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JANUS An Earth-Sun Observing L1 Mission. JANUS Team Briefing to the ISAL & IMDC July 11 th & 25 th , 2005. JANUS IMDC Briefing Agenda. Team Introduction (Gerry Lead) Science/Mission Overview (Jay/Joe Lead) Instruments Overview (Jeff Lead) Inter-instrument compatibility Issues

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An Earth-Sun Observing L1 Mission


Briefing to the ISAL & IMDC

July 11th & 25th, 2005

Janus imdc briefing agenda
JANUS IMDC Briefing Agenda

  • Team Introduction (Gerry Lead)

  • Science/Mission Overview (Jay/Joe Lead)

  • Instruments Overview (Jeff Lead)

    • Inter-instrument compatibility Issues

    • Prioritization & De-scopes

  • Operations Concept (Joe/Jay Lead)

  • Pointing Concept (Joe)

    • Pointing platform & guide telescope concept

  • Data Communications Concept (Jonathan Lead)

  • IMDC Trades (Dave Lead)

JANUS Mission Formulation Team

Dr. Jay Herman Code 613 Lead Implementation PI & Earth Spectrometer lead Co-I

Dr. Joe Davila Code 612 Lead Solar Instrument Suite Co-I

Dr. Clarence Korendyke NRL Lead NRL Instruments Co_I

Gerry Daelemans Code 462 Project Formulation/Capture Manager

Jeffery Jones Code 556 Instrument Manager

David Bundas Code 599 Missions Systems Lead

Jonathan Gal-Edd Code 581 Data Communications Lead

Eric Mentzell Code 551 Optics Design Lead

Kate Hale Code 544 Electro-mechanical Lead

Tropospheric nitrogen dioxide

Solar Coronal Mass Ejection

Dust Aerosols

Airglow at 100 km

Biomass Burning

EUV Spectroscopy


JANUS – An Earth-Sun Mission at L1

Tropospheric nitrogen dioxide

  • Mission Description

  • Delta-2 launch vehicle to L1 Halo orbit

  • 3.5 month transit, 6 months to orbit

  • 3 year lifetime, 5 year goal

  • Daily science telemetry, and real-time, low-rate broadcast mode

EUV Spectroscopy

Airglow at 100 km

  • Technology Development

  • None required

  • Measurement Strategy

  • Continuous Earth and Sun viewing, and continuous upstream particle monitoring

  • Sun (EUV) and Earth (EUV, FUV, VIS, IR) spectroscopy to provide new physical understanding

  • Coronagraph and solar wind and energetic particle measurements provide continuous space weather information

Janus science objectives
JANUS Science Objectives

  • Understand the relationship between solar activity and the structure and dynamics of Earth’s atmosphere from the surface to the thermosphere-ionosphere for a range of seasons, solar radiation and energetic particle inputs.

  • Understand the role of plasma dynamics in coronal heating, solar wind acceleration, flares and transients, and UV irradiance variations.

  • Understand the role of transport and source distribution using high-resolution synoptic mapping of environmentally important species, tracking of pollution plumes, and ozone layer dynamics with the input to GCM chemistry models.

  • Provide real-time space weather data for predictive modeling of the space environment and Earth’s upper atmosphere.

  • Provide solar storm data for the purpose of protecting satellite communication, astronaut safety, ground power distribution assets.

Earth Viewing Spectrometers

FUV, EUV (58 – 240 nm)

UV-VIS, NIR (240 – 960 nm)

(2 Telescopes with Multiple Focal Planes)

Sun Viewing Package:

Solar Coronagraph (Vis)

Solar EUV Spectrometer

Soft X-Ray Spectrometer

Solar Wind Package

Mag. Field+ Particles

  • JANUS has three suites of instruments to accomplish JANUS Science Objectives:

  • - 2 Earth Viewing Spectrometers

  • 240 – 960 nm 0.5 meter mirror Near-UV, VIS, Near-IR

  • 85 – 240 nm 16 cm mirror EUV and UV

  • - A Solar Viewing Suite of Instruments

  • NEXUS EUV Spectrometer

  • Coronagraph

  • Irradiance Monitor (Soft Xray Spectrometer?

  • - An in-situ Suite of Instruments

  • Magnetometer

  • Solar Particle Counter

JANUS System Block Diagram

Solar Guide Telescope

Solar Instrument

Suite (SIS)

Earth Instrument

Suite (EIS)

Error signal

Error signal

S/C Bus

NEXUS EUV Spectrometer

Visible Light


0.5 m


White Light Coronagraph



0.16 m


Irradiance Monitor





Internal EIS,SIS Data Bus’s

S/C to EIS,SIS Data Bus

Solar Wind

In Situ


Suite (SWIS)

SIS Mech

Drive Elect.

EIS Mech.

