Space Exploration Technologies Corp. (SpaceX) will begin testing on a vertical propulsion landing system later this year, part of a long-term project to evaluate the potential of creating a fully-reusable version of their Falcon 9 launch vehicle. SpaceX believe a fully and rapidly reusable orbital class rocket would provide a critical breakthrough for the human race’s ambition of becoming a multi-planetary species.
A Rocket Is For Life, Not Just For Launch:
SpaceX are currently closing in on the February launch of their third Falcon 9 flight, tasked with the historic mission to loft an unmanned Dragon spacecraft on a recently approved combined D2/D3 mission to the International Space Station (ISS). Should the spacecraft successfully pass both its D2 and D3 demonstration test requirements, Dragon will be the first commercial vehicle to dock with the orbital outpost.
The Falcon 9 launch vehicle, however, will not live to see the historic event, following its staging and return to Earth – at least for the First Stage (the second stage may conduct restart/reboost tests) – shortly after the ride uphill.
This is the standard approach for expendable launch vehicles, even for large elements of technically reusable space vehicle systems – such as the Space Shuttle, which saw her giant External Tank (ET) destroyed via a destructive re-entry over the Indian Ocean, after each successful ascent to orbit.
Attempts have been made to design Single-Stage-To-Orbit (SSTO) vehicles – where the entire vehicle avoided any form of staging and returned to Earth “as launched” – such as the infamous X-33/VentureStar, which failed to overcome extensive design challenges prior to its cancellation.
However, SpaceX aren’t looking to redesign the wheel with their reusable ambitions. Instead, they are looking to keep their Falcon 9 launch vehicle design, along with its staging profile, whilst making revolutionary changes to what the expended stages do once they have completed their ascent roles – in essence, a highly advanced and wider-ranging version of the flyback booster concept.
These plans were unveiled by SpaceX founder and chief executive Elon Musk back in September of last year, plans which called for an improved Falcon 9, featuring first and second stages that would fly back to the launch site under their own power – something no other aerospace company has achieved. Mr Musk had previously hinted at such an ambition in 2009.
“This is a very difficult thing to do. Even for an expendable launch vehicle, where you don’t attempt any recovery, you only get maybe two to three percent of your lift-off weight to orbit. That’s not a lot of room for error,” noted Mr Musk during a speech to the National Press Club (*Video Snippet*).
“Now you say ‘OK, now let’s make it reusable’. You have to strengthen the stages, add a lot of weight, a lot of thermal protection – a lot of things that add weight to that vehicle – and still have a useful payload to orbit. You’ve got to add all that’s necessary to bring the stages back to the launch pad to be able to re-fly them and still have useful payload to orbit.
“This has been attempted many times in the past and generally what’s happened is people have concluded that success was not one of the possible outcomes, and the project has been abandoned. It’s a very tough engineering problem.”
During the announcement, a video simulation of the concept – if not entirely accurate – outlined how the Falcon 9 would return back to the launch site, ready for safing ahead for reuse on a latter mission. (*Video Here*)
With a slightly controversial, slightly clever, yet entirely apt use of British band “Muse” – well-known to be space flight fans – and their track “Uprising” as the soundtrack to the video, a visibly modified version of the Falcon 9/Dragon combination can be seen launching uphill, prior to a nominal First Stage MECO (Main Engine Cut Off) and staging.
However, this is the point where “nominal” turns into “fascinating” as the entire first stage rotates 180 degrees via Reaction Control System (RCS) thrusters, and then reignites three of its nine engines to “boost back” the near-empty stage back to the launch site.
Descending back to the launch pad, the First Stage is seen firing one engine to decelerate to a pinpoint landing on its specially made landing legs, in an area depicted in the video as the Cape Canaveral Air Force Station (CCAFS) Skid Strip runway complex.
“We have a design that on paper – doing the calculations and simulations – that does work. Now we have to make sure those simulations and reality agree. Because generally when they don’t, reality wins. So that’s to be determined,” noted Mr Musk.
“The simulation shows a general idea of what we plan to do, which is to basically put a First Stage out to stage separation, turn the stage around, relight the engines, boost back to the launch pad – and land propulsively on landing legs.”
With the Upper Stage completing its orbital insertion burn, prior to spacecraft separation, thrusters once again rotate the stage 180 degrees, aft forward, ahead of engine restart for another burn to deorbit the Upper Stage.
Protected by what appears to be a version of the PICA-X (a proprietary variant of NASA’s phenolic impregnated carbon ablator (PICA) material) heat shield used by the Dragon spacecraft, the Upper Stage dives back to Earth, protected against the heat and force of re-entry, prior to using what is depicted as four thrusters to decelerate and land on its landing legs.
During the sequence, the landing legs are shown in several configurations, both extended – to allow for the Upper Stage Nozzle to complete its burn, as well as folded inwards – to protect against the forces of re-entry.
“With the Upper Stage, after dropping off the satellite or spacecraft, we do a deorbit burn, re-enter – you need a quite powerful heat shield – and steer aerodynamically back to the launch pad, landing propulsively on landing legs,” added Mr Musk. “(Also worth noting,) you don’t need wings to steer aerodynamically, you just need some lift over drag numbers and lift vector.”
