Now that SpaceX has a bunch of flown Block 4 Falcon 9 rockets laying around, could they theoretically do a mission to the Moon with landing even if it's just a rocket with no payload? Does it work out mathematically? In order to land they would need to have only the first stage as the second stage is not reusable yet and can't land itself. So let's say they take three first stages like a FH but omit the second stage on the central core as it would be useless weight. The mass of the first stage is: 25,600 kg empty and gets 395,700 kg of propellant therefore 421,300 kg total mass at liftoff for each core. Thrust goes from 7607kN at sea level to 8227kN in space (vacuum), Isp from 282s to 311s and burn time is 162s for the side boosters (with no throttling down). The two side boosters will be expended. Could someone do a simulation for this scenario and tell if it's possible? What about Mars?
They could certainly crash an empty upperstage into the moon, they could do this with just a regular Falcon 9. However, the Liquid Oxygen would boil off before they could attempt to land using the 2nd stage, as the trip to the moon is several days long.
They can launch a Dragon capsule towards the moon, and could even get it into a free return trajectory with falcon heavy launching it, but the Dragon capsule only has a few hundred m/s of delta-v* from the hydrazine+nitrogen tetroxide thrusters (Draco thrusters), which is not enough to land on the moon or even get into lunar orbit (requires more like 1-2 km/s delta v, see https://en.wikipedia.org/wiki/Delta-v#Delta-vs_around_the_Solar_System)
- EDIT: How much delta-v does Dragon have?
Dragon Dry mass (empty): 4200kg
Dragon Max Payload: 6000kg
Dragon Propellant Mass: 1290kg
Draco exhaust velocity (specific impulse): 2940 m/s (300s)
Rocket Equation: Delta-v=Exhaust Velocity*ln(wet mass/dry mass)
Fully loaded (cargo) Dragon:
Hypothetical Dragon with maximum payload replaced with propellant:
So a nearly empty Cargo dragon could maybe get in lunar orbit, but it wouldn't be able to get back to Earth, or get to the surface.
A highly modified dragon that replaces the trunk with a service module might be able to get to lunar orbit and back.
Work based on cargo dragon as I am more confident about its numbers. I believe Crew Dragon might have somewhat more (50% more?) propellant, but I also expect it to be heavier.
Red Dragon was already announced as a mission to Mars using the Falcon Heavy, launching essentially a barely modified Dragon 2 to Mars (unmanned). The mission has since been canceled, but primarily because NASA didn't like the feet poking through the heat shield (Or otherwise just didn't want to risk the propulsive landing), and SpaceX was unwilling to do both versions. The same spacecraft was claimed to be able to visit essentially any body in the Solar System, when launched to there by a Falcon Heavy. Note these are one-way missions.
As for whether it could do a manned mission, I've seen a few white papers that indicate that it could probably do a 2 launch mission to Mars, although the capsule and other technologies for such are not available. Dragon would be too heavy by itself most likely.
It should be noted that the propulsive capability of the Dragon doesn't have enough fuel to land on the Moon. It might have enough to land on Mars; or, at least, a special version of the craft might.