Relativistic rocket; the Frisbee Effect in space

Reply Mon 30 Apr, 2012 10:40 am
I got interested while listening to a TV H2 show on channel 116 about the Universe and wanted to learn more about the meaning of "Frisbee Effect" in space. This is what I found. BBB

Relativistic rocket
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A relativistic rocket is any spacecraft that is travelling at a velocity close enough to light speed for relativistic effects to become significant. What "significant" means is a matter of context, but generally speaking a velocity of at least 50% of the speed of light (0.5c) is required. The time dilation factor, mass factor, and length contraction factor (all these factors equal the Lorentz factor) are 1.15 at 0.5c. Above this speed Einsteinian physics are required to describe motion. Below this speed, motion is approximately described by Newtonian physics and the Tsiolkovsky rocket equation can be used.

We define a rocket as carrying all of its reaction mass, energy, and engines with it. Bussard ramjets, RAIRs,[1] light sails, and maser or laser-electric vehicles are not rockets.

Achieving relativistic velocities is difficult, requiring advanced forms of spacecraft propulsion that have not yet been adequately developed. Nuclear pulse propulsion could theoretically achieve 0.1c using current known technologies, but would still require many engineering advances to achieve this. The relativistic gamma factor (\gamma) at 10% of light velocity is 1.005. The time dilation factor of 1.005 which occurs at 10% of light velocity is too small to be of major significance. A 0.10c velocity interstellar rocket is thus considered to be a non-relativistic rocket because its motion is quite accurately described by Newtonian physics alone.

Relativistic rockets are usually seen discussed in the context of interstellar travel, since most would require a great deal of space to accelerate up to those velocities. They are also found in some thought experiments such as the twin paradox.

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Reply Mon 30 Apr, 2012 10:49 am
I also wanted to learn more about the Orion-Cygnus Arm. BBB

Orion–Cygnus Arm
From Wikipedia, the free encyclopedia
Observed structure of the Milky Way's spiral arms

The Orion–Cygnus Arm is a minor spiral arm of the Milky Way galaxy some 3,500 light years across and approximately 10,000 light years in length.[2] The Solar System (and, therefore, the Earth) is within the Orion–Cygnus Arm. It is also referred to as the Local Arm, the Orion Arm, the Local Spur or the Orion Spur.

The Orion–Cygnus Arm is named for its proximity to the stars in the Orion constellation. It is located between the Carina–Sagittarius Arm and the Perseus Arm, the latter being one of the two major arms of the Milky Way. Within the Orion–Cygnus Arm, the solar system and Earth are located close to the inner rim in the Local Bubble, about half-way along the Arm's length, approximately 8,000 parsecs (26,000 light-years) from the galactic center.

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