Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v09_4/v9_461.txt

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Subject: SPACE Digest V9 #461

SPACE Digest                                      Volume 9 : Issue 461

Today's Topics:
            Re: asteroid almost hits earth
               Re: Launch noise
             Spaceplane Propulsion (LACE)
----------------------------------------------------------------------

Date: 25 May 89 00:58:16 GMT
From: jpl-devvax![e-mail]  (Larry Wall)
Subject: Re: asteroid almost hits earth

In article <[e-mail]> [e-mail] (Keith Dancey) writes:
: True.  But you are forgetting that geology was not the issue in the
: article on the relatively sudden extinction of dinasaurs.
: The issue was whether a single impact could effect *meteriological*
: conditions such that a species would become extinct.  For instance,
: whether polluted skies would effect food chains and temperature.  But
: if that scenario was to be true, then SURELY a species would die within
: its lifetime.  If one dinosaur could survive its entire life under these
: conditions, then so could another, and so on.

Yes, but that's not really the issue.  To guarantee eventual extinction
you only have to reduce the rate of survival (to reproductive age) to
less than 2 per dinosaur family.  We all know that changes in
temperature affect fertility, not to mention fecundity...   :-)
And there could well be some relationship between temperature and
mortality.  Especially with large egg layers.  So meteorology can
certainly have long term effects on a species.

(What actually happened was the dinosaurs had an industrial revolution with
all the iron in the asteroid, and the standard of living went too high,
and too many of them became dinks.)

: If dinosaurs took a
: thousand years to become extinct, what finished off the last one that
: *didn't* manage to kill its immediate forbears.

Probably loneliness.    Only 1/3 :-)

: If anything, one would
: assume that survivors of the first five hundred years would have been
: selected to manage better under the austere conditions, rather than
: the opposite.  It is also reasonable to assume that these hostile
: conditions would *gradually* improve with time, thus *increasing*
: the chances of species survival, rather than the opposite.

There are several things to say about that.  If you trigger a mini ice
age it could well last longer than 1000 years.  Moreover, as the
dinosaurs get sparser, it becomes more difficult to find a mate and
de-sparsify the dinosaurs, a nasty form of feedback.  And even if
conditions are improving gradually, the land is now overrun with little
varmints who have a faster selection cycle and took advantage of the
new conditions while the bigger folk were still squeaking by.  Perhaps
the initial catastropic conditions favored small critters that could
get by eating almost anything, even tough dinosaur eggs.  Or malnourished
dinosaurs trying to babysit their eggs.

It's also vaguely possible that the dinosaurs adapted to the cold, but at
the price of losing the ability to adapt to the heat again.  We don't know
enough about dinosaur genetics to rule it out.  (At least, I don't.)

: >Look:  a thousand years (or even five or ten) really is just a one-nighter
: >(what a party!).  The earth may have lost a host of magnificent species, but
: >did life disappear?
: >
: When you are talking about *dramatic* changes in climate and food chains
: critically effecting species survival, then the time scales involved must
: be of the order of seasons, rather than thousands of years.  One year of
: darkness is all that it would take to destroy vegetarian dinosaurs.  But
: they lasted for generations.  How?  And if even a single generation could
: survive lower temperatures, why couldn't others?

Maybe they were allergic to the ragweed that grew so well in the cooler
climate.  I think every day I spend in these Santa Ana winds takes several
hours off my life.  (Beats having the smog though.)

If the chaoticists are to be believed, something much less dramatic
than an asteroid is capable much greater consequences than mere
extinction of dinosaurs.  Why, the flap of a butterfly's wing today may
influence whether the universe collapses next week...  well, perhaps
that's a wee bit exagerated...  Still and all, non-linear systems (and
we're not just talkin' weather) can behave oddly under seemingly mild
perturbations.  Let's remember that ecological niches aren't cast in
concrete, but at least partly in the flesh of whatever else wants to
occupy the neighboring niches, not to mention the same niche.  And
precedence matters--last one there is a rotten dinosaur egg!

