BPJ Code

Synchronous orbits have a period equal to the rotation period of the body being orbited. Watch out for bodies with very slow or very fast rotation periods; the calculated synchronous orbits may be outside the body's sphere of influence, or below the body's surface, respectively - both being nonsense!
Synchronous orbit has semimajor axis blahkm, or blahkm above the surface if the orbit is circular.
The Tsiolkovsky rocket equation relates a rocket's mass fraction and its specific impulse to the mission delta-v it can achieve. For comparison, the Space Shuttle Main Engines (SSME) achieve ve of about 4400m/s in vacuum.
Delta-v available is blahm/s.
Calculate the Schwarzschild radius of a mass in order to determine how closely you can safely approach a black hole. Note that this level of safety guarantees only that you stay within the universe; your comfort may not be what you expect from a top-tier airline.
Schwarzschild radius is at blahkm. Average density is blahg/cm3.
Some ads would go here if you were connected to the Internet. Or if you weren't using an ad blocker. Or something. It's just a placeholder, dammit.