NASA’s 100-Year Starship Project Sets Sights on Interstellar Travel
Will examine the business model needed to develop and mature a technology portfolio enabling long-distance manned space flight a century from now
https://www.space.com/11200-nasa-100-year-starship-interstellar-travel.html
https://100yearstarshipstudy.com/

Chemical Means

Video : Space Shuttle https://www.youtube.com/watch?v=4FROxZ5i67k
-Bi-Propellant/Liquid
*Rely on chemical reaction between two substances; *can be throttled; *high specific impulse; *can be re-used; *can be tested

Solid
*Burns at predictable rate; *can remain in storage for long periods; *can launch on short notice;

Heating

Nuclear thermal rocket : https://en.wikipedia.org/wiki/Nuclear_thermal_rocket
-In a nuclear thermal rocket a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor, and then expands through a rocket nozzle to create thrust.
– no nuclear thermal rocket has flown

Solar thermal rocket: https://en.wikipedia.org/wiki/Solar_thermal_rocket
Makes use of solar power to directly heat reaction mass, and therefore does not require an electrical generator as most other forms of solar-powered propulsion do
engine thrust is directly related to the surface area of the solar collector and to the local intensity of the solar radiation. Indirect solar heating involves pumping the propellant through passages in a heat exchanger that is heated by solar radiation
-Direct solar heating involves exposing the propellant directly to solar radiation

Gravitational Slingshot

https://en.wikipedia.org/wiki/Gravitational_slingshot
Gravity assistance can be used to accelerate, decelerate and/or re-direct the path of a spacecraft.
Animation – https://www.youtube.com/watch?v=I3F88w3LkiI&NR=1
+ no propellant needed
– Everything has to be in just the right spot

Electrical Propulsion

Ion Thrusters : https://en.wikipedia.org/wiki/Ion_drive
-An ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force

-Russian satellites have used electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north-south station keeping.
+ high specific impulse
– Uses a large amount of power and low thrust
Solar sail
https://en.wikipedia.org/wiki/Solar_sails
-Using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds.
-In 2010, IKAROS was the world’s first spacecraft designed to use solar sailing propulsion to be successfully launched https://www.jspec.jaxa.jp/e/activity/ikaros.html
-Video 1:24 https://www.youtube.com/watch?v=eq2DATxcft0

Fusion rocket
https://en.wikipedia.org/wiki/Fusion_rocket

Nuclear fusion reactions. In this kind of reaction, two light atomic nuclei fuse together to form a heavier nucleus and in doing so, release a large amount of energy.
– proposed reactor vessels are large and heavy, making them unsuitable to use on spacecraft in the foreseeable future
+ very high specific impulse
+ fusion rocket may produce less radiation than a fission rocket, reducing the mass needed for shielding

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Speed

Speed of light : https://en.wikipedia.org/wiki/Speed_of_light
-1,079 million km/hr :: 671 million mi/hr
-Special relativity Theory : https://en.wikipedia.org/wiki/Special_relativity
[*] The laws of physics would be unaffected by motion at a constant velocity
[*] The speed of light is constant and is the upper limit for the speeds of objects with positive rest mass

E=ymc2
* for an object at rest [ V=0 → y=1 ] → E=1*mc2 →  E=mc2
* for a moving object, as velocity → the speed of light [c],  y → Infinity as does the Energy
Visualization of Einstein’s special relativity https://www.youtube.com/watch?v=C2VMO7pcWhg

The Future? / What we know

-Based on what we know – https://www.nasa.gov/centers/glenn/technology/warp/ideaknow.html
-Faster-than-light : https://en.wikipedia.org/wiki/Faster-than-light
-Special Theory of Relativity – Does not forbid the existence of particles that travel faster than light
-Apparent/Effective FTL : Hypothesis → unusually distorted regions of spacetime might permit matter to reach distant locations faster than it would take light in the normal or undistorted spacetime

Status of Warp Drive
–https://www.nasa.gov/centers/glenn/technology/warp/warpstat.html
-Theories of making this happen, similar to Star Trek. Warping space around you.
-Emerging possibilities – https://www.nasa.gov/centers/glenn/technology/warp/possible.html

Wormholes

Alcubierre’s “Warp Drive” – the moving sidewalk / expand behind you & contract in front

Negative mass propulsion –

-Millis’s hypothetical “Space Drives” – A “space drive” can be defined as an idealized form of propulsion where the fundamental properties of matter and spacetime are used to create propulsive forces anywhere in space without having to carry and expel a reaction mass

