L1 and L2 Observatories in the Post-2010 Era Warren Wiscombe & Jay Herman NASA Goddard Francisco Valero Scripps Oceanography

Multiple Vantage Points (from NASA’s Earth Science Vision) Polesitter Molniya Orbit GEO balloons L1 Observatories L2 Observatories 23 Jun IGARSS 2002

Lagrange Points L1 and L2: New Planets! At L1 and L2, the sum of the Earth’s and Sun’s gravitational fields gives a net gravitational pull equal to that at Earth. Therefore, a spacecraft at L1 or L2 must orbit the Sun with the same period as the Earth.

L1...More to Scale 23 Jun IGARSS 2002

Simulated L1 View of Earth and Moon 23 Jun IGARSS 2002

L1 and L2 Observatories as Nerve Centers of the SensorWeb “Perhaps Triana’s most important contribution to Earth science observations is the potential for using L1 observations of Earth to integrate data from multiple spaceborne as well as surface and airborne observation platforms in a self-consistent global database for study of the planet and documenting the extent of regional and global change.” National Academy of Sciences report on Triana, March 2000 23 Jun IGARSS 2002

Unique L1/L2 Attributes Relate and connect all other observational assets Synoptic view (all times at once) High time resolution (1 min or better) Sunrise to sunset coverage Stably pull out small, delicate effects over many years Monthly Moon calibration opportunities Looong integrations for higher accuracy Assist field programs Much simpler data processing compared to LEO, GEO A true global change observing location! 23 Jun IGARSS 2002

Low Earth Orbit (LEO) and L1 Views 45-min LEO swath Sunrise to sunset instantly LEO view of Earth takes ~45 min to paint one swath covering ~1/14th of the planet — 11 hr to paint whole planet. From L1, can do same in less than 1 min (over 600x faster). 23 Jun IGARSS 2002

Geostationary (GEO) Satellite Views Each GEO takes 15-30 min to paint its covered area. 23 Jun IGARSS 2002

Spatio-Temporal Domain of a LEO Satellite vs. an L-1 Observatory LEO DOMAIN 23 Jun IGARSS 2002

The Triana Satellite NISTAR Faraday Cup EPIC Electrostatic Analyzer /Magnetometer Boom 23 Jun IGARSS 2002

NISTAR: Views Whole Earth 23 Jun IGARSS 2002

EPIC Imager: 10 channels 8–km resolution at nadir 23 Jun IGARSS 2002

Triana in Launch Configuration 23 Jun IGARSS 2002

EPIC Science Objectives Ozone Aerosols Cloud phase (ice, water) and particle shape Column water vapor UV at the surface Stratospheric dynamics “Hotspot” — vegetation direct backscatter 23 Jun IGARSS 2002

L2 Earth Atmosphere Solar-Occultation Imager Solar Occultation from Lagrange point L2 using Fourier Transform Imaging Spectrometer with 10 Meter telescope Wavelength Range: 1 – 4 mm Resolution: 5 cm-1 or better Spatial Resolution: 1–2 km in altitude Available Solar Flux ~ 12 - 15% of Total Sun L2–EASI Sun 23 Jun IGARSS 2002

Sun Eclipsed by Earth from L-2 Detector rotates around Earth limb – 2 km altitude resolution – 1 to 4 mm spectrum NightsideEarth 440 km in Earth coordinates; 53,500 km on Sun Exposed Sun: – 15% of solar area – 4% of solar radius 23 Jun IGARSS 2002

L2–EASI: Science Goals Measure greenhouse gases at sunrise, sunset... CO2, CH4, H2O, O3, O2, N2O and get their first 3-D Mapping with resolution Height, 2 km: Latitude, 1o Longitude, 2o 23 Jun IGARSS 2002

Limb View from L2, 1.5 to 2 mm 23 Jun IGARSS 2002

Other L2 Science Goals Magnetotail Cosmic rays Lightning Aurora Airglow Incoming bolides 23 Jun IGARSS 2002

L1 and L2 Synergy: Two Examples Day and night observations of clouds dynamic observations of solar disturbances outside of the bowshock and within the magnetotail L1 L2 23 Jun IGARSS 2002

Technical Challenges at L1 and L2 Large apertures (10 meter) Communications back to Earth (at all!) Data rate back to Earth Orbit design Power at L2 Rotation of Earth Thermal control (L2) 23 Jun IGARSS 2002

Backup 23 Jun IGARSS 2002

Halo Orbits can have any radius (more fuel to insert into tighter orbit)... 26,000 km 14,000 km 400 km but period is always 6 months. orbits are 3D; planar projections are Lissajous figures (orbit evolves from one quasi-ellipse to another over several years) stationkeeping once/month or more 23 Jun IGARSS 2002