March 16, 2004
The New Horizons spacecraft design includes six distinct instruments and a student-built dust counter - this is the "payload" New Horizons plans to carry to Pluto and beyond. Over the next several months, the New Horizons Web site will feature each of the instruments being developed for NASA's first mission to Pluto, Charon and the Kuiper Belt.
Alice is the ultraviolet spectrometer instrument planned for New Horizons. Its primary job is to detect a variety of important atomic and molecular species in Pluto's atmosphere, and to determine their relative abundances so that a complete picture of Pluto's atmospheric composition can be determined for the first time. Alice will also be used to search for an atmosphere around Pluto's moon, Charon, as well as the Kuiper Belt Objects (KBOs) New Horizons hopes to fly by after Pluto-Charon.
"New Horizons is designed to be a mission of firsts," says Alice Project Manager John Scherrer of the Southwest Research Institute. "A lot of space missions reveal new insights that lead us to rewrite textbooks. Given how little we know about Pluto-Charon and Kuiper Belt Objects, Alice and the other New Horizons instruments will allow us to write the textbook."
Task: Ultraviolet imaging and spectroscopy
Alice's spectroscopic range, 520 to 1,870 angstroms, extends across both the extreme and far-ultraviolet wavelength regions. "The ultraviolet region of the spectrum that Alice covers has been known to be a rich one for studying planetary atmospheres since the birth of the space age," says Alan Stern of the Southwest Research Institute, principal investigator for both the New Horizons mission and the Alice instrument itself. "In fact, ultraviolet studies are so valuable that every first mission to a new planet has carried an instrument of this type."
All ultraviolet studies in astronomy must be conducted from space because Earth's protective ozone layer shields us from ultraviolet rays.
Alice consists of a compact telescope, a spectrograph, and an electronic detector with 1,024 spectral channels at each of 32 separate spatial locations in its rectangular field of view. It is run by a microprocessor. Alice includes a sophisticated double delay line microchannel plate detector with ultraviolet photocathodes that maximize the sensitivity of the instrument. Alice also has "redundant" power supplies, which enable the instrument to keep working even if some components fail.
A first-generation version of New Horizons' Alice - smaller and a bit less sophisticated - was launched aboard the European Space Agency's Rosetta comet orbiter spacecraft in early March. That spacecraft will use remote-sensing instruments to map and examine the surface of Comet 67P/Churyumov-Gerasimenko and study its escaping atmosphere, in the most thorough investigation of a comet ever attempted, making that version of Alice the first ultraviolet spectrometer to study a comet up close.
Both the Rosetta and New Horizons Alice experiments were built at the Southwest Research Institute in San Antonio, Texas; Sensor Sciences of Berkeley, Calif., provided its microchannel plate detector. Alice uses only about three-quarters of the energy consumption of a nightlight when it operates.
New Horizons Instrument Profiles