NASA has postponed the launch of its first-ever probe to the sun due to a last-minute technical problem.

Saturday morning's launch at Cape Canaveral, Florida, was scrubbed a minute and 55 seconds before blast-off after a gaseous helium alarm went off.

NASA will try again early Sunday to launch the Delta IV rocket, which is carrying the Parker Solar Probe. The next launch window opens at 3:31 am (0731 UTC) on Sunday.

The probe's seven-year journey will bring it to within 6.16 million kilometers (3.83 million miles) of the sun's surface.

The probe is armed with a high-powered heat shield that is 11.43 centimeters (4.5 inches) thick. The shield is also built to sustain solar radiation levels 500 times greater than those that reach Earth.

The probe will fly into a region where temperatures exceed a million degrees Fahrenheit (555,000 degrees Celsius) but the sun is expected to heat the shield to a relatively modest 2,500 degrees Fahrenheit (1,370 degrees Celsius).

If everything goes according to plan, temperatures inside the spacecraft should be a mere 85 degrees Fahrenheit.

Nicky Fox, a project scientist at the Johns Hopkins University Applied Physics Lab, said: "The sun is full of mysteries."

Discovering solar winds

The Parker probe will have tools to measure the sun's expanding corona and its flowing atmosphere known as the solar wind, which was first discovered by solar physicist Eugene Parker in 1958.

Parker, now 91 and eager to watch the craft blast into space, said some people doubted his initial theory. But when NASA launched its Mariner 2 spacecraft bound for Venus in 1962, it became the first robotic probe to make a successful planetary encounter, and it verified Parker's theory.

"It was just a matter of sitting out the deniers for four years until the Venus Mariner 2 spacecraft showed that, by golly, there was a solar wind," Parker said earlier this week.

Parker described the Parker Solar Probe as a "a very complex machine," and said he was "impressed."

The probe's main goal will be to learn the secrets of the corona, the unusual atmosphere surrounding the sun.

The corona is not only 300 times hotter than the sun's surface but it also discharges powerful plasma and energetic particles that can unleash geomagnetic space storms that can wreak havoc on Earth by disrupting power grids.

NASA engineers are taking every precaution with the $1.5 billion (€1.3 billion) probe, which Thomas Zurbuchen, the head of NASA's science mission directorate, described as one of the space agency's most "strategically important missions."

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bik/jm (AP, AFP, dpa)