This guide provides a workflow for astronomers and observatories to measure and verify the timing accuracy of their systems. Accurate timing is critical for high-precision astrometry, especially for fast-moving objects like Near-Earth Objects (NEOs) and artificial satellites (ArtSats).

This process combines two key tools: the online GNSS analysis tool from Bill Grey's Project Pluto and the "Astrometric System Timing Assessment" module from the MEO Observation Assistant. (Many thanks to Bill Grey for his important contributions to the planetary defense and NEO community.)

Field Guide: High-Precision Timing Calibration

Objective: Measure and correct Total System Latency (Camera + USB + Software) to enable high-precision reporting in ADES format.

📋 Master Workflow Checklist

Follow these steps in order. Refer to the "Reference Guide" below for details.

Phase 1: Pre-Observation Readiness

• [ ] Time Source: 1PPS GPS Receiver locked >20 mins.

• [ ] Clock Discipline: Meinberg/NmeaTime active. Zero manual offsets applied.

• [ ] System: No background Windows Updates or antivirus scans.

• [ ] Software Check: Ensure capture software records milliseconds (not rounded to nearest second).

• [ ] Camera Settings: ROI and Binning EXACTLY MATCH your science target settings.

• [ ] Exposure: Set to ~0.3s - 0.5s (limit trailing, ensure stars for plate solve).

• [ ] Tracking: Mount set to Sidereal rate.

• [ ] Targets: Identified 3-5 GPS/GLONASS satellites (>45° Alt, Sunlit).

Phase 2: Acquisition (The 15-Minute Burst)

Do not pause to analyze or change settings during this burst.

• [ ] Target A: Slew -> Capture 30-40 frames -> Stop.

• [ ] Target B: Slew -> Capture 30-40 frames -> Stop.

• [ ] Target C: Slew -> Capture 30-40 frames -> Stop.

Phase 3: Analysis (Repeat for Each Target)

Perform this cycle 3 times (once for Target A, once for B, once for C).

• [ ] Reduce: Load images for Target X into Astrometrica/Tycho.

• [ ] Measure: Plate solve and generate ADES Report for this target.

• [ ] Compute: Copy ADES text to Project Pluto GNSS Tool.

• [ ] Record: Paste Pluto output into MEO Module 2. Record the Mean Offset for this target.

Phase 4: Calculation & Application

Choose one mode:

Mode A: Fresh Calibration (Zero Offset was used)

• [ ] Calculate: (Mean A + Mean B + Mean C) / 3 = New Offset

• [ ] Apply: Enter this value into your software's Offset DATE-OBS field.

Mode B: Verification (Current Offset was used)

• [ ] Check: Is the average of means close to 0.00s?

• [ ] If YES: System is Green. Proceed to Science.

• [ ] If NO: Calculate correction: Current Offset + (Average Mean) = New Offset. Update software.

📖 Reference Guide & Details

1. Introduction: The "Why" and "How"

Accurate timing is critical for high-precision astrometry. For a target moving at 35"/sec, a 0.5s timing error creates a positional error of 17 arcseconds.

The Danger of Systematic Error

Unlike random noise (which averages out over many observations), timing errors are systematic. If your clock is slow by 0.5s, every single observation you submit will be biased by 17 arcseconds in the same direction. This can severely degrade orbit calculations.

The Solution: The "Survey Strategy"

We use a Multi-Target Survey (averaging 3 satellites) to smooth out random errors in the TLE orbital models, isolating the True System Latency (Camera Readout + USB Transfer + Software Processing).

2. The "Golden Rules" of Calibration

⚠️ Rule 1: The Readout Trap (ROI & Binning)

Latency is driven by data volume. A Full Frame image takes much longer to download than a crop.

• Requirement: You MUST calibrate using the EXACT Region of Interest (ROI), Binning, and Gain settings intended for science.

⚠️ Rule 2: The Time Source

You cannot measure milliseconds if your ruler is wobbling.

• Requirement: Your 1PPS GPS Receiver must be Locked and Converged.

• Requirement: Clock discipline software must have Zero manual offsets. Correct latency in post-processing, not by shifting the system clock.

⚠️ Rule 3: The Survey Strategy

One target is not enough.

• Requirement: Acquire data on at least 3 different GNSS satellites.

