* The US National Aeronautics and Space Administration (NASA) has performed extensive experiments with UAVs, even developing UAVs for operations on other planets. This chapter outlines NASA UAV developments.
* 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), tailfins 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 tailfins, 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 fuel leaks made it hazardous to handle. NASA lost interest in the idea, and the concept of a high-altitude UAV was abandoned for the time being.
BACK_TO_TOP* NASA work on high-altitude UAVs was revived in the late 1980s. 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 agency initiated the "Environmental Research Aircraft & Sensor Technology (ERAST)" program in 1994. 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 does appear to have a long-term interest in UAV technology.
BACK_TO_TOP* 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 while the machine glided onto the runway.
* 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.
AURORA FLIGHT SCIENCES PERSEUS-A: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 21.7 meters 71 feet length 7.62 meters 25 feet max loaded weight 826 kilograms 1,820 pounds maximum speed 354 KPH 220 MPH / 190 KT service ceiling 19,800 meters 65,000 feet endurance 24 hours _____________________ _________________ _______________________
* The three-stage turbocharged engine used on the Perseus-B was particularly interesting, unusual and possibly unprecedented. Work on such engines began in the Teal Rain program. One engineer working on the technology suggested that the powerplant could be viewed as a "gas turbine system with an internal-combustion-engine combustion chamber."
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. 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.
AURORA FLIGHT SCIENCES THESEUS: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 42.7 meters 140 feet length 14.9 meters 49 feet payload 340 kilograms 750 pounds max loaded weight 2,500 kilograms 5,500 pounds maximum speed 130 KPH 80 MPH / 70 KT service ceiling 20,000 meters 65,000 feet endurance 50 hours _____________________ _________________ _______________________
Aurora Flight Sciences promoted an improved "Theseus II" follow-on for commercial use, but it doesn't appear anyone bit on the concept. As discussed earlier, NASA also obtained General Atomics UAVs for research purposes, including the Altus and Predator-series machines, as well as three Global Hawks.
BACK_TO_TOP* 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:
SCALED COMPOSITES RAPTOR/TALON: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 20 meters 66 feet length 7.6 meters 25 feet empty weight 370 kilograms 810 pounds max loaded weight 815 kilograms 1,800 pounds maximum speed 450 KPH 280 MPH / 243 KT service ceiling 20,000 meters 65,000 feet endurance 50 hours _____________________ _________________ _______________________
Along with RAPTOR/Talon, BMDO also worked on a solar-powered endurance UAV named "RAPTOR/Pathfinder" that would provide long-range sensors to help RAPTOR/Talon target TBMs.
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).
AEROVIRONMENT RAPTOR/PATHFINDER: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 30.5 meters 100 feet length 2.4 meters 8 feet weight 245 kilograms 541 pounds cruise speed 57 KPH 36 MPH / 31 KT service ceiling 21,000 meters 68,900 feet endurance indefinite (in principle) _____________________ _________________ _______________________
RAPTOR/Pathfinder was not an effective solar HALE UAV. Initial flights were still on battery power, and though it could fly using solar power, the battery storage system didn't have the capacity to keep the aircraft flying all night long.
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.
BACK_TO_TOP* The Pathfinder went into NASA service generally unchanged from its BMDO configuration, except for elimination of two motors, leaving six. 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), the number of motors restored to eight, 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, since the lightweight solar cells required were 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. Pathfinder Plus remained in service up to 2005, with the number of motors reduced to six again after the Helios crash to permit carriage of air sensing booms. It was finally retired in 2005 and is now in the Smithsonian.
BACK_TO_TOP* Along with UAVs for high-altitude research, NASA has also used them for aerodynamic studies. NASA had long had a tradition of flying scale models of aircraft, sometimes with rocket boosters, for aerodynamic tests, but in general these vehicles were basically instrumented flying wind-tunnel test models and were not really UAVs. However, in the early 1970s, NASA built three 3/8ths-scale unpowered drone versions of the new McDonnell Douglas F-15 fighter to confirm that it was as agile as the designers hoped it would be. These three machines were referred to as "remotely piloted research vehicles (RPRVs)" and were taken aloft over Edwards Air Force Base (AFB) in California by the NASA B-52 carrier aircraft, to be released at high altitude. They would glide back to earth and land with retractable skids on the dry lakebed at Edwards. The RPRVs could also be fitted with a parachute to be snagged by a helicopter in flight for recovery, just like the old Lightning Bugs.