: >I believe the metorite/asteroid collision theory to be the best put forward
: >to date to explain the demise of the dinosaurs and their ecosystem. Your
: >objection, Keith, is ill-considered.
: >
: Far from it.  There are enormous problems with a *single* catastrophy such
: as an asteriod strike *if* the palaeontological evidence is to be believed
: (unless dinosaurs lived a thousand years, that is :-).

It doesn't take much imagination to see that *something* changed to off
all the dinosaurs.  Just because we have difficulty imagining how the
bullet got from the smoking gun to the victim doesn't mean it didn't (or did).
To bend another saying to our use, we might say that "Absense of imagination
implies imagination of absence."  Just because I can't see the connection
doesn't mean there isn't one.  The "enormous problems" with a single
catastrophe are mostly problems in our head, because we ain't smart enough.
(Nothing personal, Keith.   :-)

I've got it now!  The asteroid hit an oil field situated over a fluorite
deposit sitting on a huge salt dome, and filled the atmosphere with
chlorofluorocarbons.  Anything that couldn't hide under a log and didn't
have fur or feathers had increased risk of skin cancer for the next
N thousand years.   :-)

Yes, unlikely.  But we don't know how many times Mother Nature tried before
she hit the jackpot.  Unlikeliness isn't a big problem in my book.

Go ahead, flame me, I've already reproduced.

Larry Wall
[e-mail]
"So many programs, so little time..."

------------------------------

Date: 24 May 89 04:10:36 GMT
From: [e-mail]  (Jordan Kare)
Subject: Re: Launch noise

In article <[e-mail]> [e-mail] (John Roberts) writes:
>>From: concertina![e-mail]  (Steve Hix)
>
>>In article <[e-mail]>, [e-mail] (Clive Feather) writes:
>>> The *BIG* cannon in Jules Verne's "From Earth to the Moon" was called
>>> the "Columbiad". Close enough ?
>
>>... Probably exceeds local noise limits, though.
>
>This is a legitimate concern for any earth-based ballistic launcher (explosive,
>electromagnetic, etc.) Even if the noise of the initial impulse can somehow
>be controlled, a projectile of the size generally mentioned would create a
>tremendous sonic boom, which I suspect would be painfully loud even many miles
>away. This would place constraints on a suitable location for such a launcher.
>
>Have any studies been conducted on the magnitude of the noise problem?
>                                      John Roberts
>                                      [e-mail]

It's been a significant concern for laser launching -- enough to
generate a couple of calculations.  Typical numbers are that a
100 MW launch system generates 80-90 db noise levels --
10 km from the launcher!  I've occasionally been known to suggest
modulating the laser rep rate (nominally ~100 Hz) to play
a really impressive bass line for a rock concert :-)

Along the same lines, someplace I have a nice PR mailing from
a small company promoting the electromagnetic launcher concept
that shows an artist's conception of a launcher seen from the
exit end.  The view is of a cliff face with the launcher end
embedded in it, with a line of something (power poles?) stretching
off along the far side of the ridge to show how long the thing is.
In the foreground is a nice cigar-shaped projectile flying out of
the launcher mouth.  And at the top of the cliff, perhaps 50 feet
from the launcher mouth, is a nice modern-looking control building....

with big plate glass windows!

    Jordin (Big Noise) Kare

------------------------------

Date: 24 May 89 07:01:06 GMT
From: oliveb!mipos3!omepd!mipon2![e-mail]  (Larry Smith)
Subject: Spaceplane Propulsion (LACE)


In article <[e-mail]> [e-mail] (John McKernan) writes:
^^Air liquification is an approach the Japanese are taking in their aerospace
^^plane project. The whole point of such a plane is to drastically increase
^^ ...

In article <[e-mail]> [e-mail] (James Symon) writes:
^^net, high mach numbers bring on very tricky engine issues. Couldn't a
^^hybrid be built in which oxidizer injection is gradually increased as
^^altitude and speed begin to cause combustion problems? Eventually the
^^intake ports are closed and the motors are straight liquid fuel rocket
^^ ...

