Astrobiology and Space Exploration

"Pencarian akan persahabatan di dunia luar sana, akan membutuhkan kesabaran yang panjang bagi umat manusia"

~Arip~

2. The Search for other Earths and Life in the Universe

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.



Every year Professor Marcy brings new discoveries to his lecture and this year it was 1200 new exoplanets! Read about the Kepler Team’s announcement in the Wall Street Journal or watch their video.
Save the playlist of Professor Marcy’s latest lecture.
The first of 6 parts begins here:










Also listen on Stanford iTunes to Greg Laughlin’s talk on Extrasolar Planets from 2008. With Arbesman Laughlin has tried to predict how soon an Earth-like exoplanet will be found by extrapolating the rate of discovery so far in the search for habitable exoplanets. See the New Scientist, September 21

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

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.

"There are so many benefits to be derived from space exploration and exploitation; why not take what seems to me the only chance of escaping what is otherwise the sure destruction of all that humanity has struggled to achieve for 50,000 years?"

~Isaac Asimov, speech at Rutgers University~

Further Resources:
Singh, Simon. “The Big Bang: The Origin of the Universe”. New York: Fourth Estate, 2005.
Riordan, Michael and William A. Zajc. “The First Few Microseconds”. Scientific American Magazine: May, 2006.
Roos, Matts. “Expansion of the Universe – Standard Big Bang Model”. UNESCO Encyclopedia of Life Supporting Systems, 14 Feb. 2008.

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

Relativitas Umum dan Ke Geniusan Einstein

Teori Einstein memiliki implikasi astrofisika yang penting. Teori ini memprediksikan adanya keberadaan daerah lubang hitam yang mana ruang dan waktu terdistorsi sedemikiannya tiada satu pun, bahkan cahaya pun, yang dapat lolos darinya. 

Terdapat bukti bahwa lubang hitam bintang dan jenis-jenis lubang hitam lainnya yang lebih besar bertanggungjawab terhadap radiasi kuat yang dipancarkan oleh objek-objek astronomi tertentu, seperti inti galaksi aktif dan miktrokuasar. 

Melengkungnya cahaya oleh gravitasi dapat menyebabkan fenomena pelensaan gravitasi. Relativitas umum juga memprediksikan keberadaan gelombang gravitasi. Keberadaan gelombang ini telah diukur secara tidak langsung, dan terdapat pula beberapa usaha yang dilakukan untuk mengukurnya secara langsung. 

Selain itu, relativitas umum adalah dasar dari model kosmologis untuk alam semesta yang terus berkembang. 

 

Referensi:

