# Presentation: 784133

##     	 L2-View/EASI 

**(Earth Atmosphere Solar-Occultation Imager)**

**Jay Herman Lee Feinberg Jim Watzin**

**CO****2****,  CH****4****,  H****2****O,  O****3****,  O****2****,  N****2****O**

**X**

**X**

- Nightside
-     Earth

##                  L2-View/EASI 

**                 ****L2-View/EASI**** **
**(Earth Atmosphere Solar-Occultation Imager)**
**  *********Solar Occultation from Lagrange-2**
**  *********Fourier Transform Imaging Spectrometer**
**  *********10 Meter Interferometer (lightweight design)**
**Wavelengths:  1 – 4 microns**
**Resolution: 1 nm or better**
**Spatial Resolution: 1 to 2 km**
**CCD: 1K x 1K or Linear Diode Array**
**Available Solar Flux ~ 12 - 15% of Total Sun**

**J. Herman**
**L. Feinberg**
**J. Watzin**

##    L2-View (EASI): A Mission Concept

**Earth Atmosphere Solar-Occultation Imager**

**1.****	****If a mission to Lagrange Point 2 (a position **
**	****behind the Earth relative to the Sun) were**
**	****contemplated, what science could be accomplished?**
**Is there unique Earth science that can be accomplished****from this orbit?**** **
**Are there problems that would prevent such a mission?**
**Is there other unique science that can be accomplished from **
**	****the same spacecraft?**

## Ans:	Measure Greenhouse Gases 

**Ans:****	****Measure Greenhouse Gases **
**	****	****CO****2****,  CH****4****,  H****2****O,  O****3****,  O****2****,  N****2****O**
**	****	**
**Is there unique Earth science that can be accomplished from this orbit?**
**Ans:****	****Produce the FIRST 3-D Mapping of Greenhouse gases**
**	****	**** ****Height 2 km:  Latitude 0.1****o****  Longitude 2****o**

**L2-View (EASI):**

## Ans: 	NO

**Ans:**** ****	****NO**
**	**
**Launch and orbit require conventional hardware**
**Spacecraft is derived from Triana**
**Instrument optics are conventional (flat mirrors)**
**GSFC has built in-house several IR Fourier ****	****Transform Spectrometers**
**	****(e.g., CIRS on Cassini and FIRAS on COBE).**
**The 10 meter interferometer is new, but within**
**	****today’s engineering capabilities.**

**L2-View (EASI):**

## Ans: 	YES

**Ans:**** ****	****YES**
**Unique Solar Observations at high spatial resolution in the Near IR**
**Observations of the Magnetotail**
**Observations of Lightning**
**Observations of Aurora**
**Observation of Nighttime cloud cover**

**L2-View (EASI):**

## L2-View EASI Trajectory to L-2

## EASI Solar Occultation Mission

**L-2**

**EASI Solar Occultation Mission**

**L-1**

**L-1 and L-2 points move with the Earth**

## X

**D=12,756 km**

**SUN**

**149,600,000 km**

**1,400,000 km**

**L2**

**1,500,000 km**

**D=1,392,000 km**

**Relationship of L-2 Orbit Position to the Earth’s Umbra**

**The spacecraft is always illuminated by the direct sun. This means that the atmosphere can be continuously viewed in solar occultation.**

- α

## View of the Earth-Sun System from the L-2 Orbit

**d**

**r****S**

**r****E**

**D****S**** = 1.496x10****8**** km**

**x**

**a**

- b

**R****L**** = 1.5x10****6**

**If the Earth’s atmosphere is to always be seen against the Sun, the **
**Lagrange orbit is close to the Sun-Earth line.**

