The Space Interferometry Mission, or SIM, also known as SIM Lite (formerly known as SIM PlanetQuest), was a planned

space telescope A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory, OAO-2 launched ...

proposed by the U.S.

National Aeronautics and Space Administration The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding th ...

(NASA), in conjunction with contractor

Northrop Grumman Northrop Grumman Corporation is an American multinational aerospace and defense technology company. With 90,000 employees and an annual revenue in excess of $30 billion, it is one of the world's largest weapons manufacturers and military techn ...

. One of the main goals of the mission was the hunt for Earth-sized planets orbiting in the habitable zones of nearby stars other than the Sun. SIM was postponed several times and finally cancelled in 2010. In addition to detecting extrasolar planets, SIM would have helped astronomers construct a map of the

Milky Way galaxy The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

. Other important tasks would have included collecting data to help pinpoint stellar masses for specific types of

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s, assisting in the determination of the spatial distribution of

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

in the Milky Way and in the local group of galaxies and using the

gravitational microlensing Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers ...

effect to measure the mass of stars. The spacecraft would have used optical

interferometry Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...

to accomplish these and other scientific goals. The initial contracts for SIM Lite were awarded in 1998, totaling US$200 million. Work on the SIM project required scientists and engineers to move through eight specific new technology milestones, and by November 2006, all eight had been completed. SIM Lite was originally proposed for a 2005 launch, aboard an

Evolved Expendable Launch Vehicle National Security Space Launch (NSSL) — formerly Evolved Expendable Launch Vehicle (EELV) from 1994 to 2019 — is a program of the United States Space Force (USSF) intended to assure access to space for United States Department of Defense and o ...

(EELV). As a result of continued budget cuts, the launch date was pushed back at least five times. NASA had set a preliminary launch date for 2015. As of February 2007, many of the engineers working on the SIM program had moved on to other areas and projects, and NASA directed the project to allocate its resources toward engineering risk reduction. However, the preliminary budget for NASA for 2008 included zero dollars for SIM. In 2007, the Congress restored funding for fiscal year 2008 as part of an omnibus appropriations bill which the President later signed. At the same time the Congress directed NASA to move the mission forward to the development phase. In 2009 the project continued its risk reduction work while waiting for the findings and recommendations of the

Astronomy and Astrophysics Decadal Survey The Astronomy and Astrophysics Decadal Survey is a review of astronomy and astrophysics literature produced approximately every ten years by the National Research Council of the National Academy of Sciences in the United States. The report surve ...

, Astro2010, performed by the

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nati ...

, which would determine the project's future. In 2010, the Astro2010 Decadal Report was released and did not recommend that NASA continue the development of the SIM Lite Astrometric Observatory. This prompted NASA Astronomy and Physics Director, Jon Morse, to issue a letter on 24 September 2010 to the SIM Lite project manager, informing him that NASA was discontinuing its sponsorship of the SIM Lite mission and directing the project to discontinue Phase B activities immediately or as soon as practical. Accordingly, all SIM Lite activities were closed down by the end of calendar year 2010.

Mission

SIM Lite would have operated in an Earth-trailing

heliocentric orbit A heliocentric orbit (also called circumsolar orbit) is an orbit around the barycenter of the Solar System, which is usually located within or very near the surface of the Sun. All planets, comets, and asteroids in the Solar System, and the Sun i ...

, drifting away from Earth at the rate of 0.1 AU per year ultimately reaching a distance of 82 million km from Earth. This would have taken approximately years. The Sun would have continuously shone on the spacecraft, allowing it to avoid the

occultations An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...

of target stars and eclipses of the Sun that would occur in an

Earth orbit Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi) in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes days (1 sidereal year), during which time Earth ...

.SIM PlanetQuest
", Northrop Grumman, official site, 2004–2006. Retrieved 24 April 2007.The Mission
", NASA, SIM Planetquest, ''Jet Propulsion Laboratory''. Retrieved 24 April 2007. Had it been launched, SIM would have performed scientific research for five years.

