The much-anticipated rollout of NASA's moon rocket and capsule to the launchpad at the Kennedy Space Center in Florida for a fueling test will be delayed for another few weeks, the space agency said Wednesday. But after years of setbacks and cost overruns, the Space Launch System rocket is making real progress, officials said, and could finally launch for the first time this spring.

NASA is now aiming to bring the SLS rocket to the pad in March instead of mid-February to fully load the rocket with propellant and run a simulated countdown. That would be the first time over a decade of development that it would appear fully assembled - with its side boosters attached and the second stage and Orion spacecraft stacked on top - and mark a significant milestone in the at times tortured route it has taken toward its first flight.

After years of setbacks, NASA is looking forward to showcasing the system it says is the backbone of its return-to-the moon program, known as Artemis.

The latest delay was caused by a series of small issues related to preparing the rocket for its first-ever launch, NASA said. Because it is a completely new system, the SLS and Orion are loaded with all sorts of instrumentation to monitor the systems that may not be needed on future flights. And the engineers are working to install a flight termination system that would destroy the rocket in case it veered off course.

"There's no one specific thing" causing the delay to March, Tom Whitmeyer, deputy associate administrator for exploration systems development, said during a news briefing Wednesday. "We just have a lot of things that we need to close out. It's a big vehicle and a lot of instrumentation that needs to be finished in preparing for final close out."

He compared the progress to being in the final stages of a kitchen renovation where workers are ticking off the last items on their list. "We're basically down to a punch list of things that we need to complete," he said. "It can be something as simple as a scratch that needs to be polished out, or some paint that needs to be fixed."

The most important thing, he said, is to ensure that the engineers and technicians are acting methodically to ensure a successful test flight, which would set the course for the rest of the program. He said he was recently reminded of a spaceflight axiom that "if you miss your launch date, and you have a successful launch, nobody's going to remember you missed your launch date. But if you hold your launch date, and you have an unsuccessful launch, no one is ever going to forget. And that's exactly how we treat it."

The SLS rocket has been going through a series of tests to identify and then ameliorate any problems before NASA gives the green light for a launch. Once the fueling test, known as a "wet dress rehearsal," is complete, the rocket will be rolled back into the assembly building for final tests. And then NASA will set a launch date.

NASA is now looking to launch the SLS in April or May, as part of its Artemis campaign to return astronauts to the surface of the moon for the first time since the last Apollo mission in 1972. The first test flight, known as Artemis I, would fling the autonomous Orion capsule into orbit around the moon before coming home. That mission would not have any astronauts on board. But the next flight, currently scheduled for May 2024 would carry a crew of four in orbit around the moon. By the end of 2025, NASA hopes to land astronauts on the lunar surface, and the crew would include the first woman to walk on the moon as well as a person of color.

Over the years, the program has suffered all sorts of cost overruns and schedule delays, while being derided as the "Senate Launch System" because critics say it is designed more to create jobs in key congressional districts than to explore space.

But more recently, NASA has been making significant progress with the rocket. Last year, it conducted a successful "hot fire" test, running all four RS-25 engines on the core stage of the rocket for over eight minutes, the same amount of time they would fire during flight. (A first attempt a couple months earlier was cut short after just about one minute.) After the successful test at the Stennis Space Center in Mississippi, which burned 733,000 gallons of propellant, the stage was shipped to the Kennedy Space Center, where the solid rocket motor side boosters were mounted and then the Orion crew capsule was placed on top of the fully assembled system.

Inside the giant Vehicle Assembly Building, which once housed the Saturn V rocket used in the Apollo missions as well as the space shuttle, NASA has been running a series of tests to ensure that all the components were working properly and could communicate with ground control systems.

In December, the space agency said that during one of the tests "engineers identified an issue with one of the RS-25 engine flight controllers," which serve as the "brain" for the engine that help control the engines and monitor their health. Each controller has a backup, and NASA found that one of the controller's channels was not powering up consistently. NASA has years of experience working with the engines, which were also used on the space shuttle, which was retired in 2011.

NASA said the controller had showed no signs of problem during the preliminary tests and worked well during the "hot fire" test. But it said that after "performing a series of inspections and troubleshooting, engineers determined the best course of action is to replace the engine controller, returning the rocket to full functionality and redundancy while continuing to investigate a root cause."

Last month, NASA said the engines performed well during additional tests and that "all four engine controllers were powered up and performed as expected."

Last week, NASA crews completed a simulated countdown sequence for the second time, one of the final tests before rolling the rocket to the launchpad for the wet dress rehearsal. The test checked the ground launch software and the automated sequencer, which takes over control of the rocket from ground controllers about 30 seconds before launch.