Starship Asterisk*

saturno2 wrote:
The nearest star to Earth than the Sun, is Proxima Centaury is to 4.22 light years away.
A spacecraft traveling at a speed of 30 km/sec, would take 42,200 years to reach Proxima Centaury.
The Universe is beautiful and very big.
We can to travel some planet, in the Solar Sistem, but to travel to a star .............
The stars are very faraway.
What think are you? .

Dushash wrote:I forgot to mention that in the space, it's much more easy to reach such speed, because there is no gravitation and no friction to anything, besides there is almost no deceleration. the only problem is that we have absolutely no idea what is out there, but one is more then clear, we are far away from leaving our solar system.

saturno2 wrote:
In truth, I think it¨s very difficult to travel to the stars because a spacecraft can not travel at speed of light.
Who can travel light speed?
Only photons and neutrinos, particles that have mass very small, it´s value tends to 0.
An atom, a molecule are very massive structures.

THX1138 wrote:saturno2
I am Disappointed in the fact as much as anybody I know of, 42,000 plus years to get to the nearest star. I dislike that fact so much that it actually hurts and I can only wish that I would be around in the future of say 500 or 1,000 years from now: if that is far enough into the future? When we actually have the ability to go somewhere.
As a comparison to just how miserably slow our fastest spacecraft can go at this time / 42,000 to the nearest star /
The fastest snail moves at .013 m/s there are 31,556,926 seconds in a year this means the snail travels 410,240.038 m converted to miles this is roughly 254 miles. If my math is correct that is. This would suggest that a snall could slither to the moon and back in 20 years

Chris Peterson wrote:
The fastest spacecraft we've produced were designed for the specific task of exploring the Solar System.

They weren't intended to be fast, so it doesn't make sense to say that they define our ability to produce fast spacecraft.

neufer wrote:The addition of (superfluous) humans will no doubt require faster spacecraft.

BMAONE23 wrote:The problem and purpose of robotic exploration and speed is the simple fact that to travel faster (which we could do) requires not only more fuel to gain additional speed but also to carry even more fuel to slow down once toy reach your final destination.
Economic space travel is by far slower than we are capable of.

Chris Peterson wrote:

BMAONE23 wrote:
The problem and purpose of robotic exploration and speed is the simple fact that to travel faster (which we could do) requires not only more fuel to gain additional speed but also to carry even more fuel to slow down once toy reach your final destination.
Economic space travel is by far slower than we are capable of.

I expect that the first exploration mission to another star would skip the whole process of slowing down. I imagine some sort of ion drive, which can provide continuous acceleration for many years without requiring much mass for the fuel (just a lot of energy), and would speed right through the system being studied... just like the New Horizons probe, where the observation period is only a fraction of the travel period.

I'm not sure what "economic" means in this context. We almost certainly have the technological and economic capacity to develop, in short order (no more than a few decades) a craft capable of reaching a nearby star with a travel time of a few decades. I doubt we'll do it, but that doesn't mean we couldn't.

• I'd love to know how

BMAONE23 wrote:
By then though, would anyone remember or still care that it was even sent there? Did our ancesters do anything between 5700BC and 7400BC that we were supposed to remember to track today?

http://en.wikipedia.org/wiki/Lascaux wrote:
<<Lascaux is the setting of a complex of caves in southwestern France famous for its Paleolithic cave paintings. The original caves are located near the village of Montignac, in the department of Dordogne. They contain some of the best-known Upper Paleolithic art. These paintings are estimated to be 17,300 years old. They primarily consist of images of large animals, most of which are known from fossil evidence to have lived in the area at the time.>>

neufer wrote:I'd love to know how.

Chris Peterson wrote:

neufer wrote:
I'd love to know how.

I think your example shows a certain lack of imagination.

Chris Peterson wrote:

neufer wrote:
In fact, there's no reason to think that ion thrusters can't be hugely improved with only a modest research and development effort. Prototypes already exist with exhaust velocities of several hundred thousand km/s, and specific impulse values of several tens of thousands of seconds. Experimental devices already show thrusts on the order of 10 N or more in pulse mode. All those numbers can reasonably get larger. The biggest hurdle is coming up with a multiple megawatt power source, but I think we already have experimental technology heading in that direction.

I'm not saying we can pull this off today, or next year. But I do think it's feasible to come up with a probe capable of 0.1 c within a few decades. Technically feasible. I don't remotely think we'll actually do it, nor do I really think we should.

• 1) lifted into orbit
  2) be made to escape the solar system (with it's source of solar power)
  3) on thrusts anywhere near the order of 10 N
  4) and be accelerated to 0.1 c

neufer wrote:What are you smoking out there in Colorado?

BMAONE23 wrote:If the intent is to leave the solar system, I'm not certain that Solar Power would be proper. The furthwer away from the sun you get, the less power you have. More likely some type of Thorium Reactor.

