Satellite communication does not begin and end exactly at the moment a satellite crosses the horizon. Instead, each contact is surrounded by a sequence of preparatory and wrap-up activities that determine whether the pass is successful. These activities are collectively part of acquisition timing, which defines how ground stations prepare for Acquisition of Signal (AOS) and safely conclude operations after Loss of Signal (LOS).
For mission planners and ground station operators, understanding what happens before AOS and after LOS is just as important as what happens during the pass itself. Mistimed preparation can delay acquisition, while poor shutdown procedures can cause data loss, system faults, or missed insights. This article explains acquisition timing in practical terms, focusing on how preparation and cleanup shape real-world operations.
Table of contents
- What Is Acquisition Timing
- Understanding AOS and LOS
- What Happens Before AOS
- Antenna and Pointing Preparation
- RF and System Configuration
- What Happens After LOS
- Data Finalization and Verification
- Acquisition Timing in Mission Planning
- Acquisition Timing FAQ
- Glossary
What Is Acquisition Timing
Acquisition timing refers to the coordinated sequence of actions that occur before a satellite signal is acquired and after it is lost. It defines how early systems are prepared ahead of a pass and how long they remain active after the satellite sets. These timing buffers ensure that communication systems are ready when the satellite enters view and safely transitioned when it leaves.
Unlike orbital events, acquisition timing is largely under human and system control. Operators decide when antennas move, when receivers activate, and when data flows begin and end. Well-designed acquisition timing absorbs prediction errors, Doppler uncertainty, and operational delays, turning narrow passes into reliable contacts.
Understanding AOS and LOS
Acquisition of Signal (AOS) marks the moment a ground station first detects a usable signal from the satellite. It typically occurs shortly after the satellite rises above the station’s minimum elevation angle. AOS is both a geometric and operational milestone.
Loss of Signal (LOS) marks the end of usable communication as the satellite drops below the minimum elevation threshold. Like AOS, LOS is predictable but can vary slightly due to propagation effects and system sensitivity. Operators treat both events as approximate boundaries rather than exact instants.
What Happens Before AOS
Preparation for a satellite pass begins well before the predicted AOS time. Ground station systems must be configured, verified, and placed into the correct operational state. This lead time ensures that no critical seconds are lost when the satellite becomes visible.
Pre-AOS activities often include loading pass schedules, validating orbital data, and confirming system health. Any delays or errors during this phase can reduce effective contact time or prevent acquisition entirely. For short LEO passes, pre-AOS efficiency is especially critical.
Antenna and Pointing Preparation
Antenna systems are typically positioned in advance of AOS to the predicted acquisition point. This allows tracking to begin immediately as the satellite enters view. For fast-moving satellites, even small pointing delays can result in missed acquisition.
Pointing models, mount limits, and motion profiles are verified during this phase. Operators also confirm that no physical obstructions or safety constraints will interfere with movement. Proper antenna preparation ensures smooth transition from idle state to active tracking.
RF and System Configuration
RF systems must be configured with correct frequencies, bandwidths, and Doppler compensation parameters before AOS. Receivers are often enabled early to allow time for noise floor assessment and lock acquisition. Transmitters remain inhibited until proper authorization is confirmed.
System configuration also includes networking, recording, and monitoring tools. Data paths are verified so that incoming data is not lost once acquisition occurs. This phase ensures that the entire signal chain is ready to support the contact.
What Happens After LOS
After LOS, the ground station transitions out of active tracking and communication. Antennas are returned to safe or idle positions, and RF systems are disabled or reconfigured for the next pass. This transition must be orderly to avoid equipment stress or configuration drift.
LOS does not mean operations immediately stop. Short buffers are often used to capture trailing data and confirm that no residual signals remain. A controlled shutdown reduces the risk of corrupted data or system faults.
Data Finalization and Verification
Once communication ends, data collected during the pass must be finalized and verified. Files are closed, checksums may be computed, and metadata is recorded. This step ensures data integrity before processing or delivery.
Operators review logs, performance metrics, and anomalies associated with the pass. Any issues are documented and escalated as needed. Post-LOS verification closes the operational loop and prepares the system for future contacts.
Acquisition Timing in Mission Planning
Mission planners incorporate acquisition timing buffers into schedules and capacity calculations. Contact windows are rarely used at their full geometric extent due to setup and teardown requirements. Effective planning accounts for these operational realities.
As missions scale, automation becomes essential for consistent acquisition timing. Well-defined pre-AOS and post-LOS procedures reduce variability and improve reliability. Over time, acquisition timing becomes a key indicator of operational maturity.
Acquisition Timing FAQ
Why isn’t AOS exactly when the satellite crosses the horizon?
Because signal detection depends on elevation, system sensitivity, and atmospheric effects,
not just geometric visibility.
Can data still arrive after predicted LOS?
Sometimes. Residual signal or favorable conditions may extend usable communication slightly,
which is why post-LOS buffers are often used.
Is acquisition timing more critical for LEO missions?
Yes. Short passes and rapid motion make efficient pre-AOS preparation and post-LOS handling
essential for maximizing usable contact time.
Glossary
Acquisition timing: Operational timing of preparation and cleanup around a satellite pass.
AOS: Acquisition of Signal, the start of usable communication.
LOS: Loss of Signal, the end of usable communication.
Pre-AOS buffer: Time allocated before AOS for system preparation.
Post-LOS buffer: Time allocated after LOS for shutdown and verification.
More
