Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v16_3/v16no366.txt

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Date: Fri, 26 Mar 93 05:00:12
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #366
To: Space Digest Readers
Precedence: bulk


Space Digest                Fri, 26 Mar 93       Volume 16 : Issue 366

Today's Topics:
                         Dallas Boring Snooze
                            Idle Question
                               Mach 25
     Predicting gravity wave quantization & Cosmic Noise (3 msgs)
                      SSF Redesign.... (2 msgs)
                STS-55 (Columbia) abort (was Aurora?)
                        STS-55 launch aborted
                  To 20kHz SSF power guys: take E+M
                        Uplink/downlink rates
                         waste management...
                  Why use AC at 20kHz for SSF Power?

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

Date: Thu, 25 Mar 93 14:14:18 MET
From: [e-mail]
Subject: Dallas Boring Snooze

Dillon Pyron writes (Wed, 24 Mar 1993 20:03:52 GMT):

>For those of you in the Dallas area, or who (foolishly) read the Snooze
>(aka Dallas Morning News), check out the Wed. TODAY section.  I've
>already called, they are both mortified and concerned, since their
>sources indicate the information was correct:
>
>A graphic on the progress of women shows
>1978 - Sally Ride is the first woman in space

You know what? All these guys outside the USA are just Untermenschen...

J. Pharabod

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

Date: Thu, 25 Mar 93 15:04:52 EET
From: [e-mail] (F.Baube[tm])
Subject: Idle Question

Just how much *would* it cost to get my very own Scout launch ?

How much weight would I get to lob into LEO ?

--
* Fred Baube (tm)         * In times of intellectual ferment,
* [e-mail]       * advantage to him with the intellect
* #include <disclaimer.h> * most fermented
* May '68, Paris: It's Retrospective Time !!

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

Date: 25 Mar 93 01:21:10 GMT
From: Jordin Kare <[e-mail]>
Subject: Mach 25
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (William Reiken) writes:
>    I was reading in the Popular Science "March 93" 'Science Newsfront'
>on page 35 about the Mach 25 Transporter.  Some questions:
>    1).    Power is lasers or microwaves.  What kind of lasers would
>        these be?

Extremely large (1 - 10 GWatt) free electron lasers

>    2).    How much energy would be required to operate such lasers
>        and how much loss would there be?

FEL's are 10 - 20% efficient, so the power consumed would be of order
10-100 GW.  Leik Myrabo generally assumed orbiting lasers with their own
solar power satellites.
>
>    3).    Lasers on the craft for power.  Again what kind of lasers
>        would these be?

The vehicles do not carry lasers.
>
>    4).    The lasers for driving the craft heat a small area of air
>        to 30,000 degree K.  How much energy does it take to do
>        this?

Lots.  Typical fluxes to do this are >10^8 watts/cm^2 (albeit for times
measured in nanoseconds.  Typical energy densities in the focal region
are 10's of Joules/cm^3 (10's of kJ per gram of air)
>
>    5).    Laser to electric power for MHD propulsion in space.  What
>        kind of equipment is nessasary for this kind of thing?  What
>        is the efficiency of such equipment?

Well, Leik claims he can do it with a fairly simple design using hydrogen
heated by a laser-supported plasma, seeded with something like potassium
for conductivity, and flowed out thru an MHD channel.  Nothing like this
has been demonstrated, but it's allowed by the laws of physics; the rest
is "mere engineering" :-)
>
>    6).    Rensselar Polytechnic Institute in Troy NY.. Anyone know any
>        of these people so that I may contact them direct for more
>        information?

Prof. Leik Myrabo
Dept. of Mechanical and Aeronautical Engineering
Rensselaer Polytechnic Institute
Troy NY  12180
>                            Will...
>

Leik designs some pretty fancy vehicles, and has done a good deal of
nice mechanical and aerodynamic design and testing, but he's a _very_ long
way from having something that will fly.

