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Optimizing Impulse and Chamber Pressure in Hybrid Rockets

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Optimizing Impulse and Chamber Pressure in Hybrid Rockets

Introduction

Hybrid rockets—rockets that use a liquid oxidizer and solid fuel cylindrical grains—are currently experiencing a resurgence in research rocketry due to their comparative safety benefit.1 The unique design of a hybrid rocket enables fuel and oxidizer input regulation, and thus modulation of the combustion chamber pressure.2 This reduces the risk of explosion.3 This paper will give a basic overview of the function of a hybrid rocket, the role of injector plate geometry and rocket fuel on thrust, and the results of the Rice Eclipse research team on studying the effect of injector plate geometries and rocket fuel combinations on thrust and impulse. The purpose of this research is to discover a fuel grain and injector plate combination with the thrust necessary to launch a hybrid rocket into suborbital space.

Solid Rockets

Most entry-level, low-hazard rockets use solid motors.4 Solid rockets are generally considered to be the safest option because of the consistent burn profile.5 These rockets have a solid cylinder of fuel in their combustion chamber that contains a blend of rocket fuel and oxidizer.5 Through the course of flight, the fuel/oxidizer blend gradually depletes like a high power candle until the rocket reaches its apogee.5 Since the fuel and oxidizer are initially mixed together, it is highly unlikely for a solid rocket to have a concentration of fuel necessary for instantaneous combustion, which would result in an explosion.5

Liquid Rockets

Typical rockets that are deployed in space are liquid rockets.6 These rockets contain tanks of liquid oxidizer and liquid fuel that are atomized in the combustion chamber to burn at the high efficiencies required to achieve the impulse necessary for escape velocity.7 Particularly, the atomization provides the high surface area-volume ratio that is necessary for an efficient burn and allows the rocket to have the extremely high thrust. The disadvantage of liquid rockets is the huge safety risk they pose.7 Having a liquid combustion system makes the oxidizer and fuel dangerously close to blending, which can create a concentration of oxidizer-fuel mixture susceptible to a spark and resultant explosion.

Hybrid Rockets

Hybrid rockets combine the best of both solid and liquid rockets.6 The liquid oxidizer of the hybrid rocket is atomized over the solid fuel to give a high-thrust yet controlled burn in the combustion chamber.2 Although the sophistication of hybrid rocket engineering prevents most novice rocket builders from constructing hybrids, Rice Eclipse has constructed the fifth amateur hybrid rocket in America—which we call the MK1.

Injector Plates

Injector plates are metallic structures that function like spray guns and divide the stream of oxidizer into thousands of small atomized parts.8 A variety of designs or geometries exist that serve to break up oxidizer flow; the designs we considered in this study are the showerhead and impinging designs.

Showerheads

Showerhead injectors function similarly to household showerheads.4 A series of radially placed holes taper inwards as they move through the injector plate, confining the oxidizer fluid to a very small space before releasing it as a spray in the combustion chamber.8 The fluid atomizes because the oxidizer accelerates as it travels through the constrained small holes but suddenly decelerates as it reaches into the combustion chamber due to the rapid change in pressure.8 This process of breaking up liquid streams due to sudden resistance to flow is called the venturi effect.8

Impinging Plates

The second type of injector plate studied is an impinging injector plate4. In this style of injector plate, the holes of the plate are placed facing one another.9 As the oxidizer flows through the holes of the plate, the streams impinge, or collide at a central location.9 Upon collision, the streams atomize.4

It is hypothesized that this plate structure should result in much better performance because of greater atomization compared to a corresponding showerhead plate.4 For this project, the angle of the impinging holes was chosen to be 30 degrees from the normal in order to optimize impingement and atomization at the end of the pre-combustion chamber.9

Fuel Grains

Rocket fuels are often made of various materials that complement each other’s chemical properties to produce a high efficiency burn.10 These fuel components are held together in a cylindrical grain through the use of a binder compound that is also consumed in combustion11 Therefore, it is important for both the standard fuel components and the binder to burn efficiently.11 The efficiency of a burn is quantified in the fuel regression rate, which is how fast the fuel grain is depleted.12 While this rate varies based on combustibility and other chemical properties, it also heavily depends on the surface area available for burning.12 Fuels with high surface area, like those in a liquid or gaseous state, can achieve high regression rates.12 Thus, hybrid and solid rocket enthusiasts have been attempting to develop high surface area grains for efficient burns; this is has been previously achieved by using exotic grain configurations designed to maximize the exposure of the grain.12 Rice Eclipse has taken the different approach by using a standard cylindrical fuel grain that incorporate high regression rate liquefying paraffin with conventional solid rocket fuel. These fuel grains were combusted with a nitrous oxide oxidizer.

