Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_5/V15NO572.TXT

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Date: Sun, 20 Dec 92 05:00:03
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #572
To: Space Digest Readers
Precedence: bulk


Space Digest                Sun, 20 Dec 92       Volume 15 : Issue 572

Today's Topics:
                         aerospikes (2 msgs)
                            Apollo 13 book
                 cryptocraft photography, Re: Aurora
                 DC vs Shuttle capabilities (2 msgs)
                         fast-track failures
                 Justification for the Space Program
                           MOL (and Almaz)
                              pumps etc.
                    Shuttle thermal tiles (2 msgs)
                           SSTO vs. 2 Stage
                      Stellar Evolution Research
                            What is DC ??

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

Date: Sat, 19 Dec 1992 01:41:19 GMT
From: Henry Spencer <[e-mail]>
Subject: aerospikes
Newsgroups: sci.space

In article <[e-mail]> [e-mail] ("RWTMS2::MUNIZB") writes:
>If lack of *flight-test* data is seen as the long pole in the tent
>(holding things up), why isn't it being flown on the admittedly
>experimental DC-X (and DC-Y)?

Because DC-X and DC-Y are *not* experimental in that sense.  They are
proof-of-concept vehicles for single-stage-to-orbit launchers.  They're
trying very hard *not* to be an experiment in any other way; in particular,
they are *not* in the business of advancing engine technology if they can
avoid it.

It would be a fine thing to do with a DC-Y after its main test program
has concluded, but first things first.

>"requirement for large cross range (1500 nautical miles with crew and
>cargo) and through it, the ability the ability to launch and land in one
>earth orbit."
>
>I seem to recall this as an Air Force driven requirement, and that the
>original NASA requirement was less stringent.  The paper states the
>original requirement as a return to a preselected [launch?] site every 24
>hours (approximately 15 orbits), rather than one orbit.  Any idea what
>the requirement will be for DC-Y (and DC-1)?

Depends on who's writing the specs.  I think McDD's lifting-body DC-Y
design is capable of doing the one-orbit mission.  There were people who
opposed trying for such production-oriented capabilities on the first
prototype, as an unnecessary distraction that would interfere with the
proof-of-concept mission.

Substantial cross-range is indeed primarily a military requirement,
driven by the one-orbit mission, whose basic rationale is deploying a
spy satellite -- or doing any of a number of other things -- in wartime
conditions where coming around again in a predictable orbit is likely
to result in being shot at.
--
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  [e-mail]  utzoo!henry

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

Date: 19 Dec 92 04:11:00 GMT
From: Mary Shafer <[e-mail]>
Subject: aerospikes
Newsgroups: sci.space

On Sat, 19 Dec 1992 01:41:19 GMT, [e-mail] (Henry Spencer) said:

HS> In article <[e-mail]> [e-mail] ("RWTMS2::MUNIZB") writes:
>If lack of *flight-test* data is seen as the long pole in the tent
>(holding things up), why isn't it being flown on the admittedly
>experimental DC-X (and DC-Y)?

HS> Because DC-X and DC-Y are *not* experimental in that sense.  They are
HS> proof-of-concept vehicles for single-stage-to-orbit launchers.  They're
HS> trying very hard *not* to be an experiment in any other way; in particular,
HS> they are *not* in the business of advancing engine technology if they can
HS> avoid it.

The DC-X is going to have a data collection system.  As I recall,
they're going to collect what I'd call a standard barebones set of
measurements--angles, rates, accelerations of the airframe, control
deflections, and other vehicle states, which probably include a
variety of engine parameters.

Flight data is always of great value for validating ground predictions
(e.g. CFD, wind tunnel, etc.) so the DC-X data will probably be of
greater value than one might originally think.
--
Mary Shafer  DoD #0362 KotFR NASA Dryden Flight Research Facility, Edwards, CA
[e-mail]                    Of course I don't speak for NASA
 "A MiG at your six is better than no MiG at all."  Unknown US fighter pilot

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

Date: Fri, 18 Dec 92 21:00:47 PST
From: Brian Stuart Thorn <[e-mail]>
Subject: Apollo 13 book
Newsgroups: sci.space

>I'm looking for a book I heard about a number of years ago regarding the
>Apollo 13 mission and near disaster. I believe it was called "Houston,
>We Have a Problem" or something like that. I thought it was by Buzz
>Aldrin but a library search found nothing. It's an account of the
>engineering behind the Gold Team that brought the astronauts safely
>home. Has anyone heard of or have such a book? Where can I get it?
>Thanks & happy ho ho.
>
>Phil Biehl
>Home Row, Inc.
>
>--
>[e-mail]  Public Access User --- Not affiliated with TECHbooks
>Public Access UNIX and Internet at [phone] (1200/2400, N81)
>

 "Houston, We've Had a Problem" is a NASA/Government Printing Office
 non-technical account of the Apollo 13 accident. It is about a ten
 page magazine-sized booklet.

