Technologies and Applications
Technologies and Applications
This file is intended to present some technology topics that cannot be assigned to a particular mission. The following chapters contain only short descriptions, they are presented in reverse order. The topics should be of interest to the reader community.
NASA to Advance Unique 3D Printed Sensor Technology
• February 15, 2019: A NASA technologist is taking miniaturization to the extreme. Mahmooda Sultana won funding to advance a potentially revolutionary, nanomaterial-based detector platform. The technology is capable of sensing everything from minute concentrations of gases and vapor, atmospheric pressure and temperature, and then transmitting that data via a wireless antenna — all from the same self-contained platform that measures just two-by-three-inches in size. 1)
Under a $2 million technology development award, Sultana and her team at NASA's Goddard Space Flight Center in Greenbelt, Maryland, will spend the next two years advancing the autonomous multifunctional sensor platform. If successful, the technology could benefit NASA's major science disciplines and efforts to send humans to the Moon and Mars. These tiny platforms could be deployed on planetary rovers to detect small quantities of water and methane, for example, or be used as monitoring or biological sensors to maintain astronaut health and safety.
Central to the effort, funded by NASA's Space Technology Mission Directorate's (STMD) Early Career Initiative (ECI) is a 3D printing system developed by Ahmed Busnina and his group at Northeastern University in Boston. The 3D printing system is like printers used to produce money or newspapers. However, instead of ink, the printer applies nanomaterials, layer-by-layer, onto a substrate to create tiny sensors. Ultimately, each is capable of detecting a different gas, pressure level or temperature.
Nanomaterials, such as carbon nanotubes, graphene, molybdenum disulfide and others, exhibit interesting physical properties. They are highly sensitive and stable at extreme conditions. They are also lightweight, hardened against radiation and require less power, making them ideal for space applications, Sultana said.
Under her partnership with Northeastern University, Sultana and her group will design the sensor platform, determining which combination of materials are best for measuring minute, parts-per-billion concentrations of water, ammonia, methane and hydrogen — all important in the search for life throughout the solar system. Using her design, Northeastern University will then use its Nanoscale Offset Printing System to apply the nanomaterials. Once printed, Sultana's group will functionalize the individual sensors by depositing additional layers of nanoparticles to enhance their sensitivity, integrate the sensors with readout electronics, and package the entire platform.
The approach differs dramatically from how technologists currently fabricate multifunctional sensor platforms. Instead of building one sensor at a time and then integrating it to other components, 3D printing allows technicians to print a suite of sensors on one platform, dramatically simplifying the integration and packaging process.
Figure 1: Technologist Mahmooda Sultana holds an early iteration of an autonomous multifunctional sensor platform, which could benefit all of NASA's major scientific disciplines and efforts to send humans to the Moon and Mars Image credit: NASA/W. Hrybyk)
Also innovative is Sultana's plan to print on the same silicon wafer partial circuitry for a wireless communications system that would communicate with ground controllers, further simplifying instrument design and construction. Once printed, the sensors and wireless antenna will be packaged onto a printed circuit board that holds the electronics, a power source, and the rest of the communications circuitry.
"The beauty of our concept is that we're able to print all sensors and partial circuity on the same substrate, which could be rigid or flexible. We eliminate a lot of the packaging and integration challenges," Sultana said. "This is truly a multifunctional sensor platform. All my sensors are on same chip, printed one after another in layers."
Figure 2: Meet Mahmooda Sultana, Associate Branch Head, Systems Engineering Branch at NASA's Goddard Space Flight Center in Maryland. Mahmooda uses her love of math and puzzles to develop new technologies and miniaturize instruments for NASA missions (video credit: NASA)
Wide-Ranging Uses: The research picks up where other NASA-funded efforts ended. Under several previous efforts funded by Goddard's Internal Research and Development Program and STMD's Center Innovation Fund, Sultana and her team used the same technique to manufacture and demonstrate individual sensors made of carbon nanotubes and molybdenum disulfide, among other materials. "The sensors were found to be quite sensitive, down to low parts per million. With our ECI funding, we are targeting the instrument's sensitivity to parts per billion by improving sensor design and structure," Sultana said.
According to her, the project addresses NASA's need for low-power, small, lightweight, and highly sensitive sensors that can distinguish important molecules other than by measuring the masses of a molecule's fragments, which is how many missions currently detect molecules today using mass spectrometers.
In fact, the agency has acknowledged that future sensors need to detect minute concentrations of gases and vapors in the parts per billion level. Although mass spectrometers can detect a wide spectrum of molecules — particularly useful for unknown samples — they have difficulty distinguishing between some of the important species, such as water, methane and ammonia. "It's also difficult to reach the parts per billion or beyond level with them," she said.
"We're really excited about the possibilities of this technology," Sultana said. "With our funding, we can take this technology to the next level and potentially offer NASA a new way to create customized, multifunctional sensor platforms, which I believe could open the door to all types of mission concepts and uses. The same approach we use to identify gases on a planetary body also could be used to create biological sensors that monitor astronaut health and the levels of contaminants inside spacecraft and living quarters."
New Geodesy Application for Emerging Atom-Optics Technology
• December 20, 2018: NASA and the Sunnyvale, California-based AOSense, Inc., have successfully built and demonstrated a prototype quantum sensor capable of obtaining highly sensitive and accurate gravity measurements — a stepping stone toward next-generation geodesy, hydrology, and climate-monitoring missions in space. 2)
The prototype sensor, developed in collaboration with NASA's Goddard Space Flight Center in Greenbelt, Maryland, employs a revolutionary measurement technique called atom interferometry, which former U.S. Energy Department Secretary Steven Chu and his colleagues invented in the late 1980s. In 1997, Chu received the Nobel Prize in Physics for his work.