** Long reply. **


Following is some information from one of the Japanese papers presented
at the First International Conference on Hypersonic Flight In The 21st Century.
This conference was held Sept 20-23, 1988 at the University of North Dakota.
The conference was attended by almost all significant international SSTO
(Single Stage To Orbit) projects. The exception was the Russians, who were
invited and said that Mr. A. Tupolev would give a paper, but he did not
appear. When asked later why he didn't appear, he replied: "The time for
talk has passed. Now it is time to work!" The conference was co-sponsored
by: NASA, ESA, AIAA, IEEE/AESS, NAL/STRG, AAS.

The paper is entitled: "A Concept of LACE For Space Plane To The Earth Orbit"
Authors: Hiroyuki Hirakoso, Teruyuki Aoki
     Mitsubishi Heavy Industries Ltd.
     Engine Engineering Dept.

     Tetsuichi Ito
     National Space Development Agency of Japan

The paper made the following justification for air breathing engines:

    To successfully design a reusable space plane that can carry
        payloads into orbit, its important to decrease structural
        weight and increase Isp (Specific Impulse). Isp is the more
        important of the two to increase. Currently, the most practical
        way to significantly raise Isp, is with a Air Breathing Engine
        (ABE).

        (The equation for rocket Isp is (Thrust / Propellant Weight Flow Rate).
        The Isp equation must be different for ABEs, because of ram
        pressure increases to thrust (depending on ram engine type).
        A rocket has momentum thrust and pressure thrust components
        only, in its thrust term. The propellant weight flow rate
        for a ABE probably only counts onboard propellant as well.)

        Performance, as measured by Isp, of LOX/LH2
        (Liquid Oxygen/Liquid Hydrogen) rocket engines is reaching its
        theoretical limit.

        60%-70% of carried propellants in a LOX/LH2 rocket, are used to
        attain an altitude of 40KM.

The paper made the following justification for a LACE air breathing engine:

    Air above 40KM (~131,000 ft.) is too thin to sustain a Air Breathing
        Engine.

        LACE can perform the total mission. It can accelerate from zero
        velocity on a runway/launch pad, to Mach 10 at an altitude of 40KM,
        to orbital velocity via traditional rocket propulsion in the upper
        atmosphere.

        LACE is a derivative of the rocket engine and inherits many rocket
        engine characteristics.

        LACE represents a lower development risk in that it builds on the same
        base of cryogenic technology used for current LOX/LH2 rockets.

The principle behind a LACE engine is the liquifying of air via a cryogenic
propellant. LH2 is used as the cryogenic because it has a boiling point
(20 deg. K) below that of oxygen (90 deg. K) which makes up roughly 21% of air.
LH2 is circulated through a number of cooling tubes (the Japanese have a
experimental heat exchanger for a 10 ton thrust LACE with 10,000 cooling
tubes), and intake air is circulated through the cooling tube structure.
As a result of this, some of the air is liquified and pools, I assume,
at the bottom of the heat exchanger. The circulated LH2, heats up, and becomes
H2 gas. The hydrogen and liquid air then eventually mix in the rocket's
combustion chamber.

Now, as you can see, the weight of the heat exchanger is a key factor.
They published a table with rough-estimate, engine weight components, for a
different, projected 100 ton thrust class LACE engine. There was supporting
material for their estimation of a sub 1000 Kg Heat Exchanger. It looks
like they have done allot of work on this.

    Air Intake:        200 Kg
    Air Liquifier:     900 Kg
    Liquid Air Spray:  200 Kg
    Rocket Engine:    1600 Kg
    Accessories:       100 Kg
    -------------------------
    Total:            3000 Kg

The total air-handling mechanism (Intake, Liquifier, Air Spray) is just
under the weight of the rocket itself (there may be a air compressor
with a 10 to 1 pressure ratio as well, see LACE techniques below).

