HDTenEightyP/NetNews huggingface dataset:
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: pocket satellite receivers
Date: Sat, 7 Nov 1992 05:54:39 GMT
Organization: U of Toronto Zoology

In article <1992Nov3.084856.25305@netcom.com> hage@netcom.com (Carl Hage) writes:
>... Suppose we end up with a president who places
>a higher priority on commerce rather than restricting the military buildup
>of countries like Iraq, and accurate navigation information is declassified.
>
>  1. Can the "noise" be turned off, or do we need new satellites?

The noise is entirely controlled from the ground, and can be turned off.
It was turned off during the Gulf War because US military forces were making
extensive use of commercial GPS receivers.

Certain commercial users, like aviation, are never going to be comfortable
with a system that might get noisy again without warning (any time that DoD
convinces the president that there's an emergency).  They would really like
to see a navsat system that was not run by the military.

>  2. I thought selective availability mean't that noise was injected only
>     during a military operation, e.g. the Gulf War...

Nope.  DoD's position is that selective availability is *on* by default
and is turned off only for good reason, e.g. the Gulf War.

>     ...Why do I read that commercial units still don't
>     have the accuracy that military units have, i.e. how is full precision
>     information transmitted?

The military units also make use of a more sophisticated (and potentially
secret) high-precision timing code and multi-frequency operation.

>  3. Would special or extra hardware be required to receive full precision
>     information over existing receivers?

You can get the full benefit of the low-precision code with off-the-shelf
commercial receivers.  (Well, except that there are a lot of people looking
at clever ways to get better precision out of it, so this situation might
change.)  Fancier gear is needed for the high-precision code etc.

>  4. Is differential GPS used just to overcome the selective availability
>     noise, or are there other sources of error?

There are other sources, although the primary motive for differential GPS
certainly is selective availability.
-- 
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  henry@zoo.toronto.edu  utzoo!henry
Newsgroups: sci.space
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: Scenario of comet hitting Earth
Date: Sat, 7 Nov 1992 06:41:23 GMT
Organization: U of Toronto Zoology

In article <720888184snx@syzygy.DIALix.oz.au> cam@syzygy.DIALix.oz.au writes:
>I get the feeling that there has been a serious over-estimate of the ability
>of a nuclear warhead to significantly change the delta-v of an asteroid.
>Project Icarus (from what I remember) suggested exploding a device at 
>the aphelion point so as to move the asteroid away from the earths orbit.
>I can't recall anything about doing it "near" the earth...

You need to run some diagnostics on that memory. :-)  Project Icarus's
timescale permitted nothing of the kind.  "...to make the rendezvous at
Icarus's aphelion of November 1967, the space vehicle would have to have
been launched 8 months earlier, that is, within a few weeks after the
problem was posed.  Such a launch time was of course impossible...
Launch dates in 1968 were accepted as feasible only on the basis of
adaptation of existing hardware and by postulating top emergency priority
in all related technical and industrial efforts..."

The first Icarus interception was to be at 20 million miles, 13 days
before impact, this being about the farthest possible with the assumed
hardware.  Three more would take place over the next eight days, with
range closing to 7.7 million miles.  Finally, two low-altitude attacks
would occur in fast succession less than a day before impact, at 1.41
and 1.25 million miles.  The high-altitude interceptions would use
100MT bombs and would attempt to deflect Icarus.  The low-altitude
ones would have roughly twice the payload mass available, plus much
more precise guidance, and would use the most powerful bombs available
in an attempt to destroy as much of the asteroid and/or its fragments
as possible.  The estimate for all six missions was a 71% chance of
successful deflection, with most of the remaining possibilities
involving fragmentation plus destruction of at least some fragments.

>Anyway, this
>would only work if the object was small.

Icarus is about 700m across, which is actually pretty large for an
Earth-crossing asteroid.

>Also, has anyone addressed the problem of guiding such a device to the
>precise point at short notice?  What if the object is travelling
>retrograde?  A doubt you could lob a nuclear device at an asteroid/comet
>with sufficient accuracy.  Especially if we are talking combined
>velocities of >30 Km/s.