 I only know of one other "book" about the accident, that being
 "13: The Flight That Failed". I think the author was Henry S.F. Cooper,
 but I can't swear to it.

 -Brian


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

Date: Sat, 19 Dec 1992 05:52:54 GMT
From: [e-mail]
Subject: cryptocraft photography, Re: Aurora
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Dean Adams) writes:
>
> [e-mail] (Anthony J Stieber) writes:
>>[e-mail] (Dean Adams) writes:
>  >>Were there any photos of the F-117A prior to the official release?
>  >>I don't beleive so, even though it flew for almost a decade.
>  >Yes, at least one in AW&ST, July 10, 1989, p22.
>
> Yes... but the "official release" that I was speaking of took place on
> November 10, 1988.  That is when the AF first acknowledged the F-117As
> existence and released a single photo (which AW&ST of course printed :).
>
>  >This is sometime after the first flights of the craft in 1981, but of
>  >course all the early flights were done exclusivly at night.
>
> The Have Blues flew in 1977, and the first F-117A flew on June 18, 1981.
> In all that time it seems nobody really managed to catch a good view of
> them on film (at least nobody without a Senior Trend clearance :)
>
>  >I'm sure there will be pictures of whatever this/these craft are.
> I'll certainly be waiting...  It may be a while though.
>
>  >Someone with camera and a telescope lens will catch it.
> The sky is awfully BIG...
>

Yes, indeed, it includes everything up there...

However, there are a lot of people observing.  I wish the following
observation could have been recorded on film or tape, but it was a
visual observation by two people of something we have not yet nailed
down.  If the following were a satellite, it either had to have been
high up (notice it was seen after midnight EDT) or been low enough
to pick up and reflect sufficient ground illumination.  All attempts
to match it with known satellites have found nothing. Perhaps it
was a sighting of this whatever???  I'd sure like to ID it.
Serious comments most welcome.

  description of observation:

    Observation:  Unknown
    Observers:    I. Cooper, W. H. Hathaway
    Date:         night of 8-9 JUN 1991
    Time:         ~3-5 minutes both before and after 12:40:30 am EDT
                  - this time checked via phone while object was
                  being followed
    Site:         Severn MD,  Long: 76 Dg 38 Mn W, Lat: +39 Dg 11 Mn
    With:         10" f/6 Cave Astrola
    Eyepiece:     28mm Meade Orthoscopic
    R.A./Dec:     picked up while sweeping for NGC6829 in Cygnus,
                  roughly 19-20 Hr, + 50 Degrees,
                  followed continuously to vicinity of northern Ophiuchus
                  roughly 16-17 Hr, + 10 Degrees,
                  until obscured by leaves of large maple tree
    Magnitude:    roughly 8th magnitude
    Appearance:   ! extended object !, shaped somewhat like a horseshoe, but
                  sides squeezed together, or like a sharply closed
                  boomerang.  Overall size, roughly 1 arcminute.
                  (eye-ball comparison with disk of Jupiter)
                  Each 'arm' maybe 20 arcsec in width, 40 arcsec in length,
                  and the black space between the arms about 10 arcsec in width.
                  It looked much like the picture of HST on page 32 in the
                  July 1991 Sky and Telescope, but more "U" or "V" shaped
                  rather than the skewed "H" shape.  Note that was 1 1/4
                  arcSECONDS across from a distance of 1000 kilometers.
                  The surface texture was reminescent of a planetary nebula,
                  though with less surface brightness than the Ring Nebula.
                  Slight color - creamy, light brown to tannish - not
                  distinguishable from solar reflection.
                  Starlight clearly seen in the 'notch' between the arms.
                  Starlight possibly visible when passing behind each arm.
                  The direction of motion was _not_ along the axis of the
                  arms, more like 45 degrees from their intersection.
                  No point or point-like lights, no navigation lights,
                  colored nor white.  Sketch made immediately afterward.