Each drone weighed 1,099 kilograms (2,425 pounds) and had a length of 7.01 meters (23 feet). They were made of aluminum, wood, and fiberglass and cost only $250,000 USD each. They provided extremely valuable flight data, and the exercise was regarded as highly successful. At least one remained in NASA service after the F-15 development program was completed, being used to perform spin testing and the like.
* The "Drones for Aerodynamic & Structural Testing (DAST)" program was conducted from 1977 to 1983 at the NASA Langley and Dryden Flight Centers. It involved flights of modified Ryan Firebee II supersonic target drones to test new wing designs and wing control systems. The Firebee II was selected because it had supersonic performance, its wings could be easily replaced, it used only tail-mounted control surfaces, and because it was available at low cost from the US Air Force.
After initial test flights with a Firebee II in its normal configuration but with added instrumentation, NASA fitted a Firebee II with an aeroelastic, supercritical research wing suitable for a Mach 0.98 cruise airliner. A total of ten flights were made, with initial launches from the NASA Boeing B-52 bomber and later from a DC-130 Hercules drone controller aircraft, and a NASA Lockheed F-104 Starfighter performing chase duties. The DAST drones were radio-controlled and recovered by parachute with helicopter snatch. The program encountered difficulties, with two crashes, one in 1980 and one in 1983, and was abandoned after the second crash.
* In the wake of the successful F-15 RPRV program, two "Highly Maneuverable Aircraft Technology (HIMAT)" UAVs were developed by NASA and Rockwell International in the 1970s, and used in 26 flight tests from 1979 to early 1983, with the initial flight on 27 July 1979. The HIMAT UAVs were about half the size of an F-16 fighter.
HIMAT was a joint effort of NASA's Dryden Flight Research Center at Edwards AFB, the NASA Ames Research Center in California, and the Air Force Flight Dynamics Laboratory at Wright-Patterson Air Force Base in Ohio. HIMAT was intended to demonstrate new composite materials, digital flight and engine control systems, and high-maneuverability aerodynamic concepts such as winglets and canards.
Each HIMAT vehicle was a swept-wing canard aircraft with a fighter-like configuration, featuring wings in the rear and horizontal control surfaces in the nose. HIMAT was 7.16 meters (23 feet 6 inches) long, had a wingspan of nearly 4.9 meters (16 feet), and a loaded weight of 1,830 kilograms (4,030 pounds). HIMAT was powered by a GE J85 afterburning turbojet engine with 22.3 kN (2,270 kgp / 5,000 lbf) thrust, the same engine used in the Northrop F-5E fighter. HIMAT's top speed was Mach 1.4, and the UAV could easily out-turn an F-16. About 30% of the airframe was made of composite materials, mostly fiberglass and graphite-epoxy. Cost of the two UAVs was $17.3 million USD.
The HIMATs were launched at high altitude from NASA's B-52 carrier aircraft. They were remotely piloted from the ground, using a TV imager to give the "pilot" a view of what was going on. A Lockheed F-104 chase plane, fitted with auxiliary remote controls, was used as an emergency backup. At the end of a test flight, the ground-based pilot would land the HIMAT on the dry lakebed at Edwards. The HIMAT was designed to be easily modified to a number of alternate aerodynamic configurations, such as forward-swept wings, but it appears that these alternate configurations were never implemented. The two HIMAT UAVs are now on display, one at the NASA Ames Research Center, and the other at the Smithsonian Air & Space Museum in Washington DC.
* HIMAT seemed like a good enough idea to be revived in a new form in the following decade. In March 1996, McDonnell Douglas, working with NASA, rolled out the "X-36", a quarter-scale flying model of a stealthy manned jet fighter. The X-36 was an arrowhead-like aircraft with chiseled lines and no tailfin, performing turns with wingtip "drag rudders". It was designed to study technologies for building agile, stealthy fighters.
