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(5 January 2021 – NASA Goddard) The Artemis generation of lunar explorers will establish a sustained human presence on the Moon, prospecting for resources, making revolutionary discoveries, and proving technologies key to future deep space exploration.

To support these ambitions, NASA navigation engineers from the Space Communications and Navigation (SCaN) program are developing a navigation architecture that will provide accurate and robust Position, Navigation, and Timing (PNT) services for the Artemis missions. Global Navigation Satellite System (GNSS) signals will be one component of that architecture. GNSS use in high-Earth orbit and in lunar space will improve timing, enable precise and responsive maneuvers, reduce costs, and even allow for autonomous, onboard orbit and trajectory determination.

Different areas of GNSS coverage (courtesy: NASA)

Global Navigation Satellite System

GNSS refers to PNT satellite constellations operated by the U.S., the European Union, Russia, China, India, and Japan. GPS, the PNT constellation created by the U.S. Air Force, is probably the example most Americans are familiar with.

On Earth, GNSS signals enable navigation and provide precise timing in critical applications like banking, financial transactions, power grids, cellular networks, telecommunications, and more. In space, spacecraft can use these signals to determine their location, velocity, and time, which is critical to mission operations.

“We’re expanding the ways we use GNSS signals in space,” said SCaN Deputy Director for Policy and Strategic Communications J.J. Miller, who coordinates PNT activities across the agency. “This will empower NASA as the agency plans human exploration of the Moon as part of the Artemis program.”

Spacecraft near Earth have long relied on GNSS signals for PNT data. Spacecraft in low-Earth orbit below about 1,800 miles (3,000 km) in altitude can calculate their location using GNSS signals just as users on the ground might use their phones to navigate.

This provides enormous benefits to these missions, allowing many satellites the autonomy to react and respond to unforeseen events in real time, ensuring the safety of the mission. GNSS receivers can also negate the need for an expensive onboard clock and simplifies ground operations, both of which can save missions money. Additionally, GNSS accuracy can help missions take precise measurements from space.

Expanding the Space Service Volume

Beyond 1,800 miles in altitude, navigation with GNSS becomes more challenging. This expanse of space is called the Space Service Volume, which extends from 1,800 miles up to about 22,000 miles (36,000 km), or geosynchronous orbit. At altitudes beyond the GNSS constellations themselves users must begin to rely on signals received from the opposite side of the Earth.

From the opposite side of the globe, Earth blocks much of the GNSS signals, so spacecraft in the Space Service Volume must instead “listen” for signals that extend out over the Earth. These signals extend out at an angle from GNSS antennas.

Formally, GNSS reception in the Space Service Volume relies on signals received within about 26 degrees from the antennas’ strongest signal. However, NASA has had marked success using weaker GNSS side lobe signals — which extend out at an even greater angle from the antennas — for navigation in and beyond the Space Service Volume.

Since the 1990s, NASA engineers have worked to understand the capabilities of these side lobes. In preparation for launch of the first Geostationary Operational Environmental Satellite-R weather satellite in 2016, NASA endeavored to better document side lobes’ strength and nature to determine if the satellite could meet its PNT requirements.

“Through early on-orbit measurement and documentation of the GNSS side lobe capabilities, future missions could rest assured that their PNT needs would be met,” said Frank Bauer, who began the GNSS PNT effort at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Our understanding of these signal patterns revealed a host of potential new GNSS applications.”

Navigation experts at Goddard reverse-engineered the characteristics of the antennas on GPS satellites by observing the signals from space. By studying the signals satellites received from GPS side lobes, engineers pieced together their structure and strength. Using this data, they developed detailed models of the radiation patterns of GPS satellites in an effort called the GPS Antenna Characterization Experiment.

While documenting these characteristics, NASA explored the feasibility of using side lobe signals for navigation well outside what had been considered the Space Service Volume and in lunar space. In recent years, the Magnetospheric Multiscale Mission (MMS) has even successfully determined its position using GPS signals at distances nearly halfway to the Moon.

GNSS at the Moon

To build on the success of MMS, NASA navigation engineers have been simulating GNSS signal availability near the Moon. Their research indicates that these GNSS signals can play a critical role in NASA’s ambitious lunar exploration initiatives, providing unprecedented accuracy and precision.

“Our simulations show that GPS can be extended to lunar distances by simply augmenting existing high-altitude GPS navigation systems with higher-gain antennas on user spacecraft,” said NASA navigation engineer Ben Ashman. “GPS and GNSS could play an important role in the upcoming Artemis missions from launch through lunar surface operations.”

While MMS relied solely on GPS, NASA is working toward an interoperable approach that would allow lunar missions to take advantage of multiple constellations at once. Spacecraft near Earth receive enough signals from a single PNT constellation to calculate their location. However, at lunar distances GNSS signals are less numerous. Simulations show that using signals from multiple constellations would improve missions’ ability to calculate their location consistently.

