Date: Wed, 17 Mar 93 05:21:03    
From: Space Digest maintainer <digests@isu.isunet.edu>
Reply-To: Space-request@isu.isunet.edu
Subject: Space Digest V16 #325
To: Space Digest Readers
Precedence: bulk


Space Digest                Wed, 17 Mar 93       Volume 16 : Issue 325

Today's Topics:
                    20Khz Power supplies. (3 msgs)
                7805s (was Re: 20Khz Power supplies.)
                     Charon & Pluto: definitions
    Chicago Grechko dates(was Re: Cosmonaut Georgi Grechko in USA)
                             Galileo HGA
               Just a little tap (was Re: Galileo HGA)
               Mars Observer Update - 03/16/93 (5 msgs)
                  Response to various attacks on SSF
    Sisters of Mars Observer (was Re: Refueling in orbit) (2 msgs)
                       Solar Arrays Falling Off

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

Date: 16 Mar 1993 20:12:54 -0500
From: Pat <prb@access.digex.com>
Subject: 20Khz Power supplies.
Newsgroups: sci.space

In article <16MAR199311481384@judy.uh.edu> wingo%cspara.decnet@Fedex.Msfc.Nasa.Gov writes:
>In article <1o4uh3INNobf@access.digex.com>, prb@access.digex.com (Pat) writes...
>>
>
>
Blatently stupid in your opinion pat. Are you a power engineer?
>

Power engineer, no.  I went to school, got my Bachelors  in
Technical Management/CS  back in 84.  Since then, I've been
in the software world,  but I try to keep up with the world of
analog.   Now my Roommate, who I keep in good touch with Is a 
power engineer.  He in fact, is now the chief Load engineer for
LILCO,  and we have lots of long conversations on utility power
supply, and power management issues.  He and I have had lots of
conversations on this issue.  I've also been working at passing the
NEC exam for jorneyman electrician, so I've been learning a lot about real world
electrical system design.   

>[more delted]
>
>>Gee Fred.  Several million dollars of MY tax dollars were spent on this
>>boondoggle.  Why shouldn't they justify this.  It's no different
>>then if a congress critter asked these questions.
>> 
>
>pat maybe you should go and look at the Lewis Research center budget for 
>20khz power before you talk about how many millions were wasted. I think
>the entire budget was less than one million for the demonstration system.
>

Dennis, let's not get into accounting quibbles.  Nobody knows how
much NASA ever spends on any one subject.   

>>Fred.  why don't you have them answer my quewstion, and I'll shut up.
>> 
>>|>|>Can you name any competent Electrical engineers, or Computer engineers
>>|>|>or PE's  who thought this was a good idea?
>
>I have been thinking about 20Khz and I can name a few advantages of it, buty
>only in its use in space. Well actually here on earth too.
>

Dennis, you have no idea, how much I appreciated this post.  At least you
had the guts and ability to point to arguments, I hadn't considered or
had placed different weight factors on.
Much more interesting to read, then Fred.

>1. 20Khz power is not deadly.  The human body can respond muscularly to 
>frequencies of up to aroun 800 hz.  This is the primary reason that when
>you grab high amperage currents of 60 hz your muscles lock to the power
>and you die. With 20 khz this would not happen even if you got hooked to
>a direct short.  There are several hundred to thousands of people each year
>that die from being muscularly locked to 60 hz or 400 hz power.  This to me
>would be an excellent justification for the use of 20 Khz power nationwide.
>
Muscle lock, while a problem,  seems to be what we call "acceptable risk".
You're right,  one of the Big problems with 60 Hz, is that it is coupled
to an oscillation frequency for VFib,  but on the other hand,  
"there ain't no electricians with Bad Hearts".  60 hz can be a bitch,  but
I've been stung more times then I care for.  400 hz  stings, but we don't
see airmen,sailors, submariners, computer techs dropping like flies.
High voltage still seems more of a threat then anything else.  a 7 KV
coil has a bad habit of leaping out at you.  
I've known 2 guys killed by step up transformers arcing across at them.
One was using a metal tape measure to close to the cabinet.

