[15.0] The NASA ERAST HALE UAV Program

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* The US National Aeronautics and Space Administration was a major promoter of HALE UAV development, though the agency's "Environmental Research Aircraft & Sensor Technology (ERAST)" program, outlined in this chapter.

[15.1] PRELUDE: THE NASA MINI-SNIFFER PROGRAM

* In the early 1970s, a NASA engineer named Dale Reed was investigating how to sample the atmosphere at very high altitudes, up to 21 kilometers (70,000 feet). NASA's studies into supersonic transport jets had led to questions about their possible impact on the upper atmosphere, and Reed designed a series of "Mini-Sniffer" drones to take air samples at high altitudes.

Three Mini-Sniffers were built by NASA Dryden Flight Research Center, and were flown from 1975 through 1982. The initial "Mini-Sniffer I" had a wingspan of 5.5 meters (18 meters), vertical tailplanes on the wingtips, and canard fins on the nose. It used a gasoline-powered piston engine and performed a dozen low-altitude flights to validate the design.

The Mini-Sniffer I was then modified into the "Mini-Sniffer II" by removing the canards and the wingtip tailplanes, then adding tail booms and extending the wings, giving it a wingspan of 6.7 meters (22 feet). It was still powered by a gasoline engine, and made 21 flights to a maximum altitude of 6,100 meters (20,000 feet).

To get to much higher altitudes, Reed planned to use an unusual engine that burned hydrazine. A normal internal combustion engine burns gasoline with air to generate power, but at 21 kilometers the air is too thin to keep it running. Instead of gasoline, Reed planned to use hydrazine, or (NH2)2, which breaks down spontaneously when run across a catalyst, generating heat to produce steam to drive the engine. Hydrazine is corrosive, toxic, unstable stuff, but its ability to "burn" without oxygen makes it useful for spacecraft thrusters and for such high-altitude engine applications.

"Mini-Sniffer III" was a new-build aircraft, similar to Mini-Sniffer II but with a longer fuselage and the hydrazine engine. It was designed to carry an 11.3 kilogram (25 pound) payload to 70,000 feet or higher. However, the Mini-Sniffer III only made a single flight to 6,100 meters (20,000 feet), and was not flown again because of fuel leaks. NASA lost interest in the idea, and the concept of a high-altitude UAV was abandoned for the time being.

[15.2] THE NASA ERAST PROGRAM

* NASA work on high-altitude UAVs was revived in the late 1980s, leading to the ERAST program.

In 1987 and 1988, NASA conducted atmospheric ozone-layer depletion studies using two piloted NASA aircraft: a modified DC-8 jetliner and a Lockheed ER-2, a civilian version of the U-2 spy plane. However, operating the ER-2 over Antarctica, where ozone depletion took place, was regarded as risky, since if the pilot had to bail out, survival was unlikely. The other problems were that the ER-2 had a ceiling of 20 kilometers (65,000 feet), while ozone depletion takes place at 30 kilometers (100,000 feet), and the ER-2 could not stay aloft long enough to study ozone changes during a full day-night cycle.

In 1988, NASA decided to obtain a HALE UAV named "Perseus" to deal with these problems, designating the effort the "Small High-Altitude Science Aircraft (SHASA)" program. Perseus was designed by a startup company named Aurora Flight Services of Manassas, Virginia.

The Perseus design effort struggled along on skimpy funds until 1991, when NASA was conducting a "High Speed Research Program" to evaluate designs for a future supersonic transport, and needed to learn more about the possible environmental impact of such an aircraft on the upper atmosphere. Funds became available to procure a few aircraft.

Other government agencies were also interested in HALE UAVs, and so the ERAST effort was born in September 1994 as a high-profile item in NASA'a agenda. ERAST was formally intended to promote the use of UAVs in commercial science applications, particularly high-altitude atmospheric research. ERAST also has focused on development of new miniaturized sensor and avionics systems for the UAVs and for NASA's Lockheed ER-2.

