PreviSat vs. Competitors: A Quick Comparison

Using PreviSat: Tips, Tricks, and Best PracticesPreviSat is a tool designed for planning and predicting satellite visibility, passes, and observations. Whether you’re an amateur satellite observer, a ground station operator, an educator, or a researcher, mastering PreviSat can significantly improve your observing sessions, increase successful contacts, and help you gather more reliable data. This guide covers practical tips, useful tricks, and best practices to get the most from PreviSat.

What PreviSat Does (Briefly)

PreviSat calculates satellite pass predictions and visibility windows using orbital elements (TLEs) and site coordinates. It provides rise/culmination/set times, maximum elevation, azimuths, and duration for each pass. Many users leverage PreviSat alongside radio equipment, telescopes, or optical cameras to plan observations and communications.

Getting Started: Setup and Configuration

• Create or verify your observation site: enter precise latitude, longitude, and elevation. Accurate site coordinates improve prediction precision.
• Choose the correct time zone and configure UTC offsets. Use UTC for logging to avoid daylight saving errors.
• Import current TLEs (Two-Line Element sets) from reliable sources (Celestrak, Space-Track) before planning sessions. TLE age affects accuracy — use the freshest available data.
• Set prediction span (e.g., 24–72 hours). Short spans reduce clutter and focus on immediate opportunities.

Tip: Understand TLE Limitations

TLEs are mean-element sets suited for near-term prediction. Their accuracy degrades over time, especially for low Earth orbit (LEO) objects with atmospheric drag or for objects affected by maneuvers.

• For critical events, refresh TLEs within hours of the observation.
• If tracking fast-moving or decaying objects, prefer TLEs updated within the last 24 hours.

Planning Passes: Prioritization and Filters

• Filter by minimum elevation (e.g., >20°) to focus on passes with better signal strength and optical clarity.
• Prioritize passes by maximum elevation and duration. High-elevation passes reduce atmospheric path length and improve SNR for radio/optical observations.
• Consider pass azimuths relative to local obstacles (trees, buildings) to avoid blocked tracks.
• Use dawn/dusk filters for optical observations: passes during civil twilight often provide the best opportunity to see illuminated satellites against a dark sky.

Best Practices for Optical Observations

• Observe shortly after sunset or before sunrise when satellites are sunlit but the ground is dark.
• Use predicted maximum elevation and azimuth to pre-point a telescope or camera mount.
• For wide-field imaging, calculate the angular speed from pass duration and plan exposure times to avoid excessive trailing.
• Use a star chart overlay or plate-solving tools to align frames and confirm satellite tracks.

Best Practices for Radio/Amateur Satellite Communication

• Pre-calculate doppler shift for downlink and uplink frequencies; many satellites (especially LEO) produce significant doppler.
• Program Doppler correction into your radio or use software that applies real-time adjustments.
• Time your uplink/downlink windows to start a little before rise and extend a little after set for acquisition and wrap-up.
• Note predicted pass maximums to plan mode changes (e.g., switch from telemetry to voice/SSB near peak elevation).

Automation and Integration

• Integrate PreviSat outputs with tracking/control software (e.g., Gpredict, SatPC32) where possible to automate antenna/telescope pointing.
• Export pass lists in standard formats (CSV, ICS) for sharing and scheduling.
• If available, use API or scripts to fetch latest TLEs automatically and update schedules daily.

Handling Uncertainty: When Things Don’t Match Predictions

• Expect small timing and azimuth errors due to TLE age, propagation models, and local timing differences.
• Use real-time telemetry or visual confirmation (e.g., spotting the satellite or listening for beacon) to refine pointing.
• For research-grade needs, cross-check PreviSat results with other propagators (SGP4 implementations) and observational data.

Advanced Tricks

• Combine predicted passes of multiple satellites to plan observation campaigns or multi-satellite contacts.
• Use cadence planning: schedule repeated short observations across several consecutive passes to build time-series data.
• For optical imaging, use predicted angular rate to program mount tracking rates different from sidereal.
• Use night-sky brightness/dust/humidity data alongside PreviSat outputs to select optimal nights.

Logging and Post-Session Analysis

• Keep a log: record actual acquisition time, signal strength, visual magnitude estimates, and any deviations from predictions.
• Compare logged results with PreviSat’s predictions to estimate local prediction errors and improve future planning.
• Share observations with communities (e.g., amateur satellite clubs, research groups) to contribute to collective knowledge on object behavior and TLE quality.

Safety, Legal, and Ethical Considerations

• Respect radio regulations: use licensed frequencies and authorized power levels.
• For optical observations, avoid pointing lasers at aircraft and follow local rules for night-sky observations.
• Do not attempt to interfere with satellite operations or claim ownership/control over observed assets.

Quick Checklist Before a Session

• Update TLEs.
• Verify site coordinates and time settings.
• Filter passes by elevation and lighting conditions.
• Program doppler corrections (radio) or pre-point coordinates (optical).
• Prepare logging tools and backup power.
• Confirm all equipment (antennas, radios, mounts, cameras) are operational.

Using PreviSat effectively is mostly about accurate inputs, timely data updates, sensible filters, and integrating predictions into your workflow. With a few simple routines—refresh TLEs, set realistic elevation limits, and log outcomes—you’ll make most observing sessions more productive and predictable.