Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/spacedig/V15_5/V15NO547.ZIP/V15NO547

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Date: Tue, 15 Dec 92 05:08:43
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #547
To: Space Digest Readers
Precedence: bulk


Space Digest                Tue, 15 Dec 92       Volume 15 : Issue 547

Today's Topics:
                        "trivial engineering"
                   absolutely, positively overnight
           Apollo 10 LM (was Re: pre-fire Apollo schedule)
              Cassini Undergoes Intensive Design Review
                      DC vs Shuttle capabilities
                      DoD launcher use (2 msgs)
                             Earth Movie
                               Galileo
                      Magellan Update - 12/11/92
             Need information on Infinite Universe Models
                           Orbit Question?
  Profit in space activities (was: absolutely, positively overnight)
                            Space Tourism
           Terminal Velocity of DCX? (was Re: Shuttle ...)
                           What is a VSAT?
                   what the little bird told Henry

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Date: Mon, 14 Dec 92 22:30:36 EST
From: John Roberts <[e-mail]>
Subject: "trivial engineering"

-From: [e-mail] (Donald Lindsay)
-Subject: Re: "trivial engineering"
-Date: 13 Dec 92 18:44:39 GMT
-Organization: School of Computer Science, Carnegie Mellon

[e-mail] (John Roberts) writes:
->Somebody (I think it was Goldin) commented recently on a jet engine
->company's recent design of the new engine. The design process cost
->something around a billion dollars - they hope to sell enough to pay off
->the design cost in 20 years. And it wasn't a radical new design

I believe my post was in response to an argument that since designing a new
engine for a comercial airliner (and establishing its reliability) is so
easy, that therefore designing and proving a new rocket engine ought to be
pretty easy too. I was pointing out that designing a new jet engine
*isn't* particularly easy.

-Surely, a commercial jet is harder to develop? For a jet, fuel
-efficiency is now crucial, but that's probably at the point of
-diminishing returns.

I mentioned that later in the post. There doesn't seem to be any clear
indication that launcher design has reached the point of sharply diminishing
marginal returns (at least if one is willing to challenge some of the
old assuptions).

-Plus, the jet has to be tested across a large
-parameter space - different throttle settings (including idle),
-different air densities, humidity (and rain), bird ingestion.

-I would assume that a rocket engine has slightly different problems
-(full tanks vs empty, acceleration vs liftoff, air vs vaccuum) but
-that the parameter space is smaller?

Testing is a good point, but I don't think testing rocket engines is
exactly trivial either. Remember that the DC engines are supposed to
be throttleable, restartable, and not require much maintenance between
uses. There are certain features of both types of engines that *can't* be
tested except in actual flight, and even then the results may not be
fully understood. For instance, during the first minute or so of a Shuttle
launch, strange flickering flames generally play over the aft portion of
the launcher, outside of the main exhaust paths. Last I heard, nobody
could definitely explain the exact mechanism by which these flames form.
About all they can say with reasonable confidence is that they don't seem
to hurt anything. I suspect that testing a big rocket engine in actual
flight is much more expensive than testing a big jet engine in actual flight
(just bolt it onto a multi-engine aircraft in place of one of the existing
engines).

By the way, somebody told me that tolerance to bird ingestion is tested by
means of a compressed air gun that shoots dead chickens into the engine,
to determine whether engine damage will result.

John Roberts
[e-mail]

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

Date: Tue, 15 Dec 1992 00:06:57 -0500
From: Kevin William Ryan <[e-mail]>
Subject: absolutely, positively overnight
Newsgroups: sci.space

[e-mail] (Henry Spencer)
>[e-mail] (Anthony J Stieber) writes:
>>>But they didn't call the SR-71 the Recon-STRIKE-71 before LBJ's mangling for
>>>nothing.
>>
>>Yep.  And I also heard about the drone launch accident that downed both
>>the drone and the host SR-71...
>
>That actually happened in pre-SR-71 days, to an M-12 (the drone-carrier
>variant of the A-12).  However, the problems are felt to be manageable,
>last I heard:  Lockheed was saying "feasible" when NASA Dryden talked
>to them about carrying HALO up to Mach 3 on SR-71-back.

