nasa gps applications dr. scott pace associate administrator for program analysis and evaluation...

NASA GPS ApplicationsNASA GPS Applications

Dr. Scott PaceAssociate Administrator for Program Analysis and EvaluationNASA

PNT Advisory Board

March 29, 2007

2

GPS and Human Space Flight

Miniaturized Airborne GPS Receiver (MAGR-S) • Modified DoD receiver to replace TACAN

on-board the Space Shuttle• Designed to accept inertial aiding and

capable of using PPS • Single-string system (retaining three-string

TACAN) installed on OV-103 Discovery and OV-104 Atlantis, three-string system installed on OV-105 Endeavour (TACAN removed)

• GPS taken to navigation for the first time on STS-115 / OV-104 Atlantis

STS-115 Landing

Space Integrated INS/GPS (SIGI)• Receiver tested on shuttle flights prior to

deployment on International Space Station (ISS)

• The ISS has an array of 4 antennas on the T1 truss assembly for orbit and attitude determination

• In operation

3

Navigation with GPS: Space-Based Range

• Space-based navigation, GPS, and Space Based Range Safety technologies are key components of the next generation launch and test range architecture

• Provides a more cost-effective launch and range safety infrastructure while augmenting range flexibility, safety, and operability

• Memorandum signed in November 2006 for GPS Metric Tracking (GPS MT) by January 1, 2011 for all DoD, NASA, and commercial vehicles launched at the Eastern and Western ranges

GPS-TDRSS Space-Based Range

4Science Applications of GPS: Blackjack Science Receivers

Blackjack Family (’99 to present)

Features:• Developed at JPL and available in multiple

configurations• Tracks GPS occultations in both open-loop and

closed-loop modes• Tracks simultaneously from multiple antennas

Missions:SRTM Feb 2000, CHAMP Jul 2000, SAC-C Nov 2000, JASON-1 Dec 2001, GRACEs 1 and 2 Mar 2002, FedSat Dec 2002, ICESat Jan 2003, COSMICs 1 through 6 Mar 2006, CnoFS Apr 2006, Terrasar-X Jul 2006, OSTM 2008

Results:• Shuttle Radar Topography Mission (SRTM): 230-

km alt / 45-cm orbit accuracy• CHAMP: 470-km alt / < 5-cm orbit accuracy• SAC-C: 705-km alt / < 5-cm orbit accuracy• GRACE: 500-km alt (2 s/c) / 2-cm orbit accuracy,

10-psec relative timing, 1-micron K-band ranging, few arcsecond attitude accuracy with integrated star camera heads

SRTM ClassTurbo-Rogue (c. ‘92-99)

SAC-C Class

Jason Class

Grace Class

5

Science Applications of GPS: Probing the Earth

IONOSPHEREIONOSPHEREOCEANSOCEANS SOLID EARTHSOLID EARTH

ATMOSPHEREATMOSPHERE

Significantwave heightSignificant

wave height

Ocean geoid andglobal circulationOcean geoid andglobal circulation

Surface windsand sea state

Surface windsand sea state

Short-term eddyscale circulationShort-term eddyscale circulation

OCEANSOCEANS

High resolution 3Dionospheric imagingHigh resolution 3D

ionospheric imaging

Ionospheric struc-ture & dynamics

Ionospheric struc-ture & dynamics

Iono/thermo/atmo-spheric interactionsIono/thermo/atmo-

spheric interactions

Onset, evolution& prediction ofSpace storms

Onset, evolution& prediction ofSpace storms

TIDs and globalenergy transportTIDs and globalenergy transport

Precise ion cal forOD, SAR, altimetryPrecise ion cal forOD, SAR, altimetry

IONOSPHEREIONOSPHERE

Climate change &weather modelingClimate change &weather modeling

Global profiles of atmosdensity, pressure, temp,and geopotential height

Global profiles of atmosdensity, pressure, temp,and geopotential height

Structure, evolutionof the tropopause

Structure, evolutionof the tropopause

Atmospheric winds,waves & turbulenceAtmospheric winds,waves & turbulence

Tropospheric watervapor distribution

Tropospheric watervapor distribution

Structure & evolutionof surface/atmosphere

boundary layer

Structure & evolutionof surface/atmosphere

boundary layer

ATMOSPHEREATMOSPHERE

Earth rotationPolar motion

Earth rotationPolar motion

Deformation of thecrust & lithosphereDeformation of thecrust & lithosphere

Location & motionof the geocenter

Location & motionof the geocenter

Gross massdistributionGross massdistribution

Structure, evolution of the deep interior

Structure, evolution of the deep interior

Shape of the earthShape of the earth

SOLID EARTHSOLID EARTH

6

Augmentation of GPS in Space: GDGPS & TASS• TDRS Augmentation Service for

Satellites (TASS) provides Global Differential GPS (GDGPS) corrections via TDRSS satellites

• Integrates NASA’s Ground and Space Infrastructures

• Provides user navigational data needed to locate the orbit and position of NASA user satellites

47o W171o W

85o E

~18-20o

7Search and Rescue with GPS:

Distress Alerting Satellite System

Uplink antenna

Downlink antenna

RepeaterSARSAT Mission Need:•More than 800,000 emergency beacons in use worldwide by the civil community – most mandated by regulatory bodies

•Expect to have more than 100,000 emergency beacons in use by U.S. military services

•Since the first launch in 1982, current system has contributed to saving over 20,000 lives worldwide

Status:•SARSAT system to be discontinued as SAR payloads are implemented on Galileo

•6 Proof-of-Concept DASS payloads on GPS

•$30M spent to-date by NASA

8

Maintaining and Enhancing GPS: Satellite Laser Ranging

SLR Mission Need:•Assuring of positioning quality, long term stability of GPS, by independent means