    Jordin Kare

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

Date: Wed, 24 Mar 1993 19:45:15 GMT
From: [e-mail]
Subject: Predicting gravity wave quantization & Cosmic Noise
Newsgroups: sci.space,sci.astro,sci.physics,alt.sci.planetary

In some article (Thomas E. Smith) writes:
>
>[e-mail] (Gary Coffman) writes:
>>If we assume that the gravitational wave is a classical wavefront,
>>and we assume it travels at lightspeed, then your objection only
>>occurs when the Earth, satellite, and source of gravity waves are
>>all lined up. If the gravitational disturbance is arriving from
>>some angle off that line, the EM wave and the gravity wave will
>>only be coincident at one point along the line of sight.
>>

     My original question was predicated on this situation
     occuring.  The next question is, if this occurs, why
     does it not significantly decrease the expected amplitude
     of the signal for many relevant incoming waves?
     However, since I'm not sure that what I'm saying is
     happening anyway, it's probably pointless to discuss the
     effect on the doppler shift for various incoming waves.

>That will affect the doppler shift a little, but still the gravity wave only
>affects the Earth based detector as it passes the detector. A very short
>period of time, and it stays with the EM wave for most, if not all, of its trip
>to the Earth. Though if the wave's travel is perpendicular to the line

     I'm not sure what a short period of time *is* in this context.
     It would have to be short compared to the 'reception time' of
     the electromagnetic signal.  I'm not even sure what that
     means.  Besides, in my situation it is affecting the wave
     all back the path to the receiver (or the other way around to the
     transponder on the satellite).

>connecting the spacecraft and the Earth, there will be no effect, because
>it will affect both the spacecraft and the earth in the same way. But that's
>what the other two spacecraft are there for.

     That was my original question.  Is that the reason there are three?
     I'm sure when I get a chance to read some of Estabrook's stuff,
     it will be in there.

>But that brings up a point. What is the relativistic interaction between two
>waves moving at light speed? How do they view eachother?

     I thought I had been bringing up that point all along.  I must
     write more clearly.

                            dale bass



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

Date: 25 Mar 93 07:52:00 GMT
From: Cameron Randale Bass <[e-mail]>
Subject: Predicting gravity wave quantization & Cosmic Noise
Newsgroups: sci.space,sci.astro,sci.physics,alt.sci.planetary

In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>In article <[e-mail]> [e-mail] writes:
>>In some article (Thomas E. Smith) writes:
>>>
>>>[e-mail] (Gary Coffman) writes:
>>>>If we assume that the gravitational wave is a classical wavefront,
>>>>and we assume it travels at lightspeed, then your objection only
>>>>occurs when the Earth, satellite, and source of gravity waves are
>>>>all lined up. If the gravitational disturbance is arriving from
>>>>some angle off that line, the EM wave and the gravity wave will
>>>>only be coincident at one point along the line of sight.
>>>>
>>
>>     My original question was predicated on this situation
>>     occuring.  The next question is, if this occurs, why
>>     does it not significantly decrease the expected amplitude
>>     of the signal for many relevant incoming waves?
>>     However, since I'm not sure that what I'm saying is
>>     happening anyway, it's probably pointless to discuss the
>>     effect on the doppler shift for various incoming waves.
>
>Why would there be an amplitude change? The EM wave is transverse,
>the G wave is compressive. The only thing affected is path length,
>and that translates to apparent wavelength change, IE doppler shift
>of the EM wave.

      Amplitude of the doppler shift, not either of the signals' waveforms.
      When talking about two waves, I guess amplitude was an unfortunate
      word for the size of the shift.  In any case, we were discussing
      a case where the gravitational wave and the radiowave shared
      the same space in a loose sense for a large part of their
      common path in our frame of reference.  With this, I
      was also wondering what the inevitable change in
      local time does to the signal in such a circumstance.

>>>That will affect the doppler shift a little, but still the gravity wave only
>>>affects the Earth based detector as it passes the detector. A very short
>>>period of time, and it stays with the EM wave for most, if not all, of its trip
>>>to the Earth. Though if the wave's travel is perpendicular to the line
>>
>>     I'm not sure what a short period of time *is* in this context.
>>     It would have to be short compared to the 'reception time' of
>>     the electromagnetic signal.  I'm not even sure what that
>>     means.  Besides, in my situation it is affecting the wave
>>     all back the path to the receiver (or the other way around to the
>>     transponder on the satellite).
>
>Let's digress to the wave/particle duality for a moment to answer the
>"reception time" query. The smallest signal a receiver can theoretically
>detect is one photon. The "length" of one photon is one wavelength.
>Wavelength and frequency are related by L=300/F where L is in meters
>and F is in MHz. If the satellite signal is at 1 GHz, the "reception
>time" for one photon is 1e-09 second or the time it takes light to
>travel 0.3 meter. If the G wavelength is less than this, we won't
>see an effect. If the G wavelength is significantly greater than
>this, however, the crest to crest distance between EM waves will
>be increased or decreased, and that will be detected as doppler
>shift.

