While orbiting, communication satellites must remain in a fixed position aligned with a specific ground location. Drifting may put the satellite outside the ideal beam coverage zone, causing signals to weaken before reaching the ground receivers. This affects data-transmission speeds, interrupts broadcasts, and degrades call quality.
Ground antennas can also be impacted, as they’re no longer precisely aligned in this scenario. This is bad news since the receiver operates close to the satellite’s beam footprint, which has a lower signal quality. Systems may try to make up for this issue by reducing data rates or relying on stronger, slower transmission modes to maintain connectivity.
In addition, communication satellites’ RF beams may intersect with nearby satellites that have similar frequencies. Overlapping signals like these tend to result in cross-satellite interference, thus decreasing the signal-to-noise ratio (SNR). Communication then becomes less reliable and nonfunctional in extreme cases, because the interference may overpower the weak signals.
Typically, satellite systems rely on frequency reuse schemes, which involve reutilizing frequencies across various beams. In this case, slight shifts generate unpredictable co-channel interference, where isolated beams interfere with one another. Operators combat this problem by frequently tracking satellite positions and fine-tuning beam shapes, power levels, or user handoffs, effectively diminishing the interference produced by drift.
Narrow, high-frequency (Ka-band or satellite internet) beam systems are also affected as drift moves satellites out of the ground-station antennas’ range. When this happens, user terminals or ground stations no longer have a lock on the satellite signal. It leads to broadcast disruptions, dropped connections, or service outages until the terminal locks onto the signal again.
Some ground stations and user terminals deploy tracking antennas that follow a small drift. However, too much drift causes those antennas to lose track of the satellites.
Service delays may occur if the ground stations don’t reconnect with the satellites right away. Networks relying on uninterrupted satellite handover from satellite to satellite may experience higher-frequency handovers due to drift. This can ultimately degrade service quality even further.
Will GPS Become Unusable in the Upcoming Decades?
Despite speculation, GPS won’t become obsolete in the future. Sure, satellite drift, signal errors, and aging satellites contribute to GPS inaccuracy—all of which are actively managed. Ground-control stations use tracking, telemetry, and command (TT&C) systems to constantly track satellites, updating navigation messages with new ephemeris and clock corrections to maintain their positioning.
There are valid concerns about GPS interference, including jamming and spoofing. Jamming, which uses radio signals to disrupt satellites, causes receivers to lose positioning and navigation services. It has occurred more often these days, even in regions with geopolitical tensions. On the other hand, spoofing, a growing threat, involves sending fake GPS signals to receivers, causing them to function improperly.
To address those potential jamming and spoofing threats, multi-sensor navigation systems (combining GPS with cellular, Wi-Fi, inertial sensors, or visual data) are being developed to ensure navigation services remain functional if GPS signals are compromised.
In addition, GPS is undergoing upgrades with the introduction of L2C, L5, and L1C—new civilian signals that enhance satellite performance and positioning accuracy. L5 is transmitted at higher power and in a protected aeronautical radio-navigation band to enable sub-meter accuracy when combined with other signals, such as L2C and L1C. It also makes GPS more reliable for critical applications.
What Can We Do Besides Launch More Satellites into Space?
Beyond launching more satellites to correct drift, efforts are continuously underway to manage and combat satellite drift. For starters, satellites feature small onboard thrusters that keep them in position and in their orbital slot if drift ever occurs. It’s typically used for geostationary and MEO/GEO (medium Earth orbit/geostationary earth orbit) satellites.
However, this method uses fuel, even for minor corrections, which shortens the satellite’s lifespan. When it runs out of fuel, the satellite can’t stay in position, causing it to drift out of alignment and become inoperable.
Engineers are deploying alternative propulsion systems like ion thrusters and electric propulsion (Fig. 3) for longevity and efficiency. These don’t require as much propellant as chemical thrusters, so that satellites can make slight adjustments over a long period. Satellites can then perform station-keeping maneuvers and correct orbital drift without consuming a lot of fuel, extending their lifespan.
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