Planet hunting

SIM Lite would have been the most powerful

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

hunting

ever built.Davidson, John et al., Ed.
SIM Lite Astrometric Observatory

Executive Summary
, p. ix et seq., Jet Propulsion Laboratory 400–1360, 2009. Retrieved 8 March 2010. Through the technique of

the spacecraft would be able to detect Earth-sized planets. SIM Lite was to perform its search for nearby, Earth-like planets by looking for the "

wobble Wobble or wobbles may refer to: * "Wobble" (song), a single by V.I.C. * Wobbles (equine disorder), a disorder of the nervous system in dogs and horses * Wobble base pair, a type of base pairing in genetics * Jah Wobble (born 1958), British musici ...

" in the parent star's apparent motion as the planet orbits. The spacecraft would have accomplished this task to an accuracy of one millionth of an

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

, or the thickness of a

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

viewed at the distance from Earth to the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

. Titled the Deep Search, the planet hunting program was intended to search approximately 60 nearby stars for

terrestrial planets A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Ven ...

(like

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

and

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

) in the habitable zone (where liquid water can exist throughout a full revolution (one "year") of the planet around its star). The Deep Search was to be the most demanding in terms of

astrometric Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Histor ...

accuracy, hence the name, Deep Search. This program would have used the full capability of the SIM Lite spacecraft to make its measurements. A flexible search strategy tunes SIM Lite's mass sensitivity at each star to a desired level in the habitable planet search. The value of η_Earth (Eta_Earth), the fraction of stars carrying Earth-analog planets, will be estimated by the

Kepler Mission The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...

some time before SIM Lite launches. One strategy for a habitable planet search is to do a 'deeper' search (i.e. to lower mass sensitivity in the habitable zone) of a smaller number of targets if Earth analogs are common. A 'shallower' search of a larger number of targets could have been done if Earth analogs are rarer. For example, assuming that 40% of mission time is allocated for the planet search, SIM Lite could have surveyed: * 65 stars for planets down to one Earth mass, in scaled 1 AU orbits, OR * 149 stars for planets down to two Earth masses, in scaled 1 AU orbits, OR * 239 stars for planets down to three Earth masses, in scaled 1 AU orbits. Aside from searching for Earth-sized planets SIM Lite was scheduled to perform what has been dubbed the "Broad Survey". The Broad Survey would have looked at approximately 1,500 stars to help determine the abundance of

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

-mass and larger planets around all star-types in Earth's sector of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

. A third part of the planet finding mission was the search for

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

-mass planets around young stars. The survey would have helped scientists understand more about solar system formation, including the occurrence of

hot Jupiters Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere tem ...

.Davidson, John et al., Ed., .,
SIM Lite Astrometric Observatory
''
Chapter 2
, Jet Propulsion Laboratory 400–1360, 2009. Retrieved 8 March 2010. This portion of the planet hunt was designed to study systems with one or more Jupiter mass planets before the system has reached long term equilibrium. Planet hunting techniques using a star's radial velocity cannot measure the regular, tiny to-and-fro wobble motions induced by planets against the strong atmospheric activity of a youthful star. It is through the techniques pioneered by

Albert A. Michelson Albert Abraham Michelson Royal Society of London, FFRS HFRSE (surname pronunciation anglicized as "Michael-son", December 19, 1852 – May 9, 1931) was a German-born American physicist of Polish/Jewish origin, known for his work on measuring the ...

that the SIM would have been able to execute its three primary planet-finding missions. The mission's planet finding component was set up to serve as an important complement to the future missions designed to image and measure terrestrial and other exoplanets. SIM Lite was to perform an important task that these missions will not be capable of: determining planet masses.Davidson, John et al., Ed.,
SIM Lite Astrometric Observatory
''
Chapter 3
, Jet Propulsion Laboratory 400–1360, 2009. Retrieved 8 March 2010. Another task that the SIM was envisioned to perform for the future missions will include providing the orbital characteristics of the planets. With this knowledge other missions can estimate the optimal times and projected star–planet separation angles for them to observe the terrestrial (and other) planets SIM has detected.

