SpaceX launch Q&A: Expert explains the science behind landing a reusable rocket

Sarah Spickernell
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The launch had to be postponed following a technical fault on Tuesday (Source: Getty)
Tomorrow morning at 10:09am, SpaceX will launch its Falcon 9 rocket towards the International Space Station (ISS).
Once far enough into space, the rocket will release its Dragon cargo and gradually turn around to go back on itself. Then, for the first time ever, scientists will try to land a rocket on Earth.
If all goes according to plan, it could pave the way for the use of reusable rockets in the future.
The landing point for the will be a sea barge in the Atlantic, just off the coast of Florida. Since this has never been done before, the engineers recognise there is a high chance it won't go according to plan. In fact, SpaceX founder Elon Musk put the likelihood of success at just 50 per cent.
Until now, rockets have been destroyed straight after releasing cargo, with segments falling apart and setting on fire when they enter the atmosphere.
If the mission is a success and reusable rockets become mainstream, it could save governments and private companies millions of dollars through not having to manufacture a new rocket for every launch.
The mission was originally supposed to take place on Tuesday morning, but a technical fault during final countdown meant it had to be postponed.
To find out more about the science behind landing a rocket and what it means for the future of space travel, City A.M. spoke to Paul Kostek, expert in space travel at the Institute of Electrical and Electronics Engineers.

Q: How is Falcon 9 designed for landing, rather than falling apart?

A: Just like current rockets, Falcon 9 will be a multi-stage vehicle. But unlike other models, it will have landing legs at the bottom, and a navigation system to guide it back to Earth and allow it to be stabilized. The upper parts off the rocket will be used to lift the cargo (in this case the Dragon capsule) into orbit.

Q: What will happen during the rocket's flight back down to Earth?

A: First, the segment carrying the cargo will separate from the body of the rocket. Then the engine will be restarted to slow the segment down, and guidance systems will be turned on to put it in the right position for coming back down to Earth. Finally, the landing gear will be deployed and the engine power reduced as the cargo segment returns to the rocket.

Q: What are the risks? Can they guarantee the rocket will be safe for reuse?

A: Before they are reused, the parts of the rocket would have to be inspected to ensure there is no damage. Nothing major will happen any time soon, either – the long-term plan of reuse within hours of return will take years of testing to gather data, both in terms of the impact of the landing and the number of times a system can be reused.
Unlike space shuttles going into orbit around the Earth and then through the harsh environment of re-entry these rocket segments will not be put through such a harsh environment. Any reoairs should therefore be limited.

Q: Why is landing so much more difficult than taking off?

A: When you're flying an aeroplane, all you need for take-off is maximum power and speed to lift off the ground. Landing, however, is more complicated – you need to find the runway, line up with the centre line and then reduce speed (but not so much that you stall or fall short of the runaway).
It's the same situation for a rocket – take-off is all about power and heading up, while landing involves slowing down, establishing the correct angle to the ground and then navigating back to the launch pad, adjusting speed and direction all the while.

Q: Is this the first time anyone has thought of making rockets reusable?

A: The idea isn't new, but it hasn't been put into practice before. Back in the 90's, a US company called Rocketplane Kistler designed the Kistler K-1 launch vehicle, which was supposed to have two reusable segments. They were not able to actually build the rocket though, due to a lack of funding.

Q: If the tomorrow is a success, what types of mission could rocket landings be used for in the future?

A: From a commercial perspective, it could increase the number of satellite launches and allow more small research and commercial missions to be sent into space. Crews and even visitors could be sent up to the ISS for short stays, encouraging space tourism. If any space hotels are built, this would be a means to deliver guests.

Q: Could it really transform the space economy by making missions much less expensive?

A: If successful, this would eliminate the need to build an entire new rocket for each launch, therefore reducing time and cost. It would be particularly promising for SpaceX's ultimate goal of multiple launches per day using the same rocket, because the cost of building up a system from scratch would be eliminated and the time to build each rocket decreased.

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