Wahana Peluncur Antariksa Berdasarkan Ukuran

There are many ways to classify the sizes of launch vehicles. 

The Augustine Commission that was created to review plans for replacing the Space Shuttle, used the following classification scheme: 

A sounding rocket cannot reach orbit and is only capable of sub-orbital spaceflight 

A small lift launch vehicle is capable of lofting up to 2,000 kg (4,400 lb) of payload into low earth orbit (LEO)

A medium lift launch vehicle is capable of lofting between 2,000 to 20,000 kg (4,400 to 44,000 lb) of payload into LEO

A heavy lift launch vehicle is capable of lofting between 20,000 to 50,000 kg (44,000 to 110,000 lb) of payload into LEO

A super-heavy lift vehicle is capable of lofting more than 50,000 kg of payload into LEO

Wahana Antariksa Pengorbit

Sounding rockets are normally used for brief, inexpensive space and microgravity experiments. 

Current human-rated suborbital launch vehicles include SpaceShipOne and the upcoming SpaceShipTwo, among others (see space tourism). 

The delta-v needed for orbital launch using a rocket vehicle launching from the Earth's surface is at least 9,300 m/s (31,000 ft/s). 

This delta-v is determined by a combination of air-drag, which is determined by ballistic coefficient as well as gravity losses, altitude gain and the horizontal speed necessary to give a suitable perigee. 

The delta-v required for altitude gain varies, but is around 2 km/s (1.2 mi/s) for 200 km (120 mi) altitude.

Minimising air-drag entails having a reasonably high ballistic coefficient, which generally means having a launch vehicle that is at least 20 m (66 ft) long, or a ratio of length to diameter greater than ten. Leaving the atmosphere as early on in the flight as possible provides an air drag of around 300 m/s (980 ft/s). 

The horizontal speed necessary to achieve low earth orbit is around 7,800 m/s (26,000 ft/s). 

The calculation of the total delta-v for launch is complicated, and in nearly all cases numerical integration is used; adding multiple delta-v values provides a pessimistic result, since the rocket can thrust while at an angle in order to reach orbit, thereby saving fuel as it can gain altitude and horizontal speed simultaneously

Mengenal Wahana Peluncur Antariksa

In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure.

Usually the payload is an artificial satellite placed into orbit, but some spaceflights are sub-orbital while others enable spacecraft to escape Earth orbit entirely. 

A launch vehicle which carries its payload on a suborbital trajectory is often called a sounding rocket. Launch vehicles, particularly orbital launch vehicles, have at least two stages, but sometimes up to 4 are employed.

Sumber:

http://en.wikipedia.org/wiki/Space_Launch_System

Plasma Cosmology

In 1965, Hannes Alfvén proposed a "plasma cosmology" theory of the universe based in part on scaling observations of space plasma physics and experiments on plasmas in terrestrial laboratories to cosmological scales orders-of-magnitude greater.

Taking matter–antimatter symmetry as a starting point, Alfvén together with Oskar Klein proposed the Alfvén-Klein cosmology model, based on the fact that since most of the local universe was composed of matter and not antimatter there may be large bubbles of matter and antimatter that would globally balance to equality. The difficulties with this model were apparent almost immediately.

Matter–antimatter annihilation results in the production of high energy photons which were not observed. While it was possible that the local "matter-dominated" cell was simply larger than the observable universe, this proposition did not lend itself to observational tests.

Like the steady state theory, plasma cosmology includes a Strong Cosmological Principle which assumes that the universe is isotropic in time as well as in space. Matter is explicitly assumed to have always existed, or at least that it formed at a time so far in the past as to be forever beyond humanity's empirical methods of investigation.

While plasma cosmology has never had the support of most astronomers or physicists, a small number of plasma researchers have continued to promote and develop the approach, and publish in the special issues of the IEEE Transactions on Plasma Science.

A few papers regarding plasma cosmology were published in other mainstream journals until the 1990s. Additionally, in 1991, Eric J. Lerner, an independent researcher in plasma physics and nuclear fusion, wrote a popular-level book supporting plasma cosmology called The Big Bang Never Happened. 

