Internet from Space: High and Low Orbit

1. What your child learns and why

A signal to a satellite travels at the speed of light (299,792,458 m/s, an exact value). That is a lot, but not instant: time = distance ÷ speed. For a question and an answer through a satellite the road is 4 times its height. For a geostationary satellite (35,786 km) that is at least about 480 ms; for a low one (550 km) about 7 ms. Real connections are slower: from Varna a geostationary satellite is about 37,800 km away (calculated), and measured links are usually 500–600 ms. A low orbit is faster, but the satellite passes quickly over us — so systems of many satellites are built and the receiver switches between them. Your child works it out, instead of learning it by heart.

2. Three questions for dinner

• “What is the least time for a question to reach a satellite 36,000 km up and for the answer to come back? How did you work it out?”
• “Why is the low satellite faster, yet so many satellites are needed?”
• “When you wait for someone's answer — what do you do with the waiting?”

3. 15 minutes together, no screen

1. String model. 1 cm = 1,000 km. Draw round the plate (the Earth, about 12.7 cm). A low satellite — 0.5 cm from the edge. A geostationary one — 36 cm along the string.
2. Conversation with a pause. Talk about the day. Before each answer wait as long as it takes to count “one-and” in your head (about half a second). How does it feel? Do you interrupt each other?
3. “Two Orbits” poster: the two satellites to scale, the height and the sum for the least time next to each.

4. What success looks like

• Your child works out 4 × height ÷ speed of light and gets about 480 ms and about 7 ms.
• Explains to you why a low orbit needs many satellites and why the real numbers are larger.

5. Common difficulties

• Thinks the satellite “is slow” → “Where is the delay: in the satellite or on the road?” (on the road).
• Calculates “to the satellite” and not “4 times” → trace the road with a finger: you → satellite → station → satellite → you.
• “But on the internet it is slower than 7 ms” → true: this is a lower limit; there is also the station, the network and the servers.

Say: “You don't need to remember the numbers — you need to be able to work them out.”

6. Safety

The lesson is only sums and drawings. An antenna or dish on a roof is fitted and aimed only by an adult or a technician — a roof is dangerous, keep away from power lines; in a storm nobody goes outside. We do not open devices or touch cables. We do not recommend any operator or product; the names in the lesson are history only.

7. Where to go next

Previous: DB-SV-10 “The Mobile World” · Next: DB-SV-12 “Human and Machine in Plain Text” · Related: DB-SV-05 (orbits), DB-IG-10 (lag in games).

You don't need to know the answer. Say: “Let's find out together.”