>The problem with 20Khz per se is that some women would not be able to stand 
>being around it, as a few women can hear frequencies that high. I kinda 
>doubt this is a problem since many computer monitors also run in this frequenc
>domain.
>
Ear plugs?

>2. Lighter weight tranformers.  This was another reason that 20 Khz was 
>pushed due to the fact that you could have lighter weight transformers than
>would be necessary for a 400 hz system.  With many many experiments, each with
>a transformer in the front end of the power supply thous becomes a significant
>weight driver.  Pat, many many systems use much higher frequencies to 

Transformers weigh less,  but How much less?  and given the relative 
percentage of weight sucked up by pwer systems,  how much does
this really save?   Does Higher AC operating voltage guy many of the same
savings, with less risk?   that is a solid decision criteria,  and at least
from what Henry has said, we are only talking 5% more weight savings.
Plus,  what kind of hysterises lossees are we talking about at Higher frequencies.  Efficiency of weight gained, may not help if we lose out on power
required.  Plus, these are zebra transformers,  they're not exactly
off the shelf items.

>transform power from one voltage to another.  The MCM 7805 series regulator
>that is used by the millions to regulate +5 VDC is actually a 40 Khz chopper
>regulator in architecture.  That is the DC voltage is converted to 
>40 Khz and then rectified to the new lower DC voltage.  The switching
>power supply on the PC on your desk uses a similar principle by converting
>the 60 hz power from the line to several thousand Khz some in the hundreds of
>thousands and then rectifying that down to the DC voltages used in your
>computer. Why do this? The transformers are much smaller and lighter. This is
>why your switching power supply is a fraction of the size of the old technology
>linear supplies.
>

Yeah, Dennis.  Motorola was using switching power supplies back in the
1960's.  We had them on the old plato terminals.  They worked real well,
but they had lots of funny failure modes,  which gave them a very short
service life.  We were always having to get 1 or two fixed.  
Frequency shifting is a long known technology for  power control,
Triac dimmers use the principle too,  but their reliability and MTBF
aint so hot.

Some of this crude old iron technology is virtually indestructible.
ConEd  used to have old three phase transformers that had ridden out
80 years of midwestern weather.

>
>3. Reliability of the overall system.  How often does the power supply go out
>on your desktop PC today? They use the same principle of power supply as was
>proposed for SSF by Lewis. There are millions upon million of these supplies
>out and operating every day. By far most of them operate at hundreds of
>Khz rather than 20 Khz but the prinicple is the same.
>

Dennis, there is a big difference between my PC and a space station the
size of decent sized warehouse.   Plus the environment is a lot
different.  My PC lives offa conditioned ISO transformer with gas tube
arresters  and for safety, plugged into some MOVs.  Conditions in orbit
are subject to slightly more rigorous environmental problems :-)

>>Fred  as opposed to FRED the cut down space station.  You try to explain
>>why a totally untested technology would be used on such a critical
>>project.  Name 3 projects that have used 20Khz  power.  name 3 companies
Dennis has to be a wise guy;-)  [stuff deleted]
Sure you can order some stuff with internal clock rates at 20,40 and 80Khz.
but It's a little harder getting Circuit Breakers,  UL listed relays,
etc that plug into 20Khz.  What we do on a PC board is a little different
from primary power distribution systems.


>
>The DC-DC conveter and the great strides that have been made in making this
>technology smaller, cheaper, lighter (faster cheaper better) are all totally
>
>This new (or actually very old if you remember the S-100 computers) is that
>you no longer have a central power supply that provides all of the system

Technologies for small digital systems i think are significantly differnet
from Large industrial facilities.  It's awful optimistic to scale this
activity up to such a facility.

