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?
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1$\begingroup$ I doubt that they have enough delta-v to get the central to the moon. I really doubt that the landing software could handle landing under 1/6 gravity. $\endgroup$– zeta-bandFeb 16, 2018 at 19:11
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12$\begingroup$ They couldn't land on the moon today because they've not set off yet and it takes more than a day to get there. *baddum-tsh* $\endgroup$– David RicherbyFeb 17, 2018 at 13:25
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$\begingroup$ @zeta-band Software is malleable ;-). You have enough time to patch it between Earth and Moon. $\endgroup$– Peter - Reinstate MonicaDec 1, 2020 at 15:15
2 Answers
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:
delta-v=2940m/s/*ln(12490kg/10200kg)=595m/s.
Empty dragon:
delta-v= 2940m/s/*ln(5490kg/4200kg)=787m/s.
Hypothetical Dragon with maximum payload replaced with propellant:
delta-v=2940m/s/*ln(12490kg/4200kg)=1,392 m/s.
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.
Sources:
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2$\begingroup$ Does empty-of-payload vs full-payload Dragon make a significant difference in the amount of delta v? What if some/most of the 6,000 kg payload could be converted to additional propellant for the ~4,200 kg Dragon? $\endgroup$ Feb 17, 2018 at 8:02
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1$\begingroup$ Dry mass fully loaded (cargo) Dragon: 10200kg. Wet mass: 12490kg. Draco exhaust velocity: 2940m/s (300s isp). Rocket equation: delta v=2940m/s/*ln(12490kg/10200kg)=595m/s. Empty dragon dry mass: 4200kg, wet mass 5490kg. Rocket Equation: delta-v= 2940m/s/*ln(5490kg/4200kg)=787m/s. So a nearly empty Cargo dragon could maybe get in lunar orbit, but it wouldn't be able to get back, or get to the surface. Good question! I'll get around to adding this to the answer. $\endgroup$– ORcoderFeb 17, 2018 at 18:35
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$\begingroup$ Could get away with a few hundred kg payload. 500kg of payload still had a delta v a bit over 700 m/s... $\endgroup$– ORcoderFeb 17, 2018 at 18:43
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$\begingroup$ They aren't man-rating the Falcon Heavy so the Crew Dragon is a nonstarter for it. $\endgroup$– Rob RoseFeb 18, 2018 at 3:39
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1$\begingroup$ They could use Crew Dragon without any Crew inside if it happened to have better performance. I think that was essentially the plan with Red Dragon before it got cancelled, since they needed the Super Dracos for Martian Entry-Descent-Landing $\endgroup$– ORcoderFeb 18, 2018 at 17:41
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.
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4$\begingroup$ Afaik the "feet through the heat shield" was just a fan misinterpretation, shuttle did it too for example. It sounded more like NASA would not allow to qualify the powered landing procedure on "productive" flights which would mean doing a few test missions (probably paid by SpaceX and without anything useful to do, just taking time and money) $\endgroup$– jkavalikFeb 16, 2018 at 22:11
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$\begingroup$ Could be. Added something to indicate that isn't well known. I had not heard that, so... $\endgroup$– PearsonArtPhoto ♦Feb 16, 2018 at 22:29
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1$\begingroup$ It's persistently put out there by "well connected" forum/reddit/facebook community members. It's logical on it's own, to me - legs in the shield isn't a non-starter historically. But the other logic is sound - downmass is important, NASA won't risk it on an experiment. No value to SpX to self-fund development, BFS lands different. It's a dead end. But no confirmed sources. $\endgroup$– SaibooguMar 22, 2018 at 3:57