Musk goes for methane-burning reusable rockets as step to colonise Mars

by | Nov 20, 2012 | Seradata News | 9 comments

While speaking at the Royal Aeronautical Society in London in November, the billionaire former Paypal Internet executive, Tesla electric car entrepreneur, and current Space Exploration Technologies (SpaceX) CEO and self-taught lead rocket engineer, Elon Musk, described his plan to enable a self-sustaining human colony on the planet Mars.   This plan is to use reusable rockets and along with Mars landing and ascent craft to take mankind to Mars within 15 years.  And to do it Musk announced that liquid oxygen (Lox) and Methane would be SpaceX’s principal propellants of choice.

Musk began his talk by acknowledging that all did not go well on the latest mission of the expendable launch vehicle Falcon 9 which effectively lost its secondary payload as it placed Orbcomm OG2-01 commercial communications satellite payload in an incorrect orbit.  Nevertheless Musk praised the rocket’s rugged nine-engine design (which uses armour between each engine), as it did, at least, deliver its main payload, the Dragon CRS-1 cargo craft, to the correct orbit for NASA in spite of a violent engine shutdown. 

“There is an advantage in having nine engines because if one of them does not work and has what we call a RUD, which is a Rapid Unscheduled Disassembly, it still makes it into orbit,” Musk jokingly noted.

Musk added that though the recent partial launch failure had delayed future flights, he still expected to make four Falcon 9 flights next year, including three with its new upgraded Version 1.1.

Methane and liquid oxygen are best all-rounder propellants  

“We are going to do methane.”  Musk announced as he described his future plans for reusable launch vehicles including those designed to take astronauts to Mars within 15 years, “The energy cost of methane is the lowest and it has a slight Isp (Specific Impulse) advantage over Kerosene,” said Musk adding, “And it does not have the pain in the ass factor that hydrogen has”. 

Unlike methane, hydrogen is known to have storage and handling difficulties and has the problem of hydrogen embrittlement.   Even better, if methane is used as fuel, then the same engine designs might also be able to be used on Mars itself as methane can be extracted from the Martian atmosphere.   Methane is also known to be better fuel for reusable engine operations in not having significant coking (carbon deposit) issues that kerosene has to contend with though Musk noted that this was not a main raison for methane’s selection.  While Russia’s Khrunichev firm is researching such lox/methane engines for liquid flyback boosters, Musk said that he would not be seeking collaboration with Russian rocket engineers despite their lead in this technology, though he conceded that “we might hire a few”.   

SpaceX’s initial plan will be to build a lox/methane rocket for a future upper stage codenamed Raptor.  The design of this engine would be a departure from the “open cycle” gas generator system and lox/kerosene propellants that the current Merlin 1 engine series uses. Instead, the new rocket engine would burn lox/methane in a much more efficient “staged combustion” cycle that many Russian rocket engines use.

This change in fuel choice and rocket engine cycle would not be the first time that SpaceX has changed direction when technological demands have forced it to.  Musk’s original intention to use ablative cooling on this rocket engine thrust chambers and nozzles were soon altered to the more usual regenerative cooling which uses piped propellant as the coolant.   Likewise, Musk described how the Falcon 9 now uses a much more powerful turbo-pump fed Merlin upper stage engine in its upper stage compared to the pressure-fed Kestrel upper stage engine on the Falcon 1.  

Big rockets need big engines which might also be used on Mars

The new Raptor upper stage engine is likely to be only the first engine in a series of lox/methane engines.  Larger engines will be derived from this.  For all his arguments noting the advantages of having lots of smaller engine for engine-out redundancy, it is known that Musk has long wanted to have a larger sized engine that the current Merlin 1.   Originally this larger engine dubbed Merlin 2 was to have been a generator cycle engine similar to the Merlin 1.  This has however now been dropped, again, in favour of a staged-combustion engine  using Lox/Methane as propellants.  The name of this new rocket engine which is expected to be in the 1.5 million lb thrust class has not been disclosed.

The MCT codename which was incorrectly attributed to this large rocket engine is now instead believed to related to a Mars transport/landing concept with MCT is thought to stand for either Mars Cargo or Mars Crew or Mars Colonial Transport.  Musk would neither confirm nor deny this but he did add that SpaceX was working on such a vehicle.  Whether this would a single vehicle or one with different re-entry and descent/ascent components Musk appeared to think that it might be just one vehicle:  “I think you could land with the entire thing,” said Musk.

Mars landing small.jpg

Early SpaceX concept for Mars landing vehicle based on Dragon. Courtesy: SpaceX

To launch such a crew transport vehicle on a journey to Mars, Musk envisions using a reusable heavy lift launch vehicle using a multiple of these newly developed large lox/methane engines on its first stage.   Musk declined to state the expected payload capability of such a launch vehicle but noted that it would be much larger than the currently planned Falcon 9 Heavy which will carry 53 tonnes payload to low Earth orbit.  As such, if it is built, this new reusable heavy lift launch vehicle may be stepping on the toes, performance-wise, of NASA’s own 70-150 tonne-class Space Launch System (SLS). 

In addition to reusable launch vehicles and Mars landing vehicles, Musk also noted that his team was considering the problem of solar radiation for long range flight both for humans and for mission components.  Apart from its launch vehicle-related problems, Dragon CRS 2 cargo spacecraft also had radiation problems with its unhardened computers during its NASA contracted mission to the International Space Station.