• Why GNSS? They orbit in MEO (stable orbits, no atmospheric drag) and are tracked by ground stations, offering far better TLE accuracy than LEO debris.

• Why Single Session? Ensures hardware conditions (temp, CPU load) are identical for all measurements.

3. Definitions: The ADES Fields

• Offset DATE-OBS (Systematic Bias): The average time delay of your system. Applied as a correction to timestamps.

• rmsTime (Precision): The random scatter (noise) in your timing. Reported to MPC.

• uncTime (Stability): The uncertainty of your systematic error (drift). Reported to MPC.

Total Accuracy

$$\text{Total Accuracy} = \sqrt{(\text{rmsTime})^2 + (\text{uncTime})^2}$$

4. Phase 1 Details: Setup & Configuration

1. Hardware Check:

• GPS/1PPS Locked > 20 mins.

• No background Windows Updates.

• Software Check: Verify your capture software writes milliseconds (e.g., 12:00:01.456). Some software deceptively truncates to 12:00:01, introducing a massive random error.

2. Camera Config:

• Set ROI/Binning to match Science Target.

• Set Exposure to ~0.3s - 0.5s.

• Verify Timestamp Reference (Start vs Mid).

3. Target Selection:

• Use Project Pluto.

• Criteria: Altitude >45°, Bright, Fresh TLEs.

• Avoid Shadows: Pick targets with high elongation from the Sun. Satellites in Earth's shadow disappear.

5. Phase 2 Details: Data Acquisition

Goal: Capture 30-40 points on 3 targets back-to-back. Do not change settings in between.

1. Slew to Target A: Capture ~30-40 frames.

2. Slew to Target B: Capture ~30-40 frames.

3. Slew to Target C: Capture ~30-40 frames.

6. Phase 3 Details: Data Reduction

Process each target individually.

1. Reduce: Load images -> Plate Solve -> Generate ADES.

2. Analyze: Run through Project Pluto Tool.

3. Record: Use MEO Tool to extract the Mean Offset.

7. Phase 4 Details: Calculation

Mode A: Fresh Calibration (Zero Offset Used)

Your Mean Residuals = Total Latency + Orbit Error.

• Formula: (Mean A + Mean B + Mean C) / 3 = New Offset

• Example:

  • Sat A: 0.340s

  • Sat B: 0.365s

  • Sat C: 0.345s

  • Average: 0.350s

• Action: Enter result as Offset DATE-OBS in software.

Mode B: Pre-Event Verification (Current Offset Used)

Your Mean Residuals = Residual Error.

• Diagnostic:

  • Positive (+): LATE (Under-corrected). ADD to offset.

  • Negative (-): EARLY (Over-corrected). SUBTRACT from offset.

• Formula: Current Offset + (Average of 3 Means) = New Offset

• Example:

  • Current Offset: 0.350s

  • Average Residual: +0.020s (Positive = Late/Under-corrected)

  • Calculation: 0.350s + (+0.020s) = 0.370s

8. Maintenance & FAQ

When to perform this workflow:

• 🔴 CRITICAL: Before Fast Movers/Close Approaches.

• Changes: New Hardware/Software/Cables.

• Seasonal: Quarterly (Mechanical shutter drift).

Q: How accurate do I need to be? A: Timing errors should contribute less than 20% to your total error budget.

• Example: You are tracking a fast NEO moving at 5.0 arcsec/sec with an astrometric precision of 0.5".

• A timing error of just 0.1s creates a 0.5" drag ($0.1s \times 5.0"/s$), effectively doubling your error.

• To keep timing negligible (<20%), you need an accuracy better than 0.02s (20ms).

Q: Does pixel position matter (Rolling Shutter)? A: Yes, for CMOS cameras with Rolling Shutters, the "Time of Exposure" is slightly different for the top row vs. the bottom row.

• Mitigation: Try to keep the satellite near the center of the frame. If precision is critical, some advanced software can model the readout delay based on Y-coordinate, but centering the target is usually sufficient for <10ms accuracy.

Q: Why not offset the PC clock? A: 1. Variability: Latency changes with ROI/Binning. 2. Stability: Clock discipline takes time to re-converge. 3. Integrity: Keeping raw FITS timestamps locked to UTC allows for future corrections.

