NACA and NASA, Part IX

Galileo probe

            Galileo was an unmanned spacecraft sent by NASA to study the planet Jupiter and its moons. Named after the astronomer and Renaissance pioneer Galileo Galilei, it was launched on October 18, 1989 by the Space Shuttle Atlantis on the STS-34 mission. It arrived at Jupiter on December 7, 1995, a little more than six years later, via gravitational assist flybys of Venus and Earth.

Despite antenna problems, Galileo conducted the first asteroid flyby near 951 Gaspra, discovered the first asteroid moon Dactyl around the asteroid 243 Ida, was the first spacecraft to orbit Jupiter, and launched the first probe into Jupiter's atmosphere.

The spacecraft measured the atmospheric composition of Jupiter and directly observed ammonia clouds, which seem to be created by an outflow from the lower depths of Jupiter's atmosphere. Galileo also registered Io's volcanism and the plasma interactions between its and Jupiter's atmospheres. Other studies gave support for the popular theory of liquid oceans under the icy surface of Europa. There was also indications of similar liquid-saltwater layers under the surfaces of Ganymede and Callisto, while Ganymede was shown to possess a magnetic field. New evidence was also found for the existence of exospheres around Europa, Ganymede, and Callisto.

It was furthermore discovered that Jupiter's faint ring system is formed by dust from impacts on the four small inner moons. The extent and structure of Jupiter's magnetosphere was also mapped.

Galileo also provided the only direct observation of comet Shoemaker-Levy 9's impact into the atmosphere of Jupiter in 1994.

On September 21, 2003, after 14 years in space and 8 years of service in the Jovian system, Galileo's mission was terminated by sending the orbiter into Jupiter's atmosphere at a speed of nearly 50 kilometres per second to avoid any chance of it contaminating local moons with bacteria from Earth. Of particular concern was the ice-crusted moon Europa, which, thanks to Galileo, scientists now suspect harbors a saltwater ocean beneath its surface.

            Galileo's launch had been significantly delayed by the hiatus in Space Shuttle launches that occurred after the Challenger space shuttle disaster. New safety protocols introduced as a result of the disaster forced Galileo to use a lower-powered upper stage booster rocket, instead of a Centaur booster rocket, to send it from Earth orbit to Jupiter. Several gravitational slingshots, called "VEEGA"s or Venus Earth Earth Gravity Assist maneuvers, provided the additional velocity required to reach its destination: Venus was flown by on February 10, 1990, and Earth twice, on December 8, 1990, and again on December 8, 1992. Along the way, Galileo performed close observation of the asteroids 951 Gaspra (October 29, 1991) and 243 Ida (August 28, 1993), and discovered Ida's moon Dactyl. In 1994, Galileo was perfectly positioned to watch the fragments of comet Shoemaker-Levy 9 crash into Jupiter. Terrestrial telescopes had to wait to see the impact sites as they rotated into view.

Galileo's prime mission was a two-year study of the Jovian system. The spacecraft traveled around Jupiter in elongated ellipses, each orbit lasting about two months. The differing distances from Jupiter afforded by these orbits allowed Galileo to sample different parts of the planet's extensive magnetosphere. The orbits were designed for close-up flybys of Jupiter's largest moons. Once Galileo's prime mission was concluded, an extended mission followed, starting on December 7, 1997; the spacecraft made a number of daring close flybys of Jupiter's moons Europa and Io. The closest approach was 180 km (112 mi) on October 15, 2001. The radiation environment near Io in particular was very unhealthy for Galileo's systems, and so these flybys were saved for the extended mission when loss of the spacecraft would be more acceptable.

Galileo's cameras were deactivated on January 17, 2002, after they had sustained irreparable radiation damage. NASA engineers were able to recover the damaged tape recorder electronics, and Galileo continued to return scientific data until it was deorbited in 2003, performing one last scientific experiment —a measurement of the moon Amalthea's mass as the spacecraft swung by it.