Reusability is the key for economic launch operations in the future

While Musk described his more grandiose longer range plans for getting to Mars, his commercial operation is the one that currently pays the bills.   As it competes with Arianespace and ILS on the commercial launch narket, and with the United Launch Alliance for US Government front. SpaceX has managed to achieve a significant cost advantage over all of them.   Even the low-cost Chinese space industry has marvelled at its low launch prices. . SpaceX has apparently managed this by manufacturing most of its launch vehicle components in house (more than 70% by mass) and will only use external suppliers if it is cheaper to do so. 

However SpaceX’s competitors are now planning a fight back.  For example, Arianespace is now considering building their Ariane 5 successor, the Ariane 6 expendable rocket, in response to the low-cost threat from SpaceX. Even Musk notes that Arianespace would be wise to do so stating that “any variant of Ariane 5 is not going to be able to compete with Falcon.”  

But even this might not be enough for in reality SpaceX’s competitors are somewhat behind the curve.  To reduce costs even further SpaceX launch vehicles are planning to have reusability as their key design driver.   Musk noted that propellants only accounted for about 0.3% of the $60 million cost of an expendable Falcon 9 launch, adding that If a launch vehicle could be made to be fully reusable with little changed between flights (as airlines manage to do) then launch costs would come down dramatically.  As such Musk wants to operate two-stage fully reusable launch vehicles, including heavy lift variants, in which both stages would be able to return to the launch site.   

With respect to testing the technology of a landing, SpaceX has already stated demonstrate vertical landings using its “Grasshopper” test stage.  Musk accepts that there will be some failures during this testing of a new technology and expects that there will even be “new crater formation” on Earth as rockets fall to the ground.  Neverhtless, he is adamant over the technology.

“All future vehicles will be reusable,” said Musk in an e-mail response, adding:  “The Falcon line will serve as subscale test articles for what follows.”


Grasshopperlifts off.JPG Grasshopper test vehicle lifts off during a test flight. Courtesy: SpaceX

Keeping the structural weight down for successful reusable designs

Being able to make controlled statge approaches landings is not the only key requirement for reusable launch vehicles.  Musk noted that the trick to economic viability was to add the new parts which allow reusability (thermal protection systems, landing legs, new engines etc,) without increasing the structural weight too much so that such a launch vehicle can still carry a useful payload.  Musk stated that the payload on a very efficient conventional expendable rocket might be, at best about 4%, and suggested that 2% might be a more realistic figure for a reusable two-stage launch design. 

When asked about his competitors in the reusable field, namely the UK  Reaction Engines firm’s air-breathing single stage space plane concept, Musk said he was, at present, doubtful over the compelling case for this technology though he conceded “you know I could be wrong”.  Likewise, Musk was also even cooler in his response about air-launch design concepts noting that they may not have the advantages ascribed to them despite the fact that SpaceX was, at one time, linked with the Stratolaunch project.

With respect to plans to launch humans into orbit as part of the NASA commercial crew programme, Musk admitted that SpaceX was redesigning its own Dragon space capsule.   While noting that human astronauts could return in the pressurised Dragon Version 1 cargo capsule as it currently is, Musk joked that he was working on the Version 2  Dragon redesign on account that on the first version “we really did not know what we were doing”.   

Full details of the new design have not been published but Musk has noted that the Version 2 capsule would include repositioning of the thrusters to allow powered landings on land in addition to parachute splashdowns at sea (both parachutes and landing thrusters will be carried for redundancy).   Musk stated that these “SuperDraco” thrusters would have a dual role:  apart from being used for landings they could also be used to lift the capsule away from the launch vehicle in an emergency, with the crew suffering an uncomfortable 7-8g acceleration as it performed such an escape.

Musk suggests public-private partnerships for Mars exploration

When it comes to potential targets for human exploration, Musk remains very much “Mars First” orientated as he described the Moon, NASA’s expected first exploration choice, as a rock with no atmosphere, very little water and lacking key elements.  While appreciating that NASA had its own human exploration programme via its SLS and Orion capsule combination, Musk said that he hoped that private industry and governments could work in a kind of public-private partnership in long range exploration.  

With respect to spending public money Musk noted that 0.25-0.5% of GDP was a small price to pay for mankind to pay for “life insurance policy” in getting a self-sustaining civilisation on another planet.

A happy ending as marriages and Martian retirement plans are back on

In spite of Falcon 9’s recent launch setback, Musk nevertheless he gave an amusing and assured performance during the final question and answer session at the Royal Aeronautical Society.  In fact, Musk seemed more at ease with himself than he has done previously.    There was a reason for his happiness.  In the audience was his charming and beautiful former wife, Talulah Riley, the St Trinian’s film actress who, before their divorce earlier this year, had once declared that she wanted to retire with Elon to Mars. 

However love cannot so easily be discarded and we are happy to report that Elon and Talulah are now back together again. Even better, they are both again engaged to each other and plan to remarry soon.   As such,now that their  Mars retirement plan is back on we at Flightglobal’s Hyperbola blog wishes them both the best of both British and Martian luck for their future together.

Note: The writer of this article has a small shareholding in Reaction Engines Limited.

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