At that time there was renewed interest in the subject among the cosmological community along with other non-standard cosmologies. This was due to anomalous results reported in 1987 by Andrew Lange and Paul Richardson of UC Berkeley and Toshio Matsumoto of Nagoya University that indicated the cosmic microwave background might not have a blackbody spectrum.

However, the final announcement (in April 1992) of COBE satellite data corrected the earlier contradiction of the Big Bang; the popularity of plasma cosmology has since fallen.

Sumber;

Wikipedia

Mengoptimalkan Pemanfaatan Energi di Indonesia

Oleh: Prof. Ir. Widjajono  Partowidagdo,  MSc. MSOR, MA, Ph.D.

"Negara yang baik membutuhkan adilnya Pemimpin, amalnya Pengusaha, ilmunya Akademisi (Ulama) serta kesabaran, kemandirian dan kepedulian Masyarakat."
~Alm. Prof. Widjajono~ 

‎"Saya seorang dosen, kalau gak niat ngebenerin bangsa ini, buat apa saya terjun ke pemerintahan"

Produksi dan Cadangan Minyak kita terbukti turun terus. Walaupun cadangan  gas kita empat kali lipat cadangan Minyak tetapi program konversi Minyak ke Gas Domestik terbukti tidak berjalan mulus. Program 10.000 MW PLTU (Uap) Batubara tidak berjalan mulus dan sebagian besar produksi batubara kita diekspor.

PLTA (Air)  di luar Jawa kurang berkembang.

Program Bahan Bakar Nabati tidak berjalan seperti yang diharapkan. 

PLTS (Surya) dan PLTB (Bayu) banyak yang tidak berfungsi lagi.

Berarti ada yang tidak pas di Negeri ini.

Marilah kita evaluasi satu per satu.

Minyak kurang berkembang karena sistem fiskal dan iklim investasi yang kurang menarik. Gas kurang termanfaatkan untuk domestik karena harga domestik yang tidak menarik dan tidak disiapkannya infrastruktur dimasa lalu.

Batubara 10.000 MW kurang berkembang karena terdapat masalah  negosiasi, birokrasi dan koordinasi.

Kebanyakan batubara diekspor karena harga domestik yang kurang menarik dibandingkan harga ekspor.

PLTA kurang berkembang karena masalah birokrasi, koordinasi, promosi dan kemauan politik untuk mengembangkan industri di luar Jawa.

Panasbumi kurang berkembang karena harga domestik yang tidak menarik di masa lalu.

Bioenergi kurang berkembang karena masalah harga, peraturan, insentif, birokrasi, koordinasi  dan litbang.

Surya dan bayu tidak terawat karena kurang dikembangkan litbang dan Kemampuan Nasional disamping masalah birokrasi dan koordinasi. Konservasi kurang berhasil karena harga energi murah, peraturan (kurangnya insentif untuk penghematan energi) dan kurangnya dukungan bagi litbang serta kurangnya peningkatan kemampuan nasional untuk itu.

Menurut International Sustainable Energy Organization (ISEO) Biaya Energi Terbarukan seperti Energi Surya, Energi Angin, Panasbumi, Arus Laut dan Hidrogen akan turun di masa depan, sedangkan Pembangkit Listrik Tenaga Air (PLTA) akan naik (walaupun masih tetap rendah). Biaya Energi Tak Terbarukan seperti Minyak, Gas, Batubara dan Nuklir akan naik  di masa depan.

German Working Party, 2004 memperkirakan Biaya Energi sampai tahun 2050 termasuk menggunakan Geocogen (Geothermal deepwell energy cogeneration) dan SBSP (Space Based Solar Power). Juga diperkirakan True Energy Cost dengan memperhitungkan Resiko, Biaya Lingkungan dan Carbon Credit (Sumber: Gustav R. Grob (ISEO Executive Secretary dan ICEC President).

