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NASA Team First to Demonstrate X-ray Navigation in Space

In a technology first, a team of NASA engineers has demonstrated fully autonomous X-ray navigation in space — a capability that could revolutionize NASA’s ability in the future to pilot robotic spacecraft to the far reaches of the solar system and beyond.

The demonstration, which the team carried out with an experiment called Station Explorer for X-ray Timing and Navigation Technology, or SEXTANT, showed that millisecond pulsars could be used to accurately determine the location of an object moving at thousands of miles per hour in space — similar to how the Global Positioning System, widely known as GPS, provides positioning, navigation, and timing services to users on Earth with its constellation of 24 operating satellites.

NICER’s mirror assemblies concentrate X-rays onto silicon detectors to gather data that probes the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars. Credits: NASA's Goddard Space Flight Center/Keith Gendreau

NICER’s mirror assemblies concentrate X-rays onto silicon detectors to gather data that probes the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars.
Credits: NASA’s Goddard Space Flight Center/Keith Gendreau

“This demonstration is a breakthrough for future deep space exploration,” said SEXTANT Project Manager Jason Mitchell, an aerospace technologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “As the first to demonstrate X-ray navigation fully autonomously and in real-time in space, we are now leading the way.”

This technology provides a new option for deep space navigation that could work in concert with existing spacecraft-based radio and optical systems.

Although it could take a few years to mature an X-ray navigation system practical for use on deep-space spacecraft, the fact that NASA engineers proved it could be done bodes well for future interplanetary space travel. Such a system provides a new option for spacecraft to autonomously determine their locations outside the currently used Earth-based global navigation networks because pulsars are accessible in virtually every conceivable fight regime, from low-Earth to deepest space.

Exploiting NICER Telescopes

The SEXTANT technology demonstration, which NASA’s Space Technology Mission Directorate had funded under its Game Changing Program, took advantage of the 52 X-ray telescopes and silicon-drift detectors that make up NASA’s Neutron-star Interior Composition Explorer, or NICER. Since its successful deployment as an external attached payload on the International Space Station in June, it has trained its optics on some of the most unusual objects in the universe.

“We’re doing very cool science and using the space station as a platform to execute that science, which in turn enables X-ray navigation,” said Goddard’s Keith Gendreau, the principal investigator for NICER, who presented the findings Thursday, Jan. 11, at the American Astronomical Society meeting in Washington. “The technology will help humanity navigate and explore the galaxy.”

NICER, an observatory about the size of a washing machine, currently is studying neutron stars and their rapidly pulsating cohort, called pulsars. Although these stellar oddities emit radiation across the electromagnetic spectrum, observing in the X-ray band offers the greatest insights into these unusual, incredibly dense celestial objects, which, if compressed any further, would collapse completely into black holes. Just one teaspoonful of neutron star matter would weigh a billion tons on Earth.

Although NICER is studying all types of neutron stars, the SEXTANT experiment is focused on observations of pulsars. Radiation emanating from their powerful magnetic fields is swept around much like a lighthouse. The narrow beams are seen as flashes of light when they sweep across our line of sight. With these predictable pulsations, pulsars can provide high-precision timing information similar to the atomic-clock signals supplied through the GPS system.

“We’re doing very cool science and using the space station as a platform to execute that science, which in turn enables X-ray navigation,” said Goddard’s Keith Gendreau, the principal investigator for NICER, who presented the findings Thursday, Jan. 11, at the American Astronomical Society meeting in Washington. “The technology will help humanity navigate and explore the galaxy.”

NICER, an observatory about the size of a washing machine, currently is studying neutron stars and their rapidly pulsating cohort, called pulsars. Although these stellar oddities emit radiation across the electromagnetic spectrum, observing in the X-ray band offers the greatest insights into these unusual, incredibly dense celestial objects, which, if compressed any further, would collapse completely into black holes. Just one teaspoonful of neutron star matter would weigh a billion tons on Earth.