9. Helpful Resources

• Original MEO Guide: Mind's Eye Observatory - Verifying Astrometric Timing

• Finding Targets: Project Pluto - Find GPS

• Data Reduction: Project Pluto - GNSS Astrometry

• MEO Assessment Tool: [Module 2 (Local File)]

• Time Sync Software: Meinberg NTP | NmeaTime

1. Introduction: Why Timing is Critical

Astrometry is the measurement of where and when. For slow-moving main-belt asteroids, a small timing error (e.g., 0.5 seconds) may not significantly impact the positional measurement.

However, for fast-moving NEOs or GNSS satellites (which can move at ~35 arcseconds per second), a 0.5-second timing error can introduce a positional error of over 17 arcseconds. This is larger than the measurement error of most modern systems.

Timing errors are often systematic. This means they won't cancel out over multiple observations. The goal of this workflow is to measure your system's timing errors so they can be corrected and accurately reported.

1.1 A Note on This Workflow

Please note that the methods described in this guide are based on the current workflow used at Mind's Eye Observatory. Your specific hardware, software, and observing procedures may be different. This guide should be adapted to fit your system, but the core principles of measuring and correcting for end-to-end timing errors remain the same.

2. Core Concepts: The "What"

This workflow is designed to measure the three key timing values required by the modern ADES (Astrometry Data Exchange Standard).

Based on the definitions in the MEO Timing Tool and IAWN (International Asteroid Warning Network) campaigns, these fields are:

• Offset DATE-OBS (Systematic Error / Bias):

  • What it is: The measured average offset of your clock (e.g., "your clock is, on average, 0.15 seconds fast").

  • How you use it: You can apply this value as a correction to your DATE-OBS timestamps before submitting your observations.

• rmsTime (Random Error / Precision):

  • What it is: The measured random scatter (Standard Deviation, or sigma) of your timing measurements during a single session. This represents the precision of your clock.

  • How you use it: This value is reported in the rmsTime field of your ADES submission. It tells orbit computers how much "noise" to expect from your timing.

• uncTime (Systematic Error Drift / Variability):

  • What it is: The variability (Standard Deviation) of your systematic error over time. It measures how much your clock's average offset (the bias) drifts from night to night.

  • How you use it: This value is reported in the uncTime field of your ADES submission. It requires data from at least two different sessions (e.g., two different nights) to calculate.

2.1 Understanding Your Total Timing Accuracy

Your "total accuracy" is a combination of two different types of error: the random error (precision) and the systematic error (the uncertainty in your correction).

• Random Error (Precision) = rmsTime

  • This is your Std Dev (Standard Deviation) from a single session data.

  • This value represents the precision of your measurements. It's the typical "spread" or randomness you see in your data points after the main offset has been corrected.

• Systematic Error (Uncertainty) = uncTime

  • This is your Sys. Drift, calculated from the Mean values of multiple sessions.

  • The Mean (or Offset DATE-OBS) is the main offset you identified. By applying it as a correction, you remove that known bias.

  • However, the uncTime value represents the remaining uncertainty in your systematic correction. It's the small error that you cannot fix or average out.

Calculating Your Total Accuracy

To state a single number for your total timing accuracy (or total uncertainty), you must combine these two independent error sources. The standard method for this is to add them in quadrature (taking the square root of the sum of their squares).

Note: The MEO Timing Assessment Tool (Module 2) will perform this calculation for you automatically in the "Combined Total Stats" box.

Total Accuracy = \sqrt{(Random Error)^2 + (Systematic Error)^2}

Or, using the ADES fields:

Total Accuracy = \sqrt{(rmsTime)^2 + (uncTime)^2}

Note: The "Cross Track (Y)" data (measured in arcseconds) in your analysis relates to your spatial or angular accuracy and is not included in this timing accuracy calculation.

3. The End-to-End Workflow: The "How-To"

This workflow is divided into three parts. It is an end-to-end test, using your entire imaging system (telescope, camera, mount, and computer) exactly as you would for science observations.

Part 1: Observation & Data Acquisition

The goal is to capture images of fast-moving GNSS (e.g., GPS) satellites.

1. Verify Time Source: Ensure your primary time source (e.g., a 1PPS GPS receiver) is locked with good convergence (usually a minimum of 20 minutes) and is feeding data to your observatory computer.

