Chibesa Engine properties

[sndrtj]

Hi there,

I am an avid fan of Alastair Reynold's books, and I'm wondering what the properties of a Reynolds-style Chibesa engine would be.

For those who have no clue what Chibesa engines are (I suspect that that is the majority):

Chibesa engines are fictional engines which are a result of "chibesa physics", some fictional type of physics mankind discovered around the year 2200. The details of Chibesa engines are quite scant. From his latest book, On the Steel Breeze, these are some speeds and descriptions:

1) A "slow" Chibesa-equipped ship takes 3 days to go from low Earth orbit to low Venus orbit under "somewhat favorable" conditions.

2) During this trip, the engines delivered thrust up to 1g for at least 12 hours straight.

3) The maximum speed attainable with a practical/standard Chibesa engine seems to be on the order of 13% of light speed.

4) They have a significantly better lsp than VASIMR engines.

Lets say that "most favorable" conditions for a 3-day trip to Venus means that Sun, Venus, and Earth are nearly at sygyzy (i.e., Venus is at closest approach to Earth). If one would then fly straight "up" from an equatorial Earth orbit towards an Earth escape orbit, while heading directly towards Venus, how much dV would then be required to travel that distance?

Here's a schematic of the situation at hand (planets orbit counter-clockwise):

I've done some simple calculations, assuming a direct straight line, and after accelerating for 12 hours straight at a constant 1g, one would already have traveled be 0.19 AU (28735945482 m). Since the minimum distance between Earth and Venus is 0.28 AU (4.159e+10 m), one would already be over the half-way point! That means to arrive at Venus one would have to slow down with more than 1g for a shorter time (probably something like 8-10 hours at 1.5g)! By that mark, the author's descriptions are plausible (the book mentioned "somewhat" favorable conditions, not maximally favorable conditions ). However, I feel like this is way too simplistic an idea. How do I _properly_ calculate this situation?

R code used to calculate stuff:

Note: I'm obviously considering Newtonian physics. These speeds are way too slow for relativistic effect to show up, so I won't go to the hassle of calculating stuff at the relativistic level ;-)

> g <- 9.81 # 1g is roughly 9.81m/s^2
> twelveh <- 12*24*60 # 12 in seconds
> speed_at_12h <- g*twelveh # speed after 12 hours of constant acceleration
> distance_at_12h <- speed_at_12h^2 # distance is the integral value of speed. for speed = ax --> distance = ax^2 
> venus_orbit <- 108e9 # value from wikipedia. 108 million km. This here is in meters
> earth_orbit <- 149.59e9 # again from wikipedia. 149.59 million km. This here is in meters again
> distance_to_cross <- earth_orbit - venus_orbit # distance Earth<-->Venus at sygyzy
> distance_left_12h <- distance_to_cross - distance_at_12h 
> print(distance_at_12h) # in m
[1] 28735945482 
> print(distance_to_cross) # in m
[1] 4.159e+10 
> print(speed_at_12h) # in m/s
[1] 169516.8

Edited May 24, 2014 by sndrtj

[Scotius]

http://www.projectrho.com/public_html/rocket/torchships.php

This might help