• Ibanez, L. E. (2000), "The second string (phenomenology) revolution", Class. Quant. Grav. 17: 1117–1128, doi:10.1088/0264-9381/17/5/321, arΧiv:hep-ph/9911499
• Iorio, L. (2009), "An Assessment of the Systematic Uncertainty in Present and Future Tests of the Lense-Thirring Effect with Satellite Laser Ranging", Space Sci. Rev., doi:10.1007/s11214-008-9478-1
• Isham, Christopher J. (1994), "Prima facie questions in quantum gravity", in Ehlers, Jürgen; Friedrich, Helmut, Canonical Gravity: From Classical to Quantum, Springer, ISBN 3-540-58339-4
• Israel, Werner (1971), "Event Horizons and Gravitational Collapse", General Relativity and Gravitation 2: 53–59, doi:10.1007/BF02450518
• Israel, Werner (1987), "Dark stars: the evolution of an idea", in Hawking, Stephen W.; Israel, Werner, 300 Years of Gravitation, Cambridge University Press, pp. 199–276, ISBN 0-521-37976-8
• Janssen, Michel (2005), "Of pots and holes: Einstein’s bumpy road to general relativity" (PDF), Ann. Phys. (Leipzig) 14: 58–85, doi:10.1002/andp.200410130, http://www.tc.umn.edu/~janss011/pdf%20files/potsandholes.pdf
• Jaranowski, Piotr; Królak, Andrzej (2005), "Gravitational-Wave Data Analysis. Formalism and Sample Applications: The Gaussian Case", Living Rev. Relativity 8, http://www.livingreviews.org/lrr-2005-3, retrieved 2007-07-30
• Kahn, Bob (1996–2008), Gravity Probe B Website, Stanford University, http://einstein.stanford.edu/, retrieved 2008-05-21
• Kahn, Bob (April 14, 2007) (PDF), Was Einstein right? Scientists provide first public peek at Gravity Probe B results (Stanford University Press Release), Stanford University News Service, http://einstein.stanford.edu/content/press_releases/SU/pr-aps-041807.pdf
• Kamionkowski, Marc; Kosowsky, Arthur; Stebbins, Albert (1997), "Statistics of Cosmic Microwave Background Polarization", Phys. Rev. D55: 7368–7388, doi:10.1103/PhysRevD.55.7368, arΧiv:astro-ph/9611125
• Kennefick, Daniel (2005), "Astronomers Test General Relativity: Light-bending and the Solar Redshift", in Renn, Jürgen, One hundred authors for Einstein, Wiley-VCH, pp. 178–181, ISBN 3-527-40574-7
• Kennefick, Daniel (2007), "Not Only Because of Theory: Dyson, Eddington and the Competing Myths of the 1919 Eclipse Expedition", Proceedings of the 7th Conference on the History of General Relativity, Tenerife, 2005, arΧiv:0709.0685
• Kenyon, I. R. (1990), General Relativity, Oxford University Press, ISBN 0-19-851996-6
• Kochanek, C.S.; Falco, E.E.; Impey, C.; Lehar, J. (2007), CASTLES Survey Website, Harvard-Smithsonian Center for Astrophysics, http://cfa-www.harvard.edu/castles, retrieved 2007-08-21
• Komar, Arthur (1959), "Covariant Conservation Laws in General Relativity", Phys. Rev. 113: 934–936, doi:10.1103/PhysRev.113.934
• Kramer, Michael (2004), "Millisecond Pulsars as Tools of Fundamental Physics", in Karshenboim, S. G., Astrophysics, Clocks and Fundamental Constants (Lecture Notes in Physics Vol. 648), Springer, pp. 33–54, arΧiv:astro-ph/0405178
• Kramer, M.; Stairs, I. H.; Manchester, R. N.; McLaughlin, M. A. (2006), "Tests of general relativity from timing the double pulsar", Science 314: 97–102, doi:10.1126/science.1132305, arΧiv:astro-ph/0609417, PMID 16973838
• Kraus, Ute (1998), "Light Deflection Near Neutron Stars", Relativistic Astrophysics, Vieweg, pp. 66–81, ISBN 352-806909-0
• Kuchař, Karel (1973), "Canonical Quantization of Gravity", in Israel, Werner, Relativity, Astrophysics and Cosmology, D. Reidel, pp. 237–288, ISBN 90-277-0369-8
• Künzle, H. P. (1972), "Galilei and Lorentz Structures on spacetime: comparison of the corresponding geometry and physics", Ann. Inst. Henri Poincaré a 17: 337–362, http://www.numdam.org/item?id=AIHPA_1972__17_4_337_0
• Lahav, Ofer; Suto, Yasushi (2004), "Measuring our Universe from Galaxy Redshift Surveys", Living Rev. Relativity 7, http://www.livingreviews.org/lrr-2004-8, retrieved 2007-08-19
• Landgraf, M.; Hechler, M.; Kemble, S. (2005), "Mission design for LISA Pathfinder", Class. Quant. Grav. 22: S487–S492, doi:10.1088/0264-9381/22/10/048, arΧiv:gr-qc/0411071
• Lehner, Luis (2001), "Numerical Relativity: A review", Class. Quant. Grav. 18: R25–R86, doi:10.1088/0264-9381/18/17/202, arΧiv:gr-qc/0106072
• Lehner, Luis (2002), Numerical Relativity: Status and Prospects, arΧiv:gr-qc/0202055
• Linde, Andrei (1990), Particle Physics and Inflationary Cosmology, Harwood, arΧiv:hep-th/0503203, ISBN 3718604892
• Linde, Andrei (2005), "Towards inflation in string theory", J. Phys. Conf. Ser. 24: 151–160, doi:10.1088/1742-6596/24/1/018, arΧiv:hep-th/0503195

