THE PHYSICS OF INTERSTELLAR TRAVEL Introduction Many people wonder when we will be able to go to distant solar systems every bit easy as envisioned in scientific discipline fiction. This essay will explicate the challenges of interstellar travel, the chances and restrictions of bing propulsion thoughts, and the chances emerging from scientific discipline that may one twenty-four hours supply the discoveries needed to enable practical interstellar ocean trips. Analogies to familiar scientific discipline fiction are used to simplify impressions such as the & # 8216 ; warp drive & # 8217 ; . It will demo the bit-by-bit attack towards detecting the ultimate discoveries needed to revolutionise infinite travel and enable human journeys to other star systems & # 8211 ; believable advancement towards unbelievable possibilities Abstract This essay shows the beginnings of interstellar travel and its developments as it shadows progressing and emerging scientific discipline. Reasons for the troubles of interstellar travel are explained every bit good as possible ways of short-circuiting them. It gives illustrations of past undertakings and thoughts every bit good as those which are being worked on for future utilizations. Three missions which are soon running are described and information is supplied about them. Last, a list of chief subscribers to todays apprehension of scientific discipline is given. Difficulties The propellent job The first challenge is propulsion, specifically propellent mass. Unlike aircraft that can utilize the air as their reaction mass, projectiles need to convey along their ain reaction mass, propellent, with them. By blaring propellent out the dorsum, rockets push ballistic capsule. The job is measure. Propellant needs lift exponentially with additions in warhead, finishs, or velocity. Ideally, a infinite thrust would non necessitate any propellent. A few research workers have begun analyzing how to accomplish this, seeking for something else in infinite to force against, possibly even by forcing against the very construction of space-time itself, or by happening a manner to modify gravitative or inertial forces. Examples of this include deflection thrusts, radiation canvass and worm holes. The demand for velocity The following and more obvious challenge is speed. Our nearest neighbouring star is about 26 trillion stat mis off. That is more than four old ages off at the velocity of visible radiation, and light velocity ( 3*108 ) is about 17,000 times faster than the Voyager ballistic capsule. Although the hunt for a non-propellant infinite thrust would dramatically better this velocity state of affairs, some research workers have even contemplated short-circuiting the light velocity bound for interstellar travel. We know that it is impossible to interrupt the light velocity bound, so how is it possible to go faster than visible radiation? The fast one is to acquire past the light velocity bound by falsifying the cloth of space-time itself to make & # 8220 ; wormholes, & # 8221 ; which are cutoffs in space-time, or by utilizing & # 8220 ; warp thrusts, & # 8221 ; which are traveling sections of space-time. Looking for energy The last challenge is energy. Even if we had a infinite thrust that could change over energy straight into gesture, it would still necessitate a batch of energy. Sending a shuttle-sized vehicle on a 50-year, one-way trip to the nearest star would necessitate 70 trillion ( 7*1019 ) Js of energy & # 8211 ; the equivalent of running the infinite bird & # 8217 ; s engines continuously for that same 50 old ages. This sum is approximately the same as the entire end product of a atomic power works. To get the better of this trouble, we need either a discovery where we can take advantage of the energy in the infinite vacuity, a discovery in energy production natural philosophies, or a discovery where the Torahs of kinetic energy do non use. For warp thrusts and wormholes, the energy state of affairs is much, much worse. Making a 3-foot-wide wormhole, something with the mass of Jupiter would hold to be converted into negative energy. To get the better of these troubles, a few discoveries in energy production would be needed. To happen out if we can really get down doing progress towards these expansive aspirations, NASA established the Breakthrough Propulsion Physics Program in 1996. The plan has supported conference Sessionss, workshops and Internet sites to further coactions