>
>
>[more tons deleted]
>
>Problems with 20 Khz
>
>1. IF cabin pressure is lost then the system can arc.
How do you use this on the non-pressure side of the Bird?
Extra thick insulation?  If it really needs the air di-electric
it seems very challlenging to use it in vacuum based systems.

>2. Non Standard
>3. RFI/EMI (can be solved with filters however)
>
>Actually not bad except for #1. If cabin pressure is lost you have to
>shut down your power system. No good for system recovery. From what I
>remember that is the final reason that 20Khz died.
>
>[literally tons deleted]
Yeah, even I thought the threads were getting twisted and long.

>
>>And what a can in space it was.  It was way ahead of the russains.
>>It was fast, cheap, and better then any paper design, cuz it was real.
>>The principle problem skylab had was there was no cheap way to get
>>crews and materials up there.  Saturn missions were expensive.
>
>Saturn 1B flights were pretty cheap actually.
>Why pat?
Well, I don't know much about the 1B's but the V's were pretty expensive.
Granted compared to the shuttle, maybe we should have stayed with
the Saturns,  but at the time, I thought even 1B's were considered
expensive, due to low flight rate,  need for large support force.....

>
>>Fred,  are you thinking that a few million bucks will break the budget?
>>It's my feeling that if we went metric, it's be useful for our industries.
>>The europeans are not interested in manufacturing English unit products.
>> 
>
>The Japanese have no problems doing that. Maybe that is why they are ahead
>huh. :-)
Actually, pretty much all the japanese products I've seen are metric based.
or funny mixtures.  IEEE std connectors,  that sort of thing.

>
> [Dennis, stuff deleted on power system design and on flamage restriction]

Dennis, if you lived here, and I lived there, we'd probably be
on opposite sides of the fence.  You get to live and work with
the guys trying to make things happen on shrinking and inadequate
budgets,  while i get surrounded by greasy lobbyists and
fat congresscritters.

pat

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

Date: 16 Mar 1993 20:21:37 -0500
From: Pat <prb@access.digex.com>
Subject: 20Khz Power supplies.
Newsgroups: sci.space

Actually the thing that really sets off my warning bells on 20Khz,
is that no-one knows how this would behave in the LEO environment.

Henry,  wasn't most of the Canadian Long haul grid knocked down one
time by sun spots?  Up there, god knows what kind of crzy interactions
would occur every time we had asolar flare.

pat

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

Date: 16 Mar 1993 20:33:35 -0500
From: Pat <prb@access.digex.com>
Subject: 20Khz Power supplies.
Newsgroups: sci.space

In article <1993Mar16.190731.14597@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes:
>systems. It's cheaper, smaller, and lighter than the old brute force
>methods of Tommy Edison and Georgie Westinghouse. Even Nicky Tesla
>thought higher frequencies were a good idea for power distribution.

You talk about them like they were close personal friends of yours.
Did you go to school with them ;-)

>DC was a technology of the 90s, the 1890s. Try to move into *this*
>century Pat.
>
I wasn't particularly advocating DC.  I thought 400 HZ was the way to
go.  Sure you have to buy out of aircraft catalogs,  but then the
parts are halfway to space qualified.  You must be getting
hardening of the arteries:-)  

The only reason I thought DC was an idea, was most of our manned
space background is in DC.

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

Date: Wed, 17 Mar 1993 01:11:23 GMT
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: 7805s (was Re: 20Khz Power supplies.)
Newsgroups: sci.space

In article <16MAR199316300855@judy.uh.edu> wingo%cspara.decnet@Fedex.Msfc.Nasa.Gov writes:
>>> The MCM 7805 series regulator
>>> that is used by the millions to regulate +5 VDC is actually a 40 Khz
>>> chopper regulator in architecture...
>>Is this true? Most 7805s I've come across are linear.
>
>Tom take a look at the noise spectrum output of a 7805. You will see that
>it is concentrated (fundamental frequency) at 40 Khz. Then go to a book
>on the theory on the part. ( I think the original design is from TI) and
>read about switching regulators. These are early generation parts and 
>are only about 50% efficient, although they can accept quite a range of
>input voltage. (8.5-18 VDC for +5 VDC) I think the proper term is a 
>chopper regulator for these early generation devices.  

