# Optimized Observation Sequencing in Low-Earth Orbit with the SPHEREx Survey Planning Software

## TL;DR

This paper presents the SPHEREx Survey Planning Software, an optimized algorithm for efficient sky observation in low-Earth orbit that enhances coverage and operational robustness for the NASA infrared mission.

## Contribution

It introduces a novel survey planning algorithm that optimizes target selection and operational constraints for the SPHEREx mission in low-Earth orbit.

## Key findings

- Achieved high sky coverage in the first public data release.
- Successfully mitigated operational challenges like outages and data downlink scheduling.
- Demonstrated effective in-flight performance of the planning software.

## Abstract

SPHEREx is a NASA infrared astronomy mission that launched on March 12th, 2025 and is operating successfully in low-Earth orbit (LEO). The mission is currently observing the entire sky in 102 spectral channels in four independent all-sky surveys and also achieves enhanced coverage in two deep fields. This data will resolve key science questions about the early universe, galaxy formation, and the origin of water and biogenic molecules. In this paper, we describe the survey planning software (SPS) that enables SPHEREx to observe efficiently while mitigating a range of operational challenges in LEO. Our optimal target selection algorithm achieves the required high coverage in both the All-Sky and Deep Surveys. The algorithm plans observations to stay within our time-varying allowable pointing zone, interleaves required data downlink passes, and mitigates outages due to the South Atlantic Anomaly and other events. As demonstrated by the sky coverage achieved in the first SPHEREx public data release, our approach is performing well in flight. The SPHEREx SPS is a key new capability that enables the mission to deliver groundbreaking science from LEO.