The minimum speed for a projectile to go in orbit is called orbital velocity. It depends on the mass of the celestial body it's orbiting around and the radius of the orbit.

Here's the formula to calculate orbital velocity:

v = √(GM/r)

Where:

* v is the orbital velocity

* G is the gravitational constant (6.674 × 10⁻¹¹ m³/kg s²)

* M is the mass of the celestial body (e.g., Earth)

* r is the radius of the orbit (distance from the center of the celestial body to the projectile)

For Earth, the orbital velocity at the surface is approximately 7.9 km/s (28,000 km/h or 17,500 mph). This is the minimum speed a projectile needs to be launched horizontally to achieve a stable orbit around Earth.

However, it's important to note:

* This is just the minimum speed for a circular orbit. For elliptical orbits, the speed will vary depending on the position of the projectile.

* Air resistance is not factored into this calculation. In reality, air resistance will slow down a projectile, so the actual launch speed needs to be higher to compensate.

* This is assuming a perfect orbit. In reality, there are other factors that can affect an orbit, such as the gravitational pull of other celestial bodies.

Let me know if you'd like to calculate the orbital velocity for a specific scenario!