Since the discovery, researchers worldwide have attempted to build practical, compact, more sensitive quantum sensors, such as atom interferometers, that scientists could use in space-constrained areas, including spacecraft.
Figure 3: This image demonstrates the control that the Goddard-AOSense team has over the paths of atoms. In this demonstration, they manipulated the path to form the acronym, NASA (image credit: AOSense, Inc.)
With funding from NASA's Small Business Innovation Research, Instrument Incubator, and Goddard's Internal Research and Development programs, the Goddard-AOSense team developed an atom-optics gravity gradiometer primarily for mapping Earth's time-varying gravitational field. Although Earth's gravitational field changes for a variety of reasons, the most significant cause is a change in water mass. If a glacier or an ice sheet melts, this would affect mass distribution and therefore Earth's gravitational field.
"Our sensor is smaller than competing sensors with similar sensitivity goals," said Babak Saif, a Goddard optical physicist and collaborator in the effort. "Previous atom interferometer-based instruments included components that would literally fill a room. Our sensor, in dramatic comparison, is compact and efficient. It could be used on a spacecraft to obtain an extraordinary data set for understanding Earth's water cycle and its response to climate change. In fact, the sensor is a candidate for future NASA missions across a variety of scientific disciplines."
Atom interferometry, however, hinges on quantum mechanics, the theory that describes how matter behaves at sub-microscopic scales. Atoms, which are highly sensitive to gravitational signals, can also be cajoled into behaving like light waves. Special pulsing lasers can split and manipulate atom waves to travel different paths. The two atom waves will interact with gravity in a way that affects the interference pattern produced once the two waves recombine. Scientists can then analyze this pattern to obtain an extraordinarily accurate measure of the gravitational field.
In particular, the team is eying its quantum sensor as a potential technology to gather the type of data currently produced by NASA's Gravity Recovery and Climate Experiment (GRACE) Follow-On mission. GRACE-FO is a two-satellite mission that has generated monthly gravity maps showing how mass is distributed and how it changes over time. Due to its extraordinary precision, the quantum sensor could eliminate the need for a two-satellite system or provide even greater accuracy if deployed on a second satellite in a complementary orbit, said Lee Feinberg, a Goddard optics expert also involved in the effort.
"With this new technology, we can measure the changes of Earth's gravity that come from melting ice caps, droughts, and draining underground water supplies, greatly improving on the pioneering GRACE mission," said John Mather, a Goddard scientist and winner of the Nobel Prize in Physics in 2006 for his work on NASA's Cosmic Background Explorer that helped cement the big-bang theory of the universe.
The instrument, however, could be used to answer other scientific questions.
"We can measure the interior structure of planets, moons, asteroids, and comets when we send probes to visit them. The technology is so powerful that it can even extend the Nobel-winning measurements of gravitational waves from distant black holes, observing at a new frequency range," Mather said, referring to the confirmation in 2015 of cosmic gravitational waves — literally, ripples in the fabric of space-time that radiate out in all directions, much like what happens when a stone is thrown into a pond. Since that initial confirmation, the Laser Interferometer Gravitational Wave Observatory and the European Virgo detectors have detected other events.
Since 2004, AOSense has developed quantum sensors and atomic clocks, with broad expertise and capabilities spanning all aspects of development and characterization of advanced sensors for precision navigation and timing. 3)
Figure 4: Real-world atomic sensors and other exacting applications require laser sources with specific size, environmental, and optical characteristics, placing unique constraints that most commercial laser systems do not meet. AOSense has developed a line of external cavity diode lasers (ECDLs) designed to meet these needs, offering narrow linewidth in a compact package (image credit: AOSense)
Our AOSense ECDL is built on a semi-monolithic bench with a cat's-eye design for stable operation in demanding environments. The wavelength is factory-set to the desired user wavelength; no subsequent mechanical adjustment is required. A PZT may be used for ~GHz tuning in addition to current and temperature controls. Current wavelengths include alkali (767 nm, 780 nm, 852 nm) and alkaline earth (423 nm, 461 nm, 657 nm, 689 nm, 698 nm) transitions. Additional UV/blue models at 369 and 399 nm are currently in development. The flexible design is fully translatable to additional wavelengths. The output beam is circularized to optimize fiber coupling (not available for all wavelengths). The compact laser enclosure dimensions are only 7.5 x 3.8 x 2.8 cm.
New Standard for Wireless Transmission Speed at 100 Gbit/s
• August 22, 2018: Northrop Grumman Corporation and DARPA (Defense Advanced Research Projects Agency) have set a new standard for wireless transmission by operating a data link at 100 Gbit/s over a distance of 20 kilometers in a city environment. 4)
The blazing data rate is fast enough to download a 50 GB blue ray video in four seconds. The demonstration marked the successful completion of Northrop Grumman's Phase 2 contract for DARPA's 100 Gbit/s (100G) RF Backbone program.
Figure 5: Northrop Grumman and DARPA 100 Gbit/s link demonstrated over 20 km city environment on 19 January 2018 in Los Angeles (image credit: Northrop Grumman)
The 100G system is capable of rate adaptation on a frame by frame basis from 9 to 102 Gbit/s to maximize data rate throughout dynamic channel variations. Extensive link characterization demonstrated short-term error-free performance from 9 to 91 Gbit/s, and a maximum data rate of 102 Gbit/s with 1 erroneous bit received per ten thousand bits transmitted.
The successful data link results from the integration of several key technologies. The link operates at millimeter wave frequencies (in this case, 71-76 GHz and 81-86 GHz with 5 GHz of bandwidth, or data carrying capacity, and uses a bandwidth efficient signal modulation technique to transmit 25 Gbit/s data streams on each 5 GHz channel. To double the rate within the fixed bandwidth, the data link transmits dual orthogonally polarized signals from each antenna. Additionally, the link transmits from two antennas simultaneously (spatial multiplexing) and uses multiple-input-multiple-output (MIMO) signal processing techniques to separate the signals at the two receiving antennas, thus again doubling the data rate within the fixed bandwidth.
