Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_2/V16NO266.TXT

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Date: Thu,  4 Mar 93 05:45:24
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #266
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu,  4 Mar 93       Volume 16 : Issue 266

Today's Topics:
                  Alternative Space Station designs
                         Battery help needed!
                                Blimps
               Deadhead to orbit (WAS Re: SSF Resupply)
       Jupiter and Venus followons (was Re: Refueling in orbit)
     Lunar Li and F (was Re: How to power the LEO-moon space bus)
                          Refueling in orbit
      Safety of flyby & aerobraking for large payloads at earth
software engineering vs. civil engineering (wasRe: Nobody cares about Fred?)
                     SOLAR gravity assist?  NOPE.
                    Spaceflight for under $1,000?
                     Stations vs. constellations
                        Stupid Centaur Tricks
              The Planetary Society and Mars Exploration
                      Water resupply for SSF (?)

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

Date: Tue, 2 Mar 1993 11:50:00 GMT
From: Nick Szabo <[e-mail]>
Subject: Alternative Space Station designs
Newsgroups: sci.space

[e-mail] (Edward Dansavage Wright) writes:


>I am interested in
>alternative designs such as inflatable structures, geodesic
>dome configurations etc.

For inflatables, look for technical publications on LLNL's
"Great Exploration", a proposed astronaut mission to Mars which
featured inflatables.  A very old book _Space Power_ by Cox and Stoiko
from the 1960's, discusses inflatable habitations on a lay level.

It would be fairly inexpensive to launch an inflatable LDEF,
and an inflatable greenhouse, which could serve as testing
prototypes without putting people at risk.  The inflatable
greenhouse could be quite useful in its own right, if
supplied by native comet & asteroid materials.


--
Nick Szabo                     [e-mail]

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

Date: 2 Mar 1993 16:41:09 GMT
From: Chad Barret Wemyss <[e-mail]>
Subject: Battery help needed!
Newsgroups: sci.space,sci.electronics,sci.aeronautics,sci.chem,sci.engr

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>
>I think I'd look into the sexier battery technologies, like nickel-hydrogen
>or silver-zinc, first.
>--

And just how does one decide which batteries are "sexy"  :-)

Chad Wemyss
Worcester Polytechnic Institute

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

Date: Tue, 2 Mar 1993 15:15:29 GMT
From: Frank Crary <[e-mail]>
Subject: Blimps
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Dave Rickel) writes:
>|> If we are assuming a pre-existant base, I think chemical energy would
>|> be the best option: It's quite easy to seperate carbon dioxide into
>|> carbon monoxide and oxygen. It would be fairly easy for a base to
>|> produce, and exploration vehicles to burn, this sort of fuel.

>And it could be useful as a rocket fuel.  It's quite a bit less energetic than
>H2/O2, but then Mars has a lower escape velocity.  It should be easier to
>build an SSTO on Mars burning CO/O2 than an SSTO on Earth burning H2/O2

I'm not sure about a single stage to orbit, but CO/O2 is a very
popular choice among manned Mars architectures that use local fuels.
(The Case for Mars II architecture, for example.) Methane/oxygen
runs a close second: You have to assume some small amount of hydrogen
is available (either subsurface water, permafrost, humidity slowly
leached out of the atmosphere or carried from Earth), but it is
much more energetic than carbon monoxide/oxygen...

                                                    Frank Crary
                                                    CU Boulder

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

Date: Tue, 2 Mar 1993 16:56:10 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Deadhead to orbit (WAS Re: SSF Resupply)
Newsgroups: sci.space

In <[e-mail]> [e-mail] writes:

>In article <[e-mail]>, [e-mail] (fred j mccall 575-3539) writes...
>>In <[e-mail]> [e-mail] writes:
>>
>>Are you postulating that the typical Shuttle launch will be going to
>>the station with over 20% deadhead carge space?  Sounds like time to
>>build another vehicle and switch to it, to me, if that's the case then it
>>is time to switch to another launch vehicle

>Hey Fred if you look at the Expendables, most of them go up with anwhere from
>5 to 25% deadhead.

No doubt.  And the smaller the payload the larger that percentage
probably is.  After all, if you're launching on a booster that can
loft 40k and you're only using 25k of that, why not use a cheaper
booster that can lift less in the first place?

