Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v08/v8_237.txt

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Subject: SPACE Digest V8 #237

SPACE Digest                                      Volume 8 : Issue 237

Today's Topics:
         Yet again the advantages of Mir over Skylab
       Re: Yet again the advantages of Mir over Skylab
       Re: Yet again the advantages of Mir over Skylab
       Re: Yet again the advantages of Mir over Skylab
       Re: Yet again the advantages of Mir over Skylab
               Mir predictions
----------------------------------------------------------------------

Date: Mon, 16 May 88 18:41:23 EDT
From: Glenn Chapman <[e-mail]>
Subject: Yet again the advantages of Mir over Skylab

In Space v8, 222 Karl Wagenfehr repeats on of the often quoted myths of
our space age, as have many others in recent days on the net:

> ...... Skylab was sent up, and manned.  It was no big deal, really.
> Yeah, a manned space station; big deal.  I would like to remind you
> that Skylab was a lot bigger than Mir (how much I don't recall off
> hand).  This slow turtle approach being better is just a load of bunk.
> We *had* a space station.  A much better space station than that which
> we envy the soviets today.  Permanent man presense in space is not
> such a big deal.  It just requires persistence and money.  I will
> concede on that point: the soviets are superior in that they stuck to
> their space program.  Had the united states shown just half the
> persistance of the soviets, I don't think we'd be envying them
> anything right now.  We were where they are now *15 years ago*!  Just
> we got bored, and stopped supporting Space.

   This persistant belief in the Skylab myth has gotten to be rather
disturbing.  I have started to have sympathy for Jerry Pournelle's
comment that he wished Skylab had never flown, then we would not be
trying to convince ourselves that we had done it all decades before.
For those that want a true comparison I have substantial revised a
breakdown of advantages and disadvantages of both I posted more than a
year ago (adding several more points, all to Mir's benifit).  In the
past year the advantages of Mir have increased by its operation and the
strong points for Skylab decreased.  Read it and weep.

Let us compare the advantages of the two stations.  As a reminder Soviet
stations have come in 3 generations: Their 1st containing Salyut 1 (Apr
- Oct '71), Salyut 2/Cosmos 557 (1973 - failures that were never
manned), Salyut 3 (Jun '74 - Jan '75), Salyut 4 ( Dec '74 - Feb '77),
and Salyut 5 (Jun '76 - Aug '77); Second generation with Salyut 6 (Sept
'77 - Jul '82) and Salyut 7 (Apr '82 - present); Third generation Mir
(Feb '86 - present).  Skylab was launched in May '73, the last crew left
in Feb '74, and decayed in July '79.

Where Skylab is currently ahead

(1) Skylab had a final mass of 77 Tonnes (with 2200 lbs per metric
Tonne), and the combined cluster Skylab + the Apollo Command Service
Module is listed as 90 Tonnes.  The current Soviet Mir/Kvant station has
a 33 Tonne mass as launched, while the combined Mir + Soyuz + Progress
cluster is 47 Tonnes.  However there are some caveats here.  The mass
for Skylab includes some 8 Tonnes of food, water, air, and fuel for that
were required for the entire mission.  By comparison the Progress
freighters bring that up to Mir.  There have been 12 Progresses to Mir,
each bring some 2.5 Tonnes of cargo/fuel/water for a total of 30 Tonnes
added to Mir, plus about 1.3 Tonne more brought up by the Soyuz's with
the Cosmonauts.  Of course some of that has been discarded as waste.
However the combined station mass is probably 60 Tonnes now (15 Tonnes
in the Progess + Soyuz carriers).  In Skylab all the garbage was kept in
a tank at the "bottom" of the station, so it maintained that mass (plus
the astronauts took up about 200 Kg per trip).  Also there is one other
problem with Skylab's mass - all the books I have found give the value
as launched, with both solar wings, but one was lost before orbit.  That
probably reduces the mass by 2-3 tonnes.  Note that the command/service
modules added 13 tonnes to Skylab, but little in useful capacity.  By
comparison the Soyuz solar panels feed the station about 1 KW of power
while the Progress's rocket engines are used to adjust the station's
orbit.