Drive Elect.

S/C to EIS,SIS Power

Solar Wind

Particle Counter

High Gain Antenna



Earth Viewing Instrument Descriptions

  • Spectrometer with 0.5 meter primary mirror Cassegrain operating in two focal planes. The secondary mirror is active for scanning and jitter control.

  • a. 240 to 500 nm with 1 nm resolution from 300 to 500 nm

  • b. 480 to 960 nm with 4 nm resolution from 480 to 960 nm

  • There are 10 narrow wavebands from 240 to 300 nm

  • Uses beam-splitter onto two separate slits, gratings, and detectors.

  • Uses flat folding mirrors and flat gratings.

  • Uses concave mirror for focusing

  • High data rate of 2.5 Mbps 24/7

  • Signal to Noise required of 500:1 for spatial resolution of 6 km nadir

  • Requires image stabilization to 1/3 pixel (0.25 arcseconds)

  • 2. Two NEXUS-style Spectrometers for EUV and short-wavelength UV

  • Uses ~16 cm primary and torroidal grating for minimum number of reflecting surfaces.

  • No image stabilization needed because of coarse spatial resolution ~10 arc seconds (100 km)

  • Uses xxxxx pixel detector

Instrument overview
Instrument Overview

  • Jeff: Please create the necessary charts to orient the IMDC on the instruments mentioned in the previous slide.

    • Take into account Compatibility issues between instruments that don’t come across from the data we supplied via the IMDC Web site

    • Discuss the prioritization and descope sequence

Janus operations concept
JANUS Operations Concept

  • Insert into 700 km LEO for 1 or 2 orbits

  • Perform Basic Checkout (Low Power)

  • Launch towards L-1

  • Deploy Solar Panels

  • Check Main Transmitter (High Power)

  • Perform Full checkout (High Power)

  • After 1 to 2 weeks Start Earth-Instrument Operations

  • Start solar instruments - Checkout

  • When the spacecraft is more than 15 degrees from the Earth-Sun line, point the spacecraft at the sun to obtain only solar data for the next few months.

  • Assuming we have the 18-meter Ka-band antenna, start ground-system operations at 2 hours per day to receive solar data

  • Start Earth-Sun operations at the 5 to 6 month period when within 15 degrees of L-1

  • Ground systems operation increased to 4 hours per day

  • Once L-1 orbit is stabilized, full Earth-Sun operation with data 24/7 requiring 4 hours of ground data reception.

JANUS Earth-Viewing Spectrometer Operations

• Average Exposure Time 0.1 sec

• CCD Readout 0.1 sec

• 4 exposures per line co-added onboard the spacecraft (2048x2048 pixels)

• Raster mirror moves 0.75 arcseconds in object space.

• Repeats 4-exposure cycle

• Raster mirror moves ~2000 times to cover the entire Earth disk.

Image Stabilization

• Raster mirror also moves in 2-d to stabilize the image

• Stabilization information comes from a guide telescope focused on the Sun’s limb

• Stabilization to 1/3 pixel or 0.25 arcseconds in object space

• Motions in object space are about 1/3 the motions in image space





raster lines










Janus pointing concept
JANUS Pointing Concept

  • Joe, please provide what is necessary to orient the IMDC folks around our baseline pointing platform scenario,& some more detail about our use of the guidetelescope to handle fine pointing/de-jitter, etc.

Janus trades
JANUS Trades

  • Dave, Joe Jay,,,,do we have any trades we want the IMDC to look at?

Janus data communications concept
JANUS Data Communications Concept

  • Assumptions for Earth-Viewing Spectrometer 240 to 960 nm:

  • Assume the use of a 2k x 2k detector

  • Assume a total wavelength range from 250 to 960 nm

  • Assume: 300 to 500 nm at 1 nm resolution = 200 elements

  • 500 to 906 nm at 4 nm resolution = 120 elements

  • 250 to 300 nm 10 narrow bands = 10 elements

  • Total data elements 2000 x 330 = 6.6x105 elements

  • Assume 16 bits per element => 1.06x107 bits per spatial line

  • Exposure time and readout is about 1.1seconds (~0.6 hours per full globe)

  • This yields a data rate of 9.6x106 bits per second uncompressed

  • or 4.8x106 bps compressed.

  • 10. Measurements only once per hour (*0.61) = 2.9x106 bps

  • Only illuminated pixels (*0.79 = pi/4) = 2.3x106 bps

  • 11. We need approximately 2.5 Mbps for the range 250 to 960 nm

  • 12. Estimated Ka band rate is 64 Mbps. Using a 4-hour downlink, this is

  • equivalent to about 10 Mbps continuous data acquisition.

  • 13. The remainder 7.5 Mbps is available for the solar instruments and the Earth-viewing EUV instrument