Re: sci space policy targeted by disinformation experts?

On 27 Mar, 02:52, Willie.Moo...@xxxxxxxxx wrote:
A lot of speculation - I recall reading really interesting stuff, that
just falls off the radar screen so to speak for no damned good
reason.  Usually when something doesn't work for a sound technical
reason, you can find some arcane journal article explaining why.  When
you cannot find that, there is a possibility - if the ideas are sound
otherwise, they've been taken black.

One way to check that out is to track the researchers.  Are they
teaching and not doing a damned thing, or are they busy and have moved
from where they were to points West and stopped publishing?

Thats another inferential point to anyone who cares.

Energy is a problem with high speed flight.  Aurora nominally burning
hydrogen in air in an external combustion scramjet - and a 10%
structural fraction - producing thrust by intercepting the shock
waves.  You eject the fuel into the stream at the stream velocity -
right at the shock wave at the nose - so its stationary in the flow.
By the time it reaches the thrust structure at the rear of the
aircraft, its mixed with an oxidizer - you stablize that with an
expansion shock, and detonate it with a laser or spark or particle
beam - and the shockwave and thrust surface are shaped to interact to
produce thrust.

Mach 6 and drag coefficient gives you an estimate of power. The X-15
had a drag coefficient at hypersonic speeds of Cd = 0.095

Drag force is equal to

  F = 1/2 rho V^2 * Cd * A

http://en.wikipedia.org/wiki/Aurora_aircraft

area looks to be in the 30 sq m range

http://en.wikipedia.org/wiki/Scramjet_Programs

http://en.wikipedia.org/wiki/Mach_number

Mach 6 is around 1,800 m/sec, and rho=0.01 kg/m3

So,

   F = 1/2 * 0.01 * (3.24e+6) * 0.095 * 30
      = 46,170 newtons
      = 4,701 kgf
      = 10,343 lbf

at around 50 km altitude

Force times distance is energy.
Force times speed is power

So, 46,170 newtons x 1,800 m/sec = 88.106 megawatts

Hydrogen when burned in air releases 143 megajoules per kg.  Assuming
1/4 of this energy is usefully applied to the propulsion system,and
3/4 of the energy is wasted in various ways - means 35.75 megajoules
of propulsive energy is available per kg of hydrogen.  This gives us a
burn rate of 2.46 kg/sec to maintain that thrust.  With a 50% cycle
efficiency - fuel use is cut in half 1.23 kg/sec

This is the likely fuel consumption of hydrogen for the aircraft at
this speed - from first principles.

Going back to our models of Aurora - it likely has a 600 cubic meter
fuel volume.  and hydrogen has a density of 70 kg per cubic meter
which obtains 42,000 kg fuel mass.    Enough to power the aircraft for
4 hours and 45 minutes at Mach 6 cruise - at thelower efficiency, and
9 hours 30 minutes at the higher efficiency.  Enough to fly 3/4 of the
circumference of the Earth at cruise at the lower efficiency, and 1.5x
around the world at the higher efficiency.

One can imagine a number of interesting missions for such an aircraft
if it exists.

.

We can only argue plausably in this. 0.095 is in fact quite good for
supersonic speed. It should be recalled that a typical subsonic
aircraft has an L/D of about 20. Flying wing configurations improve
this as the drag from the fusilage is eliminated.

It will be recalled that Concorde was about 7:1 and with most of its
take off weight fuel just about limped to Washington from Heathrow. We
don't know whether Aurora was 10.5:1 or some worse figure. Discussing
an L/D ratio for hypersonics is a little bit misleading as airflow is
so integrated with engine performance.


- Ian Parker
.

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