"Detailed review of rocket telemetry needed to tell if due to initial splashdown or subsequent tip over and body slam," Musk tweeted.

We're also waiting on news on the status of the planned recovery of the Falcon 9 first stage in the Atlantic Ocean, a key demonstration of the rocket's potential for reusability.

The six Orbcomm satellites should begin their deployment sequence at T+plus 15 minutes, with separation of one satellite about every three minutes until the sequence ends about 35 minute after liftoff. The satellites are mounted on an adapter ring provided by Moog Inc.

And chilldown of the second stage's vacuum-rated Merlin 1D engine should be starting in preparation for its ignition.

The command to start the ignition sequence for the first stage will be issued at T-minus 3 seconds, triggering the Merlin engines' ignitor moments before the powerplants actually ramp up to full power.

The strongback has retracted into the launch position more than 20 degrees from the rocket.

The second stage thrust vector steering system has checked out and is ready for flight.

The strongback umbilical tower will soon be lowered a few degrees to clear the rocket for launch. The procedure begins with opening of cradles gripping the rocket at attach points, then hydraulics lower the tower into launch position.

The launch danger area around Cape Canaveral is clear for launch.

All systems on the rocket and the Orbcomm OG2 satellites, along with weather, are GO for launch.

• 10th launch of a Falcon 9 rocket since 2010
• 15th launch of Falcon rocket family since 2006
• 9th Falcon 9 launch from Cape Canaveral
• 5th launch of a Falcon 9 v1.1 rocket
• 4th Falcon 9 v1.1 launch from Cape Canaveral
• 7th Falcon 9 day launch
• 3rd Falcon 9 launch of 2014
• 8th launch from Cape Canaveral in 2014

Keep up with the launch sequence with this timeline of key events during the Falcon 9's ascent to orbit.

The six 375-pound Orbcomm OG2 satellites will launch into one of four orbital planes occupied by Orbcomm's communications satellites. It will join 25 operational first-generation Orbcomm satellites, plus a pair of small ship-tracking spacecraft operated by Orbcomm.

Built by Sierra Nevada Corp., the satellites are designed for a 10-year lifetime. Eleven more OG2 second-generation satellites are set for launch on another Falcon 9 rocket before the end of 2014.

Orbcomm's 889,000 subscribers use the satellites to relay status updates, location pings, commands and other data between trucks, ships, rail cars, oil and gas infrastructure, weather buoys and other assets and their owners.

Orbcomm says the new constellation of satellites is fully compatible with existing ground terminals. Orbcomm developed a new modem with the same interface as a legacy modem to be plugged into customers' hardware.

The satellites will deploy in a pre-programmed sequence beginning about 15 minutes after liftoff and ending at approximately T+plus 35 minutes.

The first opportunity to check the health of all six satellites comes about 90 minutes after launch during a pass over a ground station in California.

Weather balloons are being launched throughout the countdown to monitor winds aloft.

If you are heading out to the beach or Port Canaveral to watch the launch, sign up for our Twitter feed to get occasional countdown updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

We expect to receive confirmation of separation of the satellites later today.

The rocket is nearly full of super-cold liquid oxygen and kerosene propellants. Both stages are being replenished with cryogenic oxidizer until the final minutes of the countdown to replace propellant that gradually boils off due to the warm ambient temperatures in Florida.

Forecasters predict a 60 percent chance of favorable weather during the launch window this morning, with cumulus clouds, anvil clouds and lightning continuing to be the major threats as showers and storms are expected to pop up over over Florida's Space Coast.

The weather outlook worsens later in the morning at Cape Canaveral, with a 50 percent chance conditions at the new launch time will violate a weather rule. Cumulus clouds, anvil clouds and lightning are the biggest weather threats.

Conditions at launch time are expected to be mostly cloudy with isolated thunderstorms. Winds will be out of the southeast at 10 to 15 mph, and temperature is expected to be 88 degrees Fahrenheit.

The second Falcon 9 launch on Dec. 8, 2010, sent SpaceX's first Dragon capsule into space on a two-orbit test flight for SpaceX's commercial cargo services to the space station. The December 2010 flight did not go to the space station, but it demonstrated Dragon's avionics and heat shield, culminating with splashdown in the Pacific Ocean.