Chris Peterson wrote:

BMAONE23 wrote:
If the intent is to leave the solar system, I'm not certain that Solar Power would be proper. The furthwer away from the sun you get, the less power you have. More likely some type of Thorium Reactor.

Almost certainly some type of nuclear power would be required.

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29 wrote:
<<Project Orion was a study of a spacecraft intended to be directly propelled by a series of explosions of atomic bombs behind the craft (Nuclear pulse propulsion). A 1955 Los Alamos Laboratory document states (without offering references) that general proposals were first made by Stanislaw Ulam in 1946, and that preliminary calculations were made by F. Reines and Ulam in a Los Alamos memorandum dated 1947.

The Orion concept offered high thrust and high specific impulse, or propellant efficiency, at the same time. The unprecedented extreme power requirements for doing so would be met by nuclear explosions, of such power relative to the vehicle's mass as to be survived only by using external detonations without attempting to contain them in internal structure. As a qualitative comparison, traditional chemical rockets—such as the Saturn V that took the Apollo program to the Moon—produce high thrust with low specific impulse, whereas electric ion engines produce a small amount of thrust very efficiently. The Partial Test Ban Treaty of 1963 is generally acknowledged to have ended the project.

Freeman Dyson performed the first analysis of what kinds of Orion missions were possible to reach Alpha Centauri, the nearest star system to the Sun. His 1968 paper "Interstellar Transport" (Physics Today, October 1968, p. 41–45) retained the concept of large nuclear explosions but Dyson moved away from the use of fission bombs and considered the use of one megaton deuterium fusion explosions instead. His conclusions were simple: the debris velocity of fusion explosions was probably in the 3000–30,000 km/s range and the reflecting geometry of Orion's hemispherical pusher plate would reduce that range to 750–15,000 km/s.

To estimate the upper and lower limits of what could be done using contemporary technology (in 1968), Dyson considered two starship designs. The more conservative energy limited pusher plate design simply had to absorb all the thermal energy of each impinging explosion (4×10¹⁵ joules, half of which would be absorbed by the pusher plate) without melting. Dyson estimated that if the exposed surface consisted of copper with a thickness of 1 mm, then the diameter and mass of the hemispherical pusher plate would have to be 20 kilometers and 5 million metric tons, respectively. 100 seconds would be required to allow the copper to radiatively cool before the next explosion. It would then take on the order of 1000 years for the energy-limited heat sink Orion design to reach Alpha Centauri.

In order to improve on this performance while reducing size and cost, Dyson also considered an alternative momentum limited pusher plate design where an ablation coating of the exposed surface is substituted to get rid of the excess heat. The limitation is then set by the capacity of shock absorbers to transfer momentum from the impulsively accelerated pusher plate to the smoothly accelerated vehicle. Dyson calculated that the properties of available materials limited the velocity transferred by each explosion to ~30 meters per second independent of the size and nature of the explosion. If the vehicle is to be accelerated at 1 Earth gravity (9.81 m/s) with this velocity transfer, then the pulse rate is one explosion every three seconds.

[b][color=#0000FF][size=150]Seawise Giant, heaviest ship of any kind.[/size] [u]Fully laden displacement: 657,000 metric tons (width: 69 m)[/u][/color][/b]

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The dimensions and performance
of Dyson's improved Orion Space Craft
---------------------------------------------------------------
Ship diameter 	           100 meters
Mass of empty ship 	      100,000 metric tons
Number of 1MT bombs         300,000
Departure mass (from orbit) 400,000 metric tons
   (vs. just 450t for the Intern. Space Station !!)
Maximum velocity     	    10,000 km/s 
Mean acceleration  	   1 g (accelerate for 10 days)
Time to Alpha Centauri	   133 years
Estimated cost 		     0.1 year of U.S. GNP

Later studies indicate that the top cruise velocity that can theoretically be achieved by a thermonuclear Orion starship, assuming no fuel is saved for slowing back down, is about 8% to 10% of the speed of light. An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light. At 0.1c, Orion thermonuclear starships would require a flight time of at least 44 years to reach Alpha Centauri, not counting time needed to reach that speed (about 36 days at constant acceleration of 1g or 9.8 m/s²). At 0.1c, an Orion starship would require 100 years to travel 10 light years. The astronomer Carl Sagan suggested that this would be an excellent use for current stockpiles of nuclear weapons.

A concept similar to Orion was designed by the British Interplanetary Society (B.I.S.) in the years 1973–1974. Project Daedalus was to be a robotic interstellar probe to Barnard's Star that would travel at 12% of the speed of light. In 1989, a similar concept was studied by the U.S. Navy and NASA in Project Longshot. Both of these concepts require significant advances in fusion technology, and therefore cannot be built at present, unlike Orion. From 1998 to the present, the nuclear engineering department at Pennsylvania State University has been developing two improved versions of the Daedalus design known as Project Ican and Project Aimstar.>>