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Re: starship-design: Infrastructure in space [was: FTLtravel...]
In a message dated 4/27/00 10:30:34 PM, lparker@cacaphony.net writes:
>> Anyway one good sized commet core in near earth orbit has
>> been identofied as
>> having nearly 1000 times as much oil as opec produced in its
>> best year.
>
>Not that I doubt you, but I would like to ask for more details. To wit:
>
>1) What was that good year worth in dollars to OPEC?
>2) What was the per barrel price of oil that year?
>3) What is the per barrel price of oil a the moment?
>4) What is the total value of that comet core?
>
>I suspect it is quite a bit of money and I can see several possibilities
>for
>soft landing the oil....
>
>Lee
Sorry, typo, it was thousands of years worth in NEO.
As to more specific numbers:
Near earth comet core 5 Kilometers in diameter
20 billion tons of water ice
20 billion tons of organic componds (crude oil / oil shale)
(i.e. 20 OPEC max years of output.)
20 billion tons of ceramic ores
1 billion tons of carbon dioxide ice
>>> Oil value <<<
600 gal of fuel < 5000 lb ???
roughly 500 lb / barrel ??
20 billion tons = 80 billion barrels-ish
= $800 billion
Note I'm not not sure if oils 300 or 500 Lb per barrel
=================================================
Delta V needed to LEO 1-2 kilometer/sec
1,000,000 secounds = 11.6 days
for accel of .002 m/s2 for 1 e6 you get a 2km/sec Delta V
thrust about 12 e6 tons thrust
Spec impulse ? (lox/LH = 300-500? Fusion/elect 3,500-5,000 solar thermal
1000-2000)
Spec impulse 1000 Reaction mass of 12 e9 tons
Spec impulse 2000 Reaction mass of about 6 e9 tons
------------------------------------------
Calc using solar thermal numbers
Delta-V 2,000 m/s Spec imp 2000
you get a 2km/sec Delta V With
===================================
Below are parts of letter about a oil shuttle idea I was playing with. Its
kind of fragmentary, but I'll forward them now and if you have trouble I can
sort things out later. Sorry.==
One problem that came up when I was looking over the numbers for the “Steel
Challenge” scenerio was how do you deliver the cargo to earth? Now the major
cost is to launch a craft to orbit, not to land it. But the sale price of
comodities on earth is very low per pound. Oil weighs about 500 pound per
barrel, and for crude costs about $16 a barrel. The cost per barrel changes
frequently. Back in the OPEC days it was up to $36 a barrel for a bit (even
higher if you account for inflation) afterwards it droped bellow $10 a
barrel. Now its $16, but it will decline as the deacades continue. Buy the
time of this senerio they could have to sell their oil for $10 a barrel, or
about two cents a pound. Steel and such usually doesn’t go for a lot more,
even specialtiy alloies seldom go for dollars a pound. So I wond up with
trillions of dollars of materials in orbit, and no way to profitably bring it
to market.
My first idea was an old one. Wrap the cargo in a thick layer of foamed
rock. Then drop it into the ocean. The foam rock would burn off and
insulate the cargo during reentry, and would help it float once in impacted
the ocean. But I wasn’t sure what it would cost to wrap this stuff, nor did
the idea of droping hundreds, if not hundreds of thousands, of tons of cargo
toward a mid ocean impact. In theory you could make stearable craft to land
more gently, and maybe you could build them cheaply enough to be a throwaway,
or make them out of valuble materials that can be profitably scraped out
after the delivery, but it didn’t seem likely.
All in all a reusable craft seemed better. After all if you could build a
throw a way drop ship cheeply enough to deliver cargo. A reusable ship should
be even more economical. One advantage these craft would have is they would
only need to launch themselves empty to orbit. They would land with a huge
weight in cargo, but empty would weigh much less for launch back to space.
Hence the name Downloader, since its built to take cargo down, not launch it
into space.
Looking over aircraft data. Some millitary bombers can lift 2.5 times their
empty weight. But the best design to lift heavy crago into the air is a
flying wing like the B-2 stelth bomber. It, as near as I can figure from
unclassified info, can lift 8 times its empty weight. The B-2 uses high
streangth composites, but using foamed alloys I'ld think 20-30 times dry
weight may be possible. (I.e. its a metal plane with 1/10th the weight) A
flying wing should be able to do better.
Now most cargo delivery has learned that big craft are proportionally easier
and cheaper to operate then fleets of small craft. One of the biggest cargo
craft are the oil supper tankers. They weigh in at one million tons fully
loaded. Obviously a big step up from a 200-300 ton airliner, but then you
have about tweenty billion tons of cargo to ferry down to market, and you
probably want to sell it fairly quickly. (The investors want their money
back.)
