Regarding to this:

viewtopic.php?f=8&t=658

It is, to find a good speed so that the planet will have a perfect orbit around its star. But I'm still quite confused. How do I find the speed? Suppose gravitational forces from other planets are neglected. I don't really know the formula either. Like if I know the force between two planets, how do I figure out the good speed? What factors should be considered?

I'll take one of the examples from the above link:

Sun (M) 1.9891×10^30 KG, or 1,989,100,000,000,000,000,000,000,000,000 in non-scientific notation.

Earth (m) 5.9736×10^24 KG, or 5,973,600,000,000,000,000,000,000 in non-scientific notation.

G = 6.67*10^-11, or 0.0000000000667 in non-scientific notation.

r = 149,597,892 kilometers

Force between Sun and Earth

35,413,401,385,356,974,509,164,227,084.496

Circumference of orbit is 939,951,276.999 in kilometers.

Travel time is 365.26 days for a full orbit.

2,573,375.888 Kilometers per day.

I've checked the orbital velocity but it only says a satellite orbiting a planet. I want to find the good speed of a planet orbiting its star.

I'm still very clueless and confused. I hope someone can really help me out