ISEO adalah International Sustainable Energy Organization sedangkan ICEC adalah International Clean Energy Consortium. Judul makalahnya adalah “Energy Status Quo and Technology towards Clean Energy”, Chengdu, China, September 28, 2010).

Batubara bisa lebih bersih lingkungan, konsekuensinya biayanya lebih mahal. Batubara bisa dibuat cair (Coal To Liquid atau CTL) atau dijadikan gas. Gas bisa dibuat cair (Gas To Liquid atau GTL). Gas bisa diperoleh dari Gas Alam (Potensi 335 TCF), dari CBM (Potensi 454 TCF), Shale Gas dan dari Methane Hydrate (Potensi 625 TCF) . Nuklir dari Uranium dan Thorium (FISI) adalah Tak Terbarukan.

Tidak benar kalau energi nuklir sangat aman karena disamping Chernobyl dan Three Mile Island, di Amerika Serikat 27 dari 104 reaktor nuklirnya pernah bocor (Tobi Raikkonen, 12 Maret 2010). Menurut USA Today 17 Juli 2007 di Jepang terjadi kebocoran nuklir 1997-2007 sebanyak 8 kali. Apalagi kemudian terjadi tragedi Fukushima (2011).

Banyak Negara-negara Eropa yang menutup PLTN (Pembangkit Listrik Tenaga Nuklir) nya 2020.

Penanganan dan penyimpanan limbah Uranium yang benar adalah mahal dan kalau tidak benar berbahaya.

Perancis bisa membantu  memproses limbah Uranium tetapi limbah terakhirnya tetap dikirim ke Negara asal yang mempunyai PLTN.

Konsorsium Uni Eropa, Jepang, Cina, India, Korsel, Rusia dan Amerika Serikat membiayai Pengembangan Nuklir FUSI yaitu ITER (International Thermonuclear Experimental Reactor) TOKAMAK di Perancis Selatan.

(ITER) TOKAMAK tersebut diharapkan bisa dikembangkan secara komersial pada tahun 2020 an dan dibuat dari reaksi FUSI antara Detrium dan Tritium yang limbahnya relatif aman (dibandingkan Uranium).

Indonesia sebaiknya fokus pada FUSI.

Andai kata Nuklir FISI ingin dikembangkan segera maka paling cepat  dioperasikan pada 2021 karena memerlukan 10 tahun untuk merealisasikan PLTN  seperti  di Malaysia. Sebaiknya Indonesia bekerjasama dengan Singapura dan Malaysia (lebih baik bila juga dengan Negara-negara Asean lainnya).

Lokasi pembangkitannya bisa di Pulau kosong di Indonesia dekat Singapura. Makin banyak Negara-negara yang mengawasi diharapkan makin aman dan makin banyak Negara-negara yang memakai makin murah.

Urutan Global Innovation Index (Maret 2009) dari beberapa Anggota Asean dan Negara Maju adalah sebagai berikut:

1. Singapore, 2. South Korea, 8. US, 9. Japan, 15. UK, 19. Germany, 20. France, 21. Malaysia, 27. China, 44. Thailand, 46. India, 49. Russia, 71. Indonesia.

Tidak benar kalau nuklir adalah energi yang paling murah. International Energy Agency atau IEA di Paris tahun 2010 memberikan Electricity Generation Costs  2010 dan Perkiraan 2050 (Tabel 1) yang menunjukkan energi lain kecuali minyak dan matahari tidak lebih mahal saat ini (2010) dan justru lebih murah di 2050 kecuali minyak.

Kita masih bisa mencukupi kebutuhan energi sampai 2030 dengan menggunakan Energi Domestik
(Minyak, Gas, CBM, Shale Gas,  Batubara, Panasbumi, Air, Surya, Angin, Laut, Biofuel dan Biogas) serta mengembangkan Kemampuan Nasional untuk memproduksikan Energi Terbarukan dan Konservasi Energi.

Bahkan kalau perlu mengimpor gas dan batubara (yang lebih murah dari BBM) serta  mengusahakan migas di luar negeri.