Paraffin Fuel

Hydroxyl-terminated polybutadiene (HTPB), is the most commonly used rocket fuel for both hybrid and solid rocket motors.13 In solid rockets, the physical properties of HTPB make it an ideal chemical to both bind the oxidizer into a strong yet elastic fuel grain and serve as source of fuel.12 However, HTPB does not burn with efficiencies required to accelerate rockets into orbital velocities.14 To improve pure HTPB grains, researchers have experimented with the addition of paraffin, a waxy compound that burns with a higher regression rate than HTPB, in the fuel grain.15 Under the high temperatures of the combustion chamber, solid paraffin wax forms a thin layer of low surface tension liquid on the face of the fuel grain cylinder that is exposed to the oxidizer.16 The layer of liquid vaporizes due to the high flow rate and pressure of the oxidizer, producing the large surface-area-to-volume ratio that is common in solid and liquid rockets.16 This liquefaction phenomena allows paraffin to produce high regression rate fuels in both hybrid and solid motors.16 However, paraffin by itself cannot be molded into a fuel grain due to its low viscosity.16 Thus, the inclusion of HTPB enables the production of a moldable fuel grain that possesses the high regression rate of paraffin wax.17

Materials and Methods

These tests were conducted in Houston, Texas in the MK1 test motor. The maximum combustion chamber pressure of MK1 was set to 500 psi. The motor used a load cell for thrust measurements and an internal pressure sensor for the combustion chamber profile. Each test fire lasted for four seconds, and three fires were conducted per configuration to ensure reproducibility and consistency of data.

We tested two types of fuel grains with HTPB and paraffin grains at 0% paraffin/100% HTPB and 50% paraffin/50% HTPB. All of these tests utilized a nitrous oxide oxidizer. Each of these grain types were cast in the Rice University, Oshman Engineering Design Kitchen.

The injector plates were made out of stock steel and were machined in the Rice University, Oshman Engineering Design Kitchen. The values used to drive the design of the injector plate are the desired mass flow rate of the oxidizer: 0.126 kg/s and the desired pressure drop across the injector plate: 1.72 MPa.

Graphite nozzles with an entrance diameter of 1.52 in, a throat diameter of 0.295 in, and an exit diameter of 0.65 in were used. Each nozzle is 1.75 in long and has a converging half angle of 40 degrees and a diverging half angle of 12 degrees.

Results

Three different fuel and injector plate combinations were studied. We performed a base case test of 0% paraffin/100% HTPB in a shower head plate. We then studied the effect of adding an impinging plate to the 0% paraffin/100% HTPB grain and went on to test a 50% paraffin/50% HTPB on the shower head palate. The reason we tested these configurations is to see how having a paraffin blended fuel grain and adding an impinging plate independently affected our rocket performance. The three scatter plots below show the thrust from each of the grains during a test fire. Thrust has a directly proportional relationship to the specific impulse of the rocket.

Discussion

50% Paraffin Test

The 50% paraffin grain showed a significant improvement compared to the 0% paraffin base case, increasing the average thrust by 58% from 380 lbf to about 600 lbf. The paraffin fuel grain also improved the consistency of the burn due to the even spread of the paraffin grains in the fuel. Although chamber pressure did increase from about 23 psi to 38 psi, this increase in pressure is well below the 50 psi operating capacity of the rocket and would not be a handicap for the fuel grain.

Impinging Plate

The third test fire, which demonstrated the impinging plate, maintained an average thrust of 700 lbf at maximum capacity—the highest average thrust. This is because the impinging injector plate increases the atomization of the oxidizer and the surface area available for combustion, intensifying the resulting burn. This increase in burn efficiency also reduces the overall burn time of the fuel and in this case shortened the fire to about two seconds from a four second burn in the base case.

