Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_3/V16NO337.TXT

Internet Message Format | 1993-07-13 | 37KB

Date: Fri, 19 Mar 93 05:15:33
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #337
To: Space Digest Readers
Precedence: bulk


Space Digest                Fri, 19 Mar 93       Volume 16 : Issue 337

Today's Topics:
                    20Khz Power supplies. (2 msgs)
                             Beyond 1000!
      moon's fate when removing gravitational influence of earth
                          NASA and congress
                     Need MIR packet Frequency's
                     One Ticket To LEO, Please...
     Predicting gravity wave quantization & Cosmic Noise (2 msgs)
              SDIO VS NASA (was Re: Retraining at NASA)
                       Solar Arrays Falling Off
                     SR-71 Maiden Science Flight
                  Why use AC at 20kHz for SSF Power?

    Welcome to the Space Digest!!  Please send your messages to
    "[e-mail]", and (un)subscription requests of the form
    "Subscribe Space <your name>" to one of these addresses: listserv@uga
    (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle
    (THENET), or [e-mail] (Internet).
----------------------------------------------------------------------

Date: 18 Mar 93 18:49:07 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: 20Khz Power supplies.
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Roland Dobbins)  writes:

>Ah, Fred, back to your old tricks again.  Seems like old times on BIX.

Yep, back to speaking my mind.  Pity some of you apparently have such
a problem with little things like 'Freedom of Speech', ain't it?

>Too bad there's no moderator here to get you thrown off . . .

Yeah.  Fortunately, this pond is just a mite too big for the kind of
petty politicking among people who are legends in their own minds that
was going on on BIX when I was there.  Frankly, despite the fact that
the concentration of technical people gives it lots of potential, as
long as it's the way it was when I was there you are more than welcome
to keep it all to your little self.

[Give Tony my love.  ;-)]

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

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

Date: 18 Mar 93 18:50:16 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: 20Khz Power supplies.
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Roland Dobbins)  writes:

>Ah, Fred, up to your old tricks still.  Reminds of of the old days, on BIX.

>Too bad there isn't a moderator to throw you out _here_ . . .

Saying it twice?  Does your BBS have the hiccups, or what?

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

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

Date: 18 Mar 1993 12:48:47 -0500
From: Pat <[e-mail]>
Subject: Beyond 1000!
Newsgroups: sci.space

References: <[e-mail]> <[e-mail]> <1o15ak$[e-mail]> <[e-mail]>
Nntp-Posting-Host: access.digex.com
Sender: [e-mail]
Source-Info:  Sender is really [e-mail]

In article <[e-mail]> [e-mail] (Bill Higgins-- Beam Jockey) writes:
>popularization.  (However, it probably led directly to my addiction to
>Tom Swift novels for a few years...)
>

QUick, bill,  Just paint some tomasite over the meteor puncture
in the inflatable module :-)

>series *Horizon* are transported across the Atlantic, get their serial
>numbers filed off, and appear on PBS as *Nova* episodes.  In some
>cases I suspect they even replace the British narration with a


Bill, Lots of British Stuff now gets US underwriting directly or
indirectly.  Things like DrWHo  pulls in so much license money,  that
for Years BBC took into account american tastes for writing the show.

Also PBS  will underwrite a serial production directly in return for
US Rights,  and oftentimes exert strong editorial control.
Now what you describe is OEM tv, where I think they shoot segments
witht he direct intention of re-narration for internationalization.
OEM TV has been around for years,  look at Commercials.
FORD,GM will produce a commercial,  and the local dealers association
will hire a narraotor to do a voice over  while a graphic comes up
with dealership Addresses and phone numbers.

Hollywood, when they film movies, now directly consider Internationalization
and will co-ordinat ethe sound re-dubbing, it's why newer import movies
have a better look then in the old days.


pat

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

Date: 18 Mar 93 17:40:29 GMT
From: Ed Faught <[e-mail]>
Subject: moon's fate when removing gravitational influence of earth
Newsgroups: sci.space

In article <[e-mail]> [e-mail]
("Hans M. Steiner") writes:
>If one could "take away" the earth in an instant (remove the influence
>of the earth on the moon), what would happen to the moon's orbit around
>the sun?