and to place low-cost research. The ideal interstellar propulsion system would be one that could acquire you to other stars as rapidly and comfortably as envisioned in scientific discipline fiction. Before this can go a world, three scientific discoveries are needed: find of a agencies to transcend light velocity, find of a agencies to impel a vehicle without propellent, and find of a agency to power such devices. This is necessary because infinite is large & # 8211 ; truly large. Interstellar distances are so astronomical ( pun intended ) that conveying this sweep is hard. See the undermentioned analogy: If the Sun were the size of a typical, 1.25cm diameter marble, the distance from the Sun to the Earth, called an & # 8220 ; Astronomical Unit ( AU ) & # 8221 ; would be about 220cm, the Earth would be hardly thicker than a sheet of paper, and the orbit of the Moon would be about a 0.5cm in diameter. On this graduated table, the closest neighbouring star is about 336km off. A less obvious challenge is get the better ofing the restrictions of projectiles. The job is fuel, or more specifically, projectile propellent. Unlike a auto that has the route to force against, or an airplane that has the air to force against, projectiles do non hold air in infinite. Today & # 8217 ; s ballistic capsule usage projectiles and projectiles use big measures of propellent. As propellent blasts out of the projectile in one way, it pushes the ballistic capsule in the other & # 8211 ; Newton & # 8217 ; s 3rd jurisprudence ( preservation of impulse ) . The farther or faster we wish to go, the more propellent we will necessitate. For long journeys to neighboring stars, the sum of propellent we would necessitate would be tremendous and prohibitively expensive.

Examples of ideasProject Orion The first illustration is from the 1950 & # 8217 ; s-60 & # 8217 ; s, Project Orion & # 8211 ; which offered to utilize atomic bombs for a constructive intent & # 8211 ; infinite travel. The proposal was that about five bombs per second would be dropped from the dorsum of the vas and detonated to impel it along. A immense daze home base with daze absorbers make up the base of the trade. Experiments utilizing conventional explosives were conducted to show the viability of this strategy. Although this vehicle was conceived to take a crew to Mars, it can besides be considered for directing smaller investigations to the stars. This undertaking ended with the atomic trial prohibition pact in the 60 & # 8217 ; s. Project Daedalus Project Daedalus, British Interplanetary Society. In the late 1970 & # 8217 ; s the British Interplanetary Society revisited the Orion propulsion construct, but at a more sensible graduated table and for in-space usage merely. Undertaking Daedalus was a design survey for directing a investigation past Barnard & # 8217 ; s star with a 50-year journey clip. ( Barnard & # 8217 ; s star is about 6 Light Old ages off. ) In this instance it used micro merger detonations that relied on obtaining the appropriate fuel isotope ( heavy hydrogen ) from Jupiter & # 8217 ; s upper atmosphere. It scoops this up on its manner out of the solar system & # 8211 ; a really hard tactic. Bussard Interstellar Ramjet An thought which allows the trade to roll up its fuel as it travels. This Bussard Interstellar Ramjet construct, from the 1960 & # 8217 ; s, relies on lift outing up the alone protons that drift in interstellar infinite, and so somehow acquiring them to blend to do a atomic projectile. There are a assortment of restrictions to this thought, such as how many protons can be scooped up, the size of the & # 8217 ; scoop & # 8217 ; , the retarding force created from lift outing them, and, non to advert, the effort of acquiring these protons to prosecute in atomic merger for a projectile. Robert Forward & # 8217 ; s interstellar optical maser canvass Light canvass are another possibility. Rather than usage projectiles, why non utilize visible radiation. When light work stoppages an object, a little sum of force per unit area is exerted. Use a batch of visible radiation over a really big country, and the forces become noticeable. Here, Robert Forward proposed utilizing a 10 million gigawatt optical maser to reflect through a 1000 kilometer Fresnel lens onto a 1000 kilometer canvas. On this graduated table, it is claimed that one could direct a thousand-ton vehicle with a crew to our nearest star in 10 old ages! The snag is the 10 