Dennis, I think you've got the part numbers mixed up.  The 7805 is a
linear device.  It drops voltage the crude way, by just interposing
a partly-turned-on transistor as a resistance.  It is not a chopper of any
kind -- where's the output filter??  It is nowhere near 50% efficient if
presented with a relatively high input voltage.  It is the classical
one-part linear (i.e., non-switching) regulator.

>I think what you are talking about is that they are listed in the linear 
>devices catalogs sometimes. TI has an exclusisve book for Regulators.

Please cite exact references.  The 1992 TI Linear Databook, Volume 3,
lists the 7805 as a linear regulator.

Switching power supplies are indeed the norm in modern computers, but
the 7805 is not used in them.
-- 
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  henry@zoo.toronto.edu  utzoo!henry

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

Date: Tue, 16 Mar 1993 23:50:59 GMT
From: Keith Mancus <mancus@sweetpea.jsc.nasa.gov>
Subject: Charon & Pluto: definitions
Newsgroups: sci.space

In article <C400n9.L0.1@cs.cmu.edu>, rcs@cs.arizona.edu (Richard Schroeppel) writes:
> It's been suggested that Charon & Pluto be called "co-satellites" because
> the system barycenter isn't inside Pluto.  This criterion depends too much
> on the distance between the bodies.  The solar system barycenter is usually
> not inside the sun; and if we were to move the moon 30% further away, the
> earth-moon barycenter would be outside the earth.
 
> Rich Schroeppel  rcs@cs.arizona.edu
 
  Indeed.  By that definition, the Sun and Jupiter are "co-stars" because
their barycenter is not inside the Sun...

-- 
| Keith Mancus    <mancus@butch.jsc.nasa.gov>                           |
|                 N5WVR                                                 |
| "Black powder and alcohol, when your states and cities fall,          |
|  when your back's against the wall...." -Leslie Fish                  |

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

Date: 16 Mar 93 18:19:56 -0600
From: Bill Higgins-- Beam Jockey <higgins@fnalf.fnal.gov>
Subject: Chicago Grechko dates(was Re: Cosmonaut Georgi Grechko in USA)
Newsgroups: sci.space

In article <1993Mar11.011037.25077@vdoe386.vak12ed.edu>, ghasting@vdoe386.vak12ed.edu (George Hastings) writes:
> Dr. Georgi Grechko, Cosmonaut
> Lecture Tour of the United States
> 
[long grueling itinerary which ends with:]
> Travel to Chicago, IL			April 6
> 
>    Other speaking engagements may be added.
>  If Dr. Gretchko is scheduled for your area, call
>  the local planetarium for mor information.

Thanks, George.  I've got some more.  Various local National Space
Society members, notably Jim Plaxco, have been hustling to set up
speaking dates for Dr. Grechko:

Harper College, Palatine IL             April 6
Schaumburg High School*, Schaumburg     April 7
14th District Activities Ctr, Chicago   April 7 
Museum of Science & Industry*, Chicago  April 8
Council on Foreign Relations, Chicago   April 8
=================================
* Not open to the public, I think.

Bill Higgins                           | "I shop at the Bob and Ray
Fermi National Accelerator Laboratory  | Giant Overstocked Surplus
Bitnet:           HIGGINS@FNAL.BITNET  | Warehouse in one convenient
Internet:       HIGGINS@FNAL.FNAL.GOV  | location and save money besides

SPAN/Hepnet:           43011::HIGGINS  | being open every evening until 9."