Darn! I thought that pesky galactic bypass project had been abandoned.
--
Ed Faught  WA9WDM  [e-mail]
   DEFINITELY NOT a spokesman for the
Superconducting Super Collider Laboratory

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

Date: 18 Mar 93 08:03:34 GMT
From: Pat <[e-mail]>
Subject: NASA and congress
Newsgroups: sci.space

Brian comments on a lack of experience making space engineering difficult.

As henry has pointed out, since the end of the 60;s no-one has had
programs related to building testing  and exploring new technologies.

The saturn was  a success, because 10 years earlier, people in the
air force and NACA started programs for Large rocket motor design.

I've pointed out shortages in space qualified hardware.   LDEF
only flew once,   why not again?  or MINI LDEF,  something that fits
into  a DELTA,  you fly it up and have shuttle retrieve it after
some other mission.

SDIO  puts a lot of effort into infrastructure  needs.  better sensors,
better transport.   I'm not saying NASA doesn't have challenging
goals, but they might do better if they went with smaller programs,
faster schedules,  ongoing basis.

Goldin seems to think so to.  The discovery missions look real good,
why not a Vanguard Program.  WHere birds just fly to prove and test
gear?  about the same size as discovery,  but solely for engineering.

pat

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

Date: 18 Mar 93 17:48:54 GMT
From: Don Woelz <[e-mail]>
Subject: Need MIR packet Frequency's
Newsgroups: sci.space,rec.ham-radio.packet,rec.radio.amateur.packet

In article <[e-mail]> [e-mail] (George Rachor) writes:
>Anyone remember the frequency's used by the MIR space station packet radio system?
>
As I recall, they can be found on 145.550.  What I don't recall is
what callsign they use.  Anybody help with that?

--
   Donald D. Woelz                    Office Phone: [phone]
   GENROCO, Inc.                      Toll Free:  800-243-6762
   205 Kettle Moraine Drive North     Office Fax: [phone]
   Slinger, WI 53086   U.S.A.         24 hr Voicemail: 414-322-3891

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

Date: 18 Mar 93 18:59:08 GMT
From: "Kieran A. Carroll" <[e-mail]>
Subject: One Ticket To LEO, Please...
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Gary Coffman) writes:
> (discussion of relative costs for launching Shuttle,
> hypothetical Delta Clipper, and trans-Pacific airliner,
> leading to...)
> ...If we take more
>reasonable marginal costs of $110 million for a Shuttle flight,
>the cost per pound is $2,750...
> It should be remembered, however,
>that projected Shuttle costs per pound were $300 at a similar stage
>of it's development.

While we're at it, it's important to remember that
the $300/lb to LEO that the Shuttle was expected to achieve
used 1973 dollars (or there-abouts...in any case, constant
dollars fixed at the time that the original Shuttle systems
designs were being done). I'm not sure what the inflation
factor is between 1973 and 1993, but my fuzzy memory
of the year-by-year inflation rates over that period lead me
to an estimate that 1973$1 equals between 1993$4 and 1993$6.
Thus, 1973$300/lb would be equivalent to between 1993$1200/lb
and 1993$1800/lb. The marginal cost of operating the Shuttle
appears to be not that far from the number that its designers were
aiming for! (i.e. within a factor of two or three).

The Shuttle's detractors like to use the $500M/flight
price tag (ignoring the few outliers who insist that it really
should $1B or $2B per flight, to fully account for all manned
spaceflight development costs from 1960 onwards), in current dollars,
and then pretend that the $300/lb cost estimate was also in current
dollars, to "prove" that manned spaceflight projects always have
cost over-runs of 3000%. Come to think of it, some of the
same people like to argue that Space Station is hundreds or
thousands of percent over budget, using similar perniciously
faulty reasoning. I wonder why...?

