Due to bad weather, SpaceX and NASA, the US space exploration technology company, have postponed their first manned space launch, scheduled for May 27, local time, at 3:22 p.m. local time on May 30 (3:22 a.m. Beijing time on Sunday, May 31). So how does SpaceX determine the time of the relaunch? This depends largely on physical factors.
Author . . . Little
Produced . . . NetEase Technology “Know No” column group
Typically, successful docking of a spacecraft into a predetermined Earth orbit and attempting to dock it with the International Space Station in orbit is like an unusually delicate two-person dance that requires precise time and angle calculations. To do this, spacecraft need to be launched within a specific time frame (or launch window) on a specific date.
The most visible orbiting reference for space launches is usually the moon. In the Apollo era, the key was not the position of the moon in the sky at the time of launch, but where the moon would be three days after launch, when the spacecraft had already flown across the distance between The Earth and the Moon. Since the moon orbits the Earth at 3,683 kilometers per hour, this requires careful calculations.
Reaching near the moon alone is not enough, but there are more difficult challenges: After a 386,000-kilometer flight, the astronauts are aiming to enter a lunar orbit just 97 kilometers from the moon’s surface. It’s like standing at one end of a football field aiming at an apple at the other end, trying to peel the apple with a bullet.
The Apollo astronauts also tried to reach the moon under the best lighting conditions for landing, when the sun was at the right angle in the lunar sky and could cast shadows that highlighted but did not exaggerate the topographical differences. This further narrows the launch window. Coupled with rain or cloudy weather during launch, the limit softens even greater.
By contrast, it is relatively simple to enter Earth’s orbit alone, but the problem of launch windows is also a headache. Spacecraft usually do not orbit the Earth’s equator in perfect orbit. Instead, they are emitted into orbits tilted relative to the equator. Cape Canaveral is located at a latitude of about 28 degrees north latitude, so the spacecraft launched from the Kennedy Space Center needs to fly at the same tilt, like a twisted hula hoop, which moves up and down 28 degrees above the equator as it orbits the Earth.
Complicating matters even more is that the Earth itself tilts 23 degrees, and although it takes 24 hours to spin around for a week, the spacecraft takes only 90 minutes to orbit it. The result: On the floor plan, the spacecraft looks like it’s drawing a sine wave pattern, moving up and down the equator, never passing through the same point on the ground in two consecutive orbits. The International Space Station’s orbital tilt is higher, reaching 51.6 degrees, a concession by the United States to Russia to launch spacecraft further north from the Baikonur launch site in Kazakhstan.
Planners who send astronauts to the International Space Station must accurately schedule the launch time so that the station is in its optimal position, minimizing the time the spacecraft spends chasing the station for more accurate docking. Unmanned cargo ships launched from Baikonur to the space station may have a relatively ample launch window, which can dock with the station in two days.
But the goods will not be because of discomfort and bitter days, people are different. Manned missions usually have narrower launch windows that allow astronauts to catch up with the International Space Station in four orbital cycles (i.e. six hours) to free them from spacecraft constraints as soon as possible.
For Bob Behnken and Doug Hurley, launching from Cape Canaveral at 28 degrees north latitude to the International Space Station at an inclination of 51.6 degrees means a relatively long 19-hour chase. But if they choose the wrong launch window, it will take longer.
Due to the weather conditions, the first manned launch window of the manned Dragon spacecraft was closed on May 27, and SpaceX subsequently set a new launch time. If Sunday’s launch fails again, they can make a third attempt at 3 p.m. local time the next day.