Science Instrumentation

1. Science Instrumentation Fall 2014 Innovative System Project for the Increased Recruitment of Emerging STEM Students

2. Outline • Atmospheric and Surface Measurements • Europa Subsurface • Temperature and Heatflow • Tables • Science Requirements Traceability Matrix • Instrument Requirements Table • Support Equipment Table

3. Basically … Two basic types of measurements: Properties & Composition

4. Science Objectives Categories Atmospheric & Surface Measurements

5. Atmospheric & Surface Science • The two basic types of atmospheric & surface measurements are: properties and composition • Properties: Qualities of the atmosphere/surface • Examples: pressure, temperature, density, viscosity, charge, pH, wind speed, humidity, … • Composition: Constituents of the atmosphere/surface • Examples: elements, compounds, ions, salts, acids, bases, minerals, metals, biologicals … • Surface only – soil mechanics (penetrability, hardness, etc) can also be tested

6. Properties • Pressure: pressure probe (transducer) • “touchy” measurement – the atmosphere must touch the probe • Temperature: thermocouple (see temp section) • Also, “touchy” measurement • Density: mass/volume • Indirect measurement from mass and volume • Viscosity: viscometers or rheometers • Can also measure via “falling” through the fluid, and measuring the accelerations/forces (finding the terminal velocity) • Charge: electrometer, galvanometer • “touchy” measurement, watch out for shorts/interference • pH: electrode, pH meter, indicators • Also must touch fluid to make measurement • Windspeed: anemometer, accelerometer • Direct measurement with anemometer – requires fixed probe and moving fluid • Indirect measurement – can be inferred from a moving probe • Humidity: hygrometer • Typically require temperature, pressure, and mass measurements • Precipitation: rain gage • Has defined directionality, opening, and orientation

7. Composition – Mass Spectrometer • Analytical technique that measures the mass-to-charge ratio of charged particles • Used for determining masses of particles, elemental composition of a sample or molecule, and the chemical structures of molecules • Works by ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios

8. Mass Spectrometer • Basic procedure • A laser (or electron beam) impacts the solid or gas to be probed • The sample is ionized, resulting in the formation of charged particles • The ions are separated, according to their mass-to-charge ratio, by an electromagnetic field • Ions detected, usually by quantitative method • This spectrum is analyzed, determining the constituents • Two basic types • “Internal” where a mass is loaded into the spectrometer, the laser impacts the sample, and the spectrum is detected – all “inside” the enclosed spectrometer • “External” where a laser is shot at a solid or gas sample, the sample emits a spectrum, and this spectrum is “seen” by a sensor which interprets the results – all this occurs “outside” of any enclosure • “Internal” usually weight more, but are more accurate than the “external” spectrometers

9. Properties & Composition Issues • Many measurements are “touchy” – they must come into contact with the material they are analyzing • Some properties can be inferred or measured indirectly (e.g., viscosity and wind speed) • Spectrometers are not robust – typically cannot handle large impact loads • There’s a trade: internal spectrometers are more accurate, but external spectrometers are easier to use (and usually less massive)

10. Science Objectives Categories Europa SubSurface

11. Internal Structure & Tectonics • The internal structure of a planet can be imaged/constructed using seismic information from quakes or vibrations in the planet • Essentially, you are measuring vibrations (movements/displacements) of the surface of the planet • Tectonics describes large scale motion of the plates that make up the crust of a planet • Longer-term movement and monitoring • Some planets have “plates” and some do not. Some planets can exhibit tectonic-like behavior, without having plates.

12. How Do Seismic Waves Image a Planet’s Interior? • Three-dimensional images of a planet’s interior using seismic signals generated by internal or external events (quakes, impacts, tidal heating, etc) • Generates a three-dimensional image by stacking two-dimensional information • Like a CAT scan - the X-ray beam moves around the patient, taking images from hundreds of different angles to put together a three-dimensional image of your inner soft tissues. X-ray beam (energy source) sends a signal to the receiver (film). • In seismometry, the energy source is stationary and the receivers are distributed around the body • The more receivers you have, and the better they are distributed, the more complete picture of the interior you build

13. Principles of Seismometry • Seismic waves (surface, compressional P, and shear S) that travel through the planet • Waves are generated together but travel at different speeds - S waves are ~50% the speed of P waves • Stations close quake record strong P, S and Surface waves in quick succession • Stations farther away record the arrival of these waves after a few minutes, and the times between the arrivals are greater.