The Jet Propulsion Laboratory built the Galileo spacecraft and managed the Galileo mission for NASA. Germany supplied the propulsion module. NASA's Ames Research Center managed the probe, which was built by Hughes Aircraft Company.

At launch, the orbiter and probe together had a mass of 2,564 kilograms (5,653 pounds) and stood seven metres tall. One section of the spacecraft rotated at 3 rpm, keeping Galileo stable and holding six instruments that gathered data from many different directions, including the fields and particles instruments. The other section of the spacecraft was an antenna, and data were periodically transmitted to it. Back on the ground,the mission operations team used software containing 650,000 lines of programming code in the orbit sequence design process; 1,615,000 lines in the telemetry interpretation; and 550,000 lines of code in navigation.

The CDH was actively redundant, with two parallel strings running at all times. It was composed of multiplexers (MUX), high-level modules (HLM), low-level modules (LLM), power converters (PC), bulk memory (BUM), data management subsystem bulk memory (DBUM), timing chains (TC), phase lock loops (PLL), Golay coders (GC), and hardware command decodes (HCD).

The spacecraft was controlled by six RCA 1802 Cosmac microprocessor CPUs: four on the spun side and two on the despun side. Each CPU was clocked at about 1.6 MHz, and fabricated on sapphire (silicon on sapphire), which is a radiation-and static-hardened material ideal for spacecraft operation. This microprocessor was the first low-power CMOS processor chip, quite on a par with the 8-bit 6502 that was being built into the Apple II desktop computer at that time. Galileo's attitude control system software was written in the HAL/S programming language, also used in the Space Shuttle program. Memory capacity provided by each BUM was 16K of RAM, while the DBUMs each provided 8K of RAM. The BUMs and DBUMs provided storage for sequences and contain various buffers for telemetry data and interbus communication.

The Propulsion Subsystem consisted of a 400 N main engine and twelve 10 N thrusters, together with propellant, storage and pressurizing tanks and associated plumbing. The 10 N thrusters were mounted in groups of six on two 2-meter booms. The fuel for the system was 925 kg of monomethylhydrazine and nitrogen tetroxide. Two separate tanks held another 7 kg of helium pressurant. The Propulsion Subsystem was developed and built by Daimler Benz Aero Space AG (DASA) (formerly Messerschmitt–Bölkow–Blohm (MBB)) and provided by Germany, the major international partner in Project Galileo.

Solar panels were not a practical solution for Galileo's power needs at Jupiter's distance from the Sun (it would have needed a minimum of 65 square metres (700 ft²) of solar panels); as for batteries, they would have been prohibitively massive due to the technological limitations of the time. The solution adopted consisted of two radioisotope thermoelectric generators (RTGs). The RTGs powered the spacecraft through the radioactive decay of plutonium-238. The heat emitted by this decay was converted into electricity for the spacecraft through the solid-state Seebeck effect. This provided a reliable and long-lasting source of electricity unaffected by the cold space environment and high radiation fields such as those encountered in Jupiter's magnetosphere.

Each GPHS-RTG, mounted on a 5-meter long boom, carried 7.8 kilograms of 238Pu. Each RTG contained 18 separate heat source modules, and each module encased four pellets of plutonium dioxide, a ceramic material resistant to fracturing. The modules were designed to survive a range of hypothetical accidents: launch vehicle explosion or fire, re-entry into the atmosphere followed by land or water impact, and post-impact situations. An outer covering of graphite provided protection against the structural, thermal, and eroding environments of a potential re-entry. Additional graphite components provided impact protection, while iridium cladding of the fuel cells provided post-impact containment. The RTGs produced about 570 watts at launch. The power output initially decreased at the rate of 0.6 watts per month and was 493 watts when Galileo arrived at Jupiter.

