Discarded devices

From Wise Nano

Molecular manufacturing will allow cheap mass-production of micrometer-scale objects like networked sensors, electronic tags (see RFID) or weapons. If they are disposed of and not recycled, they might build up and cause problems in the environment, for example causing allergic reactions or damage in animal respiratory systems. In the vacuum of space the problems might be no less severe: today (2004) space debris - centimeter-sized objects in an earth orbit crossing Space Shuttle launch trajectories and satellite and space station orbits - is considered an ever growing threat to space flight in general.

Risk

When large numbers of small devices cease function, it might be considered economical to simply abandon them and produce new devices to meet demand instead of retrieving and reusing them. Several economic factors increase this risk:

• Low production costs. Because of the nature of how a nanofactory works, the production costs of a single device will depend roughly linearly on its atom count. Since every atom will be placed after each other, the element type of each atom has little or no effect on the duration of the production cycle. While diffeent raw materials will have different costs, the overwhelming cost factor will be design costs. These, however, are spread over the number of devices actually built.

• Short generation cycles. With rapid prototyping and immediate mass-production once the design is established, generation cycles will be very short. This means that devices can be outdated in a matter of months or less. Once a low-cost device is improved upon, there is little incentive to retrieve devices of its predecessor design.

• Difficulties in reliably collecting large numbers of small devices. Once disposable devices are spread into air, water or over ground, they will be subject to strong natural forces like wind and water currents, possibly spreading them over a wide area. Small devices will be constructed as compact as possible to save resources. Additional on-board equipment to allow collection after use will increase its complexity and costs while - depending on its purpose - adding nothing to its functionality or even decreasing its usefulness. Specialized collection systems have to be designed and manufactured, again increasing total costs.

• High resistance to physical/chemical degradation. The main component of such devices will probably be the different modifications of carbon. Both diamond and carbon nanotubes show high strength at low weigth. Also, carbon nanotubes can serve as high-performance conductors or semi-conductors, allowing the realization of Integrated Circuits mainly by carbon. High physical and chemical resistance could lead to a very high durability for such devices. Thus, self-decomposition might require too much energy to be incorporated into useful designs.

Possible Solutions

Apart from being the environmentally reasonable thing to do, avoiding this risk will require economic or legal incentives. A comparable corporate policy already exists today: Some electronics and battery manufacturers take back broken or outdated devices and spent batteries; in part they do this as customer service, in part because they are obliged to by law. Once the incentive is provided, technical solutions might include:

• Add Retrieval systems. Once a device is returned, it can be repaired and refitted, or it can be scrapped and its atoms recycled.
  • Passive: The device emits a beacon signal. Larger cleaning systems - e.g. robotic vehicles - then concentrate on areas with an device density above a certain threshold. Like a vacuum cleaner such a cleaning system would suck up the devices together with the surrounding water/atmosphere/dirt and filter them out.
    • Advantages
      • A radio signal is not energy-intensive and can thus be maintained long enough to allow for a maximum collection time in the range of years, depending on the device size; at the expense of bandwith and range they can be made passive, meaning they get their power through induction by the frequency scan (compare RFID. Passive devices´ maximum collection time is not limited by battery life.
      • An RFID-like beacon system can be of low complexity and thus add only very low costs in the range of fractions of a cent per device.
    • Disadvantages
      • Without active propulsion, small devices may be driven by currents and gravity and spread over a wide area, decreasing the retrieval ratio;
      • Consequently, many collection vehicles will be required to cover large surface areas or large volumes of air, water or space.
  • Active: The device has the ability to actively move. It can be programmed to return to the nearest collection site when its task is completed or when it receives the order to return. The location of a collection site can be hard-coded in, broadcasted to or detected actively by the device.
    • Advantages:
      • Intact devices within range can be retrieved almost completely.
      • The propulsion system might add useful or required functionality to the device.
      • No extra systems other than a few passive central collectors are required for retrieval.
    • Disadvantages:
      • Seems to be practical only with devices in the millimeter range or above (the size of small insects), because active propulsion loses efficiency with decreasing device size.
      • The amount of stored energy and thus its range is limited by the device´s dimensions.
      • An autonomous power supply to increase range adds further complexity, adversely influencing costs and failure rates.
  • Hybrid: A fraction of the number of constructed devices would be 'collectors', emitting a beacon signal once the devices have to be collected. All other devices picking up this signal would actively move to the signal´s source and lump together with the emitting device. Once a device has arrived at the beacon, it could also contribute its remaining energy to increase the beacon signal´s range or duration. This way a number of concentrated heaps of devices with one collector at its core would emerge, which can be collected more easily and more thorough. This advantage combines the advantages of active and passive retrieval, while reducing their disadvantages.
    • Advantages:
      • The retrieval ratio might be the highest of the three approaches;
      • A lump of devices is larger than a single device and thus more easily detected and filtered, thus reducing the complexity of the collection system;
      • The device´s propulsion system and beacon signal strength both need not be as high as with either the Active or the Passive approach.
      • The grabbing mechanism might add to the device´s usefulness by doubling as a manipulator.
    • Disadvantages:
      • An active propulsion still requires a certain device size to be practical, though its range need not be as high as with Active retrieval;
      • The grabbing mechanism ads complexity.

• Don't build small stuff: It's easy to assume that nano-built products will be small and swarm-like, but this will generally be less efficient than larger products. Nanofactories can build big stuff as easily as small stuff.
  • Advantages:
    • Easy to keep track of.
    • Larger devices can have more functional redundancy built in, which decreases failure rates and thus increases overall efficiency.
  • Disadvantages:
    • Some medical devices may need to be small (e.g. Freitas's bloodstream robots) though these may eventually be replaced by a completely different method (Freitas's and Phoenix's Vasculoid).
    • Large-scale scientific experiments or technical applications might require a vast number of devices which need not or must not be very heavy or complex. Examples include ocean and wind currents research and, as shown _{Please find and insert link here}, excess CO₂ can be removed from the Earth´s atmosphere by dispersing large numbers of prepared Fullerenes _{not sure if it was fullerenes}, which absorb CO₂. The latter clearly demands a retrieval mechanism to prevent the collected CO₂ from being released without control.

• Discardable devices: The device is designed to be inert once its task is completed. The different structures of carbon will probably be the most common structural element both for its strength and electronic capabilities (see diamond surfaces and carbon nanotubes). Some devices with shells that are both chemically and biologically inert might be left intact, joining the dust. The toxicity of fullerenes can be varied by orders of magnitude depending on their surface treatment [1]. Diamond appears to be generally biocompatible. Some rigid structures may be dangerous simply because of their shape and size. This option would have to be considered very carefully. But it should be noted that human use of medicines dumps lots of unmetabolized bio-active chemicals (e.g. antibiotics) today. Nanotech should be held to a higher standard, but an infinitely high standard would freeze technology at the current (probably unsustainable) level.

On the other hand, increasing production rates also increase every problem caused by it, thus higher standards may be inevitable to avoid a high-gear version of today´s real environmental and health problems. Nanotechnology is probably be the best candidate to achieve clean manufacturing, but it is no innate feature of nanotechnology. As long as human beings control powerful manufacturing systems, sensible standards and - more important - their enforcement will have to rise in order to keep the pace with development.