Planetary exploration instrumentation I Planetary exploration 2017 Basic

Planetary exploration instrumentation I Planetary exploration 2017

Basic Planetary exploration approach • Ground based observations • Radio/optical telescopes, spectroscopy • Radar, laser ranging • Proximity exploration using robotic missions • Remote sensing • In-situ study (landers, probes) • Human exploration • Apollo • ISS • Laboratory studies • Naturally occurring samples (meteorites, cosmic dust) • Sample return (human/robotic-delivered)

Ground-based observations + Robust and large (e. g. interferometers) instruments can be used + Available for maintenance or upgrades + Low to medium costs + Repeatability - Earth atmosphere filters out certain wavelengths - Large distance between Earth and observed targets - Limited observational geometry

Atmospheric transparency

Ground-based observations

Reflected light observations Composition Surface roughness Phase curve Sun

Reflected light spectra of planetary surfaces LL ordinary chondrite (meteorite) Olivine Pyroxene • 1 and 2 µm absorption bands due to Fe 2+ ions • Position of the bands shifts to lower wavelengths with decreasing Fe/Mg ratio • 0. 7 µm absorption band due to Fe 3+ • Hydration of silicates

Radar observations • Asteroid shapes • Surface roughness • Rotation period • Detection of ice

Circular Polarisation Ratio (CPR) • EM waves can be either linearly (vertically, horizontally) or circularly polarized. • Typical planetary surfaces reverse the circular polarization direction of the reflection of radio waves. The ratio of received power in the same sense transmitted to the opposite sense is called the circular polarization ratio (CPR). • Most of the dry planetary surfaces has low CPR, meaning that the reversal of polarization is prevailing. • Some targets have high CPR. These include very rough, fresh surfaces (such as a young, fresh crater walls or ejecta) and ice, which is transparent to radio energy and multiply scatters the pulses, leading to an enhancement in same sense reflections and hence, high CPR. • Thus, high CPR in planetary science can be an indication of presence of the ice.

Robotic missions + Can get closer + Failure posses no risk to humans + Can observe targets for extended periods of time (semi-uninterupted view) + Medium costs - Long cruise to the target - Restrictions on mass and size, requirement of autonomous operation - Less accurate observations compared to ground/lab-based instruments - After launch no possibility of upgrade and repair

Gamma, neutron, X-ray spectroscopy • Gamma-Ray Spectrometer • Element composition to depth of ~10 cm • Surfaces of airless bodies are subject of continual bombardment of highenergy cosmic rays (solar protons, deep space radiation). • Cosmic rays excite atom nuclei and emit characteristic gamma-rays or neutrons which can be detected from orbit. • Abundance and distribution of about 20 elements including Si, O, Fe, Mg, K, Th, U, Al, Ca, S, C. • Neutron Spectrometer • Element composition (similar to gamma spectrometer) and hydrogen to depth of ~ 40 cm • H is efficient neutron energy moderator (decreases n 0 energy). • Thus fast/thermal n 0 ratio can be used as a proxy for water abundance. • X-Ray Spectrometer • Element composition within ~ 1 mm • Detection of basic silicate-building elements including Mg, Al, Si, Ca, Ti, and Fe through their characteristic X-ray fluorescence • X-rays fluorescence is caused by X-rays emitted by solar flares (depends on solar activity and solar cycle) • Energetic Particle and Plasma Spectrometers • Typically mass spectrometers • Magnetosphere, solar wind, plasma

Radar mapping (fixed vs. SAR antenna) • Radar sends a short pulse and then records a reflected signal • Parameters recoded are • Intensity • Doppler shift • Polarization • In earlier studies radar with fixed aperture was used where resolution depends on antenna diameter. • Synthetic Aperture Radar of takes advantage of spacecraft motion and simulates large aperture through imaging the same spot over spacecraft trajectory. • High resolution image is created from individual echoes using Doppler and phase shift information. • Additional imaging from two directions (side looking radar) allows for 3 D imaging.

