SpaceX Falcon Heavy's 3rd launch -- how to watch

SpaceX’s Falcon Heavy rocket is set to blast off from Kennedy Space Center in Florida. This will be the third trip for the Falcon Heavy. Its 2018 test launch lofted founder Elon Musk’s Tesla roadster into the solar system, and a second mission in April carried a Saudi communications satellite to orbit.

This time it’s carrying 24 satellites for the Defense Department and other customers, and Musk called it SpaceX’s “most difficult launch ever.” A successful mission could lead to additional business from the United States government for Falcon Heavy.

When is the launch, and how can I watch it?

The launch is scheduled for 2:30 a.m. Eastern time, and the window to blast off lasts until 3:30 a.m. Although the window to take off opened at 11:30 p.m. Monday, SpaceX pushed back the launch time for more checks of ground systems.

An hour before the rescheduled flight time, the company tweeted that it was on track to launch. Local authorities alerted the public in Florida to expect loud noise from the launch and landing attempts.

If the launch gets postponed for any reason, SpaceX can try again Tuesday night.

The launch will be streamed on the internet on SpaceX’s website.

What will Falcon Heavy carry?

The mission is called Space Test Program-2, and is a partnership between the Defense Department, NASA, the National Oceanic and Atmospheric Administration and a number of private companies. The 24 separate satellites — including an Air Force satellite for basic research as well as cremated remains of 152 people — are all packed together in an integrated payload and will be gradually deployed to a variety of orbits. Below is some of the rocket’s most interesting cargo.

— LightSail-2

The Planetary Society’s LightSail-2 cubesat has waited a decade to launch into space. First proposed and championed by Carl Sagan in the 1970s, this satellite is the size of a loaf of bread and is carrying what is known as a solar sail.

Solar sailing is much like sailing in the ocean. Instead of canvas, LightSail-2 will use mylar sails — nearly 20 miles of them — that open wide to collect as much sunlight as possible. Photons from the sun don’t have any mass, but they do have momentum, and that is just enough to slightly nudge the solar sails, like wind on the open ocean. The cubesat includes a momentum wheel so that engineers on the ground can steer the sail.

A week after launch, the massive sails will spread out and begin using sunlight to lift the cubesat into a higher orbit. The goal is to reach 450 miles above Earth, which would make LightSail-2 the first solar sail to use only the power of sunlight to enter a high orbit. It would then orbit Earth for about a year.

“We’ve made all sorts of vital and very significant improvements to the spacecraft. So I’m very excited about this.” said Bill Nye, the “science guy” and chief executive of the Planetary Society.

Proving the technology works would have significant implications for the future of deep space exploration. When robotic space explorers launch, they carry limited fuel. But solar sailing could provide an alternative propulsion method with nearly limitless fuel, improving the prospects of exploring the farthest reaches of our solar system, or even possibly a journey to other stars.

— Green Propellant Infusion Mission

A NASA payload, this small satellite is a test of rocket fuel that is more environmentally friendly.

Most spacecraft use a propellant called hydrazine, which is highly toxic. To even be near hydrazine, a person must wear a protective Hazmat suit.

This new, less toxic fuel is made of a hydroxyl ammonium nitrate fuel/oxidizer blend, called AF-M315E that was originally developed by the Air Force but never used in space. Not only does this green propellant pose less of a threat to humans handling it, but it’s also more efficient.

— Deep Space Atomic Clock

To track missions in deep space, NASA and other space agencies rely on radio signals, waiting for them to traverse the long distances. Robotic probes constantly call home to Earth to confirm the current time and their location. But space agencies need a more timely way to track their spacecraft and their future human missions.

Atomic clocks track vibrations inside an atom like cesium, to measure time accurately. Aboard Global Positioning System satellites orbiting Earth, atomic clocks help precisely triangulate distances traveled over periods of time. But the technology has never been used in deep space. If the Deep Space Atomic Clock is tested successfully, future missions in deep space could navigate the solar system with something like GPS.

Will SpaceX stick the landing?

One of SpaceX’s major selling points for those who need to go to space — including the U.S. military, NASA and private companies — is the cost-effectiveness of the company’s reusable rockets.

The company has landed the booster stages of many rockets, and then reused them. That will also occur with this launch. Its side boosters landed in April; it’s the first time the Defense Department has allowed its hardware to be launched aboard a previously used rocket.

After Falcon Heavy’s launch, SpaceX will attempt to land all three boosters back on Earth. The rocket’s two side boosters will touch down at about the same time at Kennedy Space Center, which the company has already done twice. Landing the center booster is more difficult, and the Heavy failed on its first landing attempt aboard a drone ship in the Atlantic Ocean in 2018. But it touched down successfully in April.

While the floating landing platform ship, named Of Course I Still Love You, was 25 miles off the coast of Florida for that return, it will be more than 700 miles away this time.

This article originally appeared in The New York Times.