Duration: flights to L-4 point, and 90 degrees Earth orbit

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Discussion Overview

The discussion centers on the theoretical duration of flights to the L4 Lagrange point and a position 90 degrees ahead in Earth's orbit, considering future technologies for space travel. Participants explore assumptions about spacecraft design, acceleration methods, and the implications for human health during long-duration space travel.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that with a constant 1g acceleration, the time to reach L4 or L5 could be calculated using the formula ##T=\sqrt{2d/a}##, resulting in approximately 68 hours for the journey.
  • Others question the existence of a ramp-up period for acceleration, suggesting that if it takes time to reach 1g, the overall trip duration would increase.
  • There is a discussion about the minimum acceleration necessary to maintain human health, with some suggesting that long hauls should ideally be at 1g, while shorter trips may be less harmful.
  • Participants express uncertainty about the effects of reduced gravity on humans, noting that while 0g is detrimental over long periods, 1g is beneficial.
  • Some participants request clarification on terms such as "ramp up," "turnaround," and "Lagrange points," indicating a need for better understanding of the concepts involved.
  • There is mention of the potential for smaller crafts to make more frequent trips to L1-3 and the Moon, with a focus on shorter durations for those journeys.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the specifics of acceleration methods or the implications for human health. Multiple competing views remain regarding the effects of different acceleration profiles and the definitions of key terms.

Contextual Notes

Limitations include assumptions about future technologies, the dependence on definitions of acceleration and turnaround, and unresolved questions about the effects of varying gravity on human physiology.

Fred Bobo
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Assumptions:
200+ years from now
Asteroids have been moved to all Lagrange points, and at least 90, 180, and 270 degrees on Earth's' orbit for mining, and shielding humans and equipment
Tech to acceleration/decelerate at 1 gravity without need to carry fuel. (My main fiction.)
Direct line of flight

Space craft, tube shape, with decks perpendicular to line of flight.
Transport of crew, passengers, cargo: supplies, heavy tools,...

Mass: Similar to the Mont Oil Tanker(Knock Nevis, Jahre Viking, Happy Giant, Seawise Giant)
General Characteristics:
Tonnage: 260,941 GT (214,793 NT)
Length: 458.45 m (1,504 ft)
Beam: 68.8 m (226 ft)
Draught: 4.611 m (81 ft)
Capacity: 564,763 WT

Same mass, but dimensions reflecting the change in shape: Shorter length and larger diameter.

I am most interested in the duration of trips to the L4 point, and to 90 degrees forward Earth orbit,...Including the time to ramp up to 1g, the length of midpoint turnover, and the deceleration period.

Flights to all Lagrange points and to Mars L-points,... are of interest.
 
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Fred Bobo said:
Including the time to ramp up to 1g, the length of midpoint turnover
This depends on your fictional method to accelerate.

L4 and L5 are 1 AU = 150 million km away, at a constant 1 g acceleration you can ignore orbital mechanics because you are much faster anyway. At a=1g you need ##T=\sqrt{2d/a} = 120,000 s = 34 h## to the midpoint and the same time afterwards, for a total of 68 hours or nearly three days (72 hours). Peak speed is 1200 km/s or 0.4% the speed of light.
 
Thank you.

would there not be a period of ramp up that will not exist at the end? Trying to visual.

=========

how about L1-3 and the moon for a craft 1/10-20th the size? Daily/hourly transports to the destinations within a 24 hour duration.

================

I really wish i knew how to create a spread sheet with all the correct formulas.
 
Also: what do think the minimum acceleration should be to maintain human body health?

I think long hauls will be best to be at 1g. Shorter trips, even repeated often, will be less injurious. Or else not.
 
Fred Bobo said:
would there not be a period of ramp up that will not exist at the end? Trying to visual.
That depends on how your magic drive works. If it needs an hour or more to reach 1g then the trip gets a bit longer.

Chemical rockets can start within about a second.
Fred Bobo said:
how about L1-3 and the moon for a craft 1/10-20th the size?
Just plug in different values for d (half the length). a=10 m/s2.We don't know the effect of reduced gravity on humans for a long time. We know 0 g for a long time is not so good, we know 1 g is good. For a few days it doesn't matter.
 
mfb said:
That depends on how your magic drive works. If it needs an hour or more to reach 1g then the trip gets a bit longer.

Chemical rockets can start within about a second.Just plug in different values for d (half the length). a=10 m/s2.We don't know the effect of reduced gravity on humans for a long time. We know 0 g for a long time is not so good, we know 1 g is good. For a few days it doesn't matter.

Thank you. more to think about.
 
I'm not entirely sure you know what the terms you're using mean. Could you define (or better still, look up), please...

- 1 gravity acceleration : and what it means in terms of speed/velocity, and if there's a relation to mass/weight.
- ramp up
- turnaround : what it is and why it's used.
- LaGrange/LaGrangian/L points. (I'd suggest Wikipedia "LaGrangian points")

Basic kinematics formulae for distance, time, acceleration are also in Wikipedia (or here, it's a sticky post somewhere).

As DaveC points out, if you're going from Earth to L4 or L5, or other planets, at 1g, you don't have to worry much about orbital mechanics, because you're going (averaging) too fast for it to make much a difference, in an SF story where you'll presumably be saying "a few days" or "a couple of hours".

For messing about around the Earth<>Moon system, the grav sources are right in your face and the times are short (so massive velocities aren't built up), so yeah they'll make a difference there, as well as maybe throttling back a bit for passenger comfort in various circumstances.
 

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