With what precision & timing can we send a missile to strike the moon?

Question

The question about a murderer on the moon made me wonder: if the collective governments felt very immediate capital punishment were necessary, they might strike the area that the perpetrator was located with a missile before she ran out of resources. It was the inspiration, but let's set that aside.

My question is about the current technology to have a precise and quick violent action on the moon, regardless of the reason. Setting aside reasons, politics, etc. I understand we can't even see details on the moon with our best imagery, so...?

How much time and how precise can the United States launch a missile that would eliminate a target on the moon, today?

Answer 1

The fastest space launch ever was the New Horizon mission to Pluto at 16.26 km/s ( 58,536 km/h 36,373 mph) on top of Atlas V rocket. With that speed, it took just about 9 hours to reach the Moon.

The Atlas V are too big and expensive to be used as weapons, but I guess it's not out of the realm of possibility to be weaponized, so it terms of speed, I think 9 to 10 hours is what you would expect.

As far as accuracy goes, the best you can do is laser guided bomb (since there is no GPS on the Moon). According to Wikipedia the average accuracy of laser guided bombs during Vietnam was 23 feet.

Edit: The lack of atmosphere is not a problem unless you have to use incendiary weapon. Good old fashioned bombs that fragment will work just fine. I don't know much about bombs and such, might be a problem if the target is in a bunker underground... I guess I'm assuming that the guys shooting the rocket would know what needs to be done.

Answer 2

It would be possible to build something that could do the job, but it would be difficult. As many have said, the fastest mission to cross Lunar orbit took 9 hours to so so. There has only been one high speed precision impact with the Moon that I'm aware of, and that was LADEE. If the target was in something relatively unprotected, 160m would be close enough, otherwise 20m would be required for something more hardened. The precision of LADEE was 144m. LADEE wasn't a highly precise weapon, but that's probably near the most accurate one could get with that technology.

Okay, so let's look at some actual weapons guidance systems, and how would they work.

• NASA- This uses a beacon on the spacecraft to do ranging, and carefully adjust the trajectory. It seems to work well.
• GPS- Wouldn't work well, while you can get a location fix, it will be very inaccurate at Lunar distance, more inaccurate than the NASA method.
• Laser- The laser spot, if painted from Earth, would be too large. XKCD illustrates this (With a commercial laser, but presumably a military radio will be no more than, say, 2 orders of magnitude better)

• Imaging- This could theoretically work, if you had the required maps, you could guide the spacecraft to the target using one of the above methods.

Bottom line, you could probably do it, but it would be really hard. You'd have to develop new technology to make this happen, and it would be REALLY expensive to do.

Answer 3

It's well within modern weaponry to hit a target on the moon with meter accuracy and at the speeds involved, that kind of accuracy is more than sufficient.

If the moon base is earth facing, terminal guidance won't be needed beyond perhaps a minor correction burn halfway there. New Horizons flew between Charon and Pluto with only minor correction burns over a flight of 3 billion miles. The moon is much closer so doing a single burn from LEO to hit an Earth-facing target shouldn't be difficult. If the target isn't currently Earth-facing, it will be in no more than 28 days.

New Horizons made the trip from Earth to the Moon in 9 hours. A smaller payload may be able to do it in less time since smaller payloads require less fuel to achieve a given speed than a larger payload.

Answer 4

Look at a "normal" lunar mission such as Prospector. It was a 105 hour transit. I mention Prospector because it did in fact hit a target on the moon.

So, what if a strike was not a launch of a new missile for the purpose, but was crashing a craft that was already in Lunar orbit for some purpose or another? Such a craft might have a 2-hour orbit, so if a decision was made to de-orbit a probe that was near end-of-life anyway, with the realization that it could be aimed at the right location, there might be up to a 2-hour latency for it to cycle around to the right place to dive from. Then it doesn't just drop instantly, but the burn lowers the opposite side so figure less than half an orbit more to intersect the ground.

Note that orbital probes are often crashed on purpose at end-of-life. For Lunar probes, there are several reasons:

1. The impact event at a known place and time allow other telescopes to watch, and get spectral readings on what's in the subsurface. In particular, the presence of water can be confirmed.
2. Lunar orbits are unstable, and a dead probe with no maneuvering fuel left can be a hazard to other orbiting probes or end up falling on a historical site we would rather preserve. It will crash on its own eventually.

After the precedent (and disappointing results) of Prospector, you could plausibly have precision impacts planned as end-of-mission events for various probes in service at the time of the story. Especially if proper disposal becomes mandatory in a more crowded future.

So, the probe will have telemetry including video all the way down, getting very close up "before" images of the sample site. The software will be planned to have guided impact to do corrections automatically to hit the exact target, e.g. a crater wall structure.

If a future of lunar exploration includes more prospecting missions, this will be the norm. If there is also a manned presence, then targeting will be even more careful, and you will get a free excavation pit for people to follow up with visiting to see if this is a good place for mining.

The latter case might then optimize the swan song mission profile for penetration and making a deep pit, or a long trench, or whatnot.

Note that you can use the Moon's circumference and the 120-minute figure to calculate the kinetic energy. Add the kinetic energy due to the probe's altitude.