As the launch of Galileo neared, anti-nuclear groups, concerned over what they perceived as an unacceptable risk to the public's safety from Galileo's RTGs, sought a court injunction prohibiting Galileo's launch. RTGs had been used for years in planetary exploration without mishap: the Lincoln Experimental Satellites 8/9, launched by the U.S. Department of Defense, had 7% more plutonium on board than Galileo, and the two Voyager spacecraft each carried 80% as much plutonium as Galileo did. However, activists remembered the messy crash of the Soviet Union's nuclear-powered Cosmos 954 satellite in Canada in 1978, and the 1986 Challenger accident had raised public awareness of the possibility of explosive spacecraft failures.

Also, no RTGs had ever been made to swing past the Earth at close range and high speed, as Galileo's Venus-Earth-Earth Gravity Assist trajectory required it to do. This created a novel mission failure modality that might plausibly have entailed total dispersal of Galileo's plutonium in the Earth's atmosphere. Scientist Carl Sagan, for example, a strong supporter of the Galileo mission, said in 1989 that "there is nothing absurd about either side of this argument."

After the Challenger accident, a study considered additional shielding and eventually rejected it, in part because such a design significantly increased the overall risk of mission failure and only shifted the other risks around (for example, if a failure on orbit had occurred, additional shielding would have significantly increased the consequences of a ground impact).

After arriving on December 7, 1995 and completing 35 orbits around Jupiter throughout a nearly eight year mission, the Galileo Orbiter was destroyed during a controlled impact with Jupiter on September 21, 2003.

During that intervening time, Galileo forever changed the way scientists saw Jupiter and provided a wealth of information on the moons orbiting the planet which will be studied for years to come. Culled from NASA's press kit, the top orbiter science results were:

Galileo made the first observation of ammonia clouds in another planet's atmosphere. The atmosphere creates ammonia ice particles from material coming up from lower depths.

 The moon Io was confirmed to have extensive volcanic activity that is 100 times greater than that found on Earth. The heat and frequency of eruptions are reminiscent of early Earth.

 Complex plasma interactions in Io's atmosphere create immense electrical currents which couple to Jupiter's atmosphere.

 Several lines of evidence from Galileo support the theory that liquid oceans exist under Europa's icy surface.

 Ganymede possesses its own, substantial magnetic field - the first satellite known to have one.

 Galileo magnetic data provide evidence that Europa, Ganymede and Callisto have a liquid-saltwater layer under the visible surface.

 Evidence exists that Europa, Ganymede, and Callisto all have a thin atmospheric layer known as a 'surface-bound exosphere'.

 Jupiter's ring system is formed by dust kicked up as interplanetary meteoroids smash into the planet's four small inner moons. The outermost ring is actually two rings, one embedded with the other. There is probably a separate ring along Amalthea's orbit, as well.

The Galileo spacecraft identified the global structure and dynamics of a giant planet's magnetosphere.

The star scanner was a small optical telescope used to provide the spacecraft with an absolute attitude reference. It was also able serendipitously to make scientific discoveries. In the prime mission, it was found that the star scanner was able to detect high energy particles as a noise signal. These data were eventually calibrated to show the particles were predominantly > 2 MeV electrons that were trapped in the Jovian magnetic belts.

A second discovery occurred in 2000. The star scanner was observing a set of stars which included the second magnitude star Delta Velorum. At one point, this star dimmed for 8 hours below the star scanner's detection threshold. Subsequent analysis of Galileo data and work by amateur and professional astronomers showed that Delta Velorum is the brightest known eclipsing binary, brighter at maximum than even Algol. It has a primary period of 45 days and the dimming is just visible with the naked eye.

A final discovery occurred during the last two orbits of the mission. When the spacecraft passed the orbit of Jupiter's moon Amalthea, the star scanner detected unexpected flashes of light that were reflections from moonlets. None of the individual moonlets were sighted twice, hence no orbits were determined and the moonlets did not meet the International Astronomical Union requirements to receive designations. It is believed that these moonlets most likely are debris ejected from Amalthea and form a tenuous, and perhaps temporary, ring.