Perlu Kebijakan Harga dan Infrastruktur serta Peningkatan Iklim Investasi dan Peningkatan Kemampuan Nasional  yang mendukung untuk mengoptimalkan penggunaan Energi Domestik. Untuk mencukupi kebutuhan energi 2030-2050 perlu dilihat perkembangan Teknologi dan Biaya Energi pada 2020.

Diharapkan Pertamina dan Perusahaan-perusahaan Nasional Migas lain dapat meningkatkan produksi migasnya baik di dalam dan di luar negeri seperti Petronas disamping perlu perbaikan Sistem Fiskal dan Iklim Investasi serta Sistem Informasi untuk meningkatkan Investasi Internasional Migas di Indonesia.

Terobosan Teknologi (Nano) menyebabkan Energi Terbarukan lebih murah dimasa depan. Konservasi atau Penghematan Energi mengurangi Pemakaian dan Pasokan Energi serta mengurangi Polusi. Pemakaian mobil irit bensin seperti yang dihasilkan ITS dan penghematan energi lainnya perlu didukung dan dikembangkan secara Nasional.

Peningkatan Kemampuan energi Nasional wajib dilakukan . Dana dapat diperoleh dari Penghematan yang diperoleh dari digantikannya BBM (Bahan Bakar Minyak) yang mahal dan sudah diimpor dengan energi lain yang lebih murah dan tersedia di dalam negeri (gas, batubara, panasbumi dan energi terbarukan lain).

Untuk menghindari krisis energi dimasa datang perlu dioptimalkan pemanfaatan energi di Indonesia baik dari sisi pemanfaatan sumberdaya maupun pemanfaatannya.

Untuk itu dibutuhkan kerjasama dan kasih sayang, kejujuran dan keterbukaan, kerja keras dan cerdas dari seluruh Bangsa Indonesia. Kita perlu melakukan hal-hal yang benar untuk Negeri ini.


Ketika Harry Potter "selamat" dari Voldemore (Musuhnya), Dumbledore (Kepala Sekolahnya): mengatakan:

"Someday, you will have to choose between what is right and what is easy." 

Pilihan kita, mau "benar" tetapi ,walaupun sulit, "berhasil" di jangka panjang atau mau "gampang" tetapi "standstill" tidak kemana mana.

Menurut Yasadipura (kakek Ranggawarsita) mengatakan:

"Waniya ing gampang, wediya ing pakewuh, sabarang nora tumeka." artinya: sukailah kemudahan, takutilah kesulitan, maka tidak ada yang diperoleh.

Persoalan energi dan bangsa tidak bisa hanya diselesaikan oleh Pemerintah saja.

Negara yang baik membutuhkan adilnya Pemimpin, amalnya Pengusaha, ilmunya Akademisi (Ulama) serta kesabaran, kemandirian dan keperdulian Masyarakat.

Daftar Pustaka

1.    Economics and Development Resource Center, Guidelines for the Economic Analysis of Project, ADB (Asian Development Bank), Manila, 1997.
2.    Gustav R. Grob, Energy Status Quo and Technology towards Clean Energy, Chengdu, China, September 28, 2010.
3.    IEA (International Energy Agency), Energy Thecnology Prespectives, Scenarios & Strategies to 2050, Paris, 2010.
4.    Partowidagdo, W, Migas dan Energi di Indonesia, Permasalahan dan Analisis Kebijakan, Development Studies Foundation, Bandung, 2009.
5.    Partowidagdo, W., Mengenal Pembangunan dan Analisis Kebijakan, Bandung, Development Studies Foundation, 2010.
6.    Petronas, Profitability Based Revenue-over-Cost (R/C) PSC, Manila, Philippines, 14 – 19 March 2005.
7.    The Goldman Sachs Group, Inc., 125 Projects to Change The World, New York, 2006.