The X-36 was a little over 5.5 meters (18 feet) long, including its test boom, with a wingspan of 3.17 meters (10.4 feet), a weight of almost 590 kilograms (1,300 pounds), an aluminum frame with graphic-epoxy skin, and a small Williams Research turbofan engine with 3.1 kN (320 kgp / 700 lbf) thrust, giving it a top speed of Mach 0.6. It had a vectored exhaust for maneuverability, was remotely piloted from the ground using a TV camera in the cockpit to keep the operator informed, and had a parachute for emergency recovery.
Total program costs were kept low by avoiding redundancy in flight systems and by designing the X-36 to take off and land on its own, eliminating the need to use NASA's B-52 as a launch platform. Two X-36s were built, with 31 test flights beginning in May 1997 and ending in November of that year. The two aircraft were then put in storage at NASA Dryden flight center for other possible users, though use of them has been limited by the fact that some of the data obtained by the X-36 program remains classified.
* In 1996, NASA introduced a small drone named LoFLYTE that featured a wedge-shaped "waverider" configuration designed for hypersonic flight. In reality, LoFLYTE had a top speed of about 450 KPH (280 MPH), having been built to study flight control systems for high-speed aircraft based on "neural net" logic systems. LoFLYTE was 2.5 meters (8 feet 4 inches) long, had retractable landing gear, and was powered by a turbofan engine with 225 newtons (23 kgp / 50 lbf) thrust. It was built by Accurate Automation with funding from NASA, the USAF, and the US Navy.
In 2001, NASA followed up the LoFLYTE program with a more focused UAV effort to support the agency's X-43 experimental hypersonic propulsion vehicle program. NASA researchers wanted to know how a vehicle designed for hypersonic flight would handle at the low speeds experienced after ground takeoff and before landing, and so decided to build two low-cost UAVs to find out.
The "X-43ALS", where the "LS" stands for "low speed", was built by Accurate Automation. It resembled the X-43 hypersonic vehicle aerodynamically, had a length of 3.7 meters (12 feet), weighed about 82 kilograms (180 pounds), and was powered by a small jet engine that provided about 540 newtons (55 kgp / 120 lbf) thrust. Top speed was about 550 KPH (345 MPH). First flights were in early 2002.
The "X-43BLS HYSID (Hypersonic Systems Integrated Demonstrator)" was built by SWB Turbines. It was a larger machine, with a different configuration that featured canard control surfaces. The X-43BLS had a length of 4.6 meters (15 feet), a wingspan of 2.75 meters (9 feet), a weight of 32 kilograms (180 pounds), and was powered by three SWB-100 turbojets, with 475 newtons (48.5 kgp / 107 lbf) thrust each.
* In 2007, NASA test-flew another research UAV, the "X-48B", which was a demonstrator for a "blended wing body (BWB)" transport, built in cooperation with the AFRL and with Boeing as the prime contractor -- though the airframe was actually built by Cranfield Aerospace of the UK under subcontract. It was more or less a flying wing, with a stingray-like cranked delta configuration, winglets, three small JetCat turbojet engines mounted on the rear, and fixed tricycle landing gear. The X-48B had a span of 6.4 meters (21 feet), a wing area of 9.3 square meters (100 square feet), and was powered by three JetCat P200 RC modeler turbojets with 245 N (25 kgp / 55 lbf) thrust each. Maximum speed was a modest 220 KPH (135 MPH).
The X-48B was built of composite materials, with the airframe construction by Cranfield Aerospace in the UK as a Boeing subcontractor. Two were built, with the second machine acting as a backup in case the first came to ruin.
In late 2010, it will be reconfigured into the "X-48C", initially by swapping the triple turbojets for twin geared turbofans with a thrust of 355 N (36 kgp / 80 lbf) thrust each. After validation of the new engines, the winglets will be removed, replaced by twin tailfins flanking the engines to reduce their noise signature.