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

Date: 17 Mar 1993 02:02 UT
From: Ron Baalke <baalke@kelvin.jpl.nasa.gov>
Subject: Galileo HGA
Newsgroups: sci.space

In article <1993Mar16.195742.12414@nntpd.lkg.dec.com>, fisher@skylab.enet.dec.com () writes...
> 
>Anyone have any clue as to what this "HGA receive pattern" test recently
>was all about?  Do they have plans (or last-chance hopes) to use the HGA in
>some degraded form, or is this just for contingency in case the LGAs die?

This is just a check to see if the signal from the HGA is usable.  The
antenna is partially deployed, being more open on one side than the
other.  Even though the hammerings did not free the stuck ribs, they did 
open the antenna up a little bit more.  The HGA signal is not expected to be 
usable, but the test is being done just to make sure.  
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
    | | | |  __ \ /| | | |     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: Wed, 17 Mar 1993 01:17:47 GMT
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Just a little tap (was Re: Galileo HGA)
Newsgroups: sci.space

In article <1993Mar16.182733.1@fnalf.fnal.gov> higgins@fnalf.fnal.gov (Bill Higgins-- Beam Jockey) writes:
>> You mean sideswiping an asteroid to try to knock the antenna loose is out :-)
>
>Hmm, they're going past Ida in August, and a zero-distance flyby is well
>within the propellant margins, I'm sure...

Jordin Kare, in his Clementine talk at Making Orbit, mentioned that they
had seriously discussed an "aim for dead center, it's not going to hit it
and we'll get great closeups" philosophy for the Clementine asteroid
encounter.  He said this did make people a little nervous, but more to
the point, it made it difficult to get good imaging both inbound and
outbound, because the asteroid goes from almost-dead-ahead to almost-
dead-astern very quickly and the probe can't re-point its sensors all
that rapidly.  A substantial miss distance limits the closeups but gives
better return overall.

(This is from slightly-dim memory, details may not be quite right.)
-- 
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  henry@zoo.toronto.edu  utzoo!henry

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

Date: 16 Mar 1993 19:34:13 -0500
From: Pat <prb@access.digex.com>
Subject: Mars Observer Update - 03/16/93
Newsgroups: sci.space

In article <16MAR199312462649@csa2.lbl.gov> sichase@csa2.lbl.gov (SCOTT I CHASE) writes:
|In article <16MAR199319013284@kelvin.jpl.nasa.gov>, baalke@kelvin.Jpl.Nasa.Gov (Ron Baalke) writes...
|>Forwarded from the Mars Observer Project
|> 
|>                       MARS OBSERVER STATUS REPORT
|>                              March 16, 1993
|> 
|>The Flight Team reports that spacecraft subsystems and the instrument
|>payload are performing well.  The spacecraft is in Array Normal Spin in
|>outer cruise configuration, with uplink and downlink via the High Gain
|>Antenna; uplink at 125 bps, downlink at the 2 K Engineering data rate.
|>The DSN (Deep Space Network) is providing continuous coverage to Mars
|>Observer in support of TCM-3 (Trajectory Correction Maneuver #3) activities.
|
|Why are uplink and downlink at different data rates?  Does the spacecraft
|have a better transmitter than receiver?  I presume that we can transmit
|as well as we can receive, so that the difference must be due to some 
|spacecraft design issue.
|


Well, I imagine the need for data uplink, isn't real large.
Command sequences  aren't real long, while flight engineering data
can get real long,  especially if you miss a DOwnlink.

Plus, i would expect the spacecraft Uplink receiver is omni directional,
unlike the Downlink antenna which is highly directional,  so that in
case the spacecraft takes a funny point angle,  you can still
whistle it up and tell it to SAFE.

The less gain on the antenna,  the less directional and the less
bandwidth.

Look at galileo.  HGA antenna 115 kbs at jupiter.
LGA antenna  1 KBS,  but it's probably an Omni antenna.  I think
it was meant as an engineering downlink antenna.  

pat

MO  may have a smaller conical antenna  for engineering data.