To prove and test this capability at the Moon, NASA is planning the Lunar GNSS Receiver Experiment (LuGRE), developed in partnership with the Italian Space Agency. LuGRE will fly on one of NASA’s Commercial Lunar Payload Services missions. These missions rely on U.S. companies to deliver lunar payloads that advance science and exploration technologies.

NASA plans to land LuGRE on the Moon’s Mare Crisium basin in 2023. There, LuGRE is expected to obtain the first GNSS fix on the lunar surface. LuGRE will receive signals from both GPS and Galileo, the GNSS operated by the European Union. The data gathered will be used to develop operational lunar GNSS systems for future missions to the Moon.

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JAXA, Taiyo Wire, NGK, Technosolver, and Koyo Materica develop a metal mesh for onboard deployable reflectors

JAXA Taiyo Wire NGK Technosolver and Koyo Materica develop a

(26 January 2021 – NGK Insulators) Japan Aerospace Exploration Agency (JAXA), Taiyo Wire Cloth, NGK Insulators, Technosolver Corporation and Koyo Materica Corporation have jointly developed a metal mesh for onboard deployable reflectors that has achieved a dramatic cut in costs.

Artist image of deployable reflector using metal mesh. (courtesy: JAXA)

In order to realize faster communications speeds, next generation communications satellites need to be able to work with high frequency band, which necessitates large deployable reflectors. Conventionally, the metal mesh of the antennas have been made from gold plated Molybdenum wire, which is a mixed metal of precious metal and rare metal and therefore difficult to obtain and very costly. To cut costs, the five organizations have jointly developed a new metal mesh.

The new metal mesh is made from Zirconium Copper wire and fabricated by tricot weaving. It is light weight, flexible, and has excellent electrical reflection properties at the high frequency band of Ka (30 GHz). Zirconium Copper wire has characteristics similar to Molybdenum wire and is applicable to metal mesh. On top of this, Zirconium Copper wire is strong enough to be fabricated into a metal mesh without gold plating. These two reasons make it possible to dramatically cut cost compared with conventional metal mesh.

The new metal mesh is expected to be applied primarily to next generation communications satellites and SAR (synthetic apature radar) satellites, both of which use deployable reflectors to improve satellite capabilities.

Taiyo Wire Cloth Co., Ltd, and three other corporations are planning to make the new metal mesh available on the market for commercial satellites.

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Satnav antenna built for ends of the Earth

Satnav antenna built for ends of the Earth

(27 Janaury 2021 – ESA) A new ESA-supported wide-bandwidth satnav antenna has been designed to receive both satellite and augmentation signals from anywhere in the sky, even down to just a couple of degrees above the horizon.

With a growing number of satnav constellations in operation, Canada-based Tallysman Wireless’s new VeroStar antenna aims to pick up all available signals, as well as support the availability of L-band correction service signals. Its development was supported through ESA’s Navigation Innovation and Support Program (NAVISP) programme.

The precision of GNSS fixes is routinely sharpened with correction signals from augmentation systems, such as Europe’s EGNOS and the US WAAS, which also provide ongoing integrity (or reliability) information for high-accuracy and safety-of-life uses, such as aircraft descents. However, these augmentation signals are transmitted by geostationary satellites, hanging at fixed points above the equator, meaning that they become less visible for receivers in the far north or south.

VeroStar wide-bandwidth satnav antenna (courtesy: Tallysman)

satnav 2

Petal antenna design (courtesy: Tallysman)

“If you think of a Global Navigation Satellite System (GNSS) receiver as resembling a camera, then the antenna would be the lens,” explains Allen Crawford of Tallysman. “Now, you might have an excellent top-of-the-range camera, but if it doesn’t have a clean, distortion-free, and well-focused lens, then all you’re going to get are blurred pixels that no post-processing software can fix.

“So our antenna is like a lens, except it gathers radio signals instead of light – and it is the first step in the measurement process. We want the antenna to reproduce the received satellite signals as precisely as possible, in terms of amplitude and of signal phase, on a fully representative basis, for the receiver to process.”

Available in various models and sizes, including pole-mounted, surface-mounted, and embedded versions, the VeroStar is aimed at high-performance mobile applications, such as land surveying, precision farming, maritime and autonomous vehicle navigation, typically requiring positioning accuracy down to a few centimetres.

“Different customers have differing requirements,” adds Julien Hautcouer of Tallysman. “There are plenty of GNSS antennas that work on a ‘good enough’ basis – for instance, antennas on top of cars just need to give a rough position, then the navigation receiver uses its map to estimate what street you’re on.”

“What we wanted to do, starting from scratch with this new design, for high-precision mobile users, was to be able to employ as many satellite signals from as many constellations as possible – not just GPS but also Galileo, the Russian, Chinese, Indian, and Japanese systems, plus correction service signals – and this requires good stable performance across a very wide bandwidth.”

“We want it to provide nothing but the pure right-hand circular signals, minimising any misleading reflected ‘multipath’ signals,” notes Gyles Panther, CTO of Tallysman. “We also paid special attention to the symmetry of our antenna, so that satellite signals are treated in exactly the same way, no matter where in the sky the signals are coming from. It’s like looking through a good quality wine glass when you rotate it in front of your eyes, and your view through it stays the same.”

