SEXTANT - Sta+on Explorer for X-ray Timing & Navigaon Technology Ronald J. Litchford, Ph.D., P.E. Principal Technologist NASA Space Technology Mission Directorate 593rd WE-Heraeus Seminar Physikzentrum Bad Honnef, DEU, JUNE 8-11, 2015 GSFC 1 • Millisecond Pulsar X-ray Navigaon (XNAV) – XNAV Concept & Development History – NICER/SEXTANT: Companion Science/Technology Missions • SEXTANT Mission Overview – ISS Flight Plaorm & Hardware – SEXTANT Mission ObjecQves • SEXTANT System Architecture – X-ray Timing Instrument (XTI) – Flight So`ware – Ground Testbed & End-to-End Simulaon – Ground System – CONOPS • Summary 2 • Millisecond Pulsar X-ray Navigaon – Pulsars are neutron stars that appear to pulsate across the electromagneQc spectrum, but are bright enough in X-rays to enable XNAV instrumentaon & soluQons – Some millisecond pulsars (MSPs) rival atomic clocks in long- term Qming stability – Pulse phase or Qme of arrival deviaons can update spacecra dynamics model along line of sight – Observing mulQple MSPs can yield 3D orbit data – GPS-like posiQoning & Qming throughout solar system & beyond -8 PSR B1937+21 (radio) -10 PSR B1855+09 (radio) -12 -14 PSR B1937+21 Log [Fractional Clock Stability]Log Baseline mission (NICER) -16 0.1 1 10 Time Interval (yr) NE2024 3 One column Two column • XNAV has rich history beginning with discovery of first radio pulsar – Significant body of published research • Naval Research Laboratory (NRL) (1999-2000) – UnconvenQonal Stellar Aspect (USA) Experiment • DARPA XNAV Project (2005-2006) – Ball Aerospace collaborated with Microcosm Inc. – Algorithms, Infrastructure – Detector and Pulsar modeling studies (NRL) – Modulated X-ray Source (MXS) developed, Gendreau • DARPA XTIM (2009-2012) conQnuaon DARPA XNAV, led by Lockheed with Ball Aerospace – Used Large Area Collimated Detector • NASA SBIRs with Microcosm • NICER / SEXTANT selecQon 04/2013 – SEXTANT team deeply involved in prior programs – EvoluQon of XNAV detector ideas shows NICER XTI (concentrang opQcs/ silicon det) to be pracQcally ideal • Prior work has set the stage for SEXTANT to perform the full onboard XNAV OD 4 • NICER – Neutron Star Interior ComposiQon ExploreR – Fundamental invesQgaon of ultra-dense maer: structure, dynamics, & energeQcs – Launch in Oct 2016 on Space-X Dragon – 18 Month mission on Express LogisQcs Carrier (ELC) – X-ray Timing Instrument (XTI) • X-ray (0.2–12 keV) concentrator (single-bounce) opQcs and silicon-dri` detectors • High precision Qme tagging (300 ns absolute) • Large effecQve area (>1800 cm2) • X-ray detectors with high quantum efficiency and spectral resoluQon Instrument Optical Bench Detector Photon Slow Peak Signal Shaper Detect • SEXTANT – XNAV Flight Demo Fast LLD Event X-Rays Shaper Logic – STMD/GCDP funded technology enhancement Time & Zero 28V Pulse Height Cross Detector Amplitude Trigger Power Capture x8 Reset Unit (MPU) x7 st Focal Plane Module x56 Concentrators x56 – 1 demo of real-Qme, on-board pulsar XNAV Measurement/Power Heat Microcontroller Radiator – Leverage NICER Hardware with enhanced flight RS422 Link for GPS Pulse Commands & data Per Second NE2199 XNAV so`ware Block diagram of NICER XTI 5 One column Two column You are here… Folded