Ballistic capture is a navigational technique utilized by spacecraft, and has been successfully utilized to coast into orbit around the Moon. Now, new research shows the same process may be used in flights to Mars, making trips to the Red Planet easier and less expensive.
Costs to fly to Mars can exceed hundreds of millions of dollars, and a large portion of that cost is directly related to arrival procedures once the vehicle reaches its destination. Spacecraft are usually traveling tens of thousands of miles per hour when they encounter the Martian system. Entering orbit around Mars means firing retro-rockets, powered by fuel carried from Earth, in a process called a Hohmann transfer. Any extra weight aboard rockets means additional fuel must be expended, adding to mission costs. Risks are also present in this type of operation, as spacecraft could veer off-course, or go racing straight past its target.
Ballistic capture could be used in the place of Hohmann transfer, researchers found, although there is a price to pay for the fuel savings.
Also known as low-energy transfer, ballistic capture is possible between bodies in the inner Solar System. Traditional navigation techniques involve aiming a spacecraft for a precise location near the future position of a target body, like the Moon or Mars. Once the vehicle arrives, it must then slow down into a precise trajectory for orbital placement.
Ballistic capture involves placing a spacecraft into the same orbit as the target, a little ahead of the body, traveling slower than its destination. As the Moon or Mars "catches up" to the vehicle, the spacecraft is captured by the body, entering orbit around its target. Reaching Mars or the Moon still requires as much fuel as normal, but the need for braking is greatly reduced.
"It's an eye-opener. It could be a pretty big step for us and really save us resources and capability, which is always what we're looking for," James Green, director of the Planetary Science Division at NASA, said.
The relatively high orbital velocity of Mars presented a challenge to engineers working out how to use ballistic capture for Martian missions. The process also takes a long time, greatly increasing the length of missions over traditional braking.
Once every 26 months, Mars and the Earth align in such a way that the flight distance reaches a minimum. This is the reason Mars missions tend to launch - and arrive - every two years ago.
Hiten, a Japanese spacecraft, was the first to use low-energy transfer on its mission to the Moon, arriving in 1991.
Ballistic capture and its possible utilization in future Mars missions was detailed in the journal Celestial Mechanics and Dynamical Astronomy.