In practice, ERAST was a loosely defined program that served the interests of NASA and of industry, focusing on the development of UAVs to support government research and UAV industry interests. It was an effort in the fine tradition of NASA's predecessor organization, the US National Advisory Committee on Aeronautics (NACA). ERAST was under the management of NASA's Dryden Flight Research Center, with involvement from the NASA Ames, Langley, and Glenn Flight Centers, and later from a NASA Earth science effort designated "Code Y". Industry partners included Aurora Flight Systems, AeroVironment, General Atomics, Scaled Composites, Thermo-Mechanical Systems, Hyperspectral Sciences, and Longitude 122 West.

Handling the extreme cold and the tricky aerodynamics of flight in very thin air were significant engineering challenges. All the original ERAST designs were prop-driven to reduce cost, and because low speed is needed for accurate atmospheric sensing. Powerplants under consideration included electric motors, piston engines with two-stage or even three-stage turbocharging, and piston engines that carried their own liquid oxygen. These three types of engines could all be used below 27.4 kilometers, but turbocharged engines were not regarded as useful above that altitude. Hydrogen-peroxide engines were also considered for flights above 27.4 kilometers.

ERAST efforts moved in fits and starts, reflecting available funding, complicated partnership relationships, and occasional aircraft crashes and other misfortunes. However, although the program was possibly frustrating for its staff, the general direction seemed to be to the right and, literally, upwards. The current ERAST program was finally terminated in 2003. Further formal efforts appear to be on hold for now, but NASA is likely to come back to the matter sooner or later.

[15.3] AURORA FLIGHT SYSTEMS PERSEUS & THESEUS

* The first Perseus delivered by Aurora Flight Sciences was the Perseus "Proof of Concept (POC)". As the name implied, this was strictly a technology demonstration prototype and had no high-altitude capability. It was built using US National Science Foundation (NSF) funds, and flew three test flights in November 1991.

Two "Perseus-A" variants followed, with the first flying on 21 December 1993. NASA hoped to fly one to 25 kilometers (82,000 feet), but neither of the two had gone above 15.2 kilometers when the first Perseus-A crashed in November 1994. The second Perseus-A continued test flights, but was retired and is now on display at the Aurora Flight Sciences site.

The Perseus-A was powered by a Rotax 912 gasoline engine providing 60 kW (80 HP) to a pusher propeller. The engine was fitted with its own liquid oxygen supply in a closed-cycle system. The engine could maintain sea-level power up to extreme altitudes, though there were problems with radiator design that limited high altitude power and had to be fixed.

The propeller was 4.42 meters (14 feet 6 inches) in diameter for high-altitude operation. The Perseus-A had a low-drag "bicycle" tandem landing-wheel configuration, with the wheel axles inside the aircraft fuselage, and so the propeller could not clear the ground for takeoffs and landings. The propeller was fixed in a horizontal position for takeoffs, with the Perseus-A towed behind a truck using a cable to get it into the air, where the propeller could be started. On landing, the propeller was fixed in the horizontal position again.

* The two Perseus-As were followed by the single "Perseus-B", which first flew on 7 October 1994. Perseus-B was similar to Perseus-A, but had a Rotax 912 engine with three stages of turbocharging for high-altitude operation, and long fixed tricycle landing gear, eliminating the need for towed launch.

The Perseus-B was damaged in a rough landing in 1996, but returned to service with the wingspan stretched from 17.9 meters (58 feet 9 inches) to 21.7 meters (71 feet), flying at an altitude of over 18.3 kilometers (60,000 feet) in 1998. The Perseus-B was then further modified, with avionics and engine improvements and external fuel tanks, though it was damaged again in another hard landing in late 1999.

Below an altitude of 1.5 kilometers, the engine ran without turbocharging. Above that altitude, a waste gate closed, diverting hot exhaust at 870 degrees Celsius into the turbine system. At the top altitude of 27 kilometers, the external ambient temperature is about -54 degrees Celsius, and the air pressure is about a fiftieth of that at sea level. The turbocharging system provided sea level pressure to the engine inlet. Unfortunately, some sources seem to indicate that the three-stage turbocharged engine was not a success, suffering from poor reliability.

* Aurora Flight Sciences built a bigger and better follow-on to Perseus named "Theseus", funded by NASA through the "Mission To Planet Earth" environmental observation program. The single Theseus built was delivered in 1996.

The Theseus was powered by two Rotax 912 engines, each driving a single wide-span two-bladed propeller. The pusher propellers were mounted above the wing to provide ground clearance. Unfortunately, the Theseus was lost in an accident after six flights.