    The drone in that case was quite a package, too. As I recall, the drone
was a Mach 3+ ramjet design, intended to be a drone recon plane for doing
flyovers of hostile territory. It was (bear with me here, it's been a while
since I read this) fueled by boron hydride, with roughly twice the energy
density of regular jet fuel, built almost entirely of magnesium, and intended
to fly a photo run, return to friendly territory, eject a photo package, and
self destruct with explosive charges. In fact, the charges were set to blow
if the altimeter read below 10,000 feet in operational use. At any rate, during
the first test the separation went bad, the drone either flew into the carrier
or blew up immediately adjacent, and the carrier went down.
    The project was supposedly cancelled, although the article I read said
that several of the test drones were later unaccounted for...

    I wish I could remember where I read this... anyone else out there able
to confirm this?

                                                   kwr

Internet: [e-mail]

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

Date: Mon, 14 Dec 1992 23:36:18 GMT
From: Tom A Baker <[e-mail]>
Subject: Apollo 10 LM (was Re: pre-fire Apollo schedule)
Newsgroups: sci.space.shuttle,sci.space

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Bill Higgins-- Beam Jockey) writes:
>>Henry, you imply that Apollo 10's LM couldn't actually land and
>>return.  Can you elaborate?  This is the first I've heard of this.

>talks about it.  He says that the Apollo 10 LM *probably* could have
>flown a lunar landing if some fuel had been offloaded to lighten it, but
>the margins would have been slim and hard to predict.  It would probably
>
>So, as actually flown the Apollo 10 LM was indeed a little too heavy.

Scary.  As I have often recalled, there was a subtle bug in the LM
software that flew in the Apollo 10 mission.  When in ascent mode, the
LM was supposed to automatically stay in contact with the CSM by
directional antenna.  If it wasn't, then the LM automatically would
do a "random tumble" to locate it.  During Apollo 10's simulation of
ascent, that started happening just at the beginning of the simulated
ascent.  Stafford yelled "Son of a bitch!", which we all heard on Earth
a while before we found out the problem.

I am not saying that would have happened (noflamesplease) as it is
probable that the CSM *would* be locked in, and the LM commander would
be manually overriding more tightly than Stafford was.  But it does
point up the extra risks of a "let's do it this time and surprise the
russians" landing that might have been tried.

(By the way, I remember discussing this with my circle at the time of the
flight; at that point, the space race still seemed real.)

tombaker
--------------------------------------.--------------------------------------
 Net - [e-mail]  __     | National Space Society is a nonprofit
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------------------------------

Date: Mon, 14 Dec 1992 21:27:51 GMT
From: David Seal <[e-mail]>
Subject: Cassini Undergoes Intensive Design Review
Newsgroups: sci.space

[e-mail] (Frank Crary) writes:

>After the Challenger failure, NASA added a safety requirement that
>nothing launched in by a space shuttle may use liquid fuels. That
>means Cassini must use lower-energy solid rockets instead. As a

Cassini is using a Titan IV with a centaur upper stage.  The centaur
is liquid (cryogenic).

regards,
ds
--
-----------------------------------------------------------------------------
David Seal                 |  Jet Propulsion Laboratory  |     sunset: 7:54pm
[e-mail] |       Mission Design        |   temp: 82 degrees

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

Date: 14 Dec 92 17:37:36 GMT
From: "Edward V. Wright" <[e-mail]>
Subject: DC vs Shuttle capabilities
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Greg Moore) writes:

>    You missed my point.  If your crew compartment is in the cargo
>bay, where do you put the satellite?

If your cargo bay is full of troops, where do you put the transport
vehicles?

Answer: In the other airplane.


>    Granted, but that's not what I meant.  Will you have enough time
>to rendevous and capture the satelite?  It took what 3 days for the
>shuttle to capture Intelsat VI? That's aday more than DC-?.
>Also, what type of fuel margin would DC-1 have for IN-orbit
>manevours?

