 The cluster mission was launched in 2000 and consisted of four satellites orbiting the Earth. The cluster ion spectrometry, CIS, instrument was used to measure the ion distribution in the magnetosphere from thermal energies up to 40 keV slash E. It consisted of two separate instruments, one with medium angular resolution, 22.5 degrees, and another with higher angular resolution, 5.6 degrees. The instruments were tested during commissioning activities between September 2000 and January 2001, and then operations began in February 2001. The instruments were able to obtain good data in the central plasma sheet, magnetopause crossings, magnetosheath, solar wind, and cusp measurements. This demonstrated the potential of multi-spacecraft measurements using identical instruments, opening up a new area of research into magnetospheric and solar wind magnetosphere interactions. This article was authored by H. Reem, C. Osten, J. M. Boscade, and others. We are article.tv, links in the description below.