According to Louis Christen, director, research and technology, Northrop Grumman, "This dramatic improvement in data transmission performance could significantly increase the volume of airborne sensor data that can be gathered and reduce the time needed to exploit sensor data. Next generation sensors such as hyperspectral imagers typically collect data faster, and in larger quantity than most air-to-ground data links can comfortably transmit," said Christen. "Without such a high data rate link data would need to be reviewed and analyzed after the aircraft lands."
By contrast, a 100G data link could transmit high-rate data directly from the aircraft to commanders on the ground in near real time, allowing them to respond more quickly to dynamic operations.
The successful 100G ground demonstration sets the stage for the flight test phase of the 100G RF Backbone program. This next phase, which started in June, demonstrates the 100G air-to-ground link up to 100 Gbit/s over a 100 km range and extended ranges with lower data rates. The 100G hardware will be flown aboard the Proteus demonstration aircraft developed by Northrop Grumman subsidiary Scaled Composites.
Northrop Grumman's 100G industry team includes Raytheon, which developed the millimeter wave antennas and related RF electronics and Silvus Technologies, which provides the key spatial multiplexing and MIMO signal processing technologies.
Figure 6: The 100G hardware will be flown aboard the Proteus demonstration aircraft developed by Northrop Grumman subsidiary Scaled Composites (image credit: Northrop Grumman)
Researchers develop novel process to 3D print one of the strongest materials on Earth
• August 15, 2018: Researchers from Virginia Tech (Blacksburg, VA) and Lawrence Livermore National Laboratory (Livermore, CA) have developed a novel way to 3D print complex objects of one of the highest-performing materials used in the battery and aerospace industries. 5)
Previously, researchers could only print this material, known as graphene, in 2D sheets or basic structures. But Virginia Tech engineers have now collaborated on a project that allows them to 3D print graphene objects at a resolution an order of magnitude greater than ever before printed, which unlocks the ability to theoretically create any size or shape of graphene.
Because of its strength - graphene is one of the strongest materials ever tested on Earth - and its high thermal and electricity conductivity, 3D printed graphene objects would be highly coveted in certain industries, including batteries, aerospace, separation, heat management, sensors, and catalysis.
Graphene is a single layer of carbon atoms organized in a hexagonal lattice. When graphene sheets are neatly stacked on top of each other and formed into a three-dimensional shape, it becomes graphite, commonly known as the "lead" in pencils.
Because graphite is simply packed-together graphene, it has fairly poor mechanical properties. But if the graphene sheets are separated with air-filled pores, the three-dimensional structure can maintain its properties. This porous graphene structure is called a graphene aerogel.
"Now a designer can design three-dimensional topology comprised of interconnected graphene sheets," said Xiaoyu "Rayne" Zheng, assistant professor with the Department of Mechanical Engineering in the College of Engineering and director of the Advanced Manufacturing and Metamaterials Lab. "This new design and manufacturing freedom will lead to optimization of strength, conductivity, mass transport, strength, and weight density that are not achievable in graphene aerogels."
Zheng, also an affiliated faculty member of the Macromolecules Innovation Institute, has received grants to study nanoscale materials and scale them up to lightweight and functional materials for applications in aerospace, automobiles, and batteries.
Previously, researchers could print graphene using an extrusion process, sort of like squeezing toothpaste, but that technique could only create simple objects that stacked on top of itself. "With that technique, there's very limited structures you can create because there's no support and the resolution is quite limited, so you can't get freeform factors," Zheng said. "What we did was to get these graphene layers to be architected into any shape that you want with high resolution."
This project began three years ago when Ryan Hensleigh, lead author of the article and now a third-year Macromolecular Science and Engineering Ph.D. student, began an internship at the LLNL (Lawrence Livermore National Laboratory in Livermore), California. Hensleigh started working with Zheng, who was then a member of the technical staff at Lawrence Livermore National Laboratory. When Zheng joined the faculty at Virginia Tech in 2016, Hensleigh followed as a student and continued working on this project.
To create these complex structures, Hensleigh started with graphene oxide, a precursor to graphene, crosslinking the sheets to form a porous hydrogel. Breaking the graphene oxide hydrogel with ultrasound and adding light-sensitive acrylate polymers, Hensleigh could use projection micro-stereolithography to create the desired solid 3D structure with the graphene oxide trapped in the long, rigid chains of acrylate polymer. Finally, Hensleigh would place the 3D structure in a furnace to burn off the polymers and fuse the object together, leaving behind a pure and lightweight graphene aerogel.
"It's a significant breakthrough compared to what's been done," Hensleigh said. "We can access pretty much any desired structure you want."
The key finding of this work, which was recently published with collaborators at LLNL in the journal Materials Horizons, is that the researchers created graphene structures with a resolution an order of magnitude finer than ever printed. Hensleigh said other processes could print down to 100 µm, but the new technique allows him to print down to 10 µm in resolution, which approaches the size of actual graphene sheets. 6)
"We've been able to show you can make a complex, three-dimensional architecture of graphene while still preserving some of its intrinsic prime properties," Zheng said. "Usually when you try to 3D print graphene or scale up, you lose most of their lucrative mechanical properties found in its single sheet form."
