## Saturday, 27 August 2011

### Astrobiology and Space Exploration

"Mungkin saja kehidupan lain di luar bumi sana sedang menunggu kita untuk dikunjungi"
~Arip~

# Stanford University Course

In the Stanford Astrobiology Course, our lectures follow a more or less linear path from the Big Bang all the way to the development of complex life and, finally, space exploration. It is truly amazing how evolutionary principles have operated at the macro, and micro, level ever since the birth of the universe we reside in today.

Physics, research, experimentation, astronomy, extraterrestrial life, planets, asteroids, cosmology, measurements, data, innovation, development, history, science, telescopes, observations, theories, predictions, telescopes, instruments, light, expansion.

A syllabus for the Winter, 2010 Astrobiology Course can be downloaded here.

The Big Bang created the physical universe. Of course life is part of this physical universe, but the immediate building blocks of life are chemicals. Before the Big Bang, words such as “time” had no meaning, but even in the first few minutes there could be no chemistry since there were no atoms. The nuclei of some of the lighter elements formed within minutes, atoms some time later, and elements heavier than lithium were forged in the supernovae of stars. Thus, we are primarily star dust, although the hydrogen atom you drink tonight may be nearly as old as the Big Bang.

But living organisms are more than a collection of atoms. They are a cauldron of molecules in a solvent. For life on earth, that solvent is water. The building blocks of chemical compounds had to form other molecules as well, especially ones based on carbon. Where could these compounds have been formed? Were they formed on earth or transported from elsewhere?

Most stunning are the recent discoveries in astrochemistry showing that the organic compounds that make up life on earth may possibly be THE language of the universe. In September 2010, the NASA Ames IR Spectroscopic Database was released, along with tools to access it. See the press release.

“Chemical Evolution across Space and Time: From The Big Bang to Prebiotic Chemistry”  Eds Lori Zaikowski and Jon Friedrich; Published by American Chemical Society, Wash. DC ISBN 978-0-8412-0

Amallondalla’s is chapter 5: ” Chemical Evolution in the Interstellar Medium:  Feedstock of Solar Systems.
The next volume is entitled:

“Chemical Evolution across Space and Time: From Origins of Life to Modern Society”  Eds Lori Zaikowski and Jon Friedrich; Published by American Chemical Society, Wash.

This Scientific American article  is geared to the general scientifically literate audience:  ”Life’s Far-Flung Raw Materials”,

Bernstein, Sandford, Allamandola, Scientific American, July 1999

"The space effort is very simply a continuation of the expansion of ecological range, which has been occurring at an accelerating rate throughout the evolutionary history of Man..."
~Ward J. Haas, "Biological Significance of the Space Effort," in Annals of the New York Academy of Science, 1966 ~

Below you will find a list of recommended resources. If you would like to learn more about the Big Bang, check out these books, videos, and articles.

Sumber:
1. Stanford University
2. NASA

Ucapan Terima Kasih:

1. Bapak. Prof. Dr. Ing. H. B. J. Habibie.

2. Departemen Pendidikan Nasional

3. Kementrian Riset dan Teknologi

4. Lembaga Penerbangan dan Antariksa Nasional

Disusun Ulang Oleh:

Arip Nurahman

Department of Physics, Indonesia University of Education

&

Follower Open Course Ware at MIT-Harvard University, Cambridge.USA.

Semoga Bermanfaat dan Terima Kasih

## Thursday, 25 August 2011

### The Mathematics of Super String Theory

The single most important equation in (first quantisized bosonic) string theory is the N-point scattering amplitude. This treats the incoming and outgoing strings as points, which in string theory are tachyons, with momentum ki which connect to a string world surface at the surface points zi. It is given by the following functional integral which integrates (sums) over all possible embeddings of this 2D surface in 26 dimensions.

