LIVE: SpaceX is about to take another shot at a potentially historic rocket landing

After two days of delays, SpaceX is scheduled to launch their Falcon9 rocket at 6:05 pm ET on Tuesday.

On Sunday the launch was scrubbed a couple of minutes before lift off be cause of issues with the Air Force radar malfunctioning, Elon Musk tweeted.

The launch could be historic, but it's not what goes up that's exciting, but what will come down - SpaceX is set to make it's second attempt at landing the rocket on a drone ship, so it can be recovered and reused for another launch.

Shortly after take-off, the rocket will have already returned from space and attempted to guide its way, using GPS tracking, onto a droneship in the Atlantic.

Watch the launch live here. The 22-story-tall Falcon 9 rocket is set to lift off out of Cape Canaveral Air Force Station in Florida around sunset. Live coverage of the launch will start at 5 pm ET on NASA TV, provided below:

With 17 potential rocket launches scheduled for 2015, there are plenty of opportunities to get it right even if this latest attempt doesn't work.

Reuseable rocket problems

Five years ago, a landing attempt like this was unheard of. But SpaceX is changing things up and paving the way for a new era of reusable rockets. The company, founded by billionaire entrepreneur Musk, has gone to great lengths to build the foundations for a future of cheap space travel. The key to that future is reusable rockets that can carry cargo and astronauts into space multiple times instead of only once.

SpaceX has never recovered a rocket for reuse. But if everything goes according to plan on the next attempt and the rocket lands softly, it would be a game changer.

The re-entry and landing of the rocket will be even more difficult this time around, because this mission is to send a satellite into deep space, Musk tweeted

The rocket had trouble on its most recent attempt, because it ran out of hydraulic fluid, sending it careening out of control on its way onto the drone ship:

 

The main mission

The landing attempt isn't the only exciting thing about the launch. For this launch, the rocket will also ferry an important instrument into space: the Deep Space Climate Observatory (DSCOVR).

DSCOVR, shown to the right, is the latest instrument that the National Oceanic and Atmospheric Administration will use to monitor solar winds. The sun emits gusts of high-energy particles in the form of solar wind, and when those gusts occasionally reach Earth's magnetic field it can disrupt the planet's power grids, telecommunications, aviation, and GPS.

Having a satellite like this is "the first line of defense ... for us to be able to take the appropriate action to protect our system from any impacts that could happen," said David Velazquez, the executive vice president for Pepco Holdings Inc. - a holding company for the Potomac Electric Power Company - in a NOAA video.

After the rocket detaches from DSCOVR in space, the climate observatory will begin a 110-day long journey to its final orbit while the rocket will head back toward Earth.

There's a special point in space, called Lagrangian Point 1, where a spacecraft can orbit so that it will always remain between the Earth and the Sun.

"The L1 position will provide DSCOVR with a point of 'early warning' when a surge of particles and magnetic field from the sun will hit Earth," NASA said in a statement. The observatory will sound the alarm 30 to 45 minutes ahead of time.