Adam Crowl is going to write a journal article out his blog post analyzing the details and choices for sending the Spacex BFR to the moon and Titan. The article is at his Crowlspace website.
The Spacex BFR carries 1100 tons of propellant, masses about 85 tons and carries 150 tons of payload when in reusable mode. It can carry 250 tons one way.
The Raptor engines are designed for a specific impulse (Isp) of 375 seconds but this could be increased to 385 seconds.
The Spacex BFR has available delta-vee of 6,388 m/s. With improved ISP the delta-vee might increase to 6550 m/s.
To go the moon, the Spacex BFR would first go into a Highly Elliptical Orbit, that swings out part way to the Moon. At its closest point to the Earth, perigee, the BFR is swinging past at 10 km/s. At its high point, apogee, there’s time to transfer propellant and fill the tank. Instead of 2.75 km/s for the Trans Lunar Insertion burn, the BFR might use 0.75 km/s, and the total round-trip delta-vee required is just 5.75 km/s.
Adam Crowl looks at three options for a direct flight to Saturn from Earth orbit – a Hohmann Orbit, an Elliptical Orbit and a Parabolic Orbit. Hohmann is most energy efficient but takes about 6 years instead of 2.8-3.4 years for Elliptical or 2.3 to 2.7 years for Parabolic.
The Spacex BFR has the fuel for an elliptical orbit mission to Titan.
Parabolic orbits mean double the breaking energy when reaching Titan. If magenetoshell aerocapture technology could be made to work then the mission could be six months faster than Elliptical.