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

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

3. 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.

4. L1...More to Scale
23 Jun
IGARSS 2002

5. Simulated L1 View of Earth and Moon
23 Jun
IGARSS 2002

6. 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

7. 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

8. 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

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

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

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

12. NISTAR: Views Whole Earth
23 Jun
IGARSS 2002

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

14. Triana in Launch Configuration
23 Jun
IGARSS 2002

15. 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

16. 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 ~ % of Total Sun
L2–EASI
Sun
23 Jun
IGARSS 2002

17. 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

18. 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

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

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

21. 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

22. 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

23. Backup
23 Jun
IGARSS 2002

24. 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