Radio Technology in Space Explorations Paul Song Space Science Laboratory University of Massachusetts Lowell Radio waves and radio technologies Space radio wave detection: Space radio wave transmission: flexibility, large power Sounder/radar: Transmission and then reception. Ionosonder Radio plasma imager Surface penetrating radar: mineral mine, oil field, subsurface structures (archeological sites), subsurface properties of planets and their moons Summary

Radio Waves Radio Waves: 3 kHz ~ 300 GHz (=100 km ~ 1mm) Refraction: when space medium not uniform Reflection: when index of refraction changes sharply normally over large transverse spatial scales (compared to ) Diffraction: small (compared with ) obstacles or pathways Multiple reflections: reflection +refraction (+ diffraction) Directionality: better for higher frequencies (but more dead-spots) Issues concerning frequency Antenna length: transmission most efficient when L~/2 too small => optical: laser/source, lenses, filter, frequency scan, CCD detectors too long => space structure stability and deployment Digital technologies: CPU speed or “bandwidth” ~ 3 GHz ( ~10 cm) Ionospheric reflection: ionospheric peak reflection : 20~30 MHz reflection vs penetration

Issues Concerning Space Radio Technologies Antenna Spatial size, mass Stability, deployment (no gravity and no wind, but centripetal force) Electric (straight wire, dish), magnetic (coil) 1D, arrays Receiver: sensitivity proportional to antenna length, L Broadband vs narrowband Transmitter Transmission power, for short antenna, P ~ (L/)4 (for same voltage) Frequency control: tuner for short antenna Complicated operations Space issues Radiation hardening High voltage source on satellite: discharging Interference with other instruments

Radio Technologies in Space Applications Space passive radio receptions In-situ plasma conditions Distant source of signals Space interferometry (location finding) Radio sounding (remote sensing) Ground-based: ionosonder Space-borne: radio plasma imager, ionospheric Transceiver, data processing Ground/ice penetration Subsurface properties: Earth, Mars, Moon, Jupiter and Saturn icy moons Space high power transmission

Electronics Unit RPI on IMAGE

RPI IMAGE Instrument Deck

Imager for Magnetosphere-to-Aurora Global Exploration (IMAGE) Spacecraft 500-m dipoles in spin plane 20-m dipole along z RPI: <10 W radiated power 3 kHz – 3 MHz 300 Hz bandwidth Launched on 25 Mar 2000

Sounding in Magnetosphere

The wave environment in space Meredith et al [2004] Explain scales, f, t

Dynamic Spectra Measured from IMAGE/RPI Passive Mode NLK-Washington 24.8 kHz

VLF to Satellite Propagation Mode Earth – Ionosphere waveguide Leakage out of waveguide through the ionosphere Whistler mode to the IMAGE satellite

Observations of NML station, 2001/2002 La Moure, ND, L=3.26, 500 kW

Space Transmission Air Force DSX Spacecraft

Wave-Particle Interaction in Radiation Belt Abel and Thorne, 1998 Precipitation lifetime (days) L-shell Objective: Mitigate threats to low-earth orbit satellites (LEO) from energetic electrons. Energy range: 0.5~2.5 MeV L-range: 1.7~3.5 Approach: pitch-angle scattering by whistler mode waves

Principles of Radio Sounding Radio waves are reflected at wave cutoffs (n = 0) In a cold, magnetized plasma, cutoff frequencies are Ionic or ordinary (O-mode): fc = fp Extraordinary (X-mode): fc = Echo from reflections perpendicular to density contours (at reflection point) Echo Refracted rays n=0 n>0 n<0 Use crossed-dipole antennas to identify O and X waves

UML Digisonde ionospheric ground-based sounding RCV ARRAY XMT ANTENNA DPS 4 RCV ANTENNA

Ionogram with Derived Density Profile Electron density profile

Ne(h,t) at the Magnetic Equator Cachimbo 16 October 2002 midnight noon

Interferometric Doppler Imaging The digisonde, operating in the skymap/drift mode, is designed to measure the drift velocity components on a routine basis. In this mode the ionosonde sounds at one or more fixed frequencies and receives and records the reflected signal from each antenna separately. This technique depends on the presence of ionospheric structures that are embedded in the background plasma.

Digisonde Skymaps

Real Time Digisonde F Region Drift

Global Ionospheric Radio Observatory (UML Space Science Laboratory)

Sounding in Magnetosphere

Field-Aligned Propagation RPI Plasmagram Fig 2 of GRL paper (Reinisch et al., GRL, 2002)

Plasma Density Along Field line

One Pass of IMAGE on June 8, 2001 IMAGE trajectory

Two dimensional density distribution for MLT=8.0 on June 8, 2001

Before Storm Partial Recovery Storm Peak Identified plasmasphere, plasma trough, density depletion, aurora/cusp, and polar cap The densities and the locations of these regions vary in accordance with the different solar wind/IMF conditions, not correlated with the Dst variations

Comparison of the Jupiter moons (Icy surface of Europa)

Planetary Advanced Radio Sounder (PARS) Heritage from IMAGE Radio Plasma Imager (RPI)

Ice Penetrating Radar Challenges Strong surface reflections Signal attenuation in the ice (absorption, scattering) Clutters (unwanted surface reflections) 3-D Ice Bed Mapping Gogineni, 2013

Under Glacier Channels/Trenches [Gogineni et al., 2014] ~850m ice above sea level ~570m ice above sea level

Dual-Frequency Precision Ranging Swarm spacecraft configuration for precision interferometry -- 0.1 W transmissions from each s/c - Each s/c transmits its own frequency - Each s/c receives all frequencies Swarm performs as a multi-antenna interferometer for precision angle-of-arrival measurements --High resolution interferometry for detection of radio transmitters

Magnetospheric Tomography A 7-satellite constellation Each satellite transmits and receives signals Tomography methods are used to infer the plasma density distribution within the constellation

Summary Radio technologies can be used in space for Detecting in situ radio waves in space (plasma conditions: plasma density, magnetic field strength, characteristic processes, wave sources) Sounding: local plasma conditions, remote sensing plasma density profile Monitoring ground radio sources High power transmission in space: stimulating wave-particle interaction (Ground/ice) Penetrating radars: Moon, Mars, Jupiter icy moons…(the technology can be used on Earth on airplanes) Multiple transmitters/receivers: interferometer, tomography