Interview: Elon Musk of Spacex talks reusable rockets and Mars missions

New Scientist had an interview with Elon Musk of Spacex discussing the reusable rocket work.

What kind of technology do you really want to advance, given the freedom you have to do it your own way?

EM: The really big advance, the fundamental breakthrough that’s needed, is a fully reusable rocket system. There was an attempt at that with the space shuttle but it failed. The space shuttle was only ever going to be partially reusable as the main tank – the primary flight structure to which the orbiter and booster were attached was discarded on every mission. And the parts that were reused were so difficult to reuse that the shuttle ended up costing four times more to run than an expendable rocket of equivalent payload capacity. The space shuttle was often used as an example of why you shouldn’t even attempt to make something reusable. But one failed experiment does not invalidate the greater goal. If that was the case we’d never have had the light bulb.

NS: Can you outline the economics?

EM: The fuel, oxidiser and pressurant on a Falcon 9 rocket accounts for about 0.3 per cent of the cost of the mission, about $200,000. But each mission costs $60 million because we have to make a new rocket every time.

Any reusable rocket would only last for a certain number of launches and would still have some maintenance costs. If a reusable rocket could last 200 launches then it would depreciate by $300,000 per launch and if there was $500,000 per launch in maintenance and service, then fuel + depreciation + maintenance would be $1 million. The reusable rocket would be 60 times cheaper than a single use rocket.

NS: And SpaceX manages that by doing everything possible in house, without significant outsourcing?

We are trying to make a huge difference – by advancing space technology substantially. To do that we had to design the Falcon rockets from scratch because the space supply chain is just not an effective one. At SpaceX we make the engines, the avionics, the primary structure – I think we’ve got a fundamentally better design: our airframe, engines, electronics and launch operations are much lower cost.

NS: What about performance though? Anyone can cut costs.

EM: Our engine has the highest thrust to weight ratio of any engine in the world, our airframe has the best mass fraction of any rocket in the world – and our electronics are the lightest and have have the most computing power over that of any other rocket.

NS: What is it that makes your rockets capable of scaling from low earth orbit missions to Mars trips? NASA needs a complete redesign for such ideas.

EM: I am not saying the rockets we have today are suitable for taking people to Mars. Our spacecraft would be pretty uncomfortable for a six month journey. It’s the next generation of our rockets that could do that.

NS: Will they be recognisable evolutions of the Falcon 9 series? Or radically different?

EM: The booster part of it will probably be recognisable compared to the next generation of Falcon we’re unveiling this year or early next.

NS: SpaceX is crew rating your capsule and say your “guiding star” is safety. How much of a challenge is it to crew rate the Dragon?

EM: There’s a lot of testing that needs to take place. I made sure the basic design of it is suitable for crew from the beginning. That’s why it has windows and returns safely to Earth. The technology driver there is our launch escape system, which has high thrust liquid-fuelled escape engines built into the side walls of the vehicle.

NS: I gather that these hypergolic motors might have planetary landing applications?

EM: Yes. The escape system’s motors will allow the capsule to land anywhere in the solar system, whether it has an atmosphere or not – and that’s pretty cool. These motors can even fire supersonically which is important for Mars: in the higher altitudes of Mars the atmosphere is so thin that parachutes are completely pointless. So retro thrusters have to be able to fire when you are supersonic so they have to be very high thrust.

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