So how big would a million ton flying wing be? The wing loading on a B-2
flying wing is about 70 lb per square foot. So to lift a million tons of
cargo craft (or at least to hold it in the air long enough to land it) you’ld
need:
1,000,000 tons = 2,000,000,000 pounds
2,000,000,000 (pounds) / 70 (pounds/square-foot) = 29,000,000 square foot of
wing area, about a square mile.
That comes out to a delta wing shape about a mile long with a 2 mile wing
span. REALLY big! But their are ways to drop that down a bit. First if you
fly faster you have much more lift per wing area. Tripple the flight speed
and the lifting abilaties go up about nine fold. Of course landing is a
problem, but then their ground effect. Ground effect is the interaction of
the wings air and the ground. Effectivly the air gets compressed between the
wing and the surface underneiath it. Some systems can lift 3-4 times their
flight weights while in ground effect. Given the huge wings were talking
about, the Downloader could get into ground effect while hundreds of feet
above the ground. Once in ground effect it slow down to a far lower landing
speed.
Now you can’t land to fast or your craft takes a real beeting. So lets say
the downloader flys with 4 times the wing loading of a B-2 flying wing, and
needs a long slow down in ground effect.
2,000,000,000 (pounds) / 280 (pounds/square-foot) = 7,000,000 square foot of
wing area, about a half mile on a side square.
This comes out to a craft with delta wings a half mile long and one mile
wide. Presumably the empty weight of the craft would also scale down, making
it even lighter at take-off.
Certainly better, but still monsterous. We almost certainly could build it,
we’ve designed bigger things. Could we afford to build it? Well
construction costs are hard to figure. If you scaled the costs up linearly
with the dry weight of the craft in comparison with a B-2 bomber, it would
cost about a half trillion dollars. But about half the cost of military
aircraft is for their avionics and military needs. Obviously this wouldn’t
scale up at all in cost, and would actually be largely unnessisary for a
comercial craft. Also the B-2 is precisly made to extreamly tight
tolerences, with expensive composites, to allow its stealth abilities. This
craft wouldn’t need anywhere near that degree of precision. If, as was
suggested for the Downloaders, you were runing off huge strips of the wing
like slabs of metal in a steel mill. Taking a hard temperature tolerant skin
and reenforcing it with strips of foam metal crudly welded on (nearly poored
on), and with a forest of foamed metal cross beems and trusses fused into
place by robots. Costs would be dramatically lower. More like the costs of
a skyscraper or ship. Even lower given the high levels of automation my
Jones-Sinclair emphasised. Instead of costing two three hundred billion
dollars, it might cost only a few hundred million to build. Given it lands
with forty million dollars worth of oil each trip, it could quickly pay back
that investment.
Could it function being that crudely made? Could it last very long? Given a
large ship it could be made more robustly, and hence more damage tolerant.
Also it could be made less precisely then a craft that needs to fly
efficently for long distences, so even if badly banged up it could still do
its job. With its high wing loading it would have a high reentry heating.
On the other hand given its size it could have a thick skin that could
withstand the heat better, or it could cycle water through the hot spots for
cooling and to feed steam powered retro and control rockets to help it down.
So you have a craft thats more like a ship then an aircraft in many respects.
It should see years of service.
Fuel and reaction mass costs would be negligible for this craft. Distiled
sea water, or comet melt would feed its engines reaction mass requirements
for free. A few dollars worth of fusion fuel would feed each reactor for a
year of continuous operation.
So what do we have so far? The crafts empty weigh could be 20th or 30th of
its loading landing weight, but we want it tough enough to take a lot of
abuse. So lets assume its landing weight was about 1/8th its loaded weight,
or 125 thousand tons. She’ld need about 40% that weight in water to launch
herself into space as a pure rocket, but using the fusion motors to directly
heat the outside air could drop that to 26%, but the boost to lagrage and a
little reserve for emergencies would counter that. Ad in about 25 thousand
tons of other cargo and you are taking off with a fifth the weight you landed
with. Which should be a big help in getting this monster off the ocean
surface. Assume the wings are sweept back a bit for stability, and the wings
about a half mile frount to back in the center, but the tips would hang back
about a quarter mile back farther. So:
Downloader stats
Wing span 1 mile
Wing root length 1/2 mile long
Craft length 3/4th mile
Craft height 120 feet
weight Speed
Landing 1,000,000 tons 300 mph to ground effect (?)
150 mph surface landing (?)
Take-off 200,000 tons 80 mph (?)
Take-off
reaction mass 50,000 tons
Cargo (t/o) 25,000 tons
Cargo (t/o) 875,000 tons
Empty 125,000 tons
=====================
So to land 500,000 tons would take a 20,000 ton craft.
But if we triple the landing speed, the lift should go up by a factor of 10
(I think) needing a 900 ft by 900 ft.