• Loll, Renate (1998), "Discrete Approaches to Quantum Gravity in Four Dimensions", Living Rev. Relativity 1, http://www.livingreviews.org/lrr-1998-13, retrieved 2008-03-09
• Lovelock, David (1972), "The Four-Dimensionality of Space and the Einstein Tensor", J. Math. Phys. 13: 874–876, doi:10.1063/1.1666069
• MacCallum, M. (2006), "Finding and using exact solutions of the Einstein equations", in Mornas, L.; Alonso, J. D., A Century of Relativity Physics (ERE05, the XXVIII Spanish Relativity Meeting), American Institute of Physics, arΧiv:gr-qc/0601102
• Maddox, John (1998), What Remains To Be Discovered, Macmillan, ISBN 0-684-82292-X
• Mannheim, Philip D. (2006), "Alternatives to Dark Matter and Dark Energy", Prog. Part. Nucl. Phys. 56: 340–445, doi:10.1016/j.ppnp.2005.08.001, arΧiv:astro-ph/0505266v2
• Mather, J. C.; Cheng, E. S.; Cottingham, D. A.; Eplee, R. E. (1994), "Measurement of the cosmic microwave spectrum by the COBE FIRAS instrument", Astrophysical Journal 420: 439–444, doi:10.1086/173574, http://adsabs.harvard.edu/abs/1994ApJ...420..439M
• Mermin, N. David (2005), It's About Time. Understanding Einstein's Relativity, Princeton University Press, ISBN 0-691-12201-6
• Messiah, Albert (1999), Quantum Mechanics, Dover Publications, ISBN 0486409244
• Miller, Cole (2002), Stellar Structure and Evolution (Lecture notes for Astronomy 606), University of Maryland, http://www.astro.umd.edu/~miller/teaching/astr606/, retrieved 2007-07-25
• Misner, Charles W.; Thorne, Kip. S.; Wheeler, John A. (1973), Gravitation, W. H. Freeman, ISBN 0-7167-0344-0
• Narayan, Ramesh (2006), "Black holes in astrophysics", New Journal of Physics 7: 199, doi:10.1088/1367-2630/7/1/199, arΧiv:gr-qc/0506078
• Narayan, Ramesh; Bartelmann, Matthias (1997), Lectures on Gravitational Lensing, arΧiv:astro-ph/9606001
• Narlikar, Jayant V. (1993), Introduction to Cosmology, Cambridge University Press, ISBN 0-521-41250-1
• Nieto, Michael Martin (2006), "The quest to understand the Pioneer anomaly" (PDF), EurophysicsNews 37(6): 30–34, http://www.europhysicsnews.com/full/42/article4.pdf
• Nordström, Gunnar (1918), "On the Energy of the Gravitational Field in Einstein's Theory", Verhandl. Koninkl. Ned. Akad. Wetenschap., 26: 1238–1245, http://www.digitallibrary.nl/proceedings/search/detail.cfm?pubid=2146&view=image&startrow=1
• Nordtvedt, Kenneth (2003), Lunar Laser Ranging—a comprehensive probe of post-Newtonian gravity, arΧiv:gr-qc/0301024
• Norton, John D. (1985), "What was Einstein's principle of equivalence?" (PDF), Studies in History and Philosophy of Science 16: 203–246, doi:10.1016/0039-3681(85)90002-0, http://www.pitt.edu/~jdnorton/papers/ProfE_re-set.pdf, retrieved 2007-06-11.

Kunjungi Juga:

Apa Itu Relativitas Umum Einstein? 



Sumber:


The University of Cambridge

Wikipedia

To Be Continued

Mekanika Orbit: Teknik-Teknik Matematika

"Teknik-Teknik Mekanika dalam IPTEK Antariksa Sangat Perlu Dikembangkan" 

*Arip Nurahman*

Persamaan Kepler

One approach to calculating orbits (mainly used historically) is to use Kepler's equation:

.

where M is the mean anomaly, E is the eccentric anomaly, and is eccentricty.

With Kepler's formula, finding the time-of-flight to reach an angle (true anomaly) of θ from periapsis is broken into two steps:

1. Compute the eccentric anomaly E from true anomaly θ
2. Compute the time-of-flight t from the eccentric anomaly E

Finding the angle at a given time is harder. Kepler's equation is transcendental in E, meaning it cannot be solved for E analytically, and so numerical approaches must be used. In effect, one must guess a value of E and solve for time-of-flight; then adjust E as necessary to bring the computed time-of-flight closer to the desired value until the required precision is achieved. Usually, Newton's method is used to achieve relatively fast convergence.