14. Interior Structure of Planets

15. Principles of a Seismometer • The motion sensor consists of a weight hanging on a spring that is suspended from the frame of the seismometer. • When a wave passes, the suspended weight initially remains stationary while the frame moves with the surface. The relative motion between the weight and the moon provides a measure of the ground motion. • Three sensors are combined in a single package to measure ground motion in three dimensions. • “Spring” action is optimized for specific frequency ranges

16. Principles of an Accelerometer • Measures accelerations, or changes in velocity • Behaves as a damped mass on a spring, like a seismometer • Commercial devices use piezoelectric, piezoresistive and capacitive components • Relative position can be calculated (integrated) from acceleration data • Known initial point necessary to determine final absolute position Acceleration Velocity Position

17. Inertial Measurement Unit (IMU) • Reports a craft’s velocity, orientation, and gravitational forces • Basically, a 3D accelerometer + 3D gyroscope • Some have magnetometers and barometers

18. Issues with Internal Structure • Must have a “network” of accelerometers or seismometers (at least 3) • Sensors can only see as “deep” as the distance they are separated • Need the same internal clock (all need the same t=0) • Good contact/connection with surface • Impact resistance (ability to withstand high g-loads) • Seismometers are more sensitive than accelerometers • If dropped from orbit, you will lose a percentage • Accelerometers can be used to calculate position (from a known initial point); seismometers not • Orientation on the surface • 3-dimensional accelerometers mitigate this • Distance from lander (100 m is minimum) • Lander is “noisy” to seismometers and accelerometers • How long do you operate the network? • Power, communication, thermal, structure, etc for sensors

19. Creating a Seismic Network • Since lander is at a single point, some probes must fall from altitude (orbit or high altitude) • Two options falling from altitude • Penetrating the surface • Staying on the surface

20. Internal Structure Network Options Penetrating the Surface Remaining on the Surface Not to Scale

21. Science Objectives Categories Temperature and Heat Flow

22. Temperature/Heat Flow • Temperature Measurements: Objective is to understand the thermal environment of the surface of the planet • Usually, at many points over the surface • E.g., compare temperatures of different regions • Heat Flow Measurements: Objective is to understand the thermal environment of the interior of the planet • Usually in one or two areas • For a given area, “temperature” is a single surface measurement, while “heat flow” is multiple measurements from the surface to a distance below the surface • Temperature network gives better measurements over entire planet (the “big picture”) • Heat flow is more detailed temperature measurement/(temperature profile) at one, maybe two, locations • Both measurements use basically the same instruments

23. Temperature Network • Probes reside on the surface (or near top of surface) • “Network” of probes implies they need to be dispersed • The farther apart the better • The more the better • This implies that some will probably have to fall from altitude • High impact velocities and forces • Final position (where measurement taken) important

24. Heat Flow • Scientists believe that there is very little temperature difference between the core and the surface of the planet • What is the actual difference between the core temperature and surface temperature? • Does the temperature “level off” like on Earth? • Temperature “profile” from surface to a depth • Measure temperature at specific intervals • Overall accuracy depends on temperature and position measurements • Watch out for “thermal shorts” (something that conducts heat from one position to a different depth) T Dy T Dy T Dy D T Dy T Dy T Not to Scale

25. Heat Flow • Temperature measurements at surface, to a depth below the surface (and all along the way) • The deeper the better • The more the better • Distance between each temp measurement must be known • Absolute depth position is desirable too • Getting to a depth requires energy • A few basic methods to get to a depth

26. Heat Flow – Achieving Depth • Basically three methods to achieve depth • DLR Mole (miniature pile-driver) • Drill (similar to earth-based drills) • Penetrator (kinetic energy impactor)

27. Thermocouples • Thermocouples measure temperatures in spacecraft and in labs • Two dissimilar metals pressed together • Heat/cold causes metals to expand/contract at different rates • This causes interface to flex/bend, and induces a voltage between the metals • This voltage is measured by a computer • When calibrated, you can determine the temperature of a “thing” • Thermocouples can be as small/thin as wires (so, very small/light) • Thermocouples don’t require power (but the processors and storage do require power)

28. Issues with Temp & Heat Flow • Good contact with thing being measured • Thermocouples operate by conduction – they have to “touch” the thing they are measuring … so, the thermocouple (or the extension) must “touch” the material being measured • Time/Location knowledge • Just saying, “It’s 10 degrees” tells us nothing • This includes depth knowledge • At least relative depth/distance between measurements • Getting away • Lander will influence measurements • Find a thermocouple that fits the temperature you expect to measure • Watch out for thermal shorts

29. Magnetic Fields • Description of the magnetic influence of electric currents and magnetic materials • Specified by a vector (magnitude and direction) • Produced by moving electric charges and the intrinsic magnetic moments of elementary particles

30. Magnetic Measurements • Magnetometers measure magnetic fields • Scalar: proton precession, Overhauser, Caesium, etc. • Vector: Rotating Coil, Hall effect, Magnetoresistive, Fluxgate, SQUID, SERF, etc. • Fluxgate most popular among spacecraft • Light, low power, robust, simple, sensitive • Simple two-coil probe • One coil excited (alternating) • One coil “searches” • Isolation requirement • Measures ALL magnetic fields • Other instruments, processors, etc can interfere (sometimes 2 probes used) • Magnetometers usually sense continuously for their lifetime

31. Science Traceability Matrix This is just an example! You can choose whatever Science Objective you want!

32. Instrument Requirements Matrix Use Page 40 in the notebook – many examples of instruments!!!

33. Support Equipment Use Page 41 in the notebook – many examples of instruments!!!