- SpaceX and NASA launched their Crew-1 mission on Sunday: the longest and most ambitious US space flight to date.
- Bad weather near the launch site or other delays at the time of the planned launch would cause mission leaders to cancel an attempt; SpaceX’s Falcon 9 rocket can’t wait another second.
- The Falcon 9’s super-cold fuel heats up and leaks out while sitting on the launch pad. This causes the machine to have less room for error when sending people into orbit.
- When the Crew Dragon spacecraft is on top with passengers inside, the rocket must take off 35 minutes after loading begins. It must also be aligned with the International Space Station flying overhead.
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SpaceX on Sunday night launched the most ambitious mission of the NASA crew so far: a flight of four astronauts to the International Space Station.
All day on Sunday, rain and clouds closed on the launch pad and threatened to force SpaceX to delay takeoff until Wednesday. Forecasters estimate a 50 percent chance that weather near the launch site at the Kennedy Space Center in Cape Canaveral, Florida, will violate takeoff requirements.
“Rain in the field, thick clouds and possibly static electricity at ground level could be a problem,” SpaceX engineer John Insprucker said during a live broadcast of NASA’s preparations for Sunday afternoon’s launch.
If anything had interfered with plans for the exact launch time, which was about 15 seconds after 7:27 p.m. ET, the mission managers would have cleared the experience and tried again the next day. Fortunately, the sky cleared before the time came and the spaceship, called Sustainability, roared into orbit.
Such a sensitive launch window is called “instantaneous” and exists because of the rocket’s design, NASA’s safety requirements, and the ISS’s trajectory above Earth.
As early as May, with SpaceX’s first attempt to launch humans into space – a mission called Demo-2 – the puffy clouds had to break flight rules at the time of launch, triggering friction.
“Everything looked our way, except for Mother Nature: the weather,” Insprucker said in a live broadcast of the first attempt to launch Demo-2.
With Crew-1, ground winds delayed the first launch attempt on Saturday. The SpaceX failed to enter the Falcon 9 launch vehicle position to land on it after separating from the upper stage and the Crew Dragon.
That’s why launching a SpaceX with a crew can’t wait a second longer after it has to take off.
The dual problems of ultra-cold fuel and lab moving at 17,500 mph
Once SpaceX starts loading the Falcon 9 rocket, it begins a process in which an inaccurate moment can mean life or death.
“Once you get refueling at T-minus-35 minutes, you should leave as soon as you reach zero,” Insprucker said in May before the first attempt to fly the Demo-2. “We can’t stop the countdown, wait 5 minutes.”
This is because liquid oxygen is pumped into the Falcon 9 at a very low temperature: 340 degrees Fahrenheit below zero. This keeps it fluid and seals the fuel, a type of kerosene called RP-1, which allows SpaceX to cram more of it into the rocket and squeeze more performance if the machine.
In fact, that’s part of what gives the Falcon 9 its unprecedented thrust – the power behind its launch that allows it to push more than 50,000 pounds of cargo into orbit. Additional reserves also provide more room to swing to reach orbit and for SpaceX to land and recycle a rocket booster – the largest and most expensive part of the Falcon 9.
Once in the rocket, the fuel begins to heat up, expand and boil. This fuel loss starts to run out of the start clock.
“It changes how much efficiency you put into orbit, and we don’t want to limit those fields,” Insprucker said.
In essence, each additional time the rocket is fully loaded on the launch pad increases the risk of dangerous damage – a risk that is not worth taking when there are people on board.
So Falcon 9 should start exactly at the planned second. If it misses this short satellite window, Insprucker explained, the rocket could be separated from its fuel and later refueled with fresh fuel and cold liquid oxygen. The whole process takes about an hour and a half.
But this is not an option for missions to the ISS, a football-sized laboratory that flies above the ground on a winding path (due to its slope) and at a speed of 17,500 mph.
“In the case of the International Space Station, in an hour and a half, we don’t have to be anywhere to get into orbit,” Insprucker said. After all, we can all look at Isaac Newton and Johannes Kepler for orbital dynamics, which tells us “when will we start? “It simply came to our notice then. “
This story has been updated with new information. It was originally published at 1:51 PM ET on May 30, 2020.
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