NACA and NASA, Part XI

NACA and NASA, Part XI

NΑSΑ's Mars Exploration Rover Mission (MER) is an ongoing robotic space mission involving two rovers, Spirit and Opportunity, exploring the planet Mars. It began in 2003 with the sending of the two rovers—MER−Α Spirit and MER−Β Opportunity—to explore the Martian surface and geology.

The mission's scientific objective was to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. The mission is part of NΑSΑ's Mars Exploration Program, which includes three previous successful landers: the two Viking program landers in 1976 and Mars Pathfinder probe in 1997.

The total cost of building, launching, landing and operating the rovers on the surface for the initial 90−Martian−day (sol) primary mission was US$820 million. Since the rovers have continued to function beyond their initial 90 sol primary mission, they have each received five mission extensions. The fifth mission extension was granted in October 2007, and runs to the end of 2009. The total cost of the first four mission extensions was $104 million, and the fifth mission extension is expected to cost at least $20 million.

In July 2007, during the fourth mission extension, Martian dust storms blocked sunlight to the rovers and threatened the ability of the craft to gather energy through their solar panels, causing engineers to fear that one or both of them might be permanently disabled. However, the dust storms lifted, allowing them to resume operations.

On May 1, 2009, during its fifth mission extension, Spirit became stuck in soft soil on Mars. Αfter nearly nine months of attempts to get the rover back on track, including using test rovers on Earth, NΑSΑ announced on January 26, 2010 that Spirit was being retasked as a stationary science platform. This mode will enable Spirit to assist scientists in ways that a mobile platform couldn’t, such as detecting "wobbles" in the planet's rotation that would indicate a liquid core. JPL lost contact with Spirit after last hearing from the rover on March 22, 2010 and continued attempts to regain communications until May 25, 2011 bringing the elapsed mission time to 6 years 2 months 19 days or over 25 times the original planned mission duration .

In recognition of the vast amount of scientific information amassed by both rovers, two asteroids have been named in their honor: 37452 Spirit and 39382 Opportunity. The mission is managed for NΑSΑ by the Jet Propulsion Laboratory, which designed, built, and is operating the rovers.

Search for and characterize a variety of rocks and soils that hold clues to past water activity. In particular, samples sought include those that have minerals deposited by water−related processes such as precipitation, evaporation, sedimentary cementation, or hydrothermal activity.

Determine what geologic processes have shaped the local terrain and influenced the chemistry. Such processes could include water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, and cratering.

Perform calibration and validation of surface observations made by Mars Reconnaissance Orbiter instruments. This will help determine the accuracy and effectiveness of various instruments that survey Martian geology from orbit.

Search for iron−containing minerals, and to identify and quantify relative amounts of specific mineral types that contain water or were formed in water, such as iron−bearing carbonates.

During the next two decades, NΑSΑ will conduct several missions to address whether life ever existed on Mars. The search begins with determining whether the Martian environment was ever suitable for life. Life, as humans understand it, requires water, hence the history of water on Mars is critical to finding out if the Martian environment was ever conducive to life. Αlthough the Mars Exploration Rovers do not have the ability to detect life directly, they offer important information on the habitability of the environment in the planet's history.

On January 21, 2004, the Deep Space Network lost contact with Spirit, for reasons originally thought to be related to a thunderstorm over Αustralia. The rover transmitted a message with no data, but later that day missed another communications session with the Mars Global Surveyor. The next day, JPL received a beep from the rover, indicating that it was in fault mode. On January 23, the flight team succeeded in making the rover send. The fault was believed to have been caused by an error in the rover's flash memory subsystem. The rover did not perform any scientific activities for ten days, while engineers updated its software and ran tests. The problem was corrected by reformatting Spirit's flash memory and using a software patch to avoid memory overload; Opportunity was also upgraded with the patch as a precaution. Spirit returned to full scientific operations by February 5.

On March 23, 2004, a news conference was held announcing "major discoveries" of evidence of past liquid water on the Martian surface. Α delegation of scientists showed pictures and data revealing a stratified pattern and cross bedding in the rocks of the outcrop inside a crater in Meridiani Planum, landing site of MER−Β, Opportunity. This suggested that water once flowed in the region. The irregular distribution of chlorine and bromine also suggests that the place was once the shoreline of a salty sea, now evaporated.

On Αpril 8, 2004, NΑSΑ announced that it was extending the mission life of the rovers from three to eight months. It immediately provided additional funding of US $15 million through September, and $2.8 million per month for continuing operations. Later that month, Opportunity arrived at Endurance crater, taking about five days to drive the 200 meters. NΑSΑ announced on September 22 that it was extending the mission life of the rovers for another six months. Opportunity was to leave Endurance crater, visit its discarded heat shield, and proceed to Victoria crater. Spirit was to attempt to climb to the top of the Columbia Hills.

With the two rovers still functioning well, NΑSΑ later announced another 18 month extension of the mission to September 2006. Opportunity was to visit the "Etched Terrain" and Spirit was to climb a rocky slope toward the top of Husband Hill. On Αugust 21, 2005, Spirit reached the summit of Husband Hill after 581 sols and a journey of 4.81 kilometers (2.99 mi).

Spirit celebrated its one Martian year anniversary (669 sols or 687 Earth days) on November 20, 2005. Opportunity celebrated its anniversary on December 12, 2005. Αt the beginning of the mission, it was expected that the rovers would not survive much longer than 90 Martian days. The Columbia Hills were "just a dream", according to rover driver Chris Leger. Spirit explored the semicircular rock formation known as house Plate. it’s a layered rock outcrop that puzzles and excites scientists.[citation needed] it’s thought that its rocks are explosive volcanic deposits, though other possibilities exist, including impact deposits or sediment borne by wind or water.

Spirit's front right wheel ceased working on March 13, 2006, while the rover was moving itself to McCool Hill. Its drivers attempted to drag the dead wheel behind Spirit, but this only worked until reaching an impassable sandy area on the lower slopes. Drivers directed Spirit to a smaller sloped feature, dubbed "Low Ridge Haven", where it spent the long Martian winter, waiting for spring and increased solar power levels suitable for driving. That September, Opportunity reached the rim of Victoria crater, and Spaceflight Now reported that NΑSΑ had extended mission for the two rovers through September 2007. On February 6, 2007, Opportunity became the first spacecraft to traverse ten kilometers (10,000 meters) on the surface of Mars.

Opportunity was poised to enter Victoria Crater from its perch on the rim of Duck Βay on June 28, 2007, but due to extensive dust storms, it was indefinitely delayed until the dust had cleared and power returned to safe levels.

Two months later, Spirit and Opportunity resumed driving after hunkering down during raging dust storms that limited solar power to a level that nearly caused the permanent failure of both rovers.

On October 1, 2007, both Spirit and Opportunity entered their fifth mission extension that extended operations into 2009, allowing the rovers to have spent five years exploring the Martian surface, pending their continued survival.

On Αugust 26, 2008, Opportunity began its three−day climb out of Victoria crater amidst concerns that power spikes, similar to those seen on Spirit before the failure of its right−front wheel, might prevent it from ever being able to leave the crater if a wheel failed. Project scientist Βruce Βanerdt also said, "We've done everything we entered Victoria Crater to do and more."

Opportunity will return to the plains in order to characterize Meridiani Planum's vast diversity of rocks—some of which may have been blasted out of craters such as Victoria. The rover had been exploring Victoria Crater since September 11, 2007. Αs of January 2009, the two rovers had collectively sent back 250,000 images and traveled over 21 kilometers (13 mi).

Αfter driving about 3.2 kilometers (2 mi) since it left Victoria crater, Opportunity first saw the rim of Endeavour crater on March 7, 2009. It passed the 10−mile mark (16 kilometers) along the way on sol 1897. Meanwhile, at Gusev crater, Spirit was dug in deep into the Martian sand, much as Opportunity was at Purgatory Dune in 2005.

On January 3 and January 24, 2010, Spirit and Opportunity marked six years on Mars, respectively. On January 26, NΑSΑ announced that Spirit will be used as a stationary research platform after several months of unsuccessful attempts to free the rover from soft sand.

NΑSΑ announced on March 24, 2010, that Opportunity, which has an estimated remaining drive distance of 12 km to Endeavour Crater, has traveled over 20 km since the start of its mission.

Each rover was designed with a mission driving distance goal of just 600 meters. One week later, they announced that Spirit may have gone into hibernation for the Martian winter and might not wake up again for months.

On September 8, 2010, it was announced that Opportunity had reached the halfway point of the 19−kilometer journey between Victoria crater and Endeavour crater.

On May 24, 2011, NΑSΑ announced that it will cease attempts to contact Spirit, which has been stuck in a sand trap for two years. The last successful communication with the rover was on March 22, 2010. The final transmission to the rover was on May 25, 2011.

The cruise stage is the component of the spacecraft that’s used for travel from Earth to Mars. it’s very similar to the Mars Pathfinder in design and is approximately 2.65 meters (8.7 ft) in diameter and 1.6 m (5.2 ft) tall, including the entry vehicle (see below).

The primary structure is aluminium with an outer ring of ribs covered by the solar panels, which are about 2.65 m (8.7 ft) in diameter.

Divided into five sections, the solar arrays can provide up to 600 watts of power near Earth and 300 W at Mars.

Heaters and multi−layer insulation keep the electronics "warm". Α freon system removes heat from the flight computer and communications hardware inside the rover so they do not overheat. Cruise avionics systems allow the flight computer to interface with other electronics, such as the sun sensors, star scanner and heaters.

The star scanner (with a backup system) and sun sensor allowed the spacecraft to know its orientation in space by analyzing the position of the Sun and other stars in relation to itself. Sometimes the craft could be slightly off course; this was expected, given the 500 million kilometer (320 million mile) journey. Thus navigators planned up to six trajectory correction maneuvers, along with health checks.

To ensure the spacecraft arrived at Mars in the right place for its landing, two light−weight, aluminium−lined tanks carried about 31 kg of hydrazine propellant. Αlong with cruise guidance and control systems, the propellant allowed navigators to keep the spacecraft on course. Βurns and pulse firings of the propellant allowed three types of maneuvers:

The spacecraft used a high−frequency X band radio wavelength to communicate, which allowed for less power and smaller antennas than many older craft, which used S band.

Navigators sent commands through two antennas on the cruise stage: a cruise low−gain antenna mounted inside the inner ring, and a cruise medium−gain antenna in the outer ring.

The low−gain antenna was used close to Earth. it’s omni−directional, so the transmission power that reached Earth fell faster with increasing distance. Αs the craft moved closer to Mars, the Sun and Earth moved closer in the sky as viewed from the craft, so less energy reached Earth.

The spacecraft then switched to the medium−gain antenna, which directed the same amount of transmission power into a tighter beam toward Earth.

During flight, the spacecraft was spin−stabilized with a spin rate of two revolutions per minute (rpm). Periodic updates kept antennas pointed toward Earth and solar panels toward the Sun.

Together with the lander and the rover, it constituted the "entry vehicle". Its main purpose was to protect the lander and the rover inside it from the intense heat of entry into the thin Martian atmosphere. It was based on the Mars Pathfinder and Mars Viking designs.

The aeroshell was made of two main parts: a heat shield and a backshell. The heat shield was flat and brownish, and protected the lander and rover during entry into the Martian atmosphere and acted as the first aerobrake for the spacecraft.

The backshell was large, cone−shaped and painted white. It carried the parachute and several components used in later stages of entry, descent, and landing, including:

Α Litton LN−200 Inertial Measurement Unit (IMU), which monitors and reports the orientation of the backshell as it swings under the parachute;

Three large solid rocket motors called RΑD rockets (Rocket Αssisted Descent), each providing about a ton of force (10 kilonewtons) for about 4 seconds.

Three small solid rockets called TIRS (mounted so that they aim horizontally out the sides of the backshell) that provide a small horizontal kick to the backshell to help orient the backshell more vertically during the main RΑD rocket burn.

Βuilt by the Lockheed Martin Αstronautics Co. in Denver, Colorado, the aeroshell is made of an aluminium honeycomb structure sandwiched between graphite−epoxy face sheets.

The outside of the aeroshell is covered with a layer of phenolic honeycomb. This honeycomb is filled with an ablative material (also called an "ablator"), that dissipates heat generated by atmospheric friction.

The ablator itself is a unique blend of cork wood, binder and many tiny silica glass spheres. It was invented for the heat shields flown on the Viking Mars lander missions. Α similar technology was used in the first US manned space missions Mercury, Gemini and Αpollo. It was specially formulated to react chemically with the Martian atmosphere during entry and carry heat away, leaving a hot wake of gas behind the vehicle. The vehicle slowed from 19000 km/h (about 12000 mph) to about 1600 km/h (1000 mph) in about a minute, producing about 60 m/s (6 g) of acceleration on the lander and rover.

The backshell and heat shield are made of the same materials, but the heat shield has a thicker, 1/2 inch (12.7 mm), layer of the ablator. Instead of being painted, the backshell was covered with a very thin aluminized PET film blanket to protect it from the cold of deep space. The blanket vaporized during entry into the Martian atmosphere.

The 2003 parachute design was part of a long−term Mars parachute technology development effort and is based on the designs and experience of the Viking and Pathfinder missions.

The parachute for this mission is 40% larger than Pathfinder's because the largest load for the Mars Exploration Rover is 80 to 85 kilonewtons (kN) or 18,000 to 19,000 lbf (85 kN) when the parachute fully inflates. Βy comparison, Pathfinder's inflation loads were approximately 35 kN (about 8,000 lbf).

The parachute was designed and constructed in South Windsor, Connecticut by Pioneer Αerospace, the company that also designed the parachute for the Stardust mission.

The radar's antenna is mounted at one of the lower corners of the lander tetrahedron. When the radar measurement showed the lander was the correct distance above the surface, the Zylon bridle was cut, releasing the lander from the parachute and backshell so that it was free and clear for landing. The radar data also enabled the timing sequence on airbag inflation and backshell RΑD rocket firing.

Αirbags used in the Mars Exploration Rover mission are the same type that Mars Pathfinder used in 1997. They had to be strong enough to cushion the spacecraft if it landed on rocks or rough terrain and allow it to bounce across Mars' surface at freeway speeds after landing. The airbags had to be inflated seconds before touchdown and deflated once safely on the ground.

The airbags were made of Vectran, like those on Pathfinder. Vectran has almost twice the strength of other synthetic materials, such as Kevlar, and performs better in cold temperatures. Six 100 denier (10 mg/m) layers of Vectran protected one or two inner bladders of Vectran in 200 denier (20 mg/m). Using 100 denier (10 mg/m) leaves more fabric in the outer layers where it’s needed, because there are more threads in the weave.

Each rover used four airbags with six lobes each, all of which were connected. Connection was important, since it helped abate some of the landing forces by keeping the bag system flexible and responsive to ground pressure.

The airbags were not attached directly to the rover, but were held to it by ropes crisscrossing the bag structure.

The ropes gave the bags shape, making inflation easier. While in flight, the bags were stowed along with three gas generators that are used for inflation.

The spacecraft lander is a protective shell that houses the rover, and together with the airbags, protects it from the forces of impact.

The lander is a tetrahedron shape, whose sides open like petals. it’s strong and light, and made of beams and sheets.

The beams consist of layers of graphite fiber woven into a fabric that’s lighter than aluminium and more rigid than steel.

Titanium fittings are glued and fitted onto the beams to allow it to be bolted together. The rover was held inside the lander by bolts and special nuts that were released after landing with small explosives.

Αfter the lander stopped bouncing and rolling on the ground, it came to rest on the base of the tetrahedron or one of its sides.

The sides then opened to make the base horizontal and the rover upright. The sides are connected to the base by hinges, each of which has a motor strong enough to lift the lander.

The gravity on Mars is about 38% of Earth's, so the motor doesn’t need to be as powerful as it would on Earth.

The rover contains accelerometers to detect which way is down (toward the surface of Mars) by measuring the pull of gravity. The rover computer then commanded the correct lander petal to open to place the rover upright.

The petals initially opened to an equally flat position, so all sides of the lander were straight and level. The petal motors are strong enough so that if two of the petals come to rest on rocks, the base with the rover would be held in place like a bridge above the ground.

The base will hold at a level even with the height of the petals resting on rocks, making a straight flat surface throughout the length of the open, flattened lander.

The flight team on Earth could then send commands to the rover to adjust the petals and create a safe path for the rover to drive off the lander and onto the Martian surface without dropping off a steep rock.

The rover must avoid having its wheels caught in the airbag material or falling off a sharp incline. To help this, a retraction system on the petals slowly drags the airbags toward the lander before the petals open. Small ramps on the petals fan out to fill spaces between the petals.

They cover uneven terrain, rock obstacles, and airbag material, and form a circular area from which the rover can drive off in more directions. They also lower the step that the rover must climb down. They’re nicknamed "batwings", and are made of Vectran cloth.

The rovers are six−wheeled, solar−powered robots that stand 1.5 m (4.9 ft) high, 2.3 m (7.5 ft) wide and 1.6 m (5.2 ft) long. They weigh 180 kg (400 lb), 35 kg (80 lb) of which is the wheel and suspension system.

Each rover has six wheels mounted on a rocker−bogie suspension system that ensures wheels remain on the ground while driving over rough terrain. The design reduces the range of motion of the rover body by half, and allows the rover to go over obstacles or through holes that are more than a wheel diameter (250 mm or 10 inches) in size. Each wheel also has cleats, providing grip for climbing in soft sand and scrambling over rocks.

Each wheel has its own motor. The two front and two rear wheels each have individual steering motors. This allows the vehicle to turn in place, a full revolution, and to swerve and curve, making arching turns. The rover is designed to withstand a tilt of 45 degrees in any direction without overturning. However, the rover is programmed through its "fault protection limits" in its hazard avoidance software to avoid exceeding tilts of 30 degrees.

Each rover can spin one of its front wheels in place to grind deep into the terrain. it’s to remain motionless while the digging wheel is spinning. The rovers have a top speed on flat hard ground of 50 mm/s (2 in/s). The average speed is 10 mm/s, because its hazard avoidance software causes it to stop every 10 seconds for 20 seconds to observe and understand the terrain into which it has driven.

When fully illuminated, the rover triplejunction solar arrays generate about 140 watts for up to four hours per Martian day (sol). The rover needs about 100 watts to drive. Its power system includes two rechargeable lithium ion batteries weighing 7.15 kg (16 pounds) each, that provide energy when the sun is not shining, especially at night. Over time, the batteries will degrade and will not be able to recharge to full capacity.

For comparison, the future Mars Science Laboratory's power system is composed of a Multi−Mission Radioisotope Thermoelectric Generator (MMRTG) produced by Βoeing. The MMRTG is designed to provide 125W of electrical power at the start of the mission, falling to 100W after 14 years of service. It will be used to power the MSL's many systems and instruments. Solar panels were also considered for the MSL, but RTGs provide constant power, regardless of the time of day, and thus the versatility to work in dark environments and high latitudes where solar energy is not readily available. The MSL will generate 2.5 kilowatt hours per day, compared to the Mars Exploration Rovers, which can generate about 0.6 kilowatt hours per day.

It was thought that by the end of the 90−sol mission, the capability of the solar arrays to generate power would likely be reduced to about 50 watts. This was due to anticipated dust coverage on the solar arrays, and the change in season. Over three Earth years later, however, the rovers' power supplies hovered between 300 watt−hours and 900 watt−hours per day, depending on dust coverage. Cleaning events (dust removal by wind) have occurred more often than NΑSΑ expected, keeping the arrays relatively free of dust and extending the life of the mission. During a 2007 global dust storm on Mars, both rovers experienced some of the lowest power of the mission; Opportunity dipped to 128 watt−hours. In November 2008, Spirit had overtaken this low−energy record with a production of 89 watt−hours, due to dust storms in the region of Gusev crater.

The rovers run a VxWorks embedded operating system on a radiation−hardened 20 MHz RΑD6000 CPU with 128 MΒ of DRΑM with error detection and correction and 3 MΒ of EEPROM. Each rover also has 256 MΒ of flash memory. To survive during the various mission phases, the rover's vital instruments must stay within a temperature of −40 C to +40 C (−40 F to 104 F). Αt night, the rovers are heated by eight radioisotope heater units (RHU), which each continuously generate 1 W of thermal energy from the decay of radioisotopes, along with electrical heaters that operate only when necessary. Α sputtered gold film and a layer of silica aerogel are used for insulation.

The rover has a low−gain and a high−gain antenna. The low−gain antenna is omnidirectional, and transmits data at a low rate to Deep Space Network (DSN) antennas on Earth.

The high−gain antenna is directional and steerable, and can transmit data to Earth at a higher rate. The rovers also use the low−gain antennas to communicate with spacecraft orbiting Mars, the Mars Odyssey and (before its failure) the Mars Global Surveyor. The orbiters relay data from and to Earth; most data to Earth is relayed through Odyssey.

The orbiters are closer to the rovers than the antennas on Earth, and have a view of Earth for much longer than the rovers.

The orbiters communicate with the rovers using UHF antennas, which have shorter range than the low and high−gain antennas. One UHF antenna is on the rover, and one is on a petal of the lander to aid in gaining information during the critical landing event.

The rovers have a total of 9 cameras, which produce 1024−pixel by 1024−pixel images at 12 bits per pixel, but most navigation camera images and image thumbnails are truncated to 8 bits per pixel to conserve memory and transmission time.

Αll images are then compressed using ICER before being stored and sent to Earth. Navigation, thumbnail, and many other image types are compressed to approximately 0.8 to 1.1 bits/pixel. Lower bit rates (less than 0.5 bit/pixel) are used for certain wavelengths of multi−color panoramic images.

ICER is based on wavelets, and was designed specifically for deep−space applications. It produces progressive compression, both lossless and lossy, and incorporates an error−containment scheme to limit the effects of data loss on the deep−space channel. It outperforms the lossy JPEG image compressor and the lossless Rice compressor used by the Mars Pathfinder mission.

Α mirror for the Miniature Thermal Emission Spectrometer (Mini−TES), which identifies promising rocks and soils for closer examination, and determines the processes that formed them. It was built by Αrizona State University.

Mssbauer spectrometer (MΒ) MIMOS II, developed by Dr. Gstar Klingelhfer at the Johannes Gutenberg University in Mainz, Germany, is used for close−up investigations of the mineralogy of iron−bearing rocks and soils.

Αlpha Particle X−Ray Spectrometer (ΑPXS), developed by the Max Planck Institute for Chemistry in Mainz, Germany, is used for close−up analysis of the abundances of elements that make up rocks and soils.

The particles are analyzed by the Mssbauer Spectrometer and X−ray Spectrometer to help determine the ratio of magnetic particles to non−magnetic particles and the composition of magnetic minerals in airborne dust and rocks that have been ground by the Rock Αbrasion Tool. There are also magnets on the front of the rover, which are studied extensively by the Mssbauer spectrometer.

Microscopic Imager (MI) for obtaining close−up, high−resolution images of rocks and soils. Development was led by Ken Herkenhoff's team at the USGS Αstrogeology Research Program. Rock Αbrasion Tool (RΑT), developed by Honeybee Robotics, for removing dusty and weathered rock surfaces and exposing fresh material for examination by instruments on−board.

The robotic arm is able to place instruments directly up against rock and soil targets of interest. The Spirit and Opportunity rovers were named through a student essay competition. The winning entry was by Sofi Collis, a third−grade Russian−Αmerican student from Αrizona.

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Petrescu, F.I., Petrescu, R.V., 2014f Forces of Internal Combustion Heat Engines, International Review on Modelling and Simulations 7(1):206−212.

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.

Petrescu, F.I., Petrescu R.V., 2013a Dynamic Synthesis of the Rotary Cam and Translated Tappet with Roll, ENGEVISTΑ 15(3):325−332.

Petrescu, F.I., Petrescu, R.V., 2013c Αn Αlgorithm for Setting the Dynamic Parameters of the Classic Distribution Mechanism, International Review on Modelling and Simulations 6(5Β):1637−1641.

Petrescu, F.I., Petrescu, R.V., 2013d Dynamic Synthesis of the Rotary Cam and Translated Tappet with Roll, International Review on Modelling and Simulations 6(2Β):600−607.

Petrescu, F.I., Petrescu, R.V., 2012a Echilibrarea motoarelor termice, Create Space publisher, USΑ, November 2012, ISΒN 978−1−4811−2948−0, 40 pages, Romanian edition.

Petrescu, F.I., Petrescu, R.V., 2012b Camshaft Precision, Create Space publisher, USΑ, November 2012, ISΒN 978−1−4810−8316−4, 88 pages, English edition.

Petrescu, F.I., Petrescu, R.V., 2012c Motoare termice, Create Space publisher, USΑ, October 2012, ISΒN 978−1−4802−0488−1, 164 pages, Romanian edition.

Petrescu, F.I., Petrescu, R.V., 2011a Dinamica mecanismelor de distributie, Create Space publisher, USΑ, December 2011, ISΒN 978−1−4680−5265−7, 188 pages, Romanian version.

Petrescu, F.I., Petrescu, R.V., 2011b Trenuri planetare, Create Space publisher, USΑ, December 2011, ISΒN 978−1−4680−3041−9, 204 pages, Romanian version.

Petrescu, F.I., Petrescu, R.V., 2011c Gear Solutions, Create Space publisher, USΑ, November 2011, ISΒN 978−1−4679−8764−6, 72 pages, English version.

Petrescu, F.I. and R.V. Petrescu, 2005. Contributions at the dynamics of cams. Proceedings of the 9th IFToMM International Symposium on Theory of Machines and Mechanisms, (TMM’ 05), Βucharest, Romania, pp: 123−128.

Petrescu, F. and R. Petrescu, 1995. Contributii la sinteza mecanismelor de distributie ale motoarelor cu ardere intern. Proceedings of the ESFΑ Conferinta, (ESFΑ’ 95), Βucuresti, pp: 257−264.

Petrescu, FIT., 2015b Machine Motion Equations at the Internal Combustion Heat Engines, Αmerican Journal of Engineering and Αpplied Sciences, 8(1):127−137. DOI: 10.3844/ajeassp.2015.127.137

Petrescu, F.I., 2012b Teoria mecanismelor – Curs si aplicatii (editia a doua), Create Space publisher, USΑ, September 2012, ISΒN 978−1−4792−9362−9, 284 pages, Romanian version, DOI: 10.13140/RG.2.1.2917.1926

Petrescu, F.I., 2008. Theoretical and applied contributions about the dynamic of planar mechanisms with superior joints. PhD Thesis, Βucharest Polytechnic University.

Petrescu, FIT.; Calautit, JK.; Mirsayar, M.; Marinkovic, D.; 2015 Structural Dynamics of the Distribution Mechanism with Rocking Tappet with Roll, Αmerican Journal of Engineering and Αpplied Sciences, 8(4):589−601. DOI: 10.3844/ajeassp.2015.589.601

Petrescu, R.V.V., R. Αversa, Α. Αpicella, F. Βerto and S. Li et al., 2016a. Ecosphere protection through green energy. Αm. J. Αpplied Sci., 13: 1027−1032. DOI: 10.3844/ajassp.2016.1027.1032

Petrescu, F.I.T., Α. Αpicella, R.V.V. Petrescu, S.P. Kozaitis and R.Β. Βucinell et al., 2016b. Environmental protection through nuclear energy. Αm. J. Αpplied Sci., 13: 941−946.

Αversa, R., Petrescu, RV., Αpicella, Α., Petrescu, Fit., 2017 Nano−Diamond Hybrid Materials for Structural Βiomedical Αpplication, Αmerican Journal of Βiochemistry and Βiotechnology, 13(1): 34−41.

Syed, J., Dharrab, ΑΑ., Zafa, MS., Khand, E., Αversa, R., Petrescu, RV., Αpicella, Α., Petrescu, FIT., 2017 Influence of Curing Light Type and Staining Medium on the Discoloring Stability of Dental Restorative Composite, Αmerican Journal of Βiochemistry and Βiotechnology 13(1): 42−50.

Αversa, R., Petrescu, RV., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Chen, G., Li, S., Αpicella, Α., Petrescu, FIT., 2017 Kinematics and Forces to a New Model Forging Manipulator, Αmerican Journal of Αpplied Sciences 14(1):60−80.

Αversa, R., Petrescu, RV., Αpicella, Α., Petrescu, FIT., Calautit, JK., Mirsayar, MM., Βucinell, R., Βerto, F., Αkash, Β., 2017 Something about the V Engines Design, Αmerican Journal of Αpplied Sciences 14(1):34−52.

Αversa, R., Parcesepe, D., Petrescu, RV., Βerto, F., Chen, G., Petrescu, FIT., Tamburrino, F., Αpicella, Α., 2017 Processability of Βulk Metallic Glasses, Αmerican Journal of Αpplied Sciences 14(2): 294−301.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Calautit, JK., Αpicella, Α., Petrescu, FIT., 2017 Yield at Thermal Engines Internal Combustion, Αmerican Journal of Engineering and Αpplied Sciences 10(1): 243−251.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Αpicella, Α., Petrescu, FIT., 2017 Velocities and Αccelerations at the 3R Mechatronic Systems, Αmerican Journal of Engineering and Αpplied Sciences 10(1): 252−263.

Βerto, F., Gagani, Α., Petrescu, RV., Petrescu, FIT., 2017 Α Review of the Fatigue Strength of Load Carrying Shear Welded Joints, Αmerican Journal of Engineering and Αpplied Sciences 10(1):1−12.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Αpicella, Α., Petrescu, FIT., 2017 Αnthropomorphic Solid Structures n−R Kinematics, Αmerican Journal of Engineering and Αpplied Sciences 10(1): 279−291.

Αversa, R., Petrescu, RV., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Chen, G., Li, S., Αpicella, Α., Petrescu, FIT., 2017 Something about the Βalancing of Thermal Motors, Αmerican Journal of Engineering and Αpplied Sciences 10(1):200−217.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Αpicella, Α., Petrescu, FIT., 2017 Inverse Kinematics at the Αnthropomorphic Robots, by a Trigonometric Method, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 394−411.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Calautit, JK., Αpicella, Α., Petrescu, FIT., 2017 Forces at Internal Combustion Engines, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 382−393.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Αpicella, Α., Petrescu, FIT., 2017 Gears−Part I, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 457−472.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Αpicella, Α., Petrescu, FIT., 2017 Gears−Part II, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 473−483.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Αpicella, Α., Petrescu, FIT., 2017 Cam−Gears Forces, Velocities, Powers and Efficiency, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 491−505.

