NASA has taken its research charter to embrace not only emerging aircraft technologies, but also how those technologies can be employed for a greater understanding of our world. The NASA Environmental Research Aircraft and Sensor Technology (ERAST) project is spawning some remarkable pilotless aircraft with enhanced abilities to sample earth sciences phenomena. ERAST has at its core the goal of developing advanced technologies and making them available to the emerging American uninhabited aerial vehicle (UAV) industry. The envisioned result could be a fleet of remotely piloted aircraft capable of staying aloft for months, becoming "atmospheric satellites" free from the typical constraints of crew fatigue and fuel capacity. Already, diverse aircraft have emerged from ERAST, under the management of NASA’s Dryden Flight Research Center in California’s Mojave Desert. Other NASA centers, including Langley in Virginia, Glenn in Ohio, and Ames in California, are contributors to the ERAST phenomenon. Aircraft matured as a result of ERAST include:
Helios Prototype — Most radical of the five ERAST project aircraft is the Helios Prototype, a 247-foot span flying wing with 14 engines, weighing in at barely over 2,000 pounds loaded. The 14 motors are electric, ultimately to be fed by a new solar generation system that will use the sun for immediate power as well as for storage to allow round-the-clock operations when the sun is down. The Helios Prototype was designed and built by AeroVironment, Inc., of Monrovia, Calif. With a span bigger than that of a 747 airliner or C-5 transport, the Helios Prototype derives its light weight from composite materials such as carbon fiber, Styrofoam, graphite epoxy, Kevlar, and a thin transparent skin. The aircraft’s outer wing panels incorporate a 10-degree dihedral to enhance lateral stability. A slight upward twist at the wingtip trailing edges helps prevent stalls during the aircraft’s slow landings and turns. The only flight control surfaces are 72 trailing-edge elevators for pitch. Yaw control is effected by applying differential power to the 14 propellers poking ahead of the wing. A pilot on the ground has successfully flown the Helios Prototype in a series of incremental flight tests over Rogers Dry Lake at Edwards Air Force Base, where the NASA Dryden Flight Research Center is located. Using battery power, the airframe was validated in 1999. When the solar cell arrays are installed, the Helios Prototype is expected to attain one of its ERAST milestones in 2001: flight at 100,000 feet. Two years later, after addition of the hydrogen-oxygen fuel cell energy storage system, the aircraft is slated to demonstrate its ability to stay airborne for four days. All this is just the prelude for production variants which are expected to be able to stay aloft for months. The benefits are manifold: emerging climate patterns can be monitored, and telecommunications can be provided by using these "atmospheric satellites" as relay platforms.
ERAST Research Aircraft (Predator B) — Adapted and enlarged from the military Predator UAV, the ERAST Research Aircraft from General
Atomics-Aeronautical Systems Inc. addresses requirements for a
consumable-fuel aircraft for science missions. The third iteration of the ERAST Research Aircraft (Predator B) is to fly with a 700 horsepower turboprop engine. Goals are to carry a 660-pound payload for as long as 32 hours at altitudes ranging between 42,000 and 52,000 feet. As UAVs become more enmeshed in the aviation matrix, the ERAST Research
Aircraft is tasked to demonstrate see-and-avoid ability to allow it to fly safely in FAA-controlled civil airspace, and demonstrate
over-the-horizon command and control capability from a ground station.
Perseus B — The single-engine Perseus B, built by Aurora Flight Sciences Inc., Manassas, Va., topped 60,000 feet in 1998, relying on triple supercharging of its internal combustion engine to attain that
performance. The purpose of this aircraft is to prove — and improve — propulsion, avionics, and command and control systems.
Altus II — This technology testbed has already demonstrated the ERAST milestone of four hours’ flight at 55,000 feet. It also achieved an eight-hour flight above 50,000 feet in 1999. And it flew a real-world 26-hour science mission to measure atmospheric radiation beneath clouds in 1996. Altus is built by General Atomics’ Aeronautical Systems Inc. As with Perseus, Altus II has expanded the altitude envelope for UAV piston engines.
Proteus — No stranger to the skies over Oshkosh, Scaled Composites’ unique twin-tail, twin-wing Proteus marks a departure from the
lightweight craft of other ERAST builders. Proteus can use a changeable fuselage barrel to carry diverse payloads weighing up to a ton. Proteus differs from the other ERAST creations in another significant way: it is "optionally piloted", with a cockpit for occupants during takeoff, climb, descent, and landing. For extended-duration missions, the onboard crew could be augmented by a ground station pilot. Ultimately, a Proteus iteration could be semi-autonomous. Proteus’ designer, the prolific Burt Rutan, intends for his creation to loiter up to 14 hours, capable of hefting a 2,000-pound payload above 60,000 feet. Its two Williams Research/Rolls FJ44-2 turbofan engines give it a total thrust of 4,600 pounds. Proteus’ salient contribution may be as a telecommunications platform, with commercial backing to that end. The opportunities for ERAST technology are intriguing: aircraft capable of staying aloft for months, in the case of Helios, and for many hours at great heights, for all of the contenders. These vehicles have been suggested as communications relays, weather and contingency monitoring platforms, and science observatories. Disaster response could be a burgeoning and vital task, with an ERAST-type aircraft loitering over the scene of a major disaster to provide communications services when the normal infrastructure has been crippled by the disaster. Even as NASA reaches farther into outer space, there’s a cloistered community of aviation engineers and
specialists at the agency’s Dryden Flight Research Center and other aero centers whose commitment is to improving our ability to use atmospheric flight in many ways. The environmental sensors that are key to ERAST’s ultimate productivity are being developed under the leadership of NASA’s Ames Research Center at Moffett Field, Calif. The Glenn Research Center in Ohio contributes to ERAST propulsion advances, and the Langley Research Center in Virginia assists with engineering analyses of advanced composite materials and structures.