European Space Agency's LISA Project: A Spaceborne Experiment for Fundamental Physics | Study notes Physics

PHYSICS

IN SPACE

The

European Space

Agency's

LISA

(Laser Interferometer

Space

Antenna) project is the flagship fundamental physics

experiment in space. The

LISA

mission will consist of three

spacecraft

that

will form an equilateral triangle with a distance

5 million km between any two spacecraft. Gravitational

waves

passing through the solar system will generate small

changes

in the distances between each of the spacecraft. The

distance changes can be made very accurately using laser

interferometry.

Addressing

fundamental physics questions in space is far from a

new

idea. In particular, the fascinating prospects of

testing

Einstein's

theory

to an unprecedented accuracy using the quietness of space

environment and long observation times have long been consid-

ered.

However,

was

soon realized

that

flight

conditions would have

to be controlled to a very high precision.

Europe,

the

1971-1979

Fundamental Physics

Panel,

chaired

Herman Bondi, fully recognized the great interest of such mis-

sions but concluded

that

they were "projects for the 21st century".

are now at the eve of

that

century.

European

plans

1989 the European Space

Agency

(ESA)

announced a call for

mission proposals also open to fundamental

physics.

By 1993, fun-

damental physics proposals represented close to one-third of all of

those received.

ESA

dealt with them via ad hoc committees, and in

NASA/JPL

conference on Fundamental

Physics

in Space, held

Washington

DC,

brought together the chairman and three

vice-chairmen of Commission H of the International Committee

for

Space Research

(COSPAR).

Left to right: vice-chairman

Maurice Jacob (also chairman

ofESA's

Fundamental

Physics

Advisory

Group and the author of this article), chairman Francis

Everitt

Stanford, vice-chairman Guenter Alhers of Santa Bar-

bara (also chairman of

NASA's

Fundamental

Physics

Discipline

Working

Group) and vice-chairman Stefano Vitale ofTrento.

1994 a major project, Laser Interferometer Space Antenna

(LISA),

was

listed among the key "cornerstone" elements of the Horizons

2000

programme (the

ESA

equivalent of

CERN's

LHC

programme).

Horizons

2000

projects

ESA

scientific activities up to and beyond

the year 2010.

1994,

ESA

created a special Fundamental

Physics

Advisory

Group

(FPAG)

to complement the established Astronomy Working

Group

and the Solar

System

Working

Group.

1996,

COSPAR

(the international Committee for Space

Research)

created a new commission for fundamental physics,

Commission

H. In 1997 the Alpbach Summer School provided a

useful and extensive overview of prospects as seen from Europe.

The

proceedings

(ESA-SP-420)

are a reference document for the

new

community working in

that

domain. So is the more recent

Fundamental

Physics

Road Map established by

NASA.

fundamental physics in space started with microgravity

CERN

Courier

July

1999

Fundamental

physics in space

What

better way of launching science in the new millennium than embarking on a

programme of fundamental physics research in space?

Maurice

Jacob

looks at existing

plans and new possibilities.

Partial preview of the text

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PHYSICS IN SPACE

The European Space Agency's LISA (Laser Interferometer Space Antenna) project is the flagship fundamental physics experiment in space. The LISA mission will consist of three spacecraft that will form an equilateral triangle with a distance of 5 million km between any two spacecraft. Gravitational waves passing through the solar system will generate small changes in the distances between each of the spacecraft. The distance changes can be made very accurately using laser interferometry.

Addressing fundamental physics questions in space is far from a new idea. In particular, the fascinating prospects of testing Einstein's theory to an unprecedented accuracy using the quietness of space environment and long observation times have long been consid ered. However, it was soon realized that flight conditions would have to be controlled to a very high precision. In Europe, the 1971-1979 Fundamental Physics Panel, chaired by Herman Bondi, fully recognized the great interest of such mis sions but concluded that they were "projects for the 21st century". We are now at the eve of that century.

European plans In 1989 the European Space Agency (ESA) announced a call for mission proposals also open to fundamental physics. By 1993, fun damental physics proposals represented close to one-third of all of those received. ESA dealt with them via ad hoc committees, and in

A NASA/JPL conference on Fundamental Physics in Space, held in Washington DC, brought together the chairman and three vice-chairmen of Commission H of the International Committee for Space Research (COSPAR). Left to right: vice-chairman Maurice Jacob (also chairman ofESA's Fundamental Physics Advisory Group and the author of this article), chairman Francis Everitt of Stanford, vice-chairman Guenter Alhers of Santa Bar bara (also chairman of NASA's Fundamental Physics Discipline Working Group) and vice-chairman Stefano Vitale ofTrento.