$A_N = \int{D\mu \int{D[X] exp \left( -\frac{1}{4\pi\alpha} \int{ \partial_z X_{\mu}(z,\overline{z}) \partial_{\overline{z}} X^{\mu}(z,\overline{z})}dz^2 + i \sum_{i=1}^{N}{k_{i \mu} X^{\mu}(z_i,\overline{z}_i) } \right) }}$

The functional integral can be done because it is a Gaussian to become:

This is integrated over the various points zi. Special care must be taken because two parts of this complex region may represent the same point on the 2D surface and you don't want to integrate over them twice. Also you need to make sure you are not integrating multiple times over different paramaterisations of the surface. When this is taken into account it can be used to calculate the 4-point scattering amplitude (the 3-point amplitude is simply a delta function):

$A_4 = \frac{ \Gamma (-1+\frac12(k_1+k_2)^2) \Gamma (-1+\frac12(k_2+k_3)^2) } { \Gamma (-2+\frac12((k_1+k_2)^2+(k_2+k_3)^2)) }$

Which is a beta function. It was this beta function which was apparently found before full string theory was developed. With superstrings the equations contain not only the 10D space-time coordinates X but also the grassman coordinates θ. Since there are various ways this can be done this leads to different string theories.

When integrating over surfaces such as the torus, we end up with equations in terms of theta functions and elliptic functions such as the Dedekind eta function. This is smooth everywhere, which it has to be to make physical sense, only when raised to the 24th power. This is the origin of needing 26 dimensions of space-time for bosonic string theory. The extra two dimensions arise as degrees of freedom of the string surface.

### D-Branes

D-Branes are membrane-like objects in 10D string theory. They can be thought of as occurring as a result of a Kaluza-Klein compactification of 11D M-Theory which contains membranes. Because compactification of a geometric theory produces extra vector fields the D-branes can be included in the action by adding an extra U(1) vector field to the string action.

$\partial_z \rightarrow \partial_z +iA_z(z,\overline{z})$

In type I open string theory, the ends of open strings are always attached to D-brane surfaces. A string theory with more gauge fields such as SU(2) gauge fields would then correspond to the compactification of some higher dimensional theory above 11 dimensions which is not thought to be possible to date.

### Why Five Superstring Theories?

For a 10 dimensional supersymmetric theory we are allowed a 32-component Majorana spinor. This can be decomposed into a pair of 16-component Majorana-Weyl (chiral) spinors. There are then various ways to construct an invariant depending on whether these two spinors have the same or opposite chiralities:

Superstring Model Invariant
Heterotic $\partial_zX^\mu-i\overline{\theta_{L}}\Gamma^\mu\partial_z\theta_{L}$
IIA $\partial_zX^\mu-i\overline{\theta_{L}}\Gamma^\mu\partial_z\theta_{L}-i\overline{\theta_{R}}\Gamma^\mu\partial_z\theta_{R}$
IIB $\partial_zX^\mu-i\overline{\theta^1_{L}}\Gamma^\mu\partial_z\theta^1_{L}-i\overline{\theta^2_{L}}\Gamma^\mu\partial_z\theta^2_{L}$

The heterotic superstrings come in two types SO(32) and E8xE8 as indicated above and the type I superstrings include open strings.

Sources:

Wikipedia

## Monday, 22 August 2011

### SPACE POWER REACTORS Part III

"Energi Nuklir di masa yang akan datang menjadi kunci bagi bahan bakar penjelajahan manusia ke
tempat-tempat yg sebelumnya belum dikunjungi"
~Arip~

This EOE article is adapted from an information paper published by the World Nuclear Association (WNA). WNA information papers are frequently updated, so for greater detail or more up to date numbers, please see the latest version on WNA website (link at end of article).

## Heatpipe Power System

Heatpipe Power System (HPS) reactors are compact fast reactors producing up to 100 kWe for about ten years to power a spacecraft or planetary surface vehicle. They have been developed since 1994 at the Los Alamos National Laboratory in New Mexico as a robust and low technical-risk system with an emphasis on high reliability and safety. They employ heatpipes to transfer energy from the reactor core to make electricity using Stirling cycle or Brayton cycle converters.

Energy from fission is conducted from the fuel pins to the heatpipes filled with sodium vapor that carry it to the heat exchangers and then in hot gas to the power conversion systems to make electricity. The gas is 72% helium and 28% xenon.

The reactor itself contains a number of heatpipe modules with the fuel. Each module has its central heatpipe with rhenium-clad fuel sleeves arranged around it. They are the same diameter and contain 97% enriched uranium nitride fuel, all within the cladding of the module. The modules form a compact hexagonal core.

Control is obtained by six stainless steel-clad beryllium drums, each 11 or 13 cm diameter, with boron carbide forming a 120 degree arc on each. The drums fit within the six sections of the beryllium radial neutron reflector surrounding the core, and rotate to effect control, moving the boron carbide in or out. Shielding is dependent on the mission or application, but lithium hydride in stainless steel cans is the main form of neutron shielding.

