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

Explanation:

Evolved LISA

The experiment described refers to the Evolved Laser Interferometer Space Antenna (eLISA) project, commonly referred to as LISA (Laser Interferometer Space Antenna). It involves a trio of spacecraft flying in formation in the shape of an equilateral triangle, with sides one million kilometers long, and using lasers to communicate between the craft.

LISA is a planned space mission by the European Space Agency (ESA) designed to detect and accurately measure gravitational waves — tiny ripples in the fabric of space-time — from astronomical sources. LISA aims to achieve this by deploying three spacecraft in a triangular formation, following Earth in its orbit around the Sun. The spacecraft will be positioned millions of kilometers apart, using laser interferometry to measure the minute changes in distances between them caused by passing gravitational waves.

This mission is distinct from the other options provided:

1. Voyager-2: Part of NASA’s Voyager program, which launched two spacecraft, Voyager 1 and Voyager 2, in 1977 to explore the outer planets and beyond. It is not designed for detecting gravitational waves.
2. New Horizons: A NASA mission launched to study Pluto and the Kuiper Belt. It conducted a flyby of Pluto in July 2015 and is continuing its journey through the Kuiper Belt. Like Voyager-2, it is not designed for gravitational wave detection.
3. LISA Pathfinder: A precursor mission to LISA, launched by the European Space Agency (ESA) to test technologies for detecting gravitational waves in space. While it was related to the LISA project, it was not the full gravitational wave observatory described in the question.

Therefore, the correct answer is Evolved LISA, which directly corresponds to the description of the experiment involving spacecraft in a triangular formation using lasers to detect gravitational waves.