Figure 7: (A) Four ‘‘Green'' MAG parts of differing unit-cell structures before pyrolysis from left to right octet-truss, gyroid, cubo-octahedron, and Kelvin foam; (B) optical image of pyrolyzed gyroid; (C) SEM image of pyrolyzed gyroid with intricate overhang structures (D) zoomed image of pyrolyzed gyroid in ‘‘C''; (E) optical image of pyrolyzed MAG octet-truss, of a different design than shown in ‘‘A'' supported by a single strawberry blossom filament; (F) SEM image of pyrolyzed octet-truss MAG in ‘‘E''; (G) zoomed image of octet-truss in ‘‘E'' showing the very high 10 µm resolution achievable in our process (image credit: 3D print graphene study team of Virginia Tech and Lawrence Livermore National Laboratory)
Prototype nuclear battery packs 10 times more power
• May 2018: Russian researchers from the Moscow Institute of Physics and Technology (MIPT), the Technological Institute for Superhard and Novel Carbon Materials (TISNCM), and the National University of Science and Technology, MISIS, have optimized the design of a nuclear battery generating power from the beta decay of nickel-63 (63Ni), a radioactive isotope. Their new battery prototype packs about 3,300 mW-hours of energy per gram, which is more than in any other nuclear battery based on 63Ni, and 10 times more than the specific energy of commercial chemical cells. The paper was published in the journal Diamond and Related Materials. 7) 8)
Figure 8: A nuclear battery (image credit: Elena Khavina/MIPT)
Ordinary batteries powering clocks, flashlights, toys, and other electrical devices use the energy of so-called redox chemical reactions in which electrons are transferred from one electrode to another via an electrolyte. This gives rise to a potential difference between the electrodes. If the two battery terminals are then connected by a conductor, electrons start flowing to remove the potential difference, generating an electric current. Chemical batteries, also known as galvanic cells, are characterized by a high power density—that is, the ratio between the power of the generated current and the volume of the battery. However, chemical cells discharge in a relatively short time, limiting their applications in autonomous devices. Some of these batteries, called accumulators, are rechargeable, but even they need to be replaced for charging. This may be dangerous, as in the case of a cardiac pacemaker, or even impossible, if the battery is powering a spacecraft.
Fortunately, chemical reactions are just one of the possible sources of electric power. In 1913, Henry Moseley invented the first power generator based on radioactive decay. His nuclear battery consisted of a glass sphere silvered on the inside with a radium emitter mounted at the center on an isolated electrode. Electrons resulting from the beta decay of radium caused a potential difference between the silver film and the central electrode. However, the idle voltage of the device was way too high—tens of kV (kilovolt)—and the current was too low for practical applications.
In 1953, Paul Rappaport proposed the use of semiconducting materials to convert the energy of beta decay into electricity. Beta particles—electrons and positrons—emitted by a radioactive source ionize atoms of a semiconductor, creating uncompensated charge carriers. In the presence of a static field of a p-n structure, the charges flow in one direction, resulting in an electric current. Batteries powered by beta decay came to be known as betavoltaics. The chief advantage of betavoltaic cells over galvanic cells is their longevity. Radioactive isotopes used in nuclear batteries have half-lives ranging from tens to hundreds of years, so their power output remains nearly constant for a very long time. Unfortunately, the power density of betavoltaic cells is significantly lower than that of their galvanic counterparts. Despite this, betavoltaics were used in the 1970s to power cardiac pacemakers, before being phased out by cheaper lithium-ion batteries, even though the latter have shorter lifetimes.
Betavoltaic power sources should not be confused with RTGs (Radioisotope Thermoelectric Generators), which are also called nuclear batteries, but operate on a different principle. Thermoelectric cells convert the heat released by radioactive decay into electricity using thermocouples. The efficiency of RTGs is only several percent and depends on temperature. But owing to their longevity and relatively simple design, thermoelectric power sources are widely used to power spacecraft such as the New Horizons probe and Mars rover Curiosity. RTGs were previously used on unmanned remote facilities such as lighthouses and automatic weather stations. However, this practice was abandoned, because used radioactive fuel was hard to recycle and leaked into the environment.
A research team led by Vladimir Blank, the director of TISNCM and chair of nanostructure physics and chemistry at MIPT, came up with a way of increasing the power density of a nuclear battery almost tenfold. The physicists developed and manufactured a betavoltaic battery using nickel-63 as the source of radiation and Schottky barrier-based diamond diodes for energy conversion. The prototype battery achieved an output power of about 1 µW (microwatt), while the power density per cubic centimeter was 10 µW, which is enough for a modern artificial pacemaker. Nickel-63 has a half-life of 100 years, so the battery packs about 3,300 mW-hours of power per 1 gram—10 times more than electrochemical cells.
Figure 9: A nuclear battery design (image credit: V. Bormashov et al./Diamond and Related Materials)
The nuclear battery prototype consisted of 200 diamond converters interlaid with nickel-63 and stable nickel foil layers (Figure 9). The amount of power generated by the converter depends on the thickness of the nickel foil and the converter itself, because both affect how many beta particles are absorbed. Currently available prototypes of nuclear batteries are poorly optimized, since they have excessive volume. If the beta radiation source is too thick, the electrons it emits cannot escape it. This effect is known as self-absorption. However, as the source is made thinner, the number of atoms undergoing beta decay per unit time is proportionally reduced. Similar reasoning applies to the thickness of the converter.
The goal of the researchers was to maximize the power density of their nickel-63 battery. To do this, they numerically simulated the passage of electrons through the beta source and the converters. It turned out that the nickel-63 source is at its most effective when it is 2 µm thick, and the optimal thickness of the converter based on Schottky barrier diamond diodes is around 10 µm.
The main technological challenge was the fabrication of a large number of diamond conversion cells with complex internal structure. Each converter was merely tens of micrometers thick, like a plastic bag in a supermarket. Conventional mechanical and ionic techniques of diamond thinning were not suitable for this task. The researchers from TISNCM and MIPT developed a unique technology for synthesizing thin diamond plates on a diamond substrate and splitting them off to mass-produce ultrathin converters.
The team used 20 thick boron-doped diamond crystal plates as the substrate. They were grown using the temperature gradient technique under high pressure. Ion implantation was used to create a 100 nm thick defective, "damaged" layer in the substrate at the depth of about 700 nm. A boron-doped diamond film 15 µm thick was grown on top of this layer using chemical vapor deposition. The substrate then underwent high-temperature annealing to induce graphitization of the buried defective layer and recover the top diamond layer. Electrochemical etching was used to remove the damaged layer. Following the separation of the defective layer by etching, the semi-finished converter was fitted with ohmic and Schottky contacts.
All converters were connected in parallel in a stack as shown in Figure 9. The technology for rolling 2 µm thick nickel foil was developed at the Research Institute and Scientific Industrial Association LUCH. The battery was sealed with epoxy.
The prototype battery is characterized by the current-voltage curve shown in Figure 11. The open-circuit voltage and the short-circuit current are 1.02 V and 1.27 µA, respectively. The maximum output power of 0.93 µW is obtained at 0.92 volts. This power output corresponds to a specific power of about 3,300 mW-hours per gram, which is 10 times more than in commercial chemical cells or the previous nickel-63 nuclear battery designed at TISNCM.
Figure 10: Photo of a prototype nuclear battery (image credit: Technological Institute for Superhard and Novel Carbon Materials)
In 2016, Russian researchers from MISIS had already presented a prototype betavoltaic battery based on nickel-63. Another working prototype, created at TISNCM and LUCH, was demonstrated at Atomexpo 2017. It had a useful volume of 1.5 cm3.
The main setback in commercializing nuclear batteries in Russia is the lack of nickel-63 production and enrichment facilities. However, there are plans to launch nickel-63 production on an industrial scale by mid-2020s.
There is an alternative radioisotope for use in nuclear batteries: Diamond converters could be made using radioactive carbon-14, which has an extremely long half-life of 5,700 years. Work on such generators was earlier reported by physicists from the University of Bristol (UK).
Figure 11: Prototype battery is characterized by the current-voltage curve (image credit: Study Team)
Nuclear batteries: Prospects:
The work reported in this story has prospects for medical applications. Most state-of-the-art cardiac pacemakers are over 10 cm3 in size and require about 10 µW of power. This means that the new nuclear battery could be used to power these devices without any significant changes to their design and size. "Perpetual pacemakers" whose batteries need not be replaced or serviced would improve the quality of life of patients.
The space industry would also greatly benefit from compact nuclear batteries. In particular, there is a demand for autonomous wireless external sensors and memory chips with integrated power supply systems for spacecraft. Diamond is one of the most radiation-proof semiconductors. Since it also has a large bandgap, it can operate in a wide range of temperatures, making it the ideal material for nuclear batteries powering spacecraft.
The researchers are planning to continue their work on nuclear batteries. They have identified several lines of inquiry that should be pursued. Firstly, enriching nickel-63 in the radiation source would proportionally increase battery power. Secondly, developing a diamond p-i-n structure with a controlled doping profile would boost voltage and therefore could increase the power output of the battery at least by a factor of three. Thirdly, enhancing the surface area of the converter would increase the number of nickel-63 atoms on each converter.
TISNCM Director Vladimir Blank, who is also chair of nanostructure physics and chemistry at MIPT, commented on the study: "The results so far are already quite remarkable and can be applied in medicine and space technology, but we are planning to do more. In the recent years, our institute has been rather successful in the synthesis of high-quality doped diamonds, particularly those with n-type conductivity. This will allow us to make the transition from Schottky barriers to p-i-n structures and thus achieve three times greater battery power. The higher the power density of the device, the more applications it will have. We have decent capabilities for high-quality diamond synthesis, so we are planning to utilize the unique properties of this material for creating new radiation-proof electronic components and designing novel electronic and optical devices."
The Kilopower Project of NASA
2018: When astronauts someday venture to the Moon, Mars and other destinations, one of the first and most important resources they will need is power. A reliable and efficient power system will be essential for day-to-day necessities, such as lighting, water and oxygen, and for mission objectives, like running experiments and producing fuel for the long journey home. 9)
That's why NASA is conducting experiments on Kilopower, a new power source that could provide safe, efficient and plentiful energy for future robotic and human space exploration missions. This pioneering space fission power system could provide up to 10 kW of electrical power — enough to run two average households — continuously for at least ten years. Four Kilopower units would provide enough power to establish an outpost.
Currently, power is usually generated in space by solar arrays that convert the Sun's energy into electricity or by radioisotope power systems that convert the heat from naturally decaying plutonium238 into electricity. Solar or radioisotope power systems may be impractical for future NASA missions to places where sunlight is dim or unavailable, and where more than a few hundreds of watts of power are needed. 10)
Fission power from nuclear reactors could provide abundant energy anywhere that humans or our robotic science probes might go. Fission, the splitting of an atom's nucleus, releases a great amount of heat energy: 1 pound of uranium fuel can produce as much energy as about 3 million pounds of burnable coal. With such a high energy density, fission power systems present an ideal solution for space missions that require large amounts of power, especially where sunlight is limited or not available.
Technology Demonstration Goal: Because of fission power's great potential for space exploration, the NASA Space Technology Mission Directorate's Game Changing Development (GCD) Program is funding the Kilopower project, an effort led by NASA's Glenn Research Center to demonstrate space fission power systems technology. Building on prior work by a joint NASA and Department of Energy team, the project's main goal is to assemble and test an experimental prototype of a space fission power system. In 2012, Los Alamos National Laboratory and NASA Glenn demonstrated how an innovative, small-scale heat pipe-cooled fission reactor could provide electrical power using Stirling power conversion. This proof of physics demonstration provided the basis for the Kilopower project, the goal of which is to demonstrate the readiness of a monolithic-core heat-pipe reactor power system for use in NASA's exploration missions.