2. Sync Computer Clock: Run your time synchronization software (e.g., Meinberg, NmeaTime) and confirm your computer's system clock is being conditioned and is locked to UTC.

   • Important: If your clock conditioning software allows for applying manual offsets, ensure this is set to zero. The goal of this test is to measure your total end-to-end system error (PC drift, software latencies, camera latencies, etc.), not just the clock. This total error will be corrected later in your astrometry software.

3. Observatory Prep: Perform your standard setup: polar alignment, telescope focus, camera cooling, etc.

4. Find a Target: Use an online tool (like the ones from Project Pluto or a planetarium program) to find visible GNSS satellites for your location and time.

5. Image Acquisition: Start your imaging sequence on the target satellite.

   • Use short exposures (between 0.2 to 0.5 seconds). The goal is to create a trail that is short enough to allow for an accurate centroid, yet long enough to be clearly measurable. The exposure must also be long enough to capture sufficient background stars for a successful plate solve. Targets rates are usually around 30 arc seconds per second.

   • Ensure your camera software is configured to use the correct timestamp (e.g., start, middle, or end of exposure). The mid-point is standard.

   • Capture a series of images during the pass. The goal is to get as many measurements as possible across the full usable Field of View (FOV) that you would normally use for astrometry.

6. Organize Files: Save your FITS images for that session.

Part 2: Data Reduction & Timing Analysis

This phase has two steps: reducing the images to get positions, and then analyzing those positions to find the timing error.

A. Astrometric Reduction (Measuring the Images)

1. Load Images: Open your astrometry software (e.g., Astrometrica, Tycho Tracker).

2. Plate-Solve & Measure: Load your FITS images, plate-solve them, and measure the precise RA/Dec of the GNSS satellite in each image.

3. Generate Report: Generate an observation report. ADES format is highly preferred, as it natively supports the millisecond-level precision required for this analysis. Do not apply any timing corrections at this stage.

   • Note: Ensure your software is set to export high-precision timestamps. For example, in Tycho Tracker, you must enable "precision time" in your observatory settings to include the necessary decimal places.

   • The timestamps in this report must be the uncorrected DATE-OBS values from your FITS headers.

B. Timing Reduction & Analysis (Finding the Error)

This is a two-tool process: first, use the Project Pluto tool to get the raw residuals, then use the MEO tool to parse and analyze them.

1. Run Project Pluto GNSS Tool:

   • Go to Bill Grey's Check GNSS astrometry tool.

   • Copy the entire ADES report you just generated.

   • Paste this data into the text box on the Project Pluto page and run the analysis.

   • The tool will return a block of text containing the "along-track" (timing) and "cross-track" (positional) residuals for each observation.

2. Analyze Residuals in the MEO Tool:

   • Open your MEO html Tool file and expand Module 2: Astrometric System Timing Assessment.

   • Copy the entire text output from the Project Pluto tool.

   • Paste this data into an empty dataset block (e.g., [01]). In this tool your data will be persistent.

   • Click the "Toggle Plot" button for that dataset.

3. Review the Statistical Summary:

   • The "Statistical Summary" box on the right will instantly populate.

   • Look at the Along Track values for your dataset:

     • Mean (Bias / Offset): This is your Systematic Error (Offset DATE-OBS). Write this value down.

     • Std Dev (Sigma / σ): This is your Random Error (rmsTime). Write this in.

4. Calculate uncTime (Multi-Session Analysis):

   • Repeat this entire workflow (Parts 1 and 2) on several different GNSS sats to gather multiple datasets.

   • Paste each Project Pluto output into a different dataset block in the MEO tool (e.g., Dataset 1 in [01], Dataset 2 in [02], etc.).

   • Toggle "on" all datasets you want to compare. You can toggle on and off for comparing.

   • The Systematic Error Drift (uncTime) value in the "Combined Total Stats" box is your final uncTime value.

Part 3: Final ADES Reporting

You now have all the values needed for high-precision reporting.

1. Go back to your astrometry software and prepare your science observations (e.g., of a NEO) for submission to the Minor Planet Center.

2. In the ADES configuration/reporting section:

   • Apply the Correction (Optional but Recommended): Check the box for Offset DATE-OBS (or similar) and enter the Mean (Bias / Offset) value you found. This corrects your systematic error.

