The Crew Dragon – SpaceX’s manned version of its Dragon cargo spacecraft – will undergo its first critical flight test tomorrow afternoon, Wednesday 6 May. The ‘Pad Abort Test’ and will take place from SpaceX’s Space Launch Complex 40 in Cape Canaveral, Florida.
The launch test is not part of a commercial, or operational, launch. Instead, it is a trial run of the spacecraft’s launch abort system – something otherwise known as the launch escape system. Regardless of the outcomes of the test, the event marks a highly significant moment for SpaceX in their pursuit of developing rocket technologies that will advance capabilities of space flight.
The event will be live-streamed through SpaceX’s official website.
The launch abort system is a critical feature of manned spacecraft – providing the means to rapidly propel the spacecraft and its crew away from the rocket (often referred to as the launch vehicle) at first sign of a potential failure. You can think of the launch abort system as being similarly in principal to an ejection seat of an aircraft.
The test is not just the first trial for the launch abort system. It’s also the first time that the Dragon spacecraft’s eight SuperDraco engines are to be tested in flight conditions. Previously the engines have only been tested individually and in pairs.
In the event of a launch abort, and tomorrow morning, the eight engines will ignite simultaneously, producing 120,000lbs of thrust in under a second. This force results in transporting the Crew Dragon nearly 100 meters (328 ft) in 2 seconds, and more than half a kilometer (1/3 mi) in just over 5 seconds. Put another way, the Crew Dragon will accelerate from 0 to around 100mph in one second.
The SuperDracos are big thrusters. They’re really big compared to the Dracos we fly on cargo Dragon … These have a total thrust of 120,000 pounds, so it’s a lot of kick.
Hans Koenigsmann, vice president of mission assurance at SpaceX
Significance of this Test
Tomorrow’s event is significant for many reasons. Foremost of these is that the test will demonstrate key technologies that SpaceX have been working towards for several years. These are all the more important given the consequence of these development programmes for SpaceX’s broader ambitions. For NASA, the test will demonstrate validity of a new launch system that will one day be taking its astronauts into space. And lastly concerning the rocket industry at large, the technology itself represents an innovative, and state-of-the-art departure from precedent.
Most manned spacecraft of the past have featured some form of launch abort system, but SpaceX’s design is altogether different from existing or historical configurations.
Traditionally, launch abort systems were built as ‘rocket towers’ fixed above the crewed spacecraft. You can see them on the Saturn rocket in the images below. In this configuration, during an emergency the rocket tower ignites and rapidly pulls the spacecraft to safety.
Typically a solid-rocket architecture was used in such launch abort systems. But rocket tower configurations aren’t ideal. For one, they add considerable weight to the mass of the vehicle – which requires extra fuel to compensate for, adding more mass and increasing costs. At the same time rocket towers represent an expensive (although necessary) safeguard which under ‘ideal conditions’ isn’t used at all. Thirdly, rocket towers must be separated from the launch vehicle before the spacecraft enters orbit – adding a risky separation event to the launch profile.
Perhaps unsurprisingly, SpaceX took to the drawing board to develop a new, far more innovative solution.
The company wanted a manned spacecraft fit for the 21st century. One that was built with the characteristics of safety and reusability in mind, just as their Falcon 9 rockets are.
In developing the crewed version of the Dragon, they designed and manufactured the SuperDraco engines from scratch. Functionality and efficiency were paramount in the engineers’ minds. Accordingly, SpaceX developed the SuperDraco engines to fulfil multiple roles. Roles which include, but go far beyond, providing a launch abort system in the manner described above.
Innovative, sophisticated, and safe – Crew Dragon represents a next-generation spacecraft.
A particularly important feature of the SuperDraco engines is their using liquid propellant. In contrast to solid-rockets which cannot be shut down once ignited, SuperDracos can be restarted multiple times, and throttled to control the amount of thrust they put out.
Together with performance, the use of multiple SuperDracos built into the walls of Crew Dragon is what allows them to perform multiple flight operations.
