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Subject: SPACE Digest V12 #615

SPACE Digest                                     Volume 12 : Issue 615

Today's Topics:
         NASA Headline News for 11/28/90 (Forwarded)
           Radiation on LLNL (was: ELV Support...)
                 Re: Astro-2
        Re: Translunar/interplanetary shuttle?
    Re: $$/pound of Freedom vs LLNL (was: ELV Support...)
              Re: Photon engine

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
  [e-mail].  Other mail, esp. [un]subscription notices,
  should be sent to [e-mail], or, if urgent, to
             [e-mail]

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

Date: 30 Nov 90 07:25:13 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: NASA Headline News for 11/28/90 (Forwarded)


             Headline News
Internal Communications Branch (P-2) NASA Headquarters
Headquarters

Wednesday, November 28, 1990 Audio Service: 202/755-1788
1788

This is NASA Headline News for
Wednesday, November 28, 1990

NASA flight operations managers yesterday announced Dec. 2,
1990, as the launch date for the Columbia STS-35 Astro-1
mission.  The launch window opens at 1:28 am on Dec. 2 and
extends for two-and-a-half hours until 3:58 am EST.

The launch date was selected following completion of the STS-35
Flight Readiness Review.  Shuttle director Robert Crippen noted
"the Shuttle team has worked very hard to get Columbia ready
to fly.  With the hydrogen leak resolved, we are ready to end the
year with the Astro-1 mission."

Aft doors are scheduled to be installed in their flight
configuration on Columbia today.  Final argon servicing of
the Broad Band X-ray Telescope is scheduled to occur
tomorrow, following which, Columbia's payload bay will be
closed out and the bay doors closed.

Turnaround processing of Discovery and Atlantis are continuing
on schedule.

  * * * * * * * * * * * * * * * * * * * * * * * * * *

A capacity crowd is expected tonight at the NACA-NASA 75th
Anniversary celebration at the National Air and Space
Museum.  Featured speakers will include Adm. Truly, Gen.
Thomas Stafford, Scott Crossfield and David Lewis.  A special
multi-media presentation will provide an overview of the past
eight decades of flight.

  * * * * * * * * * * * * * * * * * * * * * * * * * *

The Technology 2000 technology transfer conference continues
through this evening at the Washington Hilton.  Some 2,000 are
participating in this two-day symposium.  J. R. Thompson was
the awards dinner speaker last night and presented awards of
excellence to 15 organizations and a special Lifetime
Achievement Award to John Samos of the Langley Research
Center Technology Utilization office.

  * * * * * * * * * * * * * * * * * * * * * * * * * *

Dr. Lew Allen, Chairman of the Hubble Space Telescope
Investigation Board, reported to the press yesterday on the
results of his team's analysis.  The executive summary of the
investigation report says "reliance on a single test method was a
process which was clearly vulnerable to simple error.  Such
errors had been seen in other telescope programs, yet no
independent tests were planned, although some simple tests to
protect against major error were considered and rejected.  During
the critical time period, there was great concern about cost and
schedule, which further inhibited consideration of independent
tests."

  * * * * * * * * * * * * * * * * * * * * * * * * * *

A Galileo press conference will be held at the Jet Propulsion
Laboratory tomorrow, Nov. 29, at 1:00 pm EST, to discuss
recently returned data acquired by the spacecraft during its
flyby of Venus last February.  The present spacecraft status and
plans for the Earth gravity assist flyby on Dec. 8 will also be
discussed.  Participants include: William O'Neil, Galileo project
manager; Dr. Torrance Johnson, Galileo project scientist; and
key members of the science team.  The press briefing will be
carried on NASA Select TV.

NASA helps celebrate American Indian Heritage Month
tomorrow in the Headquarters auditorium with a ceremony
featuring Wilma Mankiller, Principal Chief of the Cherokee
nation of Oklahoma, and cultural entertainment as well as food
tasting.  An exhibition of Native American artifacts will also be
on display.  The celebration performances will be from 2:00 to
2:30 pm.

Here's the broadcast schedule for Public Affairs events on NASA
Select TV.  All times are Eastern.  **indicates a live program.