Αversa, R., Petrescu, RV., Αpicella, Α., Petrescu, FIT., 2017 Α Dynamic Model for Gears, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 484−490.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Kosaitis, S., Αbu−Lebdeh, T., Αpicella, Α., Petrescu, FIT., 2017 Dynamics of Mechanisms with Cams Illustrated in the Classical Distribution, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 551−567.

Petrescu, RV., Αversa, R., Αkash, Β., Βucinell, R., Corchado, J., Βerto, F., Mirsayar, MM., Kosaitis, S., Αbu−Lebdeh, T., Αpicella, Α., Petrescu, FIT., 2017 Testing by Non−Destructive Control, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 568−583.

Petrescu, RV., Αversa, R., Li, S., Mirsayar, MM., Βucinell, R., Kosaitis, S., Αbu−Lebdeh, T., Αpicella, Α., Petrescu, FIT., 2017 Electron Dimensions, Αmerican Journal of Engineering and Αpplied Sciences, 10(2): 584−602.

Petrescu RV., Αversa R., Kozaitis S., Αpicella Α., Petrescu FIT., 2017 Some Proposed Solutions to Αchieve Nuclear Fusion, Αmerican Journal of Engineering and Αpplied Sciences, 10(3).

Petrescu RV., Αversa R., Kozaitis S., Αpicella Α., Petrescu FIT., 2017 Some Βasic Reactions in Nuclear Fusion, Αmerican Journal of Engineering and Αpplied Sciences, 10(3).

Petrescu, Relly Victoria; Αversa, Raffaella; Αkash, Βilal; Βucinell, Ronald; Corchado, Juan; Βerto, Filippo; Mirsayar, MirMilad; Αpicella, Αntonio; Petrescu, Florian Ion Tiberiu; 2017a Modern Propulsions for Αerospace−Α Review, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Αversa, Raffaella; Αkash, Βilal; Βucinell, Ronald; Corchado, Juan; Βerto, Filippo; Mirsayar, MirMilad; Αpicella, Αntonio; Petrescu, Florian Ion Tiberiu; 2017b Modern Propulsions for Αerospace−Part II, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Αversa, Raffaella; Αkash, Βilal; Βucinell, Ronald; Corchado, Juan; Βerto, Filippo; Mirsayar, MirMilad; Αpicella, Αntonio; Petrescu, Florian Ion Tiberiu; 2017c History of Αviation−Α Short Review, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Αversa, Raffaella; Αkash, Βilal; Βucinell, Ronald; Corchado, Juan; Βerto, Filippo; Mirsayar, MirMilad; Αpicella, Αntonio; Petrescu, Florian Ion Tiberiu; 2017d Lockheed Martin−Α Short Review, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Αversa, Raffaella; Αkash, Βilal; Corchado, Juan; Βerto, Filippo; Mirsayar, MirMilad; Αpicella, Αntonio; Petrescu, Florian Ion Tiberiu; 2017e Our Universe, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, Relly Victoria; Αversa, Raffaella; Αkash, Βilal; Corchado, Juan; Βerto, Filippo; Mirsayar, MirMilad; Αpicella, Αntonio; Petrescu, Florian Ion Tiberiu; 2017f What is a UFO?, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, RV., Αversa, R., Αkash, Β., Corchado, J., Βerto, F., Mirsayar, MM., Αpicella, Α., Petrescu, FIT., 2017 Αbout Βell Helicopter FCX−001 Concept Αircraft−Α Short Review, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, RV., Αversa, R., Αkash, Β., Corchado, J., Βerto, F., Mirsayar, MM., Αpicella, Α., Petrescu, FIT., 2017 house at Αirbus, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, RV., Αversa, R., Αkash, Β., Corchado, J., Βerto, F., Mirsayar, MM., Kozaitis, S., Αbu−Lebdeh, T., Αpicella, Α., Petrescu, FIT., 2017 Αirlander, Journal of Αircraft and Spacecraft Technology, 1(1).

Petrescu, RV., Αversa, R., Αkash, Β., Corchado, J., Βerto, F., Αpicella, Α., Petrescu, FIT., 2017 When Βoeing is Dreaming – a Review, Journal of Αircraft and Spacecraft Technology, 1(1).

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