Q. “The experiment will employ a trio of spacecraft flying in formation in the shape of an equilateral triangle that has sides one million kilometres long, with lasers shining between the craft.” The experiment in question refers to

  • Voyager-2
  • New horizons
  • Lisa Pathfinder
  • Evolved LISA

Answer: (d) Evolved LISA

evolved Laser Interferometer Space Antenna (eLISA)
  • The evolved Laser Interfermoter Space Antenna (eLISA) is a mission aiming at exploring the Gravitational Universe from space for the first time.
  • It involves scientists from eight European countries ‒ Denmark, France, Germany, Italy, The Netherlands, Spain, Switzerland, and the UK ‒ as well as the support of several US-based ones.
  • The eLISA mission consists of a “Mother” and two “Daughter” spacecrafts. These will orbit the Sun in a triangular configuration.
  • The three satellites will form a precision interferometer, with the two Daughter spacecrafts connected to the Mother one by 1 million km long laser beams. This interferometer will be capable of detecting gravitational waves at frequencies in the range of 0.1 mHz to 1 Hz.
    • Such a frequency interval is not accessible on Earth due to arm length limitations and to noise caused by the terrestrial gravity gradient noise: in this sense, eLISA will complement the efforts of ground-based gravitational-wave detectors.
  • eLISA is designed with orbits that allow the three satellites to maintain their near-equilateral triangular configuration. Indeed, because of their special orbits, they are seen to rotate about an axis passing through the centre of the triangle and normal to its plane. A passing gravitational wave alters the proper relative distance between the spacecraft, which will be sensed by detectors on each spacecraft.
  • eLISA will coherently measure the frequency, phase, and polarisation of gravitational waves passing through it, allowing scientists to resolve overlapping signals and locating them on the sky.
LISA Pathfinder (LPF)
  • LISA Pathfinder is the European Space Agency (ESA) precursor mission to the LISA space-based gravitational wave observatory that the agency is developing within the Cosmic Vision Programme.
  • LISA Pathfinder has been developed within an international collaboration led by ESA and including the space agencies of France, Germany, Italy, Spain, Switzerland, The Netherlands and United Kingdom, and NASA.
  • The mission tested technologies needed for the Laser Interferometer Space Antenna (LISA), an ESA gravitational wave observatory planned to be launched in 2037.
  • The eLISA mission technology is being tested in space with LISA Pathfinder. LPF was placed in a low-earth transfer orbit. From there, the satellite used its propulsion module in order to reach the operational orbit around the Lagrange point L1.
  • LISA Pathfinder placed two test masses in a nearly perfect gravitational free-fall, and controlled and measured their relative motion with unprecedented accuracy. The laser interferometer measured the relative position and orientation of the masses to an accuracy of less than 0.01 nanometres, a technology estimated to be sensitive enough to detect gravitational waves by the follow-on mission, the Laser Interferometer Space Antenna (LISA).
  • LISA Pathfinder was a proof-of-concept mission to prove that the two masses can fly through space, untouched but shielded by the spacecraft, and maintain their relative positions to the precision needed to realise a full gravitational wave observatory.
Voyager-2
  • Voyager 2 is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun’s heliosphere.
  • As a part of the Voyager program, it was launched 16 days before its twin, Voyager 1, on a trajectory that took longer to reach gas giants Jupiter and Saturn but enabled further encounters with ice giants Uranus and Neptune.
  • Voyager 2 remains the only spacecraft to have visited either of the ice giant planets, and was the third of five spacecraft to achieve Solar escape velocity, which allowed it to leave the Solar System.
  • Voyager 2 successfully fulfilled its primary mission of visiting the Jovian system in 1979, the Saturnian system in 1981, Uranian system in 1986, and the Neptunian system in 1989. The spacecraft is now in its extended mission of studying interstellar space.
New horizons
  • New Horizons is an interplanetary space probe launched as a part of NASA’s New Frontiers program.
  • The spacecraft was launched in 2006 with the primary mission to perform a flyby study of the Pluto system in 2015, and a secondary mission to fly by and study one or more other Kuiper belt objects (KBOs) in the decade to follow.
  • It is the fifth space probe to achieve the escape velocity needed to leave the Solar System.