BACK_TO_TOP* One of the really interesting applications of UAVs is their potential use for Mars exploration. The idea of flying through the thin air of Mars precedes manned spaceflight. Back in the 1950s, COLLIER'S magazine published a popular series of articles by space pioneers promoting the exploration of space, with spectacular illustrations by painter Chesley Bonestell that are still impressive today. One of the most prominent pioneers, Werner von Braun, envisioned spacecraft landing on Mars using huge long wings.
This turned out to be overoptimistic, since space probes sent to fly past Mars in the 1960s showed that the Martian atmosphere was about ten times thinner than had been believed, with less than one percent of the atmospheric density of the Earth at sea level. Building something to fly through such a thin atmosphere was no simple task.
The Mini-Sniffer high-altitude drone of the 1970s, discussed earlier. suggested a workable solution to the problem. Its hydrazine engine could operate in the thin carbon-dioxide atmosphere of Mars. Although the atmosphere on Mars at ground level is thinner than the Earth's at a height of 21 kilometers (70,000 feet), Martian gravity is only a third that of the Earth's, and so the Mini-Sniffer could be regarded as a prototype of a Mars airplane.
In the second half of the 1970s, many researchers in the NASA Mars community were very interested in development of a Mars airplane, since the Viking landings in 1976 had done much to generate enthusiasm for Mars exploration. In 1978, members of the Mars community got in touch with Dale Reed, the father of the Mini-Sniffer, and discussed the possibilities for a Mars airplane.
That was in the days when NASA thought in grand terms, and some of the concepts for Mars airplanes were impressive. The biggest had a wingspan of 21 meters (70 feet) and a mass of 545 kilograms (1,200 pounds). It had an inverted-vee tail, a configuration that would be incorporated into Earth-based drones in the coming decades. The Mars airplane had to be folded to fit into an "aeroshell", shaped like a shallow cone and covered with a heat-resistant material, in order to survive falling into the Martian atmosphere at high speed. Once the aeroshell completed entry into the atmosphere, a parachute would extract the Mars airplane, which would unfold, start its engine, and fly away.
Initially, the Mars airplane was to simply crash at the end of its flight, but the planetary scientists involved in the discussions suggested that its sensors might be useful even when the Mars airplane was grounded after it ran out of fuel. If the airplane could land and take off again, so much the better. The airplane could fly around and explore for a time, land to take samples or simply wait for updated mission flight plans, and then take off again to fly to other sites on the planet.
To explore landing technologies, Reed took a sailplane that had a high tee tail, and connected a cable to pivot the tailplane up from the rear. Pivoting up the tailplane pitched the sailplane's nose up, causing it to float down in a reasonably controlled fashion. A Mars airplane could use hydrazine thrusters to make a soft landing, and use the thrusters to launch itself again.
* The investigations resulted in a scheme to send twelve airplanes to Mars. Three spacecraft would be launched, each with an aeroshell derived from the Viking Mars landers, and with each aeroshell carrying four airplanes. The aircraft would have a maximum range of up to 5,600 kilometers (3,500 miles), and the fleet would be able to explore Mars in great detail over wide areas. The plan was too ambitious and never went beyond the "paper plane" stage. NASA gave up on Mars airplanes in the 1980s, and in fact NASA planetary science missions fell on hard times in that decade. However, research on aircraft technologies for human powered and high altitude flight that were applicable to Mars airplane designs continued.
In 1992, NASA introduced the "Discovery" program to develop low-cost space probes, reviving the agency's sluggish planetary exploration efforts. One early Discovery proposal was for a "Mars Airplane" mission. The proposal was made by John Langford, who ran Aurora Flight Sciences, builder of the first ERAST drones for high altitude research.
One of the veterans of the NASA Mars Airplane effort in the 1970s, Larry Lemke of NASA Ames, came up with another Mars Airplane proposal. Lemke's proposal was based on a scaled-down 180 kilogram (400 pound) version of one of the big NASA Mars airplanes designed in the 1970s, and envisioned it hopping from site to site, taking pictures and obtaining surface samples. There were other Mars Airplane proposals. NASA Ames also suggested a flying wing design named MAGE, and a team formed by NASA Jet Propulsion Laboratory (JPL), AeroVironment Corporation, and others suggested a mission that would drop six gliders over the length of the huge Vallis Marineris canyon on Mars.