     And yet we're talking about gravitational waves with frequencies
     around 10^-4 Hz.  I also don't know if we can treat
     gravitational waves as if they were some sort of moving slinky.
     Time would seem to change too, and that always complicates things
     (especially my being able to visualize it).  Let's say you
     lengthen the path on the expansive part of the wave, thereby
     decreasing the frequency.  However, while the gravitational
     disturbance is doing this it also would seem to be slowing the
     local 'time standard'.  If this happens, it seems that the
     frequency one would count locally is still the same as the
     'original' frequency.

     Anyway, I can also convince myself as the wave crests and
     falls and crests, it alters the local time standard accordingly to
     cancel the wavelength shift.  Please, convince me differently.

                             dale bass

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

Date: 25 Mar 93 07:56:40 GMT
From: Cameron Randale Bass <[e-mail]>
Subject: Predicting gravity wave quantization & Cosmic Noise
Newsgroups: sci.space,sci.astro,sci.physics,alt.sci.planetary

In article <[e-mail]> [e-mail] (Gary Coffman) writes:

>>But that brings up a point. What is the relativistic interaction between two
>>waves moving at light speed? How do they view eachother?
>
>I wish there were an easy way to pass drawings in this medium. It would
>make explanations so much simpler. First lets clear up some differences
>in terminology and conditions here. A gravity wave can be viewed, like
>a sound wave, as a compression wave in spacetime. It alternately compresses
>and stretches the fabric of space (hackneyed term) like a steel ball
>rolling on a rubber sheet. Now EM waves are transverse oscillations
>of electric and magnetic vectors at right angles to each other and to
>the direction of travel. When the EM wave encounters the G wave, all
>the EM wave "sees" is a change in path length. I don't know what in
>hell the G wave "sees".

      Why doesn't the EM wave see a change in local time?

                               dale bass

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

Date: 24 Mar 1993 21:18:20 GMT
From: Andy Cohen <[e-mail]>
Subject: SSF Redesign....
Newsgroups: sci.space

In article <[e-mail]>,
[e-mail] (Brian Yamauchi) wrote:

> >The result of the changes leave us with a Station with no port truss (may
> >be scarred for growth option),
>
> Does this mean there will be no truss at all in the baseline design?
No.  It means that after the starboard side segments we will stop....
The next ? really is....if we are now looking like the phase B "Power
Tower" approach again, will controlled attitude go back to a radial
orientation...i.e., with the lighter end point toward Earth?????  This
would really simplify the GN&C model as well as the amount of work the
system has to perform to keep the desired attitude.


> Is there going to be an American experiment module, or is the station
> going to rely completely on the European/Japanese modules?
I read it as there will now be only 1 US module, the lab...let....

>
> What other non-SSF-derived concepts are being considered?  Are
> stations based on external tanks or inflatable structures being
> considered as options?
> --
The other concept most likely to make it out of the Shea committee includes
the Faget approach with wingless shuttle fuselages connected at the front
end via resource nodes or pressurized docking.


We have heard that Joe Shea has been struck ill and is hospitalized.  We
have also heard that his replacement would not agree to guarantee that he
would not work to his company's advantage (Lockheed...hey at least he was
honest about it!) and had to resign from the committee.....  As far as we
know the 35+ person redesign group is leaderless......

Just great.

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

Date: 24 Mar 1993 22:49 UT
From: Ron Baalke <[e-mail]>
Subject: SSF Redesign....
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Andy Cohen) writes...
>honest about it!) and had to resign from the committee.....  As far as we
>know the 35+ person redesign group is leaderless......