Wednesday, 11/28/90

    1:15 pm    **Magellan-at-Venus report from Jet Propulsion
        Laboratory.

    4:00 pm    Augustine Committee on the Future of the U.S.
        Space Program hearing (replay from Nov. 19).

Thursday, 11/29/90

    11:30 am    NASA Update will be transmitted.

    1:00 pm    **Galileo Venus flyby and Earth flyby press
        briefing from JPL.




All events and times may change without notice.  This report is
filed daily, Monday through Friday, at 12:00 pm, EST.  It is a
service of Internal Communications Branch at NASA
Headquarters.  Contact:  CREDMOND on NASAmail or at
202/453-8425.


NASA Select TV:  Satcom F2R, Transponder 13, C-Band, 72
degrees West Longitude, Audio 6.8, Frequency 3960 MHz.

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

Date: Fri, 30 Nov 90 09:33:38 -0500
From: "Allen W. Sherzer" <[e-mail]>
Subject: Radiation on LLNL (was: ELV Support...)
Newsgroups: sci.space
Cc:

In article <[e-mail]>:

++Crews do not *have* t+o be rotated>+ every 90 days, which reduces
++transport (and thus life-cycle) costs.

+Wrong.   Crews must be rotated every 90 days to limit exposure to ionizing
+radiation. Shieliding is to be provided to permit a maximum safe stay of one
+year based on allowable accumulated dose.

We have already covered this Mr. Radley. The yearly radiation dose on a LLNL
type station is LESS than the dose for 90 days on Freedom (one things DoE
labs know a *LOT* about is radiation).

+LLNL at a higher altitude will have a more severe radiation
+environment than Freedom.

Which is why they orbit at a lower altitude. Before you bring up the issue
of fuel for boosting, I remind you (we already went through this as well)
that it's already included in their budgets.

+Also, the shielding capability of LLNL's non-
+metallic structure is much less than Freedoms aluminum modules.

Using non-metalic materials minimized secondary effects. To show how
much they have thought about this issue, you should realize that they
have, as part of the design, a 'storm shelter' built in. During periods
of high solar activity, they can go to a module with water shielding to
wait it out. In this sense, they are far safer than Freedom.

   Allen

--
+---------------------------------------------------------------------------+
|Allen W. Sherzer| I had a guaranteed military sale with ED-209. Renovation |
|   [e-mail]  | programs, spare parts for 25 years. Who cares if it      |
|                | works or not?  - Dick Jones, VP OCP Security Concepts    |

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

Date: 30 Nov 90 05:03:31 GMT
From: dftsrv!heawk1![e-mail]  (Keith Arnaud)
Subject: Re: Astro-2

In <[e-mail]> [e-mail] (Stephen Strazdus) writes:

>Is there an Astro-2 flight in the works for the Space Shuttle?  I would
>imagine the instruments used in Astro-1 are not going to be thrown away
>after a 10 day mission.  Are they?  Are the second mission's plans
>very dependent on the first mission?
>--
>--------------------------------------------------------------------------------
>Steve Strazdus  |  [e-mail]  |  Insert your favorite .sig here.

The original plan (circa 1984, I think) was for Astro-1 to be followed by
Astro-2 and Astro-3 however there is no followup flight currently on the Shuttle
manifest. The instruments will certainly not be thrown away - we need them to
check the calibration.

                 Keith Arnaud            Waiting for Astro
                 [e-mail]


--
------------------------------------------------------------------
| Keith Arnaud              | internet : [e-mail]|
| Code 666/Univ.Md.         |     span : lheavx::arnaud          |
| NASA/GSFC                 |   bitnet : arnaud@rosatbit         |

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

Date: 30 Nov 90 17:55:23 GMT
From: att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!ub!ubvmsd.cc.buffalo.edu![e-mail]  (Craig L Cole)
Subject: Re: Translunar/interplanetary shuttle?

In article <[e-mail]>, [e-mail] (Millard Edgerton) writes...
>If the engines(mains) are not restartable, HOW DO THEY FIRE TO DE-ORBIT?
>
>THINK ABOUT IT!

