Altus Remotely Operated Unmanned Aircraft System
The snow-capped peak of Mt. San Antonio in the San Gabriel range is visible as the remotely piloted Altus II flies over Southern California's high desert. (NASA / GA-ASI) › View Larger Image The Altus II was one of several slow-flying, remotely piloted aircraft that were developed and evaluated by a NASA-industry team under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) project at the NASA Dryden Flight Research Center, Edwards, CA, in the late 1990s. There were two primary goals for the Altus II development: to be a testbed for performance and propulsion concepts leading to development of future remotely piloted or autonomous aircraft designed for high-altitude science missions, and to evaluate its practicality for use as an airborne platform for such missions.
The Altus aircraft – the name is Latin for "high" – was developed by General Atomics Aeronautical Systems, Inc., of San Diego, CA, as a civil variant of the Predator A, the remotely operated surveillance aircraft built for the U.S. Air Force. Although similar in appearance, the Altus had a slightly longer wingspan and was designed to carry atmospheric sampling and other instruments for civilian scientific research missions in place of the military reconnaissance equipment carried by the Predators.
The Altus was distinguished by a long, narrow, high aspect-ratio wing, a slender fuselage, rear-mounted engine and propeller, and inverted-V horizontal tail. It could carry up to 330 lb of sensors and other scientific instruments in a nose-mounted payload compartment, a location designed to allow air being sampled by the sensors to be undisturbed by heat or pollutants from engine exhaust. It has a tricycle-type retractable landing gear. It is powered by a four-cylinder Rotax 912 piston engine with additional airflow provided by a turbocharger built by Thermo-Mechanical Systems., Inc., of Canoga Park, CA.
General Atomics built two Altus aircraft – the Altus I, equipped with a single-stage turbocharger, for the Naval Postgraduate School and the AltusTM II, with a two-stage turbocharger, for NASA under the ERAST project.
The remotely-piloted Altus I aircraft rolls towards its takeoff from Rogers Dry Lake adjacent to NASA's Dryden Flight Research Center, Edwards, Calif. (NASA /Carla Thomas) › View Larger Image Altus Flight History
The Altus II, the first of the two craft to be completed, made its first flight on May 1, 1996. With its engine at first augmented by a single-stage turbocharger, the Altus II reached an altitude of 37,000 ft during its first series of development flights at Dryden in August 1996. In October of that year, the Altus II was flown in an Atmospheric Radiation Measurement study in Oklahoma conducted by Sandia National Laboratories for the Department of Energy (DOE). During the course of those flights, the Altus II set a single-flight endurance record for remotely operated aircraft of more than 26 hours.
The Altus I, completed in 1997, flew a series of development flights at Dryden that summer. Those test flights saw the craft reach an altitude of 43,500 ft while carrying a simulated 300-lb. payload, a record for a remotely operated aircraft powered by a piston engine with a single-stage turbocharger.
After major modifications and upgrades, including installation of a two-stage turbocharger in place of its original single-stage unit, a larger fuel tank and additional intercooling capacity, the Altus II returned to flight status in the summer of 1998. The goal of its development test flights was to reach one of the major performance milestones within NASA's ERAST program: to fly a gasoline-fueled, piston-engine remotely piloted aircraft for several hours at an altitude at or near 60,000 feet. On March 5, 1999, The Altus II maintained flight at or above 55,000 feet for three hours, reaching a maximum density altitude of 57,300 feet during the mission.
Later that spring, the Altus II flew another series of Atmospheric Radiation Measurement missions conducted by Sandia National Laboratories for the DOE. Hard-to-measure properties of high-level cirrus clouds that may affect global warming were recorded using specially designed instruments while the Altus flew at 50,000 feet altitude off the Hawaiian island of Kaua'i. Data from the study was intended to help scientists better understand how the dual roles of clouds in reflecting solar radiation back into space and absorbing longer-wave radiation from the Earth work so they can build more accurate global climate models.
In September 2001, Altus II served as the unmanned aircraft platform for a flight demonstration of remote sensing and imaging capabilities that could detect hot spots in wildfires and relay that data in near- real time via the Internet to firefighting commanders below. The demonstration, led by NASA's Ames Research Center, was flown over General Atomics' El Mirage development facility in Southern California's high desert.
Looking ever so much like an alien spacecraft, the Altus II remotely piloted aircraft shows off some of the instruments and camera lenses mounted in its nose for a lightning study over Florida flown during the summer of 2002. (NASA / Tom Tschida) › View Larger Image In the summer of 2002, The Altus II served as the airborne platform for the Altus Cumulus Electrification Study (ACES), led by Dr. Richard Blakeslee of NASA Marshall Space Flight Center. The ACES experiment focused on the collection of electrical, magnetic and optical measurements of thunderstorms, which could help scientists understand the development and life cycles of thunderstorms and in turn could allow meteorologists to more accurately predict when destructive storms may hit.
Considered an experimental developmental aircraft, the Altus II was retired upon the conclusion of the ERAST program in the early 2000s. However, its performance led to General Atomics' development of the larger, turboprop-powered Altair prototype and NASA's eventual acquisition of a production version of the General Atomics' Predator B for environmental science missions and aeronautical research.
The ERAST Program
The Environmental Research Aircraft and Sensor Technology (ERAST) program, which functioned from 1995 through 2003, was a multiyear effort to develop the aeronautical and sensor technologies for a new family of remotely piloted unmanned aircraft intended for upper atmospheric science missions. Designed to cruise at slow speeds for long durations at altitudes of 60,000 to 100,000 ft, such aircraft could be used to collect, identify, and monitor environmental data to assess global climate change and assist in weather monitoring and forecasting. They also could serve as airborne telecommunications platforms, performing functions similar to communications satellites at a fraction of the cost of lofting a satellite into space.
Additional technologies considered by the joint NASA-industry ERAST Alliance included lightweight materials, avionics, sensor technology, aerodynamics, and other forms of propulsion suitable for extreme altitudes and duration.
The ERAST program was managed by NASA's Dryden Flight Research Center, while NASA's NASA Ames Research Center, headed the sensor technology development. NASA's Glenn and Langley Research Centers contributed expertise in the areas of propulsion, structures, and systems analysis. Several small high-technology aeronautical development firms, including Altus developer General Atomics Aeronautical Systems teamed with NASA in the ERAST Alliance to work towards common goals of the program.
ALTUS II Specifications
- Wingspan: 55.3 ft.
- Wing area: 131 ft.2
- Wing aspect ratio: 24
- Length: 23.6 ft. (7 ms)
- Maximum gross takeoff weight: 2,130 lb.
- Wing loading at gross weight: 16.3 lb/ ft.2
- Payload: Up to 330 lb in nose compartment
- Propulsion: Rear-mounted Rotax 912 four-cylinder piston engine rated at 100 hp, integrated with a two-stage Thermo-Mechanical Systems turbocharger. An 84-in. diameter two-blade pusher propeller was used for flights up to about 53,000 ft. altitude; a larger 100-in. diameter lightweight carbon-fiber propeller was installed for flights above that altitude.
- Fuel capacity: 92 gal.
- Airspeed: 100 knots (115 mph) maximum; 70 kn (80 mi/h) cruise, varies with altitude.
- Maximum altitude: Above 60,000 ft. (19,500 m) with two-stage turbocharger; about 43,500 ft. with single-stage turbocharger.
- Endurance: Approximately 24 hours, depending on altitude.
- Construction: Primarily composites
- Manufacturer: General Atomics Aeronautical Systems, Inc., San Diego, Calif.