•Ensure independently from foreign sources consistency, or accuracy, between the definition of the WGS-84 reference frame and its practical realization

•Align the WGS-84 reference frame with the ITRF, the internationally accepted standard geodetic reference frame, to ensure GPS and Galileo long term interoperability

ETOPO5- Orthometric

EGM96- Orthometric

The Gravity and Topography Fields need to be referenced to WGS84 and ITRF SLR CONOPS

GPS 35/36 Solid Coated Retroreflector

Hollow Cube and Array

9

Navigation with GPS beyond LEO

•GPS Terrestrial Service Volume–Up to 3000 km altitude–Many current applications

•GPS Space Service Volume (SSV)–3000 km altitude to GEO–Many emerging space users–Geostationary Satellites–High Earth Orbits (Apogee above GEO altitude)

•SSV users share unique GPS signal challenges–Signal availability becomes more limited

–GPS first side lobe signals are important

–Robust GPS signals in the Space Service Volume needed

–NASA GPS Navigator Receiver in development

10Navigation with GPS beyond Earth Orbit

… and on to the Moon

• GPS signals effective up to the Earth-Moon 1st Lagrange Point (L1)• 322,000 km from Earth• Approximately 4/5 the distance to the Moon

• GPS signals can be tracked to the surface of the Moon, but not usable with current GPS receiver technology

11Earth-Moon Communications and Navigation Architecture

• Options for Communications and/or Navigation:– Earth-based tracking, GPS, Lunar-orbiting communication and navigation

satellites with GPS-like signals, Lunar surface beacons and/or Pseudolites• Objective: Integrated Interplanetary Communications, Time

Dissemination, and Navigation

12

• Architecture can accommodate evolutionary use of science orbiters as relays prior to deployment of any dedicated com/nav satellites at Mars

• Surface beacons possible in areas of interest

• Use of all available radiometric signals for positioning and navigation through integrated software defined radio (SDR)

– SDR combines communications and navigation into a single device

Evolutionary concept: Add Satellite/s in Areostationary orbit

Current Mars Orbit Infrastructure

Earth-Mars Communication and Navigation Architecture

13

Planetary Time Transfer Proper time as measured by clock on Mars spacecraft

Mars to Earth Communications

Proper time as measured by clocks on Mars surface

Barycentric Coordinate Time (TCB

Proper time as measured by clocks on Earth’s surface

Terrestrial Time (TT)

International Atomic Time (TAI)

Coordinated Universal Time (UTC)

GPS Time

Earth

Mars Spacecraft

Three relativistic effects contribute to different “times”:(1) Velocity (time dilation) (2) Gravitational Potential (red shift) (3) Sagnac Effect (rotating frame of reference)

So how do we adjust from one timereference to another? …

Sun

Mars

Proper time as measured by clock on GPS satellite

GPS Satellite

14

GPS as a model for a Common Solar System Time

• GPS provides a model for timekeeping and time dissemination• GPS timekeeping paradigm can be extended to support NASA

space exploration objectives• Common reference system with appropriate relativistic

transformations

Relativistic corrections in the GPS

Time dilation (s per day) − 7.1Redshift (s per day) + 45.7Net secular effect (s per day) + 38.6Residual periodic effect * 46 ns (amplitude for e = 0.02)Sagnac effect * 133 ns (maximum for receiverat rest on geoid)

*Corrected in receiver

15

The Future of Positioning, Navigation, and Timing?

Pharos of Alexandria, Egypt

Cape Henry, VA, Lighthouses (old and new)

USCG Loran-C station, Pusan, South Korea, 1950s

Transit SatellitesBeacons and/or GPS-like Satellites on

other Planetary Bodies

Ancient Sun Dial

Harrison Clock

GPS Satellites

16

Backup Slides

17

South Pole OutpostSouth Pole Outpost

• Lunar South Pole selected as location for outpost site

• Elevated quantities of hydrogen, possibly water ice (e.g., Shackelton Crater)

• Several areas with greater than 80% sunlight and less extreme temperatures

• Incremental deployment of systems – one mission at a time– Power system – Communications/navigation– Habitat– Rovers– Etc.

• Lunar South Pole selected as location for outpost site

• Elevated quantities of hydrogen, possibly water ice (e.g., Shackelton Crater)

• Several areas with greater than 80% sunlight and less extreme temperatures

• Incremental deployment of systems – one mission at a time– Power system – Communications/navigation– Habitat– Rovers– Etc.

18

Concept Outpost Build Up

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Habitation

Solar Power Unit

Surface Mobility Carrier

Power Storage Unit

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Logistics

Crew/Cargo Lander

Unpressurized Rover

Point of Departure Only – Not to Scale

Year 5-B Starts 6 month incrementsYear 5-B Starts 6 month incrementsYear 5

Year 5

19

Notional Shackleton Crater Rim Outpost Location with Activity Zones

Notional Shackleton Crater Rim Outpost Location with Activity Zones

Habitation Zone

(ISS Modules Shown)

Power Production Zone

0 5 kmPotential Landing

Approach

50-60%60-70%>70%

Monthly Illumination(Southern Winter)

Landing Zone

(40 Landings Shown)

Resource Zone(100 Football Fields

Shown)

Observation Zone

To Earth

South Pole (Approx.)

Potential Landing Approach

20

Shackleton Crater Rim Size ComparisonShackleton Crater Rim Size Comparison

The area of Shackleton Crater rim illuminated approximately 80% of the lunar day in southern winter, with even better illumination in southern summer (Bussey et al., 1999)

Note: ‘Red Zone’ = 750 m x 5 km (personal communication with Paul Spudis)

Unique navigation challenges ahead!

nasa gps applications dr. scott pace associate administrator for program analysis and evaluation...

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