The aerospace sector is all about taking people off the ground. But it's not just about airplanes, that's the end of the process of just one small piece of this sector. Aerospace is really about the science and engineering behind getting taking humans into the future. Finding the best stocks in aerospace starts with diversified suppliers like Boeing Co (NYSE:BA) and Rockwell Collins (NYSE:COL). But if you really have your eyes locked on the stars, you'll want to look at Orbital ATK (NYSE:OA).

The big kahuna
When it comes to airplanes, Boeing is one of the world's largest players, producing iconic planes like the 747. The commercial business makes up around two-thirds of sales, with the rest coming from military and government orders. Boeing, for example, has long been a key partner for NASA, helping to take man into outer space--talk about exciting!

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An icon in the air. Image source: Boeing.

But here's the thing to really like about Boeing: its backlog. A company's backlog is made up of orders that are yet to be filled -- in other words, its future work. And Boeing has around $485 billion worth of future orders lined up. That's around 5,700 airplanes that have yet to be built.

Boeing's annual revenue is in the $100 billion area, so it has nearly five years of work already on the books. That provides pretty good revenue visibility. To be fair, orders can and do get canceled during hard times. But it's worth noting that the company's revenue fell in just one year over the past decade, a period that includes the recession. If you are looking for a reliable aerospace company, Boeing is one of the best options around.

Deeper in
But Boeing isn't the only supplier that's important to the aerospace market. For example, Rockwell Collins makes some of the parts that Boeing and others put into their planes. The company's list of products spans from avionics, which allow pilots to safely fly a plane, to entertainment systems, which allow customers to enjoy their flight. But it's list of products also includes things like satellite stabilization wheels and space optics.

Like Boeing, however, commercial airplanes are only one part of the business, representing around 45% of revenue. The rest is a mix of government work and a much smaller business in the information management space, both of which are still heavily involved in the aviation industry.

The really interesting thing about the Rockwell Collins -- and one of the reasons it should be on your list of best aerospace stocks -- is that once a customer selects Rockwell Collins as a supplier, it is locked in as a customer. That's because switching to a new supplier is, at best, hard to do. And then there's the service and replacement business after a jet gets delivered to a customer, which turns into a recurring revenue stream with very long legs.

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Some of the important components that Rockwell Collins makes. Image source: Rockwell Collins.

The top and bottom lines haven't gone up in a smooth line, but have been heading generally higher over the past decade. It's also worth noting that the company has scored a number of important supply agreements for next-generation aircraft, including with key customers like Boeing and Airbus, and smaller aircraft makers like Bechraft and Dasult. So the aerospace future is looking fairly solid for Rockwell Collins, too.

Stars in your eyes
If you take aerospace to the extreme, however, you'll want to focus on companies that are building the future of intergalactic travel... OK, that's a bit extreme. But Orbital ATK is a key player in the space race. This company was created via the merger of Orbital, which was pretty much focused on space rockets, and ATK, which had a broader aerospace and military business. The marriage has created a much more diversified entity.

Around 40% of Oribital ATK is dedicated to military work. The rest is split fairly evenly between space systems (satellites) and flight systems (rockets). That said, even the military work involves aerospace expertise. The real takeaway, however, is that of the three companies here, Orbital ATK is the most focused on taking humans to the next frontier. 

The deal that created this company was only completed early in 2015, so there's still a lot of moving parts here. But Orbital is one of the few companies with the capabilities to get cargo, and humans, into space. So it's likely to be a bit player in aerospace's future.

A futuristic industry
Aerospace is so much more than airplanes, which are really just the tip of the iceberg. If you like airplanes, however, you'll find that some of the best stocks in aerospace make planes, like Boeing, and supply the aircraft makers, like Rockwell Collins. But if you want to go to infinity and beyond (last cheap space reference, honest!), Orbital ATK is knee deep in spacecraft. But don't forget that the other pair play in the area, too, they just aren't as focused on it. So, if you are looking at this industry, Boeing, Rockwell Collins, and Orbital ATK should all be on your watch list.

Reuben Brewer has no position in any stocks mentioned. The Motley Fool recommends Orbital ATK. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.