A military moon

A moon catapult

One fun thing about writing science fiction is looking at what’s happening now in the world and extrapolating. Sometimes though, you don’t need to extrapolate and come up with far-fetched ideas. Instead, you can work out what could already present but hasn’t been made public. This is science-fiction drifting close to a technical analysis; it's a fiction only in the sense that it hasn’t been proved. By comparison, science-fiction that speculates on a possible distant future is plausible fiction; it will probably never happen, but it’s still interesting.

This article is aimed at the former category and it’s to do with our moon.

Much has been written about the recent burst of activity in moon exploration by our planet’s major powers. The Chinese currently have a robot on the moon, nicknamed ‘Jade Rabbit’ which is attracting huge interest among Chinese citizens as it explores and analyses the moon’s surface. India is also investing large sums of money in visiting the moon and according to this Daily Telegraph article, both China and India plan to land people on the moon in the next ten years. The United States, who have already been to the moon, are talking about a new programme of exploration and there are reports Japan also wants to be involved.

An interesting question to ask is; why are they all doing it? It’s true that a country gains a lot of kudos if it completes a successful mission, but it’s a very expensive endeavour. According to this NASA website, it costs about $500,000,000 to send a robot to the moon. Another way of estimating the cost is per kilo of payload. According to some science websites, it costs about two million dollars for every kilogram you put on the moon. In other words, if you want to put a bicycle on the moon (probably a folding one), you’ll need to spend about twenty-million dollars. These prices don’t include all the efforts put into developing new technologies, the cost of failed missions and other related issues.

Along with the sheer expense, there is also the unedifying fact that the moon has already been landed on and it’s not an exciting place; it’s a dead, airless lump of rock. No nation is going to stay up into the small hours to see a robot land on the Sea of Tranquility. But there is a possible and very viable reason why the big nations of our planet, particularly the emerging superpowers, are racing to put robots, people and eventually bases on the moon, and it’s do with height.

In the history of warfare, height has always been of huge importance. Tribes soon noticed that attacking downhill is a lot easier, and more successful, than attacking uphill. Millennia later, as soon as people could take to the air, they used airborne craft to gain a new height advantage, bombing and strafing their enemy on the ground. When both sides had airborne craft, those craft that could climb higher gained a crucial advantage. The latest stage in this war of altitude has been the development of satellites for reconnaissance and communication, which all major nations now have. More recently the technology to knock out those satellites has been developed, with successful tests by more than one superpower showing they can knock out their own ageing or erratic satellites, and if push comes to shove, someone else’s. This satellite stage in the war of altitude is now a crowded, well-established territory. To gain a singular advantage, someone has to take the next altitude step; the moon.

A base on the moon has several strategic benefits. Firstly, it’s a super-satellite. There are a huge number of commercial and military satellites currently orbiting the Earth. They are extremely vulnerable, delicate devices. As popularised in the recent movie ‘Gravity’, there are so many satellites orbitting our planet that the destruction of just a few could release so much debris that a chain-reaction could break a huge number of the satellites currently in geosynchronous orbit around the Earth. It is also perfectly possible, as mentioned earlier, for ground-based lasers and rockets to knock them out individually. By comparison, an installation of communication or reconnaissance equipment on the moon, protected by some sort of screen, would be far harder to knock out. The moon therefore becomes an ideal back-up location for military communication and reconnaissance hardware.

But this article focusses on a second and more dramatic use, that makes full and devastating use of the moon’s position as the ultimate high ground.


Earth is big and, as a result, it has a strong gravity. By comparison, the moon is smaller and has less gravity, roughly one-seventh of Earth’s. If someone on the moon wants to attack a spot on the Earth, all they need to do is to throw a moon rock hard enough to leave the moon’s weak gravity well. The rock will then pass into Earth’s gravity well and fall down it, finally striking its appointed target on the Earth’s surface. This process is like a giant on a mountain tossing a boulder on to a fertile valley below. This is a kinetic weapon, as the damage it causes is entirely down to the speed at which it strikes the target, due to the extreme height from which the object has fallen.

To make such a weapon work on the moon, the attacker needs ammunition - rocks - of which the moon has loads, and some means to toss those projectiles in a guided way, in order for them to hit their intended target. Previous science-fiction stories have explored this idea, such as Robert Heinlein’s ‘The Moon is a Harsh Mistress’, in which rocks coated in iron are launched from the Moon, at Earth, by an electromagnetic cannon. Although Heinlein’s book was a masterwork of speculative fiction, wrapping such rocks in iron as a way to propel them is a dated method and unfeasible. Iron is heavy and rare on the moon. There is a better alternative and it involves more modern technology, that of lasers and solar power.

To launch a rock from the Moon to the Earth, you need a) a power source of some kind for the launching and b) something that launches the rocks out of the moon’s gravity. The first requirement, power, can be supplied by solar power. The moon can receive the full intensity of the sun’s rays, uninterrupted, for long periods of time, making this an ideal spot for solar power generation.

The next thing needed is something to launch the rock. Lasers can carry out this task. A possible mechanism is as follows:


On the far side of the moon, a solar array is installed on its surface, along with a robot and several lasers. The solar array charges up the robot. The robot then digs a rock out of the lunar surface and places the rock in a harness hung from poles above the ground, placed in the centre of a circle of lasers. The robot retreats and the lasers, powered by the solar array, fire beams at the rock in the harness. The heat of the laser beams on the rock causes material on its surface to heat up and boil off. This emission of gases pushes the rock in the opposite direction to the gases it emits. Using this ‘action and reaction’ effect, the lasers ‘push’ the rock upwards, against the moon’s weak gravity. By altering the intensity of their beams and where they hit the rock, the lasers guide the rock upwards and entirely away from the lunar surface, accelerating it out of the moon’s gravity well. Once the rock is free of the lunar gravity, the lasers are turned off and the rock is left to fall down the Earth’s gravity well until it finally hits the intended target.

There are many practical benefits to investing in this type of weapon. It runs entirely from its own power source. It also has effectively limitless ammo. If it is placed on the far side of the moon, it is not even vulnerable to any Earth-based lasers’ attempts to disable it. It effectively becomes the most powerful catapult ever created, firing its shot from the highest-ever castle, behind the thickest-ever wall. Although the weapon’s location would make communication with it from an Earth-based command centre very difficult, the weapon’s computer could be semi-autonomous, or even receive its instructions from probes located further away from Earth than the moon, for example at one of the Sun’s Lagrange points, that have relayed instructions to it from an Earth-based command centre.

Is such a weapon on the minds of the super-states racing to explore and colonise the moon? I don’t know, but I would very be surprised if none of them have done a feasibility study. The idea isn’t new to science-fiction and recent developments in laser efficiency, solar power efficiency and robotics make it far more achievable than when Heinlein wrote about it, fifty years ago. Knowing what we do about human-kind, it's sensible to believe that one or more super-states will install such a weapon if they think it's worth the cost. Civilisation has followed a logical path for millennia and there’s no reason to think that will change, at least until natural factors bring it to a painful end. I think the moon will be a key piece in our next global war. Someone will establish a weapon on our moon and use this new high ground to devastating effect.


Note: Thinking about this again, a day later, I'm keen to check through some more of the technical aspects. For example, how big does a lump of rock that's travelled from the moon need to be to avoid being burnt up in Earth's atmosphere? This could be tricky to work out but I'll see what I can do.