Backtrack Orbit Search Algorithm - Technical Review Comments-2

We currently use the Backtrack Orbit Search Algorithm to allow users to search for earth science data that was captured with orbiting satellites. Some of the earth science providers define their spatial regions with orbital parameters such as equatorial crossing longitude, swath width, and orbit period. Our users benefit from the Backtrack Orbit Search Algorithm which lets them use longitude and latitude coordinates, their preferred method of defining a search region. The Backtrack Search Algorithm has proven invaluable. Without it we could not allow users to easily search this orbital data.

The algorithm was originally provided by Ross Swick as a library with some example code. We were able to integrate the example code into our search component with some customizations. The library code was adequately documented. The Backtrack Algorithm documentation, available online, was useful for understanding the fundamentals of the algorithm. A basic knowledge of orbiting satellites mechanics is helpful in understanding the algorithm.

Other NASA missions would definitely benefit from the adoption of this algorithm. It provides more accurate results than traditional methods for searching orbital data due to its use of the original orbit parameters of the satellite. We appreciate that the Backtrack Algorithm generates SQL queries that can be used with any conventional relational database.

The Backtrack Algorithm does require some orbital parameters which we do not receive in an automated fashion from some providers. We have had to hard code some of these parameters for providers. It was difficult to ascertain from the documentation which equatorial crossing to use for providers with orbital data that consisted of multiple crossings.

The Backtrack Algorithm could be improved by handling changing swath widths. It currently assumes swath width and other parameters are fixed for a given orbit. There are currently some real world cases where this is not true. Also, It seems that the Backtrack Algorithm uses a spherical model of the earth. Its accuracy could potentially be improved by using an ellipsoidal model.