been depleted, thus ending its mission. At the time of the announcement, Herschel was approximately 1.5 million km from Earth. Because Herschel orbit at the L2 point is unstable, ESA wanted to guide the craft on a known trajectory. ESA managers considered two options: Place Herschel into a heliocentric orbit where it would not encounter Earth for at least several hundred years. Guide Herschel on a course toward the Moon for a destructive high-speed collision that would help in the search for water at a lunar pole. Herschel would take about 100 days to reach the Moon. The managers chose the first option because it was less costly. On 17 June 2013, Herschel was fully deactivated, with its fuel tanks forcibly depleted and the onboard computer programmed to cease communications with Earth. The final command, which severed communications, was sent from European Space Operations Centre (ESOC) at 12:25 UTC. The mission's post-operations phase continued until 2017. The main tasks were consolidation and refinement of instrument calibration, to improve data quality, and data processing, to create a body of scientifically validated data. After Herschel Following Herschel demise, some European astronomers have pushed for the joint European-Japanese SPICA far-infrared observatory project, as well as ESA's continued partnership in NASA's James Webb Space Telescope. James Webb covers the near-infrared spectrum from 0.6 to 28.5 µm, and SPICA covers the mid-to-far-infrared spectral range between 12 and 230 µm. While Herschel dependence on liquid helium coolant limited the design life to around three years, SPICA would have used mechanical Joule-Thomson coolers to sustain cryogenic temperatures for a longer period of time. SPICA's sensitivity was to be two orders of magnitude higher than Herschel. NASA's proposed Origins Space Telescope (OST) would also observe in the far-infrared band of light. Europe is leading the study for one of OST's five instruments, the Heterodyne Receiver for OST (HERO). See also Atacama Large Millimeter Array (ALMA) Spitzer Space Telescope List of largest infrared telescopes List of largest optical reflecting telescopes List of space telescopes References Further reading External links ESA Herschel mission website Herschel science website Herschel operations website Herschel science results website NASA Herschel mission website Herschel Science Center NASA/IPAC Herschel archive United Kingdom outreach website European Space Agency space probes Space telescopes Infrared telescopes Submillimetre telescopes Derelict satellites in heliocentric orbit Spacecraft using Lissajous orbits Space probes launched in 2009 Space probes decommissioned in 2013 2013 disestablishments