>The one that I am most familiar with is the Delta and
>on the GPS missions has almost 1000 pounds of excess capacity.  In addition
>to this there is over 2000 lbs of excess fuel left in the second stage after
>orbit insertion.  It is very hard in the space world to exactly match the
>capabilities of the launchers with the payload. Getting within 10% of that
>is a very good goal.

Yes, and deliberately adopting a plan that requires boosting twice as
much mass as you need to is probably *not* a very good goal.  It is,
however, the plan that is being followed and which you are defending.
How many launches do you know of that have a 'spare' 10k-15k pounds of
lifting capacity that they just don't happen to be bothering to use?

>This is why secondary payloads are a very good
>market for expendable vendors to pursue.  Why this is not done every day
>escapes me, but NASA is paying MacDac millions for our secondary payload
>of 75 kg.  Not bad for basically free money.  Arianne does this with the
>ASEP platform that launched the microsats.

And how many of them are launching 10k-12k pounds of 'secondary'
payload?

>It would be interesting to
>see a survey of launcher capability vs launcher payload.  I will bet you
>there is a lot of wasted capability in every program out there.

Yes, and there will be even more if we follow your philosophy and
simply say that it's ok if everything we send up is twice as heavy as
it needs to be because, after all, there's some amount of waste
anyway.


--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

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

Date: 2 Mar 93 05:54:19 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: Jupiter and Venus followons (was Re: Refueling in orbit)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Matthew DeLuca) writes:
> In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>
>>And if your science mission does succeed,
>>it's back to square one again (where are the followup missions for Galileo
>>or Magellan?).

Henry, you might look at the Discovery Program Workshop report. There
are, of course, no funded-and-approved followups but there is no
shortage of ideas.  Two of the 11 finalists are Venus missions.

>          % Venus Multiprobe Mission involves placement of 14
>small entry probes over one hemisphere of Venus to measure winds,
>temperature and pressure.  Principal Investigator:  Richard
>Goody, Harvard University, Cambridge, Mass.
>          % Venus Composition Probe enters Venus' atmosphere in
>daylight to measure atmospheric structure and composition on a
>parachute descent.  Principal Investigator:  Larry W. Esposito,
>University of Colorado, Boulder.

A Jupiter mission is pretty hard to do on $150M, but there is one
tricky candidate.  I don't know if it counts as a followon by your rules:

>          % Earth Orbital Ultraviolet Jovian Observer will study
>the Jovian system from Earth orbit with a spectroscopic imaging
>telescope.  Principal Investigator:  Paul Feldman, Johns Hopkins
>University, Baltimore.

Rejected misions included:

Jupiter Polar Orbiter
Radio Science & Astronomy Mission for giant planets
Jupiter Skimming Orbiter
Io Mapper (send a copy of the Pluto Fast Flyby spacecraft to orbit Io)
Venus Orbiter-- Deep Atmosphere Temperature Sounder
Venus Atmospheric Dynamics Imaging Radiometer
A really strained acronym: "A Planetary/Heliospheric Recannaissance
   of Dynamics: Ionosphere, Thermosphere, and Exosphere (APHRODITE)"
Venus Cloud Structure and Dynamics Lighntning Observations Upper Atmosphere
    Loss Processes Discovery Mission (I think it's VCSADLOUALPDM, but they
    seem to think it's CLOUD)
Venus 4-D Discovery Mission (look at atmosphere with NIMS, CCD camera, thermal
    IR scanner)
Venus Geophysical Network Pathfinder (engineering test of 1-year(!) hard lander
   using RTG-powered active refrigeration)
Discovery Venera Surface-Atmosphere Geochemistry Experiments (SAGE) (another
   Venera lander)
Venus Interior Structure Mission (three Pioneer-Venus-type hard landers with
   seismometers)
Discovery Mission Concept to Investigate Venus' [sic] Rotation and Atmospheric
    Dynamics using Grounded and Floating Radio Beacons
    (6 beacons on surface, 6 aloft.  I would worry that anybody with such a
    long-winded project name would have trouble with the "faster" part of
    "faster, cheaper, better..." Also, I'd hate to trust a
     spacecraft development program topeople who aren't sure how
     to use apostrophes or capitalize.)
University Cooperative Venus Mission (atmosphere and plasma composition)

(Be warned:  the report doesn't have more than a paragraph of description of
any of these.  If you want juicy technical details you'll have to contact
the proposers themselves.)

Back to Matt:

> Galileo and Magellan *are* followup missions, to the Pioneer and Voyager
> series of probes.

