Presentation Transcript

1. Venus Explorer Mission Potential Science Objectives

   Spring 2014 Innovative System Project for the Increased Recruitment of Emerging STEM Students
2. Outline Baseline Mission Planet Venus Overview Potential Science Objectives Outside Venus Venus Atmosphere Venus Surface Venus Sub-Surface Temperature/Heat Flow Magnetic Field What’s Next Example Science Traceability Matrix
3. Baseline Mission Trajectory Orbit Insertion Aerobraking 6-month 300km by 40,000km orbit Communication with other lander and balloon Final Orbit: 230 km, circular 4 years total (2 years primary, 2 years extended) 160-day cruise Not to Scale
4. Baseline Mission Science NASA Science Objectives What does the Venus greenhouse tell us about climate change How active is Venus? When and where did the water go? Life on Venus?
5. Baseline Mission Elements Orbiter Transit to Venus 160 days 300x40,000 km aerobraking 6 months 230 km final orbit 4 years Balloon System Two (2) balloons 55.5 km altitude 30 days Lander Two (2) landers 1-hour science descent 5-hour surface mission
6. OVERVIEW OF PLANET VENUS
7. Venus 2nd planet from Sun Hottest planet in solar system Severe greenhouse effect Radius = 95% of Earth Mass = 82% of Earth Gravity = 90% Earth g Thick cloud cover 30 missions to Venus Russians were first Russians landed on surface
8. Venus Orbit Orbital period (Venus year) is 225 earth days Only planet to rotate in retrograde Solar day = 117 earth days Sidereal day = 243 earth days Inclined at 3.4 degrees to the ecliptic plane Brightest object in the sky, besides Sun and Moon
9. Sidereal Day One complete revolution with respect to a fixed coordinate system A single point on the equator travels around, at the rate of the planets angular rotational speed, and comes back to the same location Y X
10. Venus & Solar Wind Venus has no magnetic field of its own Induced magnetic field, from solar wind Lack of magnetic field surprising Direct interaction of solar wind with Venus atmosphere Solar wind supplies energy to ions in the upper atmosphere Erodes certain elements from Venus
11. Venus Atmosphere Very thick (height) Approx 250 km Clouds up to 200 km 96.5% CO2, 3.5% N2, and other Winds blow at 60x the speed of the rotation Earth’s winds as high as 10~20% of Earth’s rotation Lightening, storms, cyclones at poles, …
12. Venus Surface Appears to be shaped by volcanic activity, but no direct evidence of volcanic eruptions 500M years ago, dramatic resurfacing 93x Earth’s pressure, ~900°F Surface basically isothermal across planet CO2 is supercritical fluid at surface, wind speeds 1~2 m/s
13. Venus Sub-Surface Not much known about internal structure of Venus Possible magma internal Single plate covering entire surface No plate techtonics Quakes thought to occur
14. OVERVIEW OF Potential Science Objectives
15. Science Objective Categories Outside Venus Venus Atmosphere Venus Surface Venus Sub-Surface
16. Science Objective Categories Outside Venus Interaction of solar wind with Venus Measure bow shock Elemental loss Venus Atmosphere Properties/Composition Greenhouse effects Weather/lightening Cyclones Jet streams Acid rain “Life” in the clouds Venus Surface Properties/Composition Soil mechanics Magnetic field Volcanoes Resurfacing (surface age) Venus Sub-Surface Internal structure Heat flow (temp gradient)
17. Science Objectives Categories Outside Venus
18. Solar Wind Interaction of solar wind with Venus
19. Science Objectives Categories Atmospheric & Surface Measurements
20. 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
21. 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
22. 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
23. 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
24. 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)
25. Venus Atmosphere Weather/lightening Greenhouse effects Cyclones Jet streams “Life” in the clouds Acid rain
26. Venus Surface Soil mechanics Magnetic field Volcanoes Resurfacing (surface age)
27. Science Objectives Categories Venus Sub-Surface
28. 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 Scientists believe that Venus does not have plates, and therefore, no tectonics
29. 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
30. 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.
31. Interior Structure of Planets
32. 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
33. 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
34. 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
35. 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
36. Internal Structure Network Options Penetrating the Surface Remaining on the Surface Not to Scale
37. Science Objectives Categories Temperature and Heat Flow
38. Temperature/Heat Flow Temperature Measurements: Objective is to understand the thermal environment of the surface of Venus 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 Venus 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
39. Temperature Network Scientists believe Venus’ temperature is relatively isothermal What are the actual temperatures? What is the real temperature variation? Poles vs equator? What are the causes of the “hot spots”?
40. 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
41. Heat Flow Scientists believe that there is very little temperature difference between the core and the surface of Venus 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
42. 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
43. 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)
44. 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)
45. 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
46. 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
47. 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
48. What’s Next … Team chooses science objective(s) What are you interested in? What interests you about this region/area? Dial down … etc. Research environmental conditions associated with your objective For example, the surface of Venus is a lot different than the upper atmosphere Seismic Network different than Heat Flow Start thinking about the instruments needed to satisfy your science objective(s) Start filling out the Science Traceability Matrix
49. Science Traceability Matrix Example Science Traceability Matrix: This is just an example! You can choose whatever Science Objective you want!