The SAFE-400 space fission reactor (Safe Affordable Fission Engine) is a 400 kWt HPS producing 100 kWe to power a space vehicle using two Brayton power systems—gas turbines driven directly by the hot gas from the reactor. Heat exchanger outlet temperature is 880°C. The reactor has 127 identical heatpipe modules made of molybdenum, or niobium with 1% zirconium. Each has three fuel pins 1 cm diameter, nesting together into a compact hexagonal core 25 cm across. The fuel pins are 70 cm long (fuelled length 56 cm), the total heatpipe length is 145 cm, extending 75 cm above the core, where they are coupled with the heat exchangers. The core with reflector has a 51 cm diameter. The mass of the core is about 512 kg and each heat exchanger is 72 kg. SAFE has also been tested with an electric ion drive.

A smaller version of this kind of reactor is the HOMER-15—the Heatpipe-Operated Mars Exploration Reactor. It is a15 kW thermal unit similar to the larger SAFE model, and stands 2.4 meters tall including the heat exchanger and 3 kWe Stirling engine (see above). It operates at only 600°C and is therefore able to use stainless steel for fuel pins and heatpipes, which are 1.6 cm diameter. It has 19 sodium heatpipe modules with 102 fuel pins bonded to them, 4 or 6 per pipe, that hold a total of 72 kg of fuel. The heatpipes are 106 cm long and fuel height 36 cm. The core is hexagonal (18 cm across) with six beryllium oxide (BeO) pins in the corners. Total mass of reactor system is 214 kg, and diameter is 41 cm.

In the 1980s, the French ERATO program considered three 20 kWe turboelectric power systems for space operation. All used a Brayton cycle converter with a helium-xenon mix as working fluid. The first system was a sodium-cooled uranium dioxide-fuelled fast reactor operating at 670°C, the second a high-temperature gas-cooled reactor (thermal or epithermal neutron spectrum) working at 840°C, and the third a lithium-cooled uranium nitride-fuelled fast reactor working at 1150°C.

## Project Prometheus 2003

In 2002, the U.S. National Aeronautics and Space Administration (NASA) announced its Nuclear Systems Initiative for space projects, and in 2003 this was renamed Project Prometheus and given increased funding. Its purpose is to enable a major step change in the capability of space missions. Nuclear-powered space travel will be much faster than is now possible, and will enable manned missions to Mars.

One part of Prometheus, a NASA project with substantial involvement by the U.S. Department of Energy (DOE), is to develop the Multi-Mission Thermoelectric Generator and the Stirling Radioisotope Generator described in the RTG section above.

A more radical objective of Prometheus is to produce a space fission reactor system such as those described above for both power and propulsion that is safe to launch and will operate for many years. This will have much greater power than RTGs. Power of 100 kW is envisaged for a nuclear electric propulsion system driven by plasma.

The fiscal year 2004 budget proposal was US$279 million, with$3 billion to be spent over five years. This consists of $186 million ($1 billion over 5 years) building on last year's allocation, plus $93 million ($2 billion over five years) towards a first flight mission to Jupiter—the Jupiter Icy Moon Orbiter—expected to launch in 2017 and explore for a decade. Project Prometheus received \$430 million in 200r budget.

In 2003, NASA's Project Prometheus successfully tested a High Power Electric Propulsion (HiPEP) ion engine. This operates by ionizing xenon with microwaves. At the rear of the engine is a pair of rectangular metal grids that are charged with 6,000 volts of electric potential. The force of this electric field exerts a strong electrostatic pull on the xenon ions, accelerating them and producing the thrust needed to propel the spacecraft. The design was tested at up to 12 kW, though twice that is envisaged. The thruster is designed for a 7- to 10-year lifetime with high fuel efficiency, and to be powered by a small nuclear reactor.

