August 03, 2011

Looking at Spacex plans for Making Falcon Rockets Reusable to get to $50 per pound launch costs

Elon Musk at Spacex has spoken several times about making the Falcon launchers reusable.

Recently Spacex indicated that they have designs worked on on paper (computer models) that would solve the issues of reusability and get launch costs down as low as $50 per pound. The Falcon Heavy could get costs down to $1000 per pound.

Previously Musk said SpaceX will continue to pursue greater reusability -- "a fundamental long-term ambition", saying that a fully reusable system "is pivotal" to his intention to support the foundation of a sustainable human civilization on another planet. He points out that the cost of propellant for a Falcon 9 flight is around $150-$200,000, compared to $50 million for the vehicle, "so there is efficiency to be had".

The latest plan appears to be from brief comments
* restart the engines in order to slow down the first stage (not a full flyback) and shed some of the velocity.
* Less payload for fuel for restarting rocket to slow descent
* better thermal shielding and increased structural margins for recovery which also reduces the payload.
* the benefits of reusability should be a lot more than the decrease in the payload that goes up each time.

Falcon 9 reusability at wikipedia

"By [Falcon 1] flight six we think it’s highly likely we’ll recover the first stage, and when we get it back we’ll see what survived through re-entry, and what got fried, and carry on with the process. ... That's just to make the first stage reusable, it'll be even harder with the second stage – which has got to have a full heatshield, it'll have to have deorbit propulsion and communication.

So a iterative process of increasing heat shielding.

Both stages are covered with a layer of ablative cork, have parachutes to land them gently in the sea and have been marinized by using materials that resist salt-water corrosion, anodizing and paying attention to galvanic corrosion.

While many commentators are skeptical about reusability, Musk has said that if the vehicle does not become reusable, "I [Elon Musk] will consider us to have failed

NASA spaceflight forum covered Spacex ambitions in 2009

One of the goals I [Elon Musk] have for the Falcon 9 – which will take us many launches to achieve – is to have the vehicle out of the hanger and into the air in under 60 minutes.

“With Falcon I’s fourth launch, the first stage got cooked, so we’re going to beef up the Thermal Protection System (TPS). By flight six we think it’s highly likely we’ll recover the first stage, and when we get it back we’ll see what survived through re-entry, and what got fried, and carry on with the process.

“That’s just to make the first stage reusable, it’ll be even harder with the second stage – which has got to have a full heatshield, it’ll have to have deorbit propulsion and communication.”

Musk also spoke about his wish to enable the first stage with flyback capability, but added that he would require a large sum of cash to achieve that goal.

“Any pound you use for reusability and re-entry (on the second stage) is a pound subtracted directly from payload, whereas first stage it’s a five to one ratio. This is a problem we’re trying to solve incrementally, but most exciting thing I’ve love to do is a flyback first stage. We’re just missing the billion dollars of capital it would take to try to do that.

A 2010, Spacex press conference coverage from Transterrestrial

An interview with Elon Musk from 2003 at Hobbyspace

Spacex Customers

Elon Musk is "very optimistic that we will soon have a contract" for the big launcher from the USAF/National Reconnaissance Office (NRO - spy agency).

The NRO currently uses the Delta IV Heavy for large satellite launches.

The Falcon Heavy's 120,000 pound payload would be double that of the Delta IV. But if the SpaceX rocket is -- as the company plans -- much less costly than the Delta IV, the NRO does not need to use its full payload, or the USAF could fill some of that capacity with ride-along payloads.

Staged Combustion Engine

Later this year or early next year, Musk expected to unveil a “super high efficiency” staged combustion engine.

Staged Combustion Engines at wikipedia

The staged combustion cycle, also called topping cycle or pre-burner cycle,is a thermodynamic cycle of bipropellant rocket engines. Some of the propellant is burned in a pre-burner and the resulting hot gas is used to power the engine's turbines and pumps. The exhausted gas is then injected into the main combustion chamber, along with the rest of the propellant, and combustion is completed.

The advantage of the staged combustion cycle is that all of the engine cycles' gases and heat go through the combustion chamber, and overall efficiency essentially suffers no pumping losses at all. Thus this combustion cycle is often called 'closed cycle' since the cycle is closed as all propellant products go through the chamber; as opposed to open cycle which dumps the turbopump driving gases, representing a few percent of loss.

Another very significant advantage that staged combustion gives is an abundance of power which permits very high chamber pressures. Very high chamber pressures mean high expansion ratio nozzles can be used, whilst still giving ambient pressures at takeoff. These nozzles give far better efficiencies at low altitude.

The disadvantages of this cycle are harsh turbine conditions, that more exotic plumbing is required to carry the hot gases, and that a very complicated feedback and control design is necessary. In particular, running the full oxidizer stream through both a pre-combustor and main-combustor chamber ("oxidizer-rich" staged combustion) produces extremely corrosive gases. Thus most staged-combustion engines are fuel-rich, as in the schematic.

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