The paper also had block diagrams of 7 different LACE engine techniques.
These techniques describe different ways in which liquification can be
performed and how it would be integrated with the rocket engine.

They also presented two engine schematics. One for a vertical launch
LACE where 6 - 100 ton thrust LACE engines, with their tankage, replace
the Solid Rocket Boosters of their H2 rocket. The Isp of the vertical
launch LACE was 700 sec (at sea level static). 700 sec is a LOW Isp
for a ABE. The reason this one is so low, is that this LACE still
burns LOX, even in Air Breathing Mode, but at a lower mixture ratio
than a standard LOX/LH2 engine. The liquid air augments the LOX
in this engine. They say the Isp is still nearly double a standard
LOX/LH2 engine (I thought LOX/LH2 engines have Isp's of ~450).
They claim they can triple their payload with this
technique!! Thrust/Weight was 33/1. The Mixture ratio for a LACE
is expressed as the Liquification Ratio (LR). For a liquid rocket,
mixture ratio is Oxidizer Flow Rate/Fuel Flow Rate, and for a typical
Booster LOX/LH2 engine, mixture ratio is in the 3-4 range (I think). For
a LACE, LR is Air Flow Rate/Fuel Flow Rate. The LR for this vertical
launch LACE engine is 6.28/1.0. They intend to build vertical launch LACE
boosters as soon as they're feasable. The other LACE schematic was for a Space
Plane. It had an Isp of 2600 sec, and a LR of 10.37/1.0. Both of their
engine designs use several of the following techniques at the same time.

Basic LACE:

                [ LH2 Tank ]
                     |
                     v
                [ LH2 Pump ]
                     |
                     |
------------         v                                       __/
<Air Intake|->-[Heat Exchanger]-->---[liquid air pump]-->---|__  Thrust ->
------------         |                                        ^\
                     |                                        |
                     ------ gaseous H2 ------------------------

Comments:
    This is the simplest form of LACE. Only LH2 is used for liquification.
    The LR is limited to around 4, and therefore hydrogen rich.
    A lower Isp is thus attained.


Oxygen Separation LACE:

                [ LH2 Tank ]
                     |
                     v
                [ LH2 Pump ]              [Liquid Nitrogen]
                     |                           ^
                     |                           |
------------         v                           |            __/
<Air Intake|->-[Heat     ]-->---[liquid]-->--[Nitrogen ]-->--|_    Thrust ->
------------   [Exchanger]      [air   ]     [Separator]       ^\
                     |          [pump  ]                       |
                     |                                         |
                     ------ gaseous H2 -------------------------

Comments:
    The poor mixture ratio of the Basic LACE is improved by making the
    oxygen more concentrated by extracting Nitrogen.


LOX Spray LACE:

                [ LH2 Tank ]
                     |
                     v
                [ LH2 Tank ]
                     |
                     |
------------         v                                          __/
<Air Intake|->-[   Heat Exchanger]-->---[liquid air pump]-->---|__  Thrust ->
------------     ^   |                                           ^\
                 |   |                                           |
                 |   ------ gaseous H2 ---------------------------
                 |
              [LOX Pump]
                 ^
                 |
              [LOX Tank]

Comments:
    To improve the poor mixture ratio of the Basic LACE, LOX is sprayed
    into the sucked-in air. This increases the oxygen concentration,
    and lowers the temperature of the air. Both contribute to increase
    the liquification of the air. The LOX tank is small compared to
    what is normally carried on a LOX/LH2 rocket.


Tank Return LACE:

                           [ LH2 Tank ]
                              |     ^
                              v     |
             [ Main ]   [ LH2  ]    |
             [ LH2  ]-<-[ Boost]    |
             [ Pump ]   [ Pump ]    |
                     |    |         |
                     |    |  _______^
------------         v    v  |                                  __/
<Air Intake|->-[   Heat Exchanger]-->---[liquid air pump]-->---|__  Thrust ->
------------     ^   |                                           ^\
                 |   |                                           |
                 |   ------ gaseous H2 ---------------------------
                 |
              [LOX Pump]
                 ^
                 |
              [LOX Tank]

Comments:
    This scheme uses the heat sink capability of the LH2 storage to cool
    down the gaseous H2 after circulating in the heat exchanger. They
    also use this technique with the onboard LOX in some of their
    designs, to have it help liquification as well.