  Identification: It had all the familiar steady motion of an
                  Earth satellite, but _not_ in a common Direct orbit from
                  West to East.  Motion actually more like from NE by N to
                  SW by S.  If a satellite, it was in a near-polar orbit, but
                  Retrograde.

Wm. Hathaway

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

Date: 19 Dec 92 01:26:06 GMT
From: Henry Spencer <[e-mail]>
Subject: DC vs Shuttle capabilities
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Greg Moore) writes:
>    Another question though:  Am I correct in recalling that the goal is
>to use pilots, and not astronauts (at least in the NASA sense) to fly the
>proposed DC-1?

Correct.  Astronauts are too expensive and too scarce.

>Who will do satellite repair?

Satellite technicians, who know how to do it right.

Except for a few of the most dedicated and conscientious ones, astronauts
make poor substitutes for people who know what they're doing.  You don't
hear much about the times when astronauts screw things up because they're
sure they know what they're doing even when they don't... but it happens.

>Who pays for training? The
>customer, or will McD (or whoever operates it) have "on-call techs" that
>you can pay extra for...

I don't think McDD plans to be in the operations business for the DCs,
any more than they are for their airliners.

In practice, it would probably make sense to have both.  Some jobs will
be involved enough to require giving specialists a crash course in
spaceflight; for simple things it will be more cost-effective to give
space-trained generalists a crash course in the particular job.
--
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  [e-mail]  utzoo!henry

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

Date: 19 Dec 92 01:49:54 GMT
From: Henry Spencer <[e-mail]>
Subject: DC vs Shuttle capabilities
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Greg Moore) writes:
>>>on rendezvous and repair.  So, now we have to get 3 objects in close
>>>proximity to each other...
>>Last time I flew back into DFW, I saw more than three planes on
>>the ground, in close proximity to one another.  I saw people and
>>baggage being transferred between flights.   Looks do-able.
>>
>    Umm, so?  Tell me, did you see 3 aircraft landing at the same
>time, or flying in formation?  Did you see baggage transferred between
>them while in flight?  I'm not talking about on the ground, I'm talking
>about in space...

Why do you assume that "in the air" is a better analogy for "in space"
than "on the ground" is?  Flying aircraft in close proximity is vastly
harder than doing the same for spacecraft, because of the complex and
unpredictable behavior of the atmosphere.  In-orbit operations resemble
on-ground operations more than in-flight operations:  the environment
is simple and predictable and you can take your time.
--
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  [e-mail]  utzoo!henry

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

Date: 19 Dec 92 01:30:24 GMT
From: Henry Spencer <[e-mail]>
Subject: fast-track failures
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (steve hix) writes:
>*Nobody* had much luck with counter-rotating props (save a handful such
>as the Shackleton and Spitfire XXII).  Using them meant that you could
>get by with a smaller prop diameter for a given powerplant, and they
>provided more yaw stability...but the stupid gearboxes never worked.

Too much American aerospace ingenuity and not enough mechanical engineering,
methinks. :-)  The Soviets licked this for their Bear bomber, since re-cast
in a variety of support roles, and (last I heard) still in production.  The
biggest counter-rotating props ever built, and they work fine.
--
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  [e-mail]  utzoo!henry

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

Date: Sat, 19 Dec 1992 00:19:36 GMT
From: Mark Schlegel <[e-mail]>
Subject: Justification for the Space Program
Newsgroups: alt.rush-limbaugh,talk.politics.space,sci.space

[e-mail] (Felix Gorney Mfg 4-6983) writes:

>: |>      Can any of you think of any moral or philosophical justification
>: |>     for using huge amounts of taxpayer money to fund the "space
>: |>     program" at all?  Not counting, of course, it provides high-
>: |>     pay, high-tech jobs for a bunch of us.
>:

 Well, I have one good reason, the space program more than pays for itself in
 new technology and spin-offs (actually the frequently quoted figure is for
 each dollar invested we have gotten a return of about seven bucks in high
 tech industry and savings)

Mark

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

Date: Fri, 18 Dec 92 21:01:19 PST
From: Brian Stuart Thorn <[e-mail]>
Subject: MOL (and Almaz)
Newsgroups: sci.space

>A mockup station (really just empty Titan tankage somewhat similar in
>size to a real station) and the first test capsule (which I believe
>was the refitted Gemini 2 capsule (with the new hatch in the heatshield)
>were launched around 1970.

