MDL News & Trends
MDL’s History with Herschel and Planck Follows Over 4 Decades
On May 14, 2009, an Ariane 5 rocket launched from Korou, French Guiana carried two astrophysics missions into space: the Herschel Space Observatory and the Planck Surveyor. Observing at millimeter wavelengths, Planck is in the process of producing an exquisitely sensitive and detailed all-sky map of the cosmic microwave background - the “afterglow” from the Big Bang that was produced when the universe was only 370,000 years old. Meanwhile, Herschel’s 3.5m telescope, the largest flown in space to date, is observing selected fields and objects at submillimeter and far-infrared wavelengths, providing critical information about the formation and evolution of stars and galaxies over the 13.7 billion year history of the universe. These European Space Agency (ESA) missions have significant NASA participation: four out of the five science instruments on Herschel and Planck rely on NASA-developed technologies. Many of the NASA technologies - in particular the photon detectors at the heart of several of the science instruments - were developed and produced at the JPL Microdevices Laboratory (MDL). The story of how JPL and MDL became involved in these projects can be traced back over nearly four decades.
The Beginnings of Microdevices Laboratory (MDL)
In 1971, and initially under NASA sponsorship, Prof. Robert Leighton at Caltech began the development of a precise 10-meter ground-based telescope capable of millimeter and submillimeter wavelength operation. By 1977, the first telescope was completed, and in part provided the inspiration for a study team at JPL (Sam Gulkis, Tom Kuiper, and Paul Swanson) to consider a large submillimeter-wavelength telescope in space. Indeed, in that year JPL scientists Robert V. Powell and Albert R. Hibbs published a paper titled “Entrée for Large Space Antennas” that presents this idea and cites Leighton's work. It is interesting to note that Hibbs, who obtained his PhD at Caltech in 1955 under the guidance of Richard Feynman, was a major figure in JPL’s history: his 1961 paper “The National Program for Lunar and Planetary Exploration” charted JPL’s course away from a guided missile laboratory and towards its present NASA role in the scientific exploration of the Earth, the solar system, and the cosmos.
Leighton’s work attracted Thomas G. Phillips to the Caltech faculty in 1979. Tom, along with his former colleagues at Bell Laboratories, had just co-invented a very promising new superconducting “SIS” detector for the millimeter and submillimeter wavelength bands; SIS detectors are now flying on Herschel. By 1982, the scientific and technical rationale for a “Large Deployable Reflector” in space were sufficiently well advanced that such a mission was recommended in the 1982 National Research Council astrophysics decadal survey report (the ”Field report“). Tom Phillips realized that a smaller precursor mission was needed and by the mid-1980s was leading the U.S. effort in this direction. Indeed, the 1986 proposal for a "Submillimeter Explorer" in many ways anticipated the science goals and general technical characteristics of Herchel. However, the detection technology needed to actually implement LDR or a smaller mission did not exist and remained a daunting challenge. Fortunately, the 1982 Field report recommendation triggered NASA funding for submillimeter technology development, and an effort to develop SIS mixers at JPL was initiated, which by 1985 had led to the successful production of niobium nitride (NbN) tunnel junctions. In parallel, the use of semiconductor GaAs Schottky diodes for submillimeter wavelength detection and generation was being explored at JPL throughout the 1980s for a variety of applications including airborne astronomy, studies of the chemistry in the Earth's upper atmosphere, and laboratory spectroscopy. The construction of the MDL in 1988 provided a new home for these activities, and by the 1990s MDL was leading the world in the development and production of advanced SIS and Schottky devices, with Dr. H. G. “Rick” Leduc leading the SIS effort and Drs. Peter Siegel and Imran Mehdi leading the Schottky effort. The devices produced under this program were demonstrated in a number of ground-based and airborne instruments.
Partership with the ESA
In Europe, plans for a submillimeter/far-infared space mission were also being developed starting in the early 1980s. By 1994, the European Space Agency had selected the Far-InfaRed Space Telescope (FIRST - now renamed Herschel) as the last of its four “cornerstone” missions, and under Tom Phillips' leadership, US scientists worked toward a NASA-ESA partnership on a joint mission; Tom now serves as the U.S. Principal Investigator for Herschel. Also in 1994, Tom played a key role in attracting Andrew Lange to join the Caltech faculty, and Andrew in turn attracted his former student Dr. James Bock to JPL. Working together, Bock and Lange initiated a program at MDL to develop extremely sensitive millimeter/submillimeter detectors known as “spiderweb bolometers”. These detectors proved extremely successful and were used in a wide variety of groundbreaking cosmological experiments such as the “BOOMERANG” balloon payload flown in Antarctica.
MDL Instruments Have Essential Roles in both Planck and Herschel Missions
The successful launch of Herschel and Planck represent the culmination of this work. Both Planck’s High Frequency Instrument (HFI) and Herschel's Spectral and Photometric Imaging Receiver (SPIRE) use JPL/MDL spiderweb bolometers; Lange is the U.S. Principal Investigator for HFI while Bock is the U.S. Principal Investigator for SPIRE. The HFI and SPIRE bolometers have now reached their ultra-cold operating temperatures in space: 0.1 and 0.3 Kelvin, respectively. A third instrument, Herschel's Heterodyne Instrument for the Far Infrared (HIFI) relies on MDL's Schottky and SIS devices. The Schottky devices are of critical importance to HIFI and are used to generate oscillator signals throughout HIFI’s 0.5 to 2 Terahertz frequency range. HIFI’s highest-frequency SIS detector at 1.2 THz uses MDL devices, developed in collaboration with Prof. Jonas Zmuidzinas’ group at Caltech. At present, all five instruments on Herschel and Planck are functioning very well and are beginning to produce astronomical data.
More information on Herschel and Planck may be found at:
A symposium honoring Tom Phillips was held at Caltech in February 2009: