starship-design: How to build a station.

[KellySt@aol.com]

Ok, to try to be more constructive in this argument.

How would you get a small craft into space?

Well one option is hobbeist.  Their are folks building and flying homemade
ejector ramjets.  The digging I attached seemed fairly comfortable with
Ramjets/scramjets getting up to, maybe above mach  6.  With a bit of work
getting a ejector ram or pulse get to funding as a rocket in hard vac is 
doable,
so the engine weight penalty wouldn't be high.

The bad nest is between there and the surface is hypersonic flight.  Slight
problems at that speed get nasty.  You have a aerodynamics problem at 400 mph,
you can probably nurse your homebuilt plane home.  At mach-3 you and ship will
look like you were run through a chiper-shredder.  Also you need to make the
hull out of high temp materials, especially for reentry.  But the exotic
material used back when are now on the hobbest market.  Pricy, but there.  
(Not
to mention new stuff like graphite composites that the 50's aerospace 
engineers
would have sold organs to get.)  Get a hold of a good aerospace scrounger and
you can find left overs at surprising prices.  I've seen folks walk off with
flight worthy titan engines and $.05 a pound scrap value.

How do you make a areo shape that can keep going in a straight line at those
speeds?  Steal!  No blushing around.  Order copies of hull info from a SR-71 
or
X-15 - or go talk to Burt Rutan who doing such work for Orbital Sciences.  
Find
a hull shape that flew at those speeds and didn't try to fly sidewise.  
Reentry?
Large wing and flat bottom and belly flop in.  Need some good high temp bottom
stuff.

If this is to much, piggyback on another group trying to build something like
it.


What about a space station?
Well you can't ship it up in a craft able to carry 1/2 ton loads.  You need 
more
then that to build a garage.  Besides the economies of scale are terrible at
that scale.  Say 5 tons and the volume of a UPS truck.  To make it simple 
build
and check most of it out down here, and disassemble it for up ship and 
assembly.
REAL embarrassing to ship it up and find things don't fit.

For the outer shell a inflatable bag with a doc port is good.  Take it out, 
pump
it out, and do the rest of your work in full air pressure.  Spray a good 
amount
of reinforced concrete in the inside for structure, shielding, and thermal 
mass.
Now you can bring up and outfit it pretty much like a normal building.  Air
processors can be adapted from marine and scuba recycling systems.  need to 
keep
brining up liquid ox to replenish, but that's not to hard.  You can get most 
of
your water recycling by condensing it out of the air.  Pump filtered brown 
water
out into reaction jets.  Use their evaporation into vacuum for attitude 
control
thrust.  Solid waste you need to bag and bring down.

Power is a serious problem.  Batteries and stuff are not good to have in a
life-support area, and solar power systems need to be outside and maintained.
Ship it up in prefab modules to socketed into dock points on the outside of 
the
docking module?

How much would all this cost?
Could be all over the map. Hobbest projects or ones done by small skilled 
teams
can cost less then a hundredth of a industrial one.  Industrial firms have
estinated it would take them about $4-6 billion to build NASA $30-80 billion
dollar station.  So you possibly into the tens of millions in cost.  Launch
costs are a big factor.  But  if you have a decent launcher you can drop up
costs so much you can save a lot of launching, and station design.  Another 
big
cost is all the exotic junk on the station there to show off NASA's ability to
make exotic junk (no I'm not kidding, I was on the program).  If you just want
some living space figure a few thousand a person for air and water processors.
$10-$30,000?  NOrmal inflatable tables and charrs (everything non flamible!!).
Bifg cost is just launching it up.  You probably looking a few tons per 
person.
Now thats great compared to station, which is about  80 tons per person?

For 70 people, assuming 8 tons per person (just a guess) thats 540 tons.  At
least a hundred flights of your 5 ton lifter.  As a rought guess thats $1-3
million dollars worth of fuel.  So you built your launcher for a extreamly 
cheap
cost  ($20-$40 million?), and can get folks to service it for free.  You MIGHT
be able to to get the stuff up there for $100 + a pound.  If you can keep that
up, you could get funding to turn your platform into a hotel, and actually pay
your staffs.

Ok, 100 flights for free servicing is rediculas, and a few industrial bargins
for design and construction work and your $100 a pound jumps to $500 a pound
real quick!  Also the station construction and design costswern't covered, and
its unlikly you can get this many REALLY helpfull friends willing to put in 
all
this time for free.  Course if your looking ar a hotel complex, a firm might 
be
willing to drop a couple $billion to do it a bit larger and much less 
scroungee.


