SEXTANT X-ray Pulsar Navigation Demonstration: Additional On-Orbit Results

Abstract

The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a technology demonstration enhancement to the Neutron-star Interior Composition Explorer (NICER) mission, a NASA Astrophysics Explorer Mission of Opportunity to the International Space Station, launched in June of 2017. In late 2017, SEX-TANT successfully completed a first demonstration of in-space and autonomous X-ray pulsar navigation (XNAV). This form of navigation relies on processing faint signals from millisecond pulsars-rapidly rotating neutron stars that appear to pulsate in the X-ray band-and could potentially provide a GPS-like navigation capability applicable throughout the solar-system and beyond. In this work, we briefly review prior SEXTANT results and then present new results focusing on: making use of the high-flux but rotationally unstable Crab pulsar, and using XNAV to estimate position, velocity, and time in the presence of an imperfect local clock.

Applications of a Particular Four-Dimensional Projective Geometry to Galactic Dynamics

“…This would mean there are three nowhere vanishing space vector fields defined everywhere on the spacetime manifold M. This is topologically perfectly feasible since M is homeomorphic to H 1,3 (or H 1,3 s ) unlike the anti-de Sitter spaces. However, this is precisely the Newtonian view of observers who attribute to certain relative distances r an absolute content independent of the observer or a cosmological content with "cosmological" rulers to evaluate distances (e.g., with for instance the Hubble constant, approaches using baryon acoustic oscillations; or, possibly more effective, relativistic localizing systems which extend the galactic, relativistic positioning systems [20,21] recently implemented by an experiment on board the ISS using X-rays detection emitted from pulsars [22]).…”

Sensor Configuration Trade Study for Navigation in Near Rectilinear Halo Orbits

“…Since X-ray pulsars are observed over the sky map and are of unique period and strength, X-ray pulsar navigation (XNav) has been proposed and used in a variety of studies [19][20][21]. XNav uses periodic X-ray pulsars emitted from a set of known pulsars in order to estimate the state of Gateway in deep space.…”

“…The measurement noise is applied based on the accuracy from SEXTANT on-orbit results, which give a value of 10 km, 3σ [21]. The four best pulsars, based on dilution of precision (DOP), are selected as navigation pulsars, with those being: B0531+21, B0540-69, B1821-24, and B1937+21.…”

Physical Justifications and Possible Astrophysical Manifestations of the Projective Theory of Relativity

“…The first experimental result implementing this protocol was performed by Ruggiero et al [24,25] using astronomical data from pulsars used to replace satellites. This galactic positioning protocol has also been very recently and successfully implemented on board the ISS by Winternitz et al [26] without any reference to the work of Coll, Tarantola, Ruggiero et al, which we quote to do them justice.…”