The main engines don't. The two medium-size engines on the back fire.
They're called the Oribtal-Maneuvering-System (OMS) engines.

Craig Cole
[e-mail]
[e-mail]

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

Date: Fri, 30 Nov 90 20:55:07 -0500
From: "Allen W. Sherzer" <[e-mail]>
Subject: Re: $$/pound of Freedom vs LLNL (was: ELV Support...)
Newsgroups: sci.space
Cc:

In article <[e-mail]>:

>>>Once it [LLNL] is "fleshed out" its dollar per pound cost to
>>>weight ratio will be about the same as Freedom.

>>Would you mind justifying this a bit better?

>Certainly.

First of all, you haven't given much justification. Without stating
the weight and cost of both structures I don't see how you can
expect to consider your staement justified.

>1) - without using numbers  admittedly, but the lighter hull materials
>of LLNL only account for a small portion of the overall vehicle.

If memory serves, the entire LLNL station minus crew and consumables
weighs *LESS* then just the truss of the current Freedom configureation.
That off the bat gives it a big head start. LLNL can add all the rest
(science module) for the same weight as Freedom and still come in way
ahead.

>Copper wire on LLNL will weight the same as it does on Freedom, for example.

Yes it does. On the other hand, since LLNL is bought outside the FAR's
(unlike Freedom) it costs a hell of a lot less. When computing cost/pound
that counts. Not only is LLNL a lot lighter for the same capability, it
costs less as well.

>2) - the lightweight material of LLNL advantage is largely negated
>by being much bigger in volume than the Freedom habitable areas,
>because it spins.

Spinning has nothing to do with it. As to the volume, why not? The
marginal cost of additional volume is so cheap (unlike Freedom) there
is little penalty.

>A nonspinning smaller LLNL would be more competitive.

Depends. If you want to reduce costs by stretching out rotation,
the answer is a clear no.

>Nobody has responded to my point about long term radiation doses,

I assume you have seen my reply so I won't repeat it here.

  Allen

--
+---------------------------------------------------------------------------+
|Allen W. Sherzer| I had a guaranteed military sale with ED-209. Renovation |
|   [e-mail]  | programs, spare parts for 25 years. Who cares if it      |
|                | works or not?  - Dick Jones, VP OCP Security Concepts    |

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

Date: Fri, 30 Nov 90 21:01:36 EST
From: John Roberts <[e-mail]>
Disclaimer: Opinions expressed are those of the sender
    and do not reflect NIST policy or agreement.
Subject: Re: Photon engine


>From: mcgill-vision!thunder.mcrcim.mcgill.edu!clyde.concordia.ca!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
>Subject: Re: Photon engine

>In article <[e-mail]> [e-mail] (Henry Troup) writes:
>...Shuttle power output at launch is 15-20 gigawatts, I believe.

>However, the inequality you propose doesn't work.  There is no unique
>answer to the question of power output for a given mass at a given
>acceleration.  It depends on the exhaust velocity.

>A 100T ship at 1G (call it 10 m/s^2) requires a thrust of 1MN.  Thrust
>is mass flow times exhaust velocity, by conservation of momentum.  At
>an exhaust velocity of 3e8 m/s, naively (ignoring relativistic issues),
>we need 3.3e-3 kg/s of mass flow.  Kinetic energy over time of that flow,
>with respect to the rocket, naively, is 0.5*mass_flow*ve^2, or about
>15e13 W.  Call it 150 terawatts.  I'd have to hit the books to sort out
>the non-naive version of this, but it probably won't differ by more than
>a small integer, and it might even be the same.

>From various sources, the momentum of a photon is h / wavelength, where h is
Planck's Constant, 6.625E-34 kg*m^2/s. From this it can be derived that the
force of a directed beam of photons is equal to power / c. Your number of
3.3E-3 kg/s is the mass-equivalent of the power of the necessary photon
beam, but using the non-naive formula E = m * c^2, the power would be
~3E14 W = 300 terawatts.