Sure, the Shuttle didn't fully deliver on the goals that
it aimed for. However, it came much closer to accomplishing
them than many people are willing to admit.
--

     Kieran A. Carroll @ U of Toronto Aerospace Institute
     uunet!attcan!utzoo!kcarroll [e-mail]

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

Date: 18 Mar 93 18:24:06 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]. (Thomas E. Smith) writes:
>>In article <[e-mail]> [e-mail] (R
>>on Baalke) writes:
>>>     Three interplanetary spacecraft, now headed quietly toward Mars,
>>>Jupiter and over the poles of the sun, soon may prove the
>>>existence of elusive waves in the universe's gravitational field by
>>>bobbing on ripples in space like corks bobbing on ripples in a pond.
>>
>>From: [e-mail] (Mark)
>>I'm betting that the following will be observed:  Cosmic Noise.  A large number
>>of components will be detected at around wavelengths of 1 AU and above with
>>VERY low intensity, if the configuration is sufficiently tuned.  The
>>components will have wavelengths that occur at discrete jumps of about 1
>>millimeter at 1 AU.
>
>Ok, I give up. Why will wavelengths be detected at around 1 AU and up at low
>intensity?
>
>As for the cosmic noise, it probably will be observed, but since gravity waves
>are the only known phenonema that can wobble all three spacecraft at almost the
>same time (I forget if gravity travels the speed of light, or is instantly
>propagated) you can filter out the noise by only looking at events that affect
>all three spacecraft.

     Okay, but how does one rule out ordinary environmental perturbations
     that happen to occur at the appropriate times?  How does one distinguish
     between an ordinary dynamical triple-coincidence event and
     a gravitational one?

                                  dale bass

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

Date: 18 Mar 1993 11:25 PST
From: SCOTT I CHASE <[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]. (Thomas E. Smith) writes...
>
>How much more sensitive is the setup with the three spacecraft than the
>ground-based interferometer antennas?

It's not, so far as I understand.  But LIGO is still vaporware, so you
do what you can do.

>I am glad to see that you have taken advantage of a fantastic opportunity!
>A High 5 to the scientists who proposed this! Let's just hope that nature
>cooperates and gives us something to listen to :)

This is not the first time it's been proposed, or even done.  See, for example.

J.D. Anderson et.al, "Gravitation and Celestial Mechanics Investigations
with Galileo," Space Science Reviews V60, no.1-4, pp 591-610, May 92.

I suspect that the experiments contained in this paper won't be done
because of the problems with Galileo...

There was also a Phys. Rev. paper in the last six months or so reporting
a measurement that actually *was* made, using one of the Voyager spacecraft,
if I am not mistaken, which found no gravity waves.

-Scott
--------------------
Scott I. Chase            "It is not a simple life to be a single cell,
[e-mail]         although I have no right to say so, having
                 been a single cell so long ago myself that I
                 have no memory at all of that stage of my
                 life." - Lewis Thomas

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

Date: 18 Mar 93 19:33:35 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: SDIO VS NASA (was Re: Retraining at NASA)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Brian Donnell) writes:

>> Talk to SDIO. Their support infrastructure for SSRT represents less then
>> 1/60 of the program cost. Yet they are doing more to support cheap routine
>> access to space than NASA has ever done.

>Good stuff, I agree. But SDIO's efforts are narrower in scope than the
>overall goals of NASA, e.g., permanent manned presence, thorough
>exploration of the solar system (manned and unmanned), etc.

SDIO's scope isn't trivial but that is beside the point. NASA could run
many or most of its projects a similar way.

Besides, nothing would have so profound a positive impact on NASA's goals
than cheap routine access to space. Their management structure has yet
to accoplish it and the first effort by another agency using a radical
(for government) approach seems to be pretty successful. There is a lesson
to learn here.

Even without SSTO, SDIO spends half to a third of what NASA does to send
a pound to LEO. Yet they both use the very same launchers in many cases
and launch similar payloads.

>BTW - I disagree with the previous estimate of infrastructure costs being
>50% of NASA's overall costs.

