195 Å image – behind 195 Å image – Sun- Earth line – SOHO/ EIT image 195 Å image – Sun- Earth line – SOHO/ EIT image 195 Å image – ahead SECCHI Extreme Ultraviolet Imager (EUVI) In Space Weather, you get ahead by being behind. 24 March 2008

Suggested Plan C Place Solar-C at L5 Earth Solar-C Sun Separation varies from ~60 to more than 90 deg from the Sun- Earth line

L5 Mission Science Joseph M. Davila NASA Goddard Space Flight Center December 2008

Science Objectives (1) Understand the origin of magnetic fields in the Sun – Nearly stable 2-point helioseismology over a long observing periods provides optimum observing – questionable, large continuous telemetry needed, out-of- ecliptic observation desirable, NEED TO TALK TO HELIOSEISMOLOGISTS – Long, uninterrupted observing periods give excellent frequency resolution of the relevant wave modes – Observation of the Tachocline region over solar cycle (or a large fraction thereof) – 3D photospheric field – accurate 3D field even in weak regions by triangulation validates vector field measurement methods – Photospheric and/or chromospheric field measurement possible depending on science and instumental ability – LAST 2 POINTS IMPORTANT FOR SPACE WEATHER, DISCUSSION: L4 OR L5 FOR B?

Science Objectives (2) Understand the 3D coronal structure and magnetic FIELDS of active regions – REDUNDANT WITH CURRENT STEREO MISSION – Determine the structure of active region fields: SPACECRAFT AT L5 AND SUN-EARTH LINE TOO FAR APART? – Triangulation of magnetic loops provides independent measure of coronal magnetic field to compare with extrapolations – How is energy stored in the active region magnetic field? – How are CMEs initiated in active regions Transients and CMEs are imaged all the time Constant view of Sun-Earth directed CMEs to study geoeffectiveness Optimum observing position to overcome the occulter and Thomson surface limitations of Earth-based instrument CIR: NEXT GENERATION HI IS SUGGESTED HERE

Science Objectives (3) – NOT A STRONG JUSTIFICATION FOR L5 How does the magnetic field of the Sun connect to the Heliosphere? – Increased surface angular coverage to improve heliospheric models – Magnetic field measurements over 75% of the solar surface (approaching 100% if one STEREO is operating) – STEREO MISSION DOES NOT HAVE A MAGNETOGRAPH! – Activity observation over 75% of Sun – How is open flux destroyed on the Sun to maintain the nearly steady state solar field strength? – How are structures observed in the IPM related to solar structure? – What is the origin of interplanetary turbulence? – What is the origin of the FIP effect, and what height does it occur? – NO NEED FOR L5 – Use composition to trace IPM structures back to solar surface

Science Objectives (4) What is the 3D structure of the corona near the Sun? – Routine tomography will provide 3D pictures of the solar streamer structure, and how it relates to the heliospheric current sheet. How is energy released in a flare – YES, BUT WANT STEREO OBSERVATIONS – How do loop top sources relate to puzzling RHESSI footpoint results? – L5 IS ONLY ADVANTAGIOUS WITH STEREO OBSERVATIONS Height information for critical flare emissions – Stereo observation of reconnecting flare regions – Flare structure in 3D How are particles accelerated near the Sun? and how do they propagate to 1AU? – What is the structure of shocks in the low corona? – What is the site of particle acceleration, and what controls the acceleration process?

L5 Mission Approach No overlap with ALL existing or planned missions And at the same time COMPLEMENTS all existing missions

Proposed Instrumentation High resolution vector magnetograph High resolution coronal soft x-ray or EUV imager High cadence UV-EUV spectrometer High resolution white light coronagraph Solar wind ions with composition and electrons Energetic ions with composition Magnetometer

L5 Orbit L5 provides quasi stable orbit Earth-sun-sc angle varies from about 40 to 90 degrees About 1 AU from Sun Insertion time 1- 2 yrs Earth Sun L5 Equipotentials

Data Downlink Capability STEREO demonstrates a minimum using X- band – Transmission rate of order 480 kbps – Contacts are 5 hours long – Total downlink varies from 5 to 7 gigabits/day – Using 30 m dish The total downlink can be improved by increasing any of these parameters

The External Environment SDO – high time and spatial resolution from geosynchronous Earth orbit, magnetograph and coronal imaging Solar Orbiter – out of the ecliptic (~30 deg) observation from ~25 Rsun Solar Probe – in ecliptic observation, in-situ instruments and coronal imager with multiple passes to 10 Rsun STEREO (Extended Mission?) – 45 degree drift/2 years, 135 degrees from Earth in 2013, directly behind Sun in 2015

Suggested Plan C Place Solar-C at L5 Earth Solar-C Sun Separation varies from ~60 to more than 90 deg from the Sun- Earth line

Overcomes Thomson Surface Problem for CME Observation SunEarth CME Direction

Technical Issues to Consider Injection into L5 orbit – tradeoff between fast arrival time, propulsion mass, and instrument mass – INVESTIGATE TRADE SPACE; NEED SPECS ON POSSIBLE INSTRUMENT PARAMETERS Maintenance of the orbit Optimize telemetry and ground system Once-a-day upload of ops plan

NRL Ideas/Instruments for Science at L5 SEP (particle instruments, coronagraph): rescue lost science of STEREO - central meridian at L1 is western for L5, characterize shock front, evolution of active region producing multiple events (take out longitudinal variation), early phases of CMEs EUV spectrograph off-limb, coronal electron profiles above the limb, spectroscopy at L5, particle measurements at L1, suprathermal distributions of ions and electrons, L1 context instruments, space weather predictive power, solar flares (standard model) Irradiance (predictive power) (zone plates are small and light) Advanced HI – image CIRs and CMEs better as well as solar wind Particle instrumentation? EUV/X-ray imaging Chromospheric/coronal magnetic field measurements Gamma ray spectroscopy (different viewpoints)? Remote observation sensing of CME magnetic field, synergy with MWA/LWA NRL proposed modification of L5 (slow moving spacecraft)