Radar mapping (fixed vs. SAR antenna) Magellan (NASA) 1. 8 GHz SAR Pioneer Venus (NASA) 1. 8 GHz pulse radar

Radar sounding Moon – basalt layers Mars – polar caps SHARAD ((Mars SHAllow RADar sounder) • Mars Reconnaissance Orbiter (NASA) • 15 and 25 MHz MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) • Mars Express (ESA) • 40 m dipole antenna, 1. 8 – 5 MHz

Radar sounding • Similar principle as ground penetrating radar (GPR) • GPR uses high frequency radio wave pulses to image subsurface. • Depth range and vertical resolution of a GPR depends on: • Frequency – higher f have higher resolution ( =v/f), but lower penetration depth • Electrical conductivity of the ground – loss of energy • Relative electric permittivity r (v 2 = 1/εμ) • Radiated power • On vertical axis two-way travel time – conversion to depth based on estimated εr Two-way travel time

Laser mapping Moon Mars

Radio science • Utilizing spacecraft – ground or spacecraft – spacecraft radio link • Gravity field determination from Doppler shift • Atmosphere / exosphere probing (phase change, Doppler shift – computation of atm. Refractive index estimation of pressure, temperature, density) Free air gravity corrected for measurement height above geoid Bouguer gravity corrected for measurement height above geoid and terrain mass

EM bands Band Wavelength Frequency range name range Notes HF 3– 30 MHz 10– 100 m coastal radar systems, over-the-horizon radar (OTH) radars; 'high frequency' P < 300 MHz 1 m+ 'P' for 'previous', applied retrospectively to early radar systems VHF 30– 300 MHz 1– 10 m Very long range, ground penetrating; 'very high frequency' UHF 300– 1000 MHz 0. 3– 1 m Very long range (e. g. ballistic missile early warning), ground penetrating, foliage penetrating; 'ultra high frequency' L 1– 2 GHz 15– 30 cm Long range air traffic control and surveillance; 'L' for 'long' S 2– 4 GHz 7. 5– 15 cm Moderate range surveillance, Terminal air traffic control, long-range weather, marine radar; 'S' for 'short' C 4– 8 GHz 3. 75– 7. 5 cm Satellite transponders; a compromise (hence 'C') between X and S bands; weather; long range tracking X 8– 12 GHz 2. 5– 3. 75 cm Missile guidance, marine radar, weather, medium-resolution mapping and ground surveillance; in the USA the narrow range 10. 525 GHz ± 25 MHz is used for airport radar; short range tracking. Named X band because the frequency was a secret during WW 2. Ku 12– 18 GHz 1. 67– 2. 5 cm K 18– 24 GHz Ka 24– 40 GHz 0. 75– 1. 11 cm mapping, short range, airport surveillance; frequency just above K band (hence 'a') Photo radar, used to trigger cameras which take pictures of license plates of cars running red lights, operates at 34. 300 ± 0. 100 GHz. mm 40– 300 GHz 7. 5 mm – 1 mm millimeter band, subdivided as below. The frequency ranges depend on waveguide size. Multiple letters are assigned to these bands by different groups. These are from Baytron, a now defunct company that made test equipment. V 40– 75 GHz 4. 0– 7. 5 mm Very strongly absorbed by atmospheric oxygen, which resonates at 60 GHz. W 75– 110 GHz 2. 7– 4. 0 mm used as a visual sensor for experimental autonomous vehicles, high-resolution meteorological observation, and imaging. UWB 1. 6– 10. 5 GHz 18. 75 cm – 2. 8 cm used for through-the-wall radar and imaging systems. high-resolution, also used for satellite transponders, frequency under K band (hence 'u') from German kurz, meaning 'short'; limited use due to absorption by water vapor, so Ku and Ka were used instead for surveillance. K 1. 11– 1. 67 cm band is used for detecting clouds by meteorologists, and by police for detecting speeding motorists. K-band radar guns operate at 24. 150 ± 0. 100 GHz.

Rovers / landers • Can do in-situ direct measurements • Soft landing is always an challenge (success rate on Mars around 50%) • Contact sample studies (alpha, X-ray spectroscopy for compositional studies, on board laboratories, heating ovens, mass spectrometers, XRD for mineralogy, etc…) • Atmospheric sensors • Almost every basic instrument used in field or laboratory was flown to Mars

Human exploration + Humans can precisely identify targets or operate instruments + In-situ / instant decision making - High costs - Complex infrastructure needed to support life - Humans exposed to dangerous environment

Apollo program • 1961 -1972 • 6 landings, 12 people on the Moon, 3 died (Apollo 1), 1 mission had to be aborted (Apollo 13) • Apollo astronauts brought back over 380 kg of rocks with geological context • Three Luna automatic sample return spacecrafts returned 326 g lunar samples • 200 lunar meteorites, 190 kg

Laboratory studies + Most precise instrumentation can be used – high quality data + Calibration available also after the measurement + Identical methodology as for geological studies - Limited source of material