Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_1/V11_152.TXT

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Subject: SPACE Digest V11 #152

SPACE Digest                                     Volume 11 : Issue 152

Today's Topics:
        Re: Resolving Power of Hubble Space Telescope
              Re: Sandia Railgun
                 test
            Teacher in Space - Wherefore?
            Shuttle glow, erosion in orbit
         Re: SR-71 Record Flight Information
        DIGITAL IMAGE PROCESSING AND ASTRONOMY
            Global Positioning System News
              Galileo Update - 03/14/90
----------------------------------------------------------------------

Date: 14 Mar 90 17:53:15 GMT
From: cs.utexas.edu!mailrus!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Resolving Power of Hubble Space Telescope

In article <[e-mail]> [e-mail] (David Ray) writes:
>... It is my understanding that this 0.1 arcsecond requirement
>is the most stringent attitude control requirement of all spacecraft
>history. Is this true?

I believe so, with the possible exception of spy satellites.  They had
some trouble making that attitude-control system work, as I recall, and
operating it will not be trivial.

>Just curious, does anyone have any information on the attitude control
>plan for the HST spacecraft? ...

Well, generally, it has momentum wheels controlled by star trackers.
It presumably has some way of desaturating the momentum wheels, and the
usual way of doing that is with a magnetotorquer system.

>1. Whenever anything moves on the spacecraft, such as filter wheels
>   on the focal plane, electrical relays tripping, etc., this "shakes"
>   the spacecraft, and I assume more than 0.1 arcseconds. How is this
>   handled? Does one wait for the atitude "jitter" to dampen, and then
>   start to take data?

Given long exposures, compensating for it as it happens seems more likely.
I wouldn't be surprised if as much as possible of this sort of thing gets
done while the telescope is slewing from one target to another.

>2. In order to know that the spacecraft attitude is within the 0.1
>   arcsecond (or whatever) allocation, a separate, independent system
>   such as a star tracker or inertial tracking system must be used.
>   What is planned to be used and what is its sensitivity?

Most of the outer portion of the telescope's field of view goes to the star
trackers.  (The wide-field/planetary camera gets one quadrant of it.)  For
any given observation, a set of guide stars are picked, such that those
stars will be within the field of view of the star trackers when the
telescope is pointed where it's supposed to go.  The trackers then hold
the precise attitude desired.  (I believe there is also a "coarse" system
with an ordinary inertial platform to control gross movements like
slewing.)  The guide-star catalog is expected to be a significant reference
work for astronomers all by itself; it's enormous.  The star trackers are
precise enough that they sort of qualify as an extra instrument, and I
think there are plans to do astrometry work with them.
--
MSDOS, abbrev:  Maybe SomeDay |     Henry Spencer at U of Toronto Zoology
an Operating System.          | uunet!attcan!utzoo!henry [e-mail]

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

Date: 15 Mar 90 20:26:25 GMT
From: pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!sunybcs!uhura.cc.rochester.edu!rochester![e-mail]  (Paul Dietz)
Subject: Re: Sandia Railgun

In article <[e-mail]> [e-mail] (Donald Lindsay) writes:
...
>Seen in a recent magazine:
...
>The Sandia prototype solves the problem of wear on the launcher by
>eliminating contact between the system and the projectile. Set to
>spinning at 100 rotations per second, the projectile floats through
>the system's rings using a girdle of metal.
...
>If anyone out there knows more, please post. What is this "girdle"
>trick? How do you build a multistage gun? - And like that.

This is NOT a railgun!  Railgun is not a generic term for electromagnetic
launcher.  This misconception is surprisingly common.

Railguns send a current through two rails and through a metal or
plasma armature behind the projectile.  Because there is direct
contact between the armature and rails, rail erosion is a serious
problem.  Rail guns are essentially one-turn linear DC motors, and use
very high currents.

The Sandia system is a coilgun, aka mass driver, where pulsed coils
along the barrel pull a current carrying ring.  In a coil gun there
need be no direct contact between the armature and the gun barrel.
The drive coils have many turns, and so can be energized by higher
voltages and lower currents.  In the Sandia launcher the coils are
triggered by a system using fiber optic sensors.

