This is the key test before astronauts get on board
SpaceX, along with Boeing, have been hired by NASA for its commercial crew program to build capsules and rockets to carry astronauts to orbit. This is a change from the past when NASA built and operated its own vehicles, like the space shuttles and the Saturn 5 rocket during the Apollo moon landings.
Sunday’s launch is a test of what is known as the in-flight abort system, and aims to verify that the capsule can whisk astronauts away safely from an exploding rocket. It is the last major milestone for SpaceX before NASA permits its astronauts on board.
How to watch the launch and when
Although the launch window opened at 8 a.m. Eastern time on Sunday, the flight time has been pushed back a few times because of weather concerns. The most recently announced launch time is 10:30 a.m.
The rocket can launch until 2 p.m. Eastern time. SpaceX is waiting for waves to subside in the ocean. However, a storm is approaching the launch site, and lightning could become an issue after noon.
The test had been planned for Saturday morning, but rough seas and high winds in the Atlantic where the capsule will splash down led a postponement.
NASA Television is to begin coverage of the test 20 minutes before liftoff.
SpaceX has another opportunity on Monday. The weather remains dicey on both Sunday and Monday, with at least a 50 percent chance of unfavorable conditions at the launchpad. But the ocean is expected to be calmer than it was on Saturday.
A test designed to go wrong
For veteran space watchers, almost every rocket launch is filled with nerve-racking worry that something will go wrong. Failures in the history of spaceflight have destroyed expensive payloads or have ended tragically, as in the case of the space shuttle Challenger in 1986, when the seven astronauts aboard were killed.
Sunday’s launch, of a SpaceX Falcon 9 rocket with a Crew Dragon capsule on top, is one of the few times you can look forward with anticipation to destruction — that, hopefully, will conclude successfully.
It will be over quickly.
About 84 seconds after liftoff, the rocket will be approximately 12 miles in the air, speeding at 1,200 miles per hour. The nine engines of the booster stage will then shut off, simulating a failure. The flight termination system — which would destroy the rocket in case it veered off course — will be active, but will not be set off by a “thrust termination” in the booster. Still, the rocket will be ripped apart and could possibly explode as powerful SuperDraco thrusters on the Crew Dragon capsule propel the capsule away from the rocket, taking it to an altitude of about 27 miles.
The Dragon capsule will then drop off the “trunk,” or bottom half of the spacecraft, and small thrusters will push it into the correct vertical orientation before parachutes deploy. It is to splash down in the Atlantic Ocean just 10 minutes after launch and about 20 miles from where it started.
SpaceX will not recover the booster this time
SpaceX now routinely recovers and reuses the booster stages of its rockets after successfully landing them at a pad near the launch site, or on a floating platform in the ocean. The booster on this flight, designated B1046, has flown to space three times previously, but this time the violent forces of the Crew Dragon blasting away will cause it to be destroyed.
The second stage of the Falcon 9 will be fully fueled, but it lacks an engine. Because the in-flight abort test occurs before the firing of the second stage, putting a real engine there would be an expensive waste.
SpaceX will clean up after itself. Four ships and at least four aircraft will scan the area and pick up debris in addition to plucking the capsule out of the water.
Once SpaceX begins the final countdown to launch — replicating the procedures it would follow for an actual launch with astronauts in the capsule — here is the sequence of events:
45 minutes before launch (or T-minus 45 minutes): The SpaceX launch director verifies all conditions are ready for loading the rocket’s fuel.
T-minus 37 minutes: The escape system is activated.
T-minus 35 minutes: Loading of rocket-grade kerosene and liquid oxygen begins.
T-minus 16 minutes: Loading of liquid oxygen to the second stage begins.
T-minus 7 minutes: Chilling of engines begins.
T-minus 5 minutes: The Falcon 9 rocket switches to internal power.
T-minus 1 minute: The flight computer begins final checks, the propellant tanks are pressurized to levels for launch.
T-minus 45 seconds: The SpaceX launch director verifies systems are go for launch.
T-minus 3 seconds: The nine engines of the booster stage ignite.
0 seconds, or T: Restraints holding the rocket down are released, and it lifts off.
A time of great pressure
The abort test will occur during the phase of the launch when the atmospheric forces on the rocket are greatest — in many ways, the most difficult time to safely halt a trip to space.
Rocket scientists call this maximum aerodynamic pressure. Think of the force you feel when sticking your hand out the window of a fast-moving car. The faster the car is moving, the greater the force. But for a rocket, the atmosphere thins at higher altitudes, so the force peaks and then diminishes as the rocket enters outer space.
The period of maximum pressure occurs roughly one minute after launch, and lasts for about 30 seconds. During this time, the Falcon 9 throttles back its engines to reduce the pressure.
In equations, the quantity of pressure is typically labeled q, so it is often referred to as max-q.
How launch abort systems have saved lives
A Soyuz launch carrying astronauts to the space station in October 2018 demonstrated the value of a working launch-abort system.
A faulty sensor prevented one of the rocket’s side boosters from falling away cleanly. It instead hit the rocket’s central core. Abort motors accelerated the capsule with two astronauts, Tyler Nicklaus Hague of NASA and Aleksey Ovchinin of Russia, away from the disintegrating rocket.
They experienced forces six to seven times the usual force of gravity during their escape, but they landed safely.