Endeavour, Houston, we see a nominal MECO welcome to space.
Hey! It's Ben here
But how do we get here?
This is the ISS or International Space Station
Now it's really really cool I would go so far as to say that it's out of this world
literally it is 400 kilometers above the earth and in order to stay up there
it's orbiting around the earth at 7 kilometers per second
Now how do we get to such a fast moving target? The answer that
is a practice known as orbital rendezvous
rendezvous meaning to meet up and orbital meaning well... In orbit
But before we can do a rendezvous we have to decide when we're
going to launch because we have to launch with very specific timing
timing is important because the International Space Station's orbit is
inclined at 51 degrees what the heck does that mean? Well what it means is
that here's the equation and here's the International Space Station's orbit
and the angle between them is 51 degrees. The inclination of the orbit means that as
the Earth rotates underneath the orbit the orbit will pass over all the launch
sites used to get to it such as the Kennedy Space Center for NASA and the
Baikonur cosmodrome for Roscosmos the Russian Space Agency
but we can't just launch at any time because, say if our launch site is here
and the International Space Station's orbit is here if we were to launch
Our orbit would be like this and it wouldn't line up with the Space Station's orbit
We could change the orbit so that it would line up but that would just take a
ridiculous amount of fuel that no spacecraft has
So it's much easier for us to just play the waiting game
wait for the earth to rotate in such a way
that our launch site is underneath the Space Station's orbital path
then we can launch and our orbit will line up with the International Space Station
And we can begin the rendezvous
Now to understand how we're going to do this rendezvous we have to know one of
the most important rules of orbital mechanics and that's that the lower your
orbit is the faster it will be. Now this does make sense, the International Space
Station orbits the earth once every hour and a half
meanwhile the moon which is much further away orbits the earth once every 27 and
a bit days. Now, this is important because we can't just launch straight up to the
same height as the International Space Station because the International Space
Station probably won't be in the right position for that, and even if it was
it's an amount of precision that we simply don't have. So we're going to
launch into a phasing orbit, this is an orbit that's below the International
Space Station. Because it's below the International Space Station's orbit it
will be faster and so we're going to catch up with the International Space Station.
Once we're in the right position we'll be able to raise our altitude and
then we'll match up with the International Space Station in the same
place at the same speed and same time to do that we need to use a Hohmann
transfer this is two burns of our engine and what its gonna do is raise us from a
circular orbit of one altitude to a circular orbit of another altitude
We'll do this by speeding up here turning our circular orbit into an ellipse and then
we're gonna wait until we get around to the other side of the ellipse
Fire up our engines to speed up again and turn our ellipse into a circle.
But wait a minute why do we have to fire our engines to
speed up I thought higher orbits with slower?
Yes that's true they are slower
but they have more energy total that's because they're higher up and so they
have more gravitational potential energy so what we're doing by speeding up here
is we're adding speed energy but as we climb up hill that speed energy gets
transferred into gravitational potential energy and so while we're going uphill
we're actually slowing down until we end up in our higher orbit
that actually has a lower speed than our low-orbit.
So yes what I told you before was true but getting between these two orbits took a bit of counter intuitive maneuvering
So yay we're right next to the International Space Station right now
parked right next to it. How do we get inside? Well that requires docking
but unfortunately that's a whole other video in itself.
This has been orbital rendezvous and it's simply space