The girdle is a solid aluminum armature.  In a properly designed coil
gun the joule heating of the armature can be kept low enough so that
the aluminum does not melt.  The proposed Sandia gun's low muzzle
velocity (about 1/2 orbital velocity) helps here, although I think
going to > orbital velocity should be possible if the aluminum is
precooled with LN2, is cooled by transpiration, and/or is replaced
with beryllium.

For more on coil guns, see IEEE Trans. on Magnetics.  They
periodically print the proceedings of the electromagnetic launcher
conference, which covers both coilguns and railguns.

I note that the proposed location for the coilgun, in Hawaii, would
launch northeast into high inclination orbits.  Brilliant pebbles,
anyone?

    Paul F. Dietz
    [e-mail]

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

Date:     Thu, 15 Mar 90 14:16 PST
From: <[e-mail]>
Subject:  test

please ignore - this is a test

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

Date: 15 Mar 90 21:06:00 GMT
From: primerd!ENI!ENS![e-mail]
Subject: Teacher in Space - Wherefore?


The final disasterous flight of Challenger, as we all know, was the first
"teacher in flight" flight.  (This is not to be confused with the first
or subsequent "congresscritter in flight" flights).

After the disaster, Kristy McAuliffe's (Sp?) backup teacher was quoted as
saying she had every intention of fulfilling the same task on some later
flight.

What happened to this?  Has the "Teacher in Space" project quietly been
shelved?  I really don't recall hearing much about this in the remainder
of the 1990 shuttle launches.  Or am I just asleep at the switch?

Not a burning question, but I'm curious.  Thanks in advance,
Jim Cook
([e-mail])
(Email may bounce to me over the weekend, we are having our network
 worked on, partly to install a router).
Disclaimer: "Just my questions, not Prime's"

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

Date: Wed, 14 Mar 90 13:20:15 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Shuttle glow, erosion in orbit


(The following is a summary of the Nov 89 Scientific American article
"Shuttle Glow")

The atmosphere in LEO contains about 10^9 particles per cc. This is far
less than at sea level (3E19), but far more than interplanetary or
interstellar vacuum. Objects in orbit at this height experience three
main phenomena: atmospheric drag (discussed elsewhere), erosion, and "glow".

Erosion effects mainly organic matter (i.e. plastics), with the exception of
Teflon and similar compounds. (Silicone also resists erosion.) It is thought
that erosion results from impact with atomic oxygen, which combines with
and breaks up long molecular chains, eventually causing pieces of them to
float off. The exact structure of the organic compound does not seem to be
particularly important. Observed erosion during testing was up to 12 microns
over 40 hours (est. 2.5mm/year). This is enough to remove organic antireflection
lens coatings in a few hours, and to weaken thin structural members over time.

Glow is a broad-spectrum emanation observed a slight distance *above* affected
surfaces. It is thought that the surface serves as a catalyst for the
combination of molecular nitrogen and atomic oxygen to form nitrogen oxides.
Surfaces which exhibit glow show very little erosion, and vice versa. The
main problem with glow is that it can interfere with optical instruments.
Unfortunately, the substance that has produced the most intense glow observed
thus far is the black antireflection paint normally used in telescopes.
Apparently this paint will not be used in HST (The article does not say what
will be used, if anything.)

Partly because of observations of glow and erosion, the space station is
scheduled to be placed in a fairly high orbit, where these effects will
be lessened.

Note: This article was written prior to the recovery of LDEF. Some of the
information may be updated.

John Roberts              July 22, 1376: The so-called Pyed Piper, disgruntled
[e-mail]                over nonpayment of rat extermination
                                         fees, leads the children of Hulberstadt
                                         to a nearby hill called Hamelen, which
                                         opens up and engulfs them.
                              1377-1990: Nothing.