Although NICER is studying all types of neutron stars, the SEXTANT experiment is focused on observations of pulsars. Radiation emanating from their powerful magnetic fields is swept around much like a lighthouse. The narrow beams are seen as flashes of light when they sweep across our line of sight. With these predictable pulsations, pulsars can provide high-precision timing information similar to the atomic-clock signals supplied through the GPS system.

This animation shows how NICER scans the sky and highlights the mission’s main features. This animation shows how NICER scans the sky and highlights the mission’s main features. Credits: NASA's Goddard Space Flight Center

This animation shows how NICER scans the sky and highlights the mission’s main features.
Credits: NASA’s Goddard Space Flight Center

 
Veteran’s Day Demonstration

In the SEXTANT demonstration that occurred over the Veteran’s Day holiday in 2017, the SEXTANT team selected four millisecond pulsar targets — J0218+4232, B1821-24, J0030+0451, and J0437-4715 — and directed NICER to orient itself so it could detect X-rays within their sweeping beams of light. The millisecond pulsars used by SEXTANT are so stable that their pulse arrival times can be predicted to accuracies of microseconds for years into the future.

During the two-day experiment, the payload generated 78 measurements to get timing data, which the SEXTANT experiment fed into its specially developed onboard algorithms to autonomously stitch together a navigational solution that revealed the location of NICER in its orbit around Earth as a space station payload. The team compared that solution against location data gathered by NICER’s onboard GPS receiver.

“For the onboard measurements to be meaningful, we needed to develop a model that predicted the arrival times using ground-based observations provided by our collaborators at radio telescopes around the world,” said Paul Ray, a SEXTANT co-investigator with the U. S. Naval Research Laboratory. “The difference between the measurement and the model prediction is what gives us our navigation information.”

The goal was to demonstrate that the system could locate NICER within a 10-mile radius as the space station sped around Earth at slightly more than 17,500 mph. Within eight hours of starting the experiment on November 9, the system converged on a location within the targeted range of 10 miles and remained well below that threshold for the rest of the experiment, Mitchell said. In fact, “a good portion” of the data showed positions that were accurate to within three miles.

“This was much faster than the two weeks we allotted for the experiment,” said SEXTANT System Architect Luke Winternitz, who works at Goddard. “We had indications that our system would work, but the weekend experiment finally demonstrated the system’s ability to work autonomously.”

Although the ubiquitously used GPS system is accurate to within a few feet for Earth-bound users, this level of accuracy is not necessary when navigating to the far reaches of the solar system where distances between objects measure in the millions of miles. “In deep space, we hope to reach accuracies in the hundreds of feet,” Mitchell said.

This illustration shows the NICER mission at work aboard the International Space Station. Credits: NASA's Goddard Space Flight Center

This illustration shows the NICER mission at work aboard the International Space Station.
Credits: NASA’s Goddard Space Flight Center

 
Next Steps and the Future

Now that the team has demonstrated the system, Winternitz said the team will focus on updating and fine-tuning both flight and ground software in preparation for a second experiment later in 2018. The ultimate goal, which may take years to realize, would be to develop detectors and other hardware to make pulsar-based navigation readily available on future spacecraft. To advance the technology for operational use, teams will focus on reducing the size, weight, and power requirements and improving the sensitivity of the instruments. The SEXTANT team now also is discussing the possible application of X-ray navigation to support human spaceflight, Mitchell added.

If an interplanetary mission to the moons of Jupiter or Saturn were equipped with such a navigational device, for example, it would be able to calculate its location autonomously, for long periods of time without communicating with Earth.

Mitchell said that GPS is not an option for these far-flung missions because its signal weakens quickly as one travels beyond the GPS satellite network around Earth.

“This successful demonstration firmly establishes the viability of X-ray pulsar navigation as a new autonomous navigation capability. We have shown that a mature version of this technology could enhance deep-space exploration anywhere within the solar system and beyond,” Mitchell said. “It is an awesome technology first.”

NICER is an Astrophysics Mission of Opportunity within NASA’s Explorers program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined and efficient management approaches within the heliophysics and astrophysics science areas. NASA’s Space Technology Mission Directorate funds the SEXTANT component of the mission through its Game Changing Development Program.