See the Project Icarus study for the gory details of how to do it with
mid-1960s technology at a closing velocity of about 40 km/s.  Not simple
but not impossibly hard.
-- 
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  henry@zoo.toronto.edu  utzoo!henry
From: amon@elegabalus.cs.qub.ac.uk
Newsgroups: sci.space
Subject: Re: Ten embarrassed questions about the moon (very long)
Date: 12 Nov 92 23:28:14 GMT
Article-I.D.: cs.BxMMM8.7Fq.1
Distribution: sci
Organization: [via International Space University]
X-Added: Forwarded by Space Digest
Original-Sender: isu@VACATION.VENARI.CS.CMU.EDU

> You don't see these phenomena on the Earth, because over the long run it
> behaves pretty much like a flexible crust floating on a liquid interior,
> so any local area of high density tends to sink down, and any region of  
low
> density tends to bob up, so out at the distance of Earth orbit, the 

> anomalous effects tend to cancel out - in other words, the Earth is in 

> 


John: A slight difference of opinion. Although what you say is true to an  
extent, there are some gravity differences on Earth. In fact, a good laser  
altimeter can read off major underwater features from the differences in  
ocean hieght. Sea level is a relative term. In some places water is  
actually going "up hill" and "down hill" in sync to the gravitational  
anomalies caused by subsea massifs and such.

There are also some differences on land. Although the isostatic  
equilibrium you name is certainly real, it doesn't always track rapid  
changes, so there can be highs and lows to some extent.
From: higgins@fnalo.fnal.gov (Bill Higgins-- Beam Jockey)
Newsgroups: sci.space
Subject: Re: SUMMARY of 1st NASA TOWN MEETING -- Raleigh NC (long)
Date: 13 Nov 92 18:51:55 GMT
Organization: Fermi National Accelerator Laboratory

In article <1992Nov13.160320.16902@samba.oit.unc.edu>, cecil@physics.unc.edu (Gerald Cecil) writes:
> Jon Leech & I were among the 700 people at the 1st NASA Town Meeting, held on 
> Monday afternoon 2-6:30 pm in nearby Raleigh.  

Thanks, Gerald, for posting your account, which was drenched in
cynicism but made very interesting reading.  I intend to show up for
the Indianapolis town meeting at IUPUI next Friday.  (I'd like to hear
from anybody else who plans to be there.)

Although he makes many negative comments, Gerald writes:

> Overall, I was fairly impressed.  I had not expected Goldin to attend & it was
> useful to spend a few minutes asking him technical questions. I hope he survives
> the change of Administration. That aspect of the format was much more successful
> than the Paine Commission hearing that I attended in '86.  NASA also solicited 
> write-in questions that they promised to answer [Netters, here's your chance!!] 
> The feel of the meeting often veered abruptly from that of an arcane 
> budgetary/technical seminar to that of a religious revival.  The 2nd stringer 
> component was less successful.  No-one in the audience appeared to have a 
> focussed question to any of the senior managers.

1. Do you think this meeting accomplished anything?  If so, what?

2. Do you think this meeting (or the whole series of meetings) will
accomplish anything that you want accomplished?  (-:

I may ask these questions again as the meetings go on across the
nation.  I'm curious about the reactions of net.people to Goldin's
effort.

     O~~*           /_) ' / /   /_/ '  ,   ,  ' ,_  _           \|/
   - ~ -~~~~~~~~~~~/_) / / /   / / / (_) (_) / / / _\~~~~~~~~~~~zap!
 /       \                          (_) (_)                    / | \
 |       |     Bill Higgins   Fermi National Accelerator Laboratory
 \       /     Bitnet:     HIGGINS@FNAL.BITNET
   -   -       Internet:  HIGGINS@FNAL.FNAL.GOV
     ~         SPAN/Hepnet:      43011::HIGGINS
From: paul@taniwha.UUCP (Paul Campbell)
Newsgroups: sci.space
Subject: Re: Metric again
Date: 11 Nov 92 16:09:51 GMT
Organization: Taniwha Systems Design

In article <1992Nov8.222219.14106@infodev.cam.ac.uk> sl25@cus.cam.ac.uk (Steve Linton) writes:

>My main beef about NASA metrication concerns precision. How often have you seen
>"This tiny widget, only about 1 inch (2.54cm) across"? If the diameter is given
>as "about 1 inch" the implied precision is about +-25%. As such, the proper
>metric form is "two or three centimeters" or "a couple of centimeters". 2.54cm
>implies a precision that just isn't there.

My father wrote a gardening book many years ago in NZ, it's still in print
and after we went metric (much easier than you think and well worth it)
they released a new version that had been 'metricfied' (my father didn't write
this bit), it included such gems as replacing:

	"Plant the seeds about an inch apart ....

with

	"Plant the seeds about 2.5cm apart ....

And this is long before anything was computerized - it wasn't done with
global search and replace ....