   • Report the Precision: Check the box for rmsTime and enter the Std Dev (Sigma / σ) value.

   • Report the Drift: Check the box for uncTime and enter the Systematic Error Drift value you calculated from multiple sessions.

3. Submit your observations. Your report now includes a statistically valid measurement of your system's timing accuracy, which greatly increases the value of your data as orbit calculations will weigh your submission based on this ADES information.

4. How Often Should You Perform This Check?

Establishing a regular cadence for timing checks is crucial for maintaining data quality.

• For Routine Observatory Maintenance: It is good practice to perform this workflow at least once per month or after any significant change to your observatory's hardware or software. This includes:

  • Operating System updates.

  • Changes to your time synchronization software or hardware (e.g., new GPS receiver).

  • Installing a new computer, camera, or mount.

• This regular checking allows you to build a robust, long-term dataset in the MEO tool, which gives you a very accurate value for your system's uncTime (drift).

• For Critical Observations (NEOs, ArtSats): For observations where timing is paramount (such as a fast-moving NEO at close approach, you should perform this check immediately before your observing run.
  This gives you the most accurate Offset DATE-OBS (systematic bias) and rmsTime (precision) for that specific night, allowing you to apply the most accurate correction possible to your critical data.

5. Helpful Resources & Links

• This Guide's Tools:

  • Project Pluto - Finding GPS Satellites: https://www.projectpluto.com/gps_find.htm

  • Project Pluto - Satellite Ephemerides: https://www.projectpluto.com/gps_eph.htm

  • Project Pluto - GNSS Astrometry (Reduce/Calculate): https://www.projectpluto.com/gps_ast.htm

  • MEO Timing Assessment Tool: (Your MEO.html file)

    • The tool that parses, visualizes, and calculates final statistics from the Project Pluto output.

• Time Synchronization Software:

  • Meinberg NTP: https://www.meinberg.de/german/sw/ntp.htm

  • NmeaTime (VisualGPS): https://www.visualgps.net/

• Further Reading & Concepts:

  • Project Pluto - GPS Explanation: https://www.projectpluto.com/gps_expl.htm

  • IAWN Timing Campaigns (Examples):

    • 2005 LW3: https://iawn.net/obscamp/2005LW3/

    • 2019 XS: https://iawn.net/obscamp/2019XS/

  • Minor Planet Center (MPC) - ADES Format: https://www.minorplanetcenter.net/doc/ADES.pdf

  • Great Shefford Observatory (Timing Methods): https://birtwhistle.org.uk/Methods.htm#timing

6. Common Pitfalls & Best Practices (FAQ)

• Q: My Mean (Bias / Offset) is large (e.g., 0.5 seconds). Is my system broken?

  • A: No, this is a successful measurement, not a failure. A large but stable offset is the expected result. This value represents your total end-to-end system latency—the combined delay from your PC's clock, imaging software, camera shutter, and all other components.
    The goal of this test is to precisely measure this number. While ideally, one could find and eliminate every source of latency, this is often not possible. The correct professional procedure is to:

    1. Determine this offset to be a robust and accurate value by making many observations.

    2. Apply this measured offset in your astrometry processing software (as described in Part 3).

  • This corrects your data and makes your final ADES submission highly accurate. A "failure" is not a large offset, but an inconsistent one (e.g., 0.1s one night, 2.0s the next), which points to an unstable clock or unreliable time source.

• Q: Why is a 1PPS GPS receiver recommended over standard internet time (NTP)?

  • A: While high-quality NTP servers are good, they can have variable jitter (latency) depending on your internet connection. A 1PPS (Pulse Per Second) signal from a local GPS receiver provides a hardware-based, extremely precise "tick" directly to your computer, eliminating internet latency and providing the most stable and accurate time source possible.

• Q: Why can't I just use the default Windows Time service?

  • A: The standard Windows Time service is not designed for high-precision scientific work. It syncs infrequently and allows the clock to "drift" significantly between corrections. Dedicated software like Meinberg conditions the clock by making tiny, constant adjustments, "disciplining" it to the time source and preventing this drift.

Field Guide: High-Precision Timing Calibration

Objective: Measure and correct Total System Latency (Camera + USB + Software) to enable high-precision reporting in ADES format.

