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A novel approach to measuring the flux of macroscopic meteoroids 

moon tracks

Satellite operations in Earth orbit are imperilled by both man-made debris and the flux of natural meteoritic material. Estimates of the relative fluxes of different types of microscopic materials have been made by analysing solar panel arrays returned from space. A significant number of the impacts detected on these arrays were, nevertheless, of indeterminate origin, even following analysis of the residue around the impact features using electron microscopes.  

Arguably, though, a greater threat to operational satellites comes from macroscopic particles in the 1 mm – 1 cm size range, which, although less numerous, have the potential to degrade and damage spacecraft in Earth orbit.  

In order to obtain a statistically significant measurement of this macroscopic population, ESA is planning a LEO mission with a deployed solar sail to sweep out a significant volume in space and count the number of impacts it receives over its lifetime in orbit. The challenge of differentiating between man-made and natural particles is likely to remain, however. Moreover, the ratio between the man-made and meteoritic material may well be different as particle sizes increase. 

As humankind prepares for a return to the Moon, it is suggested that there may be an alternative source of information about the meteoritic flux, uncontaminated by man-made debris, which could be exploited.  

The Apollo and Lunokhod rovers left tracks on the Moon. These tracks cover a significantly greater area than any satellite-borne “witness plate” could reasonably be expected to achieve, and have been exposed to the space environment for 50 years, (which is also significantly longer than is practically feasible for any orbiting hardware). These tracks in the regolith are still clearly visible in lunar reconnaissance orbiter (LRO) imagery data (as shown in the NASA LRO image above), and have not apparently been degraded significantly by geological processes on the Moon. 

Any macroscopic impact features superimposed on these tracks would necessarily have to be of relatively recent origin, and would clearly have to be a product of the natural environment, since there is a currently a negligible amount of man-made material in the vicinity of the Moon. 

The three Apollo rovers covered a total distance of around 90 km on the lunar surface, and had tyres with a width of 0.23 m. They left two parallel tracks in the lunar regolith that are estimated cover an area of around 40,000 m2. The two Lunokhod rovers travelled a total distance of around 50 km and had tyres with a width of 0.2 m. Their parallel tracks cover a total area that is estimated at around 20,000 m2 

Surface robotic missions designed to “follow in the tracks” of these lunar rovers and image any disturbance to their imprints in the lunar regolith would thus have access to a total “witness plate” area of around 60,000 m2 that has been exposed to the natural space environment since the early 1970s. 

It is recommended that, (alongside initiatives to protect the lunar hardware from trophy hunters when we return to the Moon), we should also seek to preserve the tracks that the rovers left on its surface. Uniquely, they could provide key information on the risks that we face from meteorites as we exploit orbits around the Earth, and as we travel to our nearest celestial neighbour.   

Comments (1)

I knew Stuart. I agree that natural debris is as much if not more of an operational threat. But, if you drove your car in a desert for 50 years, your windshield would have suffered so many impacts that it was virtually opaque. Stuart raises the important matter of natural threats diminishing space operations. What is the source of these particles. Tons of them reenter every day.

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