Nither did I. However, the center wrap adds about 30% to the cost of anything
NASA does. Many other examples exist of NASA paying an order of magnitude
more than private companies for the same thing.

>> Agreed that is a problem. Yet other parts of government deal with the
>> same problems all the time.

>Other govt agencies due not have to deal with unknown and volatile domains
>to the extent that NASA does.

We are talking about DoD and they do indeed deal with unknown and volatile
domanis. Even more so than NASA: DoD systems must count on an enemy actively
working to destroy your systems. NASA need only worry about the environment.

>> Clementine, Delta Clipper, Timberwind...  I'll stack SDIO's record for
>> promoting space against NASA any day. Better, cheaper, faster is new
>> to NASA but it was always SOP at SDIO.

>For their focused domain, these are good. But I will bring us back to the
>big-picture point again that NASA has to keep in mind.

Focused domain? We are talking about lunar and asteroid space probes,
experimental spacecraft, and nuclear engines for space applications.
That's hardly a narrow focus and provides a record of inovation in
space research superior to NASA.

The most innovative ideas ideas for pushing out into space are coming
from DoE and SDIO. Ditto for the most focused diciplined efforts to
make it happen. The only inovative ideas coming from NASA recently are
from the former SDIO people working there.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------90 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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

Date: 18 Mar 93 08:12:43 GMT
From: Pat <[e-mail]>
Subject: Solar Arrays Falling Off
Newsgroups: sci.space

Isn't it nice to see advanced technical argument and discussion
from people involved in all sides of the work.

pat

who would still like to see something from someone who worked on
Lewis's High frequency power proposals.

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

Date: Thu, 18 Mar 1993 19:01:21 GMT
From: Mary Shafer <[e-mail]>
Subject: SR-71 Maiden Science Flight
Newsgroups: sci.space

On Thu, 18 Mar 1993 16:05:22 GMT, [e-mail] (John S. Neff) said:


John> In article <[e-mail]> [e-mail] (Mary Shafer) writes:
>From: [e-mail] (Mary Shafer)

>Matthew> is NASA going to run the SR-71 through its paces and find out
>Matthew> what exactly IS its top speed?
>
>Only if there's a research requirement to do so.
>
>I wouldn't hold my breath waiting for this to happen.

John> Please explain the advantage of the SR-71 over a ballon for UV
John> spectrophotometry. The maximum altitude of the SR-71 listed in a previous
John> post was about the same, or a little lower, than the normal altitude of
John> a ballon flight.

Ask someone at JPL--it's their experiment.  We're just flying it for
them.  I'm sure that they have a good reason.  Availability, cost,
instrument packaging, reusability; these come to my mind as possible
factors.

The only thing I know about UV dates back to '60's black lights.  Come
to think of it, so does some of what I know about SR-71s.



--
Mary Shafer  DoD #0362 KotFR NASA Dryden Flight Research Facility, Edwards, CA
[e-mail]                    Of course I don't speak for NASA
 "A MiG at your six is better than no MiG at all."  Unknown US fighter pilot

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

Date: 18 Mar 93 19:25:00 GMT
From: "David B. Mckissock" <[e-mail]>
Subject: Why use AC at 20kHz for SSF Power?
Newsgroups: sci.space

Below are 400 some odd lines of detailed information on the
topic of the initial selection of 20 kHz as the distribution
frequency for the SSF power system. Most of what follows is
directly from a paper "Space Station Power (Why use AC at
20-kHz?) by Jim Mildice, General Dynamics, Space Systems
Division. Following the detailed info is a bibliography
listing 35 sources for additional detailed information on
20 kHz. {As an aside that nas nothing to do with 20 khz,
some folks may be amused to know that during my research, I
found out that the NASA Headquarters library subscribes
to "Space Watch", with the "One Small Step for a Space
Activist" column by our very own Allen Sherzer (and help from
Tim Kyger)}.