1994 a major project, Laser Interferometer Space Antenna (LISA), was listed among the key "cornerstone" elements of the Horizons 2000 programme (the ESA equivalent of CERN's LHC programme). Horizons 2000 projects ESA scientific activities up to and beyond the year 2010. In 1994, ESA created a special Fundamental Physics Advisory Group (FPAG) to complement the established Astronomy Working Group and the Solar System Working Group. In 1996, COSPAR (the international Committee for Space Research) created a new commission for fundamental physics, Commission H. In 1997 the Alpbach Summer School provided a useful and extensive overview of prospects as seen from Europe. The proceedings (ESA-SP-420) are a reference document for the new community working in that domain. So is the more recent Fundamental Physics Road Map established by NASA. US fundamental physics in space started with microgravity

Fundamental

physics in space

What better way of launching science in the new millennium than embarking on a

programme of fundamental physics research in space? Maurice Jacob looks at existing

plans and new possibilities.

The Alpha Magnetic Spectrometer (AMS), the pioneer major particle physics experiment for space, had a shakedown flight aboard the Space Shuttle Discovery in 1998. It is seen here in the Shuttle's payload bay.

research associated with manned space flights and, in particular, the study of helium superfluidity, to be complemented by the study of laser-cooled atoms. This was eventually extended to gravity. The important mission Gravity Probe B, testing the frame-dragging effect around the rotating earth, is soon to fly. This domain of research is monitored by NASA's Fundamental Physics Discipline Working Group. While fundamental physics at ESA did not initially include micro- gravity, things have developed in that direction with FPAG interest for the ACES mission. With its combination of a laser-cooled caes ium clock and an H-maser, this should provide the most precise clock ever (accurate to 10"^16 ). This is now approved for the International Space Station. Interest developed for Satellite Test of the Equivalence Principle (STEP) to achieve 1CT^18 accuracy (the present ground-based limit is 1CT^12 ) with a cryogenic system orbiting the Earth. There was also considerable ESA interest and, if everything goes well, this mission could fly in around 2004 as a NASA-led project with strong ESA participation. In the opposite transatlantic direction, there is now a strong US interest in LISA. An ESA-NASA collaboration on LISA could advance the project by a decade to around 2009.

At present, LISA is the flagship fundamental physics experiment. The LIGO terrestrial search for gravitational waves using laser inter- ferometry aims for phenomenal accuracy and was described by Riccardo DeSalvo in the March issue ("The quest for gravitational waves" p 10). A space experiment is in principle very similar, but could extend over several millions of kilometres and would focus on low frequen cies (10~^2 to 10"^4 Hz). Ground-based detectors are blind to anything below about 10 Hz because of gravitational noise, and they have to focus on high frequencies (10^2 to 10^4 Hz) looking for signals from supernovae and the demise of compact binary stars.

Gravity waves in space A spaceborne experiment would be sensitive to permanent emis sion from compact binaries (of the Hulse-Taylor type).Thousands of these (black hole, neutron star and white dwarf binaries) should be detectable in our galaxy. Other viewable phenomena would include the formation, accretion and merging associated with the very mas sive black holes (1 to 10 million solar masses) known to exist at the centre of most galaxies. The typical emission frequency of a black hole is inversely pro portional to its mass, and very large ones should be within range of LISA anywhere in the universe. Spaceborne experiments could thus study the strong gravity of very compact objects, while ground-based studies will be looking for effects resulting from the Big Bang, cosmic strings, etc. Both terrestrial and spaceborne studies open a new window to astronomy. Whether or not gravitational waves are soon detected on Earth, they also have to be sought in space. A LISA mission at the end of the next decade would be particularily timely.Three satellites would provide two independent laser interferometers on a heliocentric orbit trailing the earth at 20°.The LISA Pre-Phase A Report (MPQ 233) is a detailed description of the mission, which has now entered indus trial study. However, such a mission relies on technology that has still to be proven in space (exhibiting, for example, very precise accelerometry, drag-free control and very stable laser interferometry). A small dedi cated mission is planned in Europe under the codename ELITE and is entering industrial study. However, the most efficient route is prob ably via an ESA-NASA collaboration, as will also be the case for LISA.This, like other projects, will also benefit from positioning using an electric propulsion engine, which is soon to be tested by an other small ESA mission.

Particle physics and space science Some particle physicists are following with great interest the devel opment of space projects.This is in particular the case for PLANCK, an ESA Horizons 2000 project, which should improve the COBE results on the cosmic microwave background by two orders of mag nitude. The past two decades have seen increased symbiosis between particle physics, astrophysics and cosmology, and this new field of astroparticle physics is now thriving. Probing the deep structure of matter through very-high-energy laboratory collisions reveals physics such as prevailed in the early universe. Today's laboratory experi ments simulate conditionslO- 1 0 s after the Big Bang. With laboratory energies necessarily limited, the universe pro-

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Partial preview of the text

Download European Space Agency's LISA Project: A Spaceborne Experiment for Fundamental Physics and more Study notes Physics in PDF only on Docsity!

PHYSICS IN SPACE

Fundamental

physics in space

What better way of launching science in the new millennium than embarking on a

programme of fundamental physics research in space? Maurice Jacob looks at existing

plans and new possibilities.