Wing loading
B-2 70 Lb per square foot
Shuttle 75-82 Lb per square foot (lands at over 200 mph)
Venture Star 45 Lb per square foot
Maybe we could scale it up!!
Kelly
____________________________________________
There seems to be a confusion over my downloader Idea. Namely, that
its impossibly with present technology to build a craft that large
that can fly. That's not the case. Such a wing has a couple of
quirks, but it also lacks a lot of the problems you'd assume.
The structure of a mile wide flying wing is essentially a reinforced
box beam. In English a thick walled tube with lots of internal cross
bracing. With enough of this it could serve as a one mile wide
bridge. Similar structures are used to build bridges. However unlike
a bridge, or a normal aircraft wing, the load and support isn't
concentrated in particular points. The cargo (1 million tons of it)
is assumed to be a liquid (or blocks of ore) which are scattered about
the full volume of the wing. So the load for the wings structure and
cargo is only supported by the wing structure immediately around it.
(Also pumping cargo around can be used to trim for balance or maneuver
if your into that.) Since this wing lands on water, no special
structure needs to be included to support the weigh from landing gear.
The wing does need to be stiff enough to keep from fluttering around
from turbulence, but that's not as big a problem, and if necessary you
can damp it out with local aerodynamic controls.
About all the heavy loads are front to back. The engine thrust could
be scattered along the rear edge of the wing to even out the load, but
it doesn't seem worth the effort to worry about. To think of the load
factors imaging the flying wing tipped up on its tail and only
supported in the center. Each end is again a box beam a half mile
long and a half mile high. The strength of such a structure is
related to the length vrs the highth at the supporting point. A 5 or
10 to 1 ratio is good. A one to one ratio with solid skin
reinforcement is fantastic!. A half mile truss bridge isn't unusual,
and ours is way over designed. Especially given the relatively light
thrust loads.
Landing is a problem, but on the scale of this ship the ocean is
effectively glass smooth, and little turbulence can effect it.
Tipping the nose up at launch, or the nose slapping down when the
trailing edge starts to drag into the water is a high load, but
carefully landing can balance out about all of that. Again, given its
size it will give a very smooth ride, with little ability to get
gossled off is course.
The engines construction is assumed to be electric heating of water or
air as a reaction mass. Not real complicated, and very effective!
However it assumes a lot of electricity. I assumed beamed microwaves
or fusion reactors for the power source. Given this isn't going to be
needed for a couple decades, and you'd need a big powerful energy
source to get enough cargo to fill this thing, one of the other
options are highly likely to be avalible at that time. I used the
fusion reactor Bussard discussed in the papers I've already discussed.
So all in all this is not pushing the technology envelope to a great
degree. A bigger question is the cost of building it. Since it is so
crude and heavy, it should be pretty cheep compared to a aircraft.
Also given that it isn't constrained by the harbors and ground
facilities of conventional ports and airports, Its economies of scale
should make it very attractive to bulk cargo shippers like oil and
ore. Its the same logic that got us oil tankers and ore freighters
that dwarf aircraft carriers.
Kelly
============ other lets =======
$ KW-h cost per Kilogram to orbit. 1cent per kw-h at spec imp 350 = $0.138
$/kg to land with 10 to 1 lift capacity and asuming Power to orbit costs are
1/3rd cost to orbit. $0.041 kg
1 barrel of oil is 42 gallons, or 5.6145 cubic feet. Oil weighs about 53
pounds per cubic foot. (http://pump.net/liquiddata/wdspecgrav.htm) So a
barel of oil weighs 298 pounds. At $10 a barrel thats 30 pounds per dollar ,
or 3.3 cents per pound or 7.26 cents a kilo. If the electric and maintenence
costs can be kept down, it is commercially viable to sell crude oil to earth
from space. Or you could refine it in space for more profit.
As for a list of other delta V's of interest:
Table 1 Mission Velocity Requirements
(delta-v)
Earth surface to LEO 8.0 km/s
Earth surface to escape velocity 11.2 km/s
Earth surface to GEO 11.8 km/s
LEO to escape velocity 3.2 km/s
LEO to Mars or Venus transfer orbit .7 km/s
LEO to GEO 3.5 km/s
LEO to HEEO 2.5 km/s
LEO to Moon landing 6.3 km/s
LEO to Near Earth Asteroid approx 5.5 km/s
NEA to Earth transfer orbit approx 1.0 km/s
Lunar surface to LEO (with aerobraking) 2.4 km/s
Phobos / Deimos to LEO 8.0 km/s
Given the NEA to LEO number of 1.0 k/s, its not going to add much to the drop
costs. I was asuming the bulk material would be in L-5 or some orbit between
earth and moon. That isn't listed, but I remember that LEO to GEO is higher
then LEO to lunar orbit. So I figure 3.5 km/s to get there is a good guess.