📋 Master Workflow Checklist

Follow these steps in order. Refer to the "Reference Guide" below for details.

Phase 1: Pre-Flight Readiness

• [ ] Time Source: 1PPS GPS Receiver locked >20 mins.

• [ ] Clock Discipline: Meinberg/NmeaTime active. Zero manual offsets applied.

• [ ] System: No background Windows Updates or antivirus scans.

• [ ] Camera Settings: ROI and Binning EXACTLY MATCH your science target settings.

• [ ] Exposure: Set to ~0.3s - 0.5s (limit trailing, ensure stars for plate solve).

• [ ] Tracking: Mount set to Sidereal rate.

• [ ] Targets: Identified 3-5 GPS/GLONASS satellites (>45° Alt).

Phase 2: Acquisition (The 15-Minute Burst)

Do not pause to analyze or change settings during this burst.

• [ ] Target A: Slew -> Capture 30-40 frames -> Stop.

• [ ] Target B: Slew -> Capture 30-40 frames -> Stop.

• [ ] Target C: Slew -> Capture 30-40 frames -> Stop.

Phase 3: Analysis (Repeat for Each Target)

Perform this cycle 3 times (once for Target A, once for B, once for C).

• [ ] Reduce: Load images for Target X into Astrometrica/Tycho.

• [ ] Measure: Plate solve and generate ADES Report for this target.

• [ ] Compute: Copy ADES text to Project Pluto GNSS Tool.

• [ ] Record: Paste Pluto output into MEO Module 2. Record the Mean Offset for this target.

Phase 4: Calculation & Application

Choose one mode:

Mode A: Fresh Calibration (Zero Offset was used)

• [ ] Calculate: (Mean A + Mean B + Mean C) / 3 = New Offset

• [ ] Apply: Enter this value into your software's Offset DATE-OBS field.

Mode B: Verification (Current Offset was used)

• [ ] Check: Is the average of means close to 0.00s?

• [ ] If YES: System is Green. Proceed to Science.

• [ ] If NO: Calculate correction: Current Offset + (Average Mean) = New Offset. Update software.

📖 Reference Guide & Details

1. Introduction: The "Why" and "How"

Accurate timing is critical for high-precision astrometry, especially for fast-moving objects like Near-Earth Objects (NEOs) and artificial satellites. For a target moving at 35"/sec, a 0.5s timing error creates a positional error of 17 arcseconds—rendering the data useless for precise orbit determination.

The Challenge: Precision vs. Accuracy

• Precision (Stability): Your camera might consistently take exactly 0.5s to capture an image.

• Accuracy (Truth): To measure that 0.5s, you compare it against a GPS satellite. But if that satellite's orbital prediction (TLE) is wrong by 50ms, your calibration will be wrong by 50ms.

The Solution: The "Survey Strategy"

To solve the TLE error problem, we never rely on a single satellite. Instead, we image three different satellites in rapid succession. By averaging the results, the random orbital errors cancel out, isolating the True System Latency (Camera Readout + USB Transfer + Software Processing).

2. The "Golden Rules" of Calibration

Violating these rules invalidates the calibration.

⚠️ Rule 1: The Readout Trap (ROI & Binning)

Latency is driven by data volume. A Full Frame image takes much longer to download from the camera than a small crop.

• Requirement: You MUST calibrate using the EXACT Region of Interest (ROI) and Binning settings that you intend to use for your science observations.

• Example: If you plan to image a fast-moving NEO using a 640x480 central crop, you must perform this calibration using that same 640x480 crop.

⚠️ Rule 2: The Time Source

You cannot measure milliseconds if your ruler is wobbling.

• Requirement: Your primary time source (preferably a 1PPS GPS Receiver) must be Locked and Converged (running for >20 minutes) before starting.

• Requirement: Your clock discipline software (Meinberg/NmeaTime) must have Zero manual offsets applied. Do not use the clock software to correct latency; correct it in the data reduction phase.

⚠️ Rule 3: The Survey Strategy

One target is not enough.

• Requirement: You must acquire data on at least 3 different GNSS satellites (GPS, GLONASS, or GALILEO) during a single session.

3. Definitions: The ADES Fields

This workflow provides the values needed for the modern ADES astrometry format.

