(ed.). Gravitational waves (IOP, 2001)(422s).

Description of the LISA mission 117Figure 10.1. Basic geometry of the LISA antenna. The sides of the triangle are5000 000 km long.the phasing and the orientations of the orbits properly, the three spacecraft willform the desired nearly equilateral triangle, which is tipped at 60 ◦ to the ecliptic(figure 10.2). The plane of the triangle will precess around the pole of the eclipticonce per year, and the triangle will rotate in that plane at the same rate. Thecentre of the triangle is chosen to be about 50 000 000 km (20 ◦ ) behind the Earth.The arm lengths for the triangle will stay constant to about 1% for a number ofyears. Locating the triangle 60 ◦ from the Earth would keep the arm lengths moreconstant, but at the expense of more propulsion required to reach the desired orbitsand more telemetry capability to send the data back.The layout of one of the two optical assemblies in each spacecraft is shownin figure 10.3 (see [9]). Each optical assembly contains an optical bench,a transmit/receive telescope, and a low-power electronics package. Each ofthese three subassemblies is mounted by low-thermal-conductivity struts from astiffened support cylinder that forms the outside of the optical assembly. Becausethe distances between the spacecraft will change by up to 1% during the year,the angles between the sides will also change by roughly one degree. Thus, it isnecessary to provide some adjustment for the angle between the axes of the two