WHAT IS A POLAR ORBIT
Weighing in at only 15kg and about the size of a microwave oven, each GHGSat satellite is a lean, mean, emissions monitoring machine. Given their limited size, GHGSat satellites lack thrusters and therefore cannot change their trajectory or orbit once they are launched. They attain their orbital velocity and trajectory from the rocket that launched them.
This raises the question, how does a satellite with no method of changing orbit or trajectory manage to monitor for greenhouse gas emissions from industrial facilities, anywhere in the world? The answer, we let the Earth do what it does best, spin.
Each GHGSat satellite is placed more than 500km above the surface of the Earth, traveling at a speed of 7km/s, or 25,200km/hr. By the time you finish reading this sentence, our satellite will have traveled over 21km. Every orbit only takes 98 minutes to complete, which means that our satellites go around the Earth 14 times a day.
There are many different types of orbit a satellite can use. GHGSat’s satellites are in a polar orbit, which means that the spacecraft circles the Earth from north to south as the planet rotates below from west to east. This type of orbit is commonly used in Earth observation because it makes it possible to collect imagery of the entire planet over time. In a polar orbit, the satellites spend half of their time on the sunny side of the planet and the other half on the dark (night) side. GHGSat’s instrument relies on the sunlight to operate, so it can only collect imagery on the sunny side of each orbit.
Each GHGSat satellite can revisit the same site on the planet every two weeks The more satellites we have, the less time it takes for us to revisit the same location. For this reason, GHGSat has plans for a constellation of high-resolution emissions monitoring satellites placed in different polar orbital planes so we can move closer to our goal of providing daily monitoring of industrial facilities for our customers.
In order to improve the consistency of our observations, GHGSat utilizes a special kind of polar orbit called a sun-synchronous polar orbit. Because the satellite passes over a site at the same time every day, the sun angle will be the same every year for any given day at that location. It will also be very similar for observations taken within a few weeks of each other at the same site. This ensures predictable and consistent illumination from the sun for each site over time, which makes comparing results much simpler.