# Accession Number:

## AD0606568

# Title:

## A MODDEL LEEL FOR THE ERRORS IN SATELLITE ORBITAL PREDICTIONS CAAAUSED BY FLUCTUATIONS IN DRAG,

# Descriptive Note:

# Corporate Author:

## TRW SPACE TECHNOLOGY LABS LOS ANGELES CALIF

# Personal Author(s):

# Report Date:

## 1960-04-27

# Pagination or Media Count:

## 43.0

# Abstract:

By smoothing satellite observations, Jacchia discovered a variation in satellite drag which is correlated with solar radiation at 10 to 20 centimeters, and is quasi-periodic with a period of 27 days however, this variation cannot account for the erratic nature of the errors in satellite orbital predictions. Nonweiler and Jacchia have both found a correlationn of drag with solaloolar flares but their calculations are smoothed over 10 to 30 periods, so the behavior from period to period is unknown. The following model has been devised to describe the erratic behavior of the errors. It is assumed that there are three sources of error in satellite orbital predictions observational error, the sinusoidal variation, and a random fluctuation. The model for the random drag fluctuations is arrived at in the following way The fluctuations are assumed to be independennnt from period to period, because many of the geophysical effects of solar flares last from a few minutes to an hour. The root mean square value of the random fluctuation at a perigee height of 120 miles is calculated from some smoothed data on Sputnik II published by Nonweiler, by using the assumption of independence. It is then extended to other altitudes by assuming that the rms value of the random fluctuation is proportional to the amplitude of the sinusodidal variation, which was determined by Jacchia to be 10 per cent for the Russian satellites and 35 p 5 per cent for Vanguard I. The sinusoidal amplitude is here taken to vary linearly with the height of perigee.