## Citation

World Nuclear Association, Ian Hore-Lacy (Lead Author);Cutler Cleveland (Topic Editor) "Nuclear reactors for space". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth December 6, 2009; Last revised Date December 6, 2009; Retrieved October 26, 2011 <http://www.eoearth.org/article/Nuclear_reactors_for_space>

## The Authors

The World Nuclear Association is the global private-sector organization that seeks to promote the peaceful worldwide use of nuclear power as a sustainable energy resource for the coming centuries. Specifically, the WNA is concerned with nuclear power generation and all aspects of the nuclear fuel cycle, including mining, conversion, enrichment, fuel fabrication, plant manufacture, transport, and the safe disposition of spent fuel.The WNA serves its Members by facilitating their interaction on te ... (Full Bio)

Ian Hore-Lacy is Director for Public Communications at the World Nuclear Association, an international trade association based in London, and has been involved with studying uranium and nuclear power since 1995. His function is primarily focused on public information on nuclear power via the World Wide Web. He is a former biology teacher who joined the mining industry as an environmental scientist in 1974, with CRA (now Rio Tinto). He is author of Nuclear Electricity, the expanded eighth editi ... (Full Bio)

Sources:

1. Poston, D.I. 2002, Nuclear design of SAFE-400 space fission reactor, Nuclear News, Dec 2001.
2. Poston, D.I. 2002, Nuclear design of HOMER-15 Mars surface fission reactor, Nuclear News, Dec 2001.
3. Vrillon et al, 1990, ERATO article, Nuclear Europe Worldscan 11-12, 1990.
4. US DOE web site- space applications.
5. space.com 21/5/00, 16/6/00, 22/7/00, 17/1/03, 7/2/03.
6. www.nuclearspace.com
7. Delovy Mir 8/12/95.
8. G. Kulcinski, University of Wisconsin material on web.
9. Kleiner K. 2003, Fission Control, New Scientist 12/4/03.
10. OECD 1990, Emergency Preparedness for Nuclear-Powered Satellites.

## Thursday, 18 August 2011

### Question About Gravitation Part I

"Kutemukan cinta dalam gemerlapnya bintang gemintang, kasih dalam terangnya cahaya rembulan
serta Keagungan-Nya dalam hangat cahaya Mentari"
~Arip~

Arip Nurahman

Department of Physics

Faculty of Sciences and Mathematics, Indonesian University of Education

&

Follower Open Course Ware at MIT-Harvard University, M.A., U.S.A.

Gravitation is a natural phenomenon by which objects with mass attract one another. In everyday life, gravitation is most commonly thought of as the agency which lends weight to objects with mass. Gravitation causes dispersed matter to coalesce, thus accounting for the existence of the Earth, the Sun, and most of the macroscopic objects in the universe. It is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth; for the formation of tides; for convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena observed on Earth. Modern physics describes gravitation using the general theory of relativity, in which gravitation is a consequence of the curvature of spacetime which governs the motion of inertial objects. The simpler Newton's law of universal gravitation provides an accurate approximation for most calculations.
(Wikipedia)

Q: What is gravity?

A: The answer cannot be found in today's theories. Newton only claimed that gravity was an attracting force between all objects because that's the way things appear objects fall to the Earth or approach each other when floating in outer space. So Newton understandably claimed that it must be some type of attracting force emanating from objects, but he gave no scientific explanation for this force.

Why does it attract and not repel? How does it cause falling objects and orbiting planets without drawing on any known power source? Einstein was so dissatisfied with our lack of understanding about gravity even two centuries after Newton that he invented an entirely new theory of gravity, known as General Relativity.

Yet this theory doesn’t solve these problems either, adding that since everything in 3-dimensional space takes time to occur we must include our time measurement as a literal 4th physical dimension of our universe’s structure hence "4-D space-time", which somehow warps 4-dimensionally in the presence of matter for still-unexplained reasons, presumably explaining gravity.

In addition to the increase in unanswered questions with General Relativity, it has been found to completely fail even to explain the motion of stars in galaxies. This has led to the further invention of exotic "Dark Matter", said to invisibly fill galaxies, rather than questioning Einstein’s theory and the often-repeated claim that it has been tested to extreme accuracy.

Add to this the fact that there are still a half-dozen theories of gravity officially under consideration at the moment, all with different physical description of gravity, and it is no wonder many are still asking:

"What is gravity?" From "Nailing Down Gravity", Discover Magazine, Oct 2003: For Michael Martin Nieto, a theoretical physicist at Los Alamos National Laboratory in New Mexico, the mystery involves much more than a few hunks of spacefaring hardware; it reveals that there might be something wrong with our understanding of gravity, the most pervasive force in the universe.

"We don't know anything," he says. "Everything about gravity is mysterious".