Related Links:

NASA’s NICER mission website
More information on SEXTANT
Download NICER-SEXTANT multimedia resources

By Lori Keesey and Clare Skelly
Goddard Space Flight Center

 
 
 
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*Source: NASA.gov

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New NASA Mission to Study Mysterious Neutron Stars, Aid in Deep Space Navigation

Though we know neutron stars are small and extremely dense, there are still many aspects of these remnants of explosive deaths of other stars that we have yet to understand. NICER, a facility to be mounted on the outside of the International Space Station, seeks to find the answers to some of the questions still being asked about neutron stars. By capturing the arrival time and energy of the X-ray photons produced by pulsars emitted by neutron stars, NICER seeks to answer decades-old questions about extreme forms of matter and energy. Data from NICER will also be used in SEXTANT, an on-board demonstration of pulsar-based navigation.
Credits: NASA’s Johnson Space Center

 

A new NASA mission is headed for the International Space Station next month to observe one of the strangest observable objects in the universe.

Launching June 1, the Neutron Star Interior Composition Explorer (NICER) will be installed aboard the space station as the first mission dedicated to studying neutron stars, a type of collapsed star that is so dense scientists are unsure how matter behaves deep inside it.

A neutron star begins its life as a star between about seven and 20 times the mass of our sun. When this type of star runs out of fuel, it collapses under its own weight, crushing its core and triggering a supernova explosion. What remains is an ultra-dense sphere only about 12 miles (20 kilometers) across, the size of a city, but with up to twice the mass of our sun squeezed inside. On Earth, one teaspoon of neutron star matter would weigh a billion tons.

“If you took Mount Everest and squeezed it into something like a sugar cube, that’s the kind of density we’re talking about,” said Keith Gendreau, the principal investigator for NICER at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Because neutron stars are so dense, scientists are uncertain how matter behaves in their interiors. In everyday experience, objects are composed of atoms. When neutron stars form, their atoms become crushed together and merge. As a result, the bulk of a neutron star is made up of tightly packed subatomic particles — primarily neutrons, as well as protons and electrons, in various states. NICER measurements will help scientists better understand how matter behaves in this environment.

“As soon as you go below the surface of a neutron star, the pressures and densities rise extremely rapidly, and soon you’re in an environment that you can’t produce in any lab on Earth,” said Columbia University research scientist Slavko Bogdanov, who leads the NICER light curve modeling group.

The only object known to be denser than a neutron star is its dark cousin, the black hole. A black hole forms when a star more than approximately 20 times the mass of our sun collapses. A black hole’s powerful gravity establishes a barrier known as an event horizon, which prevents direct observation. So scientists turn to neutron stars to study matter at nature’s most extreme observable limit.

“Neutron stars represent a natural density limit for stable matter that you can’t exceed without becoming a black hole,” said Goddard’s Zaven Arzoumanian, NICER deputy principal investigator and science lead. “We don’t know what happens to matter near this maximum density.”

In order to study this limit, NICER will observe rapidly rotating neutron stars, also known as pulsars. These stars can rotate hundreds of times per second, faster than the blades of a household blender. Pulsars also possess enormously strong magnetic fields, trillions of times stronger than Earth’s. The combination of fast rotation and strong magnetism accelerates particles to nearly the speed of light. Some of these particles follow the magnetic field to the surface, raining down on the magnetic poles and heating them until they form so-called hot spots that glow brightly in X-ray light.

“NICER is designed to see the X-ray emission from those hot spots,” Arzoumanian said. “As the spots sweep toward us, we see more intensity as they move into our sightline and less as they move out, brightening and dimming hundreds of times each second.”

A neutron star’s gravity is so strong it warps space-time, the fabric of the cosmos, distorting our view of the star’s surface and its sweeping hot spots. NICER will measure brightness changes related to these distortions as the star spins. This will allow scientists to determine the pulsar’s radius, a key measurement needed to fully understand its interior structure.

“Once we have a measure of the mass and radius, we can tie those results directly into the nuclear physics of what goes on when you compress so much mass into such a small volume,” Arzoumanian said.

