Neutron Star Interior Composition Explorer (NICER) - 05.10.17

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Neutron stars, the glowing cinders left behind when massive stars explode as supernovas, are the densest objects in the universe and contain exotic states of matter that are impossible to replicate in any lab. They shine most brightly in narrow beams that sweep the sky as the stars spin; from a great distance, they appear to pulse like lighthouse beacons (hence the name “pulsars”). From its perch aboard the International Space Station (ISS), the Neutron star Interior Composition Explorer (NICER) payload studies the extraordinary physics of these stars, providing new insights into their nature and behavior. Through the embedded Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) demonstration, it also paves the way for a future GPS-like system for spacecraft navigation anywhere in the Solar System using pulsars as natural beacons.
Science Results for Everyone
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The following content was provided by Kristina N. Pevear, and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Keith C. Gendreau, NASA Goddard Space Flight Center, Greenbelt, MD, United States
Zaven Arzoumanian, NASA Goddard Space Flight Center, Greenbelt, MD, United States

Information Pending

NASA Goddard Space Flight Center, Greenbelt, MD, United States
Massachusetts Institute of Technology, Cambridge, MA, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
NASA Research-SMD

Research Benefits
Scientific Discovery, Space Exploration

ISS Expedition Duration
April 2017 - September 2017; September 2017 - February 2018; -

Expeditions Assigned

Previous Missions
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Experiment Description

Research Overview

  • Neutron stars are objects consisting of ultra-dense matter at the threshold of collapse to a black hole. The nature of this matter, which cannot be produced in a laboratory, is unknown.
  • Neutron stars emit X-ray radiation that enables investigations into their structure, dynamics, and energetics, but X-rays do not penetrate the Earth’s atmosphere.
  • Neutron Star Interior Composition Explorer (NICER), an articulated payload mounted on a zenith Express Logistics Carrier (ELC) on the ISS, provides full-hemisphere sky coverage for astronomical observations in the soft X-ray band (0.2 – 12 keV photon energy). These observations will help resolve competing models of neutron star composition, answer decades-old questions about extreme matter and gravity, and reveal the workings of the high-energy, dynamic phenomena that neutron stars exhibit.


Neutron Star Interior Composition Explorer (NICER) provides high-precision measurements of neutron stars (and other X-ray astrophysics phenomena) through observations in 0.2 – 12 keV X-rays, the electromagnetic band in which these stars radiate significant portions of their energy, addressing the following fundamental science questions:
  • What are the new states of matter at exceedingly high densities and temperatures?
  • How do cosmic accelerators work, and what are they accelerating?
  • Is a theory of matter and light needed at the highest energies?
  • What controls the mass, radius, and spin of compact stellar remnants?
NICER is the first mission capable of addressing these questions in-depth, with simultaneous fast timing and spectroscopy, with low background and high throughput, and ample sky coverage beyond Earth’s atmosphere.
The NICER payload comprises high-heritage components in an innovative configuration. The X-ray Timing Instrument (XTI) consists of an array of 56 grazing-incidence X-ray “concentrator” optics and matching silicon drift detectors, which detect individual X-ray photons to measure their energies and times of arrival. The payload uses an on-board GPS receiver to register photon detections to precise GPS time and position. The payload’s star tracker guides the payload’s pointing system, which uses gimbaled actuators to track and slew between inertial targets.
NICER’s primary scientific focus is an in-depth investigation of neutron stars – objects containing ultradense matter at the threshold of collapse to a black hole. Neutron stars are the smallest and densest stars in the known universe – although they have radii roughly the size of a city, their mass is typically 1.5–2 times that of the Sun. Some neutron stars, pulsars, emit powerful beams of radiation across the electromagnetic spectrum, such that they appear to pulse as their rotation sweeps these beams across the sky. Some of these objects, Millisecond Pulsars (MSPs), have such a regular and rapid pulsation rate that they rival atomic clocks in time-keeping accuracy and stability. Neutron stars are exotic objects that embody a physical environment impossible to replicate in a laboratory, in which all four fundamental forces of nature are simultaneously important.
The NICER payload uses the soft X-ray band to study the structure, dynamics, and energetics of neutron stars to:
  • Make mass and radius measurements enabled by pulse timing with unprecedented precision.
  • Enable discrimination among dozens of proposed equation of state (EOS) models, and develop constraints on a basic unknown of nuclear physics, the density-dependent nuclear symmetry energy.
  • Measure masses through phase coherent timing of binary pulsars.
  • Discover periodic and quasi-periodic pulsations in steady and transient neutron star systems.
  • Define constraints on the maximum spin rate of neutron stars.
  • Establish intrinsic rotational stabilities of MSPs on many-month timescales.
  • Provide long-term clock stabilities that support future “timing array” gravitational wave searches.
  • Derive cooling timescales of low and high-field pulsars.
  • Characterize spin variations and outbursts during “glitches.”
  • Define thermal and mechanical properties of the crust of neutron stars.
  • Study neutron star asteroseismology by measuring mode frequencies of stellar oscillations.
  • Determine radiation patterns, spectra, and relative phases across wavelength bands.
  • Test radiation models in ultra-strong magnetic and gravitational fields.
The SEXTANT technology demonstration is synergistic with NICER’s primary mission, and leverages targeting of rapidly spinning neutron stars (pulsars) with high stability in pulse timing to demonstrate the viability of pulsar-based navigation. SEXTANT uses X-ray sources to enable GPS-like autonomous navigation of spacecraft throughout the Solar System and beyond.
Although NICER’s standalone research offers definitive improvements to existing scientific understanding, NICER’s data have significant synergy with existing and future missions that can further expand humankind’s understanding of the universe. For example, NICER offers an opportunity for comprehensive study of Fermi sources consistent with young or millisecond pulsars, especially radio-quiet pulsars. NICER’s superior low-energy coverage in the X-ray band complements the Rossi X-ray Timing Explorer's (RXTE's) spectral coverage for X-ray burst spectra, even though simultaneous observations are not possible. Phase-resolved NICER spectroscopy discriminates among radiation components, defining surface and polar-cap temperatures and pulsations, while a future X-ray polarimeter mission could provide a complementary test of Comptonization in thermal polar cap models. NICER can also provide sensitive follow-up for source identification for transients and glitches observed by MAXI (an ISS Japanese Experiment Module-based X-ray camera that searches for celestial transients) and other all-sky monitors.
NICER has also planned for a Guest Observer program that enables X-ray astrophysics observations beyond neutron stars. Proposals for such guest observations are peer-reviewed to competitively select observations of targets not necessarily limited to neutron stars, enabling study of ultraluminous X-ray sources, black holes, active galactic nuclei, clusters of galaxies, nearby stars, and other scientifically significant targets.
NICER's primary mission to perform an in-depth study of neutron stars offers unrivaled astrophysics knowledge and can revolutionize the understanding of ultra-dense matter. SEXTANT's demonstration of X-ray based navigation technology can help expand the sphere of GPS-like navigation capability, providing a foundation for reliable navigation throughout our Solar System and beyond. Scientific returns are dramatically increased for all parties by leveraging the interplay between NICER and other missions across wavelengths. Further scientific returns are enabled by NICER's guest observer program. NICER/SEXTANT can significantly advance fundamental nuclear, particle, and gravitational physics, and contribute to a greater understanding of our Universe.