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

Date: Wed, 17 Mar 1993 00:56:15 GMT
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Mars Observer Update - 03/16/93
Newsgroups: sci.space

In article <16MAR199312462649@csa2.lbl.gov> sichase@csa2.lbl.gov (SCOTT I CHASE) writes:
>Why are uplink and downlink at different data rates?  Does the spacecraft
>have a better transmitter than receiver?  I presume that we can transmit
>as well as we can receive, so that the difference must be due to some 
>spacecraft design issue.

Simple:  it *needs* higher downlink data rates.  All that ever gets sent
up are commands, which are not particularly bulky and are not sent very
often.  A lot more data comes back, especially if there are imaging
instruments aboard.  So it's worth spending mass and power on a powerful
(well, relatively powerful) transmitter for high downlink rates, but
not worth busting a gut on receiver design for fast uplink.
-- 
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  henry@zoo.toronto.edu  utzoo!henry

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

Date: 17 Mar 93 02:01:21 GMT
From: "Frank Ch. Eigler" <fche@db.toronto.edu>
Subject: Mars Observer Update - 03/16/93
Newsgroups: sci.space

In article <16MAR199312462649@csa2.lbl.gov> sichase@csa2.lbl.gov (SCOTT I CHASE) writes:
>Why are uplink and downlink at different data rates?  Does the spacecraft
>have a better transmitter than receiver?  I presume that we can transmit
>as well as we can receive, so that the difference must be due to some 
>spacecraft design issue.

henry@zoo.toronto.edu (Henry Spencer) writes:
>Simple:  it *needs* higher downlink data rates.  [...]

Also, receivers can be a lot more complicated than transmitters in the
case of some error detection/correction coding systems, e.g., one of
those on the Galileo craft.  The computational requirements of
transmitting and receiving are not necessarily symmetric.
-- 

-- Frank Ch. Eigler -- Comp Eng -- <eigler@ecf.toronto.edu> -- (I'm Brian!)

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

Date: 17 Mar 93 02:36:26 GMT
From: Steve Collins <collins@well.sf.ca.us>
Subject: Mars Observer Update - 03/16/93
Newsgroups: sci.space

the data rates differ beccause the antenna and transmitter on the ground
can put out lots more power than the spacecraft transmitter.
    Steve Collins MO spacecraft team AACS

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

Date: 17 Mar 93 02:40:34 GMT
From: Steve Collins <collins@well.sf.ca.us>
Subject: Mars Observer Update - 03/16/93
Newsgroups: sci.space

We have both low and highgain antennas . The lowgain is fairly
omnidirectional.
I believe we are using highgain for both uplink and downlink at this point.
another factor in the data rates, is the need for the uplink to have
very good signal to noise. Otherwize the command decoder won't recognize
the commands and you will have to resend. Ifyou lose a little engineering
telemetry in the downlink, it s no big deal...
 steve Collins MO SCT AACS

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

Date: 16 Mar 1993 20:28:18 -0500
From: Pat <prb@access.digex.com>
Subject: Response to various attacks on SSF
Newsgroups: sci.space

In article <1993Mar16.182250.19602@aio.jsc.nasa.gov> mll@aio.jesnet.jsc.nasa.gov writes:
>be documented.  Requirements, documentation and management may not be
>the most romantic aspects of the space program, but without them,
>nothing will fly. 

Boeing has an adage : "When the weight of the Documentation exceeds the
weight of the airframe,  the plane will fly".

The differnce, is that when the airplane stops flying,  we do know who
to talk to.  Boeing has had some real problems,  but most people have
confidence, that they understand and are mostly on top of the problems.

Boeing has a small fleet of planes that just take off and land every day
to test landing cycles.  They have pressure hulls, that they pressure
cycles thousands of times to test for stress.  They have old birds on
dynamic test beds to test wing load over time.   

