Recently, SpaceX’s crew demo mission was scrubbed due to bad weather. And this is not uncommon. Dozens of times, rocket launches get postponed due to bad/unfavorable weather conditions. So why weather conditions matter so much before rocket launches?
Firstly, let’s answer these two questions:
Why don’t we make a launch vehicle that can tolerate any type of weather condition?
Yes, we can make such a vehicle that is resistant to thunderstorms and high winds; but then it would be too heavy to get the vehicle off the ground.
In spaceflight– it’s a tradeoff between weight, and money, and the ability to get into orbit.
Why can’t we predict the weather beforehand?
Predicting weather accurately is still difficult. Launch dates are decided at least weeks or months in advance, and that’s too far for meteorologists to predict the weather conditions near launchpad at the exact moment of take-off, accurately.
So what can be done? The only option left is to prepare the launch vehicle for launch, check weather conditions just before the launch window, if the weather fits into criteria, 3.. 2.. 1… LIFTOFF!
And if the weather conditions don’t fit the criteria, the launch is postponed till the weather improves.
So what are these “criteria” that mission director checks before announcing a “go”?
NASA has set eight different criteria that describe when not to launch. So let’s look at them.
Thunderstorms and Lightning
This is one of the biggest concerns during space launches, which makes sense when we are trying to get a huge metal piece into the air. If lightning struck the craft, it can cause serious damage to sensitive electronics that astronauts need to pilot the shuttle, run life-support systems, and keep in touch with Earth.
Rockets sitting on the launch pad are safe from lightning due to lightning rods around the pad, but after liftoff, they are open to being struck.
“NASA won’t fuel a rocket if there’s greater than a 20 percent chance of a lightning strike within a five-mile radius of the launch site, and won’t launch if lightning is observed within 10 miles of the flight path. That radius also includes the presence of the cloud that produced the lightning.”
Clouds and rain
“Flying through a thin layer of clouds is generally harmless to the rocket, but if the cloud layer is greater than 4,500-feet-thick and extends into freezing temperatures, it can create issues that endanger the rocket’s safety.”
When rockets tear through them they can trigger a lightning strike, as happened during Apollo 12
The height, temperature, and type of clouds near the entire path of rocket matters
And any kind of precipitation is a complete NO-NO!
Wind
Determining if the winds near the ground are suitable for launch is rather easy. If weather observations near the launch pad reach or exceed 34 mph (30 knots), the launch will be scrubbed.
Wind shear is the change of wind speed with altitude, and if there is too much wind shear, it can be too much for the rocket to handle.
weather balloons launched hours before liftoff. All of that data is collected right up until the last few seconds before launch, when the cutoff to abort occurs.
Temperature
Too cold temperature on the night before launch can cause the mission to be scrubbed. Both, upper and lower limits are set.
The 24-hour average temperature should not be less than 5 degrees celsius (41 degrees Fahrenheit). Also, the temperature should not exceed 37 degrees celsius (99 degrees Fahrenheit ) for consecutive 30 minutes.”
And that’s not even taking into account space weather. That’s a whole different story.
That’s so tough criteria to get the perfect launch window, right? That’s why it is said” SPACE is hard”
Better safe than sorry!
Launch delays come at an expensive cost. “Every Space Shuttle launch cancelation after fuel taking had begun cost somewhere around $1.2 million—half a million in fuel losses, and another $700,000 to pay for the extra labor needed to set up an additional launch.” – popsci
But it’s much cheaper price to pay compared to the losses created by months of delays due to a rocket explosion.