Japanese astronauts Takuya Onishi and Kimiya Yui will travel separately to the International Space Station on long-term missions around 2025, the country's space agency said Tuesday.

Yui, 53, was initially scheduled to travel around 2024, but his departure has been delayed by a year. Both will be staying for six months and making their second space flights, with Yui having resided at the ISS between July and December 2015 and Onishi, 47, between July and October 2016, according to the agency.

Compatriot Satoshi Furukawa, 59, is currently stationed at the orbiting laboratory, according to the Japan Aerospace Exploration Agency.

Onishi, a Tokyo native and former pilot at All Nippon Airways, and Yui, a Nagano Prefecture native and former Japanese Air Self-Defense Force pilot, are expected to lift off in a commercial spacecraft in a flight arranged by the United States' National Aeronautics and Space Administration.

The two astronauts will engage in the maintenance of facilities, including Japan's experiment module Kibo, and in scientific experiments at the ISS, JAXA said.

Onishi and Yui have a variety of space experience, with each having captured an automated cargo spacecraft with a robotic arm to help it dock with the ISS.

"I hope (they will) fly into space and obtain new knowledge and experience," science and technology minister Masahito Moriyama told a press conference Tuesday.

Related coverage:

SpaceX craft with 4 astronauts docks at Int'l Space Station

4 astronauts including Japan's Furukawa head to space station

India launches 1st space mission to sun, days after lunar landing