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PostPosted: Wed Jan 25, 2012 10:06 am 
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Location: Sonthofen / Germany
In the setting I am working on I would like to move an object with
a length of 160 meters, a width of 50 meters and a mass of appro-
ximately 30,000 metric tons (well, a ship) from a low orbit to a pla-
net's ocean as a "dead lander", with only a lifting body shell, seve-
ral parachutes and perhaps retro rockets to slow down its fall and
prevent a crash.

As I see it, this should be possible, I am not aware of any logical si-
ze or mass limit for such a "dead lander", but I may well be overloo-
king something, so I would very much like to read your opinions on
this.

Thank you very much. :)


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PostPosted: Wed Jan 25, 2012 1:43 pm 
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I think that you will need to look close at the lift to weight ratio. Thirty thousand tonnes is a lot of mass. Current flying bricks (like the shuttle orbiter) are around 4 tonnes per displacement ton. If your shell is to achieve a reasonable deceleration from atmospheric drag, a 30,000 tonne load will need a larger than 7,500 displacement ton shell.

NASA parachute recovery systems weigh 4% of their maximum payload (1 tonne parachute for a 50 tonne payload is roughly the current record), so your shell will need 600 parachutes (each 50 meters diameter) weighing about 600 tonnes total and requiring about 150 displacement tons.

An 8000 displacement ton (32,000 metric tonne) lander shell with a parachute recovery system seems possible, but a very large project - comparable in engineering scale to a mile-high skyscraper or a space elevator.


... and someone needs to repack 600 parachutes (at 1 metric tonne each) and lift an 8000 dT (2000 metric tonne) empty lander back to orbit?

[I look forward to seeing what you come up with.]

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PostPosted: Wed Jan 25, 2012 2:28 pm 
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My calculations come out a bit different. Assuming the ship is a cylinder:

volume = (25 * 25 * 3.14) * 160 = 314,000 cubic metres

dtons = 314,000 / 13.5 = 23,000

That makes for only 1.3 metrics tons per displacement ton, or about 1 metric ton per 10 cubic metres of volume.

Simon Hibbs

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PostPosted: Wed Jan 25, 2012 3:00 pm 
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Location: Sonthofen / Germany
Thank you both very much. :)

The basic idea is to transport a ship (watercraft, not spacecraft) from orbit
to the surface of a water world, because this seems less complicated and
expensive than building one on an ocean surface without any dry land for a
shipyard.

Below is a very rough draft of the ship's SWATH design, the SWATH floaters
would be retracted for the transport, and the first of the ships would have a
flat flight deck. The ship would be surrounded by a lifting body shell with the
parachute system, the shell and the parachutes would be disposable - so no
need to return anything to the orbit. Once the ship would have landed (well,
watered), a shuttle could deliver the crew and their equipment to the ship.

The 30,000 metric tons are just a guess based upon the GURPS Vehicles de-
sign system, it would probably not be difficult to reduce the ship's mass signi-
ficantly, because much of the interior fittings could be delivered later on by
shuttle.


Attachments:
SWATH-Floater.PNG
SWATH-Floater.PNG [ 8.93 KiB | Viewed 1333 times ]
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PostPosted: Thu Jan 26, 2012 1:54 pm 
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Land it in sections and "bolt" them together.

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PostPosted: Thu Jan 26, 2012 4:41 pm 
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Cyborg IM1 wrote:
Land it in sections and "bolt" them together.

Yep, this was my approach in previous settings of this kind,
but it turned out to be rather complicated, which is why I
am looking for a way to do it in only one go. :(


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PostPosted: Fri Jan 27, 2012 9:04 pm 
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Location: Northern California
If you need more lift, couldn't you increase the surface area by attaching large foam "wings" to it in order to make the glide characteristics better? The foam could also be used to absorb buffeting when it lands. Land it in the most placid sea on your world - only the size of most suitably placid sea would limit the size of your runway.

If the foam broke down in the presence of salts present in the seas, it'd solve "what do we do with the huge partially burnt, broken foam wings after we land"


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PostPosted: Fri Jan 27, 2012 9:26 pm 
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Location: Sonthofen / Germany
Thank you very much. :)
epicenter wrote:
If you need more lift, couldn't you increase the surface area by attaching large foam "wings" to it in order to make the glide characteristics better?

Yes, indeed, and those wings could probably even have retro rockets
attached, another way to reduce the impact somewhat. Since the
planet in question is a water world, there is enough space available,
and with futuristic materials it should be possible to reduce the total
weight of the ship to about 10,000 metric tons. While landing it as a
"dead lander" would still be a major engineering project, I think it is
"doable" enough to use the idea for my setting.


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PostPosted: Fri Feb 03, 2012 9:16 pm 
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While probably not in the correct spirit, what about something like THIS instead:

Image

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I really love Classic Traveller, especially without the Imperium ... There, I said it.
Now pass me a laser carbine and a couple of extra battery clips.


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PostPosted: Fri Feb 03, 2012 9:46 pm 
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Location: Sonthofen / Germany
atpollard wrote:
While probably not in the correct spirit, what about something like THIS instead:

Image

Unfortunately my browser shows only a little red cross
on a white field. :?


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