Project P.E.G.A.S.U.S. (also known as Pegasus) was the name of the joint project between S.H.I.E.L.D., NASA and the United States Air Force to study the Tesseract and harness its power. In the 1980s, project leader Wendy Lawson, who was in reality a Kree named Mar-Vell, used the Tesseract's energy to create the Light-Speed Engine in an attempt to end the Kree-Skrull War.
Following Mar-Vell's death in 1989, the project was terminated. Following the aftermath of the Battle of Puente Antiguo, the World Security Council and S.H.I.E.L.D. reactivated P.E.G.A.S.U.S. to continue their attempts in harnessing the power of the Tesseract, until the actions perpetrated by Loki rendered the project defunct.
In 1945, following the Battle in the Valkyrie, Howard Stark attempted to locate his friend Captain America. While searching in the ocean, Stark discovered the Tesseract. In the following years, Stark studied the Tesseract and co-founded S.H.I.E.L.D. Believing that the energy within the Tesseract would be beneficial to mankind, Stark was instrumental in the creation of Project P.E.G.A.S.U.S., a joint venture between S.H.I.E.L.D., NASA and the United States Air Force tasked with studying and harnessing the Tesseract's energy and to whom he relinquished custody of the Tesseract.
In the 1980s, a Kree named Mar-Vell, disguised as a human scientist Dr. Wendy Lawson, joined Project P.E.G.A.S.U.S. Her intention was to harness the Tesseract's energy to create a Light-Speed Engine and send the surviving Skrulls to a new home planet far from the reach of the Kree Empire. Carol Danvers and Maria Rambeau both served as test pilots for the project, as the Air Force did not allow women to fly combat missions. Goose, Mar-Vell's pet Flerken, was a regular fixture around the project. After successfully creating the engine, Mar-Vell took the Tesseract and hid it in her laboratory in orbit.
When Mar-Vell decided to test the finished engine, Danvers volunteered to fly the prototype craft. During the flight, they were ambushed by Kree, who had discovered Mar-Vell's plans to assist the Skrulls. After a dogfight with Kree forces, Mar-Vell and Danvers crashed. When Danvers noticed Mar-Vell's blue blood, she confessed that she was Kree and asked Danvers to destroy the power source. Yon-Rogg shot Mar-Vell and demanded that Danvers hand over the source. Instead, she destroyed the power core and absorbed its energy, rendering her unconscious. Yon-Rogg, accompanied by Minn-Erva, decided to take Danvers back to Hala and erase her memories.
The United States Air Force covered up the entire incident, informing Maria Rambeau that the test craft's Black Box had been destroyed, while Project P.E.G.A.S.U.S. was decommissioned, with the Tesseract now being lost.
Six years later, after being captured by the Skrulls and having her memories probed by Talos, Danvers was able to recall Dr. Lawson and Project P.E.G.A.S.U.S. Escaping from the Skrulls, she arrived on Earth and set out to solve the mystery of who Lawson was. Nick Fury accompanied her to the Joint NASA USAF Facility , where they asked to meet Lawson. Although asked to wait, Fury and Danvers decided to investigate on their own, breaking into Project P.E.G.A.S.U.S's archives. They discovered Lawson's file and learned about the crash and Mar-Vell's plans for the Light-Speed Engine. Following the Battle at Mar-Vell's Laboratory, the Tesseract was returned to S.H.I.E.L.D.'s custody on Earth.
Howard Stark's Legacy
While dying due to the palladium in his arc reactor, Tony Stark was informed by Nick Fury that his father Howard Stark's work would be instrumental in finding a solution, with Fury presenting Stark with a box of the elder Stark's possessions. As Stark rifled through his father's belongings, he found his father's research on the Tesseract and asked J.A.R.V.I.S. to give him the details of Project P.E.G.A.S.U.S.
Research into the Tesseract
Following the Destroyer's attack in New Mexico, Project P.E.G.A.S.U.S. was restarted on the orders of the World Security Council prior to 2012. Due to the highly sensitive nature of the research conducted there, S.H.I.E.L.D. also provided its security force, including one of S.H.I.E.L.D.'s best operatives, Clint Barton.
Project P.E.G.A.S.U.S. played host to the Tesseract for many years, its scientists completely baffled by the object. By the early 21st century, they had determined that it was an incredible source of energy, but they had found no way to tap it. This changed when S.H.I.E.L.D. found Culver University Professor Erik Selvig, and brought him in to investigate the object. Upon seeing it he readily agreed to probe deeper, although unbeknownst to everyone at the time he was also being influenced by Loki.
Eventually, Selvig came to a rudimentary understanding of the Tesseract's capabilities; although he was taken quite by surprise when it began to exhibit a curious energy build-up. Project P.E.G.A.S.U.S. was hastily evacuated, but not before Loki himself appeared, apparently having triggered the Tesseract remotely to open a portal for him to reach Earth. In the confusion, Loki made his escape, but the unrestrained energies released from his transit finally erupted to consume the entirety of the Project P.E.G.A.S.U.S. facility, leaving a vast crater in its wake. The final death toll measured in the dozens.
Project P.E.G.A.S.U.S. effectively ended when Thor took the Tesseract back to Asgard. S.H.I.E.L.D. covered any traces of the Project.