[LINK] Finally up to date on the Shuttle
Fri, 14 Feb 2003 13:56:38 +1100
>At 1:15 PM +1100 14/2/2003, Richard wrote:
>>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
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
>>to check me (the moon's orbital velocity is slow compared to a shuttle for
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. :)