That's what tankers are for.


>    Use it yes, but use it for what it can be used for economically.
>Let's see, we've added an airlock, an arm, additional on-orbit capacity.
>Hmm, that adds up, and add complexity.  Yes, let's ok at possibilities,
>but not claim t they are definites.

Take a look at the C-130 Hercules.  How many variants are flying,
in both military and commercial service?  Hint:  It's a lot more
than four.


>    I have a question about this.  EOT and LM should require roughly
>the same amount of fuel, no? (as I recall, the energy to get into lunar
>orbit is about the same as GEO? I'm ignoring landing here).  But how
>economical is it to transport that fuel TO orbit?  Am I correct in
>remembering you saying about 10 DC-1 flights?

Depends on your assumptions.  I've done some back-of-the-envelope
calculations.  If you can set up an oxygen-extraction plant on the
Moon, your costs go way down if you land the DC with its LOX tank
dry.  (This would allow the DC to carry extra cargo, probably
using external attach points.)  It might even be advantageous
to put payloads into GEO from the Moon instead of directly from
the Earth.


>    Also, does it make sense for the DC1-EOT and OMV and LM the same.
>The requirements for landing gear are different.  The requirements for
>fuel transfer MAY be different.

This depends on how many lunar missions you're going to do.  However,
replacing landing gear shouldn't be too difficult as a field modification.
If the vehicle is rugged enough, you can add attach points for external
fuel tanks.  (And if those tanks are used only in space, the vehicle
shouldn't need to be that rugged.)  And you don't *have* to top off
the fuel tank for every mission if you don't need it.


>What about thermal protection.  LM won't require any to land on
>the moon, but what about reentering earth orbit or earth landing?

But the DC-LM will require periodic maintenance and, until you
have a fully equipped service station on the Moon, that will
require bringing it back to Earth.


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

Date: 14 Dec 92 16:27:12 GMT
From: Brad Whitehurst <[e-mail]>
Subject: DoD launcher use
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>
>>>for many applications satellite is better. Recon aircraft are too easy
>>>to shoot down...
>
>>We're talking about Iraq right? No air opposition right? Complete Coalition
>>domination of the airspace right?
>
>>What can a satellite do for tactical recon that a SR71 can't?
>
>Updates of the tactical situation with SR-71 would take about 6 to 8 hours
>to get and would be several hours old by the time they get to the local
>commanders. Satellite images take seconds to get and are fresh. In the Gulf
>war, images just a few hours old would have been useless.
>
>  Allen
    Actually, as I recall, one of DoD's new goals is integration
of Joint-STARS and other airborne intelligence systems with real-time
intelligence/command/control/communications down to the tactical field
unit level.  They've already achieved that with Joint-STARS,
transmitting radar imagery in near real-time right to the field
commanders.  I assume satellites are part of that system.  The main
problem with satellites is inability to redirect, unlike recon planes
(remember the SR-71 was just one of many recon craft!).  I wonder how
close the spooks really are to doing surveillance like they showed in
the movie Patriot Games?  Don't look up folks, who knows who's
looking! :-)

--

Brad Whitehurst    |   Aerospace Research Lab
[e-mail] |   We like it hot...and fast.

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

Date: Mon, 14 Dec 1992 22:13:47 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: DoD launcher use
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Gary Coffman) writes:

>I agree that not all conflicts will be as easy as the Gulf War and that
>satellite recon is very valuable, especially for strategic recon. But the
>origninal message that I questioned said that the Space Command commander
>during *Desert Storm* said he needed tactical satellite recon *for that
>conflict*.

That is correct. He said that his satellite coverage wasn't as good as
he would have liked. With a DC like spacecraft, he could have had much
better coverage.

>And yes, A10s and Tornados doing low level attacks were lost
>to ground fire in Desert Storm as well as a few other operational type
>aircraft like an AC130, but as far as I know, no recon aircraft were lost.

I don't think much if any recon was flown. The Air Force had better things
to do with its aircraft.

