Successes and Delays: SpaceX’s Pursuit of Re-useable Rockets

DSCOVR launch

Launch of a Falcon 9 delivering the DSCOVR satellite into deep space. Image rights: SpaceX.

 

SpaceX’s plans for landing a first-stage Falcon 9 rocket on a purpose-built ship in the Atlantic will have to wait a little longer. After an unsuccessful first attempt at landing in January, the company had hoped to try again with their latest mission which launched Wednesday evening.

Unfortunately the launch – delivering the Deep Space Climate Observatory (DSCOVR) satellite into orbit – had to go ahead without the possibility to attempt a soft landing on the ship. Had the landing been a success it would have been the first time such a feat had ever been accomplished.

The launch took place from Space Launch Complex 40 at Cape Canaveral Air Force Station, Florida, after three aborted launches. The first, due to Air Force radar failure; the second, due to poor weather; and the third due to high winds.

Dashing hopes of success at landing after the eventual launch was stormy weather off the coast of Florida where the ship was positioned. Prior to launch, SpaceX released the following message:

The drone ship was designed to operate in all but the most extreme weather. We are experiencing just such weather in the Atlantic with waves reaching up to three stories in height crashing over the decks. Also, only three of the drone ship’s four engines are functioning, making station-keeping in the face of such wave action extremely difficult. The rocket will still attempt a soft landing in the water through the storm (producing valuable landing data), but survival is highly unlikely.

The missed opportunity aside, all aspects of the mission were successful. After a perfect launch and separation, the first-stage rocket’s descent was successful, arriving upright within 10m of its target destination in the Atlantic. The launch was also special as it was the first time that a Falcon 9 has been used for successful delivery of a payload into deep space.

Successful descent this time round was fraught with additional challenges not present in previous attempts. Due to nature of the deep space delivery, re-entry of the first-stage rocket faced almost twice the force, and four times the heat of its predecessor. The outcome therefore bodes well for SpaceX, demonstrating that key technology is working even under such extraordinary circumstances.

Image rights: SpaceX

Reaching a stormy sea: fins deployed and working in conjunction with engines as intended to control the decent of the first-stage Falcon 9 rocket. Image rights: SpaceX.

In the remainder of this article we take a look at SpaceX’s vision for re-useable rockets, the successes and challenges faced, and the rewards to be had.

 

Falcon 9 Rockets

Falcon 9 is a two-stage rocket designed wholly by SpaceX for transport of satellites and SpaceX’s Dragon spacecraft. What makes the Falcon 9 exception is the design of its first-stage rocket. Unique features of the rocket allow it to perform a controlled descent through the atmosphere and land itself vertically.

The first-stage is named as such on account of its providing thrust during the initial stage of the rocket’s launch. After separation, several minutes after launch, the second-stage rocket ignites, providing the thrust that takes the rocket further into space. Rockets may have several stages, something largely depending on how far into space they intend to travel. In the case of Saturn V rockets (which took man to the Moon via the Apollo missions), there were three stages.

The Falcon 9 rockets stands prior to its first launch attempt on Sunday. Image rights: SpaceX.

Recovery of an intact first-stage engine is special because it means that SpaceX can begin to recycle their first stage-rockets for subsequent use. Typically, and as was the case with all rockets prior to Falcon 9, spent rockets plummet to Earth and either disintegrate or fall into the sea. Single use of rockets like this massively increases the costs associated with rocket launches.

 

Rapid Re-useabilty: Ambitions of SpaceX

As discussed last August here at Phlebas (On the Real Value of SpaceX), success in development of rockets that may be recovered and re-used would be nothing less that a game-changer for rocket and space industries.

“If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred.  A fully reusable vehicle has never been done before. That really is the fundamental breakthrough needed to revolutionize access to space.”

Elon Musk

Establishing the technologies that will allow for full and rapid reusability of Falcon class rockets is a foremost objective of SpaceX. The company’s Reusable Launch System Development Program has been running since 2012 and has delivered novel technologies that render the Falcon 9 first-stage capable of at fulfilling this role as a multi-use rocket.

While for now it is only first-stage rockets that SpaceX are attempting to recover, the longer term goal does include recovery of all rocket stages. The Falcon 9 Heavy, which is still under development and pitched for its inaugural launch later this year, is also be being designed for recovery.

The accomplishment, when it comes, will represent a massive milestone for SpaceX’s vision. To hear SpaceX founder and CEO Elon Musk’s take on it, it is simple economics that ditching rockets after a single will remain a massive barrier to developing space flight. Relative to the costs of manufacturing a rocket, the fuel costs of a launch are relatively small. In fact, $200,000 in fuel and oxygen make up just 0.35% of SpaceX’s present launch costs; the rest goes toward their $56.5 million Falcon 9 rocket.