BRIAN GREENE The Elegant Universe

BRIAN GREENE

The Elegant Universe Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory

Themes

The book is divided into three themes in the following parts:

• Part I: The Edge of Knowledge
• Part II: The Dilemma of Space, Time, and the Quanta
• Part III: The Cosmic Symphony
• Part IV: String Theory and the Fabric of Spacetime
• Part V: Unification in the Twenty-First Century

Calling it a cover-up would be far too dramatic. But for more than half a century — even in the midst of some of the greatest scientific achievements in history — physicists have been quietly aware of a dark cloud looming on a distant horizon. The problem is this: There are two foundational pillars upon which modern physics rests. One is Albert Einstein's general relativity, which provides a theoretical framework for understanding the universe on the largest of scales: stars, galaxies, clusters of galaxies, and beyond to the immense expanse of the universe itself. 

The other is quantum mechanics, which provides a theoretical framework for understanding the universe on the smallest of scales: molecules, atoms, and all the way down to subatomic particles like electrons and quarks. Through years of research, physicists have experimentally confirmed to almost unimaginable accuracy virtually all predictions made by each of these theories. But these same theoretical tools inexorably lead to another disturbing conclusion: As they are currently formulated, general relativity and quantum mechanics cannot both be right. The two theories underlying the tremendous progress of physics during the last hundred years — progress that has explained the expansion of the heavens and the fundamental structure of matter — are mutually incompatible.

If you have not heard previously about this ferocious antagonism you may be wondering why. The answer is not hard to come by. In all but the most extreme situations, physicists study things that are either small and light (like atoms and their constituents) or things that are huge and heavy (like stars and galaxies), but not both. This means that they need use only quantum mechanics or only general relativity and can, with a furtive glance, shrug off the barking admonition of the other. For fifty years this approach has not been quite as blissful as ignorance, but it has been pretty close.

But the universe can be extreme. In the central depths of a black hole an enormous mass is crushed to a minuscule size. At the moment of the big bang the whole of the universe erupted from a microscopic nugget whose size makes a grain of sand look colossal. These are realms that are tiny and yet incredibly massive, therefore requiring that both quantum mechanics and general relativity simultaneously be brought to bear. 

For reasons that will become increasingly clear as we proceed, the equations of general relativity and quantum mechanics, when combined, begin to shake, rattle, and gush with steam like a red-lined automobile. Put less figuratively, well-posed physical questions elicit nonsensical answers from the unhappy amalgam of these two theories. 

Even if you are willing to keep the deep interior of a black hole and the beginning of the universe shrouded in mystery, you can't help feeling that the hostility between quantum mechanics and general relativity cries out for a deeper level of understanding. Can it really be that the universe at its most fundamental level is divided, requiring one set of laws when things are large and a different, incompatible set when things are small?

Superstring theory, a young upstart compared with the venerable edifices of quantum mechanics and general relativity, answers with a resounding no. Intense research over the past decade by physicists and mathematicians around the world has revealed that this new approach to describing matter at its most fundamental level resolves the tension between general relativity and quantum mechanics. In fact, superstring theory shows more: Within this new framework, general relativity and quantum mechanics require one another for the theory to make sense. According to superstring theory, the marriage of the laws of the large and the small is not only happy but inevitable.

That's part of the good news. But superstring theory — string theory, for short — takes this union one giant step further. For three decades, Einstein sought a unified theory of physics, one that would interweave all of nature's forces and material constituents within a single theoretical tapestry. He failed. Now, at the dawn of the new millennium, proponents of string theory claim that the threads of this elusive unified tapestry finally have been revealed. String theory has the potential to show that all of the wondrous happenings in the universe — from the frantic dance of subatomic quarks to the stately waltz of orbiting binary stars, from the primordial fireball of the big bang to the majestic swirl of heavenly galaxies — are reflections of one grand physical principle, one master equation.

