Livetimes of Aerospace Hardware

[Chris Russell]

Lifetimes of Aerospace Hardware

Preserving the viability of complex machines and electronics for extended periods: Is it feasible with today’s technology to design equipment that will be capable of withstanding interstellar space for a period up to 150 years? One example that illustrates some of the problems with obtaining long lifetimes is one museum’s frustrating attempts to preserve astronaut’s suits. They had difficulty preserving the rubber gaskets that were no more than a few decades old. Some other examples that illustrate how short equipment lifetimes are:

“Imagine parking your car in the garage for 20 or 30 years-or even 50 years-and then one day, you need to drive it. You would not expect it to run if you had not replaced any of the aging parts. Even if it were to remain parked in the garage, you would need to make sure it was stored safely, without leaking hazardous materials.

This is what we ask of our nuclear weapons stockpile-the Energy Department's life extension programs for nuclear weapons recently have proposed stockpile lifetimes of more than 50 years. Yet these weapons originally were designed for a 20-30-year lifetime, which means we need more understanding of how their materials and components age so that we can continue to store them reliably and safely.”

“Spacecraft engineers are normally proud if a multimillion-dollar satellite can survive in space for more than a decade.”

“It took a little extra effort, but NASA this weekend bridged a nearly seven-and-a-half billion mile span to make contact with Pioneer 10, a plucky space probe that first left Earth's gravitational pull more than 30 years ago.” Mar 4, 2002

“Design lifetimes of wind turbines are around 25 years. Experience of operating modern wind turbines is limited to around 15 years.”

“Fuel life spans depend on how much the ship is operated, and how accurately one can predict reactor performance. Current cores for the NIMITZ Class aircraft carrier, LOS ANGELES Class SSN, and OHIO Class SSBN last on average about 20 years. Efforts to extend the lives of operating reactor plants are resulting in longer ship lifetimes; NIMITZ-Class carriers are now expected to last 50 years, and OHIO-Class submarines 40 years, versus their original design lifetimes of 30 years.”

My problem: Imagine a robotic spacecraft cruising at 0.1 C on a 150 year mission. Somehow it has been designed to withstand particle and small asteroid and comet collisions. It has robotic equipment that can keep the spacecraft functioning as long as the robotic equipment remains functional. On board is other stored equipment and electronics destined for use on a extrasolar planet. This will include robotic devices designed to establish a base camp and other devices designed to explore and utilize the planet’s resources. The problem is a bit more complex than this, but I think what I’ve described will be challenging enough for any engineer. Am I correct in assuming that with today’s technology that such a mission will be impossible? A more challenging question is what has to be learned to make such a mission possible?

Discussion of the challenging questions of how to keep spacecraft intact while flying through an interstellar mine field and the challenges of propulsion and flight planning are to be saved for another time. Currently I’d like to keep the focus on the preservation and maintenance of the materials and composite artifacts required for such a mission.

I am also wondering if humanity has enough time, resources and interest to meet the challenges of interstellar space travel. Too much is going on around the world that makes be believe we may never put together a mission somewhat like the mission I described.

So there are two sets here. One that deals with the physics and another that deals with world resources, society and political realities. Please give primary focus to the former despite my concerns about the latter set.

 

[Astronuc]

Sputnik was launched in 1957, and the space program didn't take off until the 1960's, so we don't even have 50 years of experience.

“Fuel life spans depend on how much the ship is operated, and how accurately one can predict reactor performance. Current cores for the NIMITZ Class aircraft carrier, LOS ANGELES Class SSN, and OHIO Class SSBN last on average about 20 years. Efforts to extend the lives of operating reactor plants are resulting in longer ship lifetimes; NIMITZ-Class carriers are now expected to last 50 years, and OHIO-Class submarines 40 years, versus their original design lifetimes of 30 years.”

Fuel is a consumable. The length of operation and lifetime will depend on power density, and factors like corrosion if in an aqueous environment, or otherwise mechanical degradation.

The answer to the question depends on the type of hardware - structural vs. electronic.

