What are the requirements for interstellar travel at different speeds?

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Discussion Overview

The discussion revolves around the requirements for interstellar travel at various speeds, particularly focusing on energy, fuel mass, and time calculations for spacecraft accelerating at 1 g. Participants examine the implications of these calculations and clarify terms related to acceleration and velocity.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents tables detailing energy, fuel mass, and time requirements for spacecraft traveling at different percentages of light speed, seeking feedback on accuracy.
  • Another participant questions the meaning of "Acceleration time at 1 gravity" and notes the complexity of calculations for accelerating starships, highlighting the significant fuel requirements.
  • Clarification is provided regarding the definition of acceleration time at 1 g, but a subsequent participant expresses confusion about the explanation, emphasizing the need for specific impulse to determine propellant mass flow rates.
  • Concerns are raised about the relationship between constant acceleration in different frames of reference, with one participant suggesting that while acceleration may be constant in the rocket's frame, it is not so in the Earth's frame.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the clarity of the definitions and calculations presented, with some expressing confusion and others providing corrections or clarifications. Multiple viewpoints on the implications of acceleration and fuel requirements remain evident.

Contextual Notes

There are unresolved aspects regarding the integration of acceleration over time and the implications of specific impulse on propellant mass flow rates. The discussion also highlights the complexity of calculations involved in interstellar travel.

Jon0815
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Using information and calculators I found online, I have put together a series of tables illustrating the energy, fuel mass, and time requirements (both Earth and ship time, at 1 g acceleration) for a spacecraft to reach various percentages of light speed.

https://sites.google.com/site/interstellartraveltables/

I don't have a physics background myself, so I'd appreciate it if anyone who does could look it over and see if they spot any errors.
 
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I'm not going to check all of the numbers, but all of the nonaccelerated numbers look reasonable.

What is meant by, "Acceleration time at 1 gravity"? Also, these types of calculations (fuel mass, energy requirements, etc.) are particularly enlightening (and more difficult) in the case of the accelerating starship. I see you've worked out timetables, but it's also interesting to see the absurd amount of fuel necessary to maintain these accelerations :)
 
What is meant by, "Acceleration time at 1 gravity"?

The time it takes to reach to reach the speed at 1 gravity acceleration. I'll change that to make it more clear.
 
Jon0815 said:
The time it takes to reach to reach the speed at 1 gravity acceleration. I'll change that to make it more clear.
I'm sorry, but this does not make sense.

g = 9.81 m/s2 is a measure of acceleration, and speed (or magnitude of velocity) is found by integrating the acceleration over time. If one accelerates at a constant acceleration of g, the v = gt + vo.

One also needs the specific impulse in order to determine the propellant mass flow rate to achieve a given thrust, and mass flow rate integrated over time will give the total propellant to be stored. If there is a huge mass of propellant, one will require a substantial thrust to get 1 g of acceleration, and one will need substantial mass in which to store the propellant.

Ideally, one has a high Isp, which means a lot of energy per unit mass of propellant. However, high Isp systems usually have low mass flow rates.
 
Astronuc said:
I'm sorry, but this does not make sense.

g = 9.81 m/s2 is a measure of acceleration, and speed (or magnitude of velocity) is found by integrating the acceleration over time. If one accelerates at a constant acceleration of g, the v = gt + vo.

Well, acceleration might be constant in the frame of the rocket, but will not be in the static Earth frame. But I think it's now clear what was meant.
 

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