To recover, refurbish and re-use rockets has been estimated to bring launch costs down from around $60 million to something between $5 to $7 million (SpaceX President and COO Gywnne Shotwell, in interview). It is only by massively reducing the costs of space flight in this way that Musk believes we will enter into a new era of space exploration.

Aside from lowering costs dramatically, re-useability means more flights, with higher frequency. Access to space will become far more viable, even common-place, and open up new frontiers and opportunities for an array of industries. Moreover, the ability to land and re-use a rocket is critical to ventures that entail visiting other planets – something else that SpaceX are actively pursuing.

The animation beneath depicts the eventual goals of SpaceX’s Reusable Launch System programme.

 

A Falcon 9 Launch Profile

Falcon 9 blasts off using nine Merlin engines that make up the first-stage, generating 1.3 million pounds of thrust at sea level. About three minutes into launch, the first-stage engines cut off (also referred to as the main engine cutoff, or MECO). Four seconds later, and at an altitude of about 80km, the first- and second-stages separate; several seconds later the single second-stage Merlin engine ignites. The second-stage engine has a burn time of a little over six minutes, but it may be shut-off and re-ignited multiple times in order that the rocket reaches its intended orbit.

For instance, with delivery of DSCOVR, the second-stage burnt for some six minutes before a twenty-minute cut-off period followed by a brief one-minute burn prior to final cut-off and release of the DSCOVR satellite.

DSCOVR Second Stage

The single Merlin engine of the Falcon 9 second-stage rocket. As a deep-space mission, this was the furthest distance yet travelled by a Falcon 9. Image rights: SpaceX.

 

The Challenges of Controlled Descent & Recovery

There are three critical aspects to recovery of rockets fit for re-use: atmospheric re-entry, controlled descent, and so-called soft landing. Assuring success in each of these domains has necessitated the design of an exceptional rocket – one that’s capable of doing something traditionally considered infeasible within the space industry. As the only rocket to have been designed and built entirely in the 21st century, the Falcon 9 is also the first rocket ever built that’s (potentially) fit for recovery and re-use. Below is a rough outline of what’s involved in these stages.

The controlled decent of the first-stage rocket is an extraordinarily difficult set of manoeuvres spread over nine minutes beset with risks and challenges that have had to be overcome from both physics and engineering perspectives.

Atmospheric re-entry is the first challenge – there are forces at work that ordinarily result in the total disintegration of falling rockets.

After separation, the first-stage must re-orientate itself in order that it faces Earth and then adjust its angle for re-entry through the atmosphere. In the video posted above, you can briefly see the first-stage making these adjustments shortly after separation.

Typically SpaceX plan to perform a so-called ‘boostback burn’ at this point; the first of three burns that guide the rocket’s re-entry. However due to the nature of the DSCOVR mission, specifically the need to launch a payload further into space than is common, there will not be enough fuel for this manoeuvre. For this reason the first-stage will be coming in with additional forces to contend with.

trying to balance a rubber broomstick on your hand in the middle of a wind storm

As it descends, the rocket comes up against massive amounts of aerodynamic drag. This is fortunate, since it slows the rocket, but the chaotic nature of turbulence is impossible to control for entirely – at a certain point, outright engineering gives way to engineered hope. With the rocket travelling at some 3000 mph, the lattice fins deploy. These fins remain in operation from this point onward, until landing – the fins are constantly adjusting themselves to counter the forces against which the rocket must fight in order to retain control over its trajectory and profile. The fins’ operation requires hydraulic fluid – the substance that was depleted and resulted in January’s crash.

The Falcon 9 Rocket. Grid fins are clearly visible on the outer shell of the rocket. Image rights: SpaceX.

The Falcon 9 Rocket that took part in Wednesday’s launch. Grid fins are visible on the outer shell of the rocket. Image rights: SpaceX.

Next is a supersonic retro propulsion burn – slowing the rocket to a more manageable 500 mph. At this speed the landing legs may be deployed. The custom built legs are composed of carbon-fibre and aluminium, and are stowed until extending for landing.

A landing leg on show at SpaceX headquarters. Image rights: SpaceX.

A landing leg on show at SpaceX headquarters. Image rights: SpaceX.

As the rocket approaches the landing platform, continual adjustments are made to keep the rocket vertical and steady before its soft landing.

A soft landing is one in which an aircraft (or spacecraft) descends steadily, and lands intact. Performing a soft landing over water is something that SpaceX have carried out several times before, demonstrating that in theory at least, soft landing on a platform should be possible.

To a certain extent NASA’s Space Transport System was also reusable. The shuttle itself landed after all, and each one re-used many times. But the true vision of STS never panned out: the turnaround between landing and re-launching took months, not the days or weeks first imagines. The average cost per flight amounted to about $1.5 billion until 2008, when the program was terminated. Re-useability in this context is far removed from SpaceX’s intentions.