To Be Continued

Sources:

1. http://www.thefinaltheory.com/scienceflaws.html
2. http://en.wikipedia.org/wiki/Gravitation

## Wednesday, 17 August 2011

### Mari Sahabat Kita Optimalkan E-Journal Badan Tenaga Nuklir Nasional

"Nusantara Mempunyai Potensi Besar dalam Bidang Ipteks Nuklir, dalam Peringatan hari Kemerdekaan Indonesia ke-100 yakni tahun 2045, kita harus mempunyai Ilmuwan dalam bidang Ipteks Nuklir minimal sebanyak 100.000 orang"
*Arip Nurahman*

### Eksplorium Buletin Pusat Pengembangan Geologi Nuklir

Eksplorium adalah media informasi Buletin Pusat Pengembangan Geologi Nuklir, ter akreditasi LIPI No.352/Akred-LIPI/P2MBI/07/2011
Diterbitkan oleh Pusat Pengembangan Geologi Nuklir- BATAN
Lihat Jurnal | Terbitan Terkini | Daftar

### Jurnal Teknologi Bahan Nuklir

Jurnal Teknologi Bahan Nuklir, Alamat Redaksi : Penerbit Pusat Teknologi Bahan Bakar Nuklir - BATAN, Kawasan Puspiptek Serpong - Tangerang Selatan 15314, Indonesia
Lihat Jurnal | Terbitan Terkini | Daftar

### Urania Jurnal Ilmiah Daur Bahan Bakar Nuklir

Jurnal Ilmiah Daur Bahan Bakar Nuklir URANIA adalah wahana informasi tentang daur bagan bakar nuklir yang berisi hasil penelitian, pengembangan dan tulisan ilmiah terkait. terbitan pertama kali pada tahun 1995 dengan frekuensi terbit sebanyak empat kali dalam setahun yakni pada bulan Januari, April, Juli dan Oktober.

Sementara itu, mulai tahun 2011 Jurnal Daur Bahan Bakar Nuklir URANIA akan terbit tiga kali dalam setahun, yaitu Februari, Juni dan Oktober.

Lihat Jurnal | Terbitan Terkini | Daftar

Bila kita mampu membangun himpunan-himpunan peneliti kecil di tiap sekolah tinggi/kampus di Indonesia mengenai Iptek Nuklir ini, kemungkinan besar percepatan perkembangan ilmu pengetahuan Nuklir di tanah air akan semakin dahsyat dan masyarakat kita di kemudian hari dapat memetik manfaatnya.

Amin.

Kunjungi juga:

http://www.batan.go.id/  (BATAN)

http://www.iaea.org/ (International Atomic Energy Agency)

http://nuclearscienceandtechnology.blogspot.com/  (Sekolah Sains dan Teknologi Nuklir)

http://masyarakatipteksindonesia.blogspot.com/2010/02/nuklir-indonesia_8979.html (Masyarakat Nuklir Indonesia)

http://www.sttn-batan.ac.id/ (Sekolah Tinggi Teknologi Nuklir BATAN)

http://ocw.mit.edu/courses/nuclear-engineering/ (Nuclear Engineering OpenCourseWare from MIT)

http://fisika.upi.edu/ (Jurusan Pendidikan Fisika, FPMIPA Universitas Pendidikan Indonesia)

Kak Rezy Pradipta, Ph.D. (Alumni Tim Olimpiade Fisika Indonesia, Belajar di Department of Nuclear Engineering at MIT)

Dr. Mohamed Mustafa ElBaradei, J.S.D. (Former Director General of IAEA)

Prof. Mujid S. Kazimi, Ph.D. (Director, Center for Advanced Nuclear Energy Systems MIT)

Prof.Djarot Sulistio Wisnubroto, M.Sc., D.Sc. (Presiden BATAN)

Kak Iqbal Robiyana, S.Pd. (Founder Center for Nuclear Education at Indonesia University of Education)

Dr. Petros Aslanyan, M.Sc. (Joint Institute for Nuclear Research, Rusia & Yerevan State University)

Semangat Semoga Bermanfaat

## Monday, 15 August 2011

### Para Pelopor Peraih Hadiah Nobel

First Prizes

Wilhelm Conrad Röntgen received the first Physics Prize for his discovery of X-rays.

Once the Nobel Foundation and its guidelines were in place, the Nobel Committees began collecting nominations for the inaugural prizes. Subsequently they sent a list of preliminary candidates to the prize-awarding institutions.