[15.4] GENERAL ATOMICS ERAST UAVS

* NASA also adapted existing operational UAV technology for the ERAST program, obtaining a General Atomics Altus UAV. The Altus was based on and looked much like the Gnat 750 UAV but had a different fuselage and a longer wingspan.

The Altus was 7.2 meters (23 feet 7 inches) long, had a wingspan of 16.9 meters (55 feet 4 inches), and a takeoff weight of 725 kilograms (1,600 pounds). It could carry 150 kilograms (330 pounds) to 13.7 kilometers (45,000 feet) with an endurance of 24 hours. The engine was originally a Rotax 912 with a single stage of turbocharging.

An Altus spent 26 hours above 6,100 meters (20,000 feet) in 1996, and spent four hours above 16,800 feet (55,000 feet) in 1999 after being fitted with a two-stage turbocharger system, updating it to the Altus II configuration.

The Altus having proved satisfactory to NASA, in early 2000 NASA signed a $10 million USD contract with General Atomics for the construction of several of the Predator B turboprop derivatives of the current Predator UAV, discussed earlier. Current status of this effort is unclear.

The US Navy Postgraduate School in California also obtained an Altus, as well as two Predators and an "optionally piloted" Cessna 337 known as the "Pelican". These UAVs and other aircraft are loaned or hired out to other defense organizations and private companies for tests and UAV payload development.

[15.5] SCALED COMPOSITES PROTEUS

* The ERAST effort also provided assistance to Scaled Composites company, run by innovative aircraft designer Burt Rutan, in the development of the Scaled Composites' Proteus HALE aircraft. However, most of the development of the Proteus was funded by Scaled Composites, and the company's ambitions for the aircraft far exceed the scope of the ERAST program's goals.

The Scaled Composites Model 281 Proteus is, as its name implies, a highly reconfigurable HALE aircraft that can be operated either with a pilot or as a UAV, and is intended for typical HALE applications such as communications relay, military and commercial observation, and upper atmosphere research.

The Proteus was designed to provide a HALE platform with greater endurance, lower operating costs, and a cheaper price tag than the Lockheed U-2. The first prototype of the Proteus began test flights in late July 1998, and was officially "rolled out" on 23 September of that year. The Proteus is an unusual looking aircraft, featuring:

The two fanjets are optimized for operation at high altitude and low speed. Proteus can operate at altitudes from 15.2 to 19.8 kilometers (50,000 to 65,000 feet). Its pressurized cabin provides a shirt-sleeve environment for its two-man crew at any altitude.

The Proteus has reasonable takeoff and landing performance, but it has no thrust reversers, spoilers, or flaps. Feedback from test pilots during initial flights indicated a need for a drag chute to allow it to make high-speed emergency descents quickly without overstressing the airframe.

The aircraft is built mostly of graphite-epoxy composite, as the name of its builder Scaled Composites suggests. The operational version of the Proteus will have an empty weight of about 2.72 tonnes (6,000 pounds), with a fuel capacity also of 2.72 tonnes, and a maximum takeoff weight of 5.67 tonnes (12,500 pounds) to stay within US FAA class limits. Military or experimental variants could have a maximum takeoff weight of 6.57 tonnes (14,500 pounds). Typical payload is in the range of 900 kilograms (1 ton).

* The aircraft takes its name from the Greek god Proteus, who could change his form at will. While the rear wings have a "normal" span of 23.7 meters (77 feet 7 inches), they can be fitted with wingtip extensions to extend the span to 28 meters (91 feet 10 inches). The forward wings can be similarly extended. This is unusual, but not startling. What is startling is that the entire center section of the fuselage can be swapped out to fit the aircraft for different missions.

The forward section includes the pressurized cockpit, nose gear, and about half the fuel, while the rear section contains the rest of the fuel and engines, with main gear in the tail boom extensions off the rear wing. The different possible center "barrel" sections are hooked up to control, fluid lines, and electrical connections in the front and rear fuselage sections. The Proteus can provide up to 23 kilowatts of electrical power to the barrel section.

