Aster SchoolOperator track
Lesson 01 / 04
Your first orbit.
Your satellite circles 350 km up at 7.8 km/s. Change its speed at one point, then watch the far side of the path move.
Your one control
Drag the handle, use the arrow keys, or step by 0.1 km/s.
Tick these off by doing them
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Now 7.8
Set velocity
Move the handle off 7.8 km/s.
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Not yet
Run the orbit
Follow the satellite for a lap.
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0 of 2 speeds
Compare the path
Run one more speed.
Try this
Drop to 7.0 km/s, about 10% slower. Which part of the path reaches the atmosphere first?
Guess before you run it. Then press Run and watch where the satellite turns hot.
Show the answer
The far side. The burn point stays 350 km up, because that is where the satellite was when its speed changed. The opposite side of the path drops to about 40 km, well under the 100 km edge of the atmosphere.
So the satellite meets the air on its way down to the far side: about 26 minutes after the burn, 61° before it gets there.
What just happened
One change at the burn point moves the far side.
You changed one thing, in one place. The path changed half a lap away.
At 7.8 km/s the satellite falls toward the planet at the same rate that the ground curves away under it. It stays 350 km up the whole way round. That is a circular orbit.
When you change the speed, the satellite is at the burn point, so its height there cannot change. What changes is how far it swings out, or in, when it reaches the other side: faster lifts the far side, slower lets it sink.
Small nudges are close to even: +0.2 km/s lifts the far side by 104 km and −0.2 km/s lowers it by 92 km. Slow down to 7.1 km/s or less and the far side sinks under 100 km, where the air is thick enough to heat the satellite and stop it.
Recap
What you can do now
- Hold a circular orbit by keeping the speed at 7.8 km/s at this height.
- Predict which side moves when you change speed: the far side, half a lap from the burn.
- Spot a reentry before you run it: any path whose far side is lower than 100 km.
Next · Lesson 02
Changing height with a second burn
One burn moved the far side. In Lesson 02 you make a second burn when the satellite gets there, and the orbit is circular again, only higher.