How to Fly Rockets Back to Earth

On Sunday, SpaceX hopes to land a Falcon 9 rocket after delivering its payload to space -- but this isn't the only rocket return game in town.

SpaceX plans to try again Sunday to land a Falcon 9 rocket after it dispatches a Dragon cargo ship toward the International Space Station.

The company, founded and run by technology entrepreneur Elon Musk, has come close during two previous attempts to vertically land the first stage of a Falcon booster on a platform floating in the Atlantic Ocean, northeast of its Cape Canaveral, Florida, launch site.

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During the first try in January, the rocket ran out of hydraulic fluid needed to maneuver small, foldable steering fins. The rocket, which is as tall as a 14-story building, crashed into the landing platform and exploded.

SpaceX tried again to land a Falcon in April and nearly nailed it. The supersonic descent through the atmosphere was successful, but about 10 seconds before touchdown a valve that was controlling the rocket's final braking burn had a glitch that caused it to throttle down a few seconds later than planned. The 67,000-pound stage, now traveling at nearly 200 mph, lost control for a moment. It recovered, but not in time to prevent the rocket from tipping over, causing another fireball.

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Landing attempt three is expected around 10:30 a.m. EDT Sunday. The Falcon 9 rocket, carrying a Dragon cargo ship, is slated to lift off from Cape Canaveral Air Force Station at 10:21 a.m. As the capsule flies away from the rocket's upper-stage to begin a 40-hour trek to the station, Falcon's discarded first stage should have flipped around, made two engine burns, deployed grid fins, released landing legs and lit a single engine for a precision, controlled touchdown.

"We learned things," from the previous attempts, Hans Koenigsmann, SpaceX vice president for mission assurance, told reporters during a prelaunch press conference.

"SpaceX pushes innovation and part of that is to learn from your experiments, your trials. You look at the data, you evaluate this and then you make correction. That's ultimately how you succeed, in my opinion, to make a safe landing in the end," he said.

SpaceX isn't the only company working on reusable rockets. This month, Europe's Airbus unveiled a project called Adeline aimed at bringing back just the rocket's most expensive parts -- the engine and avionics.

Adeline (short for Advanced Expendable Launcher with Innovative engine Economy), could be used on any rocket. It is designed around a re-entry capsule that contains the rocket's engines and avionics.

After the rocket's first-stage is jettisoned, a rounded, winged capsule would separate from the rear of the booster and descend back toward Earth. Once in the atmosphere, two small turbo-propellers would be deployed from the module so it could fly itself, like a drone aircraft, to a landing on a conventional runway.

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Airbus said it has been working on the idea since 2010 and believes it has a better chance of actually reusing its hardware because the rocket engines aren't relit for a powered descent, like the Falcon's.

The rocket with Adeline also doesn't need to carry any extra fuel and Adeline's heat shield protects the equipment during the fiery plunge through the atmosphere.

Adeline is due to make a debut test flight in 2025.

With SpaceX poised to break its monopoly on the U.S. military's launch business, industry behemoth United Launch Alliance (ULA) is looking to expand into commercial markets. Its Atlas and Delta rockets have an impressive record, with 96 successful flights since parent companies Lockheed Martin and Boeing formed ULA in 2006.

The company's weak spot has been price and, more recently, its reliance on Russian-made rocket engines for the fleet's workhorse, the Atlas 5.

ULA intends to address both issues with a new rocket, called Vulcan, slated to debut in 2019. Later versions will incorporate a reusable engine system called SMART, an acronym for Sensible, Modular, Autonomous Return Technology.

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Like Airbus' Adeline, the idea is to just bring back the most expensive bit -- the rocket engine. ULA said future versions might add the rocket's avionics as well.

In the SMART system, after first-stage separation the booster's engine compartment would detach and an inflatable hypersonic heat shield would deploy to protect the equipment during re-entry into the atmosphere.

A steerable parafoil would then the unfurl, slowing descent so that a helicopter could pluck the engine compartment out of the sky and land it on a ship or back at the launch site. The engines would be refurbished and reflown.

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"This is a distinctly separate approach from what other people are doing," ULA chief executive Tory Bruno said at the rocket's unveiling in April.

"This allows us to avoid adding complex, expensive, heavy and performance-killing subsystems to a rocket in order to bring entire stages back that then experience complicated and expensive logistics to recover them. Instead, we took a systems engineering approach to what on the rocket is actually valuable," he said.

ULA says the engines account for just 25 percent of the first-stage's overall weight, but 65 percent of the booster's cost.

In addition to being the prime contractor for engines for ULA's new Vulcan rocket, privately owned Blue Origin is working on a suborbital vehicle called New Shepard, which is designed to return itself to a landing pad.

During a debut test flight on April 29, New Shepard dispatched a capsule, which made a successful parachute landing. The rocket then attempted to land itself back at its West Texas launch site, but its hydraulic system lost pressure and the rocket crashed.

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"We've already been in work for some time on an improved hydraulic system. Also, assembly of propulsion module serial numbers 2 and 3 is already underway -- we'll be ready to fly again soon," Blue Origin founder Jeff Bezos said after the test flight.

The company has not said if its orbital launch system, which will use the same BE-4 methane-burning engines that will power ULA's Vulcan rocket, will return its first-stage boosters intact like New Shepard and like SpaceX is attempting to do with the Falcons.

NASA thought the space shuttles would be far easier and cheaper to refly than they actually turned out to be.

Plans to reuse the shuttles' huge orange fuel tanks were quickly discarded, but the spaceships' twin solid-rocket boosters were recovered, refurbished and reflown. It wasn't a pretty process. The boosters were jettisoned two minutes after launch and splashed down into the ocean for recovery by ships, an expensive and time-consuming process.

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NASA studied using an upgraded, liquid-fuel booster that could fly itself back to the shuttle's runway, hoping to cut operational costs and improve safety. The $4 billion- to $5 billion price tag, however, was a showstopper.

The orbiters did return with their three liquid-fueled engines intact, which were refurbished and reflown. NASA now plans to use the shuttles' main engine on its heavy-lift Space Launch System rocket – for as long as they last anyway. The SLS is a throwaway rocket, and an expensive one at that.