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starship-design: HOTOL SeaDragon idea.



Worked this up a while ago.  Its more then a little rough, but might be 
interesting.



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

Was looking over SeaDragon statistics from those URL's I posted. 
Liftoff Thrust is 36,000,000 kgf, or about 36,000 tons.  The saturn 5's F-1's 
were about 780,000 kgf.  So you'ld need about 46 of them.  Good thing you 
launch them in the deep ocean.  The sound of 10 Saturn 5's taking off at once 
would play hell with anything breakable in the county.  John Chancelor was 
there for one of the forst Sat-V test launches.  The vibration shook apart 
the viewing stands set up for the reporters.  In colapsed under them adn they 
scrambled for safy.  He remembers sprawling out on the ground as it shok 
under him and he watch that giant take off.  Next time the moved the stands 
back a mile.

Anyway thats a lot of noise.  Its also a lot of engines.  Then I remembered a 
stat on injector ramjet engines.  The injectors could "entrain" in 20 times 
the exaust mass gas'es mass of air.  Thus driving a BIG ramjet/scramjet engin
e with 2 or 3 F-1 engines.  Has to be simpler to build a  36,000,000 kgf 
suite of  ramjets/scramjets then a rocket wityh that size.  Also lightens the 
take off weight by a rediculas amount.  Also given the first stage (if i did 
the math right given the burn out times adn DV given the rocket equation) 
cuts out at about Mach-6.

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

Sea Dragon-first stage
Gross Mass  11,600,000 kg.  
Empty Mass    1,300,000 kg. 

Thrust (vac)    36,400,000 kgf. 
Isp     290 sec.             [[ 300 -360 (vac) or so is normal ]]
Burn time     81 sec. 

Propellants     Lox/Kerosene    Isp(sl) 200 sec.

Diameter    21.5 m.
Span        30.0 m.
Length      68.0 m.


Comments    Sea level thrust shown. Thrust, chamber pressure varies during 
ascent. Vacuum thrust at cut-off 40 million kgf. Total mass, specific impulse 
estimated from booster performance figures. 

>>>> speed at stage 1 burn out???
The classic rocket equation gives the fuel to ship mass ratio, needed to get 
a given change in speed, with a fuel that has a given exaust velocity. 

dv = Desired change (or delta) in the ships speed.
Vexh = Exaust velocity of the material  (290 x 9.8m/s) = 2842
M = The fuel mass ratio =Exp(dV/Vexh)


Liftoff Thrust: 36,000,000 kgf. 
Liftoff Total Mass:     18,000,000 kg.
fuel mass first stage   10,300,000 kg. 
mass at stage 1 burnout   7,700,00

m =  M liftoff / (M liftoff - M fuel )  = 18,000,000 / 7,700,000

dv - Vexh  ln ( m ) - gt

dv = Vexh  ln (m ) - gt  = 2,413 - gt  = 2,413m/s - (9.8 x 81 ) = 1,619m/s

2,413m/s  = 5,212 m/hour  about mach 7
1,619m/s =  3497 m/hour  about  mach 5

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

Also noticed the Sea Dragon's first stage motor was expected to give 290 sec 
of  ISP  the F-1s were Isp (vac): 304 sec. Isp (sea level): 265 sec.   And 
the first stage had a bout a 10-1 fuel mass ratio.  If you lose most all of 
the LOx, you might spend it on Wings to lower take off thrust needs (and 
noise) and since its seaworthy, your not paying a weight price for seaplane 
abilities.  

Secound stage is Sea Dragon-second stage has a 

Gross Mass:     5,900,000 kg. 
Empty Mass:        530,000 kg. 



Thrust (vac):   6,350,000 kgf.   or about 8 F-1 engines
Isp:        320 sec.           [[ LH/LOx engine usually give 440-460!!]]
Burn time:  260 sec. 

Propellants:    Lox/LH2 


320 isp with LOx/LH??  Thats hardly better then the numbers for the 
LOx/Kerosine engines of the '60's?  Its actually worse then the current gen 
of LOx/Kero engines which get up to 350 isp!  Shuttle LOx/LH engines get 
about 450isp!


