# Kinematics effects of atmospheric friction in spacecraft flybys

## TL;DR

This paper investigates the impact of atmospheric friction on spacecraft flybys, specifically analyzing the Galileo, NEAR, and Juno missions, and concludes that atmospheric drag alone cannot explain observed velocity anomalies.

## Contribution

It provides a detailed analysis showing atmospheric friction is insufficient to account for the velocity anomalies observed during certain spacecraft flybys.

## Key findings

- Atmospheric friction accounts for less than 1 mm/sec of velocity change.
- Observed velocity anomalies cannot be fully explained by atmospheric drag.
- Analysis of specific flybys demonstrates the need for alternative explanations.

## Abstract

Gravity assist manoeuvres are one of the most succesful techniques in astrodynamics. In these trajectories the spacecraft comes very close to the surface of the Earth, or other Solar system planets or moons, and, as a consequence, it experiences the effect of atmospheric friction by the outer layers of the Earth's atmosphere or ionosphere. In this paper we analyze a standard atmospheric model to estimate the density profile during the two Galileo flybys, the NEAR and the Juno flyby. We show that, even allowing for a margin of uncertainty in the spacecraft cross-section and the drag coefficient, the observed -8 mm/sec anomalous velocity decrease during the second Galileo flyby of December, 8th, 1992 cannot be attributed only to atmospheric friction. On the other hand, for perigees on the border between the termosphere and the exosphere the friction only accounts for a fraction of a millimeter per second in the final asymptotic velocity.