[inlinetweet prefix=”” tweeter=”@mgriffin_uk” suffix=”#SpaceX #Mars #ElonMusk #NASA”]SpaceX sets its sights firmly on Mars[/inlinetweet]
This week Elon Musk’s rocket company SpaceX said it would put its Dragon spacecraft on the red planet “as soon as 2018″ making it the first private company to go interplanetary.
While it’s easy to get impatient with crackpot plans to head for the red planet SpaceX is unique in combining its dreams of Mars with well funded, hard nosed engineers and as it turns out the company’s long running quest to build reusable rockets with the aim of making it cheaper to launch satellites into Earth’s orbit has had a stealthier goal too. SpaceX’s successful landing of a rocket at sea earlier this month was just one more step towards Musk’s bigger ambition – to land on Martian soil in a way that has never done before, without parachutes, airbags or skycranes but using rockets alone.
[inlinetweet prefix=”” tweeter=”@mgriffin_uk” suffix=”#ElonMusk #SpaceX #Mars”]”My goal is to die on Mars, but not on impact” Elon Musk[/inlinetweet]
Landing on Mars
You may think that we already land on Mars with rockets but while it’s true that rockets will carry whatever we send to Mars landing on the surface once they get there is a different challenge.
It’s a quite different challenge from landing on either Earth or the Moon. Mars’s gravity is more than twice as strong as the Moon’s so a landing craft needs a lot more help decelerating than the Apollo lunar missions did but Mars’s atmosphere is more than 100 times thinner than that on Earth. So while parachutes can bring a Soyuz space capsule to a gentle splashdown in the Earth’s ocean they can’t slow a Mars lander to anywhere near a safe landing speed and the nature of the challenge depends a great deal on how big a package you’re sending.
The first rovers NASA sent to the red planet used parachutes to lose as much speed as possible then fell to the surface ensconced in a protective bubble of airbags but as the rovers got bigger, airbags became impractical so when NASA wanted to drop a 900 kg robot called Curiosity onto the surface of Mars in 2012 it had to get creative and NASA’s Jet Propulsion Lab devised a contraption known as the “Skycrane” to lower the rover gently to the ground wheels first.
Losing the chutes
Sending humans to Mars, however, requires a whole new kind of crazy.
“You’re going to have to land a two-story house on Mars, if you’re going to send humans,” says Bobby Braun, a veteran space engineer and former NASA chief technologist, who is currently a professor at the University of Georgia, “and land it right next to another two story house that’s been prepositioned and powered up and has all the fuel and food that humans will need to survive on Mars. Imagine the size of the parachute that one would need for that system. It gets to the point that its preposterous.” This is where the engineering behind SpaceX’s terrestrial landings comes in.
“The idea, essentially, is to skip the parachute and go right to the rocket,” NASA’s San Martin says.
The notion was first outlined in a 2012 white paper co-authored by Steve Davis, one of SpaceX’s more original thinkers. It noted that the Dragon space capsule, which SpaceX is developing to fly to the International Space Station and back, has powerful engines to allow it to land on Earth. It suggested that those same engines, in conjunction with a heat shield could instead be used to slow the Dragon from a high speed entry into the Martian atmosphere all the way to a landing on the surface. Doing that requires mastering a technique called “supersonic retropropulsion.” The Curiosity mission used subsonic retropropulsion – firing its rockets towards the surface of Mars to slow the craft’s descent after parachutes had already brought it below the speed of sound. The Dragon would have to do the same while traveling much faster than sound. Under those conditions the thrust from the engine and the sonic shock wave in front of the craft can interact in surprising ways that scientists don’t fully understand yet and intriguingly disrupting the shock wave could make the rocket go faster rather than slower as you might expect or create dangerous turbulence which could jeopardise the mission. While NASA wasn’t prepared to accept that level of uncertainty though SpaceX, who demonstrate the technology every time they attempt to land the first stage of one of its Falcon 9 rockets on Earth, was.
When the rocket first begins firing its engines to slow its descent, at an altitude of around 140 km, it is moving at a speed of at least 1,300 meters per second, close to Mach 4 but the real magic happens at about 70 kilometers above the earth.
“When they’re up high at altitude and turn on their engines to do the entry burn, they actually fire their engines in conditions here on the Earth that are almost identical to the planet Mars” due to the thin atmosphere, Braun says. “SpaceX has actually the first operational system that does supersonic retropropulsion and it’s technology that we will use when we send humans to Mars.”
SpaceX has been sharing the data from those landings with NASA who’ve been studying the data to learn how to design the next generation Martian lander and recently demonstrated their third successful rocket re-entry and landing on a drone ship at sea from high Earth orbit.
The digital pilot
Mastering supersonic retropropulsion isn’t the only challenge SpaceX will face. Landing on Mars will also mean putting an autonomous piloting system in charge and this is where Elon Musks other latest venture OpenAI will likely come to the rescue. The communications delay between Earth and Mars ranges anywhere from 4 to 24 minutes making remote control impossible. It’s no coincidence that every time you watch SpaceX’s rocket adjust its fins to direct its descent toward a landing platform it’s the computer inside trying to balance the optimal path to the ground with the least amount of risk.
Partners in space
Now that SpaceX has announced its intention of sending the Dragon to Mars its first obstacle is to finish developing the Falcon Heavy rocket that would carry it there. Tests of the rocket have been repeatedly delayed but it is expected to fly for the first time this autumn. The Dragon itself can carry more than a ton of cargo to Mars. Still, to some people, most notably the astronomer and space pedant Neil deGrasse Tyson the idea of SpaceX leading the charge to get to Mars is absurd. Under this view, the private sector doesn’t have the patience for the kind of long term investment or risk involved in interplanetary exploration. That’s what government agencies like NASA are for.
“The delusion is thinking that SpaceX is going to lead the space frontier. That’s just not going to happen,” Tyson told an interviewer recently.
As an analogy Tyson invoked Christopher Columbus, funded by the Spanish crown and it is certainly true that SpaceX was reliant on NASA for early funding and assistance and now serves as a workhorse for the US space agency.
“They’re bringing cargo back and forth to the space station, as should have been happening decades ago,” Tyson said. “You don’t need NASA to move cargo, you get NASA to do the things that have never been done before” but that distinction is swiftly blurring. While NASA is providing technical assistance to SpaceX’s Mars mission it’s no longer providing any funding and in return instead it’s getting important data about technology it cannot deploy itself but will need to use if it’s going to fulfil its own Martian aspirations. Meanwhile though SpaceX is doing more than just moving cargo back and forth – each time it flies to the International Space Station on a NASA contract it takes an opportunity to test the next iteration of its new systems and that kind of product development has huge advantages over NASA’s approach.
“With supersonic retropropulsion, there was no reason to believe it would not work but there was no reason to believe that it would work,” San Martin says. “In the culture of NASA, we were going to do a big testing program. Elon Musk just tried it. And if it works, it works.”