SEXTANT - Staon 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 Objecves • SEXTANT System Architecture – X-ray Timing Instrument (XTI) – Flight Soware – 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 electromagnec spectrum, but are bright enough in X-rays to enable XNAV instrumentaon & soluons – Some millisecond pulsars (MSPs) rival atomic clocks in long- term ming stability – Pulse phase or me of arrival deviaons can update spacecra dynamics model along line of sight – Observing mulple MSPs can yield 3D orbit data – GPS-like posioning & ming 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) – Unconvenonal 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) connuaon DARPA XNAV, led by Lockheed with Ball Aerospace – Used Large Area Collimated Detector • NASA SBIRs with Microcosm • NICER / SEXTANT selecon 04/2013 – SEXTANT team deeply involved in prior programs – Evoluon of XNAV detector ideas shows NICER XTI (concentrang opcs/ silicon det) to be praccally ideal • Prior work has set the stage for SEXTANT to perform the full onboard XNAV OD

4 • NICER – Neutron Star Interior Composion ExploreR – Fundamental invesgaon of ultra-dense maer: structure, dynamics, & energecs – Launch in Oct 2016 on Space-X Dragon – 18 Month mission on Express Logiscs Carrier (ELC) – X-ray Timing Instrument (XTI) • X-ray (0.2–12 keV) concentrator (single-bounce) opcs and silicon-dri detectors • High precision me tagging (300 ns absolute) • Large effecve area (>1800 cm2) • X-ray detectors with high quantum efficiency and spectral resoluon 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-me, 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 soware Block diagram of NICER XTI

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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 Objecve Provide first demonstraon of real-me, on-board X-ray Pulsar Navigaon – Primary Objecve: 10 km orbit determinaon accuracy, worst direcon, 2 weeks – Implement a fully funconal XNAV system in a challenging ISS/LEO orbit; NICER compable – Advance XNAV technologies • Secondary Objecves – 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 ulity of pulsars for me keeping & clock synchronizaon • Planned Experiments – 2-week period observing 3 – 5 pulsars early in the mission (primary) – Opportunisc experiments – Ground experiments using collected photon data • Stretch Objecve – 1 km orbit determinaon accuracy, worst direcon, using up to 4 weeks of observaons.

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 opcs 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 me-tag and packeze photon events • < 300 nsec absolute me resoluon • > 1800cm2 effecve area • Moderate (CCD-like) energy resoluon Stowed, deploying, and observing at ELC mounted locaon on ISS 9 • XNAV Flight Soware (XFSW) Sequence Flow: – XTI detects events from sequenal pulsar observaons, output via MPU – Pre-process filtering of photon events and buffer collecon to obtain stascally 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 esmate • Ground system maintains pulsar almanac used by XFSW XNAV Flight Soware

XTI/MPU Event Commands Detecon Filtering and Photon Almanac Data Events X-ray Photons Photon Processing Measurements & State Predicons GEONS Telemetry Nav Filter

10 Outline

Photon Arrival Model

¯ ¯ e (⇤(tb) ⇤(ta))(⇤¯(t ) ⇤¯(t ))k P(k;(t , t )) = b a (1) • The arrival mes of X-ray photons at the a b k! detector are modeled as a non- homogeneous Poisson process (NHPP) with quasi-periodic rate funcon: Outline ¯(t)=((t)) = + ↵h((t)) (2)

Outline Photon• h is the known pulsar Arrival Model lightcurve ⇤¯(t)= t ¯(s)ds• .periodic in [0,1) integrang to 1 with Arrival mes 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 ¯(¯t)=¯ ((t)) = + ↵h((t)) (2) e (⇤(tb) ⇤(ta))(⇤¯(t ) ⇤¯(t ))k P(k;(t , t )) = b a (1) a b k! ¯ t ¯ ⇤(t)= 0 (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 (t)= (t ⌧(t)), (1) 0

(t)=0(t ⌧(t)), (5) • The phase model at the detector is (t)= (t ⌧(t)) For a Geocenter RefObs: 0 – φ0 is the phase evoluon at a reference ~x(t) n~ ~x(t) n~ (t)= t · Outline observatory (RefObs) 0 (t)=0 t · Outline c c ✓ ◆ ✓ ◆ – provided by the standard pulsar ming soware ˜ ˜ ~x(t) n~ ~x(t) n~ ~x(t) n~ ~x(t) n~ ˜ TEMPO2 (see Hobbs et. al., Edwards et. al.) = t · + · = 0 t · + · (~x(Outlinet) from filter) 0 c c c c ! • Extremely high fidelity models ! Outline ˜ ˜ • ~x(t) n~ ~x(t) n~ ˙ ~x(t) n~ ~x(t) n~ ⌧Provides convenient piecewise polynomial (t)= · ~x˜(t) n~(6) ~x(t) n~ 0 t · + 0 t · · , c ˜ ˙ ' c c c approximaons to the full ming model φ(t)+Outline0 t · 0 · , ! ! ' c ! c – τ(t) the prop me of the pulse wavefront moving =: ˜(t)+e(t) ˜ ~x(t)=~x˜(t) ~x(t), from the detector to the RefObs at speed = (t)+e(t), c where (2) • If the RefObs is close to the detector ~x(t)=~x˜(t) ~x~x˜((tt),) n~ ~x(t) n~ ~x(t) n~ e(t):=˙ t · · ; (Geocenter) ⌧(t)= · (6) Munther Hassouneh0 Equationsc used in IEEEc AeroSpace Conference Presentation c For SEXTANT, we assume⇣ ~x˜(t) n~ ⌘~x(t) n~ where ~x( t) is the detector coordinates in a (7) e(t):=˙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) direcon 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 Esmaon 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 ˜(T )+q + f (T t ) (↵ + )(t t ) k k a b a Xk=1 ⇣ ⌘ with ✓ =(q, f , ↵, ). 3. Form phase and frequency estimates ˆ(t)=˜(t)+ˆq + fˆ(t t )andˆ˙(t)=˜˙(t)+fˆ,respectively. a