Stellar mass

Another key aspect of SIM Lite's mission was determining the upper and lower limits of star's masses. Today, scientists understand that there are limits to how small or large a star can be. Objects that are too small lack the internal

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

to initiate

thermonuclear fusion Thermonuclear fusion is the process of atomic nuclei combining or “fusing” using high temperatures to drive them close enough together for this to become possible. There are two forms of thermonuclear fusion: ''uncontrolled'', in which the re ...

, which is what causes a star to shine. These objects are known as

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

s and represent the lower end of the stellar mass scale. Stars that are too large become unstable and explode in a

supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...

.Stars, Neutron Stars, & Black Holes
, NASA, SIM Lite, Jet Propulsion Laboratory. Retrieved 9 March 2010.Stars, Neutron Stars, & SIM Lite
, NASA, SIM Lite, Jet Propulsion Laboratory. Retrieved 9 March 2010. Part of the SIM's mission was to provide pinpoint measurements for the two extremes in stellar mass and evolution. The telescope will not be able to measure the mass of every star in the Galaxy, since there are over 200 billion, but instead, it will take a "population census." Through this technique, SIM will be able to output accurate masses for representative examples for nearly every star type, including brown dwarfs, hot

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

red giant star A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

s, and elusive

black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

s. Current space telescopes, including NASA's

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

, can accurately measure mass for some types of stars, but not all. Estimates put the range for stellar mass somewhere between 8% the mass of the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

and in excess of 60 times the mass of the Sun. The entire study was to focus on

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

systems, stars coupled through a mutual gravitational attraction.

Galactic mapping

Interferometric measurements of stellar positions over the course of the mission would have permitted SIM to precisely measure the distances between stars throughout the

. This would have allowed astronomers to create a "roadmap" of the Galaxy, answering many questions about its shape and size.The Milky Way and Dark Matter
, NASA, SIM Lite, Jet Propulsion Laboratory. Retrieved 9 March 2010.SIM Lite and Dark Matter
, NASA, SIM Lite, Jet Propulsion Laboratory. Retrieved 9 March 2010. Currently, astronomers know little about the shape and size of our galaxy relative to what they know about other galaxies; it is difficult to observe the entire Milky Way from the inside. A good analogy is trying to observe a marching band as a member of the band. Observing other galaxies is much easier because humans are outside those galaxies. Steven Majewski and his team planned to use SIM Lite to help determine not only the shape and size of the Galaxy but also the distribution of its mass and the motion of its stars.Silberg, Bob.
Building a better guide to the Galaxy
", NASA, SIM PlanetQuest, 14 February 2006, ''Jet Propulsion Laboratory''. Retrieved 24 April 2007. SIM Lite measurements of Milky Way stars were to yield data to understand four topics: fundamental galactic parameters, the

Oort Limit The Oort limit is a theoretical location at the outer limits of the Oort cloud, where the amount of comets and minor planets orbiting the Sun drops drastically, or drops entirely. The exact location of such a limit, if there is such one, is uncertai ...

, disk mass potential, and mass of the Galaxy to large

radii In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

.Main Page
", Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007. The first, fundamental galactic parameters, was aimed at answering key questions about the size, shape and the rotation rate of the Milky Way.Fundamental Galactic Parameters
", Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007. The team hoped to more accurately determine the distance from the Sun to the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact rad ...

. The second topic, the Oort Limit, would have attempted to determine the mass of the galactic disk.Oort Limit
", Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007. The third project topic was disk mass potential. This topic was designed to make measurements of the distances to disk stars as well as their proper motions. The results of the third topic of study were to be combined with the results of the fundamental galactic parameters portion of the study to determine the Solar System's position and velocity in the galaxy.Disk Mass Potential
, Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007. The final topic dealt with dark matter distribution in the Milky Way. SIM data was to be used to create a

three-dimensional Three-dimensional space (also: 3D space, 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called ''parameters'') are required to determine the position of an element (i.e., point). This is the informal ...

model of mass distribution in the Galaxy, out to a radius of 270

kiloparsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s (kps). Astronomers were to then use two different tests to determine the galactic potential at large radii.Mass of the Galaxy to Large Radii
, Taking Measure of the Milky Way: A SIM PlanetQuest Key Project, University of Virginia, site updated 1 June 2005. Retrieved 25 April 2007.

