## Monday, December 28, 2015

### Falcon 9 & SpaceX

From redditor tossha
The Falcon 9 is a two-stage rocket fully designed and manufactured by SpaceX.  It is, most importantly, partially reusable.  The first stage can land upright, autonomously.  This has been compared to balancing a rubber broomstick in a windstorm.   This is important because it means that all the cost of building a first stage can be recouped.  In addition, SpaceX's crew capsule (crew dragon) can be reused.

We'll get back to the design of the Falcon 9, but first, a bit of background.
Rocket technology has not significantly advanced since the '60s, so it still costs as much as ever to put stuff in space (US$13,812 per kilogram to low earth orbit for an Atlas V), which is why President George H. W. Bush's plan (announced in July 20, 1989) for a manned Mars mission was quickly thrown out when NASA told him that it would cost 500 billion US dollars. SpaceX was started when Musk tried to create interest in space by sending a greenhouse to Mars, but everywhere he went for look for his rocket, he found it was ridiculously expensive. So he started his own space exploration company. He took the cost of the raw materials required to make a rocket, and compared them to the cost of a typical rocket price, and got about 2%. The materials cost percentage of market price for a car is about 47%. Elon Musk discovered that major aerospace firms don't want to fly unflown equipment, which means that no new technology ever gets used. The way companies cut costs is by using engines actually manufactured in the '60s. So the Falcon 9 can launch a kilogram to low earth orbit for US$4109, because that SpaceX makes almost all of the rocket in-house, so there's none of the levels of sub-contractors that all want a piece of the price tag pie.  Plus, SpaceX uses modern methods of manufacturing and assembly that all cut costs.  And, of course, reusability will make it far cheaper than before, possibly 100 times cheaper.  Here Elon Musk sums it up nicely:
Imagine if you had to have a new plane for every flight. Very few people would fly. -Elon Musk
Airplanes aren't any cheaper to build if you reuse them, but you can make the price for a flight cheaper if you can do many flights with them.

But, I hear you ask, why is Elon Musk doing all this?  Considering that he was already rich from paypal, why did he decide to revolutionize space travel?  Because he wants (in addition to running a profitable company) to put 1,000,000 people on Mars.  And he wants their ticket to cost only 500,000 US dollars.  He wants to do this for two reasons, to create a "backup" of the human race, so if a mass extinction event happens to a planet with humans on it, the human race can survive, and for this reason:

This seems like a good idea, but we should be careful not to think of this as a solution for humans' impact on Earth.  Unsustainable fuels are unsustainable on Mars, and a terraformed Mars' ecosystem would be just as fragile as Earth's.  It is, however, a partial solution for overpopulation.  Ideally, it could open up far more space for humans.  Nonetheless, that space is not infinite.  Humans would have to continuously colonize new planets to support the growth of population.

Now, if you look almost all the way to the top of the post, you'll see that this was actually a digression.  Back to the Falcon 9!

The Falcon rocket family is named after the Millennium Falcon from the Star Wars franchise.  The first version of it was called the Falcon 1.  The Falcon 1 was designed to test construction techniques for the Falcon 1, while also launching satellites for profit.  SpaceX was at this being funded directly from Elon Musk's pocket, and it had money for 3 or 4 launches when it started.  The first launch was a failure.  So was the second and third.  Finally, on the fourth launch, the Falcon 1 made it into orbit, saving SpaceX from closing.  After that, NASA awarded a US\$ 1.6 billion contract to SpaceX.

Then SpaceX built the Falcon 9.  Here we're going to be talking about the Falcon 9 v1.1 full thrust, the latest version.  The Falcon 9 has two stages, with 9 Merlin 1D engines on the first stage and one Merlin Vacuum 1D on the second stage.  First let's look at the Merlin engine:
The Merlin is developed fully in-house by SpaceX, and is the highest thrust to weight ratio (TWR) rocket ever built.  The 1D version has an absurd TWR of 165.9.  For comparison, the space shuttle main engine (SSME) gets only 73.1.  TWR is important in rocket engines because that the higher the TWR, the more mass the rocket engine can lift compared to it's mass, so you need less engine mass to lift the same amount of payload.  i.e., it's an incredible rocket engine.
Here's a Merlin 1D firing:

Now, the rocket:
The entire rocket uses many smart construction techniques, such as 3D printing to make their rockets cheaper.  Look at this first, for an idea of how it looks: http://www.spacex.com/falcon9
The first stage has one very important feature: reusability.  The first stage lands on four carbon fiber and aluminum honeycomb landing legs, which fold down for landing.
From SpaceX

The first stage also has four deployable grid fins, at the top of the first stage, which help to keep the rocket on the right course.  The honeycomb structures in the photo below are the fins:
From SpaceX

In addition to these, there are small cold gas thrusters to keep the first stage on course during landing.

The second stage is like a small version on the first stage, with only one Merlin Vacuum 1D engine and a smaller tank.  It is not reusable.