ESA is busy planning its first lunar lander for a daring mission to the South Pole of the Moon - they are so busy in fact that there's hardly any thought left for PR and publicity. Take the name of the project for example, which is currently called “the” Lunar Lander. There is plenty of time though to name it properly, as the launch is planned to happen in 2018. And what a mission it will be!

One does not simply land on the South Pole

The fact that the Lunar Lander mission is led by the Human Spaceflight and Operations directorate of ESA already tells a lot. It will be more of a technological demonstration than a full-blown scientific laboratory. Past lunar missions had plenty of room to land: the sites were selected to be safe, usually on large plains and with good illumination. Landing at the South Pole, however, is a completely different story. The place is full with large craters, steep slopes and pits where the Sun never shines. Paradoxically, that's the main reason to go there: those dark pits contain a (relatively) large portion of water ice, a crucial substance for future manned missions. But the lander will have to hit the bulls-eye: the size of acceptable landing sites will require a precision landing with a margin of only a few hundred meters.

This is how the journey will look like: the Lunar Lander will blast off atop a Soyuz rocket from French Guiana, and climb to ever higher, elliptical intermediate orbits. It will reach the final Lunar Transfer Orbit after several weeks, and enter a polar orbit around the Moon. It will then spend a few weeks circling the Moon, to check out all the instruments and to wait for the correct geometry between the orbit, the Earth, and the Sun. And that's when the fun starts.

Lunar Lander will actively track its surroundings during landing.

The Descent and Landing will start at the North Pole: the lander executes the de-orbit burn, lowering the orbit to an ellipse that leads it very close to the South Pole. As the lander flies towards the pole, it continuously monitors the Moon below it, automatically recognizing the landmarks (craters), and tracking and correcting its path precisely. This will ensure the correct positioning for the final, powered descent. At an altitude of a few kilometers, the lander will turn on the Hazard Detection and Avoidance system to evaluate the primary landing site. It will generate 2D and 3D maps of the site using a camera and a LIDAR (laser altimeter). If it deems the primary site unsafe, it will divert and look for a safe place, in range with the fuel left. Robotic missions never attempted precision landing on the Moon before - only the Apollo astronauts had the possibility to control their final descent.

We're here – now what?

Although most of the lander will consist of the fuel tanks, thrusters and all the necessary hardware to land, several scientific instruments will be squeezed aboard too. It's panoramic cameras will map the surface, and identify the horizon automatically. This will help preparing for the short periods of darkness, when the Sun, circling around just above the horizon, will get obscured by the more elevated regions.

Preliminary landing sites. All are elevated points, crater rims or mountain peaks, to have as much sunshine as possible.

It will also analyze a quite underrated element of the lunar environment that may pose serious risk for future manned missions: dust. Lunar dust is quite different from its Earth counterpart: its very adhesive and abrasive, causing all sorts of problems: it could cover solar panels, prevent proper sealing,erode moving parts, and accelerate wear and tear. And it's very likely toxic for humans. One task for the Lunar Lander will be to collect samples from the dust with its robotic arm, and inspect it closely. A small camera on the robotic arm will take close-up pictures, and microscope suite, equipped with an optical and an atomic force microscope and a Raman spectrometer, will take a very close look at the shape and size of individual particles. In parallel, chemical analysis (mass spectroscopy) will determine the composition and volatile content of the dust.

Gene Cernan (Apollo 17) looks more like a coal miner than an astronaut after his moonwalk.

However, looking at single dust particles is just part of the task. The lunar plasma and electromagnetic field environment is also very different from the conditions here on Earth. Without atmosphere and an own magnetic field, solar wind and radiation almost constantly bombards the surface, charging it electrostatically. The charge is strong enough to kick the smallest dust particles up. The constantly ascending and descending dust, along with the gaseous component of ions, creates a very thin exosphere around the Moon. Radiation and dust may pose serious risks for future human explorers. Lunar Lander will investigate these environmental issues in situ. (A small orbiter, LADEE, will also explore the dust environment of the Moon next year.)

The scoop at the end of the robotic arm, in action.

Apart from the environmental issues: health, habitability and resources, Lunar Lander will also conduct a feasibility study for low-frequency radio astronomy observations from the Moon. Below about 100 MHz, the ionosphere of Earth starts to distort radio waves coming from space and at around 10-30 MHz, it completely reflects them back. This property makes long-distance, short-wave radio communications possible, but prevents astronomers from observing celestial phenomena in those wavelengths. The best place for a permanent low-frequency radio astronomy observatory would be therefore on the Moon: low frequencies mean long wavelengths, which in turn mean that a huge antenna will be required for good angular resolution. That's why populating the Moon with simple dipole antennas, scattered all along one hemisphere, is a much better option than building one or two satellites. However, the lunar radio background was never studied before in any detail. Lunar Lander will investigate the radio background levels, effects of a suspected weak lunar ionosphere, and so on, to see if there's any practical limitation to this idea.

A look under the European hood

Europe's first soft landing was achieved far, far away, by the tiny Huygens spacecraft. The Lunar Lander will travel much less, but will be far bigger. The main body of the spacecraft is a two-meter-high cylinder with a diameter of 2.5 m. With the four legs extended, the top will reach up to 3.3 m. Its dry mass will be 750 kg, of which 30 kg will be available the science payload. Filled up with fuel, it will weigh as much as two metric tons.

Landing requires a lot of braking (losing speed), but fortunately, there is plenty of ESA expertise there. Lunar Lander will use the proven thrusters of the ATV spaceships. Five main engines, with 500 N thrust each, and six 220 N assist engines will carry out the braking maneuver. During the terminal descent, one main engine will fire, and the required thrust will be adjusted by pulse modulated firings (repeated short bursts) from the assist engines. Once the landing legs touch down, the engines cut off, and the work begins: the high-gain antenna and the camera mast deploys, and starts to survey the horizon.

Thrusters are already in testing: here the pulse-mode firing of the assist engines are inspected.

The side of the main body cylinder will be covered almost entirely with solar panels. Europe has no nuclear capacity to build RTG units, so the spacecraft will have to rely on solar power or on batteries when the Sun will be obscured by mountain peaks at the horizon. Communications to Earth will be limited by the rotation of the Moon: our planet will be below and above the horizon for about 14-14 days. Most of the scientific work will happen when both the Earth and the Sun will be visible from the lander.

But there is a lot to do before the European flag reaches the Moon: the mission is still in a very early phase. The Preliminary System Requirements Review should have happened this spring (though I couldn't find any reference to that). The scientific instruments don't exist yet: ESA collected the Declarations of Interests from various organizations, and plans an Announcement of Opportunity to propose science payloads in early 2013. And ultimately a ministerial-level ESA Council meeting will decide the fate of the entire project in November. Fingers crossed!

László Molnár

Image credits:

1.) EADS Astrium

2. 3. 5. 6. 7.) ESA

4.) NASA