Launch, Gravity & Orbit Basics
Contact Window Basics
Ground stations only hear the spacecraft when it rises above the horizon — short passes, a few times per day in LEO.
- Time estimate
- 20 min
- Complexity
- introductory
- Maturity
- pilot ready
- Simulator readiness
- implemented
- Software available now
- Implemented as Ground Station Contact Window Simulator — interactive activity on `/twin/learn/activities/orbit_contact_window_basics`; related `contact_window_pointing` experiment for attitude during pass.
Student flow
1) Choose station
2) Compare data
3) Mitigate
Evidence and self-check are local-only. Copy/export or screenshot if you want to share.
Learning outcomes
Student can explain line-of-sight, why passes are brief, and how that limits downlink time.
- Explain why a ground station cannot always hear a satellite.
- State approximately how many contact windows per day a LEO satellite has.
- Connect contact window duration to how much data can be downloaded.
Concept primer
Ground stations only hear the spacecraft when it rises above the horizon — short passes, a few times per day in LEO.
Open the Ground Station Contact Window Simulator at `/twin/learn/activities/orbit_contact_window_basics` — pass timeline and data backlog estimate (teaching geometry). Pair with `contact_window_pointing` in the experiment library for attitude during pass (ADCS lab, not RF physics).
Sketch horizon circle, satellite above horizon arc, label “in contact” vs “no contact.”
Interactive lab
Teaching-grade software activity slot — not a flight simulator or certified propagator.
Estimated passes (toy schedule): 7
Contact / pass (avg): 9.5 min
Total contact: 66.8 min
Generated: 250.64 MB
Downlinked: 1002.55 MB
Backlog: none in this estimate
Pass durations (toy timeline)
Data volume (MB)
Why intermittent? The station only sees the spacecraft when it rises above your elevation mask; LEO moves quickly, so each pass lasts minutes, not hours — operations must queue commands and data.
Local self-check
Assessment (practice only)
Use this as a self-check and discussion starter. It is local-only and not a grade.
Optional: attaches a local summary (completed / quick checks / checklist count).
Quick check
Multiple choice self-check
This is a local self-check to support discussion. It is not a grade.
Quick check: Why can’t a ground station talk to a LEO satellite all the time?
Quick check: In the toy data model, what causes backlog?
Discussion prompt
Short answer (local only)
Write notes for yourself or your group. Nothing is submitted.
Short answer: Name one mitigation if backlog is growing, and explain why it helps.
Checklist
Local checklist self-check
Use this to verify you covered key ideas. Nothing is submitted.
Checklist: I can describe contact windows and their consequences
0 / 4 checked
Local summary
Assessment summary (practice only)
Completion
0 / 4 sections complete
Quick checks
0 / 2 correct
Shown only to support self-check.
Checklist
0 / 4 items checked
Reminder
Local-only practice summary. Not a grade and not submitted anywhere.
What this preview is / is not
Assessment engine v0 boundary note
- Student view (local practice): use this as a self-check and discussion starter.
- Local-only preview/practice: your answers are not submitted.
- No backend, no accounts, no roster, and no LMS integration.
- Not a grade. No credential or official scoring is implied.
- Teacher visibility into student answers is not implemented in MVPF8.
- Evidence runtime engine arrives in Phase 9 (not in this preview).
Capture
Evidence capture (local-only)
Capture what you did, what changed, what you observed, and how you explain it. This stays in your browser unless you copy/share it manually.
Selected inputs
- Station: Islamabad (lat 33.70°)
- Altitude: 550 km
- Inclination: 51.6°
- Elevation mask: 5°
- Window: 24 h
- Payload rate: 0.5 Mbps
- Downlink rate: 2 Mbps
Generated outputs
- Passes (teaching): 7
- Total contact time: 66.8 min
- Generated (est.): 250.64 MB
- Downlinked (est.): 1002.55 MB
- Backlog: No (in this toy estimate)
Checklist
Evidence checklist
0/5 checked
Evidence artifact (local-only)
Contact Window Basics
Captured: 2026-05-16T07:38:32.698Z · Level: middle_school · Track: launch_gravity_orbit
Summary
Copyable class summary
Copy a readable summary for class notes, or copy JSON for a structured record. Local-only: nothing is submitted.
Evidence artifact (v1) Activity: Contact Window Basics Track: launch_gravity_orbit Learner level: middle_school Captured: 2026-05-16T07:38:32.698Z Mission brief: Estimate how brief contact windows constrain downlink. Compare generated data volume with downlink capacity over passes (teaching geometry). Selected inputs: - Station: Islamabad (lat 33.70°) - Altitude: 550 km - Inclination: 51.6° - Elevation mask: 5° - Window: 24 h - Payload rate: 0.5 Mbps - Downlink rate: 2 Mbps Generated outputs: - Passes (teaching): 7 - Total contact time: 66.8 min - Generated (est.): 250.64 MB - Downlinked (est.): 1002.55 MB - Backlog: No (in this toy estimate) Checklist: - [ ] I can explain line-of-sight and why contacts are intermittent. - [ ] I recorded station, passes, and total contact time. - [ ] I compared generated vs downlinked data and noted backlog yes/no. - [ ] I wrote one mitigation idea (rate, stations, prioritization). - [ ] I used “teaching estimate” language (not RF link budget truth). Observations: (not provided) Reflection: (not provided) Model boundary note: Local-only teaching model. Not a certified propagator; not STK/GMAT. Evidence is not submitted anywhere and is not a grade. Policy reminder: - Local-only capture. Not submitted anywhere. Not a grade.
Evidence capture
Expected outputs learners should be able to show after the lab (Phase 9 evidence engine preview available).
- Ground station selected
- Passes and total contact time recorded
- Whether data backlog occurs in the toy model
- One mitigation (lower data rate, higher downlink, more stations, or prioritize data)
Reflection
Use a globe: count approximate passes per day for a fast LEO walker vs a student standing still.
Responses are not persisted in this preview unless a specific activity component adds storage later.
Assessment / quick check
Why can’t the ground station talk to the satellite all the time, even if both are powered on?
Teacher notes
Bridge to “operations realism”: short passes mean planning, queues, and sometimes partial downloads.
Teacher guide
Contact Window Basics
Use this block as facilitation guidance. There is no roster, submission, or teacher visibility workflow in this phase — evidence is shared manually.
Facilitation moves
- Tell the ops story: short passes → planning → queues → sometimes partial downloads.
- Use one consistent unit set (Mbps and MB) and remind students it’s a toy estimate.
- Ask: “What would you change first: generation, capacity, or number of stations?”
Misconceptions to watch for
A ground station can talk to the satellite all the time if both are powered on.
Contact requires line-of-sight above the horizon mask; LEO moves quickly, so passes last minutes.
Boundary reminder: teaching-grade orbit models (not a certified propagator; not STK/GMAT) and local-only learning (no accounts, no submissions, not a grade).
Next activity
Suggested progression from the mission learning path. Links avoid missing activity routes.