The MIDAS array, or Mutara Interdimensional Deep-Space-Transponder Array System, was a Federation communications array that was in service with Starfleet in the late 24th century. Starfleet worked with Vulcans in deploying this array.
Located near a small gas cloud, it utilized hyper-subspace technology to greatly reduce the time it would take for a message to reach its destination. The array consisted of a hexagonal central dish, to which were attached three long arms mounting panels and three mobile emitters. When activated, the array launched a small targeting device from the center of the dish, which focused energy beams from the three emitters into a single beam.
In 2376, Deep Space 9 predicted that a pulsar would pass close to the array. By firing a tachyon beam at the pulsar, Pathfinder Project was able to create a micro-wormhole through which they made contact with USS Voyager for a brief period.
Later, Pathfinder found a way to amplify the signal from the MIDAS array by bouncing it off a class B pulsar. This allowed a brief compressed-datastream to be sent to Voyager about every 32 days, coinciding with the pulsar's rotation cycle. Initially Starfleet sent many letters, as well as tactical updates and stellar maps. The rotation cycle peaked for 17 hours, giving Voyager that long after receiving the datastream to send a response. Instead of letters, Voyager sent The Doctor (a holographic program), waiting 32 days before they could send or receive letters again so he could treat his creator, Dr. Lewis Zimmerman, who was fatally ill.
Several datastreams later, Pathfinder tried to send a Reginald Barclay-hologram but it was intercepted by a Ferengi marauder, which had passed within 20 meters of the array and stole the program. A month later, Pathfinder tried to send the datastream again - once again to be intercepted by the Ferengi, who took this chance to send an altered version of the first hologram with a plot to abduct Seven of Nine for her nanoprobes.
As part of the cover story, the Reginald Barclay-hologram that had been tampered with by the Ferengi claimed that the transmission of the unabridged version of his program overloaded the MIDAS array, making Pathfinder miss the transmission.
By 2378, Voyager was close enough to perform Operation Watson - which would allow 11 minutes of contact with the Alpha Quadrant through the array every day.