Because these features of string theory require that we drastically change our understanding of space, time, and matter, they will take some time to get used to, to sink in at a comfortable level. But as shall become clear, when seen in its proper context, string theory emerges as a dramatic yet natural outgrowth of the revolutionary discoveries of physics during the past hundred years. In fact, we shall see that the conflict between general relativity and quantum mechanics is actually not the first, but the third in a sequence of pivotal conflicts encountered during the past century, each of whose resolution has resulted in a stunning revision of our understanding of the universe.

---

The Three Conflicts

The first conflict, recognized as far back as the late 1800s, concerns puzzling properties of the motion of light. Briefly put, according to Isaac Newton's laws of motion, if you run fast enough you can catch up with a departing beam of light, whereas according to James Clerk Maxwell's laws of electromagnetism, you can't. As we will discuss in Chapter 2, Einstein resolved this conflict through his theory of special relativity, and in so doing completely overturned our understanding of space and time. According to special relativity, no longer can space and time be thought of as universal concepts set in stone, experienced identically by everyone. Rather, space and time emerged from Einstein's reworking as malleable constructs whose form and appearance depend on one's state of motion.

The development of special relativity immediately set the stage for the second conflict. One conclusion of Einstein's work is that no object — in fact, no influence or disturbance of any sort — can travel faster than the speed of light. But, as we shall discuss in Chapter 3, Newton's experimentally successful and intuitively pleasing universal theory of gravitation involves influences that are transmitted over vast distances of space instantaneously. It was Einstein, again, who stepped in and resolved the conflict by offering a new conception of gravity with his 1915 general theory of relativity. 

Just as special relativity overturned previous conceptions of space and time, so too did general relativity. Not only are space and time influenced by one's state of motion, but they can warp and curve in response to the presence of matter or energy. Such distortions to the fabric of space and time, as we shall see, transmit the force of gravity from one place to another. Space and time, therefore, can no longer to be thought of as an inert backdrop on which the events of the universe play themselves out; rather, through special and then general relativity, they are intimate players in the events themselves.

Once again the pattern repeated itself: The discovery of general relativity, while resolving one conflict, led to another. Over the course of the three decades beginning in 1900, physicists developed quantum mechanics (discussed in Chapter 4) in response to a number of glaring problems that arose when nineteenth-century conceptions of physics were applied to the microscopic world. 

And as mentioned above, the third and deepest conflict arises from the incompatibility between quantum mechanics and general relativity. As we will see in Chapter 5, the gently curving geometrical form of space emerging from general relativity is at loggerheads with the frantic, roiling, microscopic behavior of the universe implied by quantum mechanics. As it was not until the mid-1980s that string theory offered a resolution, this conflict is rightly called the central problem of modern physics.

 Moreover, building on special and general relativity, string theory requires its own severe revamping of our conceptions of space and time. For example, most of us take for granted that our universe has three spatial dimensions. But this is not so according to string theory, which claims that our universe has many more dimensions than meet the eye — dimensions that are tightly curled into the folded fabric of the cosmos. So central are these remarkable insights into the nature of space and time that we shall use them as a guiding theme in all that follows. String theory, in a real sense, is the story of space and time since Einstein.

To appreciate what string theory actually is, we need to take a step back and briefly describe what we have learned during the last century about the microscopic structure of the universe.

Sumber:

Prof. BRIAN GREENE

Dirac Large Numbers Hypothesis

The Dirac large numbers hypothesis uses the ratio of the size of the visible universe to the radius of quantum particle to predict the age of the universe. 

The coincidence of various ratios being close in order of magnitude may ultimately prove meaningless or the indication of a deeper connection between concepts in a future theory of everything. Nevertheless, attempts to use such ideas have been criticized as numerology.

The Dirac large numbers hypothesis (LNH) is an observation made by Paul Dirac in 1937 relating ratios of size scales in the Universe to that of force scales. The ratios constitute very large, dimensionless numbers: some 40 orders of magnitude in the present cosmological epoch. According to Dirac's hypothesis, the apparent equivalence of these ratios might not be a mere coincidence but instead could imply a cosmology with these unusual features:

• The strength of gravity, as represented by the gravitational constant, is inversely proportional to the age of the universe:
• The mass of the universe is proportional to the square of the universe's age: .

