Cape Canaveral - A SpaceX Falcon 9 aborted its launch May 19 moments after its engines ignited when computers detected higher pressure readings than allowed. The center engine pressure built above limits and a shutdown occurred one-half second before liftoff, SpaceX officials said.

The next launch attempt could come as early as Tuesday, May 22, but that determination won't be made until the engine itself is inspected, said Gwynne Shotwell, president of Space Exploration Technologies of Hawthorne, Calif., known as SpaceX. There also is an opportunity May 23.

"We had a nominal ignition for all nine (engines)," Shotwell said. "Engine 5 started fine and (its chamber pressure) started trending high."

She said the high pressure could be the result of high temperatures possibly from too little fuel flowing into the engine, though it is too early to know for sure. "We're going to have to spend more time looking at the data."

The rocket was poised on Space Launch Complex-40 at Cape Canaveral Air Force Station, Fla., Saturday morning for the attempt. Its hangar is next to the launch pad. Shotwell said the company is prepared to take the engine out of the rocket if it needs to and put in an engine already at the Cape.

The goal of the mission is to launch a SpaceX Dragon capsule to the International Space Station to demonstrate cargo delivery using privately built spacecraft. It will be a landmark accomplishment because no privately constructed spacecraft has docked with the orbiting laboratory.

NASA is working closely with SpaceX under the provisions of the Commercial Orbital Transportation Services contract.

"We're ready to support when SpaceX is ready to go," said Alan Lindenmoyer, NASA's manager of the Commercial Crew and Cargo Program.

Falcon 9 fires her engines only to shut down seconds later. Photo Credit: NASA

 Meals, Equipment Top Cargo List for Dragon

The Dragon spacecraft built by SpaceX will head to the International Space Station with about 1,200 pounds of cargo during its demonstration mission, including commemorative patches and pins, 162 meals and a collection of student experiments.

Since the company's rocket and spacecraft are conducting a test flight, the manifest attests to important goods for the station's crew of astronauts and cosmonauts, but not mission-critical items.

A successful flight, due to liftoff from Cape Canaveral Air Force Station, Fla.,at 4:55 a.m. EDT on May 19, is expected to lead to regular cargo missions that will carry a wider range of goods to the orbiting laboratory. Hawthorne, Calif.-based SpaceX, formally known as Space Exploration Technologies, is also deep into the work required to make Dragon suitable to carry people into orbit.

The mission is a landmark because it is the first time a privately built spacecraft will head to the International Space Station. The flight, which includes no crew members other than those already on the station who will guide Dragon's arrival, carries enormous challenges and involves numerous individual evaluations.

Most of the cargo's weight, 674 pounds, is in food and crew provisions, including the meals, crew clothing and batteries and other pantry items. A laptop and its accompanying accessories will also make the journey.

Tucked inside the Dragon capsule are two NanoRacks dedicated to student experiments that will study a range of microgravity-related areas from microbial growth to water purification.

The mission calls for the 18-foot-high Dragon to approach the station after its sensors and navigation systems are checked out thoroughly. The spacecraft will go through numerous tests during the third day of the flight as it passes within about 1.5 miles of the station. Communications networks from the spacecraft to the station will be evaluated during this phase, too.

On the fourth day of the mission, the spacecraft will perform a methodical approach to the space station. It will first fly around the station at more than 6.2 miles and then fly under it no closer than 1.6 miles. With navigation units on the spacecraft and station relaying information, the Dragon will approach slowly from beneath the station, pausing at several stages as systems are continually checked.

The crew aboard the space station will take command of Dragon briefly to test the capsule's ability to retreat from the station. The spacecraft will later move to a position about 700 feet from the station so controllers can determine whether it is safe to allow a closer rendezvous.

Assuming a "go" is given, the Dragon will close to within 98 feet of the station and pause again. The next step will bring Dragon to about 32 feet from the station, within reach of the robotic arm. Expedition 31 crewmember Don Pettit will steer the arm to latch onto the cargo craft and connect it to the Harmony module.

The station crew will unpack the Dragon during the next two weeks and load Dragon with more than 1,400 pounds of used scientific and spacewalking gear. Dragon will then be removed from the station by the arm and released to fly back to Earth.

Unlike the other cargo vehicles that resupply the station, the SpaceX craft is designed to return to Earth safely instead of burning up in the atmosphere. That means experiments and other equipment can be stowed inside the capsule and returned to scientists.

SpaceX and Orbital Sciences Corp. are conducting demonstration missions under NASA's Commercial Orbital Transportation Services contract, known as COTS.