A team led by NASA researchers has devised a miniaturized sensor system that could be a catalyst for a revolutionary new generation of small, low-cost spacecraft to explore the solar system.
The Planetary Integrated Camera-Spectrometer, or PICS, is expected eventually to replace whole suites of individual spacecraft instruments that, on some NASA missions, can weigh more than 180 kilograms (400 pounds) and take up as much room as a four-drawer filing cabinet.
Literally smaller than a breadbox, PICS combines some of the most productive and often-used space sensors into an 5-kilogram (11pound) package. Its development represents a crucial step toward enabling future NASA missions that will have to use smaller launch vehicles and, hence, smaller spacecraft to travel to distant planets and other bodies in the solar system.
In addition to being much smaller, the PICS system offers high performance and improved instrument sensitivity over previous spacecraft instruments of the same type at lower overall cost, according to PICS Program Manager Gregg Vane of NASA's Jet Propulsion Laboratory (JPL). "Many people assume that low cost implies low capability," he said, "but PICS proves you can have very high capability at low cost."
The PICS prototype, developed through a collaboration between researchers at JPL, industry, universities and the U.S. Geological Survey, recently completed successful science and engineering tests that qualify the instrument system for development as flight hardware. PICS is a candidate for flight on several future planetary spacecraft missions.
PICS is one of the first successful efforts to squeeze down multiple instrument optics, functions and electronics into a small, efficient unit that requires dramatically less power and mass than was previously achieved. It brings together in one integrated sensor system an ultraviolet imaging spectrometer, an infrared imaging spectrometer and two visible-light cameras -instruments that can characterize the chemical makeup, thermal properties, weather, atmospheric physics and geophysics of bodies in the solar system.
In the past, each of these spacecraft instruments has been built with its own separate, dedicated optical system and electronics. In PICS, the instruments share common telescope optics and extremely low-power, miniaturized instrument electronics. The result is one highly-capable integrated instrument system that requires less than five watts of power and is so small it can be tucked under an arm. In comparison, similar instruments on the Voyager spacecraft required 75 watts to operate four large, entirely separate optical sensors, in addition to a sophisticated pointable scan platform for aiming.
"PICS will be able to achieve Voyager-class science at 10 cents on the dollar," said geologist Dr. Larry Soderblom of the U.S. Geological Survey in Flagstaff, AZ. "PICS will allow the science return we are accustomed to from our flagship missions like Voyager, but at the cost of a Discovery mission -- about 1/10th to 1/20th of the cost."
PICS' initial development was triggered by a challenge from designers of NASA's Pluto Express mission, a proposed exploration of the only known planet in the solar system that still awaits close reconnaissance by a spacecraft. The Pluto mission's requirements called for an instrument incorporating two spectrometers -- one far ultraviolet and one infrared -- in addition to two visible- light cameras, all weighing in at less than about 15 pounds. Space instrument specialists say no previously existing instrument met these constraints or even came close to matching those specifications.
From the outset, the PICS team's approach was to simplify the system and to minimize the mass and power of the instruments by maximizing the extent to which components can be shared. To further reduce mass and power consumption, PICS was designed to eliminate items such as focusing mechanisms and filter wheels found on traditional spacecraft imaging systems.
Another critical innovation in the PICS design was the decision to construct all the optical and structural components of silicon carbide. The material is inexpensive, highly dimensionally stable, chemically non-reactive and possesses excellent structural capabilities and manufacturability, according to Vane.
Beyond the innovations in materials and miniaturization that made PICS work is a new management approach calling for concurrent engineering and science planning.
"This contrasts with the more traditional approach taken in past missions where the scientists defined the requirements and the engineers developed the design, often with little interaction between the two groups," Vane said. Individual instruments were developed in this way, independent of each other and delivered to the spacecraft engineers as a fait accompli, he said. "We've reengineered the process of how to design a sensor system. Simply working together as an integrated team of scientists and engineers from the start has made the difference."
"With PICS instrument technology now in hand, JPL mission planners can reasonably conceive of missions to any planet in the solar system with a Delta or similar launch vehicle," said Dr. Patricia Beauchamp, PICS instrument manager. One concept on the drawing board would send a PICS-equipped spacecraft beyond Pluto to the so-called Kuiper Belt of comets. Another would put a spacecraft in orbit around Neptune's moon, Triton.
Fully prototyped and tested, PICS has been designed for ease of manufacture, integration and test. A flight model for a candidate mission could be produced in 18 months. "We're ready to roll," Beauchamp said. "We're just waiting for a ride."
The Planetary Integrated Camera-Spectrometer is being developed at the JPL for the Research Program Management Division of NASA's Office of Space Science, Washington, DC.
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