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Date: Sun, 12 May 91 02:18:51 -0400 (EDT)
Subject: SPACE Digest V13 #532

SPACE Digest                                     Volume 13 : Issue 532

Today's Topics:
		       Re: Saturn V and the ALS
		      Re: Why the space station?
			 Re: Laser launchers
		     Re: IT'S OVER (no it isn't)
			 Re:  Saturn V vs ALS
		      Re: Why the space station?

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

Date: 8 May 91 23:20:39 GMT
From: hela!aws@uunet.uu.net  (Allen W. Sherzer)
Subject: Re: Saturn V and the ALS

In article <1991May8.200236.26166@aio.jsc.nasa.gov> dbm@icarus.jsc.nasa.gov (Brad Mears) writes:

>Your attitude is very understandable, but you left something out.  How can 
>NASA regain the trust of the general public (or even Congress)?  Presumably, 
>the only way to regain your trust is to build a launch vehicle that fulfills 
>the promises made for it.  But we can't build another launch vehicle because 
>we failed once.  Catch-22.

Well you got to remember an important factor here. NASA intends to spend
over ten billion dollars to build this thing. They need a LOT of trust to
do that. Also, the fact that other contractors are willing to sign fixed
price contracts to build a very similar vehicle for 5% of that price does
not make me think NASA needs all that money to build ALS.

>You say that we have to "prove" that ALS will work.  HOW?  How do you PROVE
>it without building it? 

First explain to me why it costs $10 billion and ten years to do what
McDonnell and Martin say can be done for $500 million and four years.
What's wrong with their approach?

>This isn't a flame.  It is a serious question.  How can NASA shake the bad
>rep it got over Shuttle?  

First, admit they have a problem. Their request for new orbiters every year
imply to me that they think things are just fine. Then I would like to see
more emphasis on commercial procurement of ordinary launch services.

>But don't condemn NASA forever or we'll never get anything built.

Why is NASA the only agency who can build things? 

>IMHO, everbody learned something from Shuttle.

What did NASA learn from the Shuttle? From what I see they think everything
is fine (except that Congress should buy more orbiters). This is also not
a flame but a serious question.

  Allen
-- 
+---------------------------------------------------------------------------+
|Allen W. Sherzer |        Allen's tactics are too tricky to deal with      |
|   aws@iti.org   |             -- Harel Barzilai                           |
+---------------------------------------------------------------------------+

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

Date: 9 May 91 01:52:53 GMT
From: stanford.edu!agate!headcrash.Berkeley.EDU!fcrary@decwrl.dec.com  (Frank Crary)
Subject: Re: Why the space station?

In article <1991May8.175644.19089@engin.umich.edu> kcs@sso.larc.nasa.gov (Ken Sheppardson) writes:
>  The requirements for carrying out the sort of vehicle processing 
>  tasks we're talking about are on the order of 14 crew and 150 kW.
>  You also need a place to put the vehicles while you're working on them
>  (e.g. to provide debris protection in LEO).
>
What are these numbers based on? I would think they would be strongly
dependant on the type of in-orbit construction, and the desired construction 
time.

    >[ I said in respect to the cost of launching Mir] 
    >A 5 Titan-launched-size modules is MUCH cheaper than Freedom
>
>  Excuse me?

If it requiresa longer statement: The Mir space station, which if it
had been configured for orbital construction would have been on par
with Freedom PMC, was/will be launched with (excuse me, my number was
incorrect) 6 modules launched on a Proton SL-13 rocket. The Proton  
places 20 tonnes into low earth orbit. It is therefore on par with the
US Titan launcher. Therefore, orbiting Mir would cost about the same
as launching 6 Titans. Freedom PMC will require 17 shuttle filghts.
6 Proton (or Titan) launches is MUCH cheaper than 17 shuttle flights.

>  Sure. Are you saying we should never build space structures larger than
>  some specific dimension? What do you propose as that limit?
>
>  One benefit of a design with lots of open space is that you have lots
>  of open space. Something you need when you want to attach all sorts
>  of payloads and vehicles.

