NASA, SpaceX Delay Demo-2 Mission: Why Weather Matters For Launches

NASA and SpaceX's Demo-2 mission was scrubbed Wednesday just minutes before lift-off because of unfavorable weather conditions. Even though weather sounds like a simple factor, launching in less than ideal conditions can have catastrophic outcomes.

Astronauts Robert Behnken and Douglas Hurley were already strapped inside the Crew Dragon when the Demo-2 mission was scrubbed just about 20 minutes before the launch. In a tweet, NASA explained the "vehicles are healthy" but the weather was something they cannot control.

Among other factors, officials cited the threat of lightning as one of the reasons. As of now, the mission, dubbed "Launch America," has been rescheduled for 3:22 p.m. ET on Saturday (May 30).

"It was a great day for NASA, it was a great day for SpaceX. I think our teams worked together in a really impressive way, making good decisions all along." NASA Administrator Jim Bridenstine said.

There are many factors that can cause a mission launch to be scrubbed due to the weather; the Falcon 9 Crew Dragon Launch Weather Criteria listed a few on Twitter.

But why is weather so important to launches? A NASA Spaceflight blog on May 24, just days before the initial schedule for the launch, explained why it's important to adhere to weather rules, which consider factors such as wind direction, temperature, humidity, cloud coverage and precipitation.

In Jan. 28, 1986, for instance, the Shuttle Challenger launched in near-freezing temperatures that were 20 degrees Fahrenheit colder than the Solid Rocket Boosters' limit.

"The cold temperatures caused the failure of the primary and secondary O-Ring seals on the aft field joint of Challenger's right-hand Solid Rocket Booster. The failure method caused a temporary seal to form as O-ring material became jammed in the hole," the NASA blog explained. "This temporary seal was shattered when Challenger encountered the most-intense upper-level windshear ever for a Shuttle (even through to the end of the program)."

The Space Shuttle Challenger broke apart just 73 seconds into the flight, killing all seven crew members.

In another case, during Apollo 12, the Saturn V was struck by lightning twice during the first minute of flight, causing several critical flight systems to fail. In this case, however, the systems were fortunately restored and the mission eventually made a successful lunar landing and returned to Earth.

At the time, there were no lightnings anywhere around the launch pad but the rocket basically acted like a giant conductor when it launched through the atmosphere. As such, it triggered a lightning strike even if the natural conditions for one were not present.

Because of the event, there are now lightning rules against launching within a certain distance from cumulus clouds or thick clouds, even if there was no lightning in the launch area.

These are just examples of the ways that certain weather conditions may possibly interfere with launches, but they are essential to keeping the people involved in the launch safe, even if the cause of the delay sometimes seems minimal.

"Yes, a launch delayed because of weather is disappointing and can often be confusing as everything can appear perfect," the blog said. "But these rules are in place to protect not just the vehicle, but all launch personnel, cargo, spectators, and, of course, the astronauts."