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Satellite Link Observation Time Estimator

The Satellite Link Observation Time Estimator calculates how much contact time is required to transfer a specified data volume at a known link rate. It adjusts the raw channel rate by an efficiency factor and optionally adds acquisition or setup time for each contact.

This is useful when planning satellite passes, telescope or sensor downlinks, relay windows, or ground-station bookings. The result answers a scheduling question: given the effective throughput, how many minutes of contact are needed? It assumes a steady data rate over the transfer period. If a link changes modulation, coding, elevation, or rate during a pass, use an average effective rate or model the phases separately.

Inputs

GB
Mbps
%
min
Result
—
Total scheduled observation time
Pure transfer time—
Setup / acquisition time—
Time per contact—

1. Enter data volume
Use the payload data that must be transferred.

2. Enter raw link rate
Use the channel rate in megabits per second.

3. Set net efficiency
Enter the fraction of raw capacity that carries useful data after overhead.

4. Enter contact count
Use the number of passes or sessions across which the transfer will be spread.

5. Add setup time
Include acquisition, synchronization, handover, or other fixed time per contact.

6. Review scheduled time
Use the total and per-contact values to compare with available windows.

Effective rate = Raw rate × Efficiency / 100 Transfer time = Data bits / Effective rate Setup time = Contacts × Setup per contact Total scheduled time = Transfer time + Setup time

The calculator uses decimal gigabytes and megabits: 1 GB = 8,000 megabits.

What the result means

The main result is total scheduled contact time, including pure data transfer and the fixed setup allowance for each contact.

Actual pass scheduling must also consider access geometry, elevation limits, interruptions, retransmissions, weather, and network availability.

Given: 80 GB, 150 Mbps raw rate, 70% efficiency, 4 contacts, and 2 minutes setup per contact.

Calculation: Effective rate = 105 Mbps. Data = 640,000 Mb. Transfer time = 640,000/105 = 6,095.24 s = 101.59 min. Setup = 4×2 = 8 min. Total = 109.59 min.

Result: Schedule about 109.6 minutes in total, or 27.4 minutes per contact if divided evenly.

Why add setup time separately?

Some contact overhead occurs once per pass rather than scaling with data volume, so a fixed per-contact term represents it more clearly.

Can I set setup time to zero?

Yes. Use zero when acquisition or setup is negligible or already included in the available contact window.

What if data rate changes during the pass?

Use a representative average effective rate or split the pass into separate calculations for different rate regimes.

Does the calculator determine how many contacts are available?

No. It uses the contact count you enter; orbital access and station scheduling must be determined separately.

How does this relate to the mission requirements estimator?

The mission requirements estimator solves for needed rate from available time; this tool solves for needed time from a known rate.