The challenges for large light-weight diffractive lenses for space telescopes

Large light-weight telescopes in space are considered key elements enabling future earth observation and space science. The first large space telescope, “Hubble”, uses a monolithic aspheric primary mirror of 2.4 m diameter. The Hubble Space Telescope primary mirror has an area density of about 180 kg/m 2 . This monolithic approach cannot be used for much larger telescopes due to mass and volume limitations imposed by today’s launch capabilities. Thus the current generation space telescope, the James Webb Space Telescope now under development, makes use of a segmented aspheric primary mirror of 6.5 m diameter. The area density will be below 20 kg/m 2 .