SpaceX's floating ship, the 'Just Read the Instruction', that the Falcon 9 first-stage landed on was positioned out at sea off the Florida coast.

SpaceX’s floating ship, the ‘Just Read the Instruction’, that Falcon 9 first-stage rockets will eventually come to land on, was positioned out at sea off the Florida coast. Image rights: SpaceX.

 

Development and Testing

Beginning in March 2014 under its Falcon 9 Reusable Development test programme, SpaceX began testing aspects of technology required for soft landings – namely using engines to control descent and trajectory, fin-control, and landing gear deployment.

The F9R development test vehicle was a prototype for the world’s first reusable rocket. The test vehicle was essentially a Falcon 9 first-stage with fixed landing legs. F9R descended from relatively low-altitudes though, and not following commercial launches into space proper (for a review of these tests, see here).

Soft landings at sea of first-stage rockets launching commercial missions came next, and were met with success. Soft landing at sea involves performing the exact same manoeuvres as are involved in a soft landing on a ship and therefore yields valuable information about the performance during descent. However upon reaching the water surface the rocket collapses over onto its side.

Having proven that Falcon 9 first-stage rockets could control their descent, SpaceX was ready to test landing on a solid surface. For safety purposes this was planned to take place at sea, on a purpose-built floating drone ship positioned some 370 miles (595 kilometers) off the coast of Florida. The ship, named ‘Just read the instructions’ (a nod to sci-fi author Iain M. Banks’ Culture series; not unlike Phlebas itself), is just 90 by 50 meters (300 by 170 feet).

The company’s first attempt at a this landing, in January of this year, ended in what Musk laconically described as a “Rapid Unscheduled Disassembly’.

The failure was revealed to have resulted from a loss of hydraulic fluid essential to the functioning of fins used to control descent. The rocket came in hard at a 45 degree angle, and as the legs and lower engine crashed into the landing platform of the ship, residual oxygen and fuel combined, resulting in a massive explosion. Damage to support equipment on its deck aside, the ship was left largely unscathed.

In spite of any sense of failure at performing a soft-landing; the descent actually achieved a great deal. The technology supporting a controlled decent performed very well: the fact that, from an altitude of some 100km, the rocket was able to navigate its way to a modestly sized landing platform in the middle of the ocean is a remarkable feat, that no others have ever attempted.

As with all matters in science, failure is fertile ground learning and future success. Shortly prior to the first scheduled launch (on Sunday) Musk had wryly noted that the rocket had ‘plenty of hydraulic fluid’ this time around – some 50% more in fact. Additional improvements will have undoubtedly also been made to the software controlling engine thrust and fins that guide descent.

 

Looking Forward

Altogether the proximity to success, over the course of the testing programme, with reaching the ship in January and with Wednesday’s descent, is indicative that principle descent technology is working. While it is surely only a matter of time before wholesale success, this enterprise remains a process of continued development. SpaceX have acknowledged that it will be some time before a tried and tested recyclable launch system is operational. It remains to be seen for instance, precisely how much refurbishment is required after recover, before rockets are fit for re-launch.

Nevertheless, we can expect further landing attempts to be made following SpaceX’s next launch – since all Falcon 9 first-stage rockets are now being manufactured with built-in descent and landing capabilities.

So while there are bound to be further challenges, for the mean time SpaceX are making great strides in pushing the boundaries of space flight. It’s a story we’ll continue to follow here at Phlebas, so stay tuned.

 

The Primary Mission Objective

Though it may be the most remarkable aspect of the mission, landing of the first-stage rocket was not the primary mission objective.

SpaceX’s customer for the DSCOVR mission was the United States Air Force, in partnership with NOAA and NASA. The mission’s principle objective was delivery of the Deep Space Climate Observatory (DSCOVR) satellite.

DSCOVR is to be positioned in orbit between the Sun-Earth Lagrangian Point 1, some 1,241,000km out from Earth – over four times the distance to the Moon.

Schematic showing the planned destination of the DSCOVR satellite. Image rights NOAA.

Schematic showing the planned destination of the DSCOVR satellite. Image rights NOAA.

Although it won’t reach its destination for a further 110 days, when it does the 570kg satellite will occupy a prominent position in the NASA / NOAA inventory – providing advanced measurement of particles and magnetic fields emitted by the sun (solar winds) as well as energy escaping Earth. DSCOVR is also sure to send back some pretty spectacular imagery of Earth as well – imagery which is slated to be real-time.

Monitoring solar winds from so far is a valuable capacity which will give NOAA forecasters advanced warning of solar storms that can affect satellites, communication systems and power grids on Earth. DSCOVR is a story in itself, with a long history and massive potential for revealing unprecedented information on climate change (See Al Gore’s article at Scientific American).

 

Resources

SpaceX website

SpaceX mission profile

NOAA mission profile & press kit

National Geographic news