Dark matter

Dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

is the matter in the universe that cannot be seen. Because of the gravitational effect it exerts on stars and galaxies, scientists know that approximately 80% of the matter in the universe is dark matter. The spatial distribution of

in the universe is largely unknown; SIM Lite would have helped scientists answer to this question. The strongest evidence for dark matter comes from galactic motion. Galaxies rotate much faster than the amount of visible

matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic partic ...

suggests they should; the gravity from the ordinary matter is not enough to hold the galaxy together. Scientists theorize that the galaxy is held together by huge quantities of dark matter. Similarly, clusters of galaxies do not appear to have enough visible matter to gravitationally balance the high speed motions of their component galaxies. Besides measuring stellar motions within the Milky Way, SIM Lite was to measure the internal and average galactic motion of some of the neighboring galaxies near the Milky Way. The telescope's measurements were to be used in conjunction with other, currently available, data to provide astronomers with the first total mass measurements of individual galaxies. These numbers would enable scientists to estimate the spatial distribution of dark matter in the local group of galaxies, and by extension, throughout the universe.

Development

Beginnings

The Space Interferometry Mission began as a four-month preliminary architecture study in March 1997. NASA selected TRW's Space & Electronics Group,

Eastman Kodak The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York, and is incorpor ...

and Hughes Danbury Optical Systems to conduct the study.McHale, John.
JPL eyes super-accurate star mapper
, (

EbscoHost EBSCO Information Services, headquartered in Ipswich, Massachusetts, is a division of EBSCO Industries Inc., a private company headquartered in Birmingham, Alabama. EBSCO provides products and services to libraries of very many types around the ...

), Academic Search Premier, ''Military & Aerospace Electronics'', March 1997, Vol. 8, Issue 3, p.1. Retrieved 26 April 2007. In 1998, TRW Inc. was selected as the contractor for the SIM Lite project; Northrop Grumman acquired part of TRW in 2002 and took over the contract. Also selected was Lockheed Martin Missiles and Space located in

Sunnyvale, California Sunnyvale () is a city located in the Santa Clara Valley in northwest Santa Clara County in the U.S. state of California. Sunnyvale lies along the historic El Camino Real and Highway 101 and is bordered by portions of San Jose to the nort ...

. The two contracts, which included the mission formulation and implementation phases, were announced in September 1998 and worth a total of over US$200 million. The formulation phase of the mission included initial mission design and planning for the full scale implementation of the mission.Platt, Jane.
Contractors chosen for Space Interferometry Mission
", (

Press Release A press release is an official statement delivered to members of the news media for the purpose of providing information, creating an official statement, or making an announcement directed for public release. Press releases are also considere ...

), NASA, 10 September 1998, ''Jet Propulsion Laboratory''. Retrieved 24 April 2007. At the time of the NASA announcement, launch was scheduled for 2005 and the mission was part of the Origins Program, a series of missions designed to answer questions such as the origin of life Earth. In August 2000, NASA asked project managers to consider looking at the

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...

, instead of the previously proposed EELV, as a launch vehicle.Unwin, Steve.
SIM Project Update
", ''Fringes: Space Interferometry Mission Newsletter'', Number 13, 24 August 2000. Retrieved 25 April 2007. In late November 2000, NASA announced that the project's scientific team was selected. The group included notable names from the world of

research including

Geoffrey Marcy Geoffrey William Marcy (born September 29, 1954) is an American astronomer. He was an early influence in the field of exoplanet detection, discovery, and characterization. Marcy was a professor of astronomy at the University of California, Berk ...

. The entire group consisted of 10 principal investigators and five mission specialists.Platt, Jane.
Science team chosen for Space Interferometry Mission
", (

), NASA, 28 November 2000, ''Jet Propulsion Laboratory''. Retrieved 24 April 2007. At the time of this NASA announcement launch was scheduled for 2009 and the mission was still part of the Origins Program.