Conclusions

The data show that the impinging injector was successful at achieving higher thrust burn. The paraffin fuels also demonstrated improved performance from the traditional HTBP fuel grains. This improvement in performance likely results from the reduced energy barrier to vaporization in the paraffin fuels compared to HTPB. The combination of improved vaporization and atomization allowed the impinging injector plate test results to show significantly better maximum thrust than all other tested plate combinations. Future testing can focus on combining the impinging plate with different concentrations of paraffin to take full advantage of increased atomization and surface area.

References

  1. Spurrier, Zachary (2016) "Throttleable GOX/ABS Launch Assist Hybrid Rocket Motor for Small Scale Air Launch Platform". All Graduate Theses and Dissertations, 1, 1-72.
  2. Alkuam, E. and Alobaidi, W. (2016) Experimental and Theoretical Research Review of Hybrid Rocket Motor Techniques and Applications. Advances in Aerospace Science and Technology, 1, 71-82.
  3. Forsyth, Jacob Ward, (2016) "Enhancement of Volumetric Specific Impulse in HTPB/Ammonium Nitrate Mixed Hybrid Rocket Systems". All Graduate Plan B and other Reports, 876, 1-36.
  4. European Space Agency, (2017) "Solid and Liquid Fuel Rockets".
  5. Whitmore S.A., Walker S.D., Merkley D.P., Sobbi M,  (2015) “High regression rate hybrid rocket fuel grains with helical port structures”, Journal of Propulsion and Power, 31, 1727-1738.
  6. Thomas J. Rudman, (2002) “The Centaur Upper Stage Vehicle”, International Conference on Launcher Technology-Space Launcher Liquid Propulsion, 4, 1-22.
  7. D. K. Barrington and W. H. Miller, (1970) "A review of contemporary solid rocket motor performance prediction techniques", Journal of Spacecraft and Rockets, 7, 225-237.
  8. Isakowitz, Steven J  International Reference Guide to Space Launch Systems; American Institute of Aeronautics and Astronautics: Washington D.C., 1999;
  9. Benjamin Waxman, Brian Cantwell, and Greg Zilliac, (2012) "Effects of Injector Design and Impingement Techniques on the Atomization of Self-Pressurizing Oxidizers", 48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Joint Propulsion Conferences, 6, 1-12
  10. Silant'yev, A.I. Solid Rocket Propellants Defense Technical Information Center [Online], August 22, 1967, http://www.redlightgreen.com/title/solid-rocket-propellants/oclc/832123905&referer=brief_results (accessed Feb. 9, 2017).
  11. F. M. Favaró, W. A. Sirignano, M. Manzoni, and L. T. DeLuca.  (2013) "Solid-Fuel Regression Rate Modeling for Hybrid Rockets", Journal of Propulsion and Power, 29, 205-215
  12. Lengellé, G., Duterque, J., and Trubert, J.F. (2002) “Combustion of Solid Propellants” North atlantic Treaty Organization Research and Technology Organization Educational Notes, 23, 27-31.
  13. Dario Pastrone, (2012) “Approaches to Low Fuel Regression Rate in Hybrid Rocket Engines” International Journal of Aerospace Engineering, 2012,1-12.
  14. Boronowsky, Kenny Michael, (2011) "Non-homogeneous Hybrid Rocket Fuel for Enhanced Regression Rates Utilizing Partial Entrainment" San Jose State University Master's Theses. Paper 4039, 3-110.
  15. McCulley, Jonathan M, (2013) "Design and Testing of Digitally Manufactured Paraffin Acrylonitrile-Butadiene-Styrene Hybrid Rocket Motors"All Graduate Theses and Dissertations from Utah State University, 1450, 1-89.
  16. T Chai “Rheokinetic analysis on the curing process of HTPB-DOA- MDI binder system”  Institute of Physics: Materials Science and Engineering, 147, 1-8.
  17. Sutton, G. Rocket propulsion elements; New York: John Wiley & Sons, 2001
  18. Isakowitz, Steven J  International Reference Guide to Space Launch Systems; American Institute of Aeronautics and Astronautics: Washington D.C., 1999

 

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Wearable Tech is the New Black

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Wearable Tech is the New Black

What if our clothes could detect cancer? That may seem like a far fetched, “only applicable in a sci-fi universe” type of concept, but such clothes do exist and similar devices that merge technology and medicine are actually quite prominent today. The wearable technology industry, a field poised to grow to $11.61 billion by 20201, is exploding in the healthcare market as numerous companies produce various devices that help us in our day to day lives such as wearable EKG monitors and epilepsy detecting smart watches. Advancements in sensor miniaturization and integration with medical devices have greatly opened this interdisciplinary trade by lowering costs. Wearable technology ranging from the Apple Watch to consumable body-monitoring pills can be used for everything from health and wellness monitoring to early detection of disorders. But as these technologies become ubiquitous, there are important privacy and interoperability concerns that must be addressed.

