Tool for spacecraft trajectory modeling and space mission design and analysis

What is it about?

SpOCK is an orbit propagator: it predicts the future locations of satellites. Modeling spacecraft trajectories is not a trivial task because there are a number of forces that perturb the motion of objects in space. For example, the Earth is not a perfect sphere and its mass is not uniformly distributed. As a result, gravity is more important at certain locations than others, which greatly modifies the trajectory of a satellite. Another important perturbing force is due to the presence of air molecules at "low" altitudes, below ~1,000 km. These air molecules cause friction on the spacecraft, which in turn loses altitude. Not only this changes its position but also its speed. Other perturbing forces are the results of the gravitational field of the Moon and the Sun, as well as radiation pressure from the sunlight. SpOCK models these perturbing forces in order to accurately predict the future trajectories of spacecraft. It also determines the solar power generated by the solar cells on the satellite, computes the coverage of ground stations (i.e., when the satellites are in contact with the ground), and predicts the probability of collision between two objects. SpOCK has been used in the CYGNSS mission to predict when the observatories can measure winds in cyclones, and for mission design and analysis of CubeSat missions. SpOCK is open public, written in C and supports parallelism, which makes it well suited for satellite constellation and Monte Carlo analyses.

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Why is it important?

Modeling spacecraft trajectories is a major component of space missions. When designing a mission, engineers need to make sure that operational and scientific requirements will be met once the satellite is in orbit. These requirements greatly depend on the trajectory of the spacecraft. For example, the amount of sunlight the satellite receives, thus the solar power solar arrays generate, depend on the direction of the orbit plane with respect to the Sun. Furthermore, for observation missions, such as CYGNSS that measures winds in cyclones, the trajectory needs to be optimized to maximize the coverage of regions of interest. Finally, another important application of spacecraft trajectory modeling is collision avoidance. There are thousands of objects in space. This represents a major threat for satellites and astronauts. To avoid collisions, mission operators need to predict the trajectory of the satellite and the object that it is potentially about to collide with.

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