The barrel sections have a diameter of 1.14 meters (3 feet 9 inches) but can be of varying length, and can include pylons to carry equipment externally. Equipment too big to clear the ground on takeoff and landing can be offset to one side. Asymmetric installation of wingtip extensions allows the Proteus to fly safely even with offset payloads.

* One of the main drivers for development of the Proteus was for use as a communications relay platform for urban areas, with the aircraft fitted with a barrel section containing a communications payload. Although this was expected to be one of the initial applications for the aircraft, it hasn't happened yet, very likely because of the difficulties the telecom industry ran into following the decline of high-tech markets in 2001.

For military reconnaissance or civilian earth-observation missions, a barrel section could be fitted with sensors internally, as well as with external sensors (such as side-looking radar) mounted in pods. For military missions, the aircraft could be operated as a UAV. The Proteus could remain over the target area for 12 hours, operating 3,700 kilometers (2,300 miles) from base, or for 22 hours at a quarter of that distance. The aircraft cruises at an optimum speed of 450 KPH (280 MPH) at high altitude.

For atmospheric research, all the sensors could be mounted inside the barrel section, improving performance. Proteus could observe the South Pole for six hours, operating out of bases in South Africa, Chile, or Australia. It could cross the entire Antarctic continent, flying from Capetown, South Africa, to Christchurch, New Zealand. Proteus could also be used as a hurricane chaser, flying into the eye of the storm at high altitude and then loitering in the eye for hours.

* Proteus flew three piloted missions for NASA in 2000, testing payloads for new satellite instruments for the US Defense Department and National Oceanic & Atmospheric Administration (NOAA). The first two flights tested a pair of atmospheric sounders, one named "NAST-I" based on infrared interferometry and one named "NAST-M" that senses microwave emissions. The two instruments were fitted into a 5.5 meter (18 foot) long pod carried under the fuselage. The third flight added an instrument to observe cirrus clouds in the far infrared.

Scaled Composite pilots also set a payload-to-altitude record in the Proteus in 2000, wearing pressure suits borrowed from NASA as a precaution against decompression at high altitude. They reached an altitude of about 19 kilometers (63,000 feet), an impressive testimonial to the aircraft's capabilities.

[15.6] THE BMDO RAPTOR UAVS

* While the Air Force was working on endurance UAVs for reconnaissance applications, the US Ballistic Missile Defense Organization (BMDO, now the Missile Defense Agency / MDA) was working on endurance UAVs to shoot down ballistic missiles, under the "Responsive Aircraft Program for Theater Operations (RAPTOR)" program.

The idea was that such UAVs would orbit on the edges of a battle area to detect launches of short-range tactical ballistic missiles (TBMs) and perform a "boost phase intercept (BPI)", shooting down the TBMs with extremely fast "hypervelocity" interceptor missiles.

The first aircraft developed by the BMDO was the "RAPTOR/Talon" demonstrator, which was designed by Burt Rutan's Scaled Composites Company. Initial tests were conducted with a pilot supervising low altitude remote control flights sitting on an exposed "saddle" on the back. RAPTOR/Talon was powered by a turbocharged Rotax 912 piston engine with 60 kW (80 HP). The UAV was designed to carry a 68 kilogram (150 pound) payload of infrared search and track sensors, plus two 22.7-kilogram (50 pound), kinetic-kill, hypervelocity Talon missiles, each with a range of almost 100 kilometers (60 miles). Other specifications included:

RAPTOR/Pathfinder was really nothing more than the AeroVironment HALSOL experimental UAV, retrieved from storage for the BMDO project and fitted with solar cells. Its wing was covered with solar panels that generated peak power of 11.4 kW to drive its eight small electric motors. The RAPTOR/Pathfinder could carry a payload of 41 kilograms (90 pounds).

BMDO found itself on increasingly shaky financial and political grounds as the 1990s progressed, and finally abandoned the RAPTOR/Talon and RAPTOR/Pathfinder. However, the two UAVs were not scrapped. They were passed on to NASA for the ERAST program. The RAPTOR/Talon became the "Demonstrator 2", and the RAPTOR/Pathfinder simply became the "Pathfinder".

The Demonstrator 2 was of conventional aircraft configuration, with a front-mounted tractor propeller. This made it unsuitable for atmospheric sampling, and it was used mostly as an engine test platform. In contrast, the Pathfinder underwent substantial evolution at NASA's hands.

