“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
This description specifies the Evolved Laser Interferometer Space Antenna (eLISA), a flagship space-based gravitational wave observatory led by the European Space Agency (ESA) in partnership with NASA:
– The eLISA mission design consists of three identical spacecraft flying in an equilateral triangular constellation separated by millions of kilometres in a heliocentric orbit trailing the Earth.
– Precision laser beams exchanged between test masses across these arms detect minute metric strain distortions in spacetime caused by passing low-frequency gravitational waves.
– LISA Pathfinder was a preceding single-spacecraft technology demonstrator mission launched in 2015 to test isolated free-fall instrumentation at the Sun-Earth L1 point, while Voyager-2 and New Horizons are deep-space planetary flyby probes.
Therefore, the experiment in question is Evolved LISA — Option D.