Wearable tech like the Garmin Vivosmart HR+ watch uses sensors to obtain insightful data about its wearer’s health. This bracelet-like device tracks steps walked, distance traveled, calories burned, pulse, and overall fitness trends over time.2 It transmits the information to an app on the user’s smartphone which uses various algorithms to create insights about the person’s daily activity. This data about a person’s daily athletic habits is useful to remind them that fitness is not limited to working out at the gym or playing a sport--it’s a way of life. Holding tangible evidence of one’s physical activity for the day or history of vital signs empowers patients to take control of their personal health. The direct feedback of these devices influences patients to make better choices such as taking the stairs instead of the elevator or setting up a doctor appointment early on if they see something abnormal in the data from their EKG sensor. Connecting hard evidence from the body to physical and emotional perceptions refines the reality of those experiences by reducing the subjectivity and oversimplification that feelings about personal well being may bring about.

Not only can wearable technology gather information from the body, but these devices can also detect and monitor diseases. Diabetes, the 7th leading cause of death in the United States,3 can be detected via AccuCheck, a technology that can send an analysis of blood sugar levels directly to your phone.4 Analysis software like BodyTel can also connect patients with doctors and other family members who would be interested in looking at the data gathered from the blood test.5 Ingestible devices such as the Ingestion Event Marker take monitoring a step further. Designed to monitor medication intake, the pills keep track of when and how frequently patients take their medication. The Freescale KL02 chip, another ingestible device, monitors specific organs in the body and relays the organ’s status back to a Wi-Fi enabled device which doctors can use to remotely measure the progression of an illness. They can assess the effectiveness of a treatment with quantitative evidence which makes decision-making about future treatment plans more effective.

Many skeptics hesitate to adopt wearable technology because of valid concerns about accuracy and privacy. To make sure medical devices are kept to the same standards and are safe for patient use, the US Food and Drug Administration (FDA) has begun to implement a device approval process. Approval is only granted to devices that provably improve the functionality of traditional medical devices and do not pose a great risk to patients if they malfunction.6In spite of the FDA approval process, much research is needed to determine whether the information, analysis and insights received from various wearable technologies can be trusted.

Privacy is another big issue especially for devices like fitness trackers that use GPS location to monitor user behavior. Many questions about data ownership (does the company or the patient own the data?) and data security (how safe is my data from hackers and/or the government and insurance companies?) are still in a fuzzy gray area with no clear answers.7 Wearable technology connected to online social media sites, where one’s location may be unknowingly tied to his or her posts, can increase the chance for people to become victims of stalking or theft. Lastly, another key issue that makes medical practitioners hesitant to use wearable technology is the lack of interoperability, or the ability to exchange data, between devices. Data structured one way on a certain wearable device may not be accessible on another machine. Incorrect information might be exchanged, or data could be delayed or unsynchronized, all to the detriment of the patient.

Wearable technology is changing the way we live our lives and understand the world around us. It is modifying the way health care professionals think about patient care by emphasizing quantitative evidence for decision making over the more subjective analysis of symptoms. The ability for numeric evidence about one’s body to be documented holds people accountable for the actions. Patients can check to see if they meet their daily step target or optimal sleep count, and doctors can track the intake of a pill and see its effect on the patient’s body. For better or for worse, we won’t get the false satisfaction of achieving our fitness goal or of believing in the success of a doctor’s recommended course of action without tangible results. While we have many obstacles to overcome, wearable technology has improved the quality of life for many people and will continue to do so in the future.