In addition to understanding how neutron stars are put together, NICER’s observations will also help scientists better understand the critical mass a star must achieve before it can turn into a black hole. This is particularly important in systems where neutron stars orbit another star, allowing them to pull material off the companion star and gain more mass.

“The more neutron stars we observe at high masses, the higher the mass threshold becomes for a star turning into a black hole,” said NICER science team member Alice Harding at Goddard. “Understanding what that critical mass is will help us determine how many black holes and neutron stars there are in the universe.”

NICER will also provide scientists and technologists with a unique opportunity to make advances in deep space navigation. Its X-ray measurements will record the arrival times of pulses from each neutron star it observes, using the regular emissions of pulsars as ultra-precise cosmic clocks, rivaling the accuracy of atomic clocks such as those used inside GPS satellites. Built-in flight software — developed for the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) demonstration — can see how the predicted arrival of X-ray pulses from a given neutron star changes as NICER moves in its orbit. The difference between expected and actual arrival times allows SEXTANT to determine NICER’s orbit solely by observing pulsars.

Although spacecraft in Earth orbit use the same GPS system that helps drivers navigate on the ground, there’s no equivalent system available for spacecraft traveling far beyond Earth.

“Unlike GPS satellites, which just orbit around Earth, pulsars are distributed across our galaxy,” said Jason Mitchell, the SEXTANT project manager at Goddard. “So we can use them to form a GPS-like system that can support spacecraft navigation throughout the solar system, enabling deep-space exploration in the future.”

Installation on the space station provides scientists and technologists with an opportunity to develop a multi-purpose mission on an established platform.

“With the NICER-SEXTANT mission, we have an excellent opportunity to use the International Space Station to demonstrate technology that will lead us into the outer solar system and beyond, and tell us about some of the most exciting objects in the sky,” Gendreau said.

NICER is an Astrophysics Mission of Opportunity within NASA’s Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined and efficient management approaches within the heliophysics and astrophysics science areas. NASA’s Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

 
Related Links:

NASA’s NICER mission website
More information on SEXTANT
Download NICER-SEXTANT multimedia resources

 
 
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*Source: NASA.gov

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Close-up View of Neutron Star Mission’s X-Ray Concentrator Optics

A new NASA mission, the Neutron Star Interior Composition Explorer (NICER), is headed for the International Space Station next month to observe one of the strangest observable objects in the universe. Launching aboard SpaceX’s CRS-11 commercial resupply mission, NICER will be installed aboard the orbiting laboratory as the first mission dedicated to studying neutron stars, a type of collapsed star that is so dense scientists are unsure how matter behaves deep inside it.

In this photo, NICER’s X-ray concentrator optics are inspected under a black light for dust and foreign object debris that could impair functionality once in space. The payload’s 56 mirror assemblies concentrate X-rays onto silicon detectors to gather data that will probe the interior makeup of neutron stars, including those that appear to flash regularly, called pulsars.

The Neutron star Interior Composition Explorer (NICER) is a NASA Explorer Mission of Opportunity dedicated to studying the extraordinary environments — strong gravity, ultra-dense matter, and the most powerful magnetic fields in the universe — embodied by neutron stars. An attached payload aboard the International Space Station, NICER will deploy an instrument with unique capabilities for timing and spectroscopy of fast X-ray brightness fluctuations. The embedded Station Explorer for X-ray Timing and Navigation Technology demonstration (SEXTANT) will use NICER data to validate, for the first time in space, technology that exploits pulsars as natural navigation beacons.

More: New NASA Mission to Study Mysterious Neutron Stars, Aid in Deep Space Navigation

Image Credit: NASA/Goddard Space Flight Center/Keith Gendreau

 
 
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*Source: NASA.gov

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X-Rays: Next-Gen Way to Travel and Talk in Space?

Galaxies

NASA scientists say they have figured out a way to use X-rays to both communicate with long-distance spacecraft, as well as navigate as they sail past the outer limits of the solar system.

They say that using X-rays is faster than existing radio wave communications, can carry more information and won’t be blocked when spacecraft enter a planet’s thick atmosphere.

“While we are using X-ray navigation to guide us to Pluto, we might also use X-ray communication to talk back to Earth,” said Keith Gendreau, principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Md.
 


