This episode of DNews is brought to you by the U.S. Air Force.
A satellite landed a probe on a COMET today, but it was launched 10 years ago.
Why did it take so long to get there?
The comet 67P/Churyumov-Gerasimenko is heading into the inner solar system on its trip around
the sun.
67P flies around the sun and then out past Jupiter every 6.45 years.
It was discovered in 1969, and selected for the Rosetta mission in the early 2000s.
Rosetta's plan is to learn about the structure and behavior of comets, but Rosetta was launched
in 2004, and 67P is still out past Mars…
It’s, at most, a year to get to Mars… so why launch it so early?
Because gravity.
When a rocket reaches space, it has to escape Earth's gravity: the escape velocity from
Earth's surface is 11.2 km/s -- Mach 33.
Yeah, it's fast.
Once in space, Rosetta will have to travel at least that fast to begin its massive, parabolic
orbit on the way to catch a comet.
The thing is, even at 11.2 km/s it needs more power!
67P is traveling at 37.5 km/s!
As the mass of the fuel increases on Earth, it is exponentially more difficult to lift
a rocket to escape velocity…
So, the most fuel-efficient solution to accelerate to that speed, as of now, is to perform gravity
assist maneuvers once in space.
To fling a craft around a planet and take advantage of its gravity.
So you're flying toward Earth, and gravity is pulling you down, you're speeding up!!
You get closer, and closer, and then ZOOM PAST THE PLANET at astronomical speeds!
YAY!
But then, the same gravity is pulling… pulling… pulling… slowing you down...
Like a biker going downhill and then back up a hill of the same size!
The net change at the end of the day would be zero!!
But, there's more to it than just the craft and the gravity.
There's the movement of the whole planet.
The flinging of a craft around a massive celestial body at JUST the right angle, speeds up the
craft by stealing a bit of energy from the planet.
For example, when Voyager 2 was flung toward Saturn in 1979, Jupiter SLOWED by 10 to the
negative 24th km/s... but Voyager GAINED 10 km/s!
A HUGE gain for Voyager, a tiny imperceptible loss for Jupiter.
We call it a slingshot.
Rosetta left Earth in 2004, on a regular orbit until it encountered Earth again almost EXACTLY
one year later.
Using Earth's gravity, Rosetta flung itself around Earth and headed for Mars.
In early 2007, Mars' gravity slapped it on again, on another path toward Earth, where
our gravity gave it a good smack later in the same year.
Finally, after a MUCH longer orbit and third Earth flyby in 2009…
It settled into giant orbit which brought us to November of 2014…
When it FINALLY caught up with 67P.
These gravity assists took a long time, but allowed the craft to accelerate to 55,000
km/hour, using only the gravity of planets and a bit of fuel to make tiny course corrections.
It's not the most direct solution, but it's efficient, and allowed it to fly past a few
asteroids on the way.
Now, thanks to the mission team, Rosetta is orbiting a body with a gravitational pull
several hundred thousand times weaker than on Earth.
It's moving at about 1 m/s relative to the asteroid, or at the speed of walk.
In the end, Rosetta stole energy from two planets and flung itself around the sun five
times in the last ten years, but now, thanks to all that physics and LOTS of math, we landed
on a comet this morning for the first time ever in human history.
Stories like this make me think, damn, trying to land a spacecraft on a moving comet seems
impossible.
But somehow science is making it happen.
You know who else is good at achieving the impossible?
The brave men and women in the United States Air Force!
Whether it’s overcoming poverty to become a nurse and officer or becoming the first
female Thunderbird pilot, these Airmen are doing what others once thought was impossible.
So, a big shout out to the U.S. Air Force for supporting DNews.
To learn more about Rosetta and the Mission click here to see that handsome devil talk
about it, or you can go into the description and check out DiscoveryNews.com, they're covering
the CRAP out of it.