Space travel questions

Oct 14, 2021
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Hello. I hope I'm posting this in the right place.


I'm writing a story that concerns space travel; not something that I know a whole bunch about. My biggest problem is “what will propel the ship?” This ship must be able to get to the Ross128 star system (11 light years from earth).


QUESTION #1 COULD THE FOLLOWING PROPELSION SYSTEM ACHIEVE MY GOAL?

I’m considering using photons. I’ve found some stuff on the internet that suggests this may be the most economical choice.

Even though photons have no mass, the microscopic particles of light do possess both energy and momentum. With a large, reflective sail, and sufficient quantities of photons, would it be possible to generate enough momentum to gradually accelerate a spacecraft to .9 light speed? And could this continue to propel the ship for the period of time it would take to arrive? Below is excerpts from the ship description from a rough draft. I’m curious if this would make sense?

Please ignore grammar ect., it’s a rough draft 😊

“An advantage of using photons as fuel was that the spaceship literally did not have to carry any fuel or engines. So, other than the mirrors and the sail, the rest of the ships mass could be made up of payload and the ships actual structure. This allows the craft to be many times smaller than other types of experimental spacecraft, such as rockets, that have to be capable of storing massive amounts of fuel.

The ship would be a pair of spacecraft linked by a long metal tube. The one in front is the actual ship, a small metal pod that provides living space and a 200-meter mirror.

Trailing behind the main ship is the towed propulsion system. This holds another 200 meter mirror and a giant sail (which looks like a huge aluminum parachute), into which the photons are bounced into, creating the momentum that accelerates the ship. The space between the two ships and their mirrors forms an active resonant optical cavity between them. By bouncing photons back and forth between the mirrors thousands of times, this amplifies the photon thrust by orders of magnitude.

A massive mirror located on earth reflects a laser to the spacecraft, providing the photons.

The light photons, bouncing between the mirrors and finally the sail, push the craft to incredible speeds, falling just short of the speed of light. Something called the “doppler shift” insures that, as the ship accelerates, the reflective process gains efficiency. So, as the spacecraft’s velocity drew near the speed of light, the efficiency of photon propulsion approaches nearly 100%, which translates to her incredible speed.

The goal is .90 speed of light.”



So, could a laser on earth pull this off? Hoping I can get some help from the experts here! Any opinions and advice on what I should do here (scrap the whole idea?) appreciated.

Oh, and one easier question:

QUESTIONS #2 TIME RADIO MESSAGE FROM NEPTUNE TO EARTH AT CLOSEST POINT?
 

Catastrophe

The devil is in the detail
Hi Davedave, and welcome to the forum.

Probably the most practical and informative approach you can find is in the book "Extraterrestrial" by Avi Loeb, John Murray (Publishers), 2021. Author is Chair of Harvard's Astronomy Department, and all the rest - one of the world's top astrophysicists.

He was approached by a billionaire (as happens a lot at the moment) over a special project. This guy wanted to fund a mission to the Centauri system, to arrive there during his lifetime - unmanned of course. Conventional chemical propulsion would require over 100,000 years. Avi came up with the idea of using a light sail. However, this is totally impracticable for anything over a few grams. They only wanted to take pictures and similar as they passed by. Obviously it would take too long to stop.

The system uses a 100 gigawatt laser beam. It is stated that everything they propose be within existing technological bounds. This is no joke. It is a serious mission. To avoid burning the sails, they had to absorb less than 1/ 100,000 of the (laser) light striking them.

There is an article published in Astrophysical Journal, October 2015, by Avi and James Guillochon on lightsails. It was decided to announce the Starshot Initiative, as they call it, on April 12 2016, On the stage were included Stephen Hawking, Freeman Dyson and Yuri Milner.

I hope this will help, but if you are thinking about manned trips using lightsails - forget it - unless you want to completely ignore the science.

Good Luck

Cat :)

Avi Loeb - Wikipedia
 
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Catastrophe

The devil is in the detail
There are some excerpts from the book here, including much of what I described on lightsails.
Note, in particular, the photograph of the chip, which has an area not much more than four fingernails.

Extraterrestrial: The First Sign of Intelligent Life Beyond Earth - Avi Loeb - Google Books

ufo - UFOs at close sight: Oumuamua (patrickgross.org)

I don't know why the word ufo appears, except to describe Oumuamua. This appears to be the October 15 article.

"He and his team calculated that a 100 GigaWatts laser beam aimed during several minutes to a photosail of about 32 square meters in surface would suffice to propel the micro-spacecraft to a fifth of the speed of light in two to three decades. Another 4 years would be needed to get the images back. The team of what became known as the "Breakthough Starshot" initiative had demonstrated that although it would cost about the same amount of money that other costly science projects cost, although it would be difficult to develop, it would be feasible, without requiring any technology that we do not yet possess."

Cat :)
 
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Oct 14, 2021
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Thank you so much for your thoughtful replies, cat. Looks like you shot me down. I'm going to look at what you provided. Meanwhile, in the story, the ship never makes it anyway, I just wanted a brief description of the means of travel.

Suggestions?
 
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Catastrophe

The devil is in the detail
Thank you so much for your thoughtful replies, cat. Looks like you shot me down. I'm going to look at what you provided. Meanwhile, in the story, the ship never makes it anyway, I just wanted a brief description of the means of travel.

Suggestions?
Davedave, I wish I could help. I don't know of any method anywhere near - neither did Avi Loeb - so I don't hold any prospects, especially if you want a manned trip. Even with a mammoth sail, it would take more than the total US energy consumption in a year to send (if I remember correctly) only about one pound weight. Could you send robots? That would reduce the weight very dramatically - saving weight of life essentials, return fuel - how would you get humans back?

Have you seen answer to Neptune question?

Cat :)
 
Oct 14, 2021
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Thanx again. My question was how long a radio message would take to get from Neptune to the earth. I guess I'm just being lazy, I could probably do the math easily by just finding out how fast radio waves in space go.

I'm off to research an alternate mode of travel. Thanx again.

edit: I just found out that radio waves move at the speed of light. My bad. thanx
 
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