Status on Anti-matter
https://www.nasa.gov/centers/glenn/technology/warp/antistat.html
-Antimatter is matter with its electrical charge reversed.
-Anti-electrons, called “positrons,” are like an electron but with a positive charge.
-Antiprotons are like protons with a negative charge.
-Positron, antiprotons and other antiparticles can be routinely created at particle accelerator labs
-Can even be trapped and stored for days or weeks at a time.
-And just last year, they made antihydrogen for the first time. It didn’t last long, but they did it.
-Also, Antimatter is NOT antigravity.
-Right now it would cost about One-Hundred-Billion dollars to create one milligram of antimatter

Hawking’s commentaries:
– Cites examples of what happened to Native Americans when Europeans settled.
– Also gives examples of ‘harvesting’ technology that could leave the Earth barren, or crippled.
– A cornerstone of his argument seems to be that advances in technology leave people cold and uncaring… nowhere in his statements does he explore the possibility of benevolent aliens.
– All of this was basically a response to the idea of “METI” — an active broadcast targeting alien civilizations.

Response from Douglas Vakoch @ SETI:
– “Even if they tend to be hateful, awful folks, can they do us any harm at interstellar distances?”
– Vakoch said it would take quite a lot of time and energy for extraterrestrials to come all the way to Earth to wage war or try to extract resources from our planet. The cost of traveling here to collect them, not to mention transporting those resources back to the aliens’ home, would far outweigh the benefit, he said. [The Strangest Extrasolar Planets]
– Seth Shostak @ SETI agreed. “It’s completely analogous to ordering a book from Amazon and paying $60,000 for shipping,”
– Link:  Interview w/ Seth Shostak (audio + transcript)

And furthermore, it’s too late to worry about it anyway:
– Signals used to transmit television and radio have been getting sent off into the cosmos since they were invented (approx. 60 years, now).  If anyone’s listening, and points in the right place, they’ll find us whether we’re telegraphing our presence or not.  It’s too late to turn off the signal.
– The earliest episodes of I Love Lucy have washed over 6000 or so star systems, and are reaching new audiences at the rate of one solar system a day. If there are sentient beings out there, the signals will reach them.

When the Allen Telescope Array comes online in 2015, SETI believes it will be less than 2 dozen years from that point, before the first alien civilization is discovered.
– Based on recalculations of the Drake Equation.
– SETI researches note that it could take an incredibly long time after that though, to actually be capable of interpreting whatever data might be received.

FASTER THAN LIGHT:

https://en.wikipedia.org/wiki/Faster-than-light
To summarize — the currently accepted special theory of relativity states that traveling AT the speed of light, would require an infinite amount of energy.  Going beyond it would require more than infinity.  Which doesn’t exist, so stop trying.

But if Hawking and others are worried about visiting aliens, then there must be a way, right?

So…. what are the leading theories?

1)  Ion Thrusters
– Already in use!
– Not powerful enough to break gravity fields, but incredibly efficient for long-term travel.
– Cannot break the speed of light, but over very long periods of time, can get very close with relatively little expenditure of energy along the way.

2)  Warp Travel (a la Star Trek)
– Most theories state this as a “relatively reasonable” idea of circumventing relativity.
– By creating ‘curves’ or ‘bends’ in space, you can shorten the distance needed to travel from one location to another.
– Would still need to be accompanied by powerful acceleration methods.
– Working theories known as the “Alcubierre Drive” in real life.
PROBLEMS:
– Warping space takes a crap-ton of energy.
– There’s no working model to “stop” the warp wave.

3)  Transversable Wormholes
– Under current physics models, the amount of energy required to punch a hole in space is astronomical, and there is no known way to guarantee where the other end would be located.
– Also would require being held open by a “sphere of exotic matter” which does not currently exist.
– However, perfectly logical if these issues were overcome.  Believe it or not, this could be more likely than other theories, despite the outlandish issues involved.

4)  “Super Force” drives
– According to Big Bang Theory, the universe is currently only about 14billion years old.
– But, it’s more than 150 billion light years across.
– The difference is solved by a theory known as “inflation” — in the universe’s infancy, the forces of Gravity, Magneticism, Strong and Weak Nuclear, were all a single Super Force, which was strong enough to ignore relativity and allow matter to travel faster than light.
– Scientists at the LHC are attempting to discover this Super Force. If harnessed, it could allow FTL travel by circumventing relativity.