At the same time, the modern radio spectrum is very crowded, so the design team paid particular attention to filtering out radio interference that could cause a situation where a drone might be forced down by local radio noise.

The VeroStar design is based on eight curled ‘petals’ of printed circuit boards, inspired by the post-war Alford loop antenna, which was originally designed for simultaneous transmission of multiple FM radio signals.

“The Tallysman team performed a long optimisation process using electromagnetic modelling to define the final shape for manufacturing,” notes ESA navigation engineer Nicolas Girault, the project’s technical officer. “They ended up with an inexpensive, easy to repeat process, which is ideal, really.”

The design maximises antenna efficiency and performance, adds ESA engineer Damiano Trenta: “Its rotational symmetry geometry and wideband behaviour help to provide a stable phase centre over frequency and angular range. Optimisation of the petals’ shape helps to improve the minimum gain at very low elevation angles, compared with the current products on the market, and keeps a very low cross-polar level for multipath mitigation. ”

Subsequent production line checks revealed this value remained consistent across all antennas.

The VeroStar models are now being marketed commercially both individually and as an element within customer products. VeroStar development was supported through NAVISP Element 2 – aiming to boost Member State competitiveness through the development of improved or innovative commercial products – as well as the Canadian Space Agency.

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NASA’s OSIRIS-REx mission plans for May asteroid departure

NASAs OSIRIS REx mission plans for May asteroid departure

(26 January 2021 – NASA) On May 10, NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft will say farewell to asteroid Bennu and begin its journey back to Earth.

During its Oct. 20, 2020, sample collection event, the spacecraft collected a substantial amount of material from Bennu’s surface, likely exceeding the mission’s requirement of 2 ounces (60 grams). The spacecraft is scheduled to deliver the sample to Earth on Sep. 24, 2023.

This illustration shows the OSIRIS-REx spacecraft departing asteroid Bennu to begin its two-year journey back to Earth. (courtesy: NASA/Goddard/University of Arizona)

“Leaving Bennu’s vicinity in May puts us in the ‘sweet spot,’ when the departure maneuver will consume the least amount of the spacecraft’s onboard fuel,” said Michael Moreau, OSIRIS-REx deputy project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Nevertheless, with over 593 miles per hour (265 meters per second) of velocity change, this will be the largest propulsive maneuver conducted by OSIRIS-REx since the approach to Bennu in October 2018.”

The May departure also provides the OSIRIS-REx team with the opportunity to plan a final spacecraft flyby of Bennu. This activity was not part of the original mission schedule, but the team is studying the feasibility of a final observation run of the asteroid to potentially learn how the spacecraft’s contact with Bennu’s surface altered the sample site.

If feasible, the flyby will take place in early April and will observe the sample site, named Nightingale, from a distance of approximately 2 miles (3.2 kilometers). Bennu’s surface was considerably disturbed after the Touch-and-Go (TAG) sample collection event, with the collector head sinking 1.6 feet (48.8 centimeters) into the asteroid’s surface. The spacecraft’s thrusters also disturbed a substantial amount of surface material during the back-away burn.

The mission is planning a single flyby, mimicking one of the observation sequences conducted during the mission’s Detailed Survey phase in 2019. OSIRIS-REx would image Bennu for a full rotation to obtain high-resolution images of the asteroid’s northern and southern hemispheres and equatorial region. The team would then compare these new images with the previous high-resolution imagery of Bennu obtained during 2019.

“OSIRIS-REx has already provided incredible science,” said Lori Glaze, NASA’s director of planetary science at the agency’s headquarters in Washington. “We’re really excited the mission is planning one more observation flyby of asteroid Bennu to provide new information about how the asteroid responded to TAG and to render a proper farewell.”

These post-TAG observations would also give the team a chance to assess the current functionality of science instruments onboard the spacecraft – specifically the OSIRIS-REx Camera Suite (OCAMS), OSIRIS-REx Thermal Emission Spectrometer (OTES), OSIRIS-REx Visible and Infrared Spectrometer (OVIRS), and OSIRIS-REx Laser Altimeter (OLA). It is possible dust coated the instruments during the sample collection event and the mission wants to evaluate the status of each. Understanding the health of the instruments is also part of the team’s assessment of possible extended mission opportunities after the sample is delivered to Earth.

The spacecraft will remain in asteroid Bennu’s vicinity until May 10, when the mission will enter its Earth Return Cruise phase. As it approaches Earth, OSIRIS-REx will jettison the Sample Return Capsule (SRC). The SRC will then travel through the Earth’s atmosphere and land under parachutes at the Utah Test and Training Range.

Once recovered, NASA will transport the capsule to the curation facility at the agency’s Johnson Space Center in Houston and distribute the sample to laboratories worldwide, enabling scientists to study the formation of our solar system and Earth as a habitable planet.

Goddard provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona in Tucson is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Littleton, Colorado, built the spacecraft and provides flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages for the agency’s Science Mission Directorate in Washington.

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