Light Curve for PSR−J0534+2200 250 folded counts fit pulse true pulse 200 ϕˆ,ωˆ 150 NICER 100 50 Instrument Folded photon arrival times (photon counts) 0 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 X-ray photons Time (sec) SEXTANT algorithms 6 • SEXTANT Primary Objec+ve Provide first demonstra2on of real-2me, on-board X-ray Pulsar Naviga2on – Primary Objecve: 10 km orbit determina2on accuracy, worst direcon, 2 weeks – Implement a fully funcQonal XNAV system in a challenging ISS/LEO orbit; NICER compable – Advance XNAV technologies • Secondary Objec+ves – Repeat XNAV demo with new NICER data & new MSP discoveries – Validate & enhance the unique Goddard XNAV Lab Testbed (GXLT) – Use SEXTANT data & GXLT to study real-world XNAV scenarios – Evaluate candidate photon processing & navigaon algorithms & develop new techniques – Study uQlity of pulsars for Qme keeping & clock synchronizaon • Planned Experiments – 2-week period observing 3 – 5 pulsars early in the mission (primary) – OpportunisQc experiments – Ground experiments using collected photon data • Stretch Objec+ve – 1 km orbit determina2on accuracy, worst direcon, using up to 4 weeks of observa2ons. 7 NICER&XTI& Flight&So:ware& Event& Concentrator& Detector& MPU+GPS& Algorithms& Filtering& XKrays& GPS&*me&stamped&& Photon&+&Background&& events& GEONS& Pulse&Phase& naviga*on& Es*ma*on& GPS&*me&stamped& processing& Photon&+&Background&& events,&GPS&telemetry& Pulsar&almanac& TLM& Pulsar&almanac&entries&(*ming&models,& Ground&System& templates)&and&alert&messages& So:ware& Ground&System& Testbed& Goddard&XNAV& Lab&Testbed& Test&s*mulus& (GXLT)& Test&s*mulus& Proving&ground&for&algorithm& Pulsar&data&from&observatories& development,&valida*on,&test&Proving&ground&for&algorithm& development,&valida*on,&test& (Arecibo,&FERMI,&etc.)& 8 • 56 co-aligned X-ray concentrator opQcs and associated Silicon Dri` Detectors (SDDs) in Focal Plane Modules (FPMs) • 7 Measurement/Power Units (MPUs) • The FPMs detect X-rays arriving from the concentrators • MPUs Qme-tag and packeQze photon events • < 300 nsec absolute Qme resoluQon • > 1800cm2 effecQve area • Moderate (CCD-like) energy resoluQon Stowed, deploying, and observing at ELC mounted loca2on on ISS 9 • XNAV Flight So`ware (XFSW) Sequence Flow: – XTI detects events from sequenQal pulsar observaons, output via MPU – Pre-process filtering of photon events and buffer collecQon to obtain stasQcally sufficient observaons of a single pulsar – Batch process events to extract single measurement of phase, Doppler, count rates – Navigaon algorithm (GEONS EKF) blends models of S/C dynamics with phase & frequency measurements to update spacecra state esQmate • Ground system maintains pulsar almanac used by XFSW XNAV Flight So`ware XTI/MPU Event Commands DetecQon Filtering and Photon Almanac Data Events X-ray Photons Photon Processing Measurements & State PredicQons GEONS Telemetry Nav Filter 10 Outline Photon Arrival Model ¯ ¯ e (⇤(tb) ⇤(ta))(⇤¯(t ) ⇤¯(t ))k P(k;(t , t )) = − − b − a (1) • The arrival Qmes of X-ray photons at the a b k! detector are modeled as a non- homogeneous Poisson process (NHPP) with quasi-periodic rate funcQon: Outline λ¯(t)=λ(φ(t)) = β + ↵h(φ(t)) (2) Outline