Offset DATE-OBS (Systematic Bias)

• Definition: The average time delay (latency) of your entire system.

• Calculation: The average of the "Mean Residuals" from your 3 survey targets.

• Usage: Applied as a correction to your timestamps before submission.

rmsTime (Precision)

• Definition: The "noise" or scatter in your timing.

• Calculation: The average Standard Deviation (Sigma) of your 3 survey runs.

• Usage: Reported in the rmsTime field. Tells orbit computers how "fuzzy" your clock is.

uncTime (Stability/Drift)

• Definition: The uncertainty of your systematic error.

• Calculation: The Standard Deviation between the 3 survey means. (e.g., if Sat A says 0.55, Sat B says 0.56, Sat C says 0.54, the uncTime is the spread of those numbers).

• Usage: Reported in the uncTime field.

4. Phase 1 Details: Setup & Configuration

1. Hardware Check:

• GPS/1PPS Locked > 20 mins.

• No background Windows Updates or antivirus scans active.

• USB cables are your standard "science" cables.

2. Camera Config:

• Set ROI/Binning to match your Science Target.

• Set Exposure to ~0.3s - 0.5s (limit trailing to allow accurate centroiding while keeping stars visible for plate solve).

• Verify Timestamp Reference: Ensure your FITS header DATE-OBS marks the Start of exposure (standard).

3. Mount Config:

• Set tracking to Sidereal. (We need round stars for plate solving; the satellite will be a streak).

4. Target Selection:

• Use Project Pluto to find targets.

• Criteria: Altitude >45°, Bright, Fresh TLEs (<24 hours old).

• Diversity: Choose 3 targets in different parts of the sky (e.g., East, South, West).

5. Phase 2 Details: Data Acquisition

Goal: Capture 30-40 points on 3 targets back-to-back. Do not change settings in between.

1. Slew to Target A:

   • Capture ~30-40 frames.

   • Stop.

2. Slew to Target B:

   • Capture ~30-40 frames.

   • Stop.

3. Slew to Target C:

   • Capture ~30-40 frames.

   • Stop.

6. Phase 3 Details: Data Reduction

Process each target individually to keep the data clean.

1. Process Target A:

   • Load images, Plate Solve, Measure.

   • Generate ADES Report A.

   • Run through Project Pluto Tool.

   • Record Mean Offset A in MEO Tool.

2. Process Target B:

   • Clear previous images. Load Target B images.

   • Generate ADES Report B.

   • Run through Pluto Tool.

   • Record Mean Offset B.

3. Process Target C:

   • Repeat for Target C.

   • Record Mean Offset C.

7. Phase 4 Details: Calculation (The Two Modes)

Choose the calculation mode based on your current state.

Mode A: Fresh Calibration

Use this if you captured data with NO OFFSET applied.

Your "Mean Residuals" represent the Total System Latency + Orbit Error.

1. Formula: Average the 3 Means.

   • (Mean A + Mean B + Mean C) / 3 = New Offset

2. Example:

   • Sat A: 0.570s

   • Sat B: 0.530s

   • Sat C: 0.565s

   • Average: 0.555s

3. Action: Enter 0.555 as your Offset DATE-OBS in your software.

Mode B: Pre-Event Verification

Use this if you captured data with your CURRENT OFFSET applied (e.g., checking before a close approach).

Your "Mean Residuals" represent the Error in your current offset.

1. Diagnostic Rule:

   • Positive (+): You are LATE (Under-corrected). ADD to offset.

   • Negative (-): You are EARLY (Over-corrected). SUBTRACT from offset.

2. Formula: Current Offset + (Average of 3 Means)

3. Example:

   • Current Offset: 0.567s

   • Average Residual: -0.040s (Negative = Early)

   • Calculation: 0.567 + (-0.040) = 0.527s

4. Action: Update your offset to 0.527s.

8. Maintenance Schedule

When to perform this workflow:

• 🔴 CRITICAL: Immediately before any Fast Mover, Close Approach, or Occultation event. Use Mode B to verify your system is green.

• Hardware Change: New camera, different USB cable, or new USB hub.

• Software Change: Major Windows update, driver update, or capture software update.

• Seasonal: Once per quarter to check for mechanical shutter drift (if applicable) or environmental changes.