I asked one of the LeRC gentleman involved in the 20 kHz
research about the problems MSFC had at their testbed with the
20 kHz components (which was raised by Dennis). The LeRC
explanation is that the MSFC system was purchased by MSFC, based
on requirements written by MSFC (i.e. Marshall was *NOT* using
hardware from the LeRC testbed, they went out and bought their
own hardware). The LeRC view is that the MSFC requirements were
flawed, so the MSFC system was "built not to work."

Why 20 kHz???

Aerospace power systems have historically been designed to
distribute power over low voltage DC busses, commonly 28-vDC.
This works fine when the power is low, the distances over which
the power is delivered are short, and there are a few closely-
controlled users. For SSF, the distances from source to load
are not short (typically greater than 50 meters), and the
power we can deliver (56 kW at PMC) is much greater than any
current spacecraft. By design, there will be many different users
on SSF. Therefore, this is an application where we need to
investigate Power Management & Distribution alternatives.

The DC Alternative

The simplest system that we could conceive would extrapolate an
ideal DC system concept used on a few small spacecraft. There is
an appealing kind of engineering logic that makes this approach
attractive, on the surface. Solar arrays and batteries are DC
sources, so it seems natural to interface them directly. The
batteries are connected directly to the output of the solar
arrays. They load the arrays, thereby controlling the bus
voltage, and automatically recharge when their terminal voltage
is low (discharged). The charge rate decreases as the terminal
voltage rises (toward fully charged), or as user loads demand
power and decrease the solar array output voltage. With proper
solar array and battery designs, the system regulates and controls
itself. Of course, the loads have to operate over a voltage
range equal to the battery voltage variation from charge to
discharge.

As the system grows, complexity increases rapidly. When we add
another solar array, we have to control the arrays' respective
output voltage so that they share the load. Even if we were to
match them initially, they wouldn't stay matched after a few
years in orbit. And if they're not matched, we can't get all the
power they're capable of supplying. So we add an array regulator
or controller.

The same is true for multiple battery strings. If we try to
eliminate a power processor and put a single regulator on the
output of a solar array-battery combination, we lose some of
the benefits of cross-strapped redundancy (often one of the
reasons tooadd another string). And as the number of users
increases, they usually want to be isolated from one another,
and DC-DC converters are added at their inputs.

If we keep the voltage low (say, at 28-vDC, a common user
voltage), distribution bus currents and masses get out of hand
as power requirements and transmission distances grow.
Therefore, transmission voltage must be increased (typically
to 150- or 270-vDC).

Since few users can utilize the increased-voltage DC power
directly, more DC-DC converters or other kinds of power
processors are added.

You can see that our simple, ideal DC system has grown to include
a lot of power processing equipment.

The AC Alternative

Since we now have power processors at the solar array and battery
interfaces, it is not much of an extrapolation to consider what
happens if we change those processors to inverters, and
distribute AC. Westinghouse's AC utility power distribution
approach won out over Edison's DC a century ago, and terrestrial
50-60 Hz utility power has been with us ever since. Most of the
reasons that applied then still apply, especially for a modern
spacecraft that provides utility-type power for a wide variety
of users and loads. Some of them are:
 o  Rotating machines - "want to operate" with AC. Alternators
    are smaller, quieter, and simpler than their DC-generator
    cousins. The same is true for AC induction motors, when
    compared to DC or universal motors. Even modern,
    electronically-computated, DC "brushless" motors generate
    significant amounts of high-frequency noise and interference,
    and must include an electrical power processor.

    A good, everyday example of the AC machine's desirability is
    in the DC power system in our cars, where AC alternators
    have replaced DC generators as the prime electrical energy
    source.

 o  Transformers - are simple, efficient components to change
    voltage levels and/or provide power source isolation. And
    while DC-DC converters are sometimes considered to be the
    DC system equivalent of the transformer, they simply cannot
    match the AC devices for reliability, efficiency, and
    simplicity.

 o  Power Supplies - Many users can utilize simple transformer-
    rectifier-filter supplies to get the many levels of AC and
    DC typicall required for modern electronic systems, rather
    than the more costly and complex DC-DC converters used to
    do the same job with DC input power.

 o  Switching - The zero-crossings in an AC power source allow
    for all the power switching to occur at zero currents,
    thereby eliminating a major source of transient EMI and
    noise in space systems. Zero-current switching also simplifies
    switchgear design and improves reliability, since switches
    never have to interrupt large currents into loads, or
    even larger currents into faults.