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Space Applications
The NICER investigation consists of an instrument that will study neutron stars with unprecedented precision, increasing understanding of some of the most extreme conditions in the universe. In addition, the investigation includes a software-based technology demonstration called the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT), which marks a milestone in the attempt to establish a pulsar-based navigation system. SEXTANT takes advantage of NICER’s observations of X-ray-emitting millisecond pulsars, which are as reliable as atomic clocks in keeping accurate time. Precise timekeeping is essential for accurate navigation. Pulsar navigation would work similarly to GPS navigation on Earth, providing precise positioning for spacecraft throughout the Solar System.

Earth Applications
In laboratories, physicists can replicate some of the most extreme physical environments in the universe, but it is impossible to recreate the incredible density of a neutron star, where unusual physical phenomena take place. This investigation enables new studies of neutron stars and other astrophysical sources of X-rays, advancing scientific understanding, education, and technical development for the benefit of people on Earth. In addition, the investigation takes steps toward a new type of accurate navigation and positioning system for spacecraft, which uses X-ray-emitting pulsars distributed throughout our Galaxy, instead of atomic clocks on Earth-orbiting satellites, as in the Global Positioning System (GPS). Pulsar-based navigation can work anywhere in the Solar System, benefiting future manned missions to Mars or other distant destinations.

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Operational Requirements and Protocols

NICER achieves its science objectives by collecting X-ray photons from neutron stars distributed across the sky. Fifteen million seconds (Msec; equivalent to 6 uninterrupted months) of total exposure time distributed over 18 calendar months for several dozen identified targets are required to achieve the baseline science objectives.
NICER requires standard ISS power (28V and 120V) and data services available at its ELC location, including the Low Rate Data Link for command and telemetry via the 1553, and the High-Rate Data Link via Ethernet. The data is transported through the existing ISS space and ground infrastructure to and from the NICER SMOC at GSFC. The primary interface for the SMOC is the Payload Operations Integration Center (POIC) that resides at the Huntsville Operations Support Center (HOSC) at NASA’s Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Telemetry data are routed to the NICER ground system via the HOSC, and NICER instrument command sequences developed in the SMOC are transferred to the HOSC for integration with other ISS uplink products.
NICER uses ISS video capability to confirm initial deploy and stow.

Typically, NICER observes two or three targets during an ISS orbit. The first target is tracked until a viewing constraint is about to be violated (e.g., solar panel or Earth blockage), then NICER slews to a second target fairly rapidly (up to 1 deg/sec), acquires the second target and tracks it until a viewing constraint is nearly violated, then NICER slews to a third target, and so on. The complete science dataset for a given target includes many individual observations, potentially accumulated over hours, days, or years. NICER carries a time and position standard based on GPS that enables multiple observations to be pieced together into a coherent dataset across the entire mission lifetime. Each photon detected by NICER is time tagged with an absolute precision of better than 100 nanoseconds and with NICER position knowledge to better than ±10 m. NICER’s instrument remains locked onto specified targets to better than 120 arcseconds.
In general, NICER operates continuously while on orbit. However, when EVA activities are in the vicinity of ELC2, NICER is stowed.

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Decadal Survey Recommendations

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Results/More Information

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Related Websites
Video Animation of NICER Deploy and Track on board ISS

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Stowed NICER -X Side

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Stowed NICER -Y Side

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First 56 NICER Flight X-Ray Concentrators

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image NICER Payload Model
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