After years of working through a thicket of regulatory matters, Virgin Orbit says it is finally ready to fly its LauncherOne rocket from the United Kingdom.

If all goes well, the modified Boeing 747-400 Cosmic Girl aircraft will take off from a spaceport in Cornwall on Monday evening, with a launch opportunity at 5:16 pm ET (22:16 UTC) over the Atlantic Ocean. This "Start Me Up" mission, bound for low Earth orbit, will carry satellites from seven customers in the United States and United Kingdom.

The air-launch mission has received considerable attention in the United Kingdom because it is being advertised as the first orbital launch from the nation. It will also be the first orbital satellite launch from the UK or Western Europe. However, it will not be a vertical launch from UK soil. Spaceports capable of such launches are under construction in several locations around the nation but probably will not be ready for an orbital launch this year. And unlike British launch companies that aim to use those spaceports, Virgin Orbit's technology was developed, built, and tested in the United States.

This has not diminished the ardor of proponents of the horizontal-launch spaceport in Cornwall.

"I feel confident and I feel focused and I feel ready to handle whatever comes our way," Melissa Thorpe, head of Spaceport Cornwall, said Sunday during a news conference with reporters. "I'm so excited. The public cannot wait for the UK to come and join that exclusive launch club because it's gonna feel good."

Thorpe has been among a team working for eight years to bring a horizontal launch capability to Spaceport Cornwall, which is situated on the site of Newquay Airport, a former Royal Air Force station. During that time, officials from the spaceport, the UK Space Agency, and Virgin Orbit have worked to address regulatory concerns about handling the rocket in Cornwall and launching it over international waters to the southwest of Ireland.

Virgin Orbit had been hoping to launch the mission during the fall of 2022, but ongoing issues with paperwork ultimately pushed the mission into early 2023. These delays meant that Virgin Orbit only managed to launch its LauncherOne rocket two times in 2022.

"We knew this was not going to be a piece of cake when we took on this opportunity," said Dan Hart, chief executive officer of Virgin Orbit, of working to obtain a launch license for the UK.

Officials at Sunday's news conference expressed hope that this launch will be the first of a regular cadence of Virgin Orbit missions from the United Kingdom.

"We’re excited to be here today," Hart said. "We’re excited about the future, and coming back maybe later this year to launch again and hopefully get a rhythm going. We want to be a part of the fabric of the space community here in the UK as well as globally. That’s our objective as a company, and I think there is great opportunity."

However, it is unclear how much of the infrastructure flown into Spaceport Cornwall to support the Cosmic Girl aircraft and LauncherOne fueling operations will remain on site after this mission. It is also unlikely that Virgin Orbit will fly another mission from the United Kingdom for at least the next 12 months, if not considerably longer.