Story 6 of 7 · 5 min reading · 2–4 min exploring
Why did liftoff wait?
Sometimes a successful mission starts with deciding to wait.
From the archive · May 27–30, 2020
With about 17 minutes left before liftoff, weather stopped Demo-2’s launch attempt on May 27, 2020. Doug Hurley and Bob Behnken were already inside Crew Dragon. The countdown ended with the rocket still on the pad.
The left panel shows Crew Dragon on Falcon 9 beside the launch pad. A cloud represents a weather concern, and a pause symbol marks the decision to wait. The right panel shows the later launch. The cloud is a symbol, not a reconstruction of the exact conditions on May 27, 2020.
1 · May 27: the first attempt stops before liftoff.
2 · Teams check conditions for another attempt.
3 · May 30: Falcon 9 launches Crew Dragon with two astronauts.
Ready does not always mean go
For a launch to proceed, the rocket, spacecraft, ground equipment, flight area and weather all need to meet the rules at the same time. On May 27, the weather did not. NASA and SpaceX scrubbed Demo-2: they called off that day’s attempt.
Waiting can be disappointing for everyone who made time to watch. But ending an attempt before liftoff is a different event from a failed ascent. The vehicle can be prepared for a later opportunity.
FROM THE MISSION
Crew Demo-2 | Launch
Archived broadcast · Demo-2 launch · May 30, 2020
What to notice
Watch Falcon 9 climbing away from the pad on May 30. The earlier decision to wait and this successful departure belong to the same mission.
Video: SpaceX
Falcon 9 launches Crew Dragon with Bob Behnken and Doug Hurley aboard. This is the successful May 30 attempt, three days after weather stopped the May 27 countdown.
Original on SpaceX ↗ (opens in a new tab)Why not wait another hour?
A hold pauses a countdown. It may be planned for checks or called when something needs attention. Whether the countdown can resume depends on the issue and the time available.
A launch window is the opportunity to leave on a path that meets the mission’s needs. Earth rotates and destinations move. A flight to the International Space Station has to line up with that moving destination. Some opportunities are so brief that waiting another hour means waiting for another launch attempt.
Weather beyond the pad
A camera might show sunshine while conditions elsewhere are unsuitable. Winds change with altitude. Clouds matter along the flight path. A crewed flight must also consider weather in places where an emergency return could bring the astronauts down.
Read the label beside a launch-weather percentage: it may describe the chance the weather allows launch or the chance of breaking a weather rule. Neither is the chance of the whole mission succeeding or a forecast of the view from your home.
Three days later, a different ending
On May 30, 2020, Falcon 9 launched Hurley and Behnken in Crew Dragon Endeavour. Hurley was spacecraft commander; Behnken was joint operations commander. It was Crew Dragon’s first flight carrying people.
They reached the International Space Station and returned to Earth on August 2, 2020. The launch-day delay was one part of a mission that continued for more than two months.
Read the plan that exists now
NET means “no earlier than.” TBC means “to be confirmed”; TBD means “to be determined.” These labels tell you how definite the published plan is.
Read the date, time zone and status together. If an older saved version and a fresh update disagree, check the latest information before making plans.
Try it for yourself
What would you tell someone waiting?
Someone has made time to watch this launch. Read the two updates, then explain what has changed.
01
Earlier · teaching example
NET Friday, 8:00 p.m., local launch-site time.
02
Latest update · teaching example
Scrubbed. Next attempt to be confirmed.
Choose a mission in Today, then open its Launch Time section. Read the date, time zone and current status together. If no suitable launch is listed, the example above is complete on its own.
Read a launch’s current planThree things to remember
- A scrub ends an attempt; the mission may launch later.
- Weather matters at the pad and along the crew’s possible routes.
- Check the updated status and time before the next attempt.
Keep exploring
Launched May 30, 2020; returned August 2, 2020.
Keep the plume viewing call separate from launch-weather percentages.
Compare the rocket with the Crew Dragon spacecraft it carried.
More about the crew
NASA · Published
VP Awards Former NASA Astronauts Congressional Space Medal of Honor
Doug Hurley and Bob Behnken received the Congressional Space Medal of Honor on January 31, 2023. The award recognized their bravery on Demo-2, the first crewed test flight of SpaceX’s Crew Dragon.
Open mission and related coverage