Originally, the Norwegian Nobel Committee appointed prominent figures including Jørgen Løvland, Bjørnstjerne Bjørnson and Johannes Steen to give the Nobel Peace Prize credibility.

The committee awarded the Peace Prize to two prominent figures in the growing peace movement around the end of the 19th century. These were Frédéric Passy, co-founder of the Inter-Parliamentary Union, and Henry Dunant the founder of the International Committee of the Red Cross
The Nobel Committee's Physics Prize shortlist cited Wilhelm Conrad Röntgen's discovery of X-rays and Philipp Lenard's work on cathode rays. The Academy of Sciences selected Röntgen for the prize.

In the last decades of the 19th century, many chemists had made significant contributions. Thus, with the Chemistry Prize, the Academy "was chiefly faced with merely deciding the order in which these scientists should be awarded the prize."

The Academy received 20 nominations, eleven of them for Jacobus van't Hoff. Van't Hoff was awarded the prize for his contributions in chemical thermodynamics. The Swedish Academy chose the poet Sully Prudhomme for the first Nobel Prize in Literature.

A group including 42 Swedish writers, artists and literary critics protested against this decision, having expected Leo Tolstoy to win. Some, including Burton Feldman, have criticised this prize because they consider Prudhomme a mediocre poet. Feldman's explanation is that most of the Academy members preferred Victorian literature and thus selected a Victorian poet.

The first Physiology or Medicine Prize went to the German physiologist and microbiologist Emil von Behring. During the 1890s, von Behring developed an antitoxin to treat diphtheria, which until then was causing thousands of deaths each year.

Sumber:

Nobel Prize

Wikipedia

## Wednesday, 10 August 2011

### Nuclear Reactors for Space Applications

"Everything is becoming science fiction. From the margins of an almost invisible literature has sprung the intact reality of the 20th century."

— J. G. Ballard, 1930.

The Martian Surface Reactor: An Advanced Nuclear Power Station for Manned Extraterrestrial Exploration

A. Bushman, D.M. Carpenter, T.S. Ellis, S.P. Gallagher, M.D. Hershcovitch, M.C. Hine, E.D. Johnson, S.C. Kane, M.R. Presley, A.H. Roach, S. Shaikh, M.P. Short, and M.A. Stawicki

Arip Nurahman
Department of Physics, Faculty of Sciences and mathematics

Indonesian University of Education
and
Follower Open Course Ware at MIT-Harvard University. M.A. USA.

Abstract

As part of the 22.033/22.33 Nuclear Systems Design project, this group designed a100 kWe Martian/Lunar surface reactor system to work for 5 EFPY in support of extraterrestrial human exploration efforts. The reactor design was optimized over the following criteria: small mass and size, controllability, launchability/accident safety, and high reliability. The Martian Surface Reactor was comprised of four main systems: the core, power conversion system, radiator and shielding.

The core produces 1.2 MWth and operates in a fast spectrum. Li heat pipes cool the core and couple to the power conversion system. The heat pipes compliment the chosen pin-type fuel geometry arranged in a tri-cusp configuration. The reactor fuel is UN (33.1w/o enriched), the cladding and structural materials in core are Re, and a Hf vessel encases the core. The reflector is Zr3Si2, chosen for its high albedo. Control is achieved by rotating drums, using a TaB2 shutter material. Under a wide range of postulated accident scenarios, this core remains sub-critical and poses minimal environmental hazards.

The power conversion system consists of three parts: a power conversion unit, a transmission system and a heat exchanger. The power conversion unit is a series of cesium thermionic cells, each one wrapped around a core heat pipe. The thermionic emitter is Re at 1800 K, and the collector is molybdenum at 950 K. These units, operating at 10+% efficiency, produce 125 kWe DC and transmit 100 kWe AC. The power transmission system includes 25 separate DC-to-AC converters, transformers to step up the transmission voltage, and 25 km of 22 gauge copper wire for actual electricity transmission. The remaining 900 kWth then gets transmitted to the heat pipes of the radiator via an annular heat pipe heat exchanger that fits over the thermionics. This power conversion system was designed with much redundancy and high safety margins; the highest percent power loss due to a single point failure is 4%.

