The Prophesy Chronicles - Discussion Thread

[TheBigDog]

Originally Posted by CraigD

You're right. I think I got 2.2e8, then wrote it "2.2 billion" instead of "0.22 billion".

That I'm using specific impulse calculations correctly to set up the calculation still needs checking, but the result makes intuitive sense - a gigantic VASIMIR engine / array of engines can get a ship from LEO to escape spending about 1% of its total mass as reaction mass.

Fantastic! We have that much just in the fuel lines!

Talking about Mass, I did some work with a spreadsheet to come up with my numbers. 19.82 billion kilos is the total wet mass of the ship. I have 480 living sections for agriculture. Each is 20 meters by 100 meters with 3 meters of soil. That makes the volume of soil the largest single part of the ship in terms of mass. I have no science to go on here, I just thought that if you were going for an indefinite farming project you would need lots of soil. 3 meters too deep? If I lower the depth from 3 meters to 2 meters we open up almost 2.69 billion kg of mass for additional fuel or other cool stuff.

Bill

[Donk]

Originally Posted by TheBigDog

We would be in an ascending orbit, increasing our altitude while we continue to spiral further from the earth until we reach a point where we exited on a long, arching tangent. Then we begin slingshot moves through the solar system until we achieve the velocity that will carry us to our first extra-solar checkpoint.

Bill

I'd have thought you'd use Venus as the first gravity assist, as it's nearer. It's also faster - 35km/sec (Earth 30, Mars 24, Jupiter 13, Saturn 10). The faster the planet or planetoid, the more power you can get out of the slingshot.

Take a look at Galileo, for instance. Starting from Earth orbit, it boosted for an hour only, then free-fell, reaching Venus in less than four months. Ten months later it was back, getting another slingshot from Earth, then another two years later. Those three manoeuvres gave it enough velocity to get to Jupiter where it could start doing its real job.

You need more, of course. You not only need Solar System escape velocity, you need enough velocity to get somewhere interesting in reasonable time. Solar escape velocity is 617.5 km/s, but you need a LOT more than that.

I tried to do the math on the first slingshot around Venus, but had to retire hurt. Party this evening, quite a lot of booze...

I was trying to calculate the Kepler orbit, Earth to Venus. Assuming free fall, and assuming a starting velocity of 30km/sec (Earth orbital velocity), it shouldn't have been hard to work out the Gravitational Potential Energy at the start, then the GPE at Venus orbit. The difference is the energy added to Prophesy, translating into quite a bit of free speed. Should be plenty enough to catch Venus and slingshot around it. The maximum speed increase from the slingshot is 70km/sec if you use Venus to do a complete U-turn. You won't, of course. You'll want to use the same manoeuver to get to your next target, so probably 40km/sec is as much as you can expect.

I'm not sure whether any of the above makes sense. Maybe I shouldn't post when drunk...

[TheBigDog]

Originally Posted by Donk

I'm not sure whether any of the above makes sense. Maybe I shouldn't post when drunk...

It didn't stop Hemmingway, why should it stop you? Venus makes great sense. What will be tricky is that our target star may be well away from the solar plane that our planets sit on, so at some point we would need to slingshot at an angle that would take us "up or down" rather than exiting to the side of the solar system.



Bill

[TheBigDog]

I am working on the first installment for the Chronicles thread. Don't be fooled by a couple days of apparent inactivity.

Bill

[TheBigDog]

My stories are moving along. I am initially doing them as a sort of collection of short stories from the point of view of various characters who live in the world of the Prophesy Chronicles. Through their narrative you will experience life on the ship, life as one of the innovators who designed the ship and the mission, and how things change over the long years of the mission. There will be pivotal moments where critical decisions will have everyone's fate in the balance, moments where the culture and society that develop are exposed and explained, and irreverent moments where people find silliness and happiness in spite of their circumstances. All of this is wrapped up in what I intend to be plausible science and understanding of human nature.

I am leaving for a week long vacation beginning the morning of the 1st, so you may not see any more postings until the 10th or so. I promise that they will be coming in steadily from then on.

Bill

[Donk]

I’m hoping to be signed on for the voyage, so I’ve been reading up on the team’s previous adventures. I have to say, though, that what I’ve read isn’t the full and frank account I’d have expected from you people. I have this testimony from an unimpeachable source:

One thing they didn’t tell me until a few hours before launch. A bunch of medics came in and gave me a final checkup, then led me through to a small side room with some unusual gadgets.

“Time for your hydrotherapy,” said a pretty young nurse.

I’m really into swimming, and wasn’t sure whether there was a pool on Prophesy, so I grinned and said “yes please!”

When they explained what they meant, my grin disappeared in a hurry! Colonic Irrigation, aka enema

For a while I thought they were going to have to strap me to the bed. (Yes, the bed did have straps on it. ) Then the doc came up with the clincher: “It’s all about minimising mass to orbit. What do you want up there with you – the contents of your bowel, or a couple of bottles of Jack Daniels?” When you put it like that...

Why keep it quiet? It’s good, sound science, after all. Either y’all were so embarrassed about the procedure that you didn’t want to talk about it, or you were keeping it back as some sort of frat initiation thing. Sorry, guys – your cover's just been blown

[TheBigDog]

I have been working on my story line and boning up on the critical elements of writing fiction. So I am doing some research as I build the characters and story line. It is a whirlwind of decisions as it all begins to take shape. There is an obvious long story about the building, launch, and journey on board the ship. What is not so obvious are the stories within the story that compel the reader to keep turning the pages. The dreams and demons of the characters. So I made a decision to start off with a murder mystery, as a sort of tribute to Isaac Asimov and how he began the Robot series. Sound like fun? Along the first story I will be planting the seeds for some other very long story lines, and I hope that they are intriguing enough to keep everyone wanting more.

Bill

[TheBigDog]

Back to the technical...

Here is our playground for finding a habitable planet.



The ship is initially heading for the Alpha Centauri trio. There is little hope of finding a habitable planet there, but there are other planets for examination that will allow a better understanding of the capability of the ship's sensors, and the three star system will allow for gravity slingshot in pretty much any direction with a large jump in velocity. Getting empirical data of what our sensory systems tell us of extra-stellar planets will help us to understand the data we are receiving and get a better idea of what targets to go after.

I personally am leaning toward Tau Ceti as being the target, if for no other reason that it is a short name to type.

Bill

Source of image: http://www.atlasoftheuniverse.com/20lys.html

[Jay-qu]

What about Gliese 581? It does have a good candidate for a habitable extrasolar planet.

[TheBigDog]

Originally Posted by Jay-qu

What about Gliese 581? It does have a good candidate for a habitable extrasolar planet.

Very nice! I hope you are looking at 581e which with a minimum mass of 1.9 times that of earth. I would not want to life on a planet where I "weigh" over 1200 lbs (Gliese 581c), 420 or so for 581e would be plenty. That begs a question. If 581e did have a natural environment for humans, could we adapt to the extra gravity? What would the outside be for planetary gravity?

Bill