	Paul

-- 
Paul Campbell    UUCP: ..!mtxinu!taniwha!paul     AppleLink: CAMPBELL.P
    "There once was a president named Bush, we started giving him a push,
     Then we went hunting Quayle, got the Republicans nailed,
     And tossed them out on their tush" - Anon.
Newsgroups: sci.space
From: higgins@fnalc.fnal.gov (Bill Higgins-- Beam Jockey)
Subject: Moon can hold its air (was Re: Mars over the Moon???)
Organization: Fermi National Accelerator Laboratory
Date: Fri, 6 Nov 1992 15:45:20 GMT

In article <1ddrqjINNns7@uranium.sto.pdb.sni.de>, sav@nanette.sni.de (Dr.Savory) writes:
> Any body to be terraformed should have sufficient gravity to retain
> an atmosphere (obvious?), so exclude the moon, OK ;)

This is unfair to the Moon.  If it were magically given an atmosphere,
the Moon would retain it for a long time, at least thousands of years.

As somebody already mentioned, the Moon is not a good candidate for
terraforming because it has no large native source of volatiles. 
However, claiming that it can't hang on to an atmosphere is not valid
for short timescales.

It seems to me that anybody who had the technology to give the Moon an
atmosphere would find it easy to freshen it up every millenium or so
with new gases...

(Should I mention this?  Oh, what the heck, go ahead, Bill.  In the
absolutely clunker TV series *Space 1999* there is an episode where
precisely this happens: a mysterious alien cylinder suddenly gives the
Moon a breathable atmosphere.  The happy human crew of Moonbase Alpha,
who have spend their whole TV career huddled underground or working in
spacesuits, run outside and begin playing volleyball.  We see a shot
from outside a window of Barbara Bain and Martin Landau watching this
magic moment. Then one of them touches a control AND THE MOONBASE
ALPHA WINDOW SLIDES OPEN ELECTRICALLY.

(Back in grade school we used to say, "That makes about as much sense
as a screen door on a submarine.")

Bill Higgins, Beam Jockey              | 
Fermi National Accelerator Laboratory  | "Get the dinosaurs in, Martha, 
Bitnet:           HIGGINS@FNAL.BITNET  |  they're predicting comets."
Internet:       HIGGINS@FNAL.FNAL.GOV  |      --Dr. Barry D. Gehm
SPAN/Hepnet:           43011::HIGGINS  |
Newsgroups: sci.space
From: roberts@cmr.ncsl.nist.gov (John Roberts)
Subject: Re: Oops!
X-Added: Forwarded by Space Digest
Organization: National Institute of Standards and Technology formerly National Bureau of Standards
Original-Sender: isu@VACATION.VENARI.CS.CMU.EDU
Distribution: sci
Date: Fri, 6 Nov 1992 13:08:21 GMT


-From: franl@centerline.com (Fran Litterio)
-Subject: Re: NASA Coverup
-Date: 6 Nov 92 00:22:39 GMT
-Organization: CenterLine Software, Inc.

-Recall that astronauts did sometimes fall down on the moon and had to
-be helped up due to the bulkiness of the suits.  That's one reason why
-there were always two of them out at once.

-Then the was the time an astronaut caught his foot on a cable and
-knocked over a rack of million dollar equipment.  It was useless
-thereafter (anyone know who did that?).  

It was our hero, John Young, who later went on to fame and fortune in the
Shuttle program. He yanked the cable out of the heat flow experiment, and
it couldn't be repaired in the time available. This was a significant loss,
because relatively few of the Apollo missions carried heat flow sensors.

He *did* say he was very sorry. :-)

John Roberts
roberts@cmr.ncsl.nist.gov

Newsgroups: sci.space
From: roberts@cmr.ncsl.nist.gov (John Roberts)
Subject: Re: Coverup - gravity doesn't exist?
X-Added: Forwarded by Space Digest
Organization: National Institute of Standards and Technology formerly National Bureau of Standards
Original-Sender: isu@VACATION.VENARI.CS.CMU.EDU
Distribution: sci
Date: Wed, 11 Nov 1992 14:34:56 GMT


-From: dj@ekcolor.ssd.kodak.com (Dave Jones)
-Subject: Re: Coverup - gravity doesn't exist?
-Date: 9 Nov 92 20:22:15 GMT
-Organization: Vonnegut Tent Rentals, Inc.

-John Roberts (roberts@cmr.ncsl.nist.gov) wrote:
-> There's an apple tree on the NIST grounds that's a direct descendant of the 
-> tree Isaac Newton was sitting under when he thought up the laws of gravitation.