>Dennis Newkirk ([e-mail])


   The Titan III / MOL launch took place in 3 November 1966.
   -Brian


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

Date: Sat, 19 Dec 1992 01:45:13 GMT
From: Henry Spencer <[e-mail]>
Subject: pumps etc.
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Scott Fisher) writes:
>Q: What drives the turbo-pumps the rocket exhaust?

There are several methods; the commonest is to burn some of the fuel and
some of the oxidizer in a separate burner and use the resulting hot gas
to drive pump turbines.

>If this is so...why can't you bleed some pressure from the exhaust to
>pressurisethe tanks?  Is this done?

Building the tanks themselves to take the full pressure needed adds a lot
more weight than the turbopumps.  Pressure-fed engines *are* simpler, but
there's a substantial weight penalty.
--
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  [e-mail]  utzoo!henry

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

Date: Sat, 19 Dec 1992 00:54:41 GMT
From: Henry Spencer <[e-mail]>
Subject: Shuttle thermal tiles
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Mary Shafer) writes:
>...The tiles are undamaged by
>snow and devastated by rain, with hail being not quite as bad as
>rain.  Of course you can cover the vehicle on the pad, but you can't
>fly through rain or hail without etching the tiles down to the felt
>pads they're glued to.

Anybody know if anything's been released on Buran's tile technology?
Allegedly the Buran tiles are not as long-lasting, but they're tougher.
A lot of people were surprised when the Soviets brought the first Buran
to the Paris air show -- flying it in atop a Mriya, straight through a
rainstorm.  (What *really* made jaws drop:  after landing, they got
directions to their parking place... and one million pounds of aircraft
turned off the runway and taxied across the *grass* to the right spot.
You won't see NASA's 747 doing that...)
--
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  [e-mail]  utzoo!henry

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

Date: Sat, 19 Dec 1992 03:59:14 GMT
From: Mary Shafer <[e-mail]>
Subject: Shuttle thermal tiles
Newsgroups: sci.space

On Sat, 19 Dec 1992 00:54:41 GMT, [e-mail] (Henry Spencer) said:

HS> A lot of people were surprised when the Soviets brought the first Buran
HS> to the Paris air show -- flying it in atop a Mriya, straight through a
HS> rainstorm.  (What *really* made jaws drop:  after landing, they got
HS> directions to their parking place... and one million pounds of aircraft
HS> turned off the runway and taxied across the *grass* to the right spot.
HS> You won't see NASA's 747 doing that...)

You won't see anybody's 747 doing that!

That's the disadvantage of civil aircraft--rarely can the big ones go
anywhere but a well-paved surface.

(I write "big" there so that no smart alec will say "What about
Markair's L-100 (civilian C-130) service onto the gravel above the
Arctic Circle?"  I know you all too well!)

Now I think that the C-17 could at least carry the weight of the
Shuttle and it certainly has a big enough vertical stab for
lateral-directional stability.  If we really want forward airfield
capability, maybe we should be looking in that direction.  Of course,
the real question is how badly do we want to taxi on the grass?

--
Mary Shafer  DoD #0362 KotFR NASA Dryden Flight Research Facility, Edwards, CA
[e-mail]                    Of course I don't speak for NASA
 "A MiG at your six is better than no MiG at all."  Unknown US fighter pilot

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

Date: Sat, 19 Dec 1992 01:50:08 GMT
From: Bruce Dunn <[e-mail]>
Subject: SSTO vs. 2 Stage
Newsgroups: sci.space

This posting consists of two parts:

1) A reply to the comments of Edward Wright on a previous posting on this
subject

2) An expanded description of the concept of using a LOX/kerosene booster as
a first stage for the DC-1


In reply to my posting attempting to show the potential virtues of building a
LOX/kerosene booster stage for the DC-1, Edward Wright writes:

Dunn:
>        If a DC-1 in SSTO mode can launch 10 tons to LEO and the two stage
>vehicle using the DC-1 as an upper stage can launch 50 tons to LEO, then we
>have the following costs for launching 50 tons:

>DC-1 in SSTO mode:  5 flights needed, incurring 5 DC-1 stage turnaround
costs

>DC-1 in 2 stage mode:  1 flight needed, incurring 1 DC-1 stage turnaround
and
>1 lower stage turnaround cost.