million gigawatt optical maser. That power degree is ten 1000 times more than the power used on all the Earth today. So, Forward revised the construct to more sensible power degrees. This clip it merely has a 10-gigawatt microwave optical maser ( still a effort unto itself ) , and this clip the vehicle is a frail 16 gms of all right wires spread over merely one kilometer. The canvas has all its detectors and proficient systems built right into its array of wires. The optical maser job would be bypassed by constructing a canvas ( made of foil merely, say, 20 atoms midst ) which is pushed by the Sun & # 8217 ; s radiation. The job with this is that the canvas receives less push the further it is from the Sun and the canvass would be hard to fabricate and maintain in good status. Wormholes Here is the premiss behind a & # 8216 ; wormhole & # 8217 ; . Although Particular Relativity forbids objects to travel faster than visible radiation within infinite clip, it is known that infinite clip itself can be warped and distorted. It takes an tremendous sum of affair or energy to make such deformations ( a heavy mass such as a planet can do a little, but noticeable curve in the way of a light beam ) , but deformations are possible. To utilize an analogy: even if there were a velocity bound to how fast a pencil could travel across a sheet of paper, the gesture or alterations to the paper is a separate issue. In the instance of the wormhole, a cutoff is made by falsifying infinite ( turn uping the paper ) to link two points that used to be separated. These theories are excessively new to hold either been discounted or proven feasible. And, wormholes invite the old clip travel paradox jobs once more. Here is an over simplified manner to construct one: First, collect a batch ( adequate to build a pealing the size of the Earth & # 8217 ; s orbit around the Sun ) of super-dense affair, such as affair from a neutron star. Then construct another ring where you want the other terminal of your wormhole. Following, bear down them up to a monolithic electromotive force, and whirl them up to near the velocity of light & # 8211 ; both of them. The jobs & # 8211 ; good if it was possible to make all that, you notice that you already had to be where you wanted to travel to, there are surely more cagey ways to go. Wormhole technology can non be expected any clip shortly. There are other thoughts out at that place excessively & # 8211 ; thoughts that use & # 8220 ; negative energy & # 8221 ; to make and to maintain the wormhole unfastened. Alcubierre & # 8217 ; s & # 8220 ; Warp Drive & # 8221 ; Here is the theory behind the Alcubierre & # 8220 ; warp drive & # 8221 ; : Although Special Relativity forbids objects to travel faster than visible radiation within spacetime,

it is unknown how fast spacetime itself can move.The warp drive idea is something like a conveyor belt, similar to those you find at many airports. By expanding space-time behind the starship and contracting it in front, a segment of space-time moves and carries the ship with it. The starship itself still moves slower than light within its space-time, but when you add the “conveyor belt” effect; the apparent motion exceeds the speed of light. There are numerous difficulties with these concepts, however.The idea of expanding spacetime is not new. Using the “Inflationary Universe” perspective, for example, it is thought that spacetime expanded faster than the speed of light during the early moments of the Big Bang. So if spacetime can expand faster than the speed of light during the Big Bang, why not for a warp drive? These theories are too new to have either been discounted or proven viable. Other problems: First, to create this effect, an immense ring of negative energy has to be wrapped around the ship. It is still debated in physics whether negative energy can exist. Classical physics tends toward a “no,” while quantum physics leans to a “maybe, yes.” Second, you’ll need a way to control this effect to turn it on and off at will. This will be especially tricky since this warp effect is a separate effect from the ship. Third, all this assumes that this whole “warp” would indeed move faster than the speed of light. It is still unknown if this could happen. And fourth, if all the previous issues weren’t complicated enough, these concepts evoke the same time-travel paradoxes as the wormhole concepts. Negative mass propulsion It has been shown that it is theoretically