No, but I think that a space structure should be as compact as possible.
I do not place a great value on expanding Freedom to fill its truss
structure. By the time we get around to doing this much, Freedom will
be VERY old. (e.g. well behind the state of the art.) Based on future
technology and experience gained from Freedom, I feel a second generation
space station would be more cost effective and usefull than expanding 
Freedom.

				 Frank Crary
				 UC Berkeley

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

Date: 9 May 91 04:35:30 GMT
From: ogicse!emory!wa4mei!ke4zv!gary@ucsd.edu  (Gary Coffman)
Subject: Re: Laser launchers

In article <40584@fmsrl7.UUCP> wreck@fmsrl7.UUCP (Ron Carter) writes:
>In article <2753@ke4zv.UUCP> gary@ke4zv.UUCP (Gary Coffman) writes:
>
>>Then add in the fact that
>>atmospheric blooming will reduce the delivered energy of the beam
>>by a factor of 1000 to 1000000 at high altitudes
>
>Support this assertion.  What conditions are you assuming?  What
>sort of optical system, etc?  The sun puts ~1KW/m^2 onto the
>California desert, and nobody notices thermal blooming.
>
>An optical system designed to avoid blooming will have many mirrors,
>and mirrors much larger than the target.  This will keep the power
>density much lower than a simplistic system, with one aperture equal
>to the size of the target.

Well we have to decide first how much power is needed at the target.
Let's assume a payload mass of 1000 kg. With a conventional rocket engine 
we are talking gigawatts. If we have unlimited working fluid, considerably 
lower power levels can be used. It would take longer to reach orbit, but 
with unlimited ground based energy, and an unlimited working fluid, the 
payload would eventually get there. The problem is that above 5 km the
sensible atmosphere is inadequate as a working fluid for any reasonably
sized payload. This means that we have to carry reaction mass along
with the payload. Now we fall under the same constraints as a chemical
rocket. We must attain the highest specific impulse that we can to keep
the amount of dead weight reaction mass to a minimum. This in turn means
that we need to deliver the same amounts of power to the payload as
would be supplied by a chemical rocket, again, gigawatts. To avoid
turning the atmosphere to plasma, we need to keep beam intensity below
about 100 Kw/m^2. To deliver a gigawatt that requires the beam to be
spread over 10,000 square meters. But that would require a collector
at the payload of 10,000 square meters. Otherwise, as the beam narrowed,
a point would be reached where the energy density per square meter would
begin to turn the atmosphere to an optically opaque plasma. A collector
of 10,000 square meters wouldn't be very aerodynamic to say the least.
A much smaller payload would require less total energy, but to minimize
reaction mass would still require high power from the beam. 

>Energy costs are a tiny part of the current cost of space launches.
>Trading energy for efficient use of capital (being able to run the
>launcher for 12 hrs/day, for example) would make laser-launchers
>practical even if they used 10x the energy/kg of rockets.

This is very true and is what makes laser launchers look attractive at
first glance.

>>but fundamental physical laws would have to be broken
>>for it to pay off.
>
>My bogosity meter pinned again.

You gotta get that thing fixed. :-)

>>At the power levels required to loft real payloads
>>into orbit, atmospheric blooming is an intractable physical problem.
>
>Consider the power level of the solar energy striking the ground,
>and tell me why sunlight isn't an intractable physical problem.
>Now consider the power levels of a laser launch.  What is the
>greatest power density which avoids blooming?  Now, how much
>aperture is required?  Did you ever ask yourself this question?
>If not, shame on you.

I have, see above.

>>Talk to the guys who have actually
>>fired high power lasers, the laser fusion folks, and see what they
>>say about the absolute necessity of having a hard vacuum to fire the
>>beam through.
>
>I'd prefer that you do sanity checks on your statements before
>posting them.  Imploding fusion pellets is a very different
>problem than vaporizing a layer of a meter-wide target.  It
>takes vastly greater power levels and faster rise times.  The
>pitfalls experienced by the LF workers will not be applicable.