References

  1. [Hunt, Amber. Experts: Wearable Tech Tests Our Privacy Limits. http://www.usatoday.com/story/tech/2015/02/05/tech-wearables-privacy/22955707/ (accessed Oct. 24, 2016).
  2. Vivosmart HR+. https://buy.garmin.com/en-US/US/into-sports/health-fitness/vivosmart-hr-/prod548743.html (accessed Oct. 31, 2016).
  3. Statistics about Diabetes. http://www.diabetes.org/diabetes-basics/statistics/ (accessed Nov. 1, 2016).
  4. Accu-Chek Mobile. https://www.accu-chek.co.uk/gb/products/metersystems/mobile.html (accessed Oct. 31, 2016).
  5. GlucoTel. http://bodytel.com/portfolios/glucotel/ (accessed Oct. 31, 2016)
  6. Mobile medical applications guidance for industry and Food and Drug Administration staff. U. S. Food and Drug Administration, Feb. 9, 2015. http://www.fda.gov/downloads/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/UCM263366.pdf (accessed Oct. 17, 2016).
  7. Meingast, M.; Roosta, T.; Sastry, S. Security and Privacy Issues with Health Care Information Technology. http://www.cs.jhu.edu/~sdoshi/jhuisi650/discussion/secprivhealthit.pdf (accessed Nov. 1, 2016).

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Algae: Pond Scum or Energy of the Future?

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Algae: Pond Scum or Energy of the Future?

In many ways, rising fuel demands indicate positive development--a global increase in energy accessibility. But as the threat of climate change from burning fuel begins to manifest, it spurs the question: How can the planet meet global energy needs while sustaining our environment for years to come? While every person deserves access to energy and the comfort it brings, the population cannot afford to stand by as climate change brings about ecosystem loss, natural disaster, and the submersion of coastal communities. Instead, we need a technological solution which will meet global energy needs while promoting ecological sustainability. When people think of renewable energy, they tend to picture solar panels, wind turbines, and corn-based ethanol. But what our society may need to start picturing is that nondescript, green-brown muck that crowds the surface of ponds: algae.

Conventional fuel sources, such as oil and coal, produce energy when the carbon they contain combusts upon burning. Problematically, these sources have sequestered carbon for millions of years, hence the term fossil fuels. Releasing this carbon now increases atmospheric CO2 to levels that our planet cannot tolerate without a significant change in climate. Because fossils fuels form directly from the decomposition of plants, live plants also produce the compounds we normally burn to release energy. But, unlike fossil fuels, living biomass photosynthesizes up to the point of harvest, taking CO2 out of the atmosphere. This coupling between the uptake of CO2 by photosynthesis and the release of CO2 by combustion means using biomass for fuel should not add net carbon to the atmosphere.1 Because biofuel provides the same form of energy through the same processes as fossil fuel, but uses renewable resources and does not increase atmospheric carbon, it can viably support both societal and ecological sustainability.

If biofuel can come from a variety of sources such as corn, soy, and other crops, then why should we consider algae in particular? Algae double every few hours, a high growth rate which will be crucial for meeting current energy demands.2 And beyond just their power in numbers, algae provide energy more efficiently than other biomass sources, such as corn.1 Fat composes up to 50 percent of their body weight, making them the most productive provider of plant oil.3,2 Compared to traditional vegetable biofuel sources, algae can provide up to 50 times more oil per acre.4 Also, unlike other sources of biomass, using algae for fuel will not detract from food production. One of the primary drawbacks of growing biomass for fuel is that it competes with agricultural land and draws from resources that would otherwise be used to feed people.3 Not only does algae avoid this dilemma by either growing on arid, otherwise unusable land or on water, but also it need not compete with overtaxed freshwater resources. Algae proliferates easily on saltwater and even wastewater.4 Furthermore, introducing algae biofuel into the energy economy would not require a systemic change in infrastructure because it can be processed in existing oil refineries and sold in existing gas stations.2

However, algae biofuel has yet to make its grand entrance into the energy industry. When oil prices rose in 2007, interest shifted towards alternative energy sources. U.S. energy autonomy and the environmental consequences of carbon emission became key points of discussion. Scientists and policymakers alike were excited by the prospect of algae biofuel, and research on algae drew governmental and industrial support. But as U.S. fossil fuel production increased and oil prices dropped, enthusiasm waned.2

Many technical barriers must be overcome to achieve widespread use of algae, and progress has been slow. For example, algae’s rapid growth rate is both its asset and its Achilles’ heel. Areas colonized by algae can easily become overcrowded, which blocks access to sunlight and causes large amounts of algae to die off. Therefore, in order to farm algae as a fuel source, technology must be developed to regulate its growth.3 Unfortunately, the question of how to sustainably grow algae has proved troublesome to solve. Typically, algae for biofuel use is grown in reactors in order to control growth rate. But the ideal reactor design has yet to be developed, and in fact, some current designs use more energy than the algae yield produces.5

