Internet from Space: High and Low Orbit
A signal to a satellite is as fast as light. But light is not instant: there is a road to space and back. Today you will work out how long it takes — and see why a low orbit changes everything.
For parents: a one-page guide — dinner questions and a game without a screen.
01Remember
Three things from earlier lessons will help today. Think first, then open the answer.
What is a geostationary orbit?
A circular orbit about 36,000 km above the equator. A satellite there goes round in about one day, as fast as the Earth turns, so from the ground it looks still. (Lesson DB-SV-05 “Satellites”.)
What is ping?
The time it takes for one move to go to the server and come back. It is measured in milliseconds (ms): 1 ms is a thousandth of a second. (Lesson “Playing Together: Network, Team and Fair Play”.)
How fast do radio waves travel?
Like light: in a vacuum about 300,000 km every second. A lot, but not infinite. (Lesson “Radio: A Message Without a Wire”.)
02Story
An idea (1945). In October 1945 the British writer Arthur C. Clarke published the article “Extra-Terrestrial Relays” in the magazine “Wireless World”. He wrote that three stations about 36,000 km above the equator, 120° apart, could cover the whole planet. At that time there was not a single satellite yet.
The first high satellites (1963–1964). In 1963 Syncom 2 became the first geosynchronous communications satellite. On 19 August 1964 Syncom 3 became the first that really “stands” above one place — a geostationary one. It was used to send the Tokyo Olympic Games to the USA. Who first sent television across the Pacific, the sources do not agree (Relay 1, November 1963, is also mentioned). So we say only what is certain.
A pause. The signal travels 4 times about 36,000 km. So in a conversation through such a satellite you feel a pause between the question and the answer. You will work it out in a moment.
Low and many (1998 → today). In 1998 the Iridium system started working: 66 satellites at about 780 km, for telephones. In May 2019 the first 60 satellites of the Starlink system were launched, at about 550 km. Today systems of thousands of satellites are being built. Low means close — and the delay is much smaller.
The names are only for history — they are not a recommendation and not advertising.
03Worked example: how long does one question take?
You type a question and the answer is on a server on the internet. We simplify: the satellite is straight above you and above the ground station. So the numbers are the smallest possible.
The speed (speed of light)
Radio waves and light in a vacuum: c = 299,792,458 m/s. This is an exact value, by the definition of the metre. For our sums we use 300,000 km/s.
The road
The question travels 4 times the satellite's height: you → satellite → ground station → satellite → you. It goes to the internet and comes back.
High: 35,786 km
4 × 35,786 = 143,144 km. 143,144 ÷ 300,000 ≈ 0.48 s. That is about 480 ms — almost half a second, only because of light.
Low: 550 km
4 × 550 = 2,200 km. 2,200 ÷ 300,000 ≈ 0.0073 s = 7.3 ms. That is about 65 times less.
Reality is slower. A satellite is rarely straight above you: from Varna to a geostationary satellite on the same meridian it is about 37,800 km (calculated), i.e. a pause of about 0.5 s. On top of that there is processing, queues and the road from the station to the server. Measured connections through a geostationary satellite are usually 500–600 ms, and through a low one tens of milliseconds. Our numbers are the lower limit. By the way, a cable is not instant either: light in glass fibre travels at about two thirds of its speed in a vacuum.
Why does a low orbit need many satellites?
- A low satellite sees only a small part of the Earth. At 550 km it moves at about 7.6 km/s and makes one orbit in about 96 minutes (calculated). It is above you only for a short time.
- So there are many satellites, arranged in rings (orbital planes) — that way there is always one above you. The receiver changes satellite on the move. It is like a phone changing tower (lesson “The Mobile World”), only here the “towers” are moving.
- Ground stations connect the satellites to the internet. Some systems also pass the signal from satellite to satellite — with a laser.
- A high orbit needs few satellites: each one stays in place and sees a large part of the Earth. The price is the distance and the pause.
A link to games
In the lesson “Playing Together” you learned that in fast games about 100 ms can already be felt (a rough guide). Because of light alone, a geostationary link cannot go below about 480 ms — fast games do not work there. A low orbit has a chance.