Accomplishing the Goal: The NS (Nuclear Systems) Kilopower project is a partnership between NASA and the Department of Energy's National Nuclear Security Administration (NNSA). Together, NASA and NNSA have designed and developed a 1 kWe reactor prototype with technology that is relevant for systems up to 10 kWe. It consists of a highly enriched uranium core built by NNSA, heat pipes provided by Advanced Cooling Technologies through a NASA Small Business Innovation Research contract, and Stirling generators provided by Sunpower, Inc. The core is a solid block of a uranium alloy, and heat pipes are clamped around the core to transfer heat to Stirling power conversion units to generate electrical power. Much smaller than terrestrial nuclear plants, Kilopower systems are small enough to be demonstrated here on Earth in existing facilities at the Nevada National Security Site.
Space Exploration Uses for Fission Power: The Kilopower project was initiated because NASA mission planning includes exploration of places in the solar system—such as deep space beyond Jupiter's orbit and the surfaces of Earth's moon and Mars—where power generation from sunlight is difficult and power from radioisotope systems is limited by the fuel supply. For human exploration, multiple 10 kWe Kilopower systems could provide the 40 kWe initially estimated to be needed by NASA's preliminary concepts for a human outpost, with the ability to add power as the outpost grows. For robotic exploration, 1 kWe Kilopower units enable abundant, reliable power for science and communications, and the potential to field deep space missions based on science return while conserving the limited supply of radioisotope fuel for its best opportunities. Characteristics of fission power that make it so beneficial for Mars outposts and deep space robotics also apply to other space missions. Nuclear fission systems could be scaled up to power nuclear electric propulsion vehicles to efficiently transport heavy cargo beyond Mars, and they could potentially shorten crewed trip times to Mars and other distant planets.
Game Changing Development Program: The Game Changing Development (GCD) program is part of NASA's Space Technology Mission Directorate. The GCD program aims to advance exploratory concepts and deliver technology solutions that enable new capabilities or radically alter current approaches.
Unlike previous technologies, the Kilopower reactor is simple, inexpensive and relies on fuels and technologies that are already well understood, NASA officials said. It uses active nuclear fission, like a conventional nuclear reactor, which will enable it to harvest far more energy from its uranium alloy core than an RTG (Radioisotope Thermoelectric Generator) could. A heat pipe clamped around the reactor core will transfer heat to the unit's power generators: small Stirling engines, a technology that was developed in 1816. The engines are simple pistons that convert heat into motion, which is then converted to electricity. The reactor will radiate excess heat from an umbrella-like cooling array.
Figure 12: The Kilopower reactor will take advantage of active nuclear fission and Stirling engines — simple devices that convert heat into motion — to increase its efficiency compared with previous nuclear power sources (image credit: NASA)
KRUSTY (Kilopower Reactor Using Stirling Technology) Experiment Results
• On 2 May 2018, NASA announced the results of the KRUSTY experiment during a news conference at GRC (Glenn Research Center). The Kilopower experiment was conducted November 2017 through March 2018 at the Nevada National Security Site (NNSS). 11)
- NASA and the Department of Energy's National Nuclear Security Administration (NNSA) have successfully demonstrated a new nuclear reactor power system that could enable long-duration crewed missions to the Moon, Mars and destinations beyond.
- "Safe, efficient and plentiful energy will be the key to future robotic and human exploration," said Jim Reuter, NASA's acting associate administrator for the Space Technology Mission Directorate (STMD) in Washington. "I expect the Kilopower project to be an essential part of lunar and Mars power architectures as they evolve."
- Kilopower is a small, lightweight fission power system capable of providing up to 10 kW of electrical power - enough to run several average households - continuously for at least 10 years. Four Kilopower units would provide enough power to establish an outpost.
- The prototype power system uses a solid, cast uranium-235 reactor core, about the size of a paper towel roll. Passive sodium heat pipes transfer reactor heat to high-efficiency Stirling engines, which convert the heat to electricity.
- According to David Poston, the chief reactor designer at NNSA's Los Alamos National Laboratory, the purpose of the recent experiment in Nevada was two-fold: to demonstrate that the system can create electricity with fission power, and to show the system is stable and safe no matter what environment it encounters. "We threw everything we could at this reactor, in terms of nominal and off-normal operating scenarios and KRUSTY passed with flying colors," said Poston.
- The Kilopower team conducted the experiment in four phases. The first two phases, conducted without power, confirmed that each component of the system behaved as expected. During the third phase, the team increased power to heat the core incrementally before moving on to the final phase. The experiment culminated with a 28-hour, full-power test that simulated a mission, including reactor startup, ramp to full power, steady operation and shutdown.
- Throughout the experiment, the team simulated power reduction, failed engines and failed heat pipes, showing that the system could continue to operate and successfully handle multiple failures.
- "We put the system through its paces," said Gibson. "We understand the reactor very well, and this test proved that the system works the way we designed it to work. No matter what environment we expose it to, the reactor performs very well."
- The Kilopower project is developing mission concepts and performing additional risk reduction activities to prepare for a possible future flight demonstration. The project will remain a part of the STMD's Game Changing Development program with the goal of transitioning to the Technology Demonstration Mission program in Fiscal Year 2020.
- Such a demonstration could pave the way for future Kilopower systems that power human outposts on the Moon and Mars, including missions that rely on In-situ Resource Utilization to produce local propellants and other materials.