Wright:
The 2-stager is a *much* larger vehicle, so your vehicle fabrication
costs will be much larger.

Reply:
Larger is a slippery word.  Measured by dry mass, the lower stage is four
times larger than the DC-1.  Measured by fueled mass, it is two times larger.
Measured by linear dimensions, it is actually smaller than the DC-1 (it uses
much denser propellants).

Fabrication costs are not only affected by size, but also strongly affected
by complexity and by how closely material limits are pressed.  A petroleum
supertanker weighing 1000 times the weight of a Boeing 747 does not cost 1000
times as much.  In fact therefore, the fact that the lower stage has a higher
dry mass than the upper stage (even though it has smaller linear dimensions)
is an indication that it is likely to be less expensive than an upper stage.
For more details as to the proposed lower stage, see below.

Dunn:
>       I will assert that turnaround cost of the lower stage will not exceed
>the turnaround cost of the upper stage (the lower stage is much less
stressed
>than the DC-1 upper stage, and uses cheap kerosene and LOX as propellants).

Wright:
Think again.  The SSTO recovers back at the launch site.  Your first
stage will splash-down or land somewhere downrange.  It needs to be
retrieved, safed, and returned to the launch site before it can be
used again.  This is not only expensive, it's time consuming.  You're
going to need a lot of extra stages to make up for the down time.

Mating the two stages will take time and manpower also.

Using a different propellent in the first stage means you're
going to have to invest in another set of propellent storage
and loading facilites.  Fueling will be more complex, requiring
more time and manpower.

Reply:
I am assuming that the first stage will return to the launch site under its
own power.  This was described in the original posting a couple of weeks ago,
although in fairness, I did not repeat it in my most recent posting.  This
subject is further discussed below.

Mating the two stages will take time and manpower, but if the system is
correctly designed the actual labor need not be too much.  The DC-1 will have
to be transported in any case from its landing spot to its launch cradle.
The use of a lower stage would merely mean that the DC-1 would be placed on
the lower stage, rather than on the launch cradle.

The lower stage uses LOX and kerosene.  The LOX delivery facilties are
already available (the DC-1 uses LOX) - it would be merely necessary to beef
up the storage facilites for LOX.  The kerosene storage facilities are
off-the-shelf items (RP-1, a refined kerosene used in rockets, can be handled
by the same equipment as your local airport uses for jet fuel).  Fueling a
two stage vehicle ***will*** be more time consuming than fueling a single
stage, but since refueling 1 lower and 1 upper stage will deliver 5 times the
payload as 1 refueling of the upper stage in SSTO mode, there is still a
lowering of the man power needed per ton orbited.


Dunn:
>Therefore, as far as turnaround costs go, the two stage vehicle costs 2/5,
or
>40% as much as the SSTO.

Wright:
That doesn't follow from anything you've said up til now.  Your second
stage is a DC-1, so that's 100% right there.  The first stage, being
much larger, will be a lot more.

Reply:
I am talking about turnaround costs per unit of cargo orbited - I think that
this was clear in my posting.  Of course the single flight turnaround cost
for a two stage vehicle is greater than that of a single stage vehicle.
However, when you figure out the turnaround cost per ton of payload orbited,
the two stage system requires only 1 flight and 2 stage turnarounds to match
the payload delivered by 5 SSTO flights (hence the 2/5).

Dunn:
>        A final advantage to the two stage design comes from the time
>necessary to perform turnaround.   Since the lower stage can be inspected
and
>prepared for another flight while the upper stage is making an orbital
>delivery, the frequency of flights will be governed by the turnaround time
of
>the upper stage after it gets back.

Wright:
Only if the first stage can teleport.

Reply:
I am assuming landing at the launch site - see below.

Dunn:
>Say that turnaround time is 1 week.  If you spend your money on two DC-1
>vehicles and operate them in the SSTO mode, then it will take 5 weeks to
>put 100 tons in orbit (two flights delivering 10 tons each per week).

Wright:
Or 5 days, flying two flights per day.

Reply:
OK, in this case two flights of the two stage vehicle can deliver the desired
total payload in a time of 2 days, as compared to 5 days and 10 flights for
the DC-1.  The advantage remains - what is your point?

Dunn:
>If you spend your money on one DC-1 and 1 lower stage, then the same
>100 tons can be put into orbit in two weeks (two flights, each
>delivering 50 tons).

