70 Ophiuchi

70 Ophiuchi is a binary star system in the constellation Ophiuchus. Apparent magnitude is 4 making it a dim star from Earth.

## Binary Star

The brighter star, designated 70 Ophiuchi A, is a yellow-orange variable star of spectral type K0, its surface temperature is 5,300 K, color is pale yellow-orange, mass is 0.9 solar masses, radius is 0.91 solar radii, and luminosity is about 0.54 that of the sun.

Its companion, 70 Ophiuchi B, is an orange star of spectral type K4. Its surface temperature is 4,350 K, color is orange, mass is 0.7 solar masses, and luminosity is 0.13 times that of the sun.

The stars of 70 Ophiuchi arbit about a common center of mass at an average of 23.2 AU (astronomical units, the average distance from the Earth to the Sun). But the eccentricity of the orbit is 0.495, quite elliptical, so the separation ranges from 11.4 to 34.8 AU, and takes 83.38 years to complete one orbit.

There have been a number of claims to have inferred that existence of one or more planets orbiting the system, but, that has since been discredited.

## Deathworld universe

In Deathworld 3 (The Horse Barbarians), Jason dinAlt and 168 Pyrrans stopped at Transfer Station 70 Ophiuchi in orbit in the system.

## Lagrange L1 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 fulcrum 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.