Elon Musk says SpaceX will try its 'most difficult launch ever' tonight. Here's how to watch live video of the third-ever Falcon Heavy rocket mission.

• SpaceX is about to launch its third-ever Falcon Heavy rocket - the world's most powerful operational launch system - on Monday around 11:30 p.m. ET.
• Elon Musk, the founder and CEO of SpaceX, said it "will be our most difficult launch ever" because the mission will take multiple rocket-engine firings and last about six hours.
• The goal is to deploy 24 different satellites into orbit around Earth, including an atomic clock for NASA and the ashes of 152 people.
• SpaceX is streaming live video of the launch, which you can watch using the YouTube player below.
• Visit Business Insider's homepage for more stories.

Elon Musk, the founder and CEO of SpaceX, says his rocket company's toughest mission yet has arrived - and you can watch it live online.

Sometime between 11:30 p.m. ET on Monday and 2:30 a.m. ET on Tuesday, a Falcon Heavy rocket will try to lift off from Cape Canaveral, Florida.

Tonight's launch attempt marks SpaceX's third-ever with Falcon Heavy. The rocket design debuted in February 2018, has three reusable boosters, and is considered the planet's most powerful launch system in use today.

"This will be our most difficult launch ever," Musk tweeted on June 19.

What makes this mission, called Space Test Program-2 (STP-2), so challenging is what's stacked inside the rocket's nosecone: 24 different government and commercial satellites that together weigh about 8,150 lbs (3,700 kg). (When fully fueled, a Falcon Heavy rocket weighs about 1,566 tons [1,420 tonnes], or more than 300 adult elephants' worth of mass.)

After getting its behemoth rocket off the pad at Launch Complex 39-A, SpaceX has to deploy the two dozen spacecraft into multiple orbits around Earth over several hours. To do this, it must shut down and reignite the engine of an upper-stage rocket four times, according to the company.

Read more: The space between Earth and the moon is mind-boggling. This graphic reveals just how big it is - and what's out there.

One satellite holds NASA's Deep Space Atomic Clock, which may change the way robots and astronauts navigate through space. Another spacecraft is Planetary Society's LightSail, an experiment that could change how vehicles propel themselves to a destination. NOAA is also launching six small weather satellites built in partnership with Taiwan.

There's even a spacecraft holding the ashes of 152 people, and it will orbit Earth for about 25 years before careening back as an artificial meteor.

But SpaceX will also be attempting to land all three of the rocket's 16-story boosters back on Earth for reuse in future launches. The two attached to the side of the Falcon Heavy rocket are set to touch down on land a few minutes after lift-off.

Meanwhile, the central or core booster - which will fire longer and disconnect from the upper-stage rocket later in the flight - will try to land on a drone ship sitting about 770 miles (1,240 km) off the coast of Florida in the Atlantic Ocean.

Watch SpaceX's launch attempt live on Monday night

SpaceX is streaming the STP-2 mission live on YouTube, and the company says its broadcast will begin about 20 minutes before lift-off (about 11:10 p.m. ET).

There's a 20% chance that SpaceX may delay its launch due to potential thunderstorms, according to a forecast issued by the US Air Force on Monday morning. If the launch is pushed to its backup window 24 hours later, there's a 30% chance of delay.

If you want to follow the launch and deployment events, we've included a detailed timeline below the YouTube embed.

Launch events and timing relative to the moment Falcon Heavy lifts off the pad are outlined below and come from SpaceX's press kit for the STP-2 mission.

-53:00 - SpaceX Launch Director verifies go for propellant load
-50:00 - 1st stage RP-1 (rocket grade kerosene) loading begins
-45:00 - 1st stage LOX (liquid oxygen) loading begins
-35:00 - 2nd stage RP-1 (rocket grade kerosene) loading begins
-18:30 - 2nd stage LOX loading begins
-07:00 - Falcon Heavy begins pre-launch engine chill
-01:30 - Flight computer commanded to begin final pre-launch checks
-01:00 - Propellant tanks pressurize for flight
-00:45 - SpaceX Launch Director verifies go for launch
-00:02 - Engine controller commands engine ignition sequence to start
-00:00 - Falcon Heavy liftoff

Once the rocket lifts off, Falcon Heavy hardware and its payload will go through a series of crucial maneuvers. The side boosters and core booster will try to separate and land. Following that, the rocket's upper or second stage will propel into orbit, then attempt to deploy its 24 satellites from a device called the Integrated Payload Stack over several hours.

The timing and events below are also relative to lift off, in hours, minutes, and seconds.

00:00:42 - Max Q (moment of peak mechanical stress on the rocket)
00:02:27 - Booster engine cutoff (BECO)
00:02:31 - Side boosters separate from center core
00:02:49 - Side boosters begin boostback burn
00:03:27 - Center core engine shutdown/main engine cutoff (MECO)
00:03:31 - Center core and 2nd stage separate
00:03:38 - 2nd stage engine starts (SES-1)
00:04:03 - Fairing deployment
00:07:13 - Side boosters begin entry burn
00:08:41 - Side booster landings
00:08:38 - 2nd stage engine cutoff (SECO-1)
00:08:53 - Center core begins entry burn
00:11:21 - Center core landing
00:12:55 - Spacecraft deployments begin
01:12:39 - Second stage engine restart (SES-2)
01:13:00 - Second stage engine cutoff (SECO-2)
02:07:35 - Second stage engine restart (SES-3)
02:08:04 - Second stage engine cutoff (SECO-3)
03:27:27 - Second stage engine restart (SES-4)
03:28:03 - Second stage engine cutoff (SECO-4)
03:34:09 - Final spacecraft deployment