I don't see that kind of approachin SSF.  All the old NASA programs
built  spares and ground simulators to test all systems.  SSF
has too much tied to the flight hardware only.  

pat

They're testing the vehicle before it flies,  but wouldn't it be nice
if they built 3 vehicles.  a pathfinder,  the flight article and
a flight spare, that they could use for ground testing, training
and advanced life cycle testing?

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

Date: Wed, 17 Mar 1993 01:49:43 GMT
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Sisters of Mars Observer (was Re: Refueling in orbit)
Newsgroups: sci.space

In article <1993Mar16.173626.17712@den.mmc.com> seale@possum.den.mmc.com (Eric H Seale) writes:
>>... There's no particularly good reason why a commercial
>>comsat or something of that ilk couldn't function perfectly well around
>>Mars or Venus, with minor adjustments to things like the size of the
>>solar arrays.
>
>Speaking as a spacecraft-type, these "minor adjustments" have a very
>nasty tendency to snowball.  At first glance, all you have to change is
>the size of your solar arrays and high-gain antenna.  But wait -- now
>your solar arrays generate TOO MUCH power while you're at Earth (gotta
>resize the power control circuitry)...

No, just tilt the arrays until you're out at Mars distance.  I believe
that's what Mars Observer did, and it's certainly what Mariner 10 did
to solve a similar problem.

>And the longer comm distances mean
>you have to have higher-power communication gear (make the solar arrays
>bigger again...)...

Higher power than a comsat's transponders?  I doubt it!  Of course, you
do need some power for the instruments as well.

>... Oh, and the bigger arrays / comm gear / computer mean the
>structure needs to be beefed up some (and of course, a commercial
>satellite isn't built to handle the loads imposed during escape from
>Earth's gravity).

Commercial comsats are typically built to use solid-fuel apogee motors,
which administer just as much of a kick as anything used for Earth escape.

>And did you remember to add the extra propulsion gear
>to get into Mars' orbit?

Why not just use a solid motor, like Magellan did?  You don't need
spacecraft mods for that (assuming power etc. for cruise is okay in
a high-gee configuration).

>It's not at first apparent, but by "customizing" an existing spacecraft,
>you can easily end up with a more expensive bird than if you had just
>started from scratch...

No argument there.  It's easy to just let change after change creep into
the design.  You need hard-nosed management that insists that the words
about "minimum changes" be taken seriously, even if it means compromises.
Controlling changes is not easy, especially if your organization is used
to doing uncompromised full-custom designs.

I'm actually being unjustly hard on Eric, here -- he raised some good
points that I've deleted, and it *can* turn out that using the existing
design just doesn't work -- but there are more variables than just the
technical ones, and I suspect those extra variables were more important
in the case of the Observer design.
-- 
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  henry@zoo.toronto.edu  utzoo!henry

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

Date: 17 Mar 93 02:52:59 GMT
From: Steve Collins <collins@well.sf.ca.us>
Subject: Sisters of Mars Observer (was Re: Refueling in orbit)
Newsgroups: sci.space

Well the MO managers I work with are pretty hard nosed when it comes to
cost...
and the GE managers tried hard to contain cost too since they were working
to a fixed price. Slipping off the shuttle was a big driver I undestand,
since it changed the spacecraft mass allowable.
Another  technical issue is radiation tolerance  since earth orbiters
are protected from the solar wind by the geomagnetic field. Knowing
what I know about MO, I feel they did a pretty good job of using existing
hardware and experince and applying it to a MARS mission. You really can't
just put a bigger booster under a commercial satelite...
steve Collins

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

Date: 16 Mar 93 20:24:00 PST
From: "RWTMS2::MUNIZB" <MUNIZB%RWTMS2.decnet@rockwell.com>
Subject: Solar Arrays Falling Off

I know this discussion took place a while ago, but I feel I should
add to it (and I've been way behind in my reading!).