I've heard the redesign team now number over 50 people.  This is not good,
there are already too many inputs going into the design, creating the
"design by committee" problem.  Also, some people want to bo back to
using a modified version of the old design.

The Space Station tug-of-war continues.....
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Don't ever take a fence
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | down until you know the
|_____|/  |_|/       |_____|/                     | reason it was put up.

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

Date: 25 Mar 93 01:12:12 GMT
From: Gary Coffman <ke4zv!gary>
Subject: STS-55 (Columbia) abort (was Aurora?)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Simon E. Booth) writes:
>
>I've wondered if using strap-on liquid fueled boosters would solve this
>problem-I mean being commited to launch at T-zero even with a main engine
>out.  Theoretically, liquid fueled boosters could be shut down after
>ignition, if the shutdown could be performed as quickly as the main
>engine's was

The GPCs start ignition at T-6.8, if all engines haven't reached at
least 90% power by T-3, an autoshutdown is done. Past T-0, the boosters
are lit and you lift off. If you shutdown immediately after liftoff, you
come back down tail first *hard*. So liquid or solid, once you light the
boosters, you're committed to getting enough altitude to do a RTLS. The
holddowns can't keep the Shuttle on the pad against both main engines and
boosters.

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

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

Date: 24 Mar 93 22:37:06 GMT
From: Henry Spencer <[e-mail]>
Subject: STS-55 launch aborted
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Simon E. Booth) writes:
>If I recall, the tire burst was caused by brakes being overheated.
>Wasn't this part of the reason KSC landings were prohibited at one
>point?

Part of it.  Landing at KSC is generally a much less error-tolerant
operation under less favorable conditions.  The weather is less predictable,
there is only one runway, with dangerous obstructions just off it and
frequent crosswinds.

The runway's extremely rough surface, although it's good for traction,
was probably a contributing factor in the tire burst.  The touchdown
areas have been smoothed down some.

>Were the other orbiter's retrofitted with drag chutes?

The drag chutes are being installed as opportunity arises, mostly during
major refits.  They'll help.  I don't think they've been fully cleared
for use, though -- they're still deploying them after full gear touchdown
rather than before.

The diciest part of an orbiter landing is nosegear touchdown.  Because
the nosegear is short, the wing angle of attack is negative from then on,
so the wing is pushing *down*, and this (not main-gear touchdown) is
the time of highest load on the main gear.  Blow a main-gear tire then,
and the other one on the same side will almost certainly blow too, at
which point you are in big trouble.

It's not an accident that the pilots try to hold the nosegear off the
ground as long as possible.  The slower they are moving when it goes
down, the better.  The drag chute will help, once it's cleared for use
before nosegear touchdown.
--
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  [e-mail]  utzoo!henry

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

Date: 24 Mar 93 15:32:49 MDT
From: [e-mail]
Subject: To 20kHz SSF power guys: take E+M
Newsgroups: sci.space

Now, about this 60hz 400hz 20Khz debate thats been going on....

Someone posted that NASA was at the cutting edge of technology in
inventing/using 20Khz AC for power.

Horseshit.

Car stereo manufacturers have been using 20Khz (up to 200 Khz) on the inversion
power supplies of power amplifiers for years.  The high frequency is beyond the
range of human hearing and is therefore not audible in the output- this
eliminates the need for really high precision supply regulation, and hence cuts
down on size, parts and cost.  The high frequency also allows very small filter
capacitors, roughly 20k/60 times smaller than used in 120 volt supplies pushing
the same current.

I have even seen high power amps (1200 watts RMS output) that take 120 volts
AC, rectify it into 170 volts DC, then invert it at 50 Khz to get the required
+-70 volt rails (and the transformer provides isolation).  This is what my
senior project has been on, as I am making one of these.

The reason that airplanes and military ships use 400 hz instead of 60 and 20K
is threefold:

    Most importantly where motors are being run, especially on ships, is
    induction motors.  Due to the mass of the rotor and phase
    considerations, the starting torque of an induction motor is much less
    at 20Khz than at 400 hz or 60 hz.