Radiation damage will be a significant factor, and that currently limits the minimum size of transistors in microchips.

In the (Van Allen) radiation belts around earth, material life will be limited. Far away - say out past Jupiter, the lifetime may be much greater.

http://voyager.jpl.nasa.gov/

Voyagers Surpass 10,000 Days Of Operation
The intrepid twin Voyager spacecraft , launched about two weeks apart in the summer of 1977 and now heading out of the solar system, continue making history. On Jan. 5, 2005 the Voyager team noted a milestone with a nice round number: 10,000 days since Voyager 2's launch. On Jan. 21, 2005 Voyager 1 also passed 10,000 days.

Only 28 years here.

 

[Chris Russell]

Thanks for the Feast

Astronuc,

You have helped give this subject a clarity that makes it easier to analyze.

50 years of experience designing aerospace devices: Some museum curators have extensive preservation technology experience. I presume they have gathered their knowledge by researching the work of engineers and technicians. In some instances, I suspect out of necessity, they have developed new techniques by trial and error. They may have techniques that engineers and others may not because of an insufficient need to develop new techniques. Do NASA contractors and those of other aerospace institutions generally strive to maximize structural and electronic lifetimes and what influence does the cost/benefit and schedule analyses have on these lifetimes? I believe manufactures of consumer products place little emphasis on achieving maximum product lifetimes; cost/benefit analyses and management greed must dampen designers attempt or desire to extend product lifetimes. I wonder if this mindset is found in the aerospace industry. What individual or group is most interested in extending material lifetimes; who benefits the most? If I anyway near correct, then I guess we must wait for there to be a sufficient need to extend material lifetimes beyond what we currently have experienced. I’m guessing only desire to send a probe to another star might drive the necessary research. Some near Earth explorers might also drive the technology.

Power density: Not certain how this plays a roll except in cases where power plants may damage the integrity of surrounding materials. You must mean power sources have a lifetime. Batteries are generally short whereas nuclear power plants are used when longer lifetimes are required.

Corrosion in various environments: Material in an aqueous environment – under what condition(s) would it be advantageous to put aerospace materials in this environment? I remember one physicist suggesting that incasing a spacecraft or part of one in water might be a means of reducing radiation damage. This is the only example I can think of and I suspect it isn’t a practical technique. However, it might be practical where what needs to be protected, humans in particular, is a small enclosure. Museums have preserved documents and other items by using non corrosive or non damaging gases. Preventing leakage of the gas(es) has been a major concern. Has the aerospace used techniques similar to these to help prevent component damage?

Mechanical degradation: Bearings wear out. Plastic components become brittle. With enough time glass flows noticeably. Lubricants used to reduce wear breakdown with time. Electromechanical devices, like those used in computer disk drives, have notoriously short lifetimes. Some gyroscopes are designed without bearings yet they have failed. Are bearing-less gyroscopes used on the Hubble telescope? What other examples must I consider?

Structural vs. electronic lifetimes: My guess is structural components have generally longer lifetimes than electronic lifetimes. My wife is in the antique business. Things made of metal and some things made of wood have lasted over a hundred years. We can go to most museums and see artifacts with considerable greater ages in mint or near mint condition. But my experience with car alternators and generators, disk drives, memory chips leads me to believe that in general electronic lifetimes are comparably short. Oh yes, let’s not forget radiation damage to electronic components. I have heard of military equipment hardened to reduce EMF damage. Do they harden them against radiation damage? How is this done? What threat does radiation present to structural materials? Is there a need to “harden” or select structural materials to withstand radiation damage?

Radiation damage near Earth vs. in distant locations: I’m aware of the damaging high energy particles from the sun. But with space flights lasting decades and where they out of the reach of sun’s high energy particles, do not cosmic ray/particles present an additional threat to the lifetime of the spacecraft ?

Thanks for the meal. It has been good food for thought.

Chris

 

[Arctic Fox]

I have heard of military equipment hardened to reduce EMF damage. Do they harden them against radiation damage? How is this done? What threat does radiation present to structural materials? Is there a need to “harden” or select structural materials to withstand radiation damage?

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