The late Carl Sagan, pondering the question of whether life on Earth could be easily detected from space, devised a set of experiments in the late 1980s using Galileo's remote sensing instruments to determine if life indeed could be detected during the first Earth flyby of the mission in December 1990. After data acquisition and processing, Sagan et al. published a paper in Nature in 1993 detailing the results of the experiment. Galileo had found what are now referred to as the "Sagan criteria for life"; these were: strong absorption of light at the red end of the visible spectrum (especially over continents) which was caused by absorption by chlorophyll in photosynthesizing plants, absorption bands of molecular oxygen which is also a result of plant activity, infrared absorption bands caused by the ~1 micromole per mole (µmol/mol) of methane in Earth's atmosphere (a gas which must be replenished by either volcanic or biological activity) and modulated narrowband radio wave transmissions uncharacteristic of any known natural source. Galileo's experiments were thus the first ever controls in the newborn science of astrobiological remote sensing.

In December 1992 during Galileo's second gravity assist planetary flyby of Earth, another groundbreaking yet almost entirely unpublicized experiment was done using Galileo to assess the possibility of optical communication with spacecraft by detecting pulses of light from powerful lasers which were to be directly imaged by Galileo's CCD. The experiment, dubbed Galileo OPtical EXperiment or GOPEX, used two separate sites to beam laser pulses to the spacecraft, one at Table Mountain Observatory in California and the other at the Starfire Optical Range in New Mexico. The Table Mountain site used a frequency doubled Neodymium-Yttrium-Aluminium Garnet (Nd:YAG) laser operating at 532 nm with a repetition rate of ~15 to 30 Hz and a pulse power (FWHM) in the tens of megawatts range, which was coupled to a 0.6 meter Cassegrain telescope for transmission to Galileo; the Starfire range site used a similar setup with a larger transmitting telescope (1.5 m). Long exposure (~0.1 to 0.8 s) images using Galileo's 560 nm centered green filter produced images of Earth clearly showing the laser pulses even at distances of up to 6,000,000 km. Adverse weather conditions, restrictions placed on laser transmissions by the U.S. Space Defense Operations Center (SPADOC) and a pointing error caused by the scan platform acceleration on the spacecraft being slower than expected (which prevented laser detection on all frames with less than 400 ms exposure times) all contributed to the reduction of the number of successful detections of the laser transmission to 48 of the total 159 frames taken. Nonetheless, the experiment was considered a resounding success and the data acquired will likely be used in the future to design laser "downlinks" which will send large volumes of data very quickly, from spacecraft to Earth. The scheme is already being studied (as of 2004) for a data link to a future Mars orbiting spacecraft.

On October 29, 1991, two months after entering the asteroid belt, Galileo performed the first ever asteroid encounter by passing about 1,600 kilometers (1,000 miles) from 951 Gaspra at a relative speed of about 8 kilometers per second (18,000 mph). Several pictures of Gaspra were taken along with measurements using the NIMS instrument to indicate composition and physical properties. The last (and best) two images were played back to Earth in November 1991 and June 1992. The imagery revealed a cratered and very irregular body about 19 by 12 by 11 kilometers (12 by 7.5 by 7 miles). The remainder of data taken, including low resolution images of more of the surface, were transmitted in late November 1992.

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Aversa, R., R.V. Petrescu, B. Akash, R.B. Bucinell and J.M. Corchado et al., 2017b. Kinematics and forces to a new model forging manipulator. Am. J. Applied Sci., 14: 60-80.

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Aversa, R., D. Parcesepe, R.V.V. Petrescu, F. Berto and G. Chen et al., 2017d. Process ability of bulk metallic glasses. Am. J. Applied Sci., 14: 294-301.

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Petrescu, F.I., Petrescu, R.V., 2014g Determination of the Yield of Internal Combustion Thermal Engines, International Review of Mechanical Engineering 8(1):62-67.

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Petrescu, F.I.T., A. Apicella, R.V.V. Petrescu, S.P. Kozaitis and R.B. Bucinell et al., 2016b. Environmental protection through nuclear energy. Am. J. Applied Sci., 13: 941-946.

