A Stereo View of Lagrangia

Twin Spacecraft To Explore Gravitational ‘Parking Lots’ That May Hold Secret Of Moon’s Origin.

The L4/5 Lagrange Points (“Lagrangia”) are 60 degrees ahead and behind Earth’s orbit around the Sun, thus 150 million kilometres away and not well placed in the sky for observation because of their proximity to the Sun in the sky and the Zodiacal Light obscuring the view. As great big gravitational traps they might retain a few asteroids, leftovers from when the planets were forming. In fact they’re such effective space-traps that the impactor which ran into Earth and made the Moon, might have formed in them aeons ago.

Now the STEREO spacecraft are paying the L4/5 points a visit on opposite sides of the Sun, as part of their mission to watch the Sun’s storms from a better vantage point than Earth’s orbit. About 30 years ago an optical search was performed from Earth for asteroids in Lagrangia, with inconclusive results, but the justification of the search from a paper back then is interesting…

The search for asteroids in the L4 and L5 libration points in the earth-sun system


The existence of Trojan-type aggregations of asteroids associated with earth and other planets aside from Jupiter is a problem which has not been fully solved either theoretically or observationally. In this paper, the dynamics of libration orbits in the earth-sun system are discussed, using both numerical integrations and simple theoretical models to outline problems of stability and effects of perturbations. It is found that the greatest potential disturbance to the stability of these orbits is due to the 13:8 synodic Venus perturbation, which resonates with the libration frequencies of most earth Trojan orbits. Problems of observation in searching for any existing asteroids include the distance, phase angle, and wide area of sky coverage corresponding to the possible orbits. The implications of the existence of earth Trojan asteroids for space industrialization based on nonterrestrial materials are discussed, with the conclusion that the short mission times and low required delta-V values to reach and retrieve them make them a potentially important resource.

That’s still true. Inspace bulk materials is a major supply issue for any future space-based industry. Mining the Moon isn’t enough because it’s deficient in light elements due to the temperature of the cloud it condensed out of after the “Big Whack”, so the asteroids – especially ones easy to get to – are vitally important. Lagrangia’s asteroids don’t move (much) relative to Earth and so are continually accessible. Getting there requires a “walking orbit” which doesn’t have to expend a lot of propellant if round-trip times a few months long are acceptable. What’s needed is the will and some forward thinking that thinks Big Enough for establishing a viable inspace materials industry.

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