possible to create a continuously propulsive effect by the juxtaposition of negative and positive mass and that such a scheme does not violate conservation of momentum or energy. A crucial assumption to the success of this concept is that negative mass has negative inertia. Their combined interactions result in a sustained acceleration of both masses in the same direction. This concept dates back to at least 1957 with an analysis of the properties of hypothetical negative mass by Bondi, and has been revisited in the context of propulsion by Winterberg and Forward in the 1980’s.Regarding the physics of negative mass, it is not known whether negative mass exists or if it is even theoretically allowed, but methods have been suggested to search for evidence of negative mass in the context of searching for astronomical evidence of wormholes. The radiation differential sail Analogous to the principles of an ideal radiometer vane, a net difference in radiation pressure exists across the reflecting and absorbing sides. It is assumed that space contains a background of some form of isotropic medium (like the vacuum fluctuations or Cosmic Background Radiation) that is constantly impinging on all sides of the sail. The radiation diode sail Has the same effect of a diode or one-way mirror, space radiation passes through one direction and reflects from the other. This creates a net difference in radiation pressure, forcing the craft foreward. The radiation induction sail Equivalent to creating a pressure gradient in a fluid, the energy density of the impinging space radiation is raised behind the sail and lowered in front to create a net difference in radiation pressure across the sail. The pitch drive This concept entertains the possibility that somehow, a localized slope in scalar potential can be induced across the vehicle which causes forces on the vehicle. It is assumed that such a slope can be created without the presence of a pair of point sources. It is not yet known if and how such an effect can be created. What’s happening now The Voyager missions Mission objective The mission objective of the Voyager Interstellar Mission (VIM) is to extend the NASA exploration of the solar system beyond the neighbourhood of the outer planets to the outer limits of the Sun’s sphere of influence, and possibly beyond. This extended mission is continuing to characterise the outer solar system environment and search for the heliopause boundary, the outer limits of the Sun’s magnetic field and outward flow of the solar wind. Penetration of the heliopause boundary between the solar wind and the interstellar medium will allow measurements to consist of the interstellar fields, particles and waves unaffected by the solar wind. The previous missions The VIM is an extension of the Voyager primary mission that was completed in 1989 with the close flyby of Neptune by the Voyager 2 spacecraft. Neptune was the final outer planet visited by a Voyager spacecraft. Voyager 1 completed its planned close flybys of the Jupiter and Saturn planetary systems while Voyager 2, in addition to its own close flybys of Jupiter and Saturn, completed close flybys of the remaining two gas giants, Uranus and Neptune. At the start of the VIM, the two Voyager spacecraft had been in flight for over 12 years having been launched in August (Voyager 2) and September (Voyager 1), 1977. Voyager 1 was at a distance of approximately 40 AU (Astronomical Unit – mean distance of Earth from the Sun, 150 million kilometres) from the Sun, and Voyager 2 was at a distance of approximately 31 AU. Voyager 1 is escaping the solar system at a speed of about 3.5 AU per year, 35 degrees out of the ecliptic plan to the north, in the general direction of the Solar Apex (the direction of the Sun’s motion relative to nearby stars). Voyager 2 is also escaping the solar system at a speed of about 3.1 AU per year, 48 degrees out of the ecliptic plane to the south. Voyager 1 is now the most distant human-made object in space. Deep Space 1 Deep Space 1 is powered by a prototype ion propulsion drive which has been developed by NASA.The engine delivers 0.044kg of thrust at full power (roughly the weight of an A4 sheet of paper). This may not seem like much but it offers ten times the thrust of conventional chemical thrusters for a given amount of fuel. These thrusters can increase the speed of DS1 to about 16,000 kph. The fuel that powers the thrusters is 399kg of Xenon (Xe). How it works (see diagram on next page):1Xe is released into a chamber ringed by magnets (these increase the efficiency of the ionisation progress).2Electrons are fired from a cathode ray tube (similar to the ones used in televisions).3The electrons knock electrons from the Xe atoms making them positively charged Xe+ ions. 4Charged grids generate an electrostatic pull which ‘yanks’ the ions past the grid at 99200 kph5To stop the Xe+ ions from coming back into the chamber, a neutralising cathode ray tube gives the Xe+ and extra electron, neutralising it. The DS1 ion propulsion drive Acceleration of the ship 1To find Xe mass ejected per second: f = (m2/t) * v2 Where f = force acting on shipm2/t = mass of Xe eject per secondv2 = speed of Xe Force acting on ship = 0.486 NTotal mass = 486.32kgSpeed of Xe ejected = 99200 kph = 27556 m/sLet x = Xe mass per second 0.486 = x * 27556x = 0.486/27556x = 1.76*10-5 kg/s 2Atoms of Xe per second: moles = mass/ar Where ar = the atomic mass moles = 1.76*10-5/131.3 moles = 1.34*10-7mole = 6.02*1023 atomsno. of atoms = (6.02*1023) * 1.34*10-7no. of atoms of Xe ejected a second = 8.07*1016 3To find the acceleration of the ship: (m2/t) * v2 = m1 .(v/t) Where:m1 = craft mass (inc. propellant)v/t = acceleration of shipm2/t = Xe mass ejected per secondv2 = speed of XeLet acceleration be x 1.76*10-5 * 27556 = 486.32 * xx = 1.76*10-5 * 27556/486.32x = 9.97*10-4 ms-2 Acceleration of DS1 = 9.97*10-4 ms-2 Lists of some intriguing emerging physics Science and technology are continuing to evolve. In just the last few years, there have been new, intriguing developments in the scientific literature. Although it is still too soon to know whether any of these developments can lead to the desired propulsion breakthroughs, they do provide new clues that did not exist just a few short years ago. A snapshot of just some of the possibilities is listed below: 1988; Morris and Thorne: Theory and assessments for using wormholes for faster-than-light space travel. 1988; Herbert: Book outlining the loopholes in physics that suggest that faster-than-light travel may be possible. 1989; Puthoff: Theory extending Sakharov’s 1968 work to suggest that gravity is a consequential effect of the vacuum electromagnetic zero point fluctuations. 1992; Podkletnov and Nieminen: Report of superconductor experiments with anomalous results – evidence of a possible gravity shielding effect. 1994; Haisch, Rueda, and Puthoff: Theory suggesting that inertia is a consequential effect of the vacuum electromagnetic zero point fluctuations. 1994; Alcubierre: Theory for a faster-than-light “warp drive” consistent with general relativity. 1996; Eberlein: Theory suggesting that the laboratory observed effect of sonoluminescence is extraction of virtual photons from the electromagnetic zero point fluctuations. Surveys & Workshops: 1972; Mead Jr.: Identification and assessments of advanced propulsion concepts. 1982; Garrison, et al.: Assessment of ultra high performance propulsion. 1986; Forward: Assessment of the technological feasibility of interstellar travel. 1990; NASA Lewis Research Centre: Symposium “Vision-21: Space Travel for the Next Millennium.” 1990; British Aerospace Co.: Workshop to revisit theory and implications of controlling gravity. 1990; Cravens: Assessment of alternative theories of electromagnetics and gravity for propulsion. 1991; Forward: Assessment of advanced propulsion concepts. 1994; Bennett, et al.: NASA workshop on the theory and implications of faster-than-light travel. 1994; Belbruno: Conference assessing: “Practical Robotic Interstellar Flight: Are We Ready?” 1995; Hujsak & Hujsak: Formation of the “Interstellar Propulsion Society.” Theory: 1988; Forward; Winterberg: Further assessments of Bondi’s 1957 theory regarding hypothetical negative mass and its propulsive implications. 1984; Forward: Conceptual design for a “vacuum fluctuation battery” to extract energy from electromagnetic fluctuations of the vacuum based on the Casimir effect (predicted 1948, measured 1958 by Sparnaay). 1994; Cramer, et. al.: Identification of the characteristics of natural wormholes with negative mass entrances that could be detectable using existing astronomical observations. 1996; Millis: Identification of the remaining physics developments required to enable “space drives,” including the presentation and assessment of seven different hypothetical “space drive” concepts.

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