Scientists have analyzed data recordedduring the lengthy decent of the US Air Force'sCommunication/Navigation Outage Forecasting System (C/NOFS) satelliteinto Earth's atmosphere. The observations will be extremely usefulfor future operations, significantly improving predictive models forsatellite trajectory and re-entry.
When the C/NOFS satellite burned upduring a scheduled re-entry on November 28, its demise was carefullyrecorded by a joint team of scientists from NASA, the US Air Force,and the University of Texas at Dallas (UT-Dallas).
It marked the end of a seven and a halfyear mission which saw the probe study a layer of charged particlesknown as the ionosphere, located between 40 and 600 miles (64 and 965 km) above thesurface of the Earth. It's a highly changeable region, being affectedby solar activity, electrical field effects and strong upperatmospheric winds. Such disruptions can alter satellite orbits, andproduces turbulence known as scintillations, which interfere withradio wave navigation and communications.
For 13 months before the satellite'seventual demise, as its orbit steadily decayed, the team madecomprehensive observations, looking at regions of the atmosphere thataren't routinely studied, as it's not possible to sustain an orbit atsuch altitudes without long-term on board propulsion.
The recorded data shows that at thelower altitudes, the upper atmosphere and ionosphere are stronglyinfluenced by small changes.
"The neutral atmosphere responds verydramatically to quite small energy inputs," said UT-Dallas' RodHeelis. "Even though the energy is put in at high latitudes –closer to the poles – the reaction at lower latitudes, near theequator, is significant."
The observations shed light on one bigmystery – why the low latitude ionosphere causes such pronouncedissues with communication and navigation radio signals at night. Asthe satellite descended through the darkness, it detected what is nowdeemed responsible for the interference – areas of the ionospherewhere charged particles flow by each other horizontally in oppositedirections.
The event also provided an opportunityto study the point at which the charged particles in the ionosphereand the neutral particles in the upper atmosphere interact. Thereadings show that neutral winds create build ups of neutral gasagainst the edge of the ionosphere, creating previously unobserveddensity variations. Allowing for such variations will improveaccuracy when modelling things like radio wave interference andspacecraft drag.
Source: NASA