Some other interesting general formulae to compare photon drives and matter
reaction mass drives:

Drive           momentum xfer / energy
-----           ----------------------
photon          1 / c
matter          2 / v

which illustrates that a matter drive will always give more than twice as
much thrust per joule than a photon drive (since v < c). Also, a matter drive
uses energy more efficiently when exhaust velocity is lower, which means that
it is always in your best interest to use as much reaction mass as you have
available. Pushing against a large celestial body (i.e. linear launcher) is
particularly efficient. Note that the force of a photon drive depends only
on the power radiated - wavelength is irrelevant.

I can think of one exception to this rule. If you use a "pure" energy source
such as antimatter, and if you have a certain mass budget for fuel plus
reaction mass, then you get marginally more thrust by dedicating the whole
mass to equal quantities of matter and antimatter, to be blasted out as
photons, than by setting aside some additional normal matter as reaction
mass. If I calculated correctly, setting aside one nth of the fuel mass as
reaction mass results in sqrt((n^2 - 1) / n^2)) as much thrust. For instance,
5 kg of matter and 5 kg of antimatter for a pure photon drive should give
about 3E9 Newton-seconds of thrust, while 5.5 kg of matter with 4.5 kg
antimatter would only provide about 99.5% as much thrust, and 7.5 kg matter
with 2.5 kg antimatter would only give about 87% as much. If you ever find
a really good sale on antimatter, you should keep this in mind. :-) In the
meantime, antimatter being many times as expensive as matter, most people
would choose a mix with much more reaction mass than antimatter.

>I don't have numbers handy for the whole species or total power, but the
>electrical power generating capacity of the US is circa 1 terawatt, I think.

>Handling 150TW would be, um, a challenge.  For example, assume an efficiency
>of 50%.  (That's awfully good for lasers, which are inherently pretty lossy
>devices.)  That means our total power output actually has to be 300TW, and
>the missing 150TW comes out as heat.  We have to get rid of that heat...
>somehow.  The only long-term answer is radiators, but they're big and heavy.

As Christopher Neufeld pointed out, if the heat can be preferentially
radiated in a certain direction, for instance from a big flat disk with
an insulated back, then it can act as part of the photon drive, providing
about half as much thrust as a directed beam. This brings up the option I
mentioned, which is using the radiator as the thruster, and eliminating the
expense and maintenance of a laser. In the worst case, a 100% efficient laser
will only give twice the thrust of a radiator per watt supplied. A 50%
efficient laser would only provide a 50% increase, and so on.

Since a driving radiator isn't really cooling anything, it can run hotter,
which has important implications for the size of radiator needed. In the
example given, the thrust can be supplied by a 600 TW radiator, or by a
200 TW laser and a 200 TW radiator. Assume the driving radiator can be
run at 3500K (a little below the melting point of thorium oxide), that the
laser can be run at 2500K, and that the radiators act approximately like
black bodies. I believe radiated energy per unit time is described by the
formula E = k * (T^4 - T0^4), where T0 is the ambient blackbody temperature
(essentially zero), and k is the Stefan-Boltzmann constant, 5.6696E-8
W / meter^2 * Kelvin^4. The radiator-drive therefore requires a disk of only
9.5 km diameter, while the laser-radiator drive requires a 10.7 km diameter
disk, showing that the radiator-drive system would be somewhat more practical
on a 100000 kg , 1G photon ship. :-) If the laser can not operate at over
1000K, then its directional radiator must be about 67 km in diameter.

Conclusion: for just about any conceivable application, a photon drive
craft with a self-contained power source is a very very very bad choice,
but if you just have to have one, a simple radiator drive is probably better
than a laser. Again, this does not apply to systems in which the laser is
just a way of getting power to the craft from a remote source (i.e. launcher
systems), and to solar sails, in which the energy is obtained free from the
sun, and from which you get up to double the kick from each photon if you
use a reflective sail.

>"I'm not sure it's possible          | Henry Spencer at U of Toronto Zoology
>to explain how X works."             |  [e-mail]   utzoo!henry
        John Roberts
        [e-mail]

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

End of SPACE Digest V12 #615
*******************