- X

**View of the Earth-Sun System from the L-2 Orbit**

**L-2 Lissajous Orbit**

**2d**

**L-2**

- rS = 6.9598x105 km
- rE = 6.373x103 km

- 26,000 km
- Orbit

- 14,000 km
- Orbit

- 400 km
- Orbit

**2d**

**2d**

**2d**

**r****S**

**r****E**

**A**

**B**

**C**

- Case C is the desired
- Orbit for solar occultation

## Sun

**View of the Earth-Sun System from L-2**

**Rotatable Detector for Occultation **

**Obs. Solar Disk=53,500 km**
**3.8% of solar disk**
**Earth atmosphere=440 km**

**Exposed Sun Area = 15%**
**Brightness < 15%**
**Because of limb darkening**

**Note:  ****The edge of the Sun is 53,500 km of the Sun’s disk, **
**but only extends 440 km above the Earth’s disk**

**Detector With**
**Interferometer Slit**
**2 km altitude resolution**
**1 to 5 microns**

- Nightside
-     Earth

## 20 km limb view

- 1 to 2.5 microns
- CO2, CH4, O2, H2O
- Band width 1 to 10 nm

- H2O:	1.12, 1.3 microns
- CO2:	1.45 microns
- O2: 	1.25 microns

## 20 km     

- Selected bands can clearly
- distinguish individual species
- The exact bands to use are a
- function of altitude. This requires
- a tunable spectrometer.

- 20 km
- 2.50 to 4.00 microns
- CH4, H2O, CO2, N2O, O3

## 5 km limb view

**5 km limb view**
**1 to 2.5 microns**

**H2O:****	****1.3 microns**
**CO2:****	****1.45 microns**
**O2: ****	****1.25 microns**

## 5 km     

**5 km     **
**2.50 to 4.00 microns**
**CH****4****, H****2****O, CO****2****, N****2****O, O****3**

**CH****4****:****	****2.58 microns**
**N****2****O:****	****3.85 microns**
**O****3****:****	****3.28, 3.60 microns**

## Sensitivity to Change @ 1570

_**Sensitivity to Change @ 1570**_
**Instrument:  1/3 %**
**Total: CO****2****    0.2% at 5 km**
**                 ****or  1 part in 500**
**	****	****0.4% at 10 km**
**	****	****2% at 20 km **

## L1

- L2

- EASI and Triana can make unique observations of Solar disturbances outside of the Bowshock and within the Magnetotail.

**EASI and Triana Synergy**

- EASI: 1.5x106 km
- Triana 1.5x106 km
- From Earth
- BowShock 5x104 km
- Day and Night Obs of Clouds for Climate Studies

- *

- *

## L2-View/EASI   Imaging Solar Occultationof the Earth from L-2

**Additional Science:**
**   ****Measurements the Earth’s magnetotail**
**	****Magnetic field, electron, proton and alpha velocity**
**  ****	****View of the aurora**
**	****Correlations with measurements at L-1**
**  ****Lightning: Observations of full night disk to observe the **
**	****frequency and location of lightning.**
**  ****Full disk observations of clouds and surface features at 4  ****	****microns.**
**  ****Spectral mapping of the solar limb, observations of solar**
**	****granulation, and other solar features (sunspots, flares).**

##                        L2-View: EASI

**Earth Atmosphere Solar-Occultation Imager**

**Goals:****	****Measure altitude profiles for 5 major Greenhouse Gases for the entire Earth and the atmospheric pressure profile**
**	**
**	****Produce a 3-D Map of the distribution of **
**	****         ****CO****2****,  H****2****O,  CH****4****,  O****3****,  N****2****O,  O****2**
**Altitude****	****2 km Resolution**
**Latitude****	****0.1****o**
**Longitude****	****2****o**
**Technical Challenges:****	****Fly large aperture (10 meter) interferometer**
**	****	****	****Extensive use of lightweight materials**
**	****	****	****Highly controlled orbit at L-2**
**	****	****	****High data rate with advanced antenna design**