Wright:
Of course, you'll only have enough money to pay for half the first
stage.

Reply:

Developing a first stage will obviously be costly, and the two stage scheme
would be most attractive if large quanties of material have to be delivered
to LEO (for example, to fuel a Mars expedition).  Once development costs are
"sunk" (or are spread over a large number of vehicles), there is no reason to
believe that a 200 ton dry mass LOX//kerosene stage should cost any more to
fabricate than a DC-1.  Remember, the first stage is build with very large
margins and low technology, and does not have to survive a high speed
ballistic re-entry.


The following is an adapation and expansion of two previous postings on the
concept of a two stage DC-1.


The design margins on the hypothetical DC-1 are quite tight.  Consider the
following performance model, which approximates a DC-1  (1 ton = 1000 kg, LEO
assumed to require 9300 m/sec, gravity and air resistance losses included)

DC-1:

Isp (LOX/LH2)                              430
Usable Ascent Propellant Fraction          0.91
Liftoff Mass (exclusive of payload)        500 tons
Ascent total propellant mass               455 tons
Structure, landing propellant              45 tons
Oxidizer/fuel mixture ratio                5.0
Ascent LOX mass                            379 tons
Ascent LOX volume                          332 cubic meters
Ascent LH2 mass                            76 tons
Ascent LH2 volume                          1083 cubic meters
Payload to LEO (SSTO mode)                 11 tons

Note that overall Isp at 430 is less than that of the engines in vacuum
(assumed to be 450), as the engines will have to spend part of their time
operating in air.


Hypothetical first stage:

Isp                                        300
Usable Ascent Propellant Fraction          0.80
Liftoff Mass (exclusive of upper stage)   1000 tons
Ascent total propellant mass               800 tons
Structure, landing propellant              200 tons
Oxidizer/fuel mixture ratio                2.3
Ascent LOX mass                            558 tons
Ascent LOX volume                          489 cubic meters
Ascent kerosene mass                       242 tons
Ascent kerosenevolume                      303 cubic meters
Payload to LEO (with DC-1 upper Stage)      58 tons


This stage is heavier than the DC-1, but is actually smaller in physical
dimensions as the LOX/kerosene propellant combination has a much higher
density than the LOX/LH2 propellants of the DC-1 (look at the tank volumes).
This can be a really low-tech vehicle with no pushing of material limits.
Add lots of redundancy, and a large fuel margin for landing.  Use 6 ex-Soviet
RD-170 engines running at partial throttle for lift (even at liftoff, four
engines at full throttle are sufficient).  Engines are in a hexagonal
arrangement, and any single engine failure and most two engine failures are
not fatal as the other engines can take up the slack. For launching the  DC-1
goes on top of the first stage.  The first stage climbs in a largely vertical
trajectory (to avoid getting too far from the launching point), accelerating
to approximately 1100 m/sec (and incurring about 1000 m/sec gravity losses
during the time).  The DC-1 is then staged, and the first stage returns to
the launch site and lands vertically.  The DC-1 then tilts over to a more
conventional ascent trajectory and continues to orbit.  Should the DC-1 have
engine ignition trouble on staging, it has both the fuel and thrust to land
at the launch site.  With only some engines working, it can burn off fuel
until it has a thrust to weight ratio of greater than 1, hover to get its
weight down further,  and then land.

Because of the necessity of keeping the first stage near the launch site, it
does not pay to build up a large horizontal velocity increment.  For this
reason, the first stage follows a more vertical trajectory than normal,
causing more gravity losses than normal.  In calculations of the payload for
the two stage vehicle therefore, I have assumed an additional 250 m/sec
penalty over the "normal" orbital requirement of 9300 m/sec.  On the positive
side, the DC-1 only has to operate in a vacuum, and its specific impulse is
therfore 450 rather than the flight average of 430 assumed for SSTO mode.

For the sake of using simple numbers in comparing the operating costs of the
DC-1 used in SSTO mode and in 2 stage mode, consider the payload of an SSTO
flight to be 10 tons (vs. 11 calculated), and a two stage flight to be 50
tons (vs. 58 calculated).

        If one assumes that development costs are "sunk" and not to be
applied against flights (or alternately assumes that large amounts of
material are being launched and thus development costs can be spread over
hundreds of flights), then the cost of launching revolves around the cost of
refueling and refurbishing the reusable vehicles.  As pointed out by many
posters, this is largely driven by manpower requirements.