-Hmmm.  After that fact was disclosed in your first-day orientation class,
-were you sent out to fetch a can of striped paint ?

Don't be silly - polka-dot is the current state of the art. Though we are 
working on a new instant-drying, non-toxic, zero-mass, non-protective 
invisible paint. It's for use on brick and natural wood, where you don't 
want to hide the appearance of the original surface. It has many advantages - 
no cleanup needed, can safely be sprayed on windy days, and if you spill some, 
nobody will ever know. There are still three bugs to be worked out: 1) hard to 
assure a uniform coating, 2) costs $50 per gallon, and 3) you can't tell 
when the can's empty.

We also made up a batch of single-can camouflage paint for the military, but
somebody set the cans outside and now we can't find them. Maybe we shouldn't
have painted the labels to show the color of the contents...

Hm, I guess I'll actually have to go out there and see what the sign says...

TROMP TROMP Tromp Tromp tromp tromp tromp tromp...
(long pause)
...tromp tromp tromp tromp Tromp Tromp TROMP TROMP (creak of chair).

OK, here it is:

..............

NEWTON APPLE TREE

"Science has its traditions as well as its frontiers."

This tree is a direct descendant of the original tree whose fruit gave
inspirational impetus to Isaac Newton's theory of gravitational forces.
It was nurtured by the U.S. Department of Agriculture and transplanted
here on the grounds of the National Bureau of Standards April 1966.

..............

No sign of the gravitationally anomalous apples underneath. Either they
floated away, or the large herd of NIST Standard Reference Material
Whitetail Deer had something to do with their disappearance.

:-)

John Roberts
roberts@cmr.ncsl.nist.gov

Newsgroups: sci.space
From: gawne@stsci.edu
Subject: Re: Hubble's mirror  or Really Costar.
Organization: Space Telescope Science Institute
Distribution: sci,na
Date: Fri, 6 Nov 1992 16:56:38 GMT

In article <BxApK7.7w7@access.digex.com>, 
prb@access.digex.com (Pat) writes:

> why not design costar to also add filters.  given wf/pcs aversion
> to the moon and sun,  if you put a filtering mirror in also,  could
> you then conduct  really hi res lunar imaging?  or is this just pointless
> cuz we already have more then enough capacity.

If you get direct sunlight onto the cassegrain secondary you risk breaking
it.  You are also faced with a problem when trying to acquire guide stars
if imaging the moon.  Guide craters have been suggested but the brightness
per unit area is too high for the Fine Guidance Sensors.  Finally, COSTAR
has corrective optics for the FOS, GHRS, and FOC only.  WF/PC II contains
its own corrective optics but still won't be used for solar or lunar 
observations.  Interestingly, we use the Earth as a flat field source
all the time with the FGS's paused.  WFPC doesn't mind a bit.

> also if you can put in filters,  i think you could reduce the cone of avoidance
> around both the sun and moon,  filters on, slew aroundthe sun to target
> filters off.  i would think simpler and easier then the complex
> pirouette they do now and safe rthen closing the main aperture door.

You still risk the secondary if you do this.  Since HST has no front end
energy rejection filter it is unwise to get anywhere near solar pointing.
Also, we don't close the aperture door under normal operations.  It only
closes in a deep safe mode.

As for an annoying problem, the South Atlantic Anomaly and flapping of
the solar arrays give a lot more headaches around here than solar avoidance.

-Bill Gawne,  Space Telescope Science Institute
Newsgroups: sci.space
From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn)
Subject: Re: Lunar "colony" reality check
Organization: MIND LINK! - British Columbia, Canada
Date: Tue, 10 Nov 1992 18:08:30 GMT

> Henry Spencer writes:
>
> However, hauling substantial amounts of LH2 to the Moon appears to pose
> no particular problem.
>


        There is a lovely way to get hydrogen from low earth orbit into lunar
orbit, if you are not in a hurry.  Put the hydrogen in a tank in LEO, and
attach a low cost solar array.  Pipe the boiloff hydrogen from the tank to a
resistojet (specific impulse 850, efficiency 75%) or arcjet (specific impulse
2000, efficiency 30%).  Over a period of a year or so, the low thrust vehicle
will spiral up into a high orbit from where it can enter lunar orbit and
spiral down.
        The mass of the solar array and resistojet are not critical as the
vehicle mass is dominated by the hydrogen, not the propulsion system.  This
means that low cost components can be used. Note that this is true only as
long as you are willing to wait for the vehicle - if you insist on speeding
up the transfer, the solar panels and resistojet must be increased to a
substantial fraction of the vehicle mass, and then their specific mass
becomes important.
        Once the liquid hydrogen is in lunar orbit, a hydrogen/oxygen lunar
lander ascends from the lunar colony and brings it down.  The lander is then
refueled using some of the hydrogen, plus oxgyen from lunar sources.  The
empty transfer vehicle can then be returned to low earth orbit using a small
amount of residual hydrogen (the transfer will be fast, as the bulk of the
mass has been left at the moon).  The hydrogen transfer vehicle can then be
refurbished and reused - the solar panels will probably have to be replaced
or repaired by thermal annealing because of radiation damage suffered during
the spiral ascent through the Van Allen radiation belts.


