You know one of the best technique but nothing happens in zero gravity. And I have turned zero gravity on but nothing happened to my rockets
The no gravity cheat only applies to the rocket you control, and those who are in a radius of 5 km or less. Other rockets won't be affected.
On the rest Horus is right, that's what I meant too. When under "no gravity", a ship moves in a straight line. The game still shows an orbit, but this orbit is calculated by taking gravity into account, so it's irrelevant in this case. That's also why the displayed orbit magically changes without any action from you. Your object doesn't actually orbit, it simply travels in a straight line.
Actually, your challenge consists rather in "making the game display an orbit", but because the cheat breaks the physics, it's not actually orbiting. Now if you find it fun this is your right to post such a challenge, it's just that the term is confusing.