Anomalous accelerations in spacecraft flybys of the Earth

TL;DR

This paper investigates the flyby anomaly, an unexplained velocity change during spacecraft Earth flybys, by analyzing orbital data with detailed models, suggesting a tiny, rapidly decaying anomalous acceleration possibly hinting at new physics.

Contribution

Developed an orbital analysis method incorporating tidal and geopotential effects to estimate the anomalous acceleration during spacecraft flybys.

Findings

Anomalous acceleration is about a fraction of a mm/s².

Acceleration decays rapidly with altitude.

Analysis suggests possible new physics in gravity at flyby altitudes.

Abstract

The flyby anomaly is a persistent riddle in astrodynamics. Orbital analysis in several flybys of the Earth since the Galileo spacecraft flyby of the Earth in 1990 have shown that the asymptotic post-encounter velocity exhibits a difference with the initial velocity that cannot be attributed to conventional effects. To elucidate its origin, we have developed an orbital program for analyzing the trajectory of the spacecraft in the vicinity of the perigee, including both the Sun and the Moon's tidal perturbations and the geopotential zonal, tesseral and sectorial harmonics provided by the EGM96 model. The magnitude and direction of the anomalous acceleration acting upon the spacecraft can be estimated from the orbital determination program by comparing with the trajectories fitted to telemetry data as provided by the mission teams. This acceleration amounts to a fraction of a mm/s$^2$ and decays very fast with altitude. The possibility of some new physics of gravity in the altitude range for spacecraft flybys is discussed.