--
Bruce Dunn    Vancouver, Canada   Bruce_Dunn@mindlink.bc.ca
Newsgroups: sci.space
From: roberts@cmr.ncsl.nist.gov (John Roberts)
Subject: Re: Man in the loop
X-Added: Forwarded by Space Digest
Organization: National Institute of Standards and Technology formerly National Bureau of Standards
Original-Sender: isu@VACATION.VENARI.CS.CMU.EDU
Distribution: sci
Date: Fri, 13 Nov 1992 04:06:43 GMT


-From: i0c0256@summa.tamu.edu (IGOR)
-Subject: Re: Man in the loop
-Date: 12 Nov 92 00:00:00 GMT
-Organization: Texas A&M University, Academic Computing Services

-Actually one is giving control to the machine so that the human can 
-THINK about what is going wrong. Most of the research in specific accidents
-such as Loss Of Coolant Accident (LOCA) are studied in a way to allow the 
-operator a safe margin of time to see what he can do to stop the whole process.

->It's true that the human is always given the last word, but then if you
->look at nuclear power plant accidents, they seem to occur most when the
->human intervenes. 

-While it might be true for the Chernobyl disaster, for Three Miles 
-Island accident even the machine
-could not do anything since they were not designed to handle this huge hydrogen
-bubble.

-Igor
-Nuclear Engineering Department
-Texas A&M University

I thought one of the the major contributors to the TMI incident was that
when things started to go wrong, the human operators panicked and *shut off*
the automatic safety systems. I had the impression that the automatic
systems might have been able to keep things relatively under control if
they hadn't been overridden.

The Chernobyl operators caused the explosion by performing a test which was
supposedly to show how safe the reactor was. In order to create a hazard
condition with which to demonstrate the recovery, they deliberately
operated the reactor far outside the specifications permitted by the safety
rules. The reactor power suddenly increased manyfold, and there was no time
for the operators to react.

This is not to say that reactors can't be designed to be much safer than
the current US models - I believe there's an ongoing effort in this direction.

John Roberts
roberts@cmr.ncsl.nist.gov

Xref: sparky sci.space:15438 rec.models.rockets:2987
From: roberts@cmr.ncsl.nist.gov (John Roberts)
Newsgroups: sci.space
Subject: Re: Ice hardness
Date: 11 Nov 92 15:30:24 GMT
Article-I.D.: cs.BxK5wn.JAz.1
Distribution: sci
Organization: National Institute of Standards and Technology formerly National Bureau of Standards
X-Added: Forwarded by Space Digest
Original-Sender: isu@VACATION.VENARI.CS.CMU.EDU


-From: andy@osea.demon.co.uk (Andrew Haveland-Robinson)
-Subject: Ice hardness
-Date: 10 Nov 92 02:15:43 GMT
-Organization: Haveland-Robinson Associates

-In article <Bx4D99.4Jy.1@cs.cmu.edu> roberts@cmr.ncsl.nist.gov writes:
->A number of science fiction writers seem to assume that water ice at
->cryogenic temperatures would be many times stronger than ice at slightly
->below freezing. Is there any indication that this is true?

-"Air temperatures down to -50'C make the near surface ice a thousand times
-stiffer than the basal ice, which geothermal heat from the underlying rock
-can bring to near melting point"

-                                    Richard Frolick, Brit Antarctic Survey
-                                            Physics World Vol5/11 p21, IOP

-I would assume that this is an indication that cryogenic ice is pretty
-hard stuff...

Thanks for the reference. I looked through the proceedings of two conferences
on ice, and all I could find is that the tensile strength of ice goes up
with decrease in temperature, at least down to -40 C.

Another characteristic of ice (at least near the melting point) is that it
"ages" - over time, it becomes more brittle.

John Roberts
roberts@cmr.ncsl.nist.gov