Neither of these two features has gained wide acceptance in mainstream physics and, though some proponents of non-standard cosmologies refer to Dirac's cosmology as a foundational basis for their own ideas and studies, some physicists dismiss the large numbers in LNH as mere coincidences.

A coincidence, however, may be defined optimally as 'an event that provides support for an alternative to a currently favoured causal theory, but not necessarily enough support to accept that alternative in light of its low prior probability.' 

Research into LNH, or the large number of coincidences that underpin it, appears to have gained new impetus from failures in standard cosmology to account for anomalies such as the recent discovery that the universe might be expanding at an accelerated rate.

Sumber:

Wikipedia

Early General Relativity Based Cosmologies

See also: De Sitter universe and Static universe

Before the present general relativistic cosmological model was developed, Albert Einstein proposed a way to dynamically stabilize a cosmological scenario that would necessarily collapse in on itself due to the gravitational attraction of the matter constituents in the universe. Such a universe would need a source of "anti-gravity" to balance out the mutual attraction, a scalar term in Einstein's equations that would come to be known as the cosmological constant. 

Einstein's first attempt at modeling relied on a cosmological constant that was finely tuned to exactly balance out matter curvature and provide a framework for an infinite and unchanging spacetime metric in which the objects of the universe were embedded. This happens to be the same as a special case of the current cosmological model where the cosmic scale factor is unchanging and the density seen in the Friedmann equations is equally divided between the cosmological constant and matter.

Willem de Sitter would later generalize Einstein's scalar potential model to a universe model that would expand exponentially. As the early development of the Big Bang theory began, De Sitter would be falsely credited for inventing the expanding universe metric because of this. In reality, it was the work of Alexander Friedman and Georges Lemaître who established the metric that would come to be the most accepted for cosmology. Nevertheless, De Sitter's model appears in two places today: in the discussion of cosmic inflation and in the discussion of dark energy dominated universes.

Sumber:

Wikipedia

Alternative metric cosmologies

The Friedmann–Lemaître–Robertson–Walker metric that is necessary for the Big Bang and Steady State models emerged in the decade after the development of Einstein's general relativity and was accepted as a model for the universe after Edwin Hubble's discovery of his eponymous law. It was not clear early on how to find a "universe solution" to Einstein's equations that allowed for a universe that was infinite, unending, and immutable (scientists of the time assumed for philosophical reasons the universe should have such a character).

Even after the development of expanding universe theories, people would engage in this exercise from time to time when looking for a replacement for general relativity. Any alternative theory of gravity would imply immediately an alternative cosmological theory since current modeling is dependent on general relativity as a framework assumption. What is included are a number of models based on alternative gravitational scenarios as well as early attempts to derive cosmological solutions from relativity.

Modern Physical Cosmology

Modern physical cosmology as it is currently studied first emerged as a scientific discipline in the period after the Shapley–Curtis debate and discoveries by Edwin Hubble of a cosmic distance ladder when astronomers and physicists had to come to terms with a universe that was of a much larger scale than the previously assumed galactic size. 

Theorists who successfully developed cosmologies applicable to the larger-scale universe are remembered today as the founders of modern cosmology. Among these scientists are Arthur Milne, Willem de Sitter, Alexander Friedman, Georges Lemaitre, and Albert Einstein himself.

After confirmation of the Hubble's law by observation, the two most popular cosmological theories became the Steady State theory of Hoyle, Gold and Bondi, and the big bang theory of Ralph Alpher, George Gamow, and Robert Dicke with a small number of supporters of a smattering of alternatives. 

Since the discovery of the Cosmic microwave background radiation (CMB) by Penzias and Robert Wilson in 1965, most cosmologists concluded that observations were best explained by the big bang model. Steady State theorists and other non-standard cosmologies were then tasked with providing an explanation for the phenomenon if they were to remain plausible. 

This led to original approaches including integrated starlight and cosmic iron whiskers, which were meant to provide a source for a pervasive, all-sky microwave background that was not due to an early universe phase transition.