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Aversa, R., Petrescu, RV., Apicella, A., Petrescu, Fit., 2017 Nano-Diamond Hybrid Materials for Structural Biomedical Application, American Journal of Biochemistry and Biotechnology, 13(1): 34-41.

Syed, J., Dharrab, AA., Zafa, MS., Khand, E., Aversa, R., Petrescu, RV., Apicella, A., Petrescu, FIT., 2017 Influence of Curing Light Type and Staining Medium on the Discoloring Stability of Dental Restorative Composite, American Journal of Biochemistry and Biotechnology 13(1): 42-50.

Aversa, R., Petrescu, RV., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Chen, G., Li, S., Apicella, A., Petrescu, FIT., 2017 Kinematics and Forces to a New Model Forging Manipulator, American Journal of Applied Sciences 14(1):60-80.

Aversa, R., Petrescu, RV., Apicella, A., Petrescu, FIT., Calautit, JK., Mirsayar, MM., Bucinell, R., Berto, F., Akash, B., 2017 Something about the V Engines Design, American Journal of Applied Sciences 14(1):34-52.

Aversa, R., Parcesepe, D., Petrescu, RV., Berto, F., Chen, G., Petrescu, FIT., Tamburrino, F., Apicella, A., 2017 Processability of Bulk Metallic Glasses, American Journal of Applied Sciences 14(2): 294-301.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Calautit, JK., Apicella, A., Petrescu, FIT., 2017 Yield at Thermal Engines Internal Combustion, American Journal of Engineering and Applied Sciences 10(1): 243-251.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Apicella, A., Petrescu, FIT., 2017 Velocities and Accelerations at the 3R Mechatronic Systems, American Journal of Engineering and Applied Sciences 10(1): 252-263.

Berto, F., Gagani, A., Petrescu, RV., Petrescu, FIT., 2017 A Review of the Fatigue Strength of Load Carrying Shear Welded Joints, American Journal of Engineering and Applied Sciences 10(1):1-12.

Petrescu, RV., Aversa, R.,  Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Apicella, A., Petrescu, FIT., 2017 Anthropomorphic Solid Structures n-R Kinematics, American Journal of Engineering and Applied Sciences 10(1): 279-291.

Aversa, R., Petrescu, RV., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Chen, G., Li, S., Apicella, A., Petrescu, FIT., 2017 Something about the Balancing of Thermal Motors, American Journal of Engineering and Applied Sciences 10(1):200-217.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Apicella, A., Petrescu, FIT., 2017 Inverse Kinematics at the Anthropomorphic Robots, by a Trigonometric Method, American Journal of Engineering and Applied Sciences, 10(2): 394-411.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Calautit, JK., Apicella, A., Petrescu, FIT., 2017 Forces at Internal Combustion Engines, American Journal of Engineering and Applied Sciences, 10(2): 382-393.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Apicella, A., Petrescu, FIT., 2017 Gears-Part I, American Journal of Engineering and Applied Sciences, 10(2): 457-472.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Apicella, A., Petrescu, FIT., 2017 Gears-Part II, American Journal of Engineering and Applied Sciences, 10(2): 473-483.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Apicella, A., Petrescu, FIT., 2017 Cam-Gears Forces, Velocities, Powers and Efficiency, American Journal of Engineering and Applied Sciences, 10(2): 491-505.

Aversa, R., Petrescu, RV., Apicella, A., Petrescu, FIT., 2017 A Dynamic Model for Gears, American Journal of Engineering and Applied Sciences, 10(2): 484-490.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Kosaitis, S., Abu-Lebdeh, T., Apicella, A., Petrescu, FIT., 2017 Dynamics of Mechanisms with Cams Illustrated in the Classical Distribution, American Journal of Engineering and Applied Sciences, 10(2): 551-567.