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

Date: 14 Mar 90 17:07:02 GMT
From: linus!alliant![e-mail]  (Paul Cantrell)
Subject: Re: SR-71 Record Flight Information

In article <[e-mail]> [e-mail] (Bruce Lowerre) writes:
>In article <[e-mail]>, [e-mail] (Peter Kapner) writes:
>> Interesting notion.  What does everyone think?  *Is* there a mach 4 bird
>> hidden deep in some hanger just waiting to come out and reconnoiter at
>> 100,000 feet?
>
>Better than that.  The replacement is the space shuttle.  The SR-71 was
>developed to replace the U-2.  The U-2 became obsolete when the Russians
>developed a cannon ball that could be blasted high enough to shoot it down.
>The SR-71 became obsolete when satellites were developed with telescopic
>cameras good enough to photograph the license plate of a car.
>
>As for mach 4 at 100,000 feet, the dream of hypersonic flight with scramjet
>engines is being researched.

The space shuttle is not useful for this. One requirement for a reconnaissance
ship is being able to launch at short notice to any part of the world. Not only
can't the shuttle launch reliably on short notice, it has a limited duration of
a week before it has to be brought back down.

As for the SR-71 being obsolete because of satellites with telescopic cameras,
I doubt that this is really true. First of all, my guess (it's only that) is
that the satellites are not as good as a U-2 or SR-71 at gathering electronic
emmission intelligence. Also, doesn't it take a fair amount of time to move
a satellite into different orbits so as to get a good look at the place you
want to observe? Satellites are also pretty predictable, so depending on what
it is you are trying to observe, the people on the ground probably can tell
with a high degree of reliability when the satellite will be overhead. I assume
that for fuel reasons you can't make the satellite vary the schedule for when
it will be over the target area.

Finally, I personally doubt whether a non-film system such as KH-11 really has
that kind of resolution. I can easilly believe that a film based system on
a satellite or an SR-71 might have that resolution. My doubt, however, is not
based on any expertise in the field, so I wouldn't be too surprised if I'm
wrong.

Finally, as for mach 4 @ 100,000 feet, my own personal guess from AW&ST is
that Aurora IS the SR-71 replacement, flies at mach 5-8 using a pulsejet
for propulsion, is unmanned, operational, and is the reason that SR-71 is
being retired.

Or maybe thats all just disinformation. Dunno.

                        PC

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

Date: 15 Mar 90 16:37:46 GMT
From: eru!luth!sunic!tut!naakka.tut.fi![e-mail]  (Kotalampi Risto)
Subject: DIGITAL IMAGE PROCESSING AND ASTRONOMY


Would someone have any information about digital image processing
applied in astronomy? Any IEEE papers? Any books? Please reply via
e-mail, because I don't read these newsgroups regularly. Thanks in advance.

# Risto Kotalampi [e-mail]   # Phones :                           #
# Tampere University of Technology # Work (room SL 212) : (931) 162 921 #
# Signal Processing Laboratory     # Home               : (931) 615 025 #
# P.O.Box 527, 33101 TAMPERE       # Radioclub (SH 101) : (931) 162 010 #

# Risto Kotalampi [e-mail]   # Phones :                           #
# Tampere University of Technology # Work (room SL 212) : (931) 162 921 #
# Signal Processing Laboratory     # Home               : (931) 615 025 #
# P.O.Box 527, 33101 TAMPERE       # Radioclub (SH 101) : (931) 162 010 #

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

Date:        Fri, 16 Mar 90 00:16:28 AST
To: [e-mail],
        "Space Digest" <[e-mail]>
From: [e-mail]
Subject:     Global Positioning System News


STUDY OF GPS AND GLONASS INTEGRITY MONITORING
---------------------------------------------
Inmarsat has awarded Trimble Navigation a six-month contract for a design of a
satellite-based worldwide integrity monitoring network for the GPS and Glonass
satellite positioning systems.  Trimble will work with the Worcester Polytechnic
Institute (Worcester, Massachusetts) and Leeds University to design a system to
monitor the status of both GPS and Glonass satellites and warn users within
seconds of satellite malfunctions.  Warnings would be transmitted over
Inmarsat's third-generation satellites.