SpaceX's next launch on May 22, 2012, launched the Dragon spacecraft on a NASA-sponsored test flight to the International Space Station. The 9-day Dragon mission delivered cargo to the space station and returned hardware from orbit with a splashdown in the Pacific Ocean on May 31.

On Oct. 7, 2012, SpaceX launched its fourth Falcon 9 rocket on the first operational Dragon resupply flight to the space station. The three-week mission delivered 882 pounds of cargo to the complex and returned to Earth on Oct. 28 with 1,673 pounds of equipment.

A Falcon 9 launch on March 1, 2013, put up another automated Dragon cargo craft en route to the space station with 1,869 pounds of supplies. It arrived at the outpost March 3 and stayed for 23 days before coming back to Earth with 2,668 pounds of return cargo.

The Falcon 9's first launch from Vandenberg Air Force Base in California occurred Sept. 29, 2013, and deployed Canada's Cassiope space weather research and communications demonstration satellite into polar orbit. The launch also marked the first flight of SpaceX's upgraded Falcon 9 v1.1 vehicle, which includes more powerful first stage engines, stretched fuel tanks and other changes.

SpaceX's first launch into geostationary transfer orbit occurred Dec. 3, 2013, with the SES 8 Ku-band and Ka-band direct-to-home broadcasting and network services to cover the Asia-Pacific region for SES of Luxembourg.

The Falcon 9 rocket launched again Jan. 6 with the Thaicom 6 telecom satellite to provide C-band and Ku-band communications services across Southeast Asia and Africa.

SpaceX's third operational cargo resupply flight to the space station lifted off April 18 on a Falcon 9 rocket, marking the first time the launcher flew with first stage landing legs in a bid to make the vehicle reusable. The Dragon spacecraft delivered supplies to the space station and returned to Earth a month later.

Today's mission was supposed to launch in early May, but issues with the rocket, spacecraft and weather conspired to delay the flight.

SpaceX encountered a helium leak during a preflight test in early May, triggering a month-long delay. Concerns with one of the Orbcomm satellites kept the mission grounded for an extra few days before SpaceX mounted its first launch attempt June 20.

The launch team aborted the June 20 countdown after detecting an unexpected drop in pressure in one the rocket's second stage propellant tanks. A source told Spaceflight Now the problem was traced to a valve in a liquid oxygen tank.

Another launch attempt June 21 was thwarted by lightning at Cape Canaveral, and SpaceX called off a planned liftoff June 22 to evaluate a steering actuator on the rocket's second stage engine.

SpaceX rescheduled the launch for July 14 to give ground crews time to resolve the issues that prevented liftoff in June. The slip to mid-July also allowed the U.S. Air Force to complete previously scheduled maintenance activities on the Eastern Range, which provides safety, tracking and communications services for all launches from Cape Canaveral.

The only concerns are with clouds and lightning over the launch site during the Falcon 9 rocket's launch window, which opens at 9:22 a.m. EDT (1322 GMT) and closes at approximately 11:55 a.m. EDT (1555 GMT).

Typical summertime afternoon thunderstorms along the East Coast sea breeze are expected Monday, but conditions should be acceptable in the morning.

"The morning launch window is favorable as weather will not begin to degrade until very late in the morning," Air Force meteorologists wrote in a forecast summary. "Therefore, the beginning of the window will have less chance of weather violations, with mostly a cumulus cloud rule concern and a threat of anvils from Atlantic Gulf Stream thunderstorms. By the end of the window, thunderstorm development is possible and with it a lightning rule violation concern."

Conditions at launch time are predicted to be partly cloudy with scattered clouds at 3,000 feet and 22,000 feet with isolated showers. Winds will be from the south at 10 to 15 mph, with a temperature of 82 degrees Fahrenheit.

Fueling of the 22-story Falcon 9 rocket with kerosene and liquid oxygen propellants should begin around 5:30 a.m. EDT (0930 GMT) Monday.

