WASHINGTON-If we’re ever to make regular journeys from Earth to Mars and other far-off destinations, we might need new kinds of engines. Engineers are exploring revolutionary new technologies that could help us traverse the Solar System in much less time.

Because of the orbital paths Mars and Earth take around the Sun, the distance between them varies between 54.6 million km and 401 million km.

Missions to Mars are launched when the two planets make a close approach. During one of these approaches, it takes nine months to get to Mars using chemical rockets - the form of propulsion in widespread use. That’s a long time for anyone to spend travelling. But engineers, including those at the US space agency (Nasa), are working with industrial partners to develop faster methods of getting us there.

So what are some of the most promising technologies?

Solar electric propulsion

Solar electric propulsion could be used to send cargo to Mars ahead of a human mission. That would ensure equipment and supplies were ready and waiting for astronauts when they arrived using chemical rockets, according to Dr Jeff Sheehy, chief engineer in Nasa’s Space Technology Mission Directorate.

With solar electric propulsion, large solar arrays unfurl to capture solar energy, which is then converted to electricity. This powers something called a Hall thruster.

There are pros and cons. On the upside, you need far less fuel, so the spacecraft becomes lighter. But it also takes your vehicle longer to get there.

“In order to carry the payload we’d need to, it would probably take between two to 2.5 years to get us there,” Dr Sheehy tells the BBC.

“For the kinds of outposts we’d need to build on Mars for crews to be able to survive for months, and the vehicles, you’d need a lot of cargo.”

AerojetRocketdyne is working on a Hall thruster for the Gateway, a proposed space station in lunar orbit.

“Solar is the best because we know we can scale it up,” Joe Cassidy, executive director of AerojetRocketdyne’s space division, explains.

“We’ve already got these flying today on communications satellites. The power level we fly at today is 10-15kW (kilowatts), and what we’re looking to do with the Gateway is to scale it up to something greater than 50kW.”

Mr Cassidy said AerojetRocketdyne’s Hall thruster will be much more fuel efficient than a liquid hydrogen and oxygen rocket engine. But a good way to make access to space cheaper would be to have fewer launches, he explains.

“I think that solar electric propulsion is very good technology, using xenon as the propellant. But the two major drawbacks are the amount of time it takes to get there, and the size of the solar arrays,” says Tim Cichan, a human spaceflight architect at aerospace giant Lockheed Martin. Dale Thomas, a professor and eminent scholar in systems engineering at the University of Alabama in Huntsville (UAH) concurs.