The main difficulty with this approach is that it can take prohibitively long to converge for the extreme elliptical orbits. For near-parabolic orbits, eccentricity e is nearly 1, and plugging e = 1 into the formula for mean anomaly, E − sinE, we find ourselves subtracting two nearly-equal values, and so accuracy suffers. For near-circular orbits, it is hard to find the periapsis in the first place (and truly circular orbits have no periapsis at all). Furthermore, the equation was derived on the assumption of an elliptical orbit, and so it does not hold for parabolic or hyperbolic orbits at all. These difficulties are what led to the development of the universal variable formulation, described below.

Perturbation theory

Main article: Perturbation theory

One can deal with perturbations just by summing the forces and integrating, but that is not always best. Historically, variation of parameters has been used which is easier to mathematically apply with when perturbations are small.

Conic orbits

For simple procedures, such as computing the delta-v for coplanar transfer ellipses, traditional approaches^{[clarification needed]} are fairly effective. Others, such as time-of-flight are far more complicated, especially for near-circular and hyperbolic orbits.

The patched conic approximation

The transfer orbit alone is a poor approximation for interplanetary trajectories because it neglects the planets' own gravity. Planetary gravity dominates the behaviour of the spacecraft in the vicinity of a planet. It severely underestimates delta-v, and produces highly inaccurate prescriptions for burn timings.

A relatively simple way to get a first-order approximation of delta-v is based on the patched conic approximation technique. One must choose the one dominant gravitating body in each region of space through which the trajectory will pass, and to model only that body's effects in that region. For instance, on a trajectory from the Earth to Mars, one would begin by considering only the Earth's gravity until the trajectory reaches a distance where the Earth's gravity no longer dominates that of the Sun.

The spacecraft would be given escape velocity to send it on its way to interplanetary space. Next, one would consider only the Sun's gravity until the trajectory reaches the neighbourhood of Mars. During this stage, the transfer orbit model is appropriate. Finally, only Mars's gravity is considered during the final portion of the trajectory where Mars's gravity dominates the spacecraft's behaviour.

The spacecraft would approach Mars on a hyperbolic orbit, and a final retrograde burn would slow the spacecraft enough to be captured by Mars.

The size of the "neighborhoods" (or spheres of influence) vary with radius r_SOI:

where a_p is the semimajor axis of the planet's orbit relative to the Sun; m_p and m_s are the masses of the planet and Sun, respectively.

This simplification is sufficient to compute rough estimates of fuel requirements, and rough time-of-flight estimates, but it is not generally accurate enough to guide a spacecraft to its destination. For that, numerical methods are required.

The universal variable formulation

To address the shortcomings of the traditional approaches, the universal variable formulation was developed. It works equally well on circular, elliptical, parabolic, and hyperbolic orbits; and also works well with perturbation theory. The differential equations converge nicely when integrated for any orbit.

Perturbations

The universal variable formulation works well with the variation of parameters technique, except now, instead of the six Keplerian orbital elements, we use a different set of orbital elements: namely, the satellite's initial position and velocity vectors x₀ and v₀ at a given epoch t = 0.

In a two-body simulation, these elements are sufficient to compute the satellite's position and velocity at any time in the future, using the universal variable formulation.

Conversely, at any moment in the satellite's orbit, we can measure its position and velocity, and then use the universal variable approach to determine what its initial position and velocity would have been at the epoch. In perfect two-body motion, these orbital elements would be invariant (just like the Keplerian elements would be).

However, perturbations cause the orbital elements to change over time. Hence, we write the position element as x₀(t) and the velocity element as v₀(t), indicating that they vary with time. The technique to compute the effect of perturbations becomes one of finding expressions, either exact or approximate, for the functions x₀(t) and v₀(t).

Non-ideal orbits

The following are some effects which make real orbits differ from the simple models based on a spherical earth. Most of them can be handled on short timescales (perhaps less than a few thousand orbits) by perturbation theory because they are small relative to the corresponding two-body effects.

• Equatorial bulges cause precession of the node and the perigee
• Tesseral harmonics of the gravity field introduce additional perturbations
• lunar and solar gravity perturbations alter the orbits
• Atmospheric drag reduces the semi-major axis unless make-up thrust is used

Over very long timescales (perhaps millions of orbits), even small perturbations can dominate, and the behaviour can become chaotic.

On the other hand, the various perturbations can be orchestrated by clever astrodynamicists to assist with orbit maintenance tasks, such as station-keeping, ground track maintenance or adjustment, or phasing of perigee to cover selected targets at low altitude.

Sumber:

Wikipedia