Earth Observation constellation design with spacestudio™
At Exotrail, we know how complex and time-consumingconstellation design can be; there are many variables and constraints toconsider. Furthermore, having to develop all the tools in-house or relying onsophisticated software that requires certification can really slow down thedesign process
With spacestudio, these problems can be solved with our unique constellation design and optimization module that helps us design constraints and verify what future constellations will look like based on specific business parameters. To illustrate this module, we will show how to exploit spacestudio in a specific use case. It is based on a future constellation that will measure the effects of climate change over the Mediterranean Sea. We need to design the constellation baseline that best meets the following mission requirements:
· Temperature evolutionof the zone of interest over the year.
· Minimum of 2 passesper day.
· 1000km +-100 km circularorbit.
· 10 deg of SOC on thepayload.
The first thing to do is to get a rough estimate of what the constellation will look like, a V0 of the geometry if you will. In spacestudio™, we can directly create the geometry of a constellation by entering only the operational metrics: in this case, the minimum revisit time of 2 passes per day which equates to at least one pass over the area of interest every 12 hours, as well as high-level constellation information such as the payload. From this, the spacestudio™ constellation generation mission computes a geometry in seconds that will meet the selected requirements. This one giving us a first estimate of the constellation shape in terms of number of planes, spacecraft per plane, altitude and inclination.
At this point, we want to analyze the performance of this V0 of the constellation, as this first batch may not meet all the requirements of our mission and some constraints may require further adjustment. Using the spacestudio™ performance analysis mission, the analysis shows that the constellation performance is excessive compared to our revisit metric. This means that the number of spacecraft in the constellation could be reduced to better meet the constraints of a revisit time every 12 hours. Currently, the maximum revisit time in our area of interest is about 4 hours as can be seen in the figure below:
In order to modify the shape of the constellation and improve our geometry to better meet our mission, the geometry is directly used in the constellation optimization mission of spacestudio™ . There, we can define the optimization goal of reducing the number of spacecraft in the geometry while maintaining the maximum revisit time of 12 hours. The spacestudio™™'s internal genetic optimization algorithm will modify the shape of the geometry to reduce the number of spacecraft in the constellation. The algorithm will change the altitude of the constellation (from 1000 km to 1057 km) and reduce the number of spacecraft from 12 to 6, while keeping the maximum revisit time below 12h. The dashboard of spacestudio™ 's results highlights the differences between our initial batch and the modified constellation as can be seen in the figure below:
The improved constellation can now be re-analyzed using spacestudio™ 's constellation performance analysis mission to check that the revisit constraint is still respected. What we can see is that every part of the Mediterranean sea is revisited at least once every 12 hours.
To continue our use case, a change in the baseline has taken place: the field of view of the payload has been modified due to some external constraints. We will quickly look at the impacts of this baseline change and see how it affects our mission scenario. This can be done very easily with spacestudio™ as all objects and missions are stored in a database. And to do this we will simply copy and paste the payload object and change its field of view:
Finally, by rerunning the spacestudio™ constellation performance analysis mission calculations and comparing the new constellation results with those from before, we can see in the figure below that with a smaller field of view, the area of interest would be seen fewer times over the course of the mission, but still meeting our requirements.
As LEO constellations grow, there is a need for a tool that allows for intuitive and iterative constellation development, where important operational metrics can be checked quickly to allow teams to move forward with the design. Here we have shared how, using spacestudio™'s interconnected constellation missions and object database management, the user controls the entire constellation engineering workflow.