BTW, flying recon is one of the most dangerous types of flying in wartime.

>But this was exactly my point. LEO satellites pass over the same ground
>track twice a day.

With a DC like vehicle you could put in a constelation of satellites to
provide fresh updates every half hour or so. It would take about a week
to put it in place compared with months today. This is an order of mganitude
faster than aircraft can provide the same information. The data is also
an order of magnitude fresher.

>Then unless
>you have realtime downlink in the footprint of the satellite, very close
>to your target, you wait for the satellite to pass over your downlink station
>and download the image.

DoD owns lots of communication satellites. With DC, they can launch more
and larger ones. This will allow the tactical satellite to dump its data
in seconds.

>You can
>launch ramp ready recon aircraft in 10 minutes if necessary, though

You don't ramp launch recon aircraft. You only ramp launch aircraft
for the defense of the airfield or similar emergencies.

>normally you'd schedule recon as part of an operational timetable.

Which BTW, takes 12 to 24 hours to plan (my last defense job was
working to automate NAVY strike planning). Not good in a rapidly
changing situation.

>You can get back immediate Mark I eyeball reports during the mission

Generally you maintain radio silence during a mission. No point in
telling the bad guys where you are.

>and photos as soon as the aircraft returns.

Hours after you got your satellite update.

    Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------131 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: Mon, 14 Dec 92 22:54:14 EST
From: John Roberts <[e-mail]>
Subject: Earth Movie

-From: [e-mail] (Ron Baalke)
-Subject: Re: Earth Movie
-Date: 9 Dec 92 03:30:37 GMT
-Organization: Jet Propulsion Laboratory

-There are two movies that will be made.  The first is called the Earth Zoom
-movie, and will cover a 48 period after the flyby as the spacecraft moves
-away from the Earth.  The second movie is called the Earth/Moon Conjunction
-movie, and the first images for that won't be taken until December 16.
-At this time from the spacecraft's perspective, the Moon will appear to
-pass very close to Earth, and can be captured in a single field of view
-of the SSI camera.  168 images are allocated for this movie and it will
-be taken over a 14 hours period.  The movie will show the Moon passing
-by as the Earth slowly rotates beneath it.  As far as I know, both movies
-will be ready for the December 22 press conference, and most people will
-see it for the first time on the evening news the same day.

Will either of the movies be comparable to the movie made for the first
Earth flyby - with the Earth appearing to be the same size over the period
of observation?

What kind of software is required to make such a movie? Based on observation
of the earlier movie, it appears to be more than simple overall magnification -
the change in magnification of the "nearest" (center) portion of the Earth
must be greater than the rest as the distance from the spacecraft to the
Earth changes - otherwise, the Earth would appear to "distort" over that
interval.

John Roberts
[e-mail]

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

Date: Mon, 14 Dec 92 22:44:07 EST
From: John Roberts <[e-mail]>
Subject: Galileo

-From: [e-mail] (Ryan Korniloff)
-Subject: Re: Relay to Follow Galileo?
-Date: 14 Dec 92 03:49:18 GMT
-Organization: University of Denver, Dept. of Math & Comp. Sci.

-Well why did the HGA have to be cloed up in the first place? If it is too
-big, then couldn't they have used a more powerful transmitter? I would
-have rather tried to avoid such a chance for failure. If thay don't get
-that HGA open then %30-%40 of the mission objectives will be lost. Or is
-the radio frequncy have something to do with he size of the HGA???

The *reason* the HGA was not opened while the Shuttle was there with
astronauts who could poke at it if necessary (aside from possible concerns
over stress from the initial boost) was that Galileo had to pass closer
to the sun than Earth's orbit, and the HGA in open configuration was not
rated for the expected thermal conditions that close to the sun. (Too bad -
if they'd tried to deploy even after initial boost, the high temperatures
near Venus orbit might have helped in opening the antenna.)

(Actually, I had worried about the antenna opening before the problem showed
up, but I didn't foresee the mechanism that's currently proposed as the
most likely.)