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With Dragon completing its mission, the capsule re-enters as expected – as much as Dragon still has one unique feature to present via its propulsive landing system, an integrated hardware element which also provides the launch abort capability during ascent.
While a backup parachute system will be available in the event of any issues, the sum total of the overall changes results in the entire launch vehicle and spacecraft hardware – minus fuel and original upmass payload – returning to Earth to be reused.
“I wasn’t sure it could be solved, but relatively recently – in the last 12 months or so – I’ve come the conclusion it can be solved and SpaceX is going to try and do it,” Mr Musk claimed. “We could fail, I’m not saying we’re certain of success, but we’re going to try to do it.”
Upcoming Development For F9r And Merlin 1D:
The first element of testing the simulations with real hardware will begin via a technology test bed called “Grasshopper”. This concept – per Federal Aviation Administration (FAA) information – points to a single-engine Falcon 9 First Stage with its own landing legs.
As confirmed by SpaceX in a response to NASASpaceflight.com, the company will begin testing on their vertical propulsion landing system for the Falcon 9 Reusable project later this year – a project they acknowledge is a long-term effort.
“We will begin testing our vertical propulsion landing system later this year. This is the research and development effort designed to help us learn more about propulsive landing systems to advance plans for producing reusable rockets,” noted SpaceX.
“This is a long-term project. SpaceX must successfully complete extensive testing before we will see reusable vehicles.”
The long-term nature of the project should place SpaceX in a good position for success, especially as they are continuing to advance and improve the performance of their in-house hardware, most notably their engines.
The Falcon 9 currently employs nine “SpaceX designed and built” Merlin main engines on the First Stage – sporting a single shaft. propellent fed, dual impeller turbo-pump, operating on a gas generator cycle which also provides the high pressure kerosene for the hydraulic actuators, which then recycles into the low pressure inlet.
The turbo-pump also provides roll control by actuating the turbine exhaust nozzle on the single second stage MVac engine.
In a response to NASASpaceflight.com, SpaceX note that an upcoming upgrades to the engine (Merlin 1D) will provide a vast improvement in performance, reliability and manufacturability – all of which could provide a timely boost to aiding the potential for success for the fully reusable Falcon 9.
“Increased reliability: Simplified design by eliminating components and sub-assemblies. Increased fatigue life. Increased chamber and nozzle thermal margins,” noted SpaceX in listing the improvements in work.
“Improved Performance: Thrust increased from 95,000 lbf (sea level) to 140,000 lbf (sea level). Added throttle capability for range from 70-100 percent. Currently, it is necessary to shut off two engines during ascent. The Merlin 1D will make it possible to throttle all engines. Structure was removed from the engine to make it lighter.
“Improved Manufacturability: Simplified design to use lower cost manufacturing techniques. Reduced touch labor and parts count. Increased in-house production at SpaceX.”
No specific date has been given for when such improvements will come on line, or if they would require debuting on a satellite launch, as opposed to a mission under NASA’s commercial contract.
A Breakthrough For Humans:
With the obvious challenge of potentially trading some of the vital upmass ratios, via the extra mass required for the additions to enable the launch vehicle to become reusable, Mr Musk pointed out just how important a breakthrough of this nature would be, by reducing the costs of a launch vehicle system, to a point it provides an enabler for the viability of a human settlement on Mars.
“The pivotal breakthrough that some company has to come up with (to make life multi-planetary), is a fully and rapidly reusable orbit class rocket. We’ll see if this works, but it’ll certainly be an exciting journey – and if it does work, it’ll be pretty huge,” noted Mr Musk at the September presser, before providing an example of the cost differential between expendable and reusable vehicles.
“If you look at the cost of a Falcon 9 rocket – which is a big, one million pounds of thrust rocket, yet the lowest cost rocket in the world, it’s still 50-60 million dollars. But if you look at the cost of the fuel and oxygen and so forth, it’s only about 200,000 dollars. So obviously if we can reuse the rocket, say one thousand times, then that would make the capital cost of the rocket per launch only about 50,000 dollars.
“(Bar) maintenance costs (etc), it would allow for a hundred fold reduction in launch costs.”
With commercial space now preparing to take over the access to Low Earth Orbit (LEO), many people have compared the current transition for the United States in space to that of the commercialization of other transportation sectors.
Mr Musk used a similar example when referring to the reusability of hardware for one of the more common modes of transport.
“This is a pretty obvious thing when applied to any other mode of transport. You can imagine if planes were not reusable, very few people would fly. A 747 is about $300 million, you’d need two of them for a round trip, yet I don’t think anyone has paid half a billion dollars to fly.
“These planes can be used tens of thousands of times and all you’re really paying for is fuel, pilots and incidentals – so the cost is relatively small. That’s why it’s such a giant difference, and that’s why I think a full reusable rocket is fundamentally required for life to become multi-planetary, for us to establish life on Mars.”
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While Mars remains a stated intention for SpaceX’s future aspirations, near-term success with their Falcon 9 and Dragon systems – not least under the Commercial Resupply Services (CRS) and CCDev (Commercial Crew Development) contracts – will provide the experience and the confidence for a company which has successfully become a household name in the global space flight arena.
(Images via SpaceX, National Press Club and NASA)