmed, that ABI can't map cloud height.
The ABI (Advanced Baseline Imager) is the camera on GOES-R series satellites. It can image faster, in more detail, and in more frequencies the previous GOES cameras. It can view the Earth in 16 different optical and infrared spectral bands, which each say something different about clouds, temperature, smoke, or some other weather phenomenon. They can be combined to create color images of the Earth.
In addition to ABI GOES-T is equipped with an advanced instrument that maps lightning. It is called the Geostationary Lightning Mapper (GLM). GLM is a first of its kind sensor that made its debut on GOES-R. It studies infrared light to detect where and when lightning strikes happen. This data can help meteorologists predict how severe a storm is going to get and give people time to prepare.
Space Weather
Another crucial thing that GOES satellites study is space weather. Solar flares set off by the Sun can mess with the Earth's magnetosphere, destroy electronics, and affect weather on Earth. Which is why GOES satellites gather data about the Sun-Earth environment in two ways, by observing the Sun, and making in-situ measurements.
In-situ measurements
All GOES satellites have had instruments to study the environment around them. The first GOES satellites had the Space Environmental Monitor (SEM), which measured x-rays, energetic particles, and the Earth's magnetosphere. More advanced versions of these instruments have been added to GOES satellites. Beginning with GOES-8 the magnetometer was placed on a boom that deployed from the spacecraft. This prevents the sensitive magnetic field data from being affected by the satellites electronics.
GOES-R series satellites have a complex system of four sensors that make up the Space Environment In-Situ Suite (SEISS). These sensors detect a wide variety of charged particles, from low energy electrons to highly ionized molecules. These sensors can be combined with data from the magnetometer (MAG), which is deployed on a boom behind the spacecraft, to give us a good understanding of how particles from the Sun are affecting Earth.
Solar observations
Beginning with GOES-8 (GOES-I) the solar panels were not placed around the spherical body of the spacecraft, but on an array that deployed from the spacecraft. The array is capable of turning to always face the Sun. This is how solar panels are typically placed on spacecraft. This allows for some instruments to be attached to the solar panels and always be pointed towards the Sun.
The X-Ray Sensor (XRS) was the first of these Sun-facing instruments, it first flew on GOES-8. It sensed the X-rays being emitted by the Sun. A more powerful instrument, the Solar X-ray Imager (SXI), was debuted on GOES-12 (GOES-M). It didn't just sense X-rays, but imaged them. It created circular images of the Sun showing where X-rays were being emitted. By studying these X-rays solar flares can be predicted and people can be warned.
The SXI has been replaced by two sensors on GOES-R satellites, the Solar UltraViolet Imager (SUVI) and the Extreme ultraviolet and X-ray Irradiance Sensor (EXIS). They are both attached to a platform near the base of the solar panels. Together they can image the Sun in a wide range of ultraviolet and X-ray wavelengths.
Into the Future
Since GOES satellites are really important for weather prediction NASA has already began work on the next generation of GOES satellites. The first in the GeoXO (Geostationary Extended Operations) series will launch around 2032. The series is still in the early design phase, but it is planned to be a major improvement over the GOES-R series.
There will be six satellites in the series instead of four. Three satellites will serve as backups to GOES-East, West, and Central, while three will be operational. GOES-Central will be a new slot for a GOES satellite. It will be positioned directly over the US and have additional instruments, including a sounder and atmospheric composition instrument.
Conclusion
GOES satellite are really important. They don't just benefit meteorologists, but benefit everyone. This is why I decided to dedicate one of my blog articles to this mission. Because GOES-T isn't about starting something new or doing something bold, but about continuing what has been done by NOAA for decades. Its about continuing to gather data about the Earth and Sun, about our place in space, and how our atmosphere functions. Its about broadcasting life-saving distress signals, and spreading weather data across the world.
The image taken by ABI further up on this page was added to this article less than 30 minutes after it was taken. This is really impressive! Have you stopped to appreciate just how impressive satellite technology has become? They receive, process, and resend thousands of signals everyday and provide data that we have come to rely on. They gather ultra precise measurements over large parts of the electromagnetic spectrum. Radio waves from antennas, X-rays and ultraviolet light from the Sun, infrared and optical light from the Earth. They predict things so precise that it is hard to comprehend.
Space exploration has gone somewhere. Only a few decades ago having images of the Earth available for everyone mere minutes after they were taken would have seemed impossible. Having high-quality data about the Earth's magnetosphere; being able to track wildfires from space; getting early solar flare warnings, was a dream shared by scientists for the future. What's amazing about GOES-T is that this has become the norm.
Sources:
Intro:
The GOES Program:
Spin-Stabilized and Three-Axis Stabilized:
Data Collection System:
Search-and-Rescue Assistance:
Images:
In-Situ Measurements:
Solar Observations:
The Future