Plutonium-238 and RTG’s use on “Curiosity” and other NASA robots

Raquel I. Quiñones Acosta

Physics laws, ideas and discoveries started out as simple curiosity of a person or group of persons. A perfect match for my curiosity launched to Mars these past days (November 26, 2011) from Kennedy Space Center, FL. “Curiosity” as the Mars new rover was named, has been set to arrive Mars soil on August 6, 2012. The huge robot weighs five times what the rovers Spirit and Opportunity did. Its mission is to find out whether Mars has or had some sort of life. Studies made, arise the thought of Mars soils possibilities to have microbial life. Something as simple as a salt mixture can create a habitable place for microbial life to take part. This because the levels of deliquescence inside the salt mixtures increase, becoming a source for life on Mars soils as it has been proven to happen on the Atacama Desert and other Mars alike soils on Earth by NASA’s scientists Christopher P. McKay  and Alfonso Dávila among others.  This mission as many other NASA missions has the capability of arising new important discoveries for our generation and the generations to come. 

Curiosity will have the capability to be a field geologist and a laboratory simultaneously. Another interesting fact would be the energy source for the rover. As the other NASA rovers, Curiosity will have solar panels to provide energy and a plutonium battery to maintain all parts of the robot working properly. NASA has employed plutonium material batteries to keep the robots warm and collect data for a longer period of time. Plutonium material batteries can make the robots work for years; and even after 10 years the battery produces 92% of its initial energy, making them a powerful tool on our engineering world. According to Michael Banks from Physics World; Curiosity will have enough energy to fire a laser with a 1067 nm wavelength and a power of 10 MW to deposit 15 mJ of energy onto a millimeter spot of rock to break it down.  Then the robot will have the capacity of analyzing the data to determine chemical composition. 

Focusing on the batteries as the source of energy, basic physics terms explain that a normal battery transforms chemical energy into electric energy. Plutonium material batteries are nuclear batteries that use thermal energy to produce electrical energy. Plutonium-238 has been used for decades in radioisotope thermal generators (RTG’s) and the heat energy or electrical energy produced by them maintains the products working for longer considerable periods of time. Plutonium-238 produces 1 kilowatt of energy per 2 kilograms of mass. In the case of the rover Curiosity this type of battery is indispensable for its proper functioning, but yet very expensive. Still alpha particles responsible for the energy on RTG’s are one of the highest energy sources employed by humanity on the military, space and heart pacemakers, because of the mentioned ability of longer-lasting useful life. Alpha particles are responsible for the high energy nuclear reactions necessary for the robots, landers, rovers and other devices prepared for space studies to last long enough for discoveries farther away from the sun than our planet Earth. Probably physicist Ernest Rutherford never imagined that his studies on alpha particles would have such a large and amazing impact on our actual studies for the search of life on other planets. 

DIGITAL CONTACT LENSES: THE EYES OF THE FUTURE

Yrret Maldonado Ortiz

Envision the idea of being constantly updated with the latest information. At the present time the possibilities are remarkable. An international team of researchers has developed the first working prototype for such a device. In a study published in the Journal of Micromechanics and Microengineering, the researchers from the University of Washington, Seattle, and Aalto University in Finland describe the construction of a computerized single pixel contact lens and demonstrated its safety by testing it on live eyes that showed no adverse side effects.

The prototype contact lens has the capacity of streaming real-time information across the field of vision; potentially providing the wearer with information updates. This device is an example of the integration of devices into miniaturization unconventional substrates. The lens display consists of an antenna to harvest power sent out by an external source, as well as an integrated circuit to store this energy and transfer it to a transparent sapphire chip containing a single blue LED. 

 

One of the mayor challenges the researchers had to face in the design process of generating the contact lens was due to the required small size of the nature of the contact lens and that due to the fact that the human eye  has a minimum focal distance which is at least several centimetre away, therefore objects on a contact lens cannot be resolved, making the information in the lens itself look blurry and out of focus. In order to resolve this problem researcher employed a set of a class of micro-lens known as micro-Fresnel lenses, which focus light by refraction in a set of concentric curved surfaces. Their design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design. Compared to conventional bulky lenses, the Fresnel lens is much thinner, larger, flatter and have shorter focal lenghts, allowing it to focus the projected image onto the retina. Therefore the use of this Fresnel lenses in the design of the contact lens is ideal, because it does not only help solve the problem of the image projection on the retina, making the lens more biocompatible but it also fits the required measurements of volume needed in order to use it in the design of the contact lens.

 

In order for the lens to acquire the necessary energy  for the system to operate without a wired connection, researchers had to developed an CMOS integrated circuit because it meet the terms of the limitation of the design of the lens. Since the strict low power consumption and small footprint requirements in the design of the contact lens prohibited the use of commercially available integrated circuits. Therefore the researchers had to design a custom IC to perform control and radio functions. In order to be able to incorporate the  wireless electronics onto a contact lens. This chip design by the researcher has the ability as the lead researcher Babak Parviz from the university of Washington establish to perform the following tasks: “the conversion of RF power received by the on-lens antenna to a dc-supply voltage, on-chip energy storage sufficient to excite the micro-LED, and generation of an on-chip clock source to duty cycle an LED driver switch.” 

 

Custom designed and fabricated power harvesting and LED driver circuit. (a) Schematic of the CMOS IC architecture and connectivity. (b) Photograph of assembled chip with rectifier and storage capacitor outlined in white, viewed through the polymer substrate. Scale bar is 250μm.

The power management circuitry consists of a ring oscillator, a pulse generator and a passive level shifter. As established by the researchers, “the ring oscillator is powered from the second stage of an eight-stage cascaded rectifier. Each inverter in the three-stage oscillator uses stacked high-threshold devices for low leakage and low-power operation.” As a result, (as the research should) the power consumption of the ring oscillator is less than 500 nW at 1.0 MHz.

The device could overlay computer-generated visual information making it easy to access information instantly from platforms such as mobile phones. The researchers claim that their device will have a wide range of uses; that goes from leisure in its use for gaming devices and navigation system as it can be employed for educational, health application, such as a biosensor and even as an aid to the hearing impaired. Significant improvements are necessary to produce fully functional, remotely powered, high-resolution displays. However the research, data, results and design that wave been obtained by this group of researcher have establish a create stepping stone in the fundamental change of how people access and interact with visual information and how they see the world.

Reference:

A single-pixel wireless contact lens display

A R Lingley1, M Ali2, Y Liao1, R Mirjalili1, M Klonner2, M Sopanen2, S Suihkonen2, T Shen3, B P Otis1, H Lipsanen2 and B A Parviz1

Journal of Micromechanics and Microengineering, Vol.21, Num.12, 125014, 2011

1317_21_12_125014.pdf>

"Digital Contact Lenses Come into Focus." Physicsworld.com. Web. 30 Nov. 2011. .

Future Contact Lenses Can Put Pixels on Our Eyeballs

By Ross A. Lincoln - 12:00 AM - November 26, 2011

http://www.tomsguide.com/us/1-Pixel-Contact-Lens-HUD-implant,news- 13298.html

"Fresnel Lenses." Michigan. Web. 01 Dec. 2011. .

^ "Fresnel lens." Encyclopædia Britannica. 2005. Encyclopædia Britannica Online. 11 November 2005.