In the storyline of Thunder Force V, the Space Probe Sekika 3 is an unmanned research probe launched by the Earth State Space Administration. In 2106, the probe reached the Oort Cloud, an enormous ring of comets encircling the outer limits of the solar system.
Sekika 3's original mission is to analyze the comets, but the probe instead makes the most profound discovery in the the history of humanity: an artificially created object floating deep within the cloud. Mankind now knows it is not alone in the universe.
In 2108, the probe returned to Earth with its precious cargo and established orbit around the lunar base of the World United Government. The world's best and brightest scientists analyze the alien object with every tool at their disposal, and quickly determine the dazzling find to be a starcraft with technology so advanced that, in the words of one stunned researcher, "it's difficult to tell where the science ends and the magic begins."
It is also possible that the Sekika 3 played a role in rescuing Vasteel's pilots, according to one of the endings in Thunder Force VI, as one of the Vastians said "I came in contact with a new friend, the human race...!"