I'm afraid that you are wrong. Newton's third law still holds.
You're going to need a lot of reaction mass heated very hot and
moving very fast to get your payload in orbit. That's going to
require very high beam power levels from very powerful lasers
focused on a relatively small target. The best experience in
that field is the work of the laser fusion folks. Their lasers
aren't as big, or as powerful, as a launch laser would have to
be, but their target is considerably smaller so their beam
power densities are comparable.

>>Tethers need to exceed the theoretical strength of materials limits by
>>orders of magnitude to work. Again, a fundamental scientific breakthrough,
>>not engineering R&D, needs to occur before tethers can become reality, if
>>ever.
>
>How many tether studies have you read?  Did you ever read anything
>about non-synchronous tethers, or work any figures yourself?  If
>not, you are talking through your hat.

I have read studies, and I have done back of the envelope calculations
myself. No chemical bond known to science has the strength to support
a geosync to earth tether. Non-synchronous tethers have so many monumental
problems that I dismiss them from consideration due to the sheer complexity
of their possible operation. Some of the designs might just be technically
possible, but the operational requirements they would impose just don't
make them realistic contenders.

I still must maintain that the best way we know of to get above the
sensible atmosphere is wings and air breathing engines. Above that
point the best way we know to drive reaction mass is to use the chemical
energy locked in that mass directly via a rocket engine. Indirect input
of the energy through laser beams adds needless complication and inefficiency
to the process without showing noticable benefits. Indeed, the problem of
delivering that much energy to a distant fast moving object through the
sensible atmosphere appears to make such a system completely impractical.

Gary

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

Date: 8 May 91 13:48:00 GMT
From: mcsun!inesc!unl!unl!jpc@uunet.uu.net  (Jose Pina Coelho)
Subject: Re: IT'S OVER (no it isn't)


In article <813@newave.UUCP> john@newave.UUCP (John A. Weeks III)
writes:
	[...]

> Now what does any of this have to do with sci.space.  Will humans ever
> develop warp drive?  Are there any holes in the quantum theory and
> relativity that might allow warp drive?

Yes, but the holes are 0.1 milimeter in diameter so, only an Hamburger
can travel above lightspeed.

--
Jose Pedro T. Pina Coelho   | BITNET/Internet: jpc@fct.unl.pt
Rua Jau N 1, 2 Dto          | UUCP: ...!mcsun!unl!jpc
1300 Lisboa, PORTUGAL       | Home phone: (+351) (1) 640767

- If all men were brothers, would you let one marry your sister ?

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

Date: 8 May 91 01:36:37 GMT
From: mintaka!think.com!rpi!dali.cs.montana.edu!milton!hardy.u.washington.edu!brettvs@bloom-beacon.mit.edu  (Brett Vansteenwyk)
Subject: Re:  Saturn V vs ALS

One other thing to consider now that the move is definitely on to find an
alternative launch system to the Shuttle:  what about spending some of this
development money in a supersonic transport?  It would seem that developing
a plane to take a 300000lb payload to high altitude at supersonic speed would
not push the technology (size would seem to be the biggest problem).

The reasoning is thus:  to support a Pegasus type launcher, if not Pegasus
itself.  This would be an extension of the "NASA supplies the launch facilities"
argument.  Such a launcher would have a prayer of being efficient and cost-
effective (as Pegasus seems to be already).  This transport would be our
flyback first stage booster equivalent (launch from a 70000ft altitude).  I have
always been curious as to what difference using the XB-70 would have made to
the X-15 or its successor.

One thing I do not have a feel for:  would the transport launch the orbital
stage while supersonic, or will it do a hard climb, drop below supersonic, and
then "toss" the vehicle?  I do not know how hard it is to do a supersonic
separation.