Air Compressor LACE:

                [ LH2 Tank ]
                     |
                     v
                [ LH2 Pump ]
                     |
                     |  ------------[Liquid Air Pump]-------
                     |  |                                  |
------------         v  |                                  v     __/
<Air Intake|->-[Heat     ]-->---[Air       ]-->-[Heat     ]-->--|_    Thrust ->
------------   [Exchanger]      [Compressor]    [Exchanger]       ^\
                     |                                            |
                     |                                            |
                     ------ gaseous H2 ----------------------------

Comments:
    Increased air pressure from a air compressor, increases the
    liquifying temperature of the air. Compressed air is sent to the next
    heat exchanger, where it is liquified more easily. The air compressor
    doesn't have to be so big because of the first stage heat exchanger
    cryo-cooling the air. Liquid air is extracted from the first stage
    heat exchanger output for efficiency of the air compression process.


Liquid Air Spray LACE:

                [ LH2 Tank ]
                     |
                     v
                [ LH2 Pump ]
                     |
                     |  ---[Liquid Air Pump]-------
                     |  |                         |
------------         v  |                         v          __/
<Air Intake|->-[Heat     ]-->---[Air       ]-->-[Mixer]-->--|_    Thrust ->
------------   [Exchanger]      [Compressor]                  ^\
                     |                                        |
                     |                                        |
                     ------ gaseous H2 ------------------------

Comments:
    An optimization of the Air Compressor LACE. Spraying
liquid air can replace the last heat exchanger stage (weight savings).


Expansion Turbine LACE:

                 [ LH2 Tank ]
                      |
                      v
                 [ LH2 Pump ]
                      |
                 -----u-----------------------------
                 |    |                            ^
------------     v    v                            |             __/
<Air Intake|->-[Heat     ]-------- air -------->[Heat     ]--->-|_    Thrust ->
------------   [Exchanger]                      [Exchanger]       ^\
                 |    |                            ^              |
                 |    |                            |              |
                 |    |-------->[Expansion ]--------              |
                 |    |         [Turbine   ]                      |
                 |    |                                           |
                 |    ------------- gaseous H2 --------------------
                 |
                 |     /
                 -----|  H2 Exhaust
                       \

Comments:
    After the first pass of the LH2 through the heat exchanger,
it becomes a gas. The gas is expanded through an expansion
turbine so that it can be chilled for re-use in another heat exchanger
stage.

General Comments:

The Japanese still have allot of work to do. Example, what about
humidity? Ie: Ice and CO2 (for that matter) buildup on the heat exchanger.
I mentioned heat exchanger weight already. Liquid Air pumps have to
be developed. A variable intake and exhaust nozzle for the very
wide performance range of this engine have to be designed.

The LACE concept originated in the USA in the late 50's. I think the Air
Force, back then, funded some research in this area. They found it to be
unfeasable, and dropped it, but materials science has sure improved
since then.

Personally, I'm glad the NASP consortium is exploring scramjets,
turbo-ramjets, and LACEs. But instead of developing one engine
technology only, why don't they develop several, and test fly them both.
They could have Pratt and Whitney develop scramjets and turbo-ramjets, and
let Rocketdyne develop the LACE principle, instead of having them both
do scramjet designs. After reading about LACEs I'm left with the feeling
that they might be easier to do than scramjets, because we're talking
about a Mach 5-10 air breathing engine (LACE), versus a Mach 25 air
breathing engine (scramjet). But don't get me wrong, scramjets and
turbo-ramjets are VERY important to develop ! At least we could use
LACEs on our vertical launched rockets as well.

Larry

------------------------------

End of SPACE Digest V9 #461
*******************