Re: Spaceship with constant acceleration

It goes beyond "engineering" challenge and into the
realm of "physics" challenge.  It's sufficiently magical
that you might as well just make up whatever numbers
you want.

No, I see that differently. Sure, it is far beyond anything we can
build today, and may be forever impossible to build, but there's still
a difference between a 10TW ship where you ignore some thermal stress
on the engine in order to allow for interplanetary travel within
weeks, and a ship with an infinite improbability drive that can pop
out anywhere in the universe at the push of a button.

Any thrust during the middle 10
to 90 percent of the journey is a waste of propellant
mass which actually increases trip time

That's the first time I hear of this, would you mind to illustrate
this with an example?

What is the basic goal, here?  You say you want to increase
credibility...of what?  

Well, I want the numbers to hold up to some scrutiny, as opposed to
for instance the engine proposed by the Traveller universe, which
magically creates 20TW thrust power out of a 1GW reactor.
On the other hand, I want the technology to allow for fast and flowing
stories, not the kind where the pilot sets a course and then has to
sit and wait for 2 months until it's time for the deceleration burn.

In your initial post, you say you wish
to calculate characteristics of spaceships capable of
continuous acceleration.  Why?  What sort of missions are
these spaceships supposed to perform, and what are they
supposed to optimize for?

I was just trying to find out if - given the power levels I'm assuming
for this setting - such flights are at all possible. For example to
transport passengers who want to travel comfortably.

You give an example of an Earth-Mars flight.  Plausibly, the
goal may be to maximize payload, while keeping the trip
time down to a certain level.  

Concerning economical payload rates, I wouldn't look just at a single
flight, but a regular schedule of return flights. The more propellant
you pack, the faster you can go, the sooner you can make the next
flight. Defining payload as _actual_ payload (i.e. not counting the
ship's empty mass), I find that the trip is the most efficient when
the ratio of propellant to payload equals the square root of the
ship's mass ratio. Requires some fiddling with the numbers, but works,
if you look at the average tons per day.

Even with some magically
powerful drives, this will almost certainly involve a significant
drift leg during the middle of the journey, rather than
continuous acceleration (which actually increases trip
time and/or reduces payload).

As I was saying, I can't quite follow how constant thrusting would be
slower than impulse. If I look at two ships with equal payload and
equal mass ratio, one flying impulse and one with constant thrust, the
latter will be faster. If they carry equal payload and take the same
travel time, the constant-thrust one will need less propellant, and
its engine can be laid out for a lower peak performance.
.

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