"David B. Mckissock" <dbm0000@tm0006.lerc.nasa.gov> writes:

<2. Yes, the Loads & Dynamics Working Group has calculated . . .
[discussion of PV array plume loads deleted]

George William Herbert <gwh@soda.berkeley.edu> replies:
<	I cannot post further information 
<from what I know about the WP problems without
<burning sources.  Suffice it to say that while the
<information you have given here is in no way indicated
<false by any source I have seen or heard, it also does
<not contradict what my sources said.

As an Engineering Specialist and the Lead Engineer for On-Orbit
Structural Loads and Dynamics analysis at Rocketdyne (WP-4),
I can verify that what Dave said is essentially correct.

However, George also said:
<	I have specific information about 
<management's impact on simulation and calculation
<methodologies from a totally non-technical standpoint
<which makes all the technical results extremely 
<QUestionable.

I would not say that management in general has compromised the
technical results by making us change numbers, but certain individuals
(at all levels of the program) have questioned our perception of the 
reality of this problem.  Additionally, the structural dynamics 
community has had to fight an uphill battle with the bureaucracy to 
resolve the situation.  Case in point, the Level II Loads and Dynamics 
Working Group (LDWG) released on-orbit plume loads in 9/91 and 1/92.  A 
Change Request was initiated 2/93 to pass these down to the Work 
Packages.  The request was approved by the Level II Control Board in 
6/92, signed by upper management in 11/92, sent to the Centers in 12/92, 
and sent to the contractors in 1/93.  During this time there were no 
official Level II loads except those that dated from the 5-meter truss 
days (very obsolete!).  Rocketdyne project management could not respond 
to these loads since they were not a contract requirement ("gold 
plating" is a no-no), despite the input of the technical community 
saying that the problem would not just go away.  I'm sure that the same 
thing has happened in other disciplines, and I hope that Goldin's 
proposal to change SSF's Byzantine management structure will allow things 
to proceed more quickly in the future.

Dave also said:
<   options list). Also, some folks question the
<   validity of the calculated loads - the computer code
<   used to calculate the plume loads is unverified.

The plume physics community is unanimous on the possibility that the 
actual loads could be different from the predictions.  But some say the 
loads are lower, and others say higher.  This puts the decision in the 
manager' hands as to risk assessment.

and:
<   Finally, NASA could always install an auto-pilot
<   on the Shuttle, to automate the docking procedure,
<   and this whole issue would become moot.

I have repeatedly brought this up before the LDWG.  There have been 
other options proposed such as making the Vernier thrusters (24 lbf, 106 
N) redundant at a cost of $ 15.5 million (1984 dollars, not including 
recertification of hard- and software), thus eliminating the need to use 
the Primaries (870 lbf, 3870 N).  However, since these would require a 
Shuttle redesign the Station program office has little authority in this 
area.  Maybe Goldin's proposed "holistic" approach to lowering 
life-cycle costs instead of only development costs will allow another 
look at some of these options.

On a more technical note,

"Dr. Norman J. LaFave" <lafave@ial4.jsc.nasa.gov> writes:
<As someone who does plume analysis, I can state that the problem
<is still there despite the distance. Furthermore, the flexible
<dynamics of the solar arrays are worsened by the truss through
<dynamic coupling.

We did some analysis that showed that PV Array the stand-alone results 
were about 10% lower than those from the coupled-system PMC model.  I 
believe that part of the difference is from plume forces on the Module 
Cluster, thus forcing the truss torsional modes which couple with the 
Array bending modes (the frequencies and mode shapes are only part of 
the calculations, the generalized force has to be considered as well).

Followups to e-mail? (since the discussion on the net has drifted away 
from this).

Disclaimer: Opinions stated are solely my own (unless I change my mind).
Ben Muniz     MUNIZB%RWTMS2.decnet@consrt.rockwell.com    w(818)586-3578
Space Station Freedom:Rocketdyne/Rockwell:Structural Loads and Dynamics
   "Man will not fly for fifty years": Wilbur to Orville Wright, 1901

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End of Space Digest Volume 16 : Issue 325
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