Although algae biofuel faces technological obstacles and dwindling government interest, many scientists today still see algae as a viable and crucial solution for future energy sustainability. UC San Diego houses the California Center for Algal Biotechnology, and Dr. Stephen Mayfield, a molecular biologist at the center, has worked with algae for over 30 years. In this time he has helped start four companies, including Sapphire Energy, founded in 2007, which focuses on developing algae biofuels. After receiving $100 million from venture capitalists in 2009, Sapphire Energy built a 70,000-square-foot lab in San Diego and a 220-acre farm in New Mexico. They successfully powered cars and jets with algae biofuel, drawing attention and $600 million in further funding from ExxonMobil. Although diminished interest then stalled production, algal researchers today believe people will come to understand the potential of using algae.2 The Mayfield Lab currently works on developing genetic and molecular tools to make algae fuel a viable means of energy production.4 They grow algae, extract its lipids, and convert them to gasoline, jet, and diesel fuel. Mayfield believes his lab will reach a low price of 80 or 85 dollars per barrel as they continue researching with large-scale biofuel production.1

The advantage of growing algae for energy production lies not only in its renewability and carbon neutrality, but also its potential for other uses. In addition to just growing on wastewater, algae can treat the water by removing nitrates.5 Algae farms could also provide a means of carbon sequestration. If placed near sources of industrial pollution, they could remove harmful CO2 emissions from the atmosphere through photosynthesis.4 Additionally, algae by-products are high in protein and could serve as fish and animal feed.5

At this time of increased energy demand and dwindling fossil fuel reserves, climate change concerns caused by increased atmospheric carbon, and an interest in U.S. energy independence, we need economically viable but also renewable, carbon neutral energy sources.4 Algae holds the potential to address these needs. Its rapid growth and photosynthetic ability mean its use as biofuel will be a sustainable process that does not increase net atmospheric carbon. The auxiliary benefits of using algae, such as wastewater treatment and carbon sequestration, increase the economic feasibility of adapting algae biofuel. While technological barriers must be overcome before algae biofuel can be implemented on a large scale, demographic and environmental conditions today indicate that continued research will be a smart investment for future sustainability.

References

  1. Deaver, Benjamin. Is Algae Our Last Chance to Fuel the World? Inside Science, Sep. 8, 2016.
  2. Dineen, Jessica. How Scientists Are Engineering Algae To Fuel Your Car and Cure Cancer. Forbes UCVoice, Mar. 30, 2015.
  3. Top 10 Sources for Biofuel. Seeker, Jan. 19, 2015.
  4. California Center for Algae Biotechnology. http://algae.ucsd.edu/. (accessed Oct. 16, 2016).
  5. Is Algae the Next Sustainable Biofuel? Forbes StatoilVoice, Feb. 27, 2015. (republished from Dec. 2013)

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Fire the Lasers

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Fire the Lasers

Imagine a giant solar harvester flying in geosynchronous orbit, which using solar energy, beams radiation to a single point 36, 000 km away. It would look like a space weapon straight out of Star Wars. Surprisingly, this concept might be the next so-called “moonshot” project that humanity needs to move forward. In space-based solar power generation, a solar harvester in space like the one discussed above would generate DC current from solar radiation using photovoltaic cells, and then convert it into microwaves. These microwaves would then be beamed to a rectifying antenna (or a rectenna) on the ground, which would convert them back into direct current (DC). Finally, a converter would change the DC energy to AC to be supplied into the grid.1

With ever-increasing global energy consumption and rising concerns of climate change due to the burning of fossil fuels, there has been increasing interest in alternative energy sources. Although renewable energy technology is improving every year, its current energy capacity is not enough to obviate the need for fossil fuels. Currently, wind and solar sources have capacity factors (a ratio of an energy source’s actual output over a period of time to its potential output) of around 34 and 26 percent, respectively. In comparison, nuclear and coal sources have capacity factors of 90 and 70 percent, respectively.2 Generation of energy using space solar power satellites (SSPSs) could pave the path humanity needs to move towards a cleaner future. Unlike traditional solar power, which relies on favorable weather conditions, SSPSs would allow continuous, green energy generation.

