Because a SpaceX rocket powered by astronauts can’t wait for bad weather

• SpaceX and NASA launched their Crew-1 mission on Sunday – the longest and most ambitious US human spaceflight ever.
• Bad weather near the launch pad, or any other delay, at the time of the planned launch, would have caused mission leaders to cancel an attempt – SpaceX’s Falcon 9 rocket can’t wait another second.
• The need for an “instant” launch window is due to physics: every time a spaceship has to reach the International Space Station, it has to launch itself as the gigantic structure flies overhead.
• The Falcon 9’s ultra-cool fuel also heats up and vents when on the launch pad. This causes the rocket to have a lower margin for error, which does not help recover expensive boosters or send people into orbit.
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SpaceX on Sunday night launched NASA’s most ambitious manned mission – flying four astronauts to the International Space Station for a six-month stay.

Called Crew-1, the mission transports NASA’s Mike Hopkins, Victor Glover, and Shannon Walker, as well as Japan Aerospace Exploration Agency’s Soichi Noguchi, inside a Crew Dragon spaceship. The close-knit group hopes to stay on the space station for six months. If crew members are successful, their mission will break the U.S. record for the longest human spaceflight.

All day Sunday, rain and clouds approached the launch pad and threatened to force SpaceX to delay takeoff until Wednesday. Meteorologists have calculated a 50% chance that the weather near the Kennedy Space Center launch site in Cape Canaveral, Florida, would violate the requirements for takeoff.

“Rain on the flight path, thick clouds, and possibly ground-level static electricity could be an issue,” said John Insprucker, a SpaceX engineer, during NASA’s live stream of preparations for launch Sunday afternoon. .

If anything interfered with the plans for the exact launch time, which was about 15 seconds after 7:27 PM ET, the mission leaders would cancel the attempt and try again another day. Fortunately, the sky cleared before the time came and the spaceship, called Resilience, roared into orbit.

Joel Kowsky / NASA

Such a sensitive launch window is called “snapshot” and exists due to the trajectory of the International Space Station on Earth. Additionally, SpaceX’s desire to recover expensive rockets and improve launch safety underlines the sensitivity of launch times.

During SpaceX’s first attempt in May to launch people into space – a mission called Demo-2 – the puffy clouds were meant to break flight rules upon launch, triggering a scrub. “Everything was looking in our direction except mother nature: time,” Insprucker said in the live stream of the first Demo-2 launch attempt.

With Crew-1, Saturday’s onshore winds forced the first launch attempt to be delayed. A SpaceX boat was unable to get into position for the Falcon 9 rocket landing after separating from the upper tier and crew dragon.

That’s why a manned SpaceX launch cannot wait a single extra second after it should take off.

The double obstacles of a high-speed, ultra-cold fuel laboratory

Joe Skipper / Reuters

Once SpaceX begins powering a Falcon 9 rocket, it sets a rigorous series of events in motion.

“Once you get into the propellant loading at T-minus-35 minutes, you have to go as soon as you get to zero,” Insprucker said in May ahead of Demo-2’s first flight attempt. “We don’t have the ability to stop the countdown [and] wait five minutes. “

This is because liquid oxygen is pumped into the Falcon 9 at a very low temperature: minus 340 degrees Fahrenheit. This keeps it liquid and densifies the fuel, a type of kerosene called RP-1, which allows SpaceX to fill more of it into the rocket and squeeze more performance out of the car.

In fact, it’s part of what gives the Falcon 9 its unprecedented thrust, or launch force, and allows it to push more than 50,000 pounds of payload into space. The extra fuel reserves also allow SpaceX to land and recycle the rocket’s 16-story booster – the largest and most expensive part of the Falcon 9 – and have more wiggle room to bring a payload into orbit.

Once the fuel is inside the rocket, however, it begins to heat up, expand and evaporate. That fuel leak starts the launch clock.

“This changes the amount of performance you get from taking it into orbit and we don’t want to cut those margins,” Insprucker said.

SpaceX via NASA

Essentially, each time the rocket remains fully powered on the launch pad, the rocket’s capacity decreases.

Although it can be drained and subsequently refilled with fresh fuel and cold liquid oxygen and RP-1, Insprucker said, the whole process takes about 90 minutes.

This isn’t an option for missions headed to the space station, a soccer-field-sized laboratory that flies over the Earth’s surface on a tortuous path and at 17,500 mph – the Falcon 9 must be launched at exactly the scheduled second. If a spaceship on top of the rocket, whether full of cargo or astronauts, misses that short window, it won’t have the right trajectory to reach the ISS.

“In the case of the International Space Station, in an hour and a half, it’s nowhere where we need to be to enter orbit,” Insprucker said in May. “In the end we can all look to Isaac Newton and Johannes Kepler for the orbital dynamics that tell us, ‘When do we launch?’ This stopped us in the middle of a period of bad weather. “

This story has been updated to clarify the meaning of an instant launch window. It was originally released at 1:51 PM ET on May 30.

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