John Roberts
[e-mail]

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

Date: 15 Dec 92 00:28:16 GMT
From: Ron Baalke <[e-mail]>
Subject: Magellan Update - 12/11/92
Newsgroups: sci.space,sci.astro,alt.sci.planetary

In article <[e-mail]>, [e-mail] (Lord Vader) writes...

>To Ron Baalke:(or anyone else who knows)
>
>re:
>
>>1.      Magellan continues to operate normally, transmitting a carrier plus
>>40 bps X-band signal which is precisely tracked by the DSN (Deep Space Network
>>stations to provide gravity data.
>
>>2.      The present command sequence is designed to automatically shift the
>>telemetry to the 1200 bps rate if the tracking pass is over a 70 m
>>station, based on the DSN station allocation schedule as of the time
>>the reference file was prepared.  In the event the station assignment
>>is changed, some telemetry may be lost because the 34 m stations
>>cannot successfully receive the 1200 bps rate due to the Transmitter B
>>noise spur.
>
>Which DSN stations are 34 m and which are 70?

All three of the DSN stations have the same complement of antennas.
Each DSN complex has one 70 meter antenna, two 34 meter antennas and one
26 meter antenna.  An additional 34 meter antenna is currently under
construction at Goldstone.  The transmitter on the Goldstone 70 meter
is more powerful of the three complexes and is often used to bounce radar
off of bodies throughout the solar system.

>Also, do some of the DSN
>stations have the capability to recieve S-band and X-band at the same time,
>and if so, which ones?

Each *antenna* is capable of receiving S-band and X-band simultaneously.
The determining factor being whether the spacecraft was designed to
transmit in both bands are not.  Magellan is such a dual channel mission,
and the normal mode of operation is to send the engineering data (status
& health of the spacecraft) down the S-band, and the high rate science data down
the X-band.

>And, who can I contact to get the parameters of
>the individual DSN stations and the entire DSN capabilites?

I'll give a summary, and if you want more details then contact the
Public Information Office at JPL at [phone].  The DSN is composed
of three parts, the Deep Space Stations (DSS) themselves located at
Goldstone, Madrid and Canberra, the NOCC (Network Operations Control Center,
and the GCF (Ground Communications Facility).  The stations track the
spacecraft, send commands to the spacecraft, and receive and process
telemetry data from the spacecraft.  The DSN stations also perform
VLBI tests.  The NOCC is located at JPL and it controls and monitors
the operations of the three complexes.  The GCF provides the communications
circuits that link the complexes and NOCC together.

>I understand that Magellan has limited capability to transmit engineering
>data over the X-band transmitter due to the noise spur in the subcarrier.
>Is this data then being transmitted via the s-band, and if so, like I asked
>above, is it being recieved at the same time as the x-band gravity data,
>or does it have to be recieved separately due to limited ground capabilities?

Both the radar and gravity data are transmitted down the X-band, and they
cannot be transmitted simultaneously because of the operational modes of the
spacecraft.  The radar mapping only requires the spacecraft to point its
High Gain Antenna at the Earth to provide a steady carrier signal
which can be at a low telemetry rate, and this is the current
operating mode of the spacecraft.  In the radar mapping mode, the spacecraft
is required to go through complicated set of maneuvers using the  High Gain
to bounce the radar off Venus, record the data  on the tape recorders,  and
then transmit it back to Earth.  Also, because of the large volume of radar
data collected, a higher transmission rate is required.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The 3 things that children
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | find the most fascinating:
|_____|/  |_|/       |_____|/                     | space, dinosaurs and ghosts.

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

Date: Mon, 14 Dec 1992 18:52:43 GMT
From: Samir Chopra <[e-mail]>
Subject: Need information on Infinite Universe Models
Newsgroups: sci.space,sci.physics,talk.philosophy.misc

I would appreciate any information on cosmological models that
consider the universe to be infinite i.e not just infinitely
expanding but actually existing in infinite space. Would
the FRW flat space model and the Hoyle_Narlikar
steady state model be considered examples of such cosmologies?

