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Date: Fri, 19 Apr 91 01:25:56 -0400 (EDT)
Subject: SPACE Digest V13 #424

SPACE Digest                                     Volume 13 : Issue 424

Today's Topics:
		     Servicing Faulty Satellites
			 Re: Laser launchers
		Re: comsat cancellations and lawsuits
			   Re: anniversary
	  Re: spacesuits (Was: Re: HST in-orbit Maintenance)
			 Re: Laser launchers
			 Re: Laser launchers
		      Re: Nuclear powered rocket

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

Date: 19 Apr 91 08:22:16 GMT
From: comp.vuw.ac.nz!am.dsir.govt.nz!marcamd!mercury!kcbbs!kc@uunet.uu.net  (George Muzyka)
Subject: Servicing Faulty Satellites

Insurance companies that sell insurance to satellite owners are of course
having to increase their insurance premiums somewhat lately, and are
expressing concern in that they don't want to have to up the premiums
so high as to scare away satellite owners. :-)

There have of course been sugesstions and proposals for robot spacecraft
to service satellites in low or medium height orbits, but have suffered
from governmental budget constraints.

Could it be better that an international group of insurance companies 
get together and jointly fund such a robot spacecraft project themselves?
They could use a slight rise in insurance premiums (to satellite owners)
to constribute money towards the project. (Satellite owners would, 
in effect, would be securing their future, at least in the sense of 
what to do if something goes wrong). Satellite owners that intend to 
have more than one satellite launched in the near future.

Are there any specific major technical (or political) barriers stopping
a robot spacecraft of this sort be commissioned in the very near future?
Funding should be considered a negligible problem if we are to solve 
this one.

In case there are numerous arguments as to what a robot spacecraft intended
to service a faulty satellite should actually comprise of, let's home 
in on what we shouldn't have to _bulk_ our service craft up with. For
instance a year's supply of garage parts. :-) A laboratory robot capable
of good enough stability and fine adjustments to me sounds an excellent
candidate. Let's get Roby up there now!

I am interested in knowing what any (and all) the major barriers are 
with getting such a project underway. I wouldn't be surprised if someone
has already built something for this purpose already. So what's stopping
you get further?? 

Maybe pull out a redundant ex-backup spacecraft/satellite that a group 
of lab specialists can mount our dear Roby onto.

Imagine the large, glossy, colour advertisements these insurance companies
could have in popular magazines and newspapers. ''Meet our space service
technician, Roby. Roby's there when you need extra insurance''.
(A picture of Roby atop his spacecraft, a big smile with his robotic
thumbs up).

(Call him what you like, Roby is just an example).

So why the fuss now? Well Freedom's service center could still be a 
long way off yet, probably in the next decade. So let's get a test
service spacecraft up there now!

George Y. Muzyka

(George_Muzyka@kcbbs.gen.nz)

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

Date: 18 Apr 91 12:46:53 GMT
From: agate!bionet!uwm.edu!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!emory!wa4mei!ke4zv!gary@ucbvax.Berkeley.EDU  (Gary Coffman)
Subject: Re: Laser launchers

In article <1991Apr9.183817.15903@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>In article <2706@ke4zv.UUCP> gary@ke4zv.UUCP (Gary Coffman) writes:
>>
>>Even to place a 20 kg payload in orbit would be quite a trick. The only
>>laser technology capable of sufficient power is the gas dynamic laser.
>
>Nonsense.  Outfits like Avco will happily build you a CO2 laser of the
>required size, if you're willing to pay for it.  (Well, it will be a bank
>of lasers rather than a single tube, but the net effect will be the same.)
>There is some small risk involved, since it will be an unprecedentedly
>large laser, but for a 20kg system it's felt to be a reasonably understood
>scaling of existing lasers.
>
>>... It would take at least 100 times
>>as much fuel to power such a laser as would be required by a chemical
>>rocket to launch the same payload.
>
>The economics of the matter have been studied; they look feasible.  CO2
>lasers run on electrical power, not chemical fuels.  The amount of power
>needed for a 20kg system is hefty, but not to the point of needing to
>build your own power plant.
>

The only *single* tube technology currently understood that can generate
the required power is a flourine gas dynamic laser. CO2 lasers have
horrible efficiencies and terrible cooling problems. Most others are
even worse. Getting a laser system to approach 10% efficiency is very
difficult. When you have to throw away over 90% of your input energy
as waste heat before you even start beaming energy through the dense
atmosphere, you've got real problems.

