NASA plans to replace an engine controller aboard its massive SLS rocket after finding a communications glitch with the system's avionics during preflight testing, the latest setback in a program for which Boeing Co. is the main contractor and that has been plagued by years of delays and billions of dollars in costs beyond its initial budget.

The National Aeronautics and Space Administration also said Friday it will explore launch dates for a test flight in March and April.

The rocket, which Congress authorized and began funding in 2010, was supposed to fly in late 2016. In October, NASA solicited ideas from the aerospace industry about ways to lower the costs associated with the Space Launch System.

Replacing the unit on one of the SLS's four RS-25 engines is "the best course of action," the agency said. The update comes after engineers preparing the rocket for flight detected a communications problem last month between the rocket's avionics system and the No. 4 engine, and began troubleshooting the issue.

NASA plans to use the Space Launch System rocket and Orion crew capsule to return astronauts to the moon later this decade.

Tiny human muscle cells will be blasted into space in an experiment that could help people live longer, healthier lives.

The experiment, called MicroAge, is set to be launched to the International Space Station (ISS) on Tuesday.

Space will be used to understand what happens to human muscles as people age, and why.

Lab-grown human muscle cells, the size of a grain of rice, have been put into small 3D-printed holders the size of a pencil sharpener.

Once in space, they will be electrically stimulated to induce contractions in the muscle tissue, and the scientists will look closely to see what happens.

Spending time without the effects of gravity can cause astronauts' muscles to get weaker, just as they do in older age, before recovering when they return to Earth.

University of Liverpool researchers, funded by the UK Space Agency, will study what happens to muscle tissue in space, and compare the findings to what happens on Earth.