Anyway

>>>> stage 2 delta-V capacity ???
dv = Desired change (or delta) in the ships speed.
Vexh = Exaust velocity of the material  (320 x 9.8m/s) = 3136m/s
m = The fuel mass ratio =Exp(dV/Vexh)

m =  M liftoff / (M liftoff - M fuel )  = 5,900,000 / 530,000 = 11.1

dv = Vexh  ln ( m ) =   3136m/s  ln ( 11.1 )  = 7548 m/s

>>>>>>>>

Given liquid hydrogens (LH) huge bulk and tank weight, not to mention cost, 
I'm thinking a pure LOx/Kerosine TSTO system makes more sence?  Up the number 
of F-1s from 2-3 for the first stage to 8 (most of which arn't turned on 
until you leave the air), and you have the thrust.


Ok, Sea Dragons second stage had a 

Gross Mass:     5,900,000 kg. 
Empty Mass:        530,000 kg.

Mass of the fuel tanks would be less without the LH.  But the LEO Payload was 
450,000 kg.  (550 tons), so your only talking about 80 tons of structure to 
orbit.

Total Liftoff  Mass was 18,000,000 kg. 

Sea Dragon-first stage
Gross Mass  11,600,000 kg.  
Empty Mass    1,300,000 kg.

Course that 10,300,000 kg of LOx and Kerosine can be reduced by a factor of 
3.5 or so if you assume airbreathing.  Thats down to 2,940,000 kg.  That 
frees up a lot  weight for structure or extra fuel.  If you can take off HTOL 
you can assend more slowly on your wings until you get to high altitudes for 
your big run to speed.  Saving more in fuel.

A 747 has a empty weight about half its max takeoff weight.  Course it has to 
takeoff at slower speeds.  I think lift is one of those V^2 things.  Given 
the size of this monster, it can handal light seas at speed.  Probably lift 
off into its ground effect, then run up into far high speeds for assent.  
(lots of open ocean out there.)  So possibly tripling its speed to 450-500ish 
mph could get you 9 times the take off weight?  That big Russuan surface 
effect ship had numbers like that.

If true the winged vehicle can lift maybe 10 times its dry weight.

First stage fuel        2,940,000 kg

2nd stage fuel and LOX  5,370,000 kg.

Cargo              450,000 kg.  (550 tons)

total - structure       8,760,000 kg

So if  you can do a 9 to 1 take off to empty weigh ratio, you need about 
100,000 kg.  for plane and drive & lift stuff.

Sea Dragon had   1,300,000 plus 370,000 kg. or 1,670,000  

Course eliminating the LOx from the first stage would cut at least half of 
the weight out of the first stage.  Getting you  under 1,000,000 total 
structure and systems.  You can lose 100,000 kg of flight structure in there 
pretty easy, but you just doubled the dry weight to orbit.  Doubling the dry 
weight to orbit would double the fuel load you'ld need to carry.  You might 
save more weight from less thrust needed for a HTOL, or by airbreathing 
longer. Or you could switch to higher efficency LH/LOx for the post 
atmosphere boost, or build the hull out of something lighter then plate 
steel.  The Russuans built whole attack subs out of titanium, so something of 
the weight of this is possible, and would more then halve the weight.  It 
also is more heat and corrosion resistent.   Pricy though.  Don't know how 
much off hand.

But anyway halving the structure weight by switch from '60's steel shouldn't 
be a big problem.

If you stick to Kerosine / LOx all around.  Thats about:

 4,480,000 kg of kerosine   $ 0.20 per kg   = $816,000
3,900,000 kg of LOx $ 0.08 per kg   = $312,000


Course thats not much of the cost of a launch now, but in mature systems it 
gets to be up to a 1/3rd.

Dev costs?  About all complex aircraft from RLV's to F-22s adn B-2s seem to 
be in the $10-$20 billion club now a days.

At 500 tons cargo to LEo per flight.  Our 3 million ton O'Neil would eat 
6,000 flights to LEO just for the material, and could take more then that for 
the support stuff to fly it to L5.  So even if we assume $60 billion in dev 
costs and only 6,000 total flights, the overhead costs should only be about a 
million dollars a flight.  About the same as the fuel costs.  Together only 
about $2 per pound of cargo to orbit.

Servicing for launch was estimated in the tens of million of dollars per 
launch by seadragon.  Course that was nearly 40 years ago, with a differnt 
configuration.  Not sure how to guess for this.