Why Is It Difficult To Land On The Moon?

Have you ever wondered why so many moon landers crash? What makes it so difficult to land, especially an unmanned craft on the moon or even Mars? It’s an interesting question and one I’m not sure I can adequately answer, but I will try.

Let’s start with the speed of a lunar orbital module. Research says that stable low lunar orbits can’t be less than 100km above the surface because of gravitational anomalies of the moon surface. The moon has a radius of 1738km and a mass of 73 billion trillion kilograms. Using the equation for orbital velocity, one gets 1600m/s or 5800 km/h. That’s quite a joy ride!

So, a landing module must decelerate from 1600 m/s to zero. When capsules land back on Earth, they have the Earth’s atmosphere to help them. This assistance generates the heat the capsule experiences during the descent. There is no atmosphere on the moon, so a lunar landing module must brake using just the fuel it carries. For weight reasons, it carries the bare minimum needed to touch down for this task.

The terrain on the surface is rough and, to some degree, unknown, since they usually select a site they have never visited. Radar scanning of the surface and other technology improves our knowledge of the surface topology, but it’s still limited.

Also, an unmanned module control system is only as good and reactive as its programming. Any human initiated change has a lag of half a second just to travel the distance from Earth to the module receiver. Much can happen in that half second period and including the time the control system takes to include the manual changes into its maneuvering to reach the surface safely. Oh, and for a human to decide the action needed, the images take half a second to travel the distance. So; image to Earth – half second, humans analyze and decide on a needed manual corrective action – time ?, signal travels from Earth to module – half second, controls incorporates intervention. That’s 10 seconds or more. The module travels a long way at 1600m/s.

It’s not surprising to me then that crash landings. Much can go wrong with little time for corrective actions. Landing on Mars amplifies the issue because of the huge time delay for signals to travel between Earth and Mars – anywhere between 15 and 24 minutes, although Mars has an atmosphere, if only a thin one.

The increased sophistication of today’s software improves the chances of success, but as the recent Russian and Japanese missions have shown, success is sometimes elusive or only partial.

We will improve the more attempts we make and experience we learn in the years ahead.

Humans traveling to the moon and beyond has its own set of hazards, but in this instance, the probability of success is, I think, greater since the pilot can make instant decisions to adjust the thrust and direction for a successful landing.

Manned flight has its advantages, after all.