Quite true.  I've asked Magellan people about followups, but the data
set will be so overwhelming that it will be a decade before anybody
can figure out what to do with *better* radar imaging!  Let's stick to
talking about Galileo.

> For myself, I'd like to see what Galileo discovers before
> trying to design a followup to it; there's no telling what we may want on
> the next probe.

A good point, but Galileo was launched in 1989 and you don't *need*
its results to start designing a successor.  And it's easy to think of
many followups, some cheap, some expensive:

--To start with, a "Galileo" multidisciplinary orbiter for the other
three gas giants (Cassini represents one for Saturn)

--Ditto for atmospheric probe

--Orbiters to map all four Galilean satellites (can they carry gamma-ray
spectrometers, or is it hopeless in the radiation belts?  Optical and
infrared multispectral, at least)

--A fleet of small particles-and-fields probe for looking at the Jovian
magnetosphere at several points simultaneously

--More atmosphere entry probes to study global variation in composition,
structure, clouds, weather, etc.

--Probes with longer duration than an hour or two (this is why Josh
Hopkins, Tom Nugent, and I are interested in balloons.  Results from
Galileo's probe may help the engineering here.)

--Landers to do chemistry or seismometry on the Galileans, or maybe
smaller satellites

--Retrograde satellite mission which uses a Jupiter assist to chase the
outer retrograde satellites (good candidate for electric propulsion,
flyby or rendezvous;  if you're ambitious it might even test Jovian
aerobraking)

There's a lot of science left to be done, just not much cash to spend
on it.  In the long run I'd like to see a propellant plant operating
at the edges of the Jovian system, so exploration could be liberated
from the need to bring all its delta-V from Earth.  Maybe Nick Szabo
will sell me one.

Bill Higgins, Beam Jockey              | ASTRONOMY:
Fermi National Accelerator Laboratory  | The early science of the sky.
Bitnet:           [e-mail]  | ASTROLOGY:
Internet:       [e-mail]  | How it was paid for.
SPAN/Hepnet:           43011::HIGGINS  | --Michael Rivero

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

Date: 2 Mar 93 06:24:37 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: Lunar Li and F (was Re: How to power the LEO-moon space bus)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Frank Crary) writes:
> In article <[e-mail]> [e-mail] (Dave Rickel) writes:
>>Further support:  my CRC gives 300 ppm (or grams/ton) Fluorine, 65 ppm Lithium
>>in the earth's crust.  That should give some indication of how common they'd
>>be on the moon.
>
> Not really: The composition of the Earth and Moon is quite different
> (which leads to interesting questions about how the Moon formed...)
> At a guess, I'd expect both lithium and fluorine to be to be more
> common on the moon than on the Earth... But perhaps a goephysicist
> could answer that better: If fluoine or lithium baring minerals
> are below that average density of terrestrial rocks, they
> would probably be more common on the Moon...

I'm not a geophysicist or a geochemist, but I *am* a beamslinger who
has checked *The Lunar Sourcebook* out of the library.  On p. 416 is a
graphical summary of the fluorine concentrations in various lunar
samples;  looks like it varies a lot but hangs around 30 to 300
micrograms per gram (30-300 ppm) in the breccias.  Page 434 discusses
the abundance of halogens and it is a tricky and ill-understood
matter; this suggests that Frank's guess is not the right way to
approach the problem.

Lithium seems to be of order 10 micrograms per gram in mare basalts
and breccias.  The chemistry discussion is lengthy and complicated, so
I skipped it. (-:

Reviewing *Time Trax*: "In this future  | Bill Higgins, Beam Jockey
police have gotten more technical,      | Fermilab
computers have gotten much smaller,     | Bitnet: [e-mail]
criminals have become much cleverer,    | Bitnet: [e-mail]
and matte painters                      | SPAN/Hepnet: 43011::HIGGINS
have lost the secrets of their ancestors." --Mark Leeper

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

Date: 2 Mar 93 19:01:34 GMT
From: Henry Spencer <[e-mail]>
Subject: Refueling in orbit
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Matthew DeLuca) writes:
>>And if your science mission does succeed,
>>it's back to square one again (where are the followup missions for Galileo
>>or Magellan?).
>
>Galileo and Magellan *are* followup missions, to the Pioneer and Voyager
>series of probes.  For myself, I'd like to see what Galileo discovers before
>trying to design a followup to it; there's no telling what we may want...

