starship-design: Re: X15 space plane

[KellySt@aol.com]

OK, I'm losing it.  I heard one to many folks involved with NASA new OSP 
(Orbital Space Plane - a program to build a winged manned upper stage craft to 
taxi people to orbit -- effectively the space station) program, state 
emphatically that it was impossible.  One winner Prof from Florida stated that it would 
take 15-20 years to develop the technology to build space planes.  

Much of the statements are pretty blatantly misleading, other ridiculously 
uninformed.

Just to calculate how BAD NASA is doing with its assumption that a winged
space plane could not be developed, I decided to go back a half century and
see what a X-15 could do.  

http://www.astronautix.com/craft/x15a.htm

Rocketplane. Year: 1959. Family: Air-Launched. Country: USA. Status:
Hardware. Manufacturer: North American.

Manned hypersonic research rocket aircraft. Launches: 290. Failures: 2.
Success Rate: 99.31% pct. First Launch Date: 10 March 1959. Last Launch
Date: 12 December 1968. Launch data is: complete.


Apogee: 107 km.

Liftoff Thrust: 23,174 kgf. 

Gross Mass: 14,184 kg.

Empty Mass: 5,158 kg.

Thrust (vac): 26,762 kgf.


Isp: 276 sec. Burn time: 90 sec. Isp(sl): 239 sec. Diameter: 1.42 m. Span:
6.80 m. Length: 15.32 m. Propellants: Lox/Ammonia No Engines: 1. XLR-99
Status: Hardware.

It couldn't get into space, but the idea of using it as an upper stage to a 
Titan booster was tossed around.  Especially if you add in the drop tanks used 
in later flights.  Those tanks provided roughly 60 seconds of additional 
engine burn and were used on the aircraft's Mach 6.7 flight. While adding to the 
speed the X-15 did achieve, the tanks also increased the aircraft's weight to 
almost 57,000 LB and added significantly to the drag experienced by the aircraft
in flight.  But neither matter a lot if it starts its burn above the 
atmosphere, as a spaceplane upper stage.


OK, the X-15 used ammonium and oxygen fueled rocket engines.  Assuming
Kerosene and oxygen burning engines (the fuels more powerful and compact,
and the tech was perfected in the early '60's).



Delta_V = Isp * g * ln(Mo/Mf)


where:
                                                    
 Delta_V change in velocity, in units compatible    
         with the value you use for g               
                                                    
 Isp     specific impulse, in seconds               
                                                    
 g       acceleration of gravity at the earth's     
         surface                                    
         32.174 ft/sec/sec (9.805 m/sec/sec)        
                                                    
ln()    natural logarithm function                 
                                                    
Mo      Mass before the burn                       
                                                    
Mf      Mass after the burn                        
                                                    



Assuming Kero/Lox and the X-15's weight limits without drop tanks that's

= 350 * 9.8 * ln (  14,184 kg. / 5,158 kg. )
= 3469 m/s delta-V  About half that needed to get to orbit

The X-15 with drop tanks upped its fuel load by 2/3rds - so

= 350 * 9.8 * ln (  20,141 kg. / 5,158 kg. )
= 4672  m/s delta-V  About 2/3rds that needed to get to orbit.

So if you could get a X-15 with drop tanks on top of a conventional 
Expendable launcher (a '60's vintage Titan 3c could lift 8 of them to the needed 
Delta-V ), it could get to orbit.  

You'd need to upgrade its skin to handle reentry, but foaming on a rubber 
ablative would do it.  Or actually adding some (post Vietnam era)  reusable high 
temp skin.  The X-15 used a tungsten alloy that was heavy as hell, so a little 
use of modern ceramics and Carbon carbon panels should be easy in its weight 
limits.

Of course NASA has proclaimed that the above vehicles would take new 
technology that would take 15-20 years to develop.

;/

Oh given the craft is compatible with added drop tanks, if you add more drop 
tanks, or a bigger first stage booster you could get the thing to Lunar orbit 
without serious issues.  It would take another 3000 m/s to get to the moon, 
but that's not huge.  About equal to tripling the size of the drop tanks or only 
launching one of the above on said '60's era Titan-3c.

Of course if you add some more post Vietnam era tech you could improve 
things, lighten them.  And you'd want to scale it up for more then one person.  But 
unless you scaled it up to 8 times the old weight for a single crewed X-15 
with drop tanks, it would be to light for the Titan-3C.  So you'd have to carry 
ballast or you'd over shoot low earth orbit.

Kelly

p.s.
Titan 3C  was going to launch Dynasoar in the 60's. 

LEO Payload: 13,100 kg. 
Liftoff Thrust: 1,079,550 kgf.   10,586.80 kN. 
Total Mass: 626,190 kg.