The Long Route to Mars
The planet Mars is one of the brightest objects in the night sky, easily visible with the unaided eye as a bright red star. Every two years or so, Mars and Earth reach their closest point, called ‘opposition’, when Mars can be as close as 55,000,000 km from Earth. And every two years, space agencies take advantage of this orbital alignment to send spacecraft to the Red Planet.
How long does it take to get to Mars?
The total journey time from Earth to Mars takes between 150-300 days depending on the speed of the launch, the alignment of Earth and Mars, and the length of the journey the spacecraft takes to reach its target. It really just depends on how much fuel you’re willing to burn to get there. More fuel, shorter travel time.
The first spacecraft ever to make the journey from Earth to Mars was Mariner 4, which launched on November 28, 1964, and arrived at Mars on July 14, 1965, successfully taking a series of 21 photographs. Mariner 4’s total flight time was 228 days.
Why It Takes So Long?
When you consider the fact that Mars is only 55 million km away, and the spacecraft is traveling in excess of 20,000 km/hour, you would expect the spacecraft to make the journey in about 115 days, but it takes much longer. This is because both Earth and Mars are orbiting around the Sun. You can’t point directly at Mars and start firing your rockets, because by the time you got there, Mars would have already moved. Instead, spacecraft launched from Earth need to be pointed at where Mars is going to be.
The other constraint is fuel. Again, if you had an unlimited amount of fuel, you’d point your spacecraft at Mars, fire your rockets to the halfway point of the journey, then turn around and decelerate for the last half of the journey. You could cut your travel time down to a fraction of the current rate, but you would need an impossible amount of fuel.
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.
Mr. Cassidy said Aerojet Rocketdyne'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.