Transfer Station 70 Ophiuchi

**Transfer Station 70 Ophiuchi** is a space station in the 70 Ophiuchi star system, in the L1 Lagrange Point between 70 Ophiuchi A and B. It was here that Jason took possession of the 427-1587 Mark IX Library (electronic library).

70 Ophiuchi is a binary star system located about 5 parsecs (16½ light years) from the solar system. From earth it appears as a 4th magnitude star in the Ophiuchus constellation, visible in a dark sky.

## Binary

70 Ophiuchi is known to consist of two stars, 70 Ophiuchi A is a yellow-orange K0 main sequence dwarf variable, while B is an orange K4 main sequence dwarf. The stars are in an elliptical orbit about a center of mass. The average separation of A and B is about 23 astronomical units (the average distance from the earth to the sun), but, at an eccentricity of almost 0.5, the actual separation varies from 11.4 to 34.8 AU. It takes more than 83 years to complete one orbit.

William Herschel in the late 18th century determined that 70 Ophiuchi was a binary star system contributing to the eventual proof of Sir Isaac Newton's law of universal gravitation.

## Lagrange 1 Point

Also in the 18th century, Joseph-Louis Lagrange, an Italian mathematician and astronomer determined five points in a binary system where the gravitational attraction of a third object by the two large objects would be neutral and somewhat stable. L1 is a point located between the larger and smaller objects where the gravitational attraction is equal.

So, let's apply this concept to the 70 Ophiuchi system.

70 Oph A has a mass of 0.9 suns, B has a mass of 0.7 suns. That means that A and B orbit around a common center of mass, A, a bit closer to it and B a bit farther out. Sorta like a big child and a smaller child on a seesaw, the big kid would sit a little closer to the pivot and the little one a little farther away.

Let's assume the orbits are circular about 23 AU apart, and we put the transfer station about 1.645 billion kilometers from the B star in a line with the A star. The gravitational attraction is equal from A and B. If the station were to drift a little ahead because of its orbital velocity, the B star would pull backward on it and pull it back into the L1 point. Likewise, if it drifted back a little, B would pull it ahead and keep it into L1. However, L1 is not completely stable, in that, if the station drifted a bit outward toward the B star, B would then have a bit greater attraction than A and the station would leave L1 and assume a different orbit. The same happens if it drifts a bit in toward the A star. So, the station would need thrusters to keep it at the L1 point. In this case L1 is even more unstable because the system has an orbital eccentricity of nearly 0.5, so the distance between A and B varies a lot, therefore the L1 point varies from 800 million to 2½ billion kilometers from the B star.

So, why orbit at L1? If the station orbits either star, visiting spacecraft would require substantial energy burns to enter and leave orbit, but, presumably, the station could expend smaller amounts of energy over a long time for statonkeeping rather than require visitors to expend larger amounts of energy in a short space of time.

In Deathworld 3, the author remarks that, at the time of the visit by *Pugnacious*, 70 Ophiuchi B was 'just over a billion miles distant'. That places the stars at the points in their orbits at the average distance rather than near the closest or the farthest distances.

## External links

70 Ophiuchi at Wikipedia.

Lagrange Point at Wikipedia.