New technologies

SIM's new technology was meant to lead to the development of telescopes powerful enough to take images of Earth-like

extrasolar planets An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

orbiting distant stars and to determine whether those planets are able to sustain life. NASA has already started developing future missions that will build on SIM's technological legacy.Planet Finding Missions: The Big Picture
", Missions, NASA, PlanetQuest, ''Jet Propulsion Laboratory''. Retrieved 24 April 2007. The technological development phase of the mission was completed in November 2006 with the announcement that the eight, mission-technology-milestones set by NASA were reached. The milestones were necessary steps in the technological development before flight control instruments could begin to be designed. The completion of each milestone meant that new systems had to be developed for

nanometer 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...

control as well as

picometer The picometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: pm) or picometer (American spelling) is a unit of length in the International System of Units (SI), equal to , or one trillionth of ...

knowledge technology; these systems enable the telescope to make its accurate measurements with extreme accuracy.Star- and Planet-Mapping Telescope Mission Ready to Move Forward
, (

), Northrop Grumman, 14 November 2006. Retrieved 24 April 2007 One of the new technologies developed for the mission were high-tech "rulers", capable of making measurements in increments a fraction of the width of a

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

atom. In addition, the rulers were developed to work as a

network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...

. The mission team also created "

shock absorber A shock absorber or damper is a mechanical or hydraulic device designed to absorb and damp shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typically heat) which is then dissipated. Most sh ...

s" to alleviate the effects of tiny vibrations in the spacecraft which would impede accurate measurements. Another of the milestones involved combining the new "rulers" and "shock absorbers" to prove that the Space Interferometry Mission craft could detect the tiny wobbles in stars caused by Earth-sized planets. The fifth of the technology milestones required the demonstration of the Microarcsecond Metrology Testbed at a performance of 3,200 picometers over its wide angle field of view. The wide angle measurements were to be used to determine the fixed positions of stars each time they were measured. This level of performance demonstrated SIM Lite's ability to calculate the

grid. Another key development, known as gridless narrow-angle astrometry ( GNAA), was the ability to apply the measurement capability worked out in the wide angle milestone and take it a step further, into narrow-angle measurements. Aiming to give an accuracy of 1 micro-arcsecond to the early stages of the SIM,A New Approach to Micro-arcsecond Astrometry with SIM Allowing Early Mission Narrow Angle Measurements of Compelling Astronomical Targets
the technique allows star positions to be measured without first setting up a grid of reference stars; instead, it sets up a reference frame using several reference stars and a target star observed from different locations, and star positions are calculated using delay measurements from separate observations. The narrow angle field was to be used by SIM to detect

terrestrial planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Ve ...

s; the team applied the same criteria to both the narrow and wide angle measurements.The eight technology milestones
", NASA, SIM PlanetQuest, ''Jet Propulsion Laboratory''. Retrieved 24 April 2007. The final requirement before beginning work on flight controls was to make sure that all of the systems developed for the mission worked cohesively; this final NASA technology goal was completed last as it was dependent upon the others.

Status after 2006

Between the end of April and June 2006 the project completed three engineering milestones and from 2–8 November 2006 SIM completed a "Spacecraft Internal Design Review." As of June 2008, all of the eight engineering milestones were successfully completed. The project had been in Phase B since June 2003.SIM Current Mission Status
," NASA, SIM PlanetQuest, Jet Propulsion Laboratory. Retrieved 25 April 2007 Jet Propulsion Laboratory's "Phase B" is called the "Preliminary Design" phase. Phase B further develops the mission concept developed during Phase A to prepare the project for entry into the Implementation Phase of the project. Requirements are defined, schedules are determined, and specifications are prepared to initiate system design and development." In addition, as part of Phase B, the SIM Lite project was to go through a number of reviews by NASA including System Requirements Review, System Design Review, and Non-Advocate Review.Doody, Dave and Stephan, George.

", ''Basics of Spaceflight'', NASA, 1993 and other editions, Jet Propulsion Laboratory. Retrieved 25 April 2007. During this phase, experiments would have been proposed, peer reviewed, and eventually selected by NASA's Office of Space Science. Experiment selections are based on scientific value, cost, management, engineering, and safety.