Scepticism about the non-standard cosmologies' ability to explain the CMB caused interest in the subject to wane since then, however, there have been two periods in which interest in non-standard cosmology has increased due to observational data which posed difficulties for the big bang.

The first occurred was the late 1970s when there were a number of unsolved problems, such as the horizon problem, the flatness problem, and the lack of magnetic monopoles, which challenged the big bang model. These issues were eventually resolved by cosmic inflation in the 1980s. 

This idea subsequently became part of the understanding of the big bang, although alternatives have been proposed from time to time. The second occurred in the mid-1990s when observations of the ages of globular clusters and the primordial helium abundance, apparently disagreed with the big bang. 

However, by the late 1990s, most astronomers had concluded that these observations did not challenge the big bang and additional data from COBE and the WMAP, provided detailed quantitative measures which were consistent with standard cosmology.

In the 1990s, a dawning of a "golden age of cosmology" was accompanied by a startling discovery that the expansion of the universe was, in fact, accelerating.

Previous to this, it had been assumed that matter either in its visible or invisible dark matter form was the dominant energy density in the universe. This "classical" big bang cosmology was overthrown when it was discovered that nearly 70% of the energy in the universe was tied up in a mysterious and difficult to characterize form of dark energy. 

This has led to the development of a so-called concordance ΛCDM model which combines detailed data obtained with new telescopes and techniques in observational astrophysics with an expanding, density-changing universe. 

Today, it is more common to find in the scientific literature proposals for "non-standard cosmologies" that actually accept the basic tenets of the big bang cosmology, while modifying parts of the concordance model.

Such theories include alternative models of dark energy, such as quintessence, phantom energy and some ideas in brane cosmology; alternative models of dark matter, such as modified Newtonian dynamics; alternatives or extensions to inflation such as chaotic inflation and the ekpyrotic model; and proposals to supplement the universe with a first cause, such as the Hartle–Hawking boundary condition, the cyclic model, and the string landscape. 

There is no consensus about these ideas amongst cosmologists, but they are nonetheless active fields of academic inquiry.

Today, heterodox non-standard cosmologies are generally considered unworthy of consideration by cosmologists while many of the historically significant nonstandard cosmologies are considered to have been falsified. 

The essentials of the big bang theory have been confirmed by a wide range of complementary and detailed observations, and no non-standard cosmologies have reproduced the range of successes of the big bang model. 

Speculations about alternatives are not normally part of research or pedagogical discussions, except as object lessons or for their historical importance. An open letter started by some remaining advocates of non-standard cosmology has affirmed that: "today, virtually all financial and experimental resources in cosmology are devoted to big bang studies...."

Sumber; Wikipedia

International Space Program

http://www.globalspaceexploration.org/

International Space Exploration Coordination Group

 

http://www.isunet.edu/

International Space University

 

http://www.isa-hq.com/ 

 International Space Agency 

 

This is a list of government agencies engaged in activities related to outer space and space exploration.

The name given is the English version, with the native language version below. The acronym given is the most common acronym: this can either be the acronym of the English version (e.g. JAXA), or the acronym in the native language. Where there are multiple acronyms in common use, the English one is given first.

The date of the founding of the space agency is the date of first operations where possible. If the space agency is no longer running, then the date when it was terminated (i.e. the last day of operations) is given. A link to the Agency's primary website is also given.

Color legend

The capabilities of the space agencies are color-coded as follows:

  Manned Lunar Exploration + Operates Space Station + Manned Space Flight + Operates Extraterrestrial Probes + Launch Capability + Operates Satellites

  Operates Space Station + Manned Space Flight + Operates Extraterrestrial Probes + Launch Capability + Operates Satellites

  Manned Space Flight + Operates Extraterrestrial Probes + Launch Capability + Operates Satellites

  Operates Extraterrestrial Probes + Launch Capability + Operates Satellites

  Launch Capability + Operates Satellites

  Operates Satellites

  None Of The Above