Even with a gas dynamic laser where the reactants pass through only once, 
the cooling problem is severe but tractable, much like a conventional
rocket engine. Then you have to look at the problem of beaming energy 
through the lower atmosphere to your spacecraft. Very high power laser beams, 
even long wave IR beams, heat the atmosphere through which they pass to a 
superheated plasma. That plasma then becomes a very good absorber of optical 
energy further heating the gas and causing rapid expansion or "blooming" that 
sharply defocuses the beam. Suddenly, you aren't delivering much energy to
your spacecraft anymore.

>>... Like the chimera of controlled nuclear fusion, they are
>>unlikely to deliver any useful results even after hundreds of billions
>>of dollars and decades of effort are expended on them.
>
>My my, aren't we negative today? :-)  These systems are somewhat speculative,
>but we'd know a whole lot more about how practical they are if we spent, say,
>a few hundred million on building and testing prototypes.  The 20kg laser
>launcher, win or lose, would not cost billions.

Both the laser fusion people and the SDI folks have been playing with the
problem for a while now without taking money from the space program. I
think we should let them play a while longer before funding a system that
wouldn't put much useful payload in orbit.

>>small clever rockets like Pegasus, and eventually, direct to orbit 
>>aerospace planes are much more likely to be sucessful at delivering
>>payloads to orbit economically and in a realistic timeframe.
>
>Ah, direct-to-orbit aerospace planes.  As Gary Hudson put it, roughly,
>"this thing is a cross between the Concorde and the Shuttle and you
>think it's going to be cheap and on schedule?".

I think that SSTO is realistically 50 years away from routine operation.
It requires a much better grasp of SCRAMJET technology and hypersonic
lifting bodies than we have at present. An interm step, advocated by 
Von Braun and the original shuttle designers, of a flyback first stage 
is closer to current technology. Rather than their design, however, I 
envision a very large scale version of the launch system used by Pegasus. 
A conventional aircraft designed to carry an orbiter to a 40,000 or 50,000 
foot starting point. Most of the fuel of a conventional rocket is expended 
gaining those first eight miles. It's surely more efficient to take advantage 
of aerodynamic lift and air breathing engines during this early phase of 
spaceflight.

Gary

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

Date: 16 Apr 91 12:44:15 GMT
From: pasteur!agate!bionet!uwm.edu!zaphod.mps.ohio-state.edu!mips!pacbell.com!iggy.GW.Vitalink.COM!widener!hela!aws@ucbvax.Berkeley.EDU  (Allen W. Sherzer)
Subject: Re: comsat cancellations and lawsuits

In article <21541@crg5.UUCP> szabo@crg5.UUCP (Nick Szabo) writes:
>* NASA does not care about their customers.  

Agreed. The US today would have had 95% of the launch market instead of
about 40% if NASA operations people cared about providing good service.

>Other examples include... the removal of microgravity scientists out of
>the Fred plan when they asked for politically unpopular design changes they 
>require for their work.

Actually, this was a pretty gutsy move by NASA. Freedom would have long term
utility as a life science lab but not much as a microgravity facility. The
appropriations people in Congress however wanted microgravity done first.
NASA is telling the people who sign the checks to go to hell which is not
good politics. 

  Allen

-- 
+-----------------------------------------------------------------------------+
|Allen W. Sherzer | If you love something, let it go. If it doesn't come back |
|   aws@iti.org   | to you, hunt it down and kill it.                         |
+-----------------------------------------------------------------------------+

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

Date: 17 Apr 91 16:31:54 GMT
From: ptolemy!ptolemy.arc.nasa.gov!glass@ames.arc.nasa.gov  (Jay Glass)
Subject: Re: anniversary

In article <SHAFER.91Apr16094320@skipper.dfrf.nasa.gov> 
shafer@skipper.dfrf.nasa.gov (Mary Shafer) writes:
> We got a little cloisenne pin and a sticker too.  Kinda cute, if you're
> in to spacy mementos.

Yup. I also noted that the above-mentioned STS-1 tenth anniversary pin 
came in a little plastic bag labeled "Made in Taiwan"...