Firstly, the engines are intended to allow the Crew Dragon to perform a controlled, propulsive landing – something that in itself is an on-going target for SpaceX (but shouldn’t be confused with landing first stage rockets). Landing propulsively will allow Crew Dragon – and its sister variant, cargo Dragon – to be reused multiple times, whilst minimising need for repairs. The technology is key to one day taking mankind to other planets.
Secondly, the same engines provide the thrust required for transit in orbit. In regard to their functioning as a launch abort system, there’s also no need for a separation event (which rocket towers necessitate). This brings added safety and much less redundancy to the overall launch vehicle system.
In sum, the multiple roles performed by the SuperDraco engines and the way they are integrated into the Dragon amounts to a very efficient, flexible spacecraft that far surpasses anything else in use today.
Launch & Flight Profile
The test will take the following format. At launch, the SuperDracos will ignite and virtually instantaneously reach maximum thrust – launching the spacecraft away from the pad.
After half a second, using controlled thrustering the spacecraft will pitch towards the ocean. Trajectory is controlled by throttling the engines individually in response to real-time measurement by on-board sensors.
After five seconds, all propellant (fuel) is expended, and the spacecraft will continue to gain altitude to a maximum of about 1500 metres. The lower ’trunk’ will be jettisoned, and the remaining Crew Dragon will rotate around so that its heat-resistant under-side faces the Earth.
Several seconds later small parachutes (known as ‘drogues’) are deployed to stablise the spacecraft. Once stablised, three main parachutes deploy to slow the descent further still. The Crew Dragon will then splash down in the Atlantic, about 2.2km downrange of the launch pad.
The whole test will be over in less than two minutes.
A Flying Instrument Deck
The purpose of the test is for SpaceX to learn as much as possible about total system performance. The data captured will inform further development of the Crew Dragon, in preparation for its first manned mission in 2017.
Hinting at the vast amounts of sensors, cameras and equipment put in place to collect information, Hans Koenigsmann, SpaceX’s vice president of mission assurance, said in a press meeting last week that the Dragon pad abort vehicle is basically a “flying instrumentation deck”.
Of course what SpaceX are especially hoping to demonstrate is the overall effectiveness of the Crew Dragon’s launch abort system. Koenigsmann was quick to emphasis that the launch is development test – this is a new system being tested for the first time. Something could go wrong, but even if it does, the outcomes will inform progress nonetheless.
Beyond demonstrating the launch abort system, SpaceX release news of several more specific objectives which they described in the following manner:
Sequencing – Demonstrate proper sequencing of the pad abort timeline particularly given that several critical commands need to execute in very short periods of time.
Closed Loop Control – Demonstrate the ability of the eight SuperDraco engines to respond in real time to incoming data in order to ensure Crew Dragon stays on the appropriate course.
Trajectory Data – Obtain accurate trajectory data both for maximum altitude as well as distance downrange.
External and Internal Environments – Obtain data on impact of various internal and external factors to Crew Dragon to help ensure safe conditions for crew transport.
To aid them in this last matter a dummy is being placed inside the Crew Dragon to simulate a crew member seated inside. A host of sensors will collect data on the forces which crew members could expect to experience in the event of an abort – it’s expected the dummy will face some 4-4.5 Gs.
After recovery from the Atlantic, the spacecraft will be taken back to Texas for inspection. The same unit will be cleaned up and feature in an in-flight abort test, scheduled for later this year.
A Little Context
The now named ‘Crew Dragon’ was unveiled as Dragon V2 in May 2014. Around the same time it was announced that SpaceX had won NASA’s contract for ferrying astronauts to the International Space Station under its Commercial Crew Program. It is primarily for this purpose that the Crew Dragon has been developed.
Aside from commercial interests, a crewed spacecraft capable to propulsive landing, is also an integral part of SpaceX’s larger ambitions for advancing space travel and mankind’s exploration of our solar system.
For more insights on the NASA contract, and the Dragon-class spacecraft in general, you can read Phlebas’ coverage of the announcement here.