SpaceX astronaut launch: here's the rocket science it must get right

Two NASA astronauts, Robert Behnken and Douglas Hurley, will make history by travelling to the International Space Station in a privately funded spacecraft, SpaceX's Falcon 9 rocket and Crew Dragon capsule. But the launch, which was due to take place on May 27, has been aborted due to bad weather, and will instead take place on May 30 at 3:22 pm EDT.

The astronauts will take off lying on their backs in the seats, and facing in the direction of travel to reduce the stress of high acceleration on their bodies. Once launched from Kennedy Space Centre, the spacecraft will travel out over the Atlantic, turning to travel in a direction that matches the ISS orbit.

With the first rocket section separating at just over two minutes, the main dragon capsule is then likely to separate from the second stage burn roughly an hour later and continue on its journey. All being well, the Dragon spacecraft will rendezvous about 24 hours after launch.

Space mission launches and landings are the most critical parts. However, Space X has conducted many tests, including 27 drops of the parachute landing system. It has also managed an emergency separation of the Dragon capsule from the rocket. In the event of a failed rocket launch, eight engines would lift the capsule containing the astronauts up into the air and away from the rocket, with parachutes eventually helping it to land. The Falcon 9 rocket has made 83 successful launches.

Docking and return
The space station has an orbital velocity of 7.7km per second. The Earth's rotation carries launch sites under a straight flight path of the ISS, with each instance providing a "launch window".

To intercept the ISS, the capsule must match the station's speed, altitude and inclination, and it must do it at the correct time such that the two spacecraft find themselves in close proximity to each other. The difference in velocity between the ISS and the Dragon capsule must then be near to zero at the point where the orbits of the two spacecraft intersect.

Once these conditions are met, the Dragon capsule must manoeuvre to the ISS docking port, using a series of small control thrusters arranged around the spacecraft. This is due to be done automatically by a computer, however the astronauts can control this manoeuvre manually if needed.

As you can see in the figure below, manoeuvring involves "translation control" as indicated by green arrows - moving left/right, up/down, forward/back. The yellow arrows show "attitude control" - rolling clockwise/anti-clockwise, pitching up/down, and yawing left/right.

This is complicated by Newton's first law of motion - that any object at rest or in motion will continue to be so unless acted upon by an external force. That means any manoeuvre, such as a roll to the right, will continue indefinitely in the absence of air resistance to provide an external force until it is counteracted by firing thrusters in the opposite direction.

So now that you have a grasp of orbital manoeuvring, why not have a go yourself? This simulator, provided by Space X, allows you to try and pilot the Dragon capsule to the ISS docking port.

The astronauts will return to Earth when a new set are ready to take their place, or at NASA's discretion. NASA are already planning the first fully operational flight of crew Dragon, with four astronauts, although a launch date for that has not yet been announced and will undoubtedly depend on the outcome of this demonstration flight.

New era for spaceflight
The launch puts SpaceX firmly ahead of the other commercial ventures looking at providing crewed space launches. This includes both Boeing's Starliner, which first launched last year but was uncrewed, and Sierra Nevada's Dream Chaser which is planned to be tested with cargo during a trip to the ISS next year.

The ability of the commercial sector to send astronauts to the ISS is an important step toward further human exploration, including establishing a human presence at the Moon, and ultimately, Mars.

With companies competing, however, an open question remains whether safety could at some point be compromised to gain a commercial edge. There is no suggestion this has happened so far, but any crewed mission which failed due to a fault stemming from economic concerns would have serious legal ramifications.

In a similar way to modern aircraft legislation, a set of space safety standards and regulations will need to be put in place sooner rather than later. For commercial lunar and beyond missions we also have to ensure that any spacecraft does not contaminate the location they are visiting with germs from Earth.

With more nations and companies developing plans for lunar missions, there are obvious advantages in international cooperation and finding cost efficient launch methods. This is not least because it's not as dependent on the whim of elected governments for direction, which can change completely from one administration to the next.

So for us scientists looking to expand our knowledge of space, it is a very exciting moment.

Related Links
Commercial Crew Program
Rocket Science News at Space-Travel.Com

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