        If a DC-1 in SSTO mode can launch 10 tons to LEO and the two stage
vehicle using the DC-1 as an upper stage can launch 50 tons to LEO, then we
have the following costs for launching 50 tons:

DC-1 in SSTO mode:  5 flights needed, incurring 5 DC-1 stage turnaround costs

DC-1 in 2 stage mode:  1 flight needed, incurring 1 DC-1 stage turnaround and
1 lower stage turnaround cost.

       I will assert that turnaround cost of the lower stage will not exceed
the turnaround cost of the upper stage (the lower stage is much less stressed
than the DC-1 upper stage, and uses cheap kerosene and LOX as propellants).
Assuming, as a worst case, that the turnaround costs of the lower stage equal
the turnaround costs of the upper stage, then turnaround of the two stage
vehicle costs 2/5, or 40% as much as the SSTO per ton of cargo orbited.  This
will be offset somewhat by the fact that facilities, spares etc for two
different stages must be maintained, but I doubt that this will eat away all
of the apparent advantage of the 2 stage design.

        I will further note that using the DC-1 as an upper stage does not
prevent it being used in SSTO mode for lighter payloads when this would be
desirable.  It also offers the opportunity to boost individual payloads 5
times greater than that achievable in SSTO mode.  A two stage design is thus
more flexible than the SSTO.

        A final advantage to the two stage design comes from the time
necessary to perform turnaround.   Since the lower stage can be inspected and
prepared for another flight while the upper stage is making an orbital
delivery, the frequency of flights will be governed by the mission length and
the turnaround time of the upper stage after it gets back.  Say that the
overall time per launch is 1 week.  If you spend your money on two DC-1
vehicles and operate them in the SSTO mode, then it will take 5 weeks to put
100 tons in orbit (two flights delivering 10 tons each per week).  If you
spend your money on one DC-1 and 1 lower stage, then the same 100 tons can be
put into orbit in two weeks (two flights, each delivering 50 tons).  This
same 2 to 5 ratio holds no matter how rapidly the stages can be turned
around.  This ability to put up a lot of payload in a very short time may be
of advantage for situations such as trying to fill the propellants tanks of a
lunar or Mars expedition vehicle with cryogenic propellants.







--
Bruce Dunn    Vancouver, Canada   [e-mail]

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

Date: Sat, 19 Dec 1992 08:37 EST
From: [e-mail]
Subject: Stellar Evolution Research

I am doing a research project at school about star lives, and stellar
evolution. Where can I find good material that is neither very plain and
simple (like Sky&Tel articles), nor extremely technical ?

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

Date: Sat, 19 Dec 1992 01:59:04 GMT
From: Henry Spencer <[e-mail]>
Subject: What is DC ??
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Steven Cooper) writes:
>Pardon my ignorance folks, but what is this DC thing?
>...Who is designing/building it?

See some of the other recent postings for details.

>Now, I'm really confused about how you make an SSTO. As far as my meagre
>understanding goes, the final velocity of a rocket is the exhaust velocity
>times the logarithm of the mass ratio.

That's correct, ignoring gravity losses and air friction and assuming
a standing start.  (Most of these assumptions can be rationalized by just
adjusting the desired final velocity a bit.)

>How easy is it to get 5 miles per second with a
>single stage? I thought that exhaust velocities were only about 3000 m/s
>which would require a mass ratio of about 14. With payload and fuel for
>landing this sounds quite difficult.

It's a bit challenging but no longer looks that hard.  Modern exhaust
velocities are up around 4500m/s, if you're willing to accept the hassles
of working with liquid hydrogen.

Note that Atlas did it with a stage and a half -- dropping two engines
but nothing else -- in 1958.  Using 3000m/s exhaust velocity, too.

Even the shuttle isn't moving that fast at SRB burnout; the second stage
(main engines burning alone) does most of the work.  Gary Hudson claims
that if you deleted the SRBs and the orbiter, and just put six SSMEs
under the external tank, it could reach orbit (with a respectable payload)
as an SSTO expendable.

Making it reusable is somewhat harder.  But everyone who's studied the
technical details says it now looks feasible.
--
"God willing... we shall return."       | Henry Spencer @ U of Toronto Zoology
       -Gene Cernan, the Moon, Dec 1972 |  [e-mail]  utzoo!henry

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End of Space Digest Volume 15 : Issue 572
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