Aerobraking | Universe Today

Written by Tega Jessa

Aerobraking is a spaceflight technique used by interplanetary aircraft. It basically involves using the friction of a planet’s atmosphere in order to slow the air craft down and enter into a stable orbit. As we know from satellites the faster a satellite moves the higher its orbit around a larger center of mass. This is what keeps natural satellites like the moon and artificial satellites in their orbit. Normally interplanetary space craft are already at a high velocity as they approach their destination. In order to stop them from simply crashing into the planet and wasting millions of dollars in government the spacecraft has to slow down enough so it can enter orbit around the target planet. This is especially important for satellites taking data on planets such Cassini or Voyager.

So how does aerobraking work? It works on the same principal as reentry only instead of trying to enter the atmosphere the spacecraft grazed the top the planet’s atmosphere creating a sort of aerial friction called drag. This allows the space vehicle to slow down to come more directly under the influence of the planet’s gravity and enter into a lower, more elongated elliptical orbit.

So why do we even use aerobraking? Couldn't we just install rockets on the spacecraft that will slow it down? Well at the moment we still use liquid fuel based propulsion. An interplanetary craft travels at a speed that is on a magnitude of several orders faster than normal fuel powered aircraft while working without the benefits of significant friction in the void of space.

As we all learned from the Newton’s law of motion an object in motion tend to stay in motion. To do this by using rockets the craft would have to burn a significant amount of fuel in order to slow itself down. This creates two problems. First, the space vehicle only carries a finite amount of fuel even if the amount of fuel required to slow it down, there would be barely any fuel left to help it maintain its orbit for the necessary period of time. Second, in order to successfully brake, the majority of the mass of the vehicle has to be rocket fuel. In the end both of these problems make this solution costly.

Aerobraking is at the moment the most cost effective and efficient measure available to slow down an interplanetary vehicle and adjust its orbit effectively. However it does come with its own risks. Like the friction of reentry into the atmosphere grazing the atmosphere creates a lot of heat. The craft’s structure has to be designed in a way that effectively dissipates this heat and maintain its structural integrity.

We have written many articles about aerobraking for Universe Today. Here's an article about how a Mars spacecraft did its aerobraking maneuver, and here's a similar article about the aerobraking maneuvers of the Mars Reconnaissance Orbiter.

This article from NASA explains more about aerobraking.

And this episode of Astronomy Cast, called Getting Around the Solar System, explains aerobraking in more detail.

Filed under: Astronomy