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According to Orbcomm, the schedule gives engineers time to resolve the issues that prevented liftoff last weekend and allows the U.S. Air Force to complete previously scheduled maintenance activities on the Eastern Range, which provides safety, tracking and communications services for all launches from Cape Canaveral.

The six 375-pound satellites on the Falcon 9 rocket will orbit 466 miles above Earth, starting the deployment of Orbcomm's second-generation, or OG2, constellation. Eleven more OG2 satellite are due for launch before the end of the year on another Falcon 9 rocket.

The 17 second-generation satellites will join Orbcomm's 25 operational first-generation spacecraft in orbit, plus two more satellites used by Orbcomm to monitor maritime traffic.

The satellites help Orbcomm clients track ships, trucks, cargo containers, remote oil and gas infrastructure, weather buoys, research stations and other assets.

"We are now targeting Monday, July 14th with Tuesday, July 15th as a back-up for launch of Orbcomm's OG2 Mission 1 pending approval from the Air Force Range," Orbcomm wrote in an update on the company's website.

"This provides the necessary time to ensure the highest possible mission assurance and allows the Range to complete their previously scheduled maintenance," the update said. "The OG2 payload and Falcon 9 launch vehicle are in good condition, and engineering teams are moving forward with the necessary steps to prepare for launch."

Weather and technical problems last weekend prevented liftoff of the 22-story Falcon 9 rocket on three consecutive launch attempts.

A countdown on June 20 was scrubbed to fix a problem with the rocket's second stage liquid oxygen pressurization system, then lightning thwarted another try June 21.

Engineers called off a launch attempt June 22 after encountering an issue with an actuator on the rocket's second stage engine steering system.

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"Today's Orbcomm launch attempt has been scrubbed to address a potential concern identified during pre-flight checks. The vehicle and payload are in good condition, and engineering teams will take the extra time to ensure the highest possible level of mission assurance prior to flight. The rocket will remain vertical on the launch pad with the next available launch opportunity targeting Tuesday, June 24th."

The forecast predicts an 80 percent chance conditions will violate one of the weather rules for liftoff today, with widespread showers and thunderstorms expected over the Space Coast.

The outlook calls for broken clouds at 2,500 feet, 10,000 feet and 30,000 feet, southeast winds at 12 to 16 mph, and a temperature of 84 degrees Fahrenheit at launch time.

"Showers and thunderstorms will form on the sea breeze in the early afternoon and, with southwesterly flow [and] stay near the Cape through the afternoon," the Air Force weather team wrote in a forecast synopsis. "Conditions will gradually improve near sunset and through the evening hours. The primary concerns are cumulus clouds, lightning, anvil clouds and high electric fields within the window. With conditions not appearing to change through mid-week, similar weather concerns will persist for a few days."

"Today's OG2 Mission 1 launch attempt has been scrubbed due to weather concerns. Both Falcon 9 and the Orbcomm satellites are safe. We are targeting launch for tomorrow, Sunday, June 22 at 5:30 pm ET. We will continue to post updates as we get closer to launch."

"Today's ORBCOMM launch attempt has been scrubbed due to weather. Currently reviewing next available launch opportunities."

Orbcomm CEO Marc Eisenberg says the countdown was scrubbed after a nearby lightning strike at T-minus 18 minutes, violating a launch weather rule.

"We've actually been ready to move away from the webcasts for awhile," she wrote in an email to Spaceflight Now. "It takes a lot of resources but the main reason is these launches are becoming more routine and the full webcast isn't really appropriate anymore."

The launch window extends to 6:39 p.m. EDT (2239 GMT).

Kerosene and liquid oxygen are being pumped aboard the two-stage Falcon 9 rocket. Both stages burn the mix of liquid propellants to fuel 10 Merlin 1D engines.

If you are heading out to the beach or Port Canaveral to watch the launch, sign up for our Twitter feed to get occasional countdown updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

Fueling of the two-stage rocket should begin around 2 p.m. EDT (1800 GMT).

Read our full story.

All systems on the rocket and the Orbcomm OG2 satellites, along with weather, are GO for launch.