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Hello Orion's Arm, my name is Dan Saranich. I'm 17 years old, from Connecticut (United States), and have a penchant for hard science fiction and space travel. I've been reading for almost a year now and I love some of your content, though disagree on certain things.

I have a question that I wanted a serious answer to.

When calculating the travel time for a spacecraft going from Planet A to Planet B, should I divide the spacecraft's exhaust velocity by the distance between points.

For Example, a spacecraft going from Earth to Mars with an exhaust velocity of 11,000,000 m/s. The mean distance between Earth and Mars is 1.7 AU (254,000,00 km).

1.7 AU / 11,000,000 m/s
= 6 Hours, 25 Minutes.

Is this the correct way to calculate how long a hypothetical flight would take place? Just wanted to know.

Thanks!
Welcome to the forums what's your favourite part of OA?

That's not the correct way to calculate the flight time of such a journey no. Exhaust velocity relates to thrust but you can't use it to derive travel time directly. For that you need to know the velocity of the craft, though in a lot of science fiction (and OA) rockets exist that have enough delta-V to accelerate for the whole journey. This equation works out how much time an object would take to cross a given distance at constant acceleration:

t = sqrt(2d/a)

Where d is distance in metres, a is acceleration in metres per second, t is time in seconds. This equation isn't for a journey however, it assumes the object constantly accelerates. It's good for working out fly-bys or impacts. Assuming we want the payload to arrive in one piece it needs to flip over half way and decelerate. In which case we just work out the equation above for half the distance and then double it:

t = sqrt(d/a)*2

This website does the calculation automatically for you:
http://www.transhuman.talktalk.net/iw/TravTime.htm

For a mean distance trip to Mars a spacecraft able to maintain a constant 10 centigee acceleration would do the journey in just under 12 days.
(02-08-2018, 05:57 AM)Rynn Wrote: [ -> ]Welcome to the forums what's your favourite part of OA?

That's not the correct way to calculate the flight time of such a journey no. Exhaust velocity relates to thrust but you can't use it to derive travel time directly. For that you need to know the velocity of the craft, though in a lot of science fiction (and OA) rockets exist that have enough delta-V to accelerate for the whole journey. This equation works out how much time an object would take to cross a given distance at constant acceleration:

t = sqrt(2d/a)

Where d is distance in metres, a is acceleration in metres per second, t is time in seconds. This equation isn't for a journey however, it assumes the object constantly accelerates. It's good for working out fly-bys or impacts. Assuming we want the payload to arrive in one piece it needs to flip over half way and decelerate. In which case we just work out the equation above for half the distance and then double it:

t = sqrt(d/a)*2

This website does the calculation automatically for you:
http://www.transhuman.talktalk.net/iw/TravTime.htm

For a mean distance trip to Mars a spacecraft able to maintain a constant 10 centigee acceleration would do the journey in just under 12 days.

Thank You, I love the hardness of the universe and the devotion to scientific realism without ruining the fun. For the last year I've been becoming increasingly addicted to Hard Science Fiction; of course I don't hate softer franchises like Star Wars, Star Trek, etc, but I can't watch A New Hope without thinking to myself about how unrealistic it all is. And don't get me started on the "Parsecs" quote, dear god!  I love the aliens, original and not just Humans with prosthetics (even genuine hard sci-fi series do that). The Encyclopedia Galactica is very informative, though I'm not really a fan of the Bernd Helfert artwork, it doesn't really fit. I would like to see more original artwork in the Encyclopedia. The History is not bad, I like the basic set up; The Singularity > Nanodisaster > Technocalypse > Great Expulsion > Dark Age. I don't agree with some of the Transhumanist elements in the universe, I think sentient AI will exist but I don't know if they'll become godlike entities within the next several millennia. Definitely not within the next 15 years as Ray Kurzweil and Elon Musk propose. Clarktech/Godtech seem like a stretch, though the Wormholes are cool.

I expect that Provolved Tree Kangaroos exist in Y11k.

Thanks for the equations, I've used these before. I just wanted to find an easily way to calculate travel time of a spacecraft without getting into the complicated equations. I've been looking up equations from Atomic Rockets and translating them into Wolfram Alpha with mixed results. I like the calculator you sent me, wish it was more interactive it seems very limited.

