Interplanetary and Interstellar Communication and Navigation Prof. Philip Mauskopf Arizona State University Cosmology instrumentation Superconducting detectors Optical Communications Technologies Mission Ops for SPHEREx FISW 2019 Wotton-Under-Edge Navigation questions: 1. If we could build an interstellar propulsion system, can we navigate between the stars? • Yes – there are many possible technologies (e.g. Richards, JBIS, 28, 1975, Smith, Sheikh and Swinney, JBIS, 69, 2016). This is an easier problem than getting close to light speed but there are details to be worked out: • What are the best navigation tools for interstellar travel? • What are the mass and power requirements? 2. Can we navigate the tiny flyby probes (e.g. Breakthrough Starshots) to the nearest stars and obtain images of planets? • Hopefully yes but this is a more difficult problem because of the extreme mass and power constraints. There are lots of questions and trade-offs, e.g. • Do we need on-board navigation? • What communication links are needed during the trip for course correction? Communication questions: 1. Can we communicate with interstellar spaceships? • Yes – there are many possible technologies but there are details to be worked out: • What are the best communication tools? • What are the mass and power requirements on board and at the home base? 2. Can we send and receive images from the tiny flyby probes (e.g. Breakthrough Starshots) at the nearest stars? • Hopefully yes but this is a more difficult problem because of the extreme mass and power constraints (see Lubin, Messerschmidt and Morrison, 2018). There are lots of questions and trade-offs, e.g. • What is the power source on board? • How do we focus and point a signal towards the earth? • Etc. Technologies for Deep Space Navigation • Star trackers • Relative positions and periods of objects in orbits (e.g. moons, planets, binary stars, exoplanet transits, etc.) • Clocks • Doppler/lighthouse velocity measurements • Radio sources • Earth-based radio Orientation: • Radio pulsars Which way am I • Artificial radio pulsars • Radio extragalactic background (e.g. CMB) pointed? • Optical to X-ray • Optical or X-ray pulsars • Artificial optical pulsars • Stellar colours and magnitudes or absorption lines • Range finding • One or two way light travel time • Sizes and separation of objects – e.g. stars Technologies for Deep Space Navigation • Star trackers • Relative positions and periods of objects in orbits (e.g. moons, planets, binary stars, exoplanet transits, etc.) • Clocks • Doppler/lighthouse velocity measurements Position: • Radio sources Where am I • Earth-based radio • Radio pulsars with respect to • Artificial radio pulsars • Radio extragalactic background (e.g. CMB) my origin • Optical to X-ray /destination? • Optical or X-ray pulsars • Artificial optical pulsars • Stellar colours and magnitudes or absorption lines • Range finding • One or two way light travel time • Sizes and separation of objects – e.g. stars Technologies for Deep Space Navigation • Star trackers • Relative positions and periods of objects in orbits (e.g. moons, planets, binary stars, exoplanet transits, etc.) • Clocks Velocity: Which • Doppler/lighthouse velocity measurements • Radio sources way am I going • Earth-based radio • Radio pulsars and how fast? • Artificial radio pulsars • Radio extragalactic background (e.g. CMB) • Optical to X-ray • Optical or X-ray pulsars • Artificial optical pulsars • Stellar colours and magnitudes or absorption lines • Range finding • One or two way light travel time • Sizes and separation of objects – e.g. stars Navigation on or around Earth Predominantly uses GPS: • System of satellites in medium earth orbit • Trilateration (range finding) • Equipped with atomic clocks • Three satellites give X, Y, Z – need fourth to close loop and also get time • Small hand-held devices Deep Space Navigation in the Solar System Currently uses: • Radio Doppler and range finding with DSN • Orientation and location with images of stars and solar system objects (e.g. planets, moons and asteroids) • Near-object navigation with imaging of destination target and autonomous software • Need for more standardisation and automation for future solar system travel Deep Space Positioning System (from Caltech/JPL) The proposed solution DPS: Deep Space Positioning System • Develop a multi-use instrument capable of: – Navigation measurement (optical and radio) – Data processing and orbit determination – Path planning and maneuver estimation – Course correction implementation • Make the hardware and software generally applicable enough that: – Only moderate (if any at all) modifications would be required for each particular mission Joseph E. Riedel, Joseph R. Guinn, Shyam Bhaskaran, Ryan S. Park, Andrew