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Scott Ruggels

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On 3/29/2019 at 4:34 PM, Scott Ruggels said:

Welp... I found the Rocket  Rabbit hole to fall into. Atomic Rockets  is the place for all thrust all the time space travel, plus  Space colonies and all sorts of hard science, near future-y goodness. Pulling a lot of material on that. Might be of use to others of you here as well.

 

Winchel Chung’s site is great.

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On 1/15/2019 at 4:34 PM, C-Note said:

I'm assuming all in-system travel involves acceleration to midpoint, and deceleration to the destination.  This great chart is from Classic Traveller.1432504796249.png

 

 

Am I reading this travel time chart wrong, or do those numbers seem way, way off? 

 

According to that chart going to Mars from Earth (on average 225 million KM away) would only take less the 88.7hours at 1G. That is obviously wrong, as we send probes to Mars at more then 1G and it takes months to get there. 

Heck, Mars at its closest to Earth is only 55 million KM away, and so by that chart it would take less then two days to get there. 

 

I mean a simple reverse math check shows that if a ship could go 255,000,000 km in 88.7 hours, that means the ship would be going 2.87million km/hour!!!!  (255,000,000km/88.7hrs= 2,874,859 km/hour)

 

The moon is 384,000Km from Earth, lets round up to 400,000KM which is on the chart. According to that it would only take 211 minutes to get to the Moon at 1G. That's only 3 hours and 31 minutes. Avengers: Endgame has a longer runtime then a trip to the moon according to this chart. 

 

So either that chart is wrong or my math skills are seriously off. 

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You're confusing acceleration with velocity.  Current spacecraft and probes are accelerated to a specific velocity where they remain for the duration of the trip, so most of their trip is spent at zero-G acceleration.  This chart assumes constant acceleration to midpoint and then constant deceleration to destination.  The physics and formulae are correct.

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But then I have a question, if these numbers are correct, why don't we do space travel this way currently? 

Is the technology not there currently to keep a passenger alive/cargo intact at that acceleration or is it a matter of carrying enough fuel? 

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2 minutes ago, mallet said:

But then I have a question, if these numbers are correct, why don't we do space travel this way currently? 

Is the technology not there currently to keep a passenger alive/cargo intact at that acceleration or is it a matter of carrying enough fuel? 

 

My guess is the inability to carry enough fuel.

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I believe Titan is the furthest satellite or planetary object which would be regarded as remotely habitable.  So, beyond that, you'd probably have some kind of deep space outpost out around the Uranian/Neptunian/Plutonian orbits, then some periodic unmanned probes sent into the Kuiper belt and Oort Cloud.  Presumably everyone's working on FTL but it's decades away if ever.  Maybe there's a series of robot probes sent to nearby stars?    Presumably the atmosphere/culture in different space settings--the Moon, Mars, the various lagrange and orbital habitats--will vary according to who owns them, the reasons for the colony/habitat, relative prosperity/availability of resources, etc.  

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Continuous acceleration is a nice solution, but the power requirements are prodigious.  Ion rockets do this (more or less continuous, more or less constant thrust -- which for a more or less constant ship mass is constant acceleration) but with accelerations much smaller than 1g.  You don't launch from planet surface with such an engine, but you can go from asteroid to asteroid that way, as long as you aren't in a hurry.

 

I scratched out some dirty estimates a couple decades back for a sci-fi campaign, assuming an X-ray laser photon rocket ... to drive a more or less empty Space Shuttle (~1000 tons) with continuous acceleration of 1g, required a power supply that was greater than the entire aggregate electrical power generation of Planet Earth in ~1995.  Not ten times greater, but greater by a factor of several.

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