Planned launch

The launch date for the SIM Lite mission was pushed back at least five times. At the program's outset, in 1998, the launch was scheduled for 2005. By 2000, the launch date had been delayed until 2009, a date that held through 2003; though some project scientists cited 2008 in late 2000.Halverson, Peter G., et al.
Progress towards picometer accuracy laser metrology for the Space Interferometry Mission
", NASA, PlanetQuest, ''Jet Propulsion Laboratory''; paper originally released 17 October 2000 and presented at the International Conference of Space Optics, ICSO 2000, 5–7 December 2000,

Toulouse Toulouse ( , ; oc, Tolosa ) is the prefecture of the French department of Haute-Garonne and of the larger region of Occitania. The city is on the banks of the River Garonne, from the Mediterranean Sea, from the Atlantic Ocean and from Par ...

, France. Retrieved 25 April 2007. Between 2004 and 2006, contractor Northrop Grumman, the company designing and developing SIM, listed a launch date of 2011 on their website. With the release of the FY 2007 NASA budget, predictions changed again, this time to a date no earlier than 2015 or 2016. The delay of the launch date was primarily related to budget cuts made to the SIM Lite program. The 2007 change represented a difference of about three years from the 2006 launch date, outlined in NASA's FY 2006 budget as being two years behind 2005 budget predictions. Other groups predicted dates matching officially predicted launch dates; the NASA Exoplanet Science Institute (formerly the Michelson Science Center) at the

California Institute of Technology The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

also set the date at 2015.Space Interferometry Mission (SIM)
", Missions, Michelson Science Center, ''California Institute of Technology''. Retrieved 24 April 2007. As of June 2008, NASA has postponed the launch date "indefinitely". A May 2005 NASA operating plan put the mission into a replanning phase through the spring of 2006. The launch was planned to be via an

(EELV), likely an Atlas V 521 or equivalent.

Budget

SIM Lite was to be considered the flagship mission of NASA's Exoplanet Exploration Program (formerly known as the Navigator Program). According to the 2007 Presidential Budget for NASA, the program is, "a coherent series of increasingly challenging projects, each complementary to the others and each mission building on the results and capabilities of those that preceded it as NASA searches for habitable planets outside of the Solar System."FY 2007 NASA Budget
''NASA'', pg. 80–81. Retrieved 2 November 2006. The program, in addition to the Space Interferometry Mission, includes the

Keck Interferometer The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when comp ...

and the

Large Binocular Telescope The Large Binocular Telescope (LBT) is an optical telescope for astronomy located on Mount Graham, in the Pinaleno Mountains of southeastern Arizona, United States. It is a part of the Mount Graham International Observatory. When using both 8 ...

Interferometer. When originally approved in 1996, the mission was given a $700 million cap (in 1996 dollars) which included launch costs and five years of operation. The first contracts, for the preliminary architecture study, were worth $200,000 each. NASA's budget outlined plans for the three projects for

fiscal year A fiscal year (or financial year, or sometimes budget year) is used in government accounting, which varies between countries, and for budget purposes. It is also used for financial reporting by businesses and other organizations. Laws in many ...