Figure 13: Artist's concept of new fission power system on the lunar surface (image credit: NASA)
• Testing: As of September 2017 a test reactor has been constructed, called KRUSTY (Kilopower Reactor Using Stirling Technology). It is designed to produce up to 1 kW of electric power and is about 1.9 m tall. The goal of the KRUSTY experiment is to closely match the operational parameters that would be required in NASA deep space missions. The prototype Kilopower uses a solid, cast uranium-235 reactor core, about the size of a paper towel roll. Reactor heat is transferred via passive sodium heat pipes, with the heat being converted to electricity by Stirling engines. 12)
- Testing to gain TRL 5 started in November 2017 and continued into 2018. The first tests used a depleted uranium core manufactured by Y-12 National Security Complex in Tennessee. The depleted uranium core is exactly the same material as the regular high-enriched uranium (HEU) core with the only difference being the level of uranium enrichment. The testing of KRUSTY represents the first time the United States has conducted ground tests on any space reactor since the SNAP-10A experimental reactor was tested and eventually flown in 1965.
Figure 14: Marc Gibson, Kilopower lead engineer, and Jim Sanzi, Vantage Partners, install hardware on the Kilopower assembly at the Nevada National Security Site in March 2018 (image credit: NASA) 13)
Top Tomatoes thanks to Mars Missions
11 April 2018: Inspired by an Obama speech in 2010 on human missions to Mars, the Dutch company Groen Agro Control started investigating the best way to grow and fertilize plants in space, and whether that could also lead to improving the growth of vegetables on Earth. 14)
"In space, you can fertilize plants only with the minerals you take with you, but you still want them to produce the best possible crops," explains the company's Lex de Boer. "Ideally, you would also use the water that evaporates from the plants as a source of drinking water, with the minimum amount of purification. That means you have to apply doses of each mineral extremely carefully, so that as little as possible ends up unused in the drain water."
To study this, the company built an enclosed system in which tomato and pepper plants received doses of 16 different minerals, looking at how the uptake of each mineral correlated with growth.
In 2013, the company met an ESA team at the Space-MATCH event organized by Netherlands Organization for Applied Scientific Research TNO and ESA's Technology Transfer Office to bring ESA engineers and industry together to exchange knowhow. Here, the company was inspired to spin off a smart service helping horticulturalists to fertilize plants better on Earth.
Figure 15: Next time you eat a tomato or sweet pepper, take a closer look, because there's a good chance that its healthy appearance is thanks to one of former US President Barack Obama's speeches and ESA research for sending people on long-duration space missions (image credit: M. Barel (CC BY-NC 2.0))
To study the optimal dosing of minerals for growing tomato and pepper plants, Dutch Groen Agro Control built an enclosed system in which the plants received doses of 16 different minerals. The doses of each mineral were extremely carefully controlled, so that as little as possible ends up unused in the drain water.
Figure 16: Dosing of minerals for growing tomato and pepper plants (image credit: Groen Agro Control)
Triggered by the requirement to provide for the needs of humans on long missions to the Moon and Mars, ESA's MELiSSA (Micro-Ecological Life Support System Alternative) project focuses on a ‘closed' life support system, where all supplies are reused and recycled. So, for example, organic waste and carbon dioxide should be entirely converted into oxygen, water and food.
"MELiSSA recognizes that we have to develop a self-supporting system for long missions, as astronauts will not be able to rely on regular deliveries of supplies, especially as they move further from Earth," explains ESA's Christel Paille. "One key issue is food and water supplies. Astronauts will need to grow their own food with limited resources, and reclaim as much water as possible from that growth cycle. Hence it's vital that we develop a scheme that tells them exactly the right amount of fertilizer to apply at every stage in the plant growth."
Figure 17: The AlgoSolis facility is offering researchers and industry an opportunity to experiment with microalgae on larger scales than before. Based in Saint-Nazaire, France, the site is a stepping stone to industrial production of algae-based products (image credit: Université de Nantes) 15)
Legend to Figure 17: Microalgae offer huge benefits because they promise many products for human use, from biofuels to oxygen and food, as well as clean contaminated water or extract carbon dioxide from the atmosphere. ESA's MELiSSA project is using algae and other organisms and chemicals to develop a compact closed ecosystem to keep astronauts alive on long missions.
Spin-off from research as if in space
Based on its initial experiments, and the results it gained from growing vegetables in closed and well-controlled environments conceptually as if in space, the company developed a scheme for horticulturists, this time with the goal of maximizing plant growth and yield through very careful use of fertilizers.
In the service now offered to growers, samples are taken every week of both the fertilizer solution dripped into the plants – including tomatoes, peppers, cucumbers, eggplant, roses and gerbera – and the liquid that drains away.
These are analyzed at the company's laboratory and the results sent back to the growers, with advice on any changes they should make to the amounts of each of the 16 minerals given to the plants.
"There is a separate approach for each mineral, but these are also linked with each other because the uptake of certain minerals – such as potassium, magnesium and calcium – are closely related," says Lex. "The amount of each mineral that a plant needs also varies across its lifecycle. It will need a different combination when it is producing stalks and leaves early in its life compared with when it is producing flowers and fruit."
Horticulturalists also face challenges in altering fertilizer doses to match changing growing conditions. For example, rising energy prices have encouraged growers to keep greenhouse windows closed. However, this causes higher humidity, resulting in a fall in evaporation from plants.
That, in turn, makes it harder for tomato plants to transport calcium to the top of the plant, which can result in a condition that leaves and the plant top becomes necrotic. The company's scheme shows growers how to compensate for this by altering not just the amount of calcium in the drop water, but also magnesium and potassium levels.
Production increase: In less than one season, Dutch customer Zwingrow has already started to see positive results from using the scheme for its crop of orange bell peppers.