    Induction motors run at a speed proportional to the frequency and
    inversely proportional to the number of poles.  So a 20Khz induction
    motor has to have 666 poles (separate windings) to run the same 3600
    rpm as a 2 pole motor at 60hz, and a 14 pole motor at 400hz.  This is
    the main reason that standard 120v-60hz is still only 60hz:  Big, heavy
    applications in industry usually involve large masses and low
    speeds/angular velocities.

    The higher the frequency, THE MORE SHIELDING IS NEEDED.   In an
    amplifier, the freq cutoff is usually limited to 20 khz anyway,  and
    in a spaceship things are usually shielded so well to protect against
    outside interference that 20 khz radiation simply never goes anywhere.
    But in the real world,  radiation even at 60hz can be significant.
    To illustrate this point, a large power company recently converted a
    high voltage 60 hz line (that was running several hundred miles) to a
    high voltage DC line (1amp @ millions of volts), then built a station
    at the other end of the line to take ten million volts DC and invert it
    down to 120 v @ 60hz.
    They did this because the line was radiating enough energy at 60hz to
    justify building two WHOLE NEW PLANTS.

        Something else, perhaps not as important, but from personal experience:

    20 khz HURTS LIKE HELL if you touch it at 120 volts.  60 hz just
    tickles or shocks you, but the same voltage @ 20khz causes severe pain,
    and can even burn you.  I know this effect diminishes at much higher
    frequencies because of the skin effect. (see tesla coils)

There are other reasons, Including the fact that mechanical devices that use
20 khz simply are not commonplace... its called inertia.

Trey Azagthoth (DennisT)

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

Date: Wed, 24 Mar 1993 22:39:58 GMT
From: [e-mail]
Subject: Uplink/downlink rates
Newsgroups: sci.space

>
>The antenna gains will be the same in both directions as long as the
>same antennas are used for transmit and receive.  (They usually are.)
>
 Antenna Gain is frequency dependent.


>Given a pair of antennas and a distance, data rates will be limited
>by transmitter power and receiver noise.  The DSN receivers are the
>best that can be built.  Spacecraft receivers are fairly noisy, but
>very reliable and lightweight.  They could no doubt be made quieter
>if there were a requirement to do so, but uplink does not generally
>require high data rates, and even if high rates are required, it's
>usually easier to raise the transmitter power.
>--
>Steve Willner            Phone [phone]         Bitnet:   willner@cfa
>Cambridge, MA 02138 USA                 Internet: [e-mail]
>  member, League for Programming Freedom; contact [e-mail]
Satellite link budgets are a function of power, antenna gain, POINTING LOSS,
distance, Receiver noise, cosmic or background noise.  Antenna gain cannot
be increased without penalty because pointing loss is also a function of
antenna size and an optimal antenna size exists given frequency and the
expected error.

                 [e-mail]

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

Date: 25 Mar 93 04:17:07 GMT
From: Henry Spencer <[e-mail]>
Subject: waste management...
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Shari L Brooks) writes:
>>It is not practical to recycle human wastes within the mass (etc.)
>>constraints of the shuttle...
>
>out of curiosity, are wastes dumped overboard gravitationally bound to
>earth?  Do they dissociate and get blown away by the solar wind or do
>they end up in the atmosphere?

Depends on where you do it.  At shuttle altitudes, you are still pretty
much within the Earth's atmosphere, thin though it be.  The stuff will
eventually sublime and dissociate into individual molecules, which will
end up as part of the Earth's (outer) atmosphere.  If you dump while
en route to the Moon, the molecules get swept out of the solar system
by the solar wind.
--
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  [e-mail]  utzoo!henry

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

Date: 24 Mar 93 13:32:16
From: Steinn Sigurdsson <[e-mail]>
Subject: Why use AC at 20kHz for SSF Power?
Newsgroups: sci.space

As this discussion just made t.p.s Flame War of the month
it is probably well past time to stop. Suffice to say I disagree
with you on several points, even though you do make some good
objections.

|  Steinn Sigurdsson    |I saw two shooting stars last night        |
|  Lick Observatory    |I wished on them but they were only satellites    |
| [e-mail] |Is it wrong to wish on space hardware?        |
| "standard disclaimer"    |I wish, I wish, I wish you'd care - B.B. 1983    |

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

End of Space Digest Volume 16 : Issue 366
------------------------------