AC System Frequency

Since it is now clear that AC has many advantages and is the
probable choice for a large spacecraft with utility-type power
distribution, the frequency we choose becomes the final
consideration. Of course, our terrestrial systems are 60 or
50-Hz (depending on whether we are in the US or abroad). When
aircraft became sophisticated enough to start worrying about
shaving weight to improve payloads, their AC systems went to
400-Hz, primarily because of reduced size and weight. With
space shuttle delivery costs very high (see Wales Larrison
or Allen Sherzer posts), we need to at least think about
higher frequencies again.

The systems components which are most strongly effected by the
frequency choice are field-generating devices, like inductors,
capacitors, and transformers. They all seem to follow an
exponential decrease, and the curve looks relatively flat
above 10-kHz, if we consider high power equipment (at least
10 kW) and start the comparisons back near 60 Hz. So
there isn't a strong size and weight driver, pushing us above
that frequency region. If we're conserned about a manned
vehicle, we should probably move to at least 20 khz to get the
power line noise above the audio region. (That 400 Hz whine
in my airliner stereo head-set is really annoying if I have to
listen for very long).

But how high can we comfortably go? The answer comes from the
DC power processing folks. When we design DC to DC converters
in this power range, readily-available component technologies
for semiconductor switching devices, transformers, capacitors,
etc. limit us to a maximum frequency of about 50kHz. So if we
stay comfortably below that, and continue with our initial
thought to chose something close to 20 kHz, we can expect
to find a good selection of qualified power components and
materials, and a good body of design data, with which to
implement hardware designs.

But one of the biggest drivers for a high frequency choice also
comes from modern DC power processor technology. As discussed
earlier, when we have to interface with a source having a
voltage that is significantly different from that which we
need, or when we need ground isolation, we insert a DC to DC
converter. A typical modern DC to DC converter contains a
switching (or chopper) stage which takes the input DC and
converts it to high-frequency AC. A transformer then raises
or lowers the voltage to the required value, usually in
conventional AC power system fashion. This AC is then
rectified and filtered to output the DC power to the load.

So, in the actual DC system on a large general-purpose
spacecraft (like SSF), including all the load and source
power processing, it looks like the figure below. As you
can see, several DC to AC to DC conversions are required
(at the source interface, battery interface, and most load
interfaces). It becomes an obvious extrapolation to take
away some of the hardware, so the normal high frequency
in the DC to DC converter intermediate stages is simply
applied tooand taken from the distribution busses, and
the power system is nothing more than a large, distributed
DC to DC converter, which eliminates about half of the
hardware in a conventional DC system.

   Here is my attempt at the Figure ...

Source-IF-Chpr-Xfer-R-OF--Dist Bus--IF-Chpr-Xfer-R-OF-Load
                            DC

Source-IF-DC to AC--Distribution Bus-Xfr-R-OF-Load
                            AC

Where:
   IF - Input Filter
   Chpr - Choppper, DC to AC
   Xfer - Transformer
   R - Rectifier, AC to DC
   OF - Output Filter

Because of the nature of space station users, the above
reduction in equipment is even greater than we would forecast
by inspection. Many factors (duty cycling, experiment down
time, user change overs, etc.) influence the actual amount of
loads that are actively powered at any one time. Since everyone
forcasts that the SSF power system will always be loaded to
near-capacity, there will always be load hardware "waiting its
turn." Depending on the conservatism of the analysis,
estimates have projected that the ration of "installed" to
"active" loads will be between two and four. The reduction
in hardware would then bet between 675 and 1575 pounds

But even those large-sounding weight savings would not be
enough to justify the adoption of a technology that was this
new for space systems (even though it has been extensively
used elsewhere). The most powerful reason for selecting systems
like the one on SSF comes from improved efficiency.