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Source*: Discovery.com

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NASA Taps the Power of Zombie Stars in Two-in-One Instrument

NICER/SEXTANT Payload

This artist’s rendition shows the NICER/SEXTANT payload that NASA recently selected as its next Explorer Mission of Opportunity. The 56-telescope payload will fly on the International Space Station. Credit: NASA

Neutron stars have been called the zombies of the cosmos. They shine even though they’re technically dead, occasionally feeding on neighboring stars if they venture too close. Interestingly, these unusual objects, born when a massive star extinguishes its fuel and collapses under its own gravity, also may help future space travelers navigate to Mars and other distant destinations.
 


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Source*: NASA.gov

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NICER/SEXTANT

SEXTANT/NICER production parts Credits: NASA

SEXTANT/NICER production parts Credits: NASA

Untitled-2 Untitled-21DSC_0486DSC_0484On April 15, 2010, the President challenged NASA to “break through the barriers” to enable the “first-ever crewed missions beyond the Moon into deep space” by 2025. One of these barriers is navigation technology.In the 18th century, the advancement of clock technology and resulting improvement in navigation fidelity brought us to the New World that we now call home. In support of NASA’s push to explore new worlds beyond low Earth orbit (LEO), and to serve a variety of national needs, the NICER (Neutron star Interior Composition ExploreR) team proposes to use the International Space Station (ISS) to validate a revolutionary navigation technology.

The NICER/SEXTANT (NICER is the name given to the instrument for the SMD proposal, but NICER and SEXTANT are the same instrument) concept uses a collection of pulsars— stellar “lighthouses”—as a time and navigation standard just like the atomic clocks of the Global Positioning System (GPS). Unlike GPS satellites, NICER pulsars are distributed across the Galaxy, providing an infrastructure of precise timing beacons that can support navigation throughout the Solar System. Since their discovery in 1967, pulsars have been envisioned as a tool for Galactic navigation (Figure 1). An NICER system measures the arrival times of pulses through the detection of X-ray photons; a sequence of measurements is then stitched together into an autonomous on-board navigation solution.

NASA’s plans for distant exploration demand breakthrough navigation tools. The best current capabilities are resource-intensive and degrade as explorers recede from Earth. At Mars, they yield crossrange spacecraft positions to a few kilometers, but impose scheduling burdens on the Deep Space Network (DSN). For critical applications such as orbit insertion at Jupiter and beyond, the current state-of-the-art is pushed to its practical limit. NICER complements the existing navigation toolbox, promising three-dimensional position accuracies better than 500 m anywhere in the Solar System.  Ultimately, a small (~0.1 m3), low mass (<~10 kg) NICER package will offer a cost effective on-board navigation option for the redundancy and reliability required for human exploration beyond LEO, and will enable deep-space missions that are not feasible with Earth-based tracking.

X-ray pulsar timing applications address the navigation and exploration goals of the National Space Policy of June 28, 2010, and NASA, DoD, and NIST are investing in technology development to exploit them. As celestial clocks, pulsars offer a new time standard that can be independently generated anywhere. The DoD is exploring applications enabled by a network of spacecraft with synchronized clocks, including mitigation of vulnerabilities in GPS. DARPA has funded the X-ray Timing (XTIM) program, which, in collaboration with the ISS NICER experiment, will demonstrate distributed time-synchronization using celestial sources.

 

sextant-copy

Figure 1: NICER/SEXTANT brings to practical reality the concept of a pulsar based map, first used on the Pioneer Plaque to encode (radial lines at left) the Sun’s location in the Galaxy [3].

NICER (Neutron Star Interior Composition Explorer) is a SMD science mission chosen to go into Phase A. NICER represents a science aspect of SEXTANT, where looking at many of the same Neutron Stars we need to enable pulsar navigation, scientists can also learn about the densest objects in the universe and study extreme physics.

The combination of the science and technology demonstration represented by SEXTANT reflects a true cost sharing between very different parts of NASA and the US Government.

The selection notice is at:
http://www.nasa.gov/home/hqnews/2011/sep/HQ_11-328_Science_Proposals.html

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