[LINK] Finally up to date on the Shuttle

Frank O'Connor foconno1@bigpond.net.au
Fri, 14 Feb 2003 13:56:38 +1100


Mmmm,

>At 1:15 PM +1100 14/2/2003, Richard wrote:
>>Frank,
>>HOTOL also has penalties. One of the aims of the launch is to get the
>>spacecraft ouut of the atmosphere as quickly as is feasible. This way, the
>>heat/vibration load of atmospheric flight is minimised.
>>
>>To achieve a similar result in a HOTOL environment would require extremely
>>high velocity at ground level; and (according to NASA), we don't have either
>>the tyres or the runways able to survive hotol spaceflight launch
>>velocities.

But NASA was being pushed by their Von Braun adherents at the time.

A few points to make ... viz-a-viz HOTOL.

1. The idea is that you go from normal sub-sonic at low level (where 
atmospheric density is highest), to  supersonic, to supra sonic and 
finally to a speed necessary to achieve orbit. Each increase in speed 
occurs at a level where atmospheric density most suits it. Not a 
24000 mile per hour rocket assisted horizontal take-of ... or even a 
high speed takeoff ... simply a takeoff similar to what you would do 
in a 747.

2. A problem they had in the 60's was leading edge friction on the 
wings ... and nobody was happy with the ability of the materials they 
had at the time to handle it. Then again, the Shuttle (which does the 
return half of what a HOTOL enabled craft would do ... but less 
aerodynamically ... essentially faces the same problem on re-entry.) 
and has the rather unsatisfactory tile solution. Even the SR71 
BlackBird - which only does about Mach 4 or 5 from memory - heats up 
big-time at speed. But, on a bird the size of a HOTOL orbiter though 
you could pack a lot more ablative shielding and electronic based 
solutions  (plasma charging etc) to help dissipate friction heat 
effects or protect your more vulnerable surfaces.

3. Engine technology for HOTOL is also a problem ... they've never 
been able to make Ramjets work reliably. My contention there is 
two-fold ... first they've never put the time or money into research 
(it's largely been done by amateurs and academics), and second that 
there was too much investment in VTOL by agencies and bodies that 
could do it for it ever to be seriously considered..

4. At the end of the 1960's NASA had a hell of an investment in von 
Braun type vertical lift solutions ... in bods, in materials, in 
expertise, in support infrastructure, in massive ground station 
investment like the Cape ... and no reason to push an alternative 
that would negate the need for a lot of that. They were committed to 
a centralised massive investment in vertical launch ... and I doubt 
they even looked at the alternatives (except with a view to disparage 
them in any way they could.) Surprise ... the Shuttle concept was the 
one that got the nod.

I suppose my bottom line is this: I fail to see how spending months 
to organise and prepare for a single mission, and sitting people on 
top of thousands of tons of precariously balanced highly explosive 
and very expensive technology and rocket fuel, 'lighting the fire' 
underneath them, so they can lift of vertically on top of what is 
essentially a very precariously controlled and staged explosion, 
where the room for error until orbit is reached (and on return) is 
almost non existent, to get payload into orbit at what NASA now 
admits costs about $10,000 per pound (or $US 22,000 per kilo), and 
then having them return to the atmosphere in a heavy vehicle with all 
the flight characteristics of brick .. 'flight' really is a 
precariously 'controlled fall' in the shuttle ... represents the best 
way to operate a low orbit freight service.

The economics. The safety record. The launch regularity. The list of 
achievements. All of these bear me out. The shuttle is simply not a 
viable low orbit service vehicle.

>At 1:15 PM +1100 14/2/2003, you wrote:
>>A question in return, - I seem to see contradictory information about the
>>relationship between shuttle velocity and altitude. On the one hand, orbital
>>calculators make it quite clear that a body at a lower orbit has higher
>>velocity than one at higher orbit. Look at
>>http://liftoff.msfc.nasa.gov/academy/rocket_sci/orbmech/vel_calc.html
>>to check me (the moon's orbital velocity is slow compared to a shuttle for
>eg).

Mmmm ... orbital mechanics are a funny branch of science ... but what 
you read is essentially true ... in an orbit which orbital 
equilibriium has been achieved a stable lower orbit has to have a 
faster speed than a stable higher orbit. So you have to accelerate to 
catch up with a body orbiting below you, and decelerate to match 
speeds with one orbiting above you. (You also have to expend some 
energy to counteract the gravity of the body you are orbiting when 
making said orbital changes ... which makes the energy/velocity 
equations a bit nightmarish ... especially when you have to change 
orbital vectors and the like.

Personally I think the whole thing is a pain and wish somebody would 
invent viable countergravity.         :)

						Regards,