Jay Glass
glass@ptolemy.arc.nasa.gov

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

Date: 18 Apr 91 13:46:18 GMT
From: agate!bionet!uwm.edu!caen!sol.ctr.columbia.edu!emory!wa4mei!ke4zv!gary@ucbvax.Berkeley.EDU  (Gary Coffman)
Subject: Re: spacesuits (Was: Re: HST in-orbit Maintenance)

In article <1991Apr13.183925.11365@walter.uucp> fred@walter.uucp (Fred Walter) writes:
>
>But 100kg suits aren't a problem in a weightless environment (once you've
>actually got them up there). So this isn't that big of a disadvantage.

Can you say "inertia"? I knew you could.

Gary

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

Date: 18 Apr 91 12:54:40 GMT
From: agate!bionet!uwm.edu!caen!sol.ctr.columbia.edu!emory!wa4mei!ke4zv!gary@ucbvax.Berkeley.EDU  (Gary Coffman)
Subject: Re: Laser launchers

In article <11295@exodus.Eng.Sun.COM> fiddler@concertina.Eng.Sun.COM (Steve Hix) writes:
>In article <2706@ke4zv.UUCP> gary@ke4zv.UUCP (Gary Coffman) writes:
>>Even to place a 20 kg payload in orbit would be quite a trick. The only
>>laser technology capable of sufficient power is the gas dynamic laser.
>
>Shouldn't that be "currently capable"?
>
>Free-electron lasers have been listed fairly commonly as potential future
>laser launch candidates.
>
>So far, any type of laser is still only a candidate for laser launch system.

Well that's true, but the gas dynamic laser does have a substantial edge
in the cooling department since it's a pass through system. Any electrically
powered laser is going to be less efficient overall than a system using
primary reactants since electricity generation is, at best, a 40% efficient
system. 10% of 40% gives a 4% efficient system and that neglects all
conversion losses which would probably cut the figure in half again. And
it neglects the very real energy costs of *cooling* the laser. Electrically
powered gigawatt lasers present some awesome engineering problems.

Gary

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

Date: 18 Apr 91 13:42:51 GMT
From: agate!bionet!uwm.edu!wuarchive!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!emory!wa4mei!ke4zv!gary@ucbvax.Berkeley.EDU  (Gary Coffman)
Subject: Re: Laser launchers

In article <21528@crg5.UUCP> szabo@crg5.UUCP (Nick Szabo) writes:
>In article <2706@ke4zv.UUCP> gary@ke4zv.UUCP (Gary Coffman) writes:
>>...Lasers in general 
>>are very inefficient with less than ten percent of their input power delivered
>>as usable energy in the beam. It would take at least 100 times
>>as much fuel to power such a laser as would be required by a chemical
>>rocket to launch the same payload.
>
>Wow.  Let's start from the top:
>
>* Rocket fuel is primarily used to lift rocket fuel, not payload.  
>  Given this, rocket fuel turns out to be much less than 10% efficient.
>  Laser launch will use less fuel than chem launch of the equivalent
>  payload, not your fantastic factor of 100.

Well consider that for an electrically powered laser, conversion of
primary fuel to electricity is, at best, 40% efficient. Transmission,
control, and application of the electrical energy is, at best, 80%
efficient. And laser conversion is, at best, 10% efficient. That's
an overall efficiency of 3.2% right there. 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, and you have a system
with terrible efficiency. While for a rocket, the longer it runs, the
faster it goes since it's mass ratio is continually improving right
up until burnout.

>* The laser fuel is stored on the ground, in a convenient, cheap
>  tank or capacitor (depending on the kind of laser), not in a fragile, 
>  aerodynamic, high-tolerance, throw-away structure.  This makes all the 
>  difference in the world, as this tank and controlling this
>  tank through flight is a major part of chem rocket launch costs
>  and reliability problems.

This is *the* advantage of the laser scheme. If the power stored in
those ground mounted tanks could really be delivered to a spacecraft
at high altitude with good efficiency, then laser launching would
be practical.