Book references, pointers to online sources of information, article
refrences, archived discussions are all welcome. If someone feels
like enlightening me via E-mail please do so.

Thanks in advance,

Samir
--
"You guys are gonna smoke in the other room, the smoke will come drifting in
here..it'll look like rose stems, but there's tiny nooses hanging from them.."
Support the Freedom of Choice Act | 11/3/92: Restoration of Democracy Day

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

Date: Mon, 14 Dec 1992 23:52:15 GMT
From: Tom A Baker <[e-mail]>
Subject: Orbit Question?
Newsgroups: sci.space

In article <[e-mail]> <[e-mail]> writes:
>The trajectories of the russian com-sats are called Molnyia or Tundra
>trajectories. They are highly inclined and do one rev in 12 or 24 hours.
>
>where the node is placed above the equator. They are spending halftime of
>a rev either above each hemisphere.
>Regards
>         -Thorsten-

The perigee of Molinyas is 100 miles (at least one of them.)  The apogee is
just under the Clarke Orbit's height.

The result is an orbit of exactly twelve hours.  Um ... not to be picky, but
they spend only about a half an hour south of the equator, and the other
11 and a half north of it.  Very efficient.  I wonder why the Canadians
don't lease time on the CIS's satellites?

tombaker

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

Date: Mon, 14 Dec 1992 21:41:24 GMT
From: "Michael V. Kent" <[e-mail]>
Subject: Profit in space activities (was: absolutely, positively overnight)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Mitchell E. Gold) writes:

>The last I'd heard, the companies flying Concordes (British Air, anyone else?)
>had decided to write off the amount of money that was used in development of
>the aircraft, but the aircraft do make a good profit over operational costs.

Sounds like a good accounting method to use for a certain Space Shuttle NASA
has.

Mike

--
Michael Kent                                   [e-mail]
Flight Test Engineer                           Tute-Screwed Aero '92
McDonnell Douglas                              Rensselaer Polytechnic Institute
These views are solely those of the author.    Apple II Forever !!

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

Date: 14 Dec 92 17:59:04 GMT
From: "Edward V. Wright" <[e-mail]>
Subject: Space Tourism
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Josh 'K' Hopkins) writes:

>Anyone ever priced a trip to Antarctica?

International Expeditions charges $4750 for 17 days, plus air fare.
The cruise departs from Patagonia, so you can add about another $1000
for air.

This is not the most expensive trip you can take.  Air fare to
Africa starts at around $2400 and the ground cost for an African
safari can easily run to $6000-8000.

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

Date: 14 Dec 92 17:17:11 GMT
From: "Edward V. Wright" <[e-mail]>
Subject: Terminal Velocity of DCX? (was Re: Shuttle ...)
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Brian Stuart Thorn) writes:

>  DC-1 would only be able to carry 20 people if it used a special
>  passenger module in the payload bay. If you built such a module
>  for the Shuttle, you'd get alot more than 10 people in it. Maybe
>  50 or so.

Nope.  You might get more than 10 people in it, but it would
never get off the ground.  NASA studied this idea years ago.
It was dropped because it couldn't meet minimum safety requirements.

Also note that the cost of one Shuttle flight is about the same
as the entire DC development program.

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

Date: Mon, 14 Dec 1992 23:21:55 GMT
From: Tom A Baker <[e-mail]>
Subject: What is a VSAT?
Newsgroups: sci.space,sci.astro

In article <[e-mail]> [e-mail] (Dave Rogers) writes:
>In article <[e-mail]>, [e-mail] (Patrick C. Mock) writes:
>|>
>|> Does anyone know what does VSAT (Very Small Aperature Terminal) mean
>|> in the context of satellite communications?
>|>
>
>A VSAT is a C-band system which provides one-way, two-way and broadcast
>capabilities for audio, video and data.  Data rates up to DS-1 (1.5 M
>bits per second) are available.  Dishes are typically 1-3 meters in
>diameter.  Complete systems (one-end) sell for $6-15K.  You must lease
>time on a transponder from one of the many companies which do this (AT&T
>Spacenet, GTE Skynet, Comstream, Vitacom).
>

Furthermore, a company can get a "satellite network" up for cheap.  The
design of a satellite system traditionally had the basic tradeoff:  Should
it have its brains in the satellite (expensive satellite, but cheap ground
station) or in the gfround station (expensive ground station versus cheap
satellite).