Although space-based solar power (SBSP) might sound pioneering, scientists have been flirting with the idea since Dr. Peter Glaser introduced the concept in 1968. Essentially, SBSP systems can be characterized by three elements: a large solar collector in geostationary orbit fitted with reflective mirrors, wireless transmission via microwave or laser, and a receiving station on Earth armed with rectennas.3 Such an implementation would require complete proficiency in reliable space transportation, efficient power generation and capture, practical wireless transmission of power, economical satellite design, and precise satellite-antenna calibration systems. Collectively, these goals might seem insurmountable, but taken separately, they are actually feasible. Using the principles of optics, scientists are optimizing space station design to maximize energy collection.4 There have been advancements in rectennas that allow the capture of even weak, ambient microwaves.5 With the pace of advancement speeding up every year, it’s easy to feel like the future of renewable energy is rapidly approaching. However, these advancements will be limited to literature if there are no global movements to utilize SBSP.

Japan Aerospace Exploration Agency (JAXA) has taken the lead in translating SBSP from the page to the launch pad. Due to its lack of fossil fuel resources and the 2011 incident at the Fukushima Daiichi nuclear plant, Japan, in desperate need of alternative energy sources, has proposed a 25-year technological roadmap to the development of a one-gigawatt SSPS station. To accomplish this incredible feat, Japan plans on deploying a 10,000 metric ton solar collector that would reside in geostationary orbit around Earth.6 Surprisingly, the difficult aspect is not building and launching the giant solar collector; it’s the technical challenge of transmitting the energy back to earth both accurately and efficiently. This is where JAXA has focused its research.

Historically, wireless power transmission has been accomplished via laser or microwave transmissions. Laser and microwave radiation are similar in many ways, but when it comes down to which one to use for SBSP, microwaves are a clear winner. Microwaves have longer wavelengths (usually lying between five and ten centimeters) than those of lasers (which often are around one micrometer), and are thus better able to penetrate Earth’s atmosphere.7 Accordingly, JAXA has focused on optimizing powerful and accurate microwave generation. JAXA has developed kW-class high-power microwave power transmission using phased, synchronized, power-transmitting antenna panels. Due to current limitations on communication technologies, JAXA has also developed advanced retrodirective systems, which allow high-accuracy beam pointing.8 In 2015, JAXA was able to deliver 1.8 kilowatts accurately to a rectenna 55 meters away which, according to JAXA, is the first time that so much power has been transmitted with any appreciable precision . Although this may seem insignificant compared to the 36,000 km transmissions required for a satellite in geosynchronous orbit, this is huge achievement for mankind. It demonstrates that large scale wireless transmission is a realistic option to power electric cars, transmission towers, and even satellites. JAXA,continuing on its roadmap, plans to conduct the first microwave power transmission in space by 2018.

Although the challenges ahead for space based solar power generation are enormous in both economic and technical terms, the results could be revolutionary. In a manner similar to the introduction of coal and oil, practical SBSP systems would completely alter human civilization. With continuous green energy generation, SBSP systems could solve our energy conflicts and allow progression to next phase of civilization. If everything goes well, air pollution and oil spills may merely be bygones.

References

  1. Sasaki, S. IEEE Spec. 2014, 51, 46-51.
  2. EIA (U.S. Energy Information Administration). www.eia.gov/electricity/monthly (accessed     Oct. 29, 2016).
  3. Wolfgang, S. Acta Astro. 2004, 55, 389-399.
  4. Yang, Y. et al. Acta Astro. 2016, 121, 51-58.
  5. Wang, R. et al. IEEE Trans. Micro. Theo. Tech. 2014, 62, 1080-1089.
  6. Sasaki, S. Japan Demoes Wireless Power Transmission for Space-Based Solar Farms. IEEE Spectrum [Online], March 16, 2015. http://spectrum.ieee.org/ (accessed Oct. 29, 2016).
  7. Summerer, L. et al. Concepts for wireless energy transmission via laser. Europeans Space Agency (ESA)-Advanced Concepts Team [Online], 2009. https://www.researchgate.net/profile/Leopold_Summerer/ (accessed Oct. 29, 2016).
  8. Japan Space Exploration Agency. Research on Microwave Wireless Power Transmission Technology. http://www.ard.jaxa.jp/eng/research/ssps/hmi-mssps.html (accessed Oct. 29, 2016).