Nonsense; there is considerable telling what we may want.  You can't
fill in every detail, but it's easy to sketch the broad outlines of
a set of Galileo follow-on missions.  For example, the atmosphere
people want a long-term imaging orbiter, all the more so because they
are the ones who get screwed most by the Galileo antenna fiasco.  The
particles-and-fields people likewise want a long-term orbiter, although
it might not be possible to use the same one (partly because of the
standing conflict between imaging and p/f design requirements -- which
is why half of Galileo is three-axis stabilized and the other half
spins -- and partly because they probably want different orbits).  Both
of these groups badly want *long-term* *continuous* data, not a snapshot
every decade or two.  These two missions could easily be planned and
well underway before Galileo results arrive, with a very high probability
that no significant changes would be needed.  Better atmosphere probes
and Jovian-moon orbiters likewise could start bending metal right now
without serious risk.  About the only thing you might perhaps want to
put a hold on is design of Jovian-moon landers, pending better imaging
data from Galileo... and even there you could get a lot done before
having to commit yourself to a model of the surface.  (After all,
Huygens is going *with* Cassini, not twenty years later as a follow-on,
despite very sketchy knowledge of Titan's atmosphere and virtually
none about its surface...)

You could probably fill two or three eminently worthwhile missions
just carrying all the instruments that were rejected in the final
selection for Galileo.  For example, there was an imaging system for
the atmosphere probe...

Especially given the delays involved in getting from proposal to data
return, it is madness not to have follow-ups well underway by the time
data comes back from their precursors... if you are trying to do a
systematic campaign of scientific study.  We aren't.
--
C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology
effect since OS/360.                    |  [e-mail]  utzoo!henry

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

Date: Tue, 2 Mar 1993 11:33:33 GMT
From: Nick Szabo <[e-mail]>
Subject: Safety of flyby & aerobraking for large payloads at earth
Newsgroups: sci.space,rec.arts.sf.science,alt.sci.planetary

In a future solar system of large-scale space industrialization,
what are the costs and benefits of using the earth
for gravity assist and aerobraking of large payloads?
What should be the policies concerning these flybies?

Here's how a gravity assist works. The planet is moving,
so there's our energy source. The slingshot can be computed
with the patched-conics approximation.  If we do a Hohmann
ellipse to the planet in the inertial frame, the trajectory
is a hyperbola in the frame of the planet.  The energy of
the vehicle is the same at symmetric points on opposite sides
of the hyperbola in the planet frame.  If we exit the rendezvous
moving in the same direction as the planet, we gain velocity
in that direction in the inertial frame.  If we exit the
rendezvous moving opposite the direction of the planet, we lose
inertial velocity.  Either gaining or losing velocity can
be useful, depending on where we're going.

Aerobraking is simpler to understand.  In layman's terms,
the air slows the spacecraft down, just like wind
resistance slows down a bicycle.  In orbital mechanics
terms, the spacecraft exchanges momentum with the particles
in the atmosphere.  An interesting variant, called cometary
aerobraking, vaporizes a piece of ice a split second before
it intercepts the spacecraft at high velocity.  The spacecraft
uses the temporary cloud of gas to aerobrake, as if it were
a planetary atmosphere.

All these maneuvers allow us to tap into the energy
already stored in the orbits of the planets and minor
planets.  They can greatly reduce the mass of propellant
and tank needed for a mission; in the case of Galileo
the Venus-Earth-Earth-Jupiter trajectory saved it from
being cancelled when it had to substitute a smaller
upper stage for the powerful Centaur.

Very large payloads can benefit from these trajectories
for the same reason, especially at earth, which raises
the important question of safety.  We cannot tolerate
bringing a dinosaur-killer sized asteroid anywhere near
earth, or coming towards earth near an intercept trajectory.
Reentry of c. 100 ton Shuttles is safely performed and
tolerated towards inhabited areas, and natural fireballs
and meteorites massing several tons each hit the earth
harmlessly every year.  Somewhere between these two extremes,
we need to figure out the margins of safety and enforce them.

There are several techniques for using earth to change the orbital
trajectory of objects:

* fast aerobraking (eg Shuttle, Apollo)
* slow aerobraking (eg Hiten)
* gravity assist (eg Galileo)

All three of these can play important roles in reducing the costs of
capturing space materials from comet fragments and asteroids into
various earth orbits.  The delta-v savings are roughly up to an order
of magnitude for gravity flyby, and up to two orders of magnitude for
aerobraking.