I other news, did you watch the Falcon Heavy launch yesterday. Absolutely beautiful!  The Tesla Roadster sent into orbit, (the dummy driving it has gotten the nickname Starman) I've been seeing it reference all over Reddit and 4chan.

What did you think of the launch?
(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]Thank You, I love the hardness of the universe and the devotion to scientific realism without ruining the fun. For the last year I've been becoming increasingly addicted to Hard Science Fiction; of course I don't hate softer franchises like Star Wars, Star Trek, etc, but I can't watch A New Hope without thinking to myself about how unrealistic it all is. And don't get me started on the "Parsecs" quote, dear god!  I love the aliens, original and not just Humans with prosthetics (even genuine hard sci-fi series do that).

I find them enjoyable for different reasons, mostly I find franchises without good worldbuilding to be a pain and hard SF tends to be better at that.

(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]The Encyclopedia Galactica is very informative, though I'm not really a fan of the Bernd Helfert artwork, it doesn't really fit. I would like to see more original artwork in the Encyclopedia. The History is not bad, I like the basic set up; The Singularity > Nanodisaster > Technocalypse > Great Expulsion > Dark Age. I don't agree with some of the Transhumanist elements in the universe, I think sentient AI will exist but I don't know if they'll become godlike entities within the next several millennia. Definitely not within the next 15 years as Ray Kurzweil and Elon Musk propose. Clarktech/Godtech seem like a stretch, though the Wormholes are cool.

I'm also not a Kurzweil fan (IMO he's a bit of a hack) but it's worth keeping in mind that OA isn't a futurology project, it's a fictional worldbuilding site. We don't purport to predict the future so much as have tried to take the ideas of transhumanist fiction and run with it for entertainment and interest "Godlike" is in the eye of the beholder imo. If it's mentally as beyond you as you are a worm, can do things you can barely understand and output as much economic activity in one thought as your entire civilisation does then why not use the term godlike?

(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]I expect that Provolved Tree Kangaroos exist in Y11k.

If there's something in the EG that you think should be there then go forth and conquer anyone's free to write an article.

(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]Thanks for the equations, I've used these before. I just wanted to find an easily way to calculate travel time of a spacecraft without getting into the complicated equations. I've been looking up equations from Atomic Rockets and translating them into Wolfram Alpha with mixed results. I like the calculator you sent me, wish it was more interactive it seems very limited.

As far as I'm aware that's the quickest and easiest equation to figure out non-relativistic journey times using continuous acceleration. Relativistic journeys, anything involving orbital transfers and working through the rocket equation to figure out fine details are all much more of an effort.

(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]I other news, did you watch the Falcon Heavy launch yesterday. Absolutely beautiful!  The Tesla Roadster sent into orbit, (the dummy driving it has gotten the nickname Starman) I've been seeing it reference all over Reddit and 4chan. What did you think of the launch?

I did watch, it was very impressive. Tbh I hated putting the car in their, I don't think it says something great about our species that we turn momentus rocket launches into marketing, but the reusability of the rocket is very cool. The footage of the two boosters landing side-by-side within a second of each other was a thing of beauty.
How do I use the quote boxes?
(02-08-2018, 08:17 AM)Daniel S Wrote: [ -> ]How do I use the quote boxes?

Press reply on the message you want to quote. If you want to edit the quotes (for example you want to divide them up like I have above or because the message has quotes of quotes and needs to be cut down) click the "view source" button on the toolbar. Then you can just manually put [quote=...) and [/quote) around the text you want.
(02-08-2018, 08:09 AM)Rynn Wrote: [ -> ]
(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]Thank You, I love the hardness of the universe and the devotion to scientific realism without ruining the fun. For the last year I've been becoming increasingly addicted to Hard Science Fiction; of course I don't hate softer franchises like Star Wars, Star Trek, etc, but I can't watch A New Hope without thinking to myself about how unrealistic it all is. And don't get me started on the "Parsecs" quote, dear god!  I love the aliens, original and not just Humans with prosthetics (even genuine hard sci-fi series do that).

I find them enjoyable for different reasons, mostly I find franchises without good worldbuilding to be a pain and hard SF tends to be better at that.