 

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Haptics: Touching Lives

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Haptics: Touching Lives

Everyday you use a device that has haptic feedback: your phone. Every little buzz for notifications, key presses, and failed unlocks are all examples of haptic feedback. Haptics is essentially tactile feedback, a form of physical feedback that uses vibrations. It is a field undergoing massive development and applications of haptic technology are expanding rapidly. Some of the up-and-coming uses for haptics include navigational cues while driving, video games, virtual reality, robotics, and, as in Dr. O’Malley’s case, in the medical field with prostheses and medical training tools.

Dr. Marcia O’Malley has been involved in the biomedical field ever since working in an artificial knee implant research lab as an undergraduate at Purdue University. While in graduate school at Vanderbilt University, she worked in a lab focused on human-robot interfaces where she spent her time designing haptic feedback devices. Dr. O’Malley currently runs the Mechatronics and Haptic Interfaces (MAHI) Lab at Rice University, and she was recently awarded a million dollar National Robotics Initiative grant for one of her projects. The MAHI Lab “focuses on the design, manufacture, and evaluation of mechatronic or robotic systems to model, rehabilitate, enhance or augment the human sensorimotor control system.”1 Her current research is focused on prosthetics and rehabilitation with an effort to include haptic feedback. She is currently working on the MAHI EXO- II. “It’s a force feedback exoskeleton, so it can provide forces, it can move your limb, or it can work with you,” she said. The primary project involving this exoskeleton is focused on “using electrical activity from the brain captured with EEG… and looking for certain patterns of activation of different areas of the brain as a trigger to move the robot.” In other words, Dr. O’Malley is attempting to enable exoskeleton users to control the device through brain activity.

Dr. O’Malley is also conducting another project, utilizing the National Robotics Initiative grant, to develop a haptic cueing system to aid medical students training for endovascular surgeries. The idea for this haptic cueing system came from two different sources. The first part was her prior research which consisted of working with joysticks. She worked on a project that involved using a joystick, incorporated with force feedback, to swing a ball to hit targets.2 As a result of this research, Dr. O’Malley found that “we could measure people’s performance, we could measure how they used the joystick, how they manipulated the ball, and just from different measures about the characteristics of the ball movement, we could determine whether you were an expert or a novice at the task… If we use quantitative measures that tell us about the quality of how they’re controlling the tools, those same measures correlate with the experience they have.” After talking to some surgeons, Dr. O’Malley found that these techniques of measuring movement could work well for training surgeons.

The second impetus for this research came from an annual conference about haptics and force feedback. At the conference she noticed that more and more people were moving towards wearable haptics, such as the Fitbit, which vibrates on your wrist. She also saw that everyone was using these vibrational cues to give directional information. However, “nobody was really using it as a feedback channel about performance,” she said. These realizations led to the idea of the vibrotactile feedback system.

Although the project is still in its infancy, the current anticipated product is a virtual reality simulator which will track the movements of the tool. According to Dr. O’Malley, the technology would provide feedback through a single vibrotactile disk worn on the upper limb. The disk would use a voice coil actuator that moves perpendicular to the wearer’s skin. Dr. O’Malley is currently working with Rice psychologist Dr. Michael Byrne to determine which frequency and amplitude to use for the actuator, as well as the timing of the feedback to avoid interrupting or distracting the user.

Ultimately, this project would measure the medical students’ smoothness and precision while using tools, as well as give feedback to the students regarding their performance. In the future, it could also be used in surgeries during which a doctor operates a robot and receives force feedback through similar haptics. During current endovascular surgery, a surgeon uses screens that project a 2D image of the tools in the patient. Incorporating 3D views would need further FDA approval and could distract and confuse surgeons given the number of screens they would have to monitor. This project would offer surgeons a simpler way to operate. From exoskeletons to medical training, there is a huge potential for haptic technologies. Dr. O’Malley is making this potential a reality.

References

  1. Mechatronics and Haptic Interfaces Lab Home Page. http://mahilab.rice.edu (accessed   Nov. 7, 2016).
  2. O’Malley, M. K. et al. J. Dyn. Sys., Meas., Control. 2005, 128 (1), 75-85.

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