[15.7] PATHFINDER & HELIOS / LONG ENDURANCE UAV DEVELOPMENTS

* The Pathfinder went into NASA service originally unchanged from its BMDO configuration. NASA test flights demonstrated its usefulness for the agency's purposes, and in fact the Pathfinder set several records. In 1997, the Pathfinder broke a world's record for high-altitude flight by a propeller-driven aircraft when it reached an altitude of over 21,650 meters (71,000 feet), beating the Boeing Condor's record by a comfortable margin.

Following the good results obtained in the original Pathfinder flights, NASA then upgraded the Pathfinder to an improved configuration, the "Pathfinder Plus". Pathfinder Plus featured a 6.7 meter (22 foot) wing stretch to give a total wingspan of about 37 meters (121 feet), two more electric motors and propeller for a total of ten, and more and improved solar cells. The enhancements gave the Pathfinder Plus an increased take-off weight of 315 kilograms (694 pounds).

In August 1998, Pathfinder Plus broke the Pathfinder's altitude record by reaching an altitude of over 24,400 meters (80,000 feet). However, was intended simply as a stepping stone to an even bigger solar-powered UAV, the "Centurion". AeroVironment rolled out the Centurion in the summer of 1998, and the UAV made its first flight in November 1998, with a pilot at the controls. It had a span of 62.8 meters (206 feet), was powered by twelve electric motors, had four gondolas instead of two, and weighed 630 kilograms (1,385 pounds). It was expected to reach up to 30,500 meters (100,000 feet).

AeroVironment's ultimate goal was the fully operational Helios solar-powered UAV. The Centurion prototype was expanded to act as a Helios prototype, with a wingspan of 75.3 meters (247 feet), five gondolas, and fourteen electric motors. The Helios prototype first flew in the fall of 1999. It flew under battery power, as the lightweight solar cells required are expensive. On 13 August 2001, the Helios prototype established an absolute altitude record for a non-rocket-propelled aircraft of 29,420 meters (96,500 feet), flying from the Hawaiian island of Kauai. It still lacked an energy storage system.

There was a little disappointment that the UAV did not clear 30,450 meters (100,000 feet), but takeoff of the Helios was postponed by cloud cover, limiting the amount of daylight available for its climb, and the "miss distance" was too small to make the cost of a second altitude attempt worthwhile. Work continued on bringing the Helios up to a production specification, but the aircraft was finally lost in a crash on Kauai on 26 June 2003.

* It is not clear if AeroVironment plans to move on to a bigger and better Helios. In June 2005, the company began flying a demonstrator for the "Global Observer", which will be a HALE UAV powered strictly by fuel cells burning hydrogen, capable of carrying a 450 kilogram (1,000 pound) payload for up to 10 days. The demonstrator features a wing with eight little motors along the lines of the Helios wing, but the overall configuration is more conventional, with a bulbous central fuselage and a tail assembly. There was consideration of using solar cells with the UAV, but an analysis of cost versus benefits showed it didn't make sense.

AeroVironment has now proposed a series of production Global Observers. The "GO-1" would have a wingspan of 48.8 meters (160 feet), a gross takeoff weight of 1,800 kilograms (3,970 pounds), a payload of 160 kilograms (350 kilograms), and an endurance of seven days. The "GO-2" would have an 80 meter (262 foot) wingspane, a gross takeoff weight of 4,100 kilograms (9,040 pounds), a payload of 450 kilograms (990 pounds), and an endurance of eight days.

* If AeroVironment appears to be moving away from the solar-powered UAV, at least for the time being, AC Propulsion (ACP), a startup company based in San Dimas, California, is trying to move into the vacuum. During the summer of 2005, ACP began test flights of their own solar-powered UAV, the "SoLong", with an early flight lasting two days.

The SoLong is a small UAV, with a weight of 12.8 kilograms (28.2 pounds), a span of 4.76 meters (15 feet 7 inches), and a 1 horsepower electric motor. It has a conventional sailplane appearance, with an upright vee tail; the wings are covered by solar sails, with night power provided by a bank of lithium batteries. The SoLong is strictly a technology demonstrator, with no real operational payload, and is intended to lead to larger operational machines.

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