Rockets that return home – SpaceX pushing the boundaries

by Chris Bergin

SpaceX is continuing to advance the technology that is aimed at creating a fully – and rapidly – reusable launch system, with the recent addition of two key milestones towards that goal. While the F9-R Dev-1 rocket enjoyed a debut hop at the McGregor Test Facility in Texas, the first stage of the Falcon 9 v1.1 – that successfully lofted the CRS-3 Dragon en route to the ISS – achieved a soft splashdown in the Atlantic Ocean.

SpaceX Reusable Rocket Drive:

The ambitious plans for creating an advanced flyback booster-style vehicle were unveiled by SpaceX founder Elon Musk back in September of 2011, 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.

Z6“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 two years later, in 2011.

“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.”

At the time of the announcements, industry sources believed the concept had potential to work, but cautioned that SpaceX would lose so much performance in their payload to orbit capability, the plan wouldn’t be financially viable.

Z3However, live testing of this concept on the first stage has already been conducted via missions that have successfully lofted nominal payloads – in part aided by the additional performance offered by the upgraded Falcon 9 v1.1 launch vehicle.

The debut of the Falcon 9 v1.1 – carrying the CASSIOPE satellite – involved the first “boost back” test of the first stage, while sources note there was also a boost back test during the SES-8 mission, or at least the restart of the first stage post staging.

More testing was involved on the F9 v1.1 mission, which successfully lofted the Thaicom-6 satellite.

“Extended and precise high altitude reentry burns have occurred (on previous Falcon 9 v1.1 missions) that are similar to a boost back, but we did not attempt to bring the rocket close to land,” noted SpaceX Spokesperson Emily Shanklin to earlier this year.

Z3AAccording to a speech by Tom Mueller, Co-Founder and VP Propulsion for SpaceX – at the “Exploring the Next Frontier: The Commercialization of Space is Lifting Off” event in Santa Barbara, California, this year  – the F9 first stage involved in the CASSIOPE launch crashed into the water during the return test.

The problem related to the stage spinning during its return, causing the fuel to centrifuge.

According to Mr. Mueller, the baffles in the tanks were not designed for those stresses, causing debris to get into the engines, resulting in them shutting down prematurely.

The latest test was the most ambitious, with the First Stage of the Falcon 9 v1.1 – tasked with lofting the CRS-3 Dragon for her mission at the International Space Station – aiming for a soft splashdown in the Atlantic.

Z7Ironically, the rocket got her feet wet at ignition, as a plume of dirty water flew out of the flame trench, providing a visual example of the power of the nine Merlin 1D engines, as they hit full thrust.

The cause of the plume relates to SpaceX using a procedure employed during the Titan rocket days, where a large amount of water would be stood in the flame trench, so as to protect the concrete base from being damaged in the event of a liquid oxygen leak from the rocket or Ground Support Equipment (GSE).

Three feet of standing water is usually called for, as much as slightly more was likely to have been in the trench when this Falcon 9 lifted off, causing the plume.

“We splashed dirty water on ourselves, it was a little embarrassing,” joked Mr. Musk.

However, the launch was nominal, with sources noting quick look information showed a smooth flight of the upgraded F9 that was carrying the Dragon uphill for the first time.

Z90Following staging, the stage rotated, pointing the Merlin 1D engines into the direction of travel, before executing the reentry burn using three of the nine engines. This supersonic retro propulsion burn was successfully conducted, with the stage returning back to Earth.

After this point, the test proved to be an advancement on previous attempts, with the stage previously suffering from spinning. This time the stage behaved itself.

“I consider (the test to be) a success as we were able to control the rocket to a zero roll rate, via improved nitrogen thrusters used to overcome the aerodynamic torque,” noted Mr. Musk after the CRS-3 launch. “With these more powerful thrusters and additional nitrogen we were able to null the roll rate.”

With Range assets – and a SpaceX plane – keeping a close eye on the returning stage, immediate telemetry from the coast noted the stage was returning as planned during the first part of the test.

“We have good data down to a pretty low level to roughly around Mach 1.1 and we’re awaiting additional data to see how the landing burn went, but we have very high sea states – I heard reports of 20 foot waves – so I wouldn’t give good odds on the rocket being able to splash down successfully,” Mr. Musk added, ahead of receiving telemetry data from the chase plane.

SpaceX sources note video of the returning stage was captured. However, SpaceX is yet to release any footage.

Z6It is not known how good the imagery is, although it is unlikely to beat a video – available in L2 – of a returning Solid Rocket Booster (SRB) during the STS-95 mission, when the booster recovery boat found itself closer to the splashdown point than usual, ahead of its role in recovering the motor for its tow back to Port Canaveral.

A NASA plane was also set to monitor the return – in order to collate data on the Agency’s Entry Descent and Landing (EDL) ambitions. However, only the SpaceX plane was used.

This second set of data from the plane gave a positive indication of a successful attempt to softly splashdown into the Atlantic.

Z8“Data upload from tracking plane shows landing in Atlantic was good! Flight computers continued transmitting for 8 seconds after reaching the water. Stopped when booster went horizontal,” added the SpaceX boss in a series of enthusiastic tweets.

