ASP: Lagrangian Point or Bust!

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Lagrangian Point or Bust!

Mercury, January/February 2005 Table of Contents

Artist's conception of James Webb Space Telescope

Courtesy of NASA.

by Thomas J. Sherrill

A solar-monitoring telescope is being placed "in orbit around L1." The James Webb Space Telescope (successor to the Hubble Space Telescope) is planned for launch in the year 2011 to "L2." In the past there was a group of space habitation enthusiasts called the "L5 Society" (now part of the National Space Society). The "L" in these terms stands for Lagrangian, and the designations L1, L2, L3, L4, and L5 are the so-called "Lagrangian points." But what exactly are these points, and what makes them such special destinations for spacecraft?

Table 1. Six missions and counting...... The future of the Lagrangian points as space destinations seems assured as new generations of space-based observatories in the planning stage seriously consider using L2 halo orbits because of their attractive operational environment. In a few cases the Lagrangian option is only one of several. Launch dates become more uncertain for farther-down-the-line missions, as forerunner programs may be delayed or extremely ambitious projects find that technology has a lot of catching up to do. The question marks in the Lagrangian Point column indicate that L1 or L2 may not be the most preferred orbital option.

Past and Current Missions:

Mission	Operational	At LP	Lagrang Pt	Program	Science Mission
ISEE-3/ICE	8/78 - 5/97	4 yrs	L1	Explorer	(International Sun-Earth Explorer / International Comet Explorer) Investigate solar-terrestrial relationships, solar wind, earth's magnetosphere, and cosmic rays
Wind	11/94 - pres	1 yr	L1	Global Geospace Science Initiative	(GGSI = U.S. portion of International Solar-Terrestrial Physics Program [ISTP]) Study solar wind before and as it encounters earth's day-side magnetosphere
SOHO	12/95 - pres	8.8 yrs	L1	ESA/NASA/COSTR	(Solar and Heliospheric Observatory, part of Collaborative Solar-Terrestrial Research Program of the ISTP) Study solar corona, structure and interior dynamics
ACE	8/97 - pres	7 yrs	L1	Explorer	(Advanced Composition Explorer) Determine composition of interplanetary and interstellar particles from solar wind particles to high-energy galactic cosmic rays
WMAP	6/01 - pres	3.3 yrs	L2	Medium Class Explorer	(Wilkinson Microwave Anisotropy Probe) Map cosmic microwave background temperature to high angular resolution and sensitivity
Genesis	8/01 - 9/04	2.5 yrs	L1	Discovery	Collect solar wind particles and return them to earth for retrieval

Proposed Future Missions:

Mission	Launch	Duration	Lagrang Pt	Program	Science Mission
Triana	TBR	2-5 yrs	L1	SMEX-Lite	Full-time observation of whole earth; s/c built and tested, in storage, unlikely to fly
LISA Pathfinder	2006-7	6 mos - 1 yr	L1 or L2	ESA	Precursor to Laser Interferometry Space Antenna (LISA) mission, to demonstrate precise formation flying and measurements to detect gravitational waves
Herschel (FIRST)	2007	> 3 yrs	L2	ESA Cornerstone	(Formerly Far Infrared and Submillimeter Telescope) Photometric and spectroscopic study of early galaxy and star formation
Planck	2007	21 mos	L2	ESA Horizon 2000	(Formerly COBRAS/SAMBA -- to be launched with Herschel) Map cosmic microwave background temperature to highest angular resolution and sensitivity
SPICA (H2L2)	2010	3 yrs	L2	Institute of Space & Astronaut Sci	(Space Infrared Telescope for Cosmology and Astrophysics, aka HII/L2 -- Japanese mission) IR observatory, successor to ASTRO-F/IRIS infrared survey mission
Geostorm	2010?	> 5 yrs	< L1	NOAA/NASA/DoD	Monitor solar dynamics, flare activity, warn of geomagnetic storms (spacecraft maintained 3.3 million km beyond L1 using solar sail techniques)
SPIRIT	> 2010	5 yrs	L2	Origins	(Space Infrared Interferometric Telescope) Precursor to SPECS, structurally connected interferometer to demonstrate key far infrared interferometry technologies
JWST	2011	5-10 yrs	L2	Origins	(James Webb Space Telescope, formerly Next Generation Space Telescope) Successor to HST, telescope operating from visible to infrared
MAXIM Pathfinder	2011-15	3-5 yrs	L1 or L2?	New Millennium Program	Precursor to MAXIM, separate optics and detector spacecraft in formation flight to demonstrate X-ray interferometry
GAIA	2012	5-10 yrs	L2	ESA Cornerstone	(Global Astrometric Interferometer for Astrophysics) Utilize visible-wavelength interferometry to measure positions and characteristics of 1 billion stars
TPF-C	2014	5-10 yrs	L2?	Origins	(Terrestrial Planet Finder - Coronagraph) Detect and characterize terrestrial planets about nearby stars using visible wavelength coronagraphy (reflected light)
Darwin	> 2014	5 yrs	L2	ESA Cornerstone	IR interferometer to study terrestrial planets about nearby stars using six formation-flying telescopes and beam combiner (mission may be combined with TPF-I)
SPECS	> 2015	5-10 yrs	L2	Origins	(Submillimeter Probe of the Evolution of Cosmic Structure) Submillimeter interferometer to study early universe using 4 tethered spacecraft in formation flight
Constellation-X	2016,17	4-9 yrs	L2	Structure & Evol of the Universe	Successor to Chandra, large-collecting-area X-ray observatory using 4 spacecraft, 1 soft X-ray and 3 hard X-ray telescopes on each
SAFIR	2017	5-10 yrs	L2	Origins	(Single Aperture Far-Infrared Observatory) Successor to Spitzer and Herschel, to study early galaxy and star formation, planetary systems
L1 Diamond	2018	3-6 yrs	< L1	Sun-Earth Connection	Monitor solar dynamics, flare activity, warn of geomagnetic storms (spacecraft maintained beyond L1 using solar sail techniques)
Inflation Probe	2018	4 yrs	L2	SEU Einstein Probe	Map polarization of cosmic microwave background, search for signature of gravitational waves from Big Bang
Stellar Imager	2019	5-10 yrs	L2	Origins	Image surface features of other stars, measure spatial and temporal variations, using 30 mirrors in formation flight around beam-combining hub
TPF-I	< 2020	5-10 yrs	L2	NASA (Origins)/ESA	(TPF - Interferometer) Detect and characterize terrestrial planets about nearby stars using nulling IR interferometry, 4 telescopes and combiner in formation flight
SUVO	2021	5-10 yrs	L2	Origins	(Space Ultraviolet Optical Telescope) Study universe during period when 0 < z < 3, after first galaxies, quasars, and stars emerged into their present form
Life Finder	2024	5-10 yrs	L2	Origins	Utilize high-resolution spectroscopy on habitable zone planets identified by TPF to detect biomarkers, for example using 4 25-m class telescopes and beam combiner
MAXIM	> 2025	5-10 yrs	L2	Structure & Evol of the Universe	(Micro-Arcsecond X-ray Imaging Mirror) Image energetic, compact objects using high-resn X-ray interferometry, 32 telescopes and beam combiner in formation flight
Generation-X	> 2025	5-10 yrs	L2	Structure & Evol of the Universe	Ultra-large-aperture X-ray observatory using 6 spacecraft, to probe X-ray emission from universe at z = 5-10
Planet Imager	2029	5-10 yrs	L2	Origins	Ultrahigh-resolution imaging using array of visible light coronagraphs, for example, 25 40-m class telescopes operating over a 360-km baseline

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