# starship-design: Revised Engine Parameters

```Nels,

Those were peak accelerations, not sustained. The high end version would
only sustain 1 g for any length of time (preferably continuously). Obviously
no engine design would be run at maximum power continuously, So I was using
a ratio  of about 1 to 10 to be cautious.

The low end would peak at 1 g and therefore would "cruise" at 1/10 g, the
middle range would peak at 3 g's and cruise at 1/3 g, and the high end would
peak at 9 g's and cruise at 1 g. There was no special reason for picking
these exact figures, I just wanted a safety margin and they sounded good.

> An acceleration of 90 m/ss for your high engine performance is
> impractical.  This is for the simple reason that this equals about nine
> gee's.  Even if an engine could be made to do this, no human frame can
> take that much acceleration for more than a few minutes (here I assume we
> continue with the idea of manned missions, even an unmanned vessel's
> electronics would have to be special built to take the strain).
> Military pilots wearing g-suits are limited to 9.5 gees for a few
> seconds.
>       As for the middle range, having done some aerobatics myself, I can
> truthfully relate that taking three gees is somewhat uncomfortable, and
> doctors know that it isn't good for you in the long run.
>       NASA has probably done gee tolerance studies that give better
> numbers, but I personally would be loath to spend the next several years
> at more than 1.5 gees.

Okay, here they are reworded:

LOW: Thrust is not continuous, normal acceleration is 1 m/sec, may never
exceed 10 m/sec, total change in delta v of 100,000 km/sec (1/3 c)

MEDIAN: Thrust may extend for long periods but is not normally for entire
mission duration, normal acceleration is 3 m/sec, may achieve transient
thrust levels of up to 30 m/sec, total delta v limited to 200,000 km/sec
(2/3 c)

HIGH: Thrust is typically continuous over duration of mission, normal
acceleration is 10 m/sec, maximum acceleration is 90 m/sec, total delta v is
300,000 km/sec (0.99 c)

Lee
```