Technologies Employed To Ensure Precise Landing Of SQUALL Lunar Lander


What technologies are needed to ensure precise and smooth landing of our lunar lander? In this entry, IDXA would like to share several components developed by us to achieve this objective.

Precise landing on the surface of the moon represents big challenges posed by environmental issues such as regolith-covered terrain, uneven surface, boulder field and prominent impact craters. The term regolith is defined by layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials.  Lunar soil is composed of fine grains of regolith particles of one centimeter in diameter or less while lunar dust are generally fine grains less than 50 micrometers in diameter[1].



Lunar surface cross-section

Lunar regolith is highly abrasive in nature, thus it can damage our equipment. Other than that, our lunar lander will also be exposed to extreme temperatures varying from -153°C to 123°C and vacuum environment that can destroy the packaging of electronic components due to their chemical properties.

IDXA plans to integrate two technologies onto our system to resolve on issues stated above. First, we will highlight solutions built around Optical Flow and Radio Detection and Ranging (RADAR) technologies to determine positioning and altitude. Both parameters are keys to achieve good landing.



How they work together?

So, how these two technologies will work in tandem to help us achieve our goals? Optical flow is defined as pattern of apparent motion of objects, surfaces, and edges in a visual scene caused by the relative motion between an observer (an eye or a camera) and the scene [2][3]. Using this, we can obtain information about movement of our lunar lander relative to the surface of the moon. An everyday example is an optical computer mouse.  A mouse will detect the changes of motion of the surface under it viewed by its optical flow sensor. According to a given pattern, the movement of the mouse is sent to a computer and the computer will then translate this motion to move the pointer on a computer screen.


An optical flow sensor works by generating a visual scene in form of pixels of a scanned surface. If our module is moving, it will change the generated pixels of scanned surface. From this information, we can know if our device is in movement or not. Therefore, in order to have a precise landing on a predetermined target, we need to make sure that our sensor output fixed pixels. Any differences will be supplied to control systems which in the other hand orchestrating other components to maintain fixed pixels output of our sensor.

RADAR is an object detection technology widely known as Radio detection and Ranging using radio waves as medium to determine range, altitude and speed of objects. Equivalent systems are LIDAR which uses light and SONAR which uses sound.


Source: wikipedia, continous wave radar

Above figure explained a simple mechanism how RADAR works. A system is composed of a transmitter and a receiver. It works by emitting radio waves in target direction. When these come into contact with an object they are reflected in many directions (echo). Some of these can be detected by the receiver. The distance between the transmitter and the object can be calculated by measuring the time of travel of the radio waves. Radar can also be used to measure speed of an object, due to a phenomenon called Doppler shift. This extra information can be extracted to control the descent speed of our landing module.

For our application, we target to execute our precise-landing function once the spacecraft is in the final approach phase, hovering at an altitude of about 300 ft AGL. The landing radar senses the velocity and slant range of the LM relative to the lunar surface by means of a three-beam Doppler velocity sensor and a radar altimeter. This would enable fine adjustments to be made by the auto-pilot to ensure a smooth and soft descent and touchdown.


SQUALL on Final Approach


Combination of optical flow and RADAR technologies would be implemented onto our spacecraft system in order to achieve precise and smooth landing. Optical flow is to maintain a fixed vertical approach onto landing side and RADAR is to be employed for distance measurement and descent speed control.We’re currently working on beacon-deployment mechanism to complement these technologies. Stay tuned for our next entry.



[1] Regolith, http://en.wikipedia.org/wiki/Regolith

[2] Andrew Burton and John Radford (1978). Thinking in Perspective: Critical Essays in the Study of Thought Processes. Routledge. ISBN 0-416-85840-6.

[3] David H. Warren and Edward R. Strelow (1985). Electronic Spatial Sensing for the Blind: Contributions from Perception. Springer. ISBN 90-247-2689-1.

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