The radiator is a series of potassium heat pipes with carbon-carbon fins attached. For each core heat pipe there is one radiator heat pipe. The series of heat pipe/fin combinations form a conical shell around the reactor. There is only a 10 degree temperature drop between the heat exchanger and radiator surface, making the radiating temperature 940 K. In the radiator, the maximum cooling loss due to a single point failure is less than 1%.

The shielding system is a bi-layer shadow shield that covers an 80º arc of the core. The inner layer of the shield is a boron carbide neutron shield; the outer layer is a tungsten gamma shield. The tungsten shield is coated with SiC to prevent oxidation in the Martian atmosphere. At a distance of 11 meters from the reactor, on the shielded side, the radiation dose falls to an acceptable 2 mrem/hr; on the unshielded side, an exclusion zone extends to 14 m from the core. The shield is movable to protect crew no matter the initial orientation of the core.

When combined together, the four systems comprise the MSR. The system is roughly conical, 4.8 m in diameter and 3 m tall. The total mass of the reactor is 6.5 MT.

# Nuclear Reactors for Space Applications

With the renewed interest in deep space applications, Professor A. Kadak has instituted several studies on nuclear power systems for space applications using the nuclear engineering design course offered for both graduate and undergraduate students. The first such study considered the design of nuclear electric power for propulsion and a terrestrial power station for manned Mars missions. This project was presented to NASA senior project planners in Washington DC in 2003.

Following that meeting and a subsequent meeting with Naval Reactors engineers, feedback was used to redesign the reactor from a highly efficient spent fuel Plutonium core to a highly enriched uranium core by a Master’s thesis student. This year, due to President Bush’s desire to test the new concepts on the Moon, a terrestrial 100 kwe plant was redesigned for use on both Mars and the Moon in the design project in the fall of 2004. As a result of these projects, the nuclear engineering department is gaining valuable experience in nuclear space applications.

# Publications

## Nuclear Space Applications (NSA) Program

 Abstract MIT-NSA-TR-001 V. Dostal, K. Gezelius, J. Horng, J. Koser, J.P. Iv, E. Shwageraus, P. Yarsky, and A.C. Kadak, "Mission to Mars: How to Get People There and Back with Nuclear Energy" (September 2004). Abstract MIT-NSA-TR-002 P. Yarsky, A.C. Kadak, and M.J. Driscoll, "Design of a Sodium-cooled Epithermal Long-term Exploration Nuclear Engine" (September 2004). Abstract MIT-NSA-TR-003 A. Bushman, D.M. Carpenter, T.S. Ellis, S.P. Gallagher, M.D. Hershcovitch, M.C. Hine, E.D. Johnson, S.C. Kane, M.R. Presley, A.H. Roach, S. Shaikh, M.P. Short, and M.A. Stawicki, "The Martian Surface Reactor: An Advanced Nuclear Power Station for Manned Extraterrestrial Exploration" (December 2004).

"Aplikasi IPTEK NUKLIR dalam Penjelajahan Angkasa Luar, Akan menjadi Power Utama"
~Arip~

Sources:

1.MIT Nuclear Space Research
2.SPACE POWER REACTORS
3.Nuclear Reactors for Space

## Saturday, 6 August 2011

### Einstein dan Relativitas Umum yang Legendaris

Dari mekanika klasik menuju relativitas umum Relativitas umum dapat dipahami dengan baik dengan mengevaluasi kemiripannya beserta perbedaannya dari fisika klasik.

Langkah pertama adalah realisasi bahwa mekanika klasik dan hukum gravitasi Newton mengijinkan adanya deskripsi geometri.

Kombinasi deskripsi ini dengan hukum-hukum relativitas khusus akan membawa kita kepada penurunan heuristik relativitas umum.

Generalisasi relativistik

Geometri gravitasi Newton pada dasarnya didasarkan pada mekanika klasik. Ia hanyalah kasus khusus dari mekanika relativitas khusus.

Dalam bahasa simetri: ketika gravitasi dapat diabaikan, fisika yang berlaku bersifat invarian Lorentz pada relativitas khusus daripada invarian Galileo pada mekanika klasik.

Perbedaan antara keduanya menjadi signifikan apabila kecepatan terlibat di dalamnya mendekati kecepatan cahaya dan berenergi tinggi.

Referensi:

Kunjungi Juga:

Relativitas Umum dan Ke Geniusan Einstein

Sumber:

The University of Cambridge

Wikipedia

The End