PMD Presentation Outline LISA Ben Versal and Douglas Todd

1. PMD Presentation OutlineLISABen Versal and Douglas Todd

2. LISA: Introduction • What is it: Laser Interferometer Space Antennae • What are the applications: Detection of space time warping due to “snacking”, an effect predicted by Einstein. • What is the primary objective: To search for gravitational waves. With this information we can study the mergers of super massive black holes, and test Einstein’s theory of general relative. • Who has funded LISA: The project is co-funded by European Space Agency (ESP) and NASA • What are it’s Core Technologies: Gravitational Reference Sensors, Micro-Newton Thrusters, optical bench, and Laser Interferometry. • How it Works: Three spacecraft separated by 4.8 million km (3 million miles) which keep track of their relative positions very carefully in order to detect the passing of gravitational waves from “Snacking” • Where will it be located: LISA will be either 20 degrees in front of or behind earths orbit relative to the sun.

3. What are Gravitational Waves • Einstein’s Theory of Relativity: when the mass of a system accelerates (i.e. there is a change in the distribution of mass in the system) the space-time surrounding the system undergoes a change in curvature and spreads outward as Gravitational Waves (GW’s) at the speed of light, which carries energy and angular momentum away from the original system. • Visual Example of GW’s: The picture to the right shows how a ring of particles would react after being acted upon by GW’s. The ring oscillates between two ellipses separated by a 90 degree rotation Examples of detectable systems: supernovas, binary neutron star pairs, binary black-hole pairs, “Snacking”, a coalescence of a binary neutron star pair or a black-hole binary pair, accretion onto Massive Black Holes, etc.

4. The Size of Things • The LISA spacecrafts will be separated by over 3 million miles, while the gravitational waves alter the distance between them by far less than the width of an atom, 1/100th the wavelength of light. • To get a rough idea of how difficult it is to detect Gravitational Waves from these sources, a rule of thumb is that the strain in space from such a wave is 10-21 to 10-23. • For Comparison • -Gravity-Wave detectors with an arms 4 km long (LIGO) • deltaL= 10-21 x 4,000m = 4E-18m. • -For an arm of 3,000,000 miles or 4.828E9 meters (LISA) • deltaL= 10-21x 4.8E9m = 4.8E-12m. • Note: the size of an atomic nucleus is about 10-15 meters.

5. Core Technologies:Laser Interferometer • Laser Interferometer: LISA is arranged so that the three satellites form an equilateral triangle that can be used as a giant Michelson Interferometer with a resolution in a frequency range of 10-4 to 0.1 Hz, and a sub-nanometer accuracy range. • Main differences to a Michelson Interferometer: • The Laser beam is not be reflected back since the beam will be weakened after it has traveled such a long distance. Each satellite emits a new beam, in phase with the incoming beam to the previous satellite. • Arm length distance of the three satellites can vary because the satellite positions are not fixed, this in turn does not allow laser phase noise to cancel out. • Tinto and Armstrong method: post-processing method of time-delay interferometry (TDI) • Requirements for the time measurement and clock synchronization in the moving spacecraft.

6. Core Technologies:Gravitational Reference Sensors • Gravitational Reference Sensors: Perfectly symmetric highly polished cubes that were designed for two purposes. • To work in zero gravity • To reflect laser light allowing them to act as a mirror at the end of the interferometer arms. • LISA was designed: to protect and shield the cubes from external and internal disturbances so that the cubes move only under the influence of gravitational forces, not other forces. • The relative motion of these cubes on different spacecraft are what will detect passing gravitational waves.

7. Core Technologies:Micro-Newton Thrusters & Optical Bench Micro-Newton Thrusters: If the distance of the Gravitation Reference Sensors shifts toward the optical bench, micro thrusters fire to move the cubes back into position by repositioning the satellite. • The optical bench: • Is used as the metrology frame for the satellite. It is a solid block of glass that all of the components mount to • It contains the main optics: the laser beam injection, detection, and beam shaping optics, as well as the gravitational reference sensor. • Primarily passive components, except for: • the motorized positioner for fiber selection and focusing • photodiodes for signal detection • and a phase modulator that allows transfer of information between spacecraft.

8. Kinematic Constraints Gravitational reference mass: The movement of this mass is used to detect gravitational waves, this object is completely free floating in space, UNCONSTRAINED Optical Bench: The glass base is used as metrology frame that everything is mounted to and referenced. Secondary Mirror: supported by a three-leg “spider” system, consisting of three flat plate constraints. This fully constrains the mirror in all direction.

9. Errors Sources • External disturbances noise: • Pressure from solar photons • the Sun's magnetic field • Earth's gravitational field • Confusion Noise • -disturbances caused by unresolved galactic or cosmological sources. • Internal sources of noise: • thermal heating of the instruments, • charged test masses • -electric field on the test masses from its interaction with the spacecrafts' computers • In space: it won't have any error sources from environmental noise that affects ground detectors on Earth's surface. i.e. Earthquakes, and other vibrations limit ground detectors to observations at frequencies above 1 hertz.

10. The instrument is protected at all times by thermal shielding, this protects the instruments from solar brightness by using Designing Out Errors • gold-coated • suspended by stressed fiberglass bands • A cover across the top of the spacecraft cylinder prevents sunlight from striking the thermal shield, and thus the instrument, during science operations. • Inside the Y-shaped tube, the instrument's optical assemblies are surrounded by additional thermal shielding. • The primary mirror is a double-arch light-weight ultra-low expansion design. • The secondary mirror is supported by a three-leg "spider" made of a graphite-epoxy material with low thermal expansion. • The optical bench within each assembly contains the main optics: the laser beam injection, detection, and beam shaping optics, as well as the gravitational reference sensor. This bench consists of a solid glass block to which all components are rigidly attached.

11. Conclusion • What is LISA: LISA is the Laser Interferometer Space Antennae co-funded by European Space Agency (ESP) and NASA. Its primary purpose it to search for gravitational waves. With this information we can study the mergers of super massive black holes, and test Einstein’s theory of general relative. • What are Gravitational Waves: • They are energy and angular momentum of a system that is released when it changes it’s mass distribution. Which can most commonly be seen in black-hole binary pair, accretion onto Massive Black Holes, etc. • What are it’s Core Technologies: Gravitational Reference Sensors, Micro-Newton Thrusters, optical bench, and Laser Interferometry. • What is the accuracy of LISA: Lisa will use Laser interferometer to get a Milli-hertz resolution range, and a sub-nanometer accuracy range. • What are the error sources • External: pressure from the light of the Sun and its very small variations • the variable solar magnetic field • distortion of the LISA array by the gravitational effects of the Earth and Moon • Internal: electrical field generated by the spacecraft computer • residual gas pressure near the test masses • thermal radiation by the electrodes used to measure the spacecraft position

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13. Reference’s What is LISA on NASA JPL web sight http://lisa.jpl.nasa.gov/WHATIS/intro.html Berkeley’s website relating to LISA http://astron.berkeley.edu/~imaran/cosmology1.html Caltech information on LISA and links to three related posters http://www.ligo.caltech.edu/LIGO_web/9904news/9904cit.html Einstein's contribution to LIGO and LISA http://www.einsteinathome.org/gwaves/detectors/geo-ligo.html LISA: some guys home page http://www.dragfreesatellite.com/index.html LISA: article from "Universe Today" http://www.universetoday.com/am/publish/lisa_snacking_black_holes.html?1812005 Michelson Interferometer http://www.3dimagery.com/michelsn.html