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Munther Hassouneh Equations used in IEEE AeroSpace Conference Presentation • The Cramér–Rao lower bound (CRLB) gives limit of achievable accuracy of any esmator with fully specified stascal model. • We can compute CRLB for NHPP model assuming α, β known – For XNAV the CRLB is smallest for short period, for highly peaked pulsars with high SNR • ML esmators asymptocally (many photons) achieve CRLB • CRLB useful for – performance esmaon – determining target observaon mes • There are other error sources including those associated with model mismatch – best you can do with a stascal model

14 • Goddard Enhanced Onboard Navigaon System (GEONS) – Flight-proven, Award-winning, NPR 7150.2 Compliant UD-Factorized Extended Kalman Filter – Esmate mulple spacecra absolute and/or relave states – Enables data fusion and regime independence Outline – Earth, Moon, LPOs, Deep Space – GPS, TDRSS, DSN/USN/GN, Crosslink, Celesal Object, Accelerometer, and XNAV measurements. ~x(t) n~ ⌧(t)= · (6) – Used (and will be used) on Terra, EO-1, GPM, MMS, NICER/SEXTANT c – Licensed to Orbital, Ball, ITT, Moog/Broad Reach • SEXTANT team added an XNAV measurement model to GEONS ~x(t) n~ (t)= t · + ⌫(t), where ⌫ is noise 0 c ✓ ◆ connects pulse phase observable with spacecra state (7) • Differenate to get a frequency measurement equaon

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~x(t) (8)

n~(t) (9)

Munther Hassouneh Equations used in IEEE AeroSpace Conference Presentation Level 0 simulaon Level 2 simulaon • Soware only XNAV measurement simulaon • Hardware-in-the-loop simulaon • Useful for long term studies (deep space • Test-as-you-fly trajectories, etc) • Use the Modulated X-ray source (MXS) to Level 1 simulaon generate the photon events • Soware only photon event simulaon • X-ray detector & electronics me-tag the • Photon Processing algorithm implemented for photon events measurement generaon • Useful for tesng flight hardware • Primary mode of development for SEXTANT

Measurement) Simula,on)

Scenario) Pulsars) Defini,on) Pulsars) X

Modulated)) Mission) True) Visibility)/) Observa,on) Pulse)Phase) Meas.)) )X

Legend( Pulsars)

I/O)Data) Alternate(simula-on(paths( Es,mated) SoIware)accelerated)mode:) Ephemeris) SoIware) measurement

16 Light Curve & MXS/XDET Detections Driver v1

MXS/XDET Driver v2

Control SDD MXS Program

17 • Achieving performance GEONS filtered pos/vel errors 15 levels that meet SEXTANT requirement 10 (10km worst direcon aer 14 days) with 5 margin. • Three pulsars: pos errors (km) 0 0 2 4 6 8 10 B1937+21,B1821-24, time into sim (days)

J0218+4232 0.015 • Large inial errors added errors covariance to the state 0.01 • Rapid divergence occurs without processing XNAV 0.005 measurements 0

velocity errors (km/s) 0 2 4 6 8 10 time into sim (days)

18 • Generate and maintain the pulsar • Monitor performance almanac – Trending – Timing models – Alerts – Profile templates (light-curves) • Driven inially with radio – NICER data aer sufficient data collected observaons • Maintain and update applicaon – Pulsar upload tables – GEONS maintenance commands Ground&Radio&&&Space& Observatories& NICER&

& Genera:on&of& &Products&for& Raw&Timing& SEXTANT&Pulsar& Timing&Models,& XFSW&Upload& Data&Analysis& Catalog& NICER&SMOC& Templates,&Rates,&Etc.&& Commands& & & XNAV&& Monitoring&and& Analysis& & 19 20 21 22 • NICER in Phase C • Successful review progress – SEXTANT Baseline Review Aug 2013 – NICER PDR Dec 2013 – SEXTANT CDR-EPR Aug 2014 – GCD Connuaon Review Aug 2014 – NICER IFSW Aug 2014 – NICER CDR Sep 2014 • Milestones – XFSW Build 0 (internal) Dec 2013 – XFSW Build 1 Apr 2014 – XFSW Build 1.1 (clean-up) May 2014 – IFSW Build 1 integraon & tesng Jun 2014

23 • NICER/SEXTANT is an excellent partnership between science and technology (SMD & STMD) • SEXTANT will be a: – First demonstraon of real-me, on-board XNAV – Significant historical event enabled by ISS – Bridge between science, technology & exploraon to connect with the public • Near-term milestones – XFSW Build 2 Mar 2015 – IFSW Build 2 tesng • NICER URL – http://heasarc.gsfc.nasa.gov/docs/nicer/!

24 25 ELC MPU (7) GPS Star Tracker GCE Ethernet 1553 RS-422 (7) RS-422 RS-422 RS-422

Power Telemetry Remote Memory Inst. Poinng ✔ Orbit Data Data Data Analog XNAV Output Terminal Scrub Manager Control Models I/O GPS I/O STS I/O GCE Thermal

Inter-task Message Router (SW Bus)

File Data Flash Commander Ingest File Manager

Soware Time Execuve Event Table Bus Services Services Services Services

CFE/S Reuse Checksum House Memory Scheduler Data File CFDP File Keeping Dwell Storage Manager Transfer New

Health & Limit Memory Stored Heritage Safety Checker Manager Command Local Storage 26