OSIRIS-REx and Bennu

Just how did OSIRIS-REx get to Bennu anyway?

OSIRIS-REx is the name of one of NASA's interplanetary probes. It's just edging towards a skyscraper-sized asteroid called Bennu right now. Apart from the composition of the asteroid, its "potentially Earth hazardous" orbit makes it of some, er, shall we say, "interest"?

Bennu's orbit is not terribly much bigger than Earth's, but it is way more egg-shaped. For some of its time, Bennu is closer to the Sun than the Earth, but for the rest of the time it's further out. This means the orbits come very close about once every six years or so.

Who else out there has played Kerbal Space Program? I have to say, this is by far my favourite computer game - if it can be called a game. Suffice to say that everything I know about orbital dynamics I learned from Kerbal.

To get from one orbit to another, NASA engineers had to do a very complicated dance with OSIRIS-REx. It had to take off, pull away from Earth, make a few burns to get its orbit wobbly enough to swoop back past Earth right where the orbits all meet. The spacecraft then did a "gravity assist" manoeuvre to swap into Bennu's orbit. It's like a train changing tracks.

Once it was all lined up, all OSIRIS-REx had to do was approach Bennu very, very slowly. One push too much and OSIRIS-REx will find itself drifting uselessly away in an orbit around the Sun, much like George Clooney in the movie Gravity. In fact, that's pretty much the way the spacecraft will start its journey back to Earth after having grabbed some of the dust from Bennu.

So let the science begin!

PS - can you see Bennu? Nope. Not at all. Although with a 16" go-to computerised Dobsonian telescope, you could have an incredible time trying.