Petrescu, RV., Aversa, R., Akash, B., Bucinell, R., Corchado, J., Berto, F., Mirsayar, MM., Kosaitis, S., Abu-Lebdeh, T., Apicella, A., Petrescu, FIT., 2017 Testing by Non-Destructive Control, American Journal of Engineering and Applied Sciences, 10(2): 568-583.

Petrescu, RV., Aversa, R., Li, S., Mirsayar, MM., Bucinell, R., Kosaitis, S., Abu-Lebdeh, T., Apicella, A., Petrescu, FIT., 2017 Electron Dimensions, American Journal of Engineering and Applied Sciences, 10(2): 584-602.

Petrescu, RV., Aversa, R., Kozaitis, S., Apicella, A., Petrescu, FIT., 2017 Deuteron Dimensions, American Journal of Engineering and Applied Sciences, 10(3).

Petrescu RV., Aversa R., Apicella A., Petrescu FIT., 2017 Transportation Engineering, American Journal of Engineering and Applied Sciences, 10(3).

Petrescu RV., Aversa R., Kozaitis S., Apicella A., Petrescu FIT., 2017 Some Proposed Solutions to Achieve Nuclear Fusion, American Journal of Engineering and Applied Sciences, 10(3).

Petrescu RV., Aversa R., Kozaitis S., Apicella A., Petrescu FIT., 2017 Some Basic Reactions in Nuclear Fusion, American Journal of Engineering and Applied Sciences, 10(3).

Petrescu, Relly Victoria; Aversa, Raffaella; Akash, Bilal; Bucinell, Ronald; Corchado, Juan; Berto, Filippo; Mirsayar, MirMilad; Apicella, Antonio; Petrescu, Florian Ion Tiberiu; 2017a Modern Propulsions for Aerospace-A Review, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Aversa, Raffaella; Akash, Bilal; Bucinell, Ronald; Corchado, Juan; Berto, Filippo; Mirsayar, MirMilad; Apicella, Antonio; Petrescu, Florian Ion Tiberiu; 2017b Modern Propulsions for Aerospace-Part II, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Aversa, Raffaella; Akash, Bilal; Bucinell, Ronald; Corchado, Juan; Berto, Filippo; Mirsayar, MirMilad; Apicella, Antonio; Petrescu, Florian Ion Tiberiu; 2017c History of Aviation-A Short Review, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Aversa, Raffaella; Akash, Bilal; Bucinell, Ronald; Corchado, Juan; Berto, Filippo; Mirsayar, MirMilad; Apicella, Antonio; Petrescu, Florian Ion Tiberiu; 2017d Lockheed Martin-A Short Review, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Aversa, Raffaella; Akash, Bilal; Corchado, Juan; Berto, Filippo; Mirsayar, MirMilad; Apicella, Antonio; Petrescu, Florian Ion Tiberiu; 2017e Our Universe, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Aversa, Raffaella; Akash, Bilal; Corchado, Juan; Berto, Filippo; Mirsayar, MirMilad; Apicella, Antonio; Petrescu, Florian Ion Tiberiu; 2017f What is a UFO?, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, RV., Aversa, R., Akash, B., Corchado, J., Berto, F., Mirsayar, MM., Apicella, A., Petrescu, FIT., 2017 About Bell Helicopter FCX-001 Concept Aircraft-A Short Review, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, RV., Aversa, R., Akash, B., Corchado, J., Berto, F., Mirsayar, MM., Apicella, A., Petrescu, FIT., 2017 Home at Airbus, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, RV., Aversa, R., Akash, B., Corchado, J., Berto, F., Mirsayar, MM., Kozaitis, S., Abu-Lebdeh, T., Apicella, A., Petrescu, FIT., 2017 Airlander, Journal of Aircraft and Spacecraft Technology, 1(1).

Petrescu, RV., Aversa, R., Akash, B., Corchado, J., Berto, F., Apicella, A., Petrescu, FIT., 2017 When Boeing is Dreaming – a Review, Journal of Aircraft and Spacecraft Technology, 1(1).

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