SpaceX hoisted the first Falcon 9 rocket atop its Cape Canaveral launch pad on Saturday, beginning several days of compatibility checks to be punctuated by a dramatic ground-shaking engine test next week.

Pulled by an aircraft tug normally found on airport tarmacs, the rocket and its transporter rolled 600 feet along rail tracks from the steel assembly hangar to the launch pad at Complex 40 on Friday.

The Falcon 9 rocket is put together inside a hangar at Complex 40 in early February. Credit: SpaceX

After emerging from the hangar Friday, the 15-story rocket was rotated vertical around midday Saturday.

A small team of technicians began methodically hooking up the transporter to the launch pad. The transporter also functions as the mechanism to lift the rocket vertical and service the Falcon 9 and payload.

A practice countdown and engine test will follow next week, if engineers can work through the expected kinks common to new launch vehicles.

"We're going to do a couple of quick pad checks with the rocket to pick out any high-risk items so we don't have to find them on wet dress [rehearsal] day," said Tim Buzza, SpaceX's vice president of launch operations.

Buzza will serve as the launch director for the Falcon 9's first launch, which is now scheduled for no sooner than March 22, according to company leaders.

But Elon Musk, SpaceX's wealthy founder and chief architect, is reticent to discuss specific launch dates.

"I've only talked about a date range of March-May," Musk wrote in an e-mail to Spaceflight Now. "It is not possible to get more accurate than that due to the unknown unknowns surrounding a new vehicle development. What I want to avoid are a series of articles citing schedule slips when the schedule was never a firm date to begin with. The Range date is just a placeholder for the earliest possible countdown attempt."

Other rockets, including secret military launches, routinely announce target dates months in advance. But Musk is closely guarding official launch dates and times for SpaceX.

"I'd rather not specify an exact day and definitely not a time," Musk wrote. "That would imply greater predictive ability than is possible."

In all likelihood, Musk said, launch would probably not occur until late April or May.

"People should not think that the rocket is going to launch on whatever the first countdown day is," Musk said in an interview last month. "They shouldn't think of any day that we have planned as launch day, but it is simply an aspiration for the first day that we will try to do a countdown."

Friday's rollout was the first time a flight-ready Falcon 9 rocket reached the seaside launch pad, which is situated between the homes of the expendable Atlas 5 and Delta 4 vehicles.

Working in a control center near Cape Canaveral Air Force Station's south gate, the launch team plans to flow kerosene and liquid oxygen propellants into the Falcon 9 at the beginning of the week.

About 29 people will be on console inside the launch control center during the final countdown. More than 100 engineers are involved in the first launch, including technicians and support crews.

Both stages of the Falcon 9 burn the same propellant, simplifying equipment on the rocket and on the ground.

Engineers will load nearly 39,000 gallons of super cold liquid oxygen and almost 25,000 gallons of kerosene fuel into the first stage tanks. About 7,300 gallons of liquid oxygen and 4,600 gallons of kerosene will go into the second stage.

The tanking exercise will be as much practice for the launch team as a test of the rocket, according to Buzza.

The rehearsal's "primary purpose is the ground system's interaction with the rocket, whether it be propellants, helium, or nitrogen, and then it's getting the timeline cadence down," Buzza said.

"I'm sure for the first wet dress rehearsal and the static fire, it's going to be broken up where we start and stop and start and stop," Buzza said. "It's going to be a long day since we don't have a [launch time] to worry about."

"Our goal is not to stay on the timeline, it's to get the cadence down and talk about what we're doing. Once we're through that and figure out all the ground systems, we put all that behind us and figure out how we light the first stage," Buzza told Spaceflight Now.

The engine firing is currently scheduled for late in the week, if no serious problems arise during the tanking test. The rocket will stay on the pad between the countdown rehearsal and the static fire, if no problems are discovered requiring a rollback, according to SpaceX.

Artist's concept of the Falcon 9 and Dragon combo launching from Florida. Credit: SpaceX

The nine first stage engines will fire for about four seconds, enough time for computers to gauge their health and readiness for flight. The military-run Eastern Range, which oversees all launch operations at Cape Canaveral, will also be heavily involved with the engine test.

"That will be a combined operation with the [Eastern Range]," Buzza said. "We're planning to use it like a mission dress rehearsal. Both sides will get to practice everything. We're going to do static fire just like it's launch day, so we'll get the cadence between the two groups."

Friday and Saturday's milestones were the first steps in a series of key fit checks between the rocket, transporter and launch pad.

"It's horizontal when it rolls out," Buzza said. "The first thing we do is come up and engage with two pins on the trunnions, then we engage the hydraulic actuators. That's step 1 and step 2."

After the sleek white booster was lifted upright Saturday, engineers were expected to begin checking out mechanical, plumbing, electrical and communications interfaces between the launcher and ground facilities.

Workers must manually insert a total of six pins and connect five flanges between the transporter and infrastructure at Complex 40. Teams carefully line up the launch tower atop the concrete flame pit at the pad.

"When we first started developing this, my biggest worry was how do you take something this large and roll it out over and over, and just stick a pin in a hole like that," Buzza said.

Technicians will also hook up a panel of electrical, fluid and gas lines.

"When we do come out, we have to hook up about 16 electrical connectors and maybe 20 hoses," Buzza said. "Once all that's connected in, and we put the rest of the pins in, the thing goes up and we lock in the front two pins and hook up those last five [flange] connections and we're ready to go."

The flanges will link the rocket with ground storage tanks containing liquid oxygen, kerosene fuel, helium, gaserous nitrogen and the first stage ignitor source called triethylaluminum-triethylborane, better known as TEA-TAB.

SpaceX fashioned the transporter in 2008 to be ready for pathfinder tests with a Falcon 9 test vehicle in January 2009. Engineers beefed up the structure and added cables and fluid lines throughout 2009, culminating in a series of loads tests late in the year.

The Falcon 9 was already plugged into the transporter inside the Complex 40 hangar, a glorified steel building spanning 225 long and 75 feet wide at the southern perimeter of the pad.

Barring any problems, workers don't expect to tinker with rocket's plug-in ports when it is on the launch pad. Although Complex 40 was originally designed to launch the labor-intensive Titan 4 booster, SpaceX officials transformed the pad into a "plug and play" facility capable of being ready to launch the Falcon 9 with only a handful of connections, all of which are routed through the transporter.

SpaceX says the preparation paradigm is based on the Ukrainian Zenit rocket, which was built to automatically roll to the pad and launch in less than 90 minutes.

But those lofty goals are far in the future. For now, SpaceX is taking it slow.

The Falcon 9 rocket moved to the pad Friday stretches 154 feet long and 12 feet wide. Its payload will be a test article of the company's Dragon capsule being developed to carry equipment to the International Space Station for NASA.

The Dragon on the inaugural flight will stay attached to the second stage of the launcher after arriving in orbit.