At the Mercy of Florida’s Weather
Credit: SpaceX

At the Mercy of Florida’s Weather

29/05/2020Written by Sophie Allan

Why does the weather play such an important role in rocket launches?

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On Wednesday 27th May, the National Space Centre, along with millions of others across the planet were glued to their internet streams in anticipation of the historic Nasa/SpaceX CrewDragon launch. This would have been the first time in nearly a decade that two NASA astronauts, Doug Hurley and Bob Behnken, would launch to the international space station from US soil – and officially marking a new era of competitive commercial human spaceflight.

We were treated to a feast of shots of the stylish, futuristic interior of the crew cabin, and many space nerds of my age, were overjoyed to see the return of the iconic ‘NASA worm’. But with 16 minutes to go to launch, the final weather report came in. Some readings were still red, and while the Falcon rocket may have been able to launch with an additional 10 minutes, the mission had to be scrubbed for the day with the next attempt to be made on Saturday 29th May.

So why does the weather play such an important role in rocket launches? And why does the falcon rocket have to launch at such a specific time?

Sending rockets into space is hard. Gravity and air resistance is a tough thing to beat, and when you have thousands of individual mechanical and electrical systems needing to work flawlessly, you want to give your rocket the best chance possible of having a trouble free lift-off. This is especially important when that rocket is carrying the most precious cargo possible at the top – humans.

On launch day, many variables must be considered. The 45th wing of the Space Force (the US military space department) will carefully monitor the weather, taking many readings from planes and stations not only at the launch site at Kennedy Space Centre itself, but also many kilometres down range. Factors like ground and upper atmosphere wind speed, wind direction, temperature, humidity, cloud type and cover, precipitation and more are all carefully considered, and must sit within certain pre-determined ‘launch commit criteria’ before a rocket can be given a go for launch. Some of these factors are set by the rocket operators and are specific to the unique systems of their rocket. Others, known as range safety requirements, are put in place by Kennedy to protect staff and the public who may be viewing, or under the path of the rocket on land, sea and air.

Lightning strikes a Russian Soyux rocket carrying a satellite. (Source: Spaceflight now)

This NASA page details the specific launch criteria for the Falcon 9 rocket that will carries the Dragon capsule.

The big problem on Wednesday was with the possibility of lightning. The shape and speed of rockets means that they can actually trigger lightning if passing through a sufficiently charged cloud layer – and this could affect or even break some of the delicate electronics on board.

And it is not just the land and atmospheric conditions that need to be considered. Should anything go wrong with the launch, the rocket has a Launch Escape System – the dragon capsule can detach from the top of the rocket and, powered by a set of Draco rockets, can be boosted up to a mile away from the rocket before deploying it’s parachutes. And the likely landing point for this capsule is in the ocean. Waves higher than 4 metres can flip the capsule in the water, so sea conditions at a range of possible abort sites must be considered.

This might all seem like a bit of overkill, but weather has played a disastrous role in previous missions. During Apollo 12’s launch, the Saturn V was hit twice by lightning shortly after launch damaging a number of critical systems which thankfully excluded the flight computer. In 1987 an Atlas Centaur rocket exploded after triggering lightning 49 seconds into its flight. And, tragically, extremely cold launchpad conditions caused the failure of the primary and secondary O rings on the right-hand solid rocket booster of the shuttle, causing a catastrophic failure 73 seconds into launch result in the loss of all crew members.

Credit: SpaceX

But why couldn’t they wait an extra ten minutes? In the coverage, the weather report states that things might be looking better ‘if you can give us an extra ten minutes’. Unfortunately, this historic demonstration launch has an ‘instantaneous launch window’. That is, once fuelling starts, launch time is set. During the live stream, SpaceX principal integration engineer John Insprucker said:

“We do the flight analysis assuming that the temperatures of the propellants are below a certain amount, so that we know how much performance is available to the rocket — how much margin we’re going to have. Once you get into propellant loading at T-35 minutes, you have to go as soon as you get to zero.”

So, what do the 45th Wing of the Space Force have to say about Saturday’s launch? Currently they are saying there is a 60% chance of not launching, but this can change very quickly and in truth, we really won’t know until about 16 minutes before zero time. If it gets scrubbed again, there is another window on Sunday, but we may be looking at an early June launch. The National Space Centre will be keeping everything crossed that the weather allows a flawless launch, and we invite you to join us from 8pm UK time on our Facebook page to watch the stream with live commentary from Professor Anu Ojha, Director of the National Space Academy and a Q and A following the stream.

Please note: This event is entirely free and is hosted just on our Facebook page. Please do NOT click on any links directing you to another site, asking for money or data.