(FY) 2007. Of the three missions, SIM Lite was delayed further and the Keck Interferometer saw budget cuts. The 2007 NASA budget stipulated, "SIM Phase B activity will continue while new cost and schedule plans are developed, consistent with recent funding decisions." The funding decisions included a US$118.5 million cut over the FY 2006 NASA budget request for the Exoplanet Exploration Program. The budget also laid out projections for the program through the year 2010. Each year will have successive funding cuts, if compared to the 2006 request numbers. Starting with FY 2008, the Exoplanet Exploration Program will receive around $223.9 million less compared to 2006. The following years will have cuts of $155.2 million in 2009 and $172.5 million in 2010, compared to the 2006 request. When SIM Lite entered what JPL terms "Phase B" in 2003 ''Fringes: Space Interferometry Mission Newsletter'', called it a most important milestone on the way to a 2009 launch.SIM enters Phase B!
", ''Fringes: Space Interferometry Mission Newsletter'', 20 June 2003. Retrieved 2 November 2006. The delays are budgetary in nature.FY 2006 NASA Budget
''NASA'', p. 65. Retrieved 25 April 2007. In 2006, the mission received $117 million, an increase of $8.1 million over the previous year, but 2007 cuts amounted to $47.9 million less for the SIM program. In 2008, $128.7 million of the $223.9 million estimated to be cut from the Exoplanet Program budget would come from the SIM Lite mission. After an additional $51.9 million decrease in FY 2009,FY 2007 NASA Budget
(PDF), NASA, pg. 83. Retrieved 2 November 2006. the program was reduced to $6 million in FY 2010 supplemented by substantial carryover from the previous year while awaiting the results of the Astronomy and Astrophysics Decadal Survey, Astro2010.Astro2010: The Astronomy and Astrophysics Decadal Survey
", , National Academy of Sciences. Retrieved 31 March 2010. By February 2007 many of the budget cuts outlined in the FY 2007 budget were already being felt within the project. Engineers who worked on SIM were forced to find other areas to work in. A February 2007 editorial in the ''Space Interferometry Mission Newsletter'' described the situation as, "entirely due to budget pressures and priorities within the Science Mission Directorate at NASA (with) scientific motivation for the mission...as strong as ever." NASA, per the budget cuts, directed the SIM project to refocus its efforts toward engineering risk reduction. As of the February 2007 newsletter the plans for the refocus were in the process of being completed.Unwin, Steve, ed.
Editorial
", ''Fringes: Space Interferometry Mission Newsletter'', No. 40, 27 February 2007. Retrieved 24 April 2007.

Instruments

Optical interferometry

Interferometry is a technique pioneered by

in the 19th century.Albert Michelson: The pioneer of interferometry
", NASA, PlanetQuest, ''Jet Propulsion Laboratory''. Retrieved 25 April 2007. Optical interferometry, which has matured within the last two decades, combines the light of multiple telescopes so that precise measurements can be made, akin to what might be accomplished with a single, much larger telescope. It is the interaction of

light wave In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) ligh ...

s, called

interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extr ...

, that makes this possible. Interference can be used to cancel out the glare of bright stars or to measure distances and angles accurately. The construction of the word partially illustrates this: interfere + measure = interfer-o-metry. At

radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz (GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (short ...

lengths of the

electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging from ...

, interferometry has been used for more than 50 years to measure the structure of distant galaxies.A new window on the universe
", NASA, PlanetQuest, ''Jet Propulsion Laboratory''. Retrieved 25 April 2007. The SIM Lite telescope functions through

optical interferometry Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opti ...

. SIM was to be composed of one science

interferometer Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...

(50 cm collectors, 6 m separation aseline, a guide interferometer (30 cm collectors, 4.2 m baseline), and a guide telescope (30 cm aperture).SIM Lite Astrometric Observatory
Response to the Request for Information from Astro2010", p. 8, Jet Propulsion Laboratory, April 2009. Retrieved 9 March 2010. The sophisticated guide telescope stabilizes instrument pointing in the third dimension. The spacecraft's operational limiting magnitude would have gone down to 20 at 20 millionths of an

(μas) and its planet-finding, astrometric accuracy of 1.12 μas is for single measurements. The accuracy of its global, all-sky astrometric grid would have been 4 μas. SIM's design since 2000 consisted of two light collectors (strictly speaking, they are Mersenne telescopes) mounted on opposite ends of a six-meter structure. The observatory would have been able to measure the small wobbles in stars and detect the planets causing them down to one Earth mass at distances up to 33 light years (10 parsecs) from the Sun.A roadmap for planet-hunting
, (

), Academic Search Premier, ''Economist'', 8 April 200, Vol. 355, Issue 8165, p. 87–89. Retrieved 26 April 2007.

Notes

References

* *

External links

"Fringes: Space Interferometry Mission Newsletter" Index

* ttps://web.archive.org/web/20071113050032/http://solarsystem.nasa.gov/missions/profile.cfm?MCode=SIM SIM PlanetQuest Mission Profileb
NASA's Solar System Exploration

Optical Long Baseline Interferometery News, from NASA
{{Good article Interferometric telescopes Cancelled spacecraft Space astrometry missions Space telescopes Exoplanet search projects Lockheed Corporation Astronomy projects