===================


Subject:  urls



<http://www.friends-partners.org/~mwade/lvs/novr10r2.htm>
>

>
>Adjusting the Shroud to act as a Ramjet, and mounting the "Ejectors" as
>a combustion ring inside might work. Though, again, reentry becomes a bit
>of a problem. But the shape would give "body-side" compression for the
>jet and allow a vertical take off and landing also.


>(BTW, if you folks haven't checked out this site yet, you might want to
>take a look:
>http://www.ptw.com/~oglenn/trimode/3m-arla.htm
>Check out the "Back-Page" section, he's done and quoted some research through
>the old NACA records on Ramjets and fuel)


Two gross estimating methods of thrust for ramjet were found. The first is 20
lbf/sq in combustion chamber cross section. The
second is 90 lbf/sq in inlet area (ref Jaumotte). The first is probably
conservative for a lean burning engine and the second is
more of a maximum.


For comparison, liquid oxygen/kerosene rockets typically
get only 350 seconds of Isp. A ramjet typically gets 1,200-1,800 seconds, 
though
 theory says they can get 2,400 seconds. For
this reason the ramjet gets 4-5 times as much thrust per pound of fuel. For
amateur rocketeers the cost of the fuel is small but
this higher Isp means that the stage can be 8-10 times smaller.

The traditional jet engine fuel is kerosene. Other fuels that have been used 
are
 diesel, alcohol, propane, butane, and hydrogen.
Each fuel has it's benefits and drawbacks. For example, alcohol has a lower
energy density but, because of this, the engine will
run a little cooler.


Ramjets can operate on a wide range of fuels including solid plastics, liquid
hydrocarbons, and hydrogen. The solid fueled
ramjets were not researched for this study. The German Lippisch P13a
experimental fighter used coal as its fuel. Each fuel has
certain characteristics that may be preferable, depending on the particular
design of the ramjet.

Kerosene is the traditional ramjet fuel. It is widely available for about
$0.45/lb in bulk and is much safer than gasoline. Diesel
fuel is very similar to kerosene. Gasoline is slightly less dense than 
kerosene
and has about the same density Isp. It is easier to
ignite but can be very explosive. Alcohol has a lower density Isp and a lower
flame temperature. For this reason it would be
useful if lowering the flame temperature were needed.

Hydrogen provides almost twice the Isp of kerosene but is about a fourth as
dense. Because of this the fuel tank will be about
twice as large for hydrogen as for kerosene but the fuel will weigh less. The
flame temperature for stoichiometric hydrogen
operation will be much higher than for kerosene and so will cause problems 
with
combustion chamber and nozzle design.
Hydrogen is considered by some, but not all, to be essential above Mach 7.

Fuel/Air Mixture Ratio

Ramjets operate most efficiently with a stoichiometric fuel/air ratio (about
1/17) but for a variety of reasons have been operated
otherwise. To limit velocity, pressures, and temperatures they are often
operated very lean. They can also be operated very rich,
especially for very high velocity operations. An excess of fuel allows for 
full
combustion of the available air plus some cooling
and increased mass flow. This has the benefit of reducing thermal stresses in
the hot section of the engine but requires more fuel.
This cooling can also be achieved by water or alcohol injection as is done in
the Mig 25 and the older B-52s.

When hydrocarbon fuels, such as kerosene, are used above about Mach 5 the
exhaust temperature is high enough to begin
dissociating some of the exhaust products. While this reduces the Isp it does
not become a major factor until about Mach 7.
Because the CO2 dissociates easier than the H2O the net effect of operating 
very
 fuel rich at high speeds is that the ramjet
begins to act like the fuel is hydrogen with some excess carbon thrown in. An
interesting effect is that the very hot carbon
particles would probably burn after they exit the exhaust nozzle and cause a
comet-like tail of flame behind the vehicle.

I especialy like the amature ramjet projects. Literally garage built from 
scrap.
  (A coffe can for the flame holder??!)
http://www.ptw.com/~oglenn/trimode/rj-const.htm
http://home3.inet.tele.dk/kennethm/index.htm
http://pfranc.com/projects/turbine/top.htm

http://www.webcreations.com/ptm/me2.htm   Scott Lowther home ejector ramjet
maker.