Analysis of information sources in references of the Wikipedia article "Orbital station-keeping" in English language version.
Three heliophysics missions – the Advanced Composition Explorer (ACE), Solar Heliospheric Observatory (SOHO), and the Global Geoscience WIND – have been orbiting the Sun-Earth interior libration point L1 continuously since 1997, 1996, and 2004 ... the typical interval between burns for this trio is about three months, and the typical delta-V is much smaller than 0.5 m/sec. Typical annual stationkeeping costs have been around 1.0 m/sec for ACE and WIND, and much less than that for SOHO. All three spacecraft have ample fuel remaining; barring contingencies all three could, in principle, be maintained at L1 for decades to come.