(Source: Aviation Week & Space Technology, 5 March 1990)


GEOLOGICAL SURVEY OF CANADA LAUNCHES AUTOMATED GPS MONITORING SYSTEM
--------------------------------------------------------------------
In mid-December, the Geophysics Division of the Geological Survey of Canada
(GSC) began the continuous operation of two GPS monitor stations located at the
Algonquin Radio Observatory (ARO) in Ontario and the Pacific Geoscience Centre
(PGC) on Vancouver Island.  The GPS monitoring is performed using Texas
Instruments TI 4100 RAM receivers, HP A900 minicomputers, and a monitor software
system developed in-house over the past year.

The GPS (30 second samples) binary and meteorological data are collected and
archived at each station, then daily transmitted via the DATAPAC packet network
to a central minicomputer located in Ottawa.  All operations are fully automatic
with no operator intervention required.  As soon it is received in Ottawa, the
phase data is preprocessed and reduced in near real-time, providing a daily
baseline solution and improved orbits.  The data transmission, reduction, and
archiving is typically completed before 07:00 EST.  Currently (23 February
1990), the visibility window between PGC and ARO for satellites 3, 6, 9, 11, 12,
13, 14, and 16 is between 04:15 and 11:15 UT.

The GSC GPS monitoring system incorporates a number of unique features including
o  automatic synchronization of tracking between selected sites
o  complete station control and display from remote terminals
o  switching between satellites to effectively increase the number of satellites
   that can be tracked with a TI 4100
o  complete on-line help and other useful functions.

The GSC system is a contribution to the Active Control System pilot project of
the Geodetic Survey of Canada.

For more information, tracking data, or improved orbits, contact Jan Kouba,
Geological Survey of Canada, at [phone]

========================================================================
Richard B. Langley                  BITnet:  [e-mail] or [e-mail]
Geodetic Research Laboratory        Phone:   [phone]
Dept. of Surveying Engineering      Telex:   014-46202
University of New Brunswick         FAX:     [phone]
Fredericton, N.B., Canada  E3B 5A3
========================================================================

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

Date: 14 Mar 90 20:14:25 GMT
From: pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!usc!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov![e-mail]  (Ron Baalke)
Subject: Galileo Update - 03/14/90



                     GALILEO MISSION STATUS
                         March 14, 1990

     The distance from spacecraft to Earth today is 62 million
miles, which means that it takes a radio signal more than 11
minutes to go up to the spacecraft and back.  The heliocentric
velocity is 88,211 mph, and declining as the spacecraft pulls
away from the Sun.  Galileo has gone more than 256 million miles
since launch and has about 391 million to go before the first
Earth gravity assist in December.

     Spacecraft health continues to be excellent, with most
measured temperatures, pressures, and electrical parameters as
expected, except for the voltage imbalance in the AC and DC power
bus, which has been relatively stable for the past six weeks.
The system power margin is at 58 watts. A total of 1818 real-time
commands have been transmitted to Galileo.  Of these, 959 have been
pre-planned in the sequence design and 859 were not. In the past
week, a total of 10 real-time commands were transmitted; 4 were
pre-planned and 6 were not. Galileo is routinely doing sun-point
maneuvers about every two days; the telemetry rate is now 10 bits
per second.

     Major activities this week included memory readouts of
Star Intensity Data Buffer, Reset Command Loss Timer, switching
the telemetry rate to 10 bps.

     In addition to the three photos sent back from Galileo's flyby
of Venus last month, some infrared light measurements designed to
study Venus' lower atmosphere has been sent back as well as
ultraviolet measurements and data from sensors designed to detect
dust and magnetic fields in space around Venus.

 Ron Baalke                       |    [e-mail]
 Jet Propulsion Lab  M/S 301-355  |    [e-mail]
 4800 Oak Grove Dr.               |
 Pasadena, CA 91109               |

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

End of SPACE Digest V11 #152
*******************