			--Brett Van Steenwyk

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

Date: 8 May 91 17:21:41 GMT
From: elroy.jpl.nasa.gov!sdd.hp.com!caen!news@decwrl.dec.com  (Ken Sheppardson)
Subject: Re: Why the space station?

yamauchi@cs.rochester.edu (Brian Yamauchi) writes:
>kcs@sso.larc.nasa.gov (Ken Sheppardson) writes:
>>yamauchi@cs.rochester.edu (Brian Yamauchi) writes:
>
>>>Perhaps now that the scientists have said, in effect, that they don't
>>>want Freedom, the design could be moved back toward the initial goals
>>>of supporting lunar and planetary exploration.
>
>>  Given the station we have today, there's not a whole lot of extra
>>  capability that you could cut if you were to decide that SSF was going to
>>  be dedicated to the support of lunar and planetary exploration. You still
>>  need to habitation space, the power generation capability, and the limited
>>  lab space of the current design.
>
>How about cutting the materials science research altogether?  For that
>matter, since the ESA and NASDA modules are going to be devoted to
>research, how about eliminating the lab space and power requirements
>from the NASA modules and doing the life sciences research in the
>ESA/NASDA modules?

   Amazing...I actually have _numbers_ for some of these things...

   In terms of power and crew, your requirements are about the same
   whether you're performing a 'core R&D' function or a 'vehicle
   processing' function. You need approx 150 kW and around 14 crew
   members.

   In terms of experiment racks, given the traffic models we have for
   utilization by the various disciplines, things break down like this
   for the 'core R&D' utilization emphasis:

       19.5   International Users
       13.5   General Lab Support Facilities/Lab Support Equipment
       10.0   Life Sciences
       10.0   Technology Development
        6.0   Commercial Payloads
        5.0   Microgravity Research
       ----
       64.0   Racks required

   During vehicle processing, you don't use any more/less racks, your
   power and crew are just allocated to the processing activities. If
   you wanted to eliminate _all_ materials processing functions and
   only do vehicle processing and the life science necessary to support
   SEI, you'd probably be able to eliminate the micro-g racks, some of
   the technology development, and some or all of the commercial payloads.
   I'm not sure how many of the technology development racks are dedicated
   to material science, but I think the number is fairly low. At MOST
   you're going to be able to reduce your total number of racks by
   21 (assumes all tech dev is for mat sci)...so...

       64.0
      -21.0
       ----
       43.0  Racks required (no material science capability)

   The 27' US Lab module has 24 racks. At PMC, 12 are system racks (i.e.
   ventilation, power distribution, etc) and 12 are 'User Racks'. As of
   March, ESA had 23 user racks available and JEM had 11. That give you
   a total available of 46 at PMC. Since then ESA has reduced their
   modules volume by ~20%. I don't know how that translates into number
   of racks, but you can see that you NEEDED 43 racks to do only life
   sciences, you HAD 46, and now you have even fewer. If you assume the
   ~20% reduction in ESA module volume translates into a 20% reduction
   in available user racks, you now have something like 41 racks total.

   As you can see, you're not going to be able to eliminate the US Lab
   if you hope to retain your ability to accomodate the life sciences
   necessary to support SEI.

>>  PMC is pretty much the minimum
>>  viable permanently manned station one can come up with given the
>>  constraints imposed by launch vehicle, the current program structure,
>>  contracts already awarded, consideration of sunk cost, and politics.
>
>Hmmm...  Interesting that only one of these constraints (the launch
>vehicle) is technical.  

  I see I made my point. :)

>I wonder whether it wouldn't be cheaper (and faster) to start over from
>scratch.

  Good question. 

>Why not put together a small (!) team of experts (technical personnel,
>not bureaucrats) from the various NASA centers (and perhaps other
>labs, companies, and universities, as well) to design a space station
>with clear goals in mind (orbital support of lunar/planetary
>exploration) -- with the only constraints being engineering, cost, and
>time?

  That's what we did during Restructuring. Really. Honest. :/

>If this were done right, it might not even delay construction. (Is
>first element launch still scheduled for 1995?)  In fact, given the
>remaining budget ($26 billion) and time (nine years to PMC) of the
>current station, I would be surprised if such a team couldn't come up
>with a station that was much better suited to the goals of space
>exploration.

  Heh.

===============================================================================
 Ken Sheppardson                                  Email: kcs@sso.larc.nasa.gov
 Space Station Freedom Advanced Programs Office   Phone: (804) 864-7544
 NASA Langley Research Center, Hampton VA         FAX:   (804) 864-1975
===============================================================================

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

End of SPACE Digest V13 #532
*******************