> In the cited example, an airframe type ship comes down through an
> atmosphere and happily lands on a planet using lift from the wings
> to flare at touchdown.
>
> When an unstreamlined ship attempts to do the same thing, OOPS no
> wings: no lift. Crash and burn.
Well, if there's no atmosphere I doubt it will burn well... :-)
Ports without an atmosphere are also likely to have low gravity -
hence landing under thrust should be easier than on Earth.
> Question: How then does our airframe, wing dependant ship, land
> with no atmosphere? Wings don't help when you have no air. The
> airframe ship will crash from a lack of lift just as the
> unstreamlined ship did.
If the thrust is less than the surface gravity of the landing site,
it will have *serious* problems.
> There MUST be downward pointing rockets on ships in order for them
> to land in such circumstances.
Maybe they are not designed to land under such circumstances? The
incidence of high-G airless planets should be rather low, shouldn't it?
Besides which, why would any ship equipped with rockets *not* call
the direction of thrust 'down'? In space, it won't matter much (it
will probably simplify artificial gravity or inertial compensation).
If you need thrust in order to land, it makes sense to get the most
effective use of it by directing it (largely) straight down. Beside
which, the ship will be designed to take a large force along the axis
of the main drive - if you wanted to land the ship on it's side, there
would need to be extra support for that, too.
> As an unstreamlined ship will not
> be able to use lift at ANY time, this will be the only normal way
> the ship could land at ALL.
How about a high-tech version of a parachute? Of course, launching
would be extremely difficult. Perhaps it would need to make use of a
separate launching vehicle?
> Barring specially fitted rockets, in order to maneuver properly, a
> ship's rocket engines must be able to be gymbaled. (You can't have
> them pointing in one direction only all the time.)
Why not? I imagine a fixed main thrust engine, with a number of smaller
maneuver thrusters. It's certainly a lot easier than engineering a
gimbal that will work reliably under the high-stress (probably high-
temperature and vibratory) conditions of a main rocket.
> It is true that
> the amount that the engines must be deflected is limited, but with
> contra-gravitic drives, you won't need much deflection at all.
> >From my reading of the paragraph outtake from FF&S, the contragrav
> takes care of 99% of the weight. So, you need a 1/100th of a G
> vector from your engines in order to get a full G upward to equal
> your weight and a bit more to take off. Well, if you have 1 G
> engines, the necessary deflection is Less than one degree.
If you're using a 1G drive to counter 0.01G of weight, what about the
0.99995G that's propelling you *forward*? Surely you want the smallest
possible speed when you land?
> A 1 degree deflection gives you a net thrust of .0075 G's upward.
> Just barely enough. Fear not, a deflection of 6.3 degrees will
> give you a full net thrust of 0.1 G in an upward direction. This
> is a negigable defection and plenty of thrust for landing.
Too much thrust! There's still 0.995G thrust pushing you forawrd.
(After 1 minute on an airless planet, this is 2100 km/h)
> The main difficulty in landing an unstreamlined ship in a real
> atmosphere will be avoiding the structual limitations on the ship.
I agree - but it would be 'easy' with enough thrust to counter gravity.
> As we have seen in the case of the streamlined ship, we can not
> exceed the 1000kph limit on the structure.
None of the early manned space capsules were airframe - and they re-
entered at *much* higher speeds than this. Heat was a large problem,
of course.
> In the case of an unstreamlined ship, the limit is 300kph.
What does a ship have to look like to qualify as `unstreamlined'?
For instance, is a pure sphere considered `streamlined'?
> This is a VERY low speed
> for you to try to enter the atmosphere at. One would have to come
> to almost zero ground speed for a ship to enter the upper
> atmosphere. You would have to have some pretty good meteorological
> data to avoid winds of 300kph on re-entry.
I assume the 300kph limit is for `standard' atmospheres (100 kPa).
At higher altitudes, the limit would (should?) be higher due to lower
density. Also, if there are no high-shear regions, the problem will be
self-correcting.
(In a long-distance flight, the difference in air velocity between start
and finish points can be around 3000 km/h. The difference is gradually
accomodated during the flight)
> Doing so, even with
> good data, and a ground side weather station at the starport should
> be pretty dang close to impossible.
Compared to the task of instellar navigation? Or even getting into an
orbit that is guaranteed not to hit anything else up there?
Are you kidding?
- --
Tim Little