* NASA didn't bite on the Mars Airplane proposals, at least not immediately. A Princeton University physicist named Edgar Choneri was the one who got the ball rolling again. Choneri noticed the fact the 2003 Mars window coincided with the centennial of the Wright Brothers flight in 1903, and mentioned it to Norman Augustine, a former chief executive of Lockheed Martin who was living in Princeton. Augustine had NASA Administrator Daniel S. Goldin's ear and sold him on the concept. In early 1999, Goldin announced that the agency planned to send a small robot aircraft to Mars, to arrive on 17 December 2003 to commemorate the first flight of the Wright Brothers' aircraft, exactly a century before.
The Mars Airplane effort was one of the low-cost experimental "Mars Micromissions" that NASA was planning in cooperation with CNES, the French space agency, and was partly intended to serve as a project that would bridge the gap between NASA's aeronautics and space research centers. Bridging the gap proved a little troublesome, but after some wrangling on who should do what, NASA's Langley Research Center in Hampton, Virginia, was assigned to build the Mars Airplane for launch in November 2002. The only catch was that the Mars Airplane project had to be done on a shoestring budget. These missions were to be launched as microspacecraft payloads on an French Ariane V booster, hitching a ride into space as the Ariane put communications satellites or other payloads into Earth orbit. A microspacecraft would be tossed off into space on a highly elliptical orbit, and then sent on Moon flybys that would eventually "slingshot" it towards Mars.
The Mars Airplane microspacecraft was constrained to fit into an aeroshell no more than about 76 centimeters (30 inches) in diameter. This meant a very small airplane that had to fold up into a compact package, implying a complicated folding scheme. To make matters worse, the thin Martian atmosphere would not provide enough resistance to help unfold the airplane, and so it had to be unfolded with springs, increasing weight and complexity.
NASA Langley issued a request to potential contractors for a Mars Airplane in September 1999. The request described general specifications for what the Mars Airplane had to do, but did not specify how it was to be implemented. However, Langley had investigated some possibilities on their own to focus their own thinking and provide some hints to contractors. Langley came up with a number of designs, focusing primarily on aircraft powered by a hydrazine thruster rocket, which the design engineers felt would be simpler and more reliable than a propeller-driven design using a hydrazine engine. Some of the designs used straight wings, others had swept wings.
The designs all had to confront the difficulties imposed by the thin Martian atmosphere, which reduced lift to a bare minimum. For example, once deployed, the Mars Airplane would fall like a brick for several kilometers until it finally obtained enough lift to fly straight and level. Even when it was flying it would have very limited maneuverability, with, for example, a turning radius of several kilometers.
The Mars Airplane would have to use a preprogrammed autopilot, since the time lags in communications between Mars and Earth were far too long to allow it to be remotely controlled. It would carry a two kilogram (4.4 pound) science payload, with cameras for observing terrain, a magnetometer to measure magnetic fields, and a miniaturized spectrometer to perform analyses of materials. Data from the Mars Airplane would be sent to a orbiting spacecraft for storage and then relay it back to Earth. Dependence on an orbiter meant the Mars Airplane wouldn't be able to usefully fly for longer than about 20 minutes, the total amount of time an orbiter was in line of sight.
* Unfortunately, after the loss of two NASA Mars probes in 1999, the agency was forced to reconsider Mars efforts, and Mars Airplane work was put on hold. Some of the companies involved with Mars Airplane studies have continued research at a low level. NASA is now conducting a series of low-cost planetary "Scout" missions, and one of the early proposals was for a Mars airplane, designated the "Aerial Regional-scale Environmental Survey (ARES)". ARES was designed by NASA Langley and Aurora Flight Sciences, and of course it was just a continuation of Langley's earlier work. Langley researchers had already tested a 50% scale prototype, named the "Mars Eagle", in the fall of 2002.
There was no commitment to ARES, but the idea hasn't gone away. More recently, in 2008 the Swiss Federal Institute of Technology in Zurich flew a demonstrator of a solar-powered Mars aircraft for a European Space Agency research program. Still, nobody is ready to fly an airplane on Mars just yet.
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