The direct use of high frequency allows us to use Resonant
Inversion. The approach we selected for SSF excites a series
resonant inductance-capacitance circuit which "rings" at its
natural frequency. Using a principle proposed by Neville
Mapham more than 30 years ago, the output power is taken from
across the resonant capacitor, and is a low distortion, low
impedance, sine wave voltage source that can be used to power a
"utility" type system. However, the most important feature
of this approach is that all the switching associated with the
power conversion occurs when the current is zero, when the
resonant network has forced it to go there. This eliminates a
major source of losses in modern power processing equipment,
and typically cuts inverter losses in half, from approximately
10% to approximately 5%. Since a percent is around 500 W (on
the PMC station), that means a savings on the PMC station of
about $25 million. If we also add total life cycle costs
for the entire mission, that savings can grow to between
$100 million and $150 million, depending on how conservative
your analysis rules are.

The last question the die-hards finally ask is, "Since it's so
good, why not use resonant inversion to produce 400-Hz or
60 Hz? Then we can have the best of both worlds, a familiar
frequency and all the benefits of the new technology." If
you do the math, you find that a direct-generation resonant
inverter for 60-Hz or 400-Hz has resonant network values that
would yield to enormous (and impractical) inductors and
capacitors. We could (and do) use resonant processors to change
to an intermediate high-frequency and then synthesize the low
frequency by steering the high frequency pulses. While this
would design a superior inverter or DC to DC converter with
higher efficiencies than the conventional approaches, it
would look a lot like a standard Dc to DC converter, and we
would lose most of what we gained.

For the SSF application, the "Science Users" provided the final
rejection of low-frequency AC. To properly perform some of their
measurements, they require that the external fields from power
processing and transmission be at least three orders of
magnitude (actualy ~70 db) lower than the typical performance
of today's 400-Hz aircraft systems. Most experts in the field
believe that this would not be possible. If a high-enough AC
frequency (such as 20 kHz) is used, shielding to provide the
lower interference levels is easier, and even more important,
the interference the system might generate is well-above
the frequency response of their instrumentation, and therefore
will not cause a measurement problem.

 -- end of article by Jim Mildice --

Bibliography of the 20 kHz Research

1967
(1) Mapham, N., "An SCR Inverter with Good Regulation and
    Sine-Wave Otuput," IEEE Trans. on Industr. Gen. Application,
    Vol. IGA-3, No. 2, 1967, pp. 176-

1983
(2) Renz, D., Finke, R., Steven N., Tringer, J. and Hansen, I.
    "Design Considerations for Large Space Electric Power
    Systems", NASA TM-83064

1985
(3) Hoffman, A.C., Hansen, I.G., Beach, R.F., Plencer R.M.,
    Dengler R.P., Jefferies K.S. and Frye R.J., "Advanced
    Secondary Power System for Transport Aircraft,"
    NASA TP-2463

1986
(4) Mildice, J. and Waapes, L. "Resonant AC Power System: Proof
    of Concept" NASA CR-175069

(5) Mildice, J., "AC Power System Test Bed" NASA CR-175068

(6) Mildice, J. "Bidirectional Power Converter Control
    Electronics," NASA CR-175070

(7) "High Frequency Power Distribution System" NASA CR-175071

(8) Hansen, I.G., "Description of a 20 Khz Power Distribution
    System" NASA TM-87346

(9) Hansen, I.G. and Wolf, F.J. "20 Khz Space Station Power
    System," NASA TM-88801, 1986. 19th Annual Electronics and
    Aerospace Systems Conference, Sept 8-10, 1986.

(10)Hansen, I.G. and Sundberg, G.R. "Space Station 20 Khz Power
    Management and Distribution System." NASA TM-87314. 1986
    IEEE Power Electronics Specialists Conference

(11)Zelby, L.W., Mathes, J.B., and Shawver, J.W., "Transmission
    Line Design for a Power Distribution System at 20 Khz,"
    NASA CR-3987, July 1986. NASA Contract NAG3-508

1987
(12) Tofigh, F., "208 VAC, 20 Khz Hybrid Remote Power Controller,"
     Energy-New Frontiers, 22nd IECEC, AIAA, New York.