The VSAT approach sidesteps it all.  The "HUB" of the network is a ground
station with all the works.  It transmits/receives via some transponder on
a satellite, which does not have to be too souped up.  Then the signals
are passed/received from the very cheap VSATs throughout your network.
(My source, W. Stallings "Data Communications", (1991), says that individual
VSAT stations can be leased for $400/month.)

So the far-flung ground stations don't need a lot of power, and the satellite
doesn't devote a lot of resources, either.  The "hub" has most of the
resources that run the network.

tombaker
--------------------------------------.--------------------------------------
 Net - [e-mail]  __     | National Space Society is a nonprofit
uucp - uunet!world!tombaker   /  \  / | public organization dedicated to
 BIX - tombaker              /  O  /  | promoting the eventual establishment
 AOL - [e-mail]      /  \__/   | of a spacefaring civilization.
______________________________________|______________________________________

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

Date: 14 Dec 92 16:19:03 GMT
From: Brad Whitehurst <[e-mail]>
Subject: what the little bird told Henry
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Dan Swartzendruber) writes:
>In article <[e-mail]> [e-mail] (Edward V. Wright) writes:
>>In <[e-mail]> [e-mail] (Gary Coffman) writes:
>>
>>>They're also heavy as I recall, something you don't need in a SSTO.
>>>I appreciated the summary you gave earlier, Henry. It looks like they
>>>have a better test program planned than what has been outlined here
>>>before. I still think their schedule is extremely optimistic and
>>>success oriented, but we'll see.
>>
>>I'd be curious to know the exact date, sometime in the last 20 years,
>>when "success oriented" became a pejorative phrase.  Yeah, the project
>>is success oriented.  Just like Project Apollo.  The alternative, I
>>guess, is for a project to be "failure oriented."  I like success better.
>
>
>Look, it's pretty clear (at least to me, and going by some other recent
>postings, to other people as well) that Gary has some kind of axe to
>grind against the whole SSTO concept.
>
>Dan S.

    Actually, I feel most of his posts have been fairly
thoughtful.  It is entirely possible to have varying opinions,
technical, political, and economic, about the DC proposals without
having "an axe to grind".  He has brought up some legitimate concerns
about the engineering difficulties of bringing a system like the DC to
fruition.  He is basically a little more skeptical than Allen and
Henry, but is far from ruling it out.  I have to admit to sharing some
of his skepticism about the ease of designing, building, and operating
ANY new space transport.  No matter how optimistic one is, losing
sight of the pitfalls before one while looking at the shining goal
ahead can result in real problems!
    My cut on the DC is that the X should be tried, but I think
you'll want to get a LOT more info before the Y is built.  I'm really
bummed that people are writing off the X-30 concept also, because it
seems like it will be "too long" to build an operational craft based
on it.  That was the initial error of the NASP project, I think.
Promoting the first X-30 as a "real" space-plane was not a good idea.
We work on SCRAMjet technology (not the actual engines) and can tell
you that there is a lot of work yet to do to really understand the
physics of fluid flow and combustion in that environment.  Unless you
want to spend seriously painful sums making and breaking engines
(these puppies AIN'T easy to test!), we need detailed info on the
physics so that what is built has a higher chance of success.  Even
so, the performance of the first article is likely to disappoint
(ref.: XP-59 Airacomet), so overblowing the first one, like was done
with NASP, is risky to the program as a whole.  I think this lesson
also can and will apply to the DC.
    So, please, let's thrash out details technical and economic,
but leave the rotten tomatoes at home, folks!
--

Brad Whitehurst    |   Aerospace Research Lab
[e-mail] |   We like it hot...and fast.

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End of Space Digest Volume 15 : Issue 547
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