>[Technology problems need to be solved for laser launch to work] 
>
>No duh.  That's why I am calling for R&D funding here.  It's no
>wonder that a launch technology that has gotten practically zero funding
>from the space establishment still has problems that need to be
>solved.  These problems are considered tractable by the folks who 
>have done the most high-power laser R&D, SDI.  The basic rationale 
>for funding the new launch technologies are the potential improvements to 
>be made in the basic launch cost variables, like what fuel is used and 
>where/how it is stored.  Laser launch is far superior to the current
>art in these basics, therefore it should be researched.  To argue that 
>R&D problems remain, therefore we should not fund the R&D, shows a 
>massive conservativism opposed to progress in reducing the costs of 
>getting into space.  

I wasn't arguing that R&D engineering problems need to be solved so
much as I was arguing that fundamental physical laws prevent the system 
from being a practical, efficient, alternative to rockets. We could
throw hundreds of billions into an R&D engineering program to develop
anti-gravity too, but fundamental physical laws would have to be broken
for it to pay off. At the power levels required to loft real payloads
into orbit, atmospheric blooming is an intractable physical problem.
Once the air is ionized into a plasma, the plasma is optically opaque
cutting off further power transfer. 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.

>>Another technique discussed here recently is the railgun.
>
>It is thought by most that the best EML for space launch
>is a coilgun, not railgun.  You also ignore gas gun, tethers, and
>several other options that have been discussed as potentially
>delivering large improvements and needing more R&D funding.
>You mention NASP, which is also interesting, but the potential
>advance is probably not more than a factor of two, and unless the 
>development costs can be brought down significantly it will not 
>lower launch costs.   If costs can be brought down, a comparable 
>share, about 10%, of funding for hypervelocity and scramjet research 
>is desirable.

Railgun, coilgun, gasgun, whatever, all are technically feasible for
small payloads that don't mind thousands of Gs. If you try to scale
them up to worthwhile payload size, or try to stretch them out for
reasonable G forces, then either the enviornmental problem of ground
level hypersonic shock waves, or the sheer physical size of the launcher
make them impractical.

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.

Science fiction is all well and good, but the best way we know to go
up through the atmosphere is with wings and air breathing engines.
Above the sensible atmosphere, the rocket is still king. A combination
of the two technologies, either with a flyback carrier, like Pegasus,
or with a scramjet hypersonic lifting body is the technically feasible
path to the future.

Gary

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

Date: 18 Apr 91 17:26:06 GMT
From: agate!bionet!uwm.edu!zaphod.mps.ohio-state.edu!rpi!news-server.csri.toronto.edu!utzoo!henry@ucbvax.Berkeley.EDU  (Henry Spencer)
Subject: Re: Nuclear powered rocket

>From: rcg@lpi.liant.com (Rick Gorton)
>>I remember some program back in the 50s-60s era of a nuclear rocket engine that
>>left radioactive material all over the atmosphere...
>The name of the project was Project Pluto...
>	[Hmm, sounds like Project Orion.  You're better off
>	 asking in sci.space anyway. --CDR]

Actually this confuses two separate projects, and asking about Project Pluto
in sci.space might be unproductive.

Project Orion was a (large!) rocket propelled by nuclear bombs.  Fallout
from an Orion launch would have been comparable to a single atmospheric
hydrogen bomb test, and it would have launched several thousand tons of
payload into orbit.  Despite some attempts to get funding out of the
military, Orion was basically a civilian space project.

Project Pluto was an intercontinental cruise missile powered by a nuclear
ramjet, with a cruising speed of Mach 3 at sea level and an essentially
infinite range.  This is what the Air&Space article was about.  Pluto was
undertaken more or less as a backup project when ICBMs still looked iffy.
The extremely high speed would have made it fiercely difficult to intercept.
Design work got as far as a test firing of an experimental (not flight
ready) engine, which worked.  The success of the ICBM projects removed much
of the need for Pluto, and certain practical problems started to get more
attention:  it was decidedly unstealthy, the need to fly it over friendly
territory to reach the Soviet Union was troublesome because its radiation
(an unshielded gigawatt reactor) and shock wave were lethal to anything
near its path, and the final nail in its coffin was the impossibility of
testing it safely.
-- 
And the bean-counter replied,           | Henry Spencer @ U of Toronto Zoology
"beans are more important".             |  henry@zoo.toronto.edu  utzoo!henry

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

End of SPACE Digest V13 #424
*******************