For gravity assist, the following need to be considered:

* what is the margin of error due to fringe atmospheric density,
  gravity anomaly and trajectory measurement error?
* how quickly and precisely can the on-board engines compensate for
  trajectory errors directly before and during the flyby?
* can the operation be timed so that a worst-case error will cause
  reentry over an uninhabited area (eg the ocean)?
* how much material on board is strongly toxic or radioactive?
* what is the worst-case scenario wrt the mass, composition, and
  worst-case error trajectory of the payload?

For slow aerobraking, we must also consider the above points, paying
close attention to the fringe atmospheric density, since that is what
we are using to change the trajectory.

For fast aerobraking, we need to pay very close attention to upper
atmospheric density at all levels.  The error margins are much less.
Unless the worst-case scenario is trivial or the spacecraft is
well-controlled aerodynamically, fast aerobraking is much more
dangerous than slow aerobraking or gravity flyby.

Given these data points, we must then determine whether the project
is ethically and politically tolerable, and whether it can be insured.

For the sake of discussion, I make the following initial proposed rules
of thumb:

gravity assist & slow aerobrake
    * <.0001% chance of trajectory error sufficiently large for reentry
    * if reentry, >98% chance it will occur over & towards
      uninhabited area
    * payload mass limits:
          solid metallic materials: 5,000 tons (no piece > 1 ton)
        stony materials: 10,000 tons (no piece > 5 tons)
        carbonaceous materials or loose regolith: 30,000 tons
        volatile ices w/pores: 50,000 tons
        strongly toxic or radioactive material:
            (varies by material; 1 ton typical)

The shape and attitude of the container also play a major role.
For example a long, thin cylinder will be dispersed more widely
than a sphere if it hits the atmosphere sideways instead of
headlong.

fast aerobrake:
    * aerobrake must contain control surfaces sufficient to
      give <.001% chance of reentry due to error
    * if reentry, >98% chance it will occur over & towards
      uninhabited area
    * no strongly toxic or nuclear materials on board
    * mass limits:
solid metallic materials: 200 tons
all other materials: 400 tons (note: ceramic heat shield will
        be significant % of mass for any payload)

Significant amounts of simulation, study of real-life artificial
and natural reentries, and benefit/risk analysis need to go into
determining the actual safety margins.  Calculations like those
done by Zdenek Sekanina, to predict the ability of comet material
to penetrate the earth's atmosphere, need to be perfected.

Privately financed insurance with unlimited liability
should be required for all such payloads.  If no insurance
company is willing to underwrite the risk it is a good sign
for the public that the maneuver is too risky and should be
not be allowed.  On the other hand if the insurance industry
volunteers to take on the risk, this is a good sign that the
risks, financial and physical, are minimal, and that the payoff
directly to the companies, and indirectly to mankind as a whole,
are well worth it.


--
Nick Szabo                     [e-mail]

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

Date: Tue, 2 Mar 1993 16:50:49 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: software engineering vs. civil engineering (wasRe: Nobody cares about Fred?)
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Jim Kissel) writes:

>[e-mail] (fred j mccall 575-3539) writes:
>: In <[e-mail]> [e-mail] (Spiros Triantafyllopoulos) writes:
>:
>: Great quote; pity you didn't try for something just a touch more
>: *accurate*.
>:

>"Software Engineering is at about the same state as Civil Engineering was
>before the discovery of the right angle."

Only if you have a very large "about".

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

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

Date: 2 Mar 93 20:47:43 GMT
From: "Robert M. Unverzagt" <[e-mail]>
Subject: SOLAR gravity assist?  NOPE.
Newsgroups: sci.space,alt.sci.planetary

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
> In article <[e-mail]> [e-mail] (Robert M. Unverzagt) writes:
> >>     In addition to a direct solar gravity assist for a Pluto, there might
> >>be some benefit in carrying propellant deep into the energy well of the sun,
> >>and burning it there to provide a boost to Pluto.  Is anyone familiar enough
> >>with the calculations to estimate what the benefit might be?
> >
> >Sure, I'll take a stab at it.  The delta-v for a direct injection
> >to Pluto is about, er, 38,771 ft/sec...
> >...If we wanted to do a close pass of the sun, we
> >could add that 38,771 IN THE OPPOSITE DIRECTION OF EARTH'S MOTION
> >AROUND THE SUN to give us a periapsis closer to the sun...
> >Do I need to go any further to show that there is no net benefit
> >of doing this?  Maybe I do -- obviously more delta-V will have to
> >be added at closest approach to raise apoapsis to Pluto's orbital radius...
> >Can the person who originally claimed a benefit for this please
> >explain again? ...
>
> Sure you need to go further -- one data point does not a graph make,
> much less a proof.  Especially when you're disagreeing with no less
> an authority than Hermann Oberth.