(13) Temple, V.A.K. "MOS COntrolled Thyristors in Energy Conversion
     Systems," Energy-New Frontiers. 22nd IECEC, AIAA, New York

(14) Mildice, J., Schreiner, K. and Woff, F., "Control
     Considerations for High Frequency, Resonant, Power Processing
     Equipment Used in Large Systems," NASA TM-89926. Energy-New
     Frontiers, 22nd IECEC, AIAA, New York

(15) Lipo, T.A. and Sood, P.K. "Study of the Generator/Motor
     Operation of Induction Machines in High Frequency Link
     Space Power Systems," NASA CR-179600, 1987.

1988
(16) Sood, P.A., Lip, T.A., and Hansen, I.G. "A Versatile Power
     Converter for High Frequency Link Systems," IEEE Trans.
     on Power Electronics, Oct 1988

(17) Hansen, I.G. "Status of 20 kHz Space Station Power
     Distribution Technology," IEEE Applied Power Electronics
     Conference, APEC 88

(18) Renz, D. D., "Power Components for the Space Station Power
     Distribution System," IECEC 1988, July 31-Aug 5

(19) Hansen, I.G., "Power Distribution Technology for Aerospace
     Applications," Power Magazine, July 1988

(20) F, Sgebg Tsaum, F.C. Lee "Computer Modeling and Simulation
     of a 20 Khz AC Distribution System for Space Station,"
     IECEC, 1988, pp 338-344.

(21) O. Wasynczuk, PC Krause "Simulation and Control of a 20 Khz
     Spacecraft Power System" IECEC, 1988, pp 663-669.

(22) F. Tsai, F.C. Lee "Effects of Load on the Performance of
     the Mapham Resonant Inverter," IECEC, 1988, pp. 655-661.

(23) K. Schreiner, "AC Bidirectional Motor Controller," IECEC 1988

(24) O. Wasynczuk, PC. Krause "Dynamic Characteristics of a 20 Khz
     Resonant Power Systems: Fault Identification & Fault
     Recovery" IECEC, 1988, pp 663-669.

1989
(25) Mildice, J. "In Space, its 20 khz ac Power," Powertechnics
     Magazine, Feb 1989, pp 29-32

(26) Sundberg, R., Brush, A., Patterson, A. Button, R.
     "Distribution and regulation Characteristics of a Mapham
     Inverter," 24th IECEC, Aug. 6-11, 1989

(27) Brush A., Sundberg, R. and Button R., "Frequency Domain
     Model of Parallel Series Output-Connected Mapham Inverter,"
     24th IECEC, Aug. 6-11, 1989.

(28) Hansen, I.G., "Variable Speed Induction Motor Operation
     from a 20 Khz Power Bus," 24th IECEC, Aug 1989

(29) Leskovich, R. and Hansen, I.G. "The Effects of Nonlinear
     Loading upon the SSF 20 Khz Power System," 24th IECEC,
     Aug 1989

(30) R. Sundberg, A. Brush, R. Button & A. Patterson "Distribution
     Regulation Characteristics of a Mapham Inverter." IECEC 1989

(31) R. Button, A. Brush, R . Sundberg "Development and Testing
     of a 20 Khz Component Test Bed" IECEC, 1989

(32) P. Jain, J. Bottril "An Improved Mapham's Inverter for High
     Frequency Space Power Conversion," IECEC, 1989, pp. 611-616

(33) K. Schreiner, "AC Bidirectionaly Motor Controller," IECEC,

(34) S. K. Sul, I. Alan & T.A. Lipo "Performance Testing of a High
     Frequency Link for Space Power Distribution System" IECEC

1990
(35) O. Wasynczuk, PC. Krause "Steady-state and Dynamic
     Characteristics of a 20 Khz Space Craft Power Systems:
     Control of Harmonic Resonance" IECEC, 1990, pp. 471-476.

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

End of Space Digest Volume 16 : Issue 337
------------------------------