This information pointed to a successful landing burn, which involved the relighting of the center engine to stabilize the stage and reduce the vehicle’s velocity prior to contact with the water.

Also previously noted by SpaceX to was the deployment timing of the landing legs, newly attached to the Falcon 9 v1.1, which was to be timed about 10 seconds into the landing burn.

Z11No information on the deployment sequence during the CRS-3 launch has yet been revealed. However, Mr. Musk was pleased that the flight data proved the legs held no negative impacts to both the ascent and return of the stage.

“We were able to show on ascent that the legs don’t have any negative impact and that we were able to come back through hypersonic velocity,” he added, before noting the next challenge involved the potential recovery of the stage from the ocean.

This effort is still classed as ongoing, despite SpaceX run ship, the US Army’s LSV Besson, having to abandon attempts to sail out to the stage’s location due to heavy seas.

Z55According to L2 sources, SpaceX recruited the US Navy to head out and try and find the stage for potential recovery. However, as of Tuesday, no definitive updates have been posted as to the success of this effort, pointing to the potential the stage has succumb to the rough seas.

A US Coast Guard alert has noted a 150 foot long rocket booster was adrift in the ocean, as a hazard report. However, it is unclear as to how up to date this information is, with the warning since expiring without being updated.

If stage is recovered, it won’t be returning to Port Canaveral, instead the plan – per sources – was for it to be towed back to Charleston in South Carolina.

Regardless of whether the stage is recovered or not, SpaceX had already said the chances of recovering it were low, with the main aim to collect data from the test, which was achieved.

Z6This test data will feed into the baseline understanding and refinements required to fine-tune the reusability goals, which are much more than just being able to recover a returned stage.

“There are conditions on re-use, in order to make re-use have a big effect on the space industry. Re-use must be both rapid and complete – like an aircraft or a car,” added Mr. Musk.

“We don’t just need to recover it, we have to show it can be reflown, quickly and easily, with the only thing changing being the reloading of propellent.”

The incremental testing will likely result in a returned stage being reflown next year. After which, SpaceX will aim to push on with the return goals for the Upper Stage, in tandem with continued work on the already recoverable Dragon spacecraft.

“This year we’ll be able to recover a rocket booster, but I’m not sure we’ll be able to refly it this year,” Mr. Musk continued.

“That is likely next year. That’ll complete the picture as far as the booster stage is concerned.”

Falcon 9-R Dev -1:

The return of the first stage during the CRS-3 mission wasn’t the only recent milestone for SpaceX’s reusability aspirations, as the company completed another test towards their ambitious goal at the McGregor test facility in Texas.

Home for testing the stages that are tasked with launching missions, the facility has also hosted the Grasshopper test system.

Grasshopper test

Numerous tests have involved the Grasshopper showing its ability to carry out incremental objectives, opening with a short hop of just six feet during Test 1, through to a massive 1,066 foot leap during Test 6.

The seventh test proved to be the most stunning, as the Grasshopper did much more than rise upwards before returning to its concrete pad.

That leap completed a divert test, flying to a 250m altitude with a 100m lateral maneuver before returning to the center of the pad.

Ultimately, the test demonstrated the vehicle’s ability to perform more aggressive steering maneuvers than have been attempted in previous flights, allowing for testing to move on to the next test vehicle, known as the Falcon 9-R Dev -1

Z3This new test vehicle also resides at the Texas test site, an impressive looking vehicle, that appears to be a mirror of a Falcon 9 v1.1 first stage dimensions.

Photos taken by several local people from a public road in the vicinity of the test site – some of which were provided to L2 (along with newly added video) – provide the first glimpse of the landing leg structures that appear to be closely based on the hardware that SpaceX is now employing on their latest Falcon 9 missions.

Z9The F9-R Dev-1 vehicle enjoyed its first hop this month. Once again, it was a complete success.

Notably, limitations at the Texas site result in an AGL (Altitude above Ground Level) ceiling that is somewhat restrictive.

As a result, another test vehicle – the Falcon 9-R Dev -2 – will take up residency at Spaceport America in New Mexico, where the vehicle will be able to fly at much higher altitudes.

“We’re going to keep doing tests at McGregor with the F9-R Dev 1 and F9-R Dev 2 will be at Spaceport America. Anything we can test at a relatively low altitude – below around 10,000 feet – will continue to be tested at McGregor,” noted Mr. Musk.

Z11“The high altitude stuff – where it’s going atmospheric, 300,000 feet plus – will be tested in New Mexico as we need a much bigger clear area.”

Again noting the importance of ensuring reusability is much more than ‘just’ being able to reuse the hardware, Mr. Musk once again stressed the need to prove the naysayers wrong about the viability of creating such a rocket system.

“We’ll continue to refine the technology over time, because reusability will only work if it’s rapid and complete, otherwise you don’t get the economic benefit that has the huge potential to open up space flight.”

(Images: SpaceX, NASA, US Navy and via L2’s Special Sections. L2 SpaceX section now includes thousands of unreleased images from all Dragon ISS missions – including CRS-3)

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