No claim for giving a proof was made.

> However, I can save you the effort. :-)  A pretty algebra problem...
> a lot of the variables eventually drop out, if you persist.

Agreed -- it is a pretty problem.

> It turns out that the crucial question is:  do you want to reach more
> than solar escape velocity, and if so, how much more?

No, I don't.  I want to go to Pluto.  Why would you want to
go on a hyperbola?  The trip time is shorter, but so what?  The
"planetary exploration community" seems willing to wait several
years while Venus-Earth-Earth gravity assists take place -- what's
the time difference between the "drop into the gravity well and
take a hyperbola out" vs. a cotangential transfer?  And what
about the probe's relative velocity once it gets to Pluto --
is it only in the neighborhood for a two speed-blurred photos
as it heads towards interstellar space?

> If the desired
> velocity at infinity is less than sqrt(2) times the orbital velocity
> of the circular orbit you start from, then dipping closer to the Sun
> hurts performance.

That's what my original numbers assumed -- velocity at infinity
less than circular, in fact, you aren't going to infinity.

> But if you want v_infinity greater than that,
> then lowering your perihelion as much as you can, and doing the main
> burn at perihelion, is a net win.  The win can be large, if you want
> lots of v_infinity and you can survive a very low perihelion.
>
> To be exact... if i = v_infinity/v_circular and p = r_perihelion/r_circular
> (note that v_circular = sqrt(G * M_sun / r_circular)), then the ratio of
> total delta-v for the gravity-well maneuver to total delta-v for doing
> it in one burn is:
>
> sqrt(i^2 + 2/p) + 1 - sqrt(2 + 2/p)
> -----------------------------------
>     sqrt(i^2 + 2) -1
>
> It is therefore obvious :-) that if i > sqrt(2), the ratio is less than 1.

OK.  If we call this quantity J, what's the partial derivative of
J with respect to i?  (I too lazy to chain-rule it out, and I
suspect that Henry has this handy, since it's an obvious question :-).
What I'm looking for is the magnitude of the benefit we're
talking about here.  For example, for certain bielliptic transfers
the delta-V benefit (vs a Hohmann transfer) can be as large as
something like 5%, if memory serves.  Are we talking a 0.001% benefit,
for only very large v_infinities?

Shag

--
       Rob Unverzagt        |   Last call for alcohol.
  [e-mail]   |   Last call for freedom of speech.
[e-mail] |                            - Jello Biafra

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

Date: 3 Mar 93 05:34:14 GMT
From: Russell Mcmahon <[e-mail]>
Subject: Spaceflight for under $1,000?
Newsgroups: sci.space

Pegasus is nominally capable of putting a man into space but getting
him (her) back would be difficult. Cost is several million dollars US

per launch although this could probably be reduced to well under a million
dollars if not done "properly". Whether anyone would want to volunteer
for a one way poorly engineered trip into orbit is another question.

If you forget about launching men and simply look at satellites the
picture is quite different. The smallest possible "useful" satellite
would be somewhat smaller than the smallest existing amateur microsats.
This could be only a few kilograms. Using latest technology (LOX/LH2)
you could manage a single stage to orbit design with a payload percentage
of around 1% of all up launch weight. A two stage design would be very
feasible. The all uop weight would therefore be rather less than one
ton (or tonne). This should be entirly within the reach of a small private
firm or group of enthusiasts.

One of these days ....