04Try it now
This is our own drawing, not to scale and not of a real system. Nothing is saved or sent.
1 · Predict
A question through a geostationary satellite. What is the least time before you see the answer, if everything else is instant?
2 · Run
Choose an orbit and press “Send a question”. The orange dot is the signal. The clock shows the real time of the light, while the drawing is slowed down.
3 · Change: the height
Slide the satellite's height. What happens to the path, the time and the orbit? At what height is one orbit about a day?
05No screen: “String model” and “Conversation with a pause”
You need: a sheet of paper, a pen, a string or tape about 40 cm long, a ruler, a plate or bowl (about 13 cm across) and one more person.
Model. Let 1 cm be 1,000 km. Draw round the plate — that is the Earth (its diameter is 12,742 km, so about 12.7 cm). Draw a low satellite 0.5 cm from the edge: almost touching the Earth.
Stretch the string from the edge and put a geostationary satellite 36 cm away. How many times further is it? Add another sheet or use the table. Why does the signal have a pause?
Conversation with a pause. You and the other person talk about your day. Before every answer wait until you count “one-and” in your head (about half a second). How does it feel? Do you start to talk over each other?
Swap roles. Think of what people do so as not to interrupt in such a conversation (for example they say “over” when they finish).
06Make your own
Make a “Two Orbits” poster.
- Draw the Earth and the two satellites at the scale of the model. Next to each, write its height and the sum for the least time.
- Add one sentence: what is good for a conversation or a game, and what is not.
- Show the poster to someone at home and explain why the low satellite is faster, but many are needed.
07What I learned
- Light is fast but not instant: time = distance ÷ speed. To a satellite and back for a question and an answer the road is 4 × the height.
- Geostationary (36,000 km): at least about 480 ms. Low (550 km): at least about 7 ms. Real connections are slower.
- A low orbit is faster, but the satellite passes quickly — so many satellites are needed, and the receiver switches between them.
Even light needs time to get there. And you — what do you do while you wait for an answer?
Check yourself
1. Why does a link through a geostationary satellite have a pause of at least about half a second?
2. Why are many satellites needed in a low orbit?
3. Which number is closest to the least time for a question and an answer through a satellite at 550 km (because of light alone)?
It is yours when you can explain to someone how the least time to a satellite and back is worked out, and why a low orbit needs many satellites. No points and no rankings — just a skill.
08I have a question
Do you still have a question? Write it here. It goes to your parent, not to strangers. Your parent confirms their e-mail first.
The form is loading… If it does not appear, write your question on paper and show it to a parent or teacher.
·Sources
- Title: Internet from Space: High and Low Orbit (DB-SV-11) · Author: Children's Library, East Accelerator Foundation · Source: original content, 2026; the facts are retold in our own words, the calculations are our own · Rights: CC BY-SA 4.0.
- Facts (checked 02.10.2026): BIPM — SI defining constants (c = 299,792,458 m/s, exact) · ESA — Types of orbits (geostationary: 35,786 km above the equator, 23 h 56 min 4 s; low: below 2,000 km) · ESA — Orbits · Arthur C. Clarke Institute — “Extra-Terrestrial Relays”, Wireless World, 1945 · Wikipedia — Syncom (Syncom 2, 1963; Syncom 3, 19 Aug 1964; Tokyo 1964; cites NASA D-2911 and TIME) · eoPortal — Iridium NEXT (66 satellites, about 780 km) · Wikipedia — Starlink (first 60 satellites, May 2019, about 550 km; laser links) · ITU-T G.114 — One-way transmission time · Viavi — Reference Guide to Fiber Optic Testing (speed in glass fibre).
- The drawings, the simulator and the calculations are our own. The lesson has no photos, logos, sounds or pictures of real systems. The names are used only as history.
- Related lessons: DB-SV-05 · DB-IG-10 · DB-SV-10 · DB-SV-02.
- Licence: CC BY-SA 4.0 · Children's Library, East Accelerator Foundation, 2026. You may share and adapt this lesson if you credit the author and keep the same licence. Learning is free forever.