## IFTS

- 10 Meters

**Block Diagram of EASI Interferometer With Beam Entering An Imaging Fourier Transform Spectrometer**

**0.7m**

**0.2m**

**Flat**
**Mirror**

**Rigid Composite Bar**
**With Precise Mirror Positioning**

**Shutter**

**Interferometer and Imaging Package**

## EASI Mirror-Boom Assembly

**EASI Mirror-Boom Assembly**

**Closed Shutters**

**Tip-Tilt Mirrors**

**Interferometer and Imaging Package**

**Sunlight**

**Sunlight**

**Open**

**Open**

**10 Meter Boom**

## Advanced L2 Mission ArchitectureUsing Wide-field Imaging Interferometry

**Advanced L2 Mission Architecture****Using Wide-field Imaging Interferometry**

**Incoming Light**

**Incoming Light**

**Active**
**Delay Line for**
**Michelson**

- Note:  Figure is simplified
- Beam reducers not shown
- Fizeau configuration also possible

**Detector**

**Boom**

**B=Collecting Baseline=10 meters**

**Tip/Tilt **
**Mirrors/mechanisms**

**Sample Pair of **
**Collecting Mirrors**

**Spatial Resolution=********/B**

**Lens**

**Simplified Diagram of Interferometer and Imaging Package**

## Boom Technology Has Heritage on SIM

- Outer Layer
-  Silverized Teflon (s = 0.25)

- Inner MLI Blanket
-  low e* (0.015)

- Structural Panel

- Radiative Separator

- Feedback Control Sensor
- on Heater

**Control Heater**
- Computer controlled
- On/Off Deadband < 1°C
- Large Area, Low Power Density
- Integral Feedback Control Sensors
-  Radiative Thermal Coupling to Panel

- The thermal control environment will be much more stable than SIM
- SIM requires supporting many different pointing angles relative to sun
- SIM boom technology should easily meet our requirements
- SIM approach to isolate reaction wheel vibrations should also work

## GSFC Spatial-Spectral Imaging Interferometry Roadmap

**GSFC Spatial-Spectral ****Imaging Interferometry Roadmap**

**Time from Present**

**Aperture**

**EASI**

**SPIRIT**

**SPECS**

- .5 meter

- 8.5  meter

- 40 meter

- 1 Km

- 1 year

- 7 years

- 15 years

- 20+ years

**WIIT**

**0.25 Arc Sec at 1****μ**

**10 meters at L-2 Earth Viewing**

**     ****0.5m Laboratory**

**     ****20 meters**
**    ****Astronomy 0.12 arc sec at **1μ

**     ****1 km **
**   ****Astronomy**
**0.02 arc sec at **1μ

## Technology Readiness:

| Technology | Current | Challenge | Risk |
| --- | --- | --- | --- |
| 1-D Spatial-Spectral Interferometer + Algorithms
(2-D algorithms desirable) | .5m Wide Field Imaging Interferometer Testbed in Build
(funded by IR+D, ROSS) | Extension to large 10 meter aperture for space flight | MED |
| Light-weight beam splitters
Low vibration shutters | New
Disk shutter | Lightweight
Low vibration
 | Low
MED |
| Extremely stable 10 meter lightweight truss | SIM composite material truss |  | MED |
| Repeatable tip-tilt mirrors
Delay lines
Near IR detectors
Light flat mirrors
 | Current Techn.
CIRS Heritage
Current Techn.
Current Techn. | Need flight qualified
Modify for Near IR
Tailored readout desirable
Flat pass band for BS
 | LOW
LOW
LOW
LOW |

**Vibration/thermal control**
**to avoid complex metrology**

## L2-View  EASI Spacecraft and Instrument

**EASI Stowed Configuration on Triana-Heritage Gyroscopic Upper Stage**

**Stowed Solar Array 26 m****2**

**Rigid Composite Interferometer Bar with 20 mirrors stowed internally and accessed using pairs of shutters**

**Fourier Transform Instrument and Electronics**

**L2-View  EASI Spacecraft and Instrument**

##     EASI Instrument

**      ****and**
**Spacecraft**
**Mounted in**
**Shuttle **
**Carrier**

## Instrument

**Spacecraft**
**     ****And**
**   ****Carrier**
**Mounted in**
**Shuttle Bay**