Schematic diagram of the layout of the LISA interferometer, showing the labeling scheme adopted. The three spacecraft are labeled A, B and C and each spacecraft contains two optical benches, labeled A1, A2, B1, B2, C1 and C2. The arms of the interferometer are defined between the optical benches e.g. arm 1 is between optical benches A1 and C2. Note that all designations progress counterclockwise around the triangle.
From LISA System and Technology Study Report (2000) (Fig 5.1)
ESA-SCI(2000)11