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

Date: Tue, 2 Mar 1993 11:40:39 GMT
From: Nick Szabo <[e-mail]>
Subject: Stations vs. constellations
Newsgroups: sci.space

A fundamental problem with the concept of a space station is that
a large "stepping stone" or "centerpiece" of "the space program"
will by its very nature be in the wrong orbit.   If we choose 28.5
degrees, we lock out participation by the Soviet launch sites and
the largest users of space, our military in polar orbit.  If we put it
at 50 degrees the penalty for using it as a "way station" to Clarke
orbit, the Moon, Mars, or asteroids is prohibitive.  In turn, 28.5
xdegrees still puts a significant penalty over going straight to Clarke
orbit, the Moon or Mars.  If we put it in polar orbit, it is useful
for the military, useless as a way station, and we can't get to
it from Canaveral.

This, among other reasons, is why military and commercial users have
thrown out the concept of a hyper-centralized space station in favor
decentralized networks of standardized satellites: constellations.  These
small space platforms are launched into orbits specific to the application
at hand, instead of pretending they can open up the solar system from
one orbit.   Comsats live in Clarke and Molniya, GPS lives in 12-hour
orbits, spysats live in polar orbits, etc.  It's time for NASA and
the space activist community to catch up with the space users; it's
time to create new visions that take advantage of the physical reality
of working in space.


--
Nick Szabo                     [e-mail]

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

Date: Tue, 2 Mar 1993 18:01:01 GMT
From: [e-mail]
Subject: Stupid Centaur Tricks
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Gary Coffman)
writes:
>Indeed. An engineering maxim is the fewer parts you have, the fewer
>can fail. In the last two Centaur failures, it's been a failure of
>one of the two engines to ignite. Neither mission could succeed with
>one engine out, not enough thrust. Fewer parts generally translate
>into cheaper production costs too.
   I don't think the problem with one engine is not enough thrust.
The problem is that the engines are not on the vehicle centerline
and only gimbal a few degrees, so if one is out, you tend to get the
spins.  Even if the single working engine could gimbal to point the
thrust vector thru the center of gravity of the vehicle, during an
ascent the aerodynamic forces would not allow this "sideslip" flight
path.

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

Date: 2 Mar 93 03:47:13 GMT
From: Ken Hayashida <[e-mail]>
Subject: The Planetary Society and Mars Exploration
Newsgroups: sci.space

Hi friends.

My name is Ken Hayashida.  I'm a third-year medical student at USC School
of Medicine in Los Angeles.  I am working with the Planetary Society to
research the possibility of forming an electronic think tank to address the
technical issues of crewed deep space exploration, focusing on the issues
related to Mars exploration (but not limited to that mission).

I am interested in hearing the views of sci.space readers on their interest
in this idea.  I have already met several times with the director of
the Planetary Society, Dr. Louis Friedman.  He has requested that I post this
message in order to ascertain interest in this concept across Internet.

I am specifically interested in the life sciences aspects of long-duration
spaceflight.  However, technical expertise in every other facet of space
exploration is welcome.

If you are interested in this effort, please send me an e-mail message
to "[e-mail]".  If response is overwhelming, then I might take
awhile to respond.  Please forward your e-mail address, your full name,
your area of personal expertise or interest, and state previous experience
in space exploration.

In case you are not familiar with the Planetary Society, it is an internation-
al organization that fosters political support for scientific cooperation in
space.  Founded by Drs. Carl Sagan, Bruce Murray, and Louis Friedman, the
Planetary Society has over 100,000 members around the world.  It currently
sponsors international projects, including SETI and Mars exploration projects.

If sufficient interest exists, we will be forming an advisory panel in the next
three months.

Thanks for your time and interest.

Kenneth H. Hayashida, Jr.  Medical Student
University of Southern California School of Medicine

>[e-mail]

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

Date: 2 Mar 93 12:01:02 GMT
From: Nick Szabo <[e-mail]>
Subject: Water resupply for SSF (?)
Newsgroups: sci.space

[e-mail] (Henry Spencer) writes:

>>[automated comet mining]
>Someday.  Not today.  This is *far* beyond what can be done with current
>robotic systems.

The two most complicated pieces of automation needed are
(a) ice extraction and (b) solar mirror deployment (for the solar
thermal version).  Surely you have some confidence in (b), or you
wouldn't have been designing solar sails for the contest.  As for
(a), a similarly complex operation, the extraction and return of
several comet core samples, keeping them pristine-pure the entire way
back to earth and through reentry, has been considered feasible
in the space science community since the mid-1980s.  Neither that
mission (Rosetta) nor comet mining require anthropomorphic robots or
undiscovered "AI".


--
Nick Szabo                     [e-mail]

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End of Space Digest Volume 16 : Issue 266
------------------------------