T. Vaughan, William M. Owen, Todd A. Ely, Matthew Abrahamson, Tomas J. Martin- Mur from SCAN Workshop on Autonomous Navigation DPS: Deep Space Positioning System 14 Deep Space Positioning System (from Caltech/JPL) Elements of the DPS concept Camera, radio, clock, steering actuators and flight software Integrated DPS Instrument Iris Software Defined Radio Extracts one-way radio observables and hosts AutoNav FSW MRO OpNav Camera 2.1° FOV high-sensitivity camera ASC Star-tracker Deep Impact AutoNav STMD Deep Space Atomic Clock OCO-3 Actuators Provides autonomous in situ Provides “DSN-Quality” frequency and time navigation (via optical and/or radio) reference for one-way radio DPS: Deep Space Positioning System 15 Joseph E. Riedel, Joseph R. Guinn, Shyam Bhaskaran, Ryan S. Park, Andrew T. Vaughan, William M. Owen, Todd A. Ely, Matthew Abrahamson, Tomas J. Martin-Mur from SCAN Workshop on Autonomous Navigation Deep Space Atomic Clock (DSAC): NASA/JPL Mass 17.5 kg Operating specs: Dimensions 29 × 26 × 23 cm • Uses Hg ion transition in (11 × 10 × 9 in) microwave cavity at 40.5 GHz Number launched 1 • No cryogenics or lasers -15 Power consumption 44 W • Stability ~ 3 x 10 at one day (~ 1 nanosecond) Launched Tuesday on • ~ 50x more accurate than SpaceX Falcon Heavy current GPS clocks Proposal for Deep Space Positioning System in the Solar System Similar to GPS: • Fly multiple satellites with radio or optical beacons and on- board DSACs • Spread them throughout the solar system • Emission will be in the plane of the solar system • Act like artificial pulsars – positions monitored by DSN just like GPS • Spacecraft have small DPS receivers and are independent of earth ground stations Earth Orbiting Radio Beacons • GPS satellites • Radio transmitters • Atomic Clocks • Time and location references • MEO (~20000 km) • Precision limited by on-board clocks, drag, gravity flucutations, atmosphere, etc. Solar System Beacons • Antenna or dish emitting in the ecliptic plane • Pulsed laser/RF – On-board atomic clocks (like GPS) – Pulsed or modulated RF or laser signal (like GPS) • Spinning laser/RF – No atomic clock needed (but still could be used to generate emitted signal) – Miniature pulsars Solar System Beacons for navigation • Detectable by interplanetary spacecraft with on-board antenna • Provides information about location and velocity (complements star camera information about orientation) • Autonomous navigation – no need for guidance from earth, faster response time, etc. Comparison with Natural Radio Pulsars • Brightest radio pulsar ~ 1 Jy peak pulse • 10 Watt transmitter on pulsat (pulsar satellite) • Assume 50% modulation at 90 GHz in a 1 Hz bandwidth with a 60 cm dipole antenna – Beam size is 2p x 1/200 sr – Peak power at 5 AU on a 10 cm diameter dish = 6 x 10-24 W à 60000 Jy – Noise power is about 5 x 10-22 W in a 1 Hz bandwidth so not quite enough power to have a small receiver Galactic Beacons for Interstellar Navigation Pulsars • Orbital period -> stable time reference • Known sky location gives position reference • Can be used for navigation • Radio signal strength is weak ~ 1 Jy peak for the brightest pulsar so you need a big dish to detect • Optical signal is also weak (brightest ~ 16th magnitude = Crab) • X-ray signals are stronger but fewer photons and require large detectors (e.g. SEXTANT – demo on NICER) Galactic Beacons for Interstellar Navigation Pulsars can also be used for gravitational wave detection Extragalactic Beacons/Reference frames Cosmic Microwave Background or Extragalactic Backgrounds • Traveling at 0.2c there will be a dipole temperature anisotropy in the Cosmic Microwave Background (CMB) of ��~ 550 �� • A small passively cooled coherent radiometer with 10 GHz bandwidth at any frequency where the CMB is dominant (i.e. 30 GHz – 200 GHz) can have a noise temperature of < 100 K and temperature sensitivity of < 1 mK * � • Can measure the CMB dipole with high signal to noise very quickly and get velocity direction and speed • Use a phased array on light sail to improve angular resolution Other Relativistic effects Relativistic image distortion • Objects in front will appear to be smaller or closer together and objects behind will be spread out • Can use a regular star camera and compare positions in the image with fiducial positions at rest and determine velocity and orientation • For the AB Centauri system, can use the separation between the stars to measure distance Two photographs of the gate. Top: The camera is at rest. Bottom: The camera approaches the gate at 90% of the speed of light c. Both photographs are taken at the same distance to the gate (see sketch). The camera is looking towards the gate. https://spacetimetravel.org Interstellar Communications: e.g. Sending images of planets