(02-08-2018, 08:09 AM)Rynn Wrote: [ -> ]
(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]The Encyclopedia Galactica is very informative, though I'm not really a fan of the Bernd Helfert artwork, it doesn't really fit. I would like to see more original artwork in the Encyclopedia. The History is not bad, I like the basic set up; The Singularity > Nanodisaster > Technocalypse > Great Expulsion > Dark Age. I don't agree with some of the Transhumanist elements in the universe, I think sentient AI will exist but I don't know if they'll become godlike entities within the next several millennia. Definitely not within the next 15 years as Ray Kurzweil and Elon Musk propose. Clarktech/Godtech seem like a stretch, though the Wormholes are cool.

I'm also not a Kurzweil fan (IMO he's a bit of a hack) but it's worth keeping in mind that OA isn't a futurology project, it's a fictional worldbuilding site. We don't purport to predict the future so much as have tried to take the ideas of transhumanist fiction and run with it for entertainment and interest "Godlike" is in the eye of the beholder imo. If it's mentally as beyond you as you are a worm, can do things you can barely understand and output as much economic activity in one thought as your entire civilisation does then why not use the term godlike?

I know that Orion's Arm is a worldbuilding project, I just wanted to state my views on Transhumanism.

(02-08-2018, 08:09 AM)Rynn Wrote: [ -> ]
(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]I expect that Provolved Tree Kangaroos exist in Y11k.
If there's something in the EG that you think should be there then go forth and conquer anyone's free to write an article.

Look them up, there the cutest things in the universe.

(02-08-2018, 08:09 AM)Rynn Wrote: [ -> ]
(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]Thanks for the equations, I've used these before. I just wanted to find an easily way to calculate travel time of a spacecraft without getting into the complicated equations. I've been looking up equations from Atomic Rockets and translating them into Wolfram Alpha with mixed results. I like the calculator you sent me, wish it was more interactive it seems very limited.

As far as I'm aware that's the quickest and easiest equation to figure out non-relativistic journey times using continuous acceleration. Relativistic journeys, anything involving orbital transfers and working through the rocket equation to figure out fine details are all much more of an effort.

Well I know a few Constant Acceleration calculators, both are good but don't good into the specific details I prefer

(02-08-2018, 08:09 AM)Rynn Wrote: [ -> ]
(02-08-2018, 07:43 AM)Daniel S Wrote: [ -> ]I other news, did you watch the Falcon Heavy launch yesterday. Absolutely beautiful!  The Tesla Roadster sent into orbit, (the dummy driving it has gotten the nickname Starman) I've been seeing it reference all over Reddit and 4chan. What did you think of the launch?

I did watch, it was very impressive. Tbh I hated putting the car in their, I don't think it says something great about our species that we turn momentus rocket launches into marketing, but the reusability of the rocket is very cool. The footage of the two boosters landing side-by-side within a second of each other was a thing of beauty.
I agree it was beautiful, I couldn't catch it live by it did watch it after and I was impressed. Its even more epic if you play some epic music in the background. As more the Tesla Roadster, it was supposed to be the Falcon Heavy's boilerplate, a dummy payload used for test flights. Musk made it a publicity stunt. The car has become a meme across the Internet.
Hi - Welcome to OA!

Re continuous acceleration - it looks like Rynn has covered the basics of figuring acceleration.

As he mentions there are lots of different continuous acceleration calculators floating around the web. This one is what I use most of the time.

Re Provolved Tree Kangaroos - They are cute. Almost certainly they exist in the setting - although the EG we see only contains portions of the presumed full document that exists in the setting, it is mentioned that over 130,000 species have been provolved. Also, there are groups in the setting that approach provolution with what might be seen as religious fervor.

As Rynn says, if you would like to do a write up on them, please feel free. Otherwise, someone else may get around to it eventually. I can see them in several different forms, ranging from the basic provolve, with human level intelligence and hands of some kind, along with versions adapted to low gravity or zero G. Maybe also cyborg versions and even some transapients.

Re the SpaceX launch - I just watched it on YouTube in the last hour - very impressive and aspiring

Once again, welcome to OA and see you around the forum.

Todd