SALISBURY, Md. — What's at stake Sunday night when NASA and Orbital ATK plan to launch their first rocket at Wallops Flight Facility in Virginia in nearly two years?

A whole lot.

If the five launch delays since May are any indication, engineers are making especially sure everything goes right this time around. They don't want a repeat of the fiery explosion that occurred just after takeoff nearly two years ago on the same launch pad.

The unmanned Antares rocket is set to launch at 8:03 p.m. ET, carrying a supply-laden Cygnus spacecraft on the first leg of its journey to the International Space Station. It will be its first return to flight at Wallops since Oct. 28, 2014, the day that forever changed the program.

Everything looked to be going smoothly at first: the burst of smoke, the streak of fire, the rocket ascending skyward. Then it seemed to hover in midair. There was a flash. Then down came the rocket in a blast that shook the earth for miles around.

After an internal investigation attributed the problem to a faulty turbo prop inside the engines, Orbital ATK ramped up efforts to replace the decades-old Soviet-made engines it had been using with newly built ones. The Wallops flight will mark the debut of Antares' RD-181 engines, made by the Russian company Energomash.

The launch pad underwent $15 million in repairs and upgrades after the explosion. While the rocket missed Pad-0A on its descent, it still caused extensive heat damage to the $120 million facility.

In the safety-first world of rocket science, test flights are the norm — but not this time. NASA's inspector general raised a red flag about the omission in a September 2015 report.

Orbital conducted a "hot fire" test last May in which the new engines fired while the rocket remained bolted to the pad. But the contractor's schedule was too tight to allow for a separate test flight, according to the inspector general report.

Cygnus is set to rendezvous with the space station on Wednesday. Flight Engineers Takuya Onishi of the Japan Aerospace Exploration Agency and Kate Rubins of NASA will grapple Cygnus, using the space station’s robotic arm, beginning at around 7:20 a.m.

The spacecraft's cargo includes 5,100 pounds of supplies and experiments.

Orbital has a $1.9 billion contract with NASA to ferry supplies to the space station. It is one of the crew's few lifelines.

Japan's space agency has announced a postponement of its spacecraft because of an air leak, while Orbital's U.S. counterpart, SpaceX, is still reeling from a Sept. 1 pad accident at Cape Canaveral, Fla.

Orbital has just a five-minute window for Sunday's takeoff. If it doesn't make that window, the next opportunity is Monday at 7:40 p.m.

The weather forecast for Sunday calls for partly cloudy conditions, a southwest wind of 9 mph and a low of about 59 degrees. NASA scientists have put the chances of launch Sunday at a 95% "go."

If the sky is clear enough, the launch is expected to be visible across wide swaths of the Eastern United States, ranging from South Carolina to southern New Hampshire.