(2) Working volume for the Skylab complex was 357 cubic meters.  The
current Mir/Kvant combination is about 160 cubic meters.  From a
psychological point of view that was definitely better for Skylab crews
(each crewman had about 48% more volume).  However much of that volume
had little useful value, and pictures of Skylab show that its walls are
not completely covered with equipment, the way the Mir's is.  Also it
should be noted that the new NASA station has a volume per crew that is
about the same as Mir's, or perhaps a bit smaller.

Where Mir & other Soviet stations are ahead

(1) All Russian stations, right from Salyut 1 in 1971, have had orbital
manoeuvring rockets that use Hydrazine (UMHD) fuel and Nitrogen
Tetroxide oxidzer.  This allows the Soviets to do extensive orbital
changes with their systems. For example this lets them lower the orbit
to meet supply ships and Soyuz's (usually by letting the orbit decay a
bit so this does not cost them fuel), thus allowing those systems to
bring up more material.  Then they raise the orbit to keep the space
station up there.  Thus with this the orbital working lifetime of the
second generation Soviet Stations was about 5 years, and none of their
working stations have decayed from orbit (Salyut 2 and Comos 557 were
two early stations that were damaged on orbit, never manned, and allowed
to decay - the others were brought down by command from the ground).
Skylab had only a small Nitrogen gas system with 0.8 Tonnes of gas.  As
a result only small changes could be made to Skylab's orbit.  As we all
know it reentered in 1979 due to this.

(2) All second generation Russian space stations had 2 docking ports,
while Mir has 6.  Skylab had two, one axial and one on the side (the
side one was never used and was mostly ment for a rescue if needed).
The Soviet stations have 2 axial ports (Mir has 4 additional side
ports).  Axial ports are easier to dock to. Having several ports has
many implications.  First one crew could be docked to the station while
a second crew came up for a visit or to replace the first crew.  Without
multiple ports crew exchanges, where all or part of cosmonauts releaved
those currently manning the station, would be extremely difficult.
Secondly this allows cargo to be brought to the station while a crew is
on board (see point 3 also).  Thirdly the extra ports can be used to
expand the current station.  Salyut 6 & 7 had one extra module added to
them at a time (Salyut 7 had this done twice to it).  Mir currently has
one expansion module added (Kvant) but is designed to take at least 5
modules, plus a Soyuz and one other vehicle.  Skylab was a one shot deal
- no plans for expansion.  Indeed the TRS rocket system that was being
designed to attached Skylab from the shuttle had two plans for it - one
to boost it to a higher orbit, the other to send it to reentry in the
ocean areas.

(3) The Russians developed an automatic docking system back on Salyut 6
(1977) which allows unmanned cargo craft like Progress, or large "star"
modules (20 Tonne expansion units) to attach to the system.  Since the
cargo craft are unmanned they do not need heat shields and can carry
more material.  This naturely cuts the effort and cost in supplying the
station and makes their long duration missions possible.  Indeed Skylab
was launched with 140 days worth of supplies on board.  The Apollo
capsule could only bring a few weeks worth up with them.  The plans for
a fourth mission to Skylab called for only a 30 day stay, due to supply
problems.  Again the Soviet autodocking system means the expansion
modules need no crew, making their design and testing simpler.  Skylab
had nothing like that developed for it.  Sure we could supply a station
from the shuttle and expand it that way, but not without developing
equipment which we do not have.  The Russians have had automatic systems
doing this for 11 YEARS!

(4) All Soviet stations since Salyut 6 (1977) have been refuelable via
Progress tanker craft.  To date (May 16, 1988) 36 Progress tankers have
flown, 12 to each of the three last stations, all successfully as far
can be told.  In addition their to the fuel the station's water and air
was resupplied from the same vehicles via similar lines and transfer
systems from the Progress to the station.  Fuel supplied to Salyut 6 or
7 was about 5.3 Tonnes each, to Mir I estimate the same so far.  Since
UMHD/Nitrogen Tetroxide has a much higher specific impulse than Nitrogen
gas that gives them much more boost capability.  Water and air totaled
about 11 Tonnes each for the Salyuts.  Mir, even this early in its cycle
has been supplied with the same amount.  The first generation Russian
stations where like Skylab - throw away cans.  You used them until they
ran out of supplies and then tossed them.  Second generation and the new
Mir can be used as long as you need or want them.