"We're always trying to improve the health and quality of the plants we grow, but using this weekly analysis means we are acting proactively, delving deeper into the needs of the plants and getting better results," says Ted Zwinkels, co-owner of Zwingrow. "Even though we started using it after the start of the season last year, the plants grew better and were healthier. I'd estimate that overall production increased by around 5%. It's impossible to know how much of this was due to the new regime, as variations in sunlight from year to year also play a part. However, already this season, using the service from the very start, we've seen stronger, better plants, and fewer vulnerable ones."
Groen Agro Control now has clients across the world. While it still has plans for experiments on crop growth in space, it is also widening its horizons on Earth, including a potential service for crops grown outside using drop water application of fertilizers, such as asparagus.
Production of NEXT-C ion propulsion engine
• 10 April 2018: Aerojet Rocketdyne's (Redmond WA) NEXT-C ion propulsion engine has successfully cleared NASA's CDR (Critical Design Review), confirming the technology achieved all program requirements and is ready for final production of the flight units. NEXT-C (NASA's Evolutionary Xenon Thruster-Commercial) was developed by NASA and is being commercialized by Aerojet Rocketdyne. NEXT-C has 7 kW of maximum power and an Isp > 4100 s. Its high Isp (Specific Impulse) and flexible operational capabilities make NEXT ideal for scientific space missions. 16)
NEXT-C will be the ion thruster used on a 2021 mission, named DART (Double Asteroid Redirection Test), led by the Johns Hopkins University Applied Physics Laboratory for NASA. DART is a kinetic impact mission designed to collide with a moonlet around the Didymos asteroid and slightly alter its orbit. This mission will be a critical step in demonstrating NASA's impact threat mitigation capabilities for redirection of a potentially hazardous object such as an asteroid.
"Serving as the primary propulsion source for DART, NEXT-C will establish a precedent for future use of electric propulsion to enable ambitious future science missions," said Eileen Drake, CEO and President of Aerojet Rocketdyne. "Electric propulsion reduces overall mission cost without sacrificing reliability or mission success."
Under a cost-sharing agreement with NASA's Science Mission Directorate through the agency's Glenn Research Center, Aerojet Rocketdyne is developing the NEXT-C electric propulsion engine and power processing unit. In addition to DART, additional NEXT-C units may be launched on future NASA planetary missions.
New dimension in design
• 11 April 2018: An alternative to conventional circuit boards, these 3D-molded interconnect devices (Figure 18) add electrical connectivity to the surface of three-dimensional structures. The aim is to combine mechanical, electronic and potentially optical functions in a single 3D part, allowing the creation of intricate, precisely aligned designs using fewer parts while delivering significant savings in space and weight compared to conventional electronic manufacturing. 17)
"These prototype interconnect devices were produced using injection-moulded plastics incorporating electrical metallisation," explains ESA's Jussi Hokka. "In principle, however, other materials can also be used, allowing the incorporation of sensors or the integration of shielding or cooling systems."
Figure 18: Illustration of 3D-molded prototype interconnect devices procuded for ESA by Art of Technology AG in Switzerland, through the Agency's Advanced Research in the Telecommunications Systems program (image credit: ESA/Art of Technology AG)
Twisting laser light offers the chance to probe the nano-scale
• 5 April 2018: A new method to sensitively measure the structure of molecules has been demonstrated by twisting laser light and aiming it at miniscule gold gratings to separate out wavelengths. The technique could potentially be used to probe the structure and purity of molecules in pharmaceuticals, agrochemicals, foods and other important products more easily and cheaply than existing methods. 18)
Developed by physicists at the University of Bath (Bath UK), working with colleagues at the University of Cambridge and UCL (University College London), the technique relies on the curious fact that many biological and pharmaceutical molecules can be either 'left-handed' or 'right-handed'.
Figure 19: A twisted laser beam hits a nanoscopic U-shaped gold grating which further twists the beam in either a right or left-handed direction. This deflects the beam in many directions and further splits it into its constituent wavelengths across the color spectrum (image credit: University of Bath, Ventsislav Valev)
Although such molecules are built from exactly the same elements they can be arranged in mirror images of each other, and this configuration sometimes changes their properties drastically.
Notoriously the morning sickness drug Thalidomide caused birth defects and deaths in babies before it was pulled from the market in the 1960s. Investigation showed that the drug existed in two mirror images - the right-handed form was effective as a morning sickness drug, but the left-handed form was harmful to foetuses. This is one example of why testing what 'handedness', or chirality, a molecule has is essential for many valuable products.
The research team from the Centre for Photonics and Photonic Materials, and the Centre for Nanoscience and Nanotechnology at the University of Bath, used a special white-light laser built in-house and directed it through several optical components to put a twist on the beam. The twisted laser beam then hits a nano-scopic U-shaped gold grating which serves as a template for the light, further twisting the beam in either a right or left-handed direction. This deflects the beam in many directions and further splits it into its constituent wavelengths across the colour spectrum.
By carefully measuring the deflected light scientists can detect tiny differences in intensity across the spectrum which inform them about the chirality of the grating the laser beam interacts with.
The study, published in the journal Advanced Optical Materials, demonstrates the technique as a proof of principle. 19)
Christian Kuppe, the PhD student who conducted the experiments, said: "At the moment chiral sensing requires high molecular concentrations because you're looking for tiny differences in how the light interacts with the target molecule. By using our gold gratings we aim to use a much smaller amount of molecules to conduct a very sensitive test of their handedness. The next step will be to continue to test the technique with a range of well-known chiral molecules. We hope that this will become a valuable way to perform really important tests on all sorts of products including pharmaceuticals and other high-value chemicals."
Dr Ventsislav Valev, who oversaw the work, said: "There's a great deal of scientific excitement about miniaturisation and working on nano-sized dimensions at the very small scale. However, in the rush to go as small as possible, some opportunities have been overlooked. Working with chiral nano-gratings is a great example of that."
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).