To comment a little on that, this is the type of thing that is unfortunate about sci-fi games. We're really far away from the kind of propulsion performance that Traveller or The Expanse has and the scifi is so pervasive that there's no real concept of what spaceflight might really look like now. With few exceptions, nearly all delta-v in spaceflight outside of gravity boost is applied as instant as possible and the majority of the flight is coasting. Well planned flights might not have a single burn outside of the initial trans mars injection until orbit insertion at mars. For example a 160 day mission to mars launching at the august 3 2020 window would require a 3.91 km/sec delta-V earth departure burn and a 1.1 km/sec mars insertion burn. Aside from those few minutes of thrust, the entire 160 day journey would be "coasting". For missions outside of Mars or Venus, gravity assists are relied on a lot and there might be thrusts at close approach time for those gravity assists as mechanical advantage at that point greatly increases the value of the thrust.

On Sun, Jul 19, 2020 at 10:03 PM <xxxxxx@gmail.com> wrote:

So this article https://www.bbc.com/future/article/20150809-how-fast-could-humans-travel-safely-through-space got me thinking....

The Apollo 11 capsule was doing around 40K km/h at top speed coming back. The distance to the moon was 377,349km at that time.

Now, I've seen some discussion of the S shaped curve to enter a retrograde orbit around the moon as well, but it was lacking in some of the information I wanted (I did find out about 600 m/s was the velocity you need to enter said orbit).

So if they left the moon starting with 600 m/s and accelerated half way back, flipped, and decelerated, and they were doing 40K km/h at flip over, if I get my math right, they would have reached 40 K km/hr  minus 600 m/s in half the distance of 377K km.

Close to 250 minutes at the flip.

Now, I don't think they did constant acceleration nor constant deceleration nor did they need to get intercept velocity to zero (the atmo helps here on the return).

Punching in:
V(0) = 600 m/s (orbital velocity of the moon)
V(final at th flip) = 40,000,000 m/s
Time = 250 mins

Acceleration then looks to be 42 m/s^2.

That looks like 4 gees for nearly 5 hours accel then flip and decel at the same, so that's about 10 hours of 4 gees... that seems pretty hard on the astronauts.

Am I off in space with my numbers? The G load would be worse if you accelerated like mad for some minutes and then cut off for the rest of the trip to the mid-point.

I'm trying to figure out what sorts of acceleration you could reasonably sustain during system travel without grav plates if the journey took more than a short window (say 10 minutes or so)...

Would system ships in these settings then boost at a maximum of about 1.25 gees for a long haul? Or would they burst at 2-3Gs or more for up to 15 or 30 minutes, then come down, then have another heavy accel again if needed every (insert period of hours)?

Thoughts?

(I'm also thinking about, for say a trip to mars with a conventional rocket, how much would be coasting and what sort of Gs would be applied to get you moving? I'm assuming you couldn't burn all the way due to fuel weight...)

(Also curious if some form of maglev launch from the moon (lower escape velocity) might get you some of your initial velocity for a trip out to mars ...)

(Also curious - having trouble figuring out (via research) how fast one could 'fly' with a good push off inside a station in zero-G - I'm not sure what sort of velocity a straight jump from a surface using strong leg muscles could produce...)

Tom B






--
“The only stable state is the one in which all men are equal before the law.” ― Aristotle

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