Photon• h is the known pulsar Arrival Model lightcurve ⇤¯(t)= t λ¯(s)ds• .periodic in [0,1) integrang to 1 with Arrival Qmes follow a NHPP 0 minimum value 0 R ¯ ¯ • b is total background rate e (⇤(tb) ⇤(ta))(⇤¯(t ) ⇤¯(t ))k P(k;(t , t )) = − − b − a (1) • a is the mean signal rate a b k! Photon Arrival Model Munther Hassouneh Equations used in IEEE AeroSpace Conference Presentation The probability of k events arriving in the interval (ta, tb ) is given by λ¯(¯t)=λ¯ (φ(t)) = β + ↵h(φ(t)) (2) e (⇤(tb) ⇤(ta))(⇤¯(t ) ⇤¯(t ))k P(k;(t , t )) = − − b − a (1) a b k! ¯ t ¯ ⇤(t)= 0 λ(s)ds. R Lightcurve recovery by “pulse folding” 11 Munther Hassouneh Equations used in IEEE AeroSpace Conference Presentation Munther Hassouneh Equations used in IEEE AeroSpace Conference Presentation Outline Outline φ(t)=φ (t ⌧(t)), (1) 0 − φ(t)=φ0(t ⌧(t)), (5) • The phase model at the detector is − φ(t)=φ (t ⌧(t)) For a Geocenter RefObs: 0 − – φ0 is the phase evoluQon at a reference ~x(t) n~ ~x(t) n~ φ(t)=φ t · Outline observatory (RefObs) 0 φ(t)=φ0 t · Outline − c − c ✓ ◆ ✓ ◆ – provided by the standard pulsar Qming so`ware ˜ ˜ ~x(t) n~ δ~x(t) n~ ~x(t) n~ δ~x(t) n~ ˜ TEMPO2 (see Hobbs et. al., Edwards et. al.) = φ t · + · = φ0 t · + · (~x(Outlinet) from filter) 0 − c c − c c ! • Extremely high fidelity models ! Outline ˜ ˜ • ~x(t) n~ ~x(t) n~ ˙ ~x(t) n~ δ~x(t) n~ ⌧Provides convenient piecewise polynomial (t)= · ~x˜(t) n~(6) δ~x(t) n~ φ0 t · + φ0 t · · , c ˜ ˙ ' − c − c c approximaons to the full Qming model φφ(t)+Outlineφ0 t · 0 · , ! ! ' − c ! c – τ(t) the prop Qme of the pulse wavefront moving =: φ˜(t)+e(t) ˜ δ~x(t)=~x˜(t) ~x(t), from the detector to the RefObs at speed = φ(t)+e(t), c where (2) − • If the RefObs is close to the detector δ~x(t)=~x˜(t) ~x~x˜((tt),) n~ δ~x(t) n~ ~x(t) n~ e(t):=φ˙ t · · ; (Geocenter) ⌧(t)= · (6) Munther Hassouneh0 − Equationsc used in IEEEc AeroSpace Conference Presentation c − For SEXTANT, we assume⇣ ~x˜(t) n~ ⌘δ~x(t) n~ where ~x( t) is the detector coordinates in a (7) e(t):=φ˙0 t · · ; My name Beamer slide examples − c (cq and f are frame centered at the RefObs~x and(t) n~ is the e(t) q + f (t ta) ⌧(t)= · '(6) ⇣ − ⌘ constants) direcQon to the given pulsar c - If the RefObs is not so close to the detector (e.g., Alternate models are possible but this SSB), parallax and Solar Shapiro delay terms are linear model works well in simulaons needed as well (with short observaon intervals) - SEXTANT’s algorithms are based on a Geocentric n~(t) (8) RefObs but can support SSB RefObs 12 Munther Hassouneh Equations used in IEEE AeroSpace Conference Presentation ~x(t) n~ ⌧(t)= · (7) My name Beamer slide examples c My name Beamer slide examples Munther Hassouneh Equations used in IEEE AeroSpace Conference Presentation ~x(t) n~ ⌧(t)= · (7) c Munther Hassouneh Equations used in IEEE AeroSpace Conference Presentation Outline Pulse Phase EsQmaon Algorithm 1. Observe arrival times T N during a fixed interval [t , t ]. { k }k=1 a b 2. Determine estimates (ˆq, fˆ) of the parameters (q, f )inthe model e(t)=q + f (t t ) by maximizing the log-likelihood − a function with T N { k }k=1 N L(✓ˆ)= log λ φ˜(T )+q + f (T t ) (↵ + β)(t t ) k k − a − b − a Xk=1 ⇣ ⌘ with ✓ =(q, f , ↵, β).