The red signals have been one of Star Trek: Discovery season 2's primary mysteries, but the penultimate episode, "Such Sweet Sorrow," has now clarified the true purpose of the bursts of light in space. With five of the seven red signals now revealed, we know how they factor into the final battle against the evil A.I. called Control that wants to end all sentient life in the galaxy, and who sent the red signals in the first place: a future version of Michael Burnham.
Most of Star Trek: Discovery season 2 was focused on learning the identity of the time-traveling Red Angel, who was revealed to be Michael's mother, Dr. Gabrielle Burnham. However, Gabrielle claimed that in her 841 failed attempts to stop the timeline where Control annihilates the galaxy, she never sent any red signals to warn the Discovery. Compounded with the Red Angel's DNA match to Michael, Spock concluded that Michael herself was a second Red Angel who sent the red signals from the future. This also means that future Michael is partially responsible for Spock's mental breakdown earlier in the season, though it was the present version of Burnham who enabled the healing of Spock's mind with the help the psychic inhabitants of Talos IV.
The first three red signals led the U.S.S. Discovery on rescue missions, but it later became clear the starbursts were being sent by an individual with conscious design: Michael herself. Once Michael realized she was also the Red Angel in "Such Sweet Sorrow," Burnham decided on her plan to save the galaxy: she would wear a newly-built Red Angel time suit to tow the U.S.S. Discovery into the far future to keep the sphere data that Control needs to evolve and achieve consciousness away from the A.I. Unfortunately, it would be a one-way trip and Michael would be unable to return to the 23rd century. But once she is in the future, Michael would then send the red signals to enable the Discovery to achieve the vital steps necessary to enable her plan in the first place.
As Star Trek: Discovery season 2 plays out its endgame, here is the purpose of the five red signals that have been revealed thus far and what important steps they led the Starfleet Officers to take in order to save the galaxy:
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Red Signal #1: Rescue Jett Reno
The red signals first appeared in Star Trek: Discovery's season 2 premiere, "Brother." The first signal led the Discovery to an asteroid field and the crashed U.S.S. Hiawatha, which had been there for 10 months and eleven days after being damaged during the Klingon War. There, Michael Burnham, Captain Pike, and Commander Nhan met Commander Jett Reno, a Starfleet engineer who had rebuilt the ship's medical equipment to keep some of the Hiawatha's crew alive. The Discovery crew rescued Reno, though Michael was injured in the escape and saw a vision of the Red Angel.
Rescuing Jett was the purpose of the first red signal. Reno isn't just an acerbic comic foil for Lieutenant Paul Stamets; as a brilliant engineer she is vital in making sure the time crystal is able to be sufficiently charged so that Michael's Red Angel suit can open a wormhole into the future. Jett also received a vision from the crystal about specific damage the Starship Enterprise will incur in the battle against Section 31's fleet; she could then be vital in saving Captain Pike and his crew in the season 2 finale. Basically, without Jett Reno coming aboard the Discovery, Ensign Sylvia Tilly would be lost in the mycelial network and Burnham's time travel gambit would automatically fail.
Red Signal #2: Find Terralysium
The second red signal led the Discovery to a planet in the Beta Quadrant called Terralysium, as seen in the second episode, "New Eden." At Terralysium, Pike, Burnham, and Lieutenant Owosekun found over 11,000 human beings descended from a group that was originally from Earth. Their ancestors were saved from a World War III nuclear holocaust by the Red Angel and transported to the Beta Quadrant. The multi-faith-worshipping people on Terralysium abandoned technology and were subsequently saved from an extinction-level event by the Red Angel and the U.S.S. Discovery.
It was vital that the Discovery's crew learned about Terralysium, which was the purpose of the second red signal. The Red Angel/Dr. Gabrielle Burnham was using Terralysium as her home base and anchor point for time traveling from 950 years in the future. Because Terralysium lacks technology, it's a haven from Control, which had conquered the galaxy. Part of Michael's plan involves hiding the Discovery at Terralysium in the future to keep the sphere data safe from Control.
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