(5) Since Salyut 6 (1977) Russian stations have had a working partial
water recovery system.  The older versions recovered about 50% of the
water (Mir may be better from some comments).  Since water a human uses
about 4.5 Kg of water a day, but only 0.8 Kg of oxygen and 0.7 Kg of
food (dry) this is the most important thing to recover first.  Sure
better systems have been built on earth, but nothing else has flown in
zero g.  This is vital for a real station or long voyages to the
planets.  Nothing like this on Skylab.  There also appears to be tests
of newer Carbon Dioxide removal and oxygen recovery systems on Mir,
though it is not certain they have replace the old absorption filter
system as of yet.

(6) Mir has a data/communications relay system through their TDRS system
(the Eastern Data Relay Network).  While the shuttle has this Skylab did
not.  They have had some some problems with this at the satellite end,
but the station capability is still there.

(7) Mir's solar power system puts out twice the power, 12-14 KW, of
Skylab's.  People think Skylab was better because some books talk about
the total possible power there as 23 KW.  However Skylab's max
deliverable power was only 8.5 KW before they lost the solar wing, and
about 6-7 after the repairs.  The difference comes from looking at the
area of the solar cells and their efficiency, while ignoring shadowing
effects, losses in the power cables, and other power system losses which
reduce the output to 33% of the max value.  Mir's values are for the
actual system output power. 2.5 KW of Mir's comes from solar panels
added to the station in a space walk last year.

(8) The Russians have put a lot of work into making the crew
psychologically comfortable on their stations, from the experience they
have gotten from their long voyages.  They send up gifts from home and
fresh fruits on the Progress tankers, have a TV studio set up to set up
weekly video conversations with friends and families.  Color schemes on
the station are for maximum comfort etc.  Again we can do this, but they
have 11 years of experience of what people miss most in orbit (they get
great pleasure in tending the small gardens in the space station for
example).

(9) Mir has currently 547 days of occupation (1136 man-days) in its 815
current existance and has been permanently manned since Feb. 9, 1987.
Skylab had only 171 days occupation (513 man-days) of 235 operational
days.  Furthermore Mir is still behind Salyut 6 which had 669 days of
occupancy, and Salyut 7 which had 712 days.  Skylab was not in good
shape at the end - one gyro had failed another of the 3 was showing
signs of failing, which was part of the decision to bring the last crew
home when they did.  Salyut 7 by comparison is still in orbit after 6
years, still under control and held a crew for 50 days just last year.

(10) Almost certainly the computers on Mir are far in advance of those
on Skylab.  Skylab's were of 1972 vintage, and the Soviets are probably
5 years behind us in computers, 10 years at the outside (there are
several DOD reports on this).  Hence that puts Mir's computers of the
equivalent of 1976 to 1980 vintage here.

Where Mir will probably exceed Skylab in the near future:

(1) The Mir complex will exceed the combined Skylab complex mass when
two more 20 Tonne "star" modules are added, probably by the end of this
year.

(2) The Skylab's working volume record will fall if the Soviets add the
announced 4 "star" expansion modules that Mir was designed to take.
This will take several years to occur.

All of this was only hardware.  It ignores the experience the Soviets
have gained: 11 years of materials science experiments, zero g life
science work, the knowledge of how space station system work in orbit,
how joined structures behave in orbit over years of time.  If you think
that the Russians having more than twice the number of man hours of
space experience means nothing then you must argue that space is
different in that reguard than any activity on here earth - experience
counts when things must be done well or quickly.  Right now the US is
not even on the top 10 list of space flight durations.

Look it, Skylab was a wonderful house in space, but we have done nothing
real in space stations since.  Saying that Skylab is better than Mir is
like arguing that the Titanic ocean liner is better than a flying 747
aircraft.  Sure the ocean liner was more comfortable and larger, but it
was older technology, goes less places, is generally less flexible than
the 747, and no longer exists.  We have no working space shuttle, and a
space station which will not be operating for another decade.  To say
that there is no problem because we are still ahead of the Russians on
the basis of Skylab is to deny the reality of the world.  It makes
people feel good in this country but it does not help solve our
problems.  As the saying goes "it is not the things that you do not know
that hurt you, but rather those that you do "know" that are not true".

                                          Glenn Chapman
                                          MIT Lincoln Lab

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

Date: 18 May 88 15:56:49 GMT
From: attcan!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Yet again the advantages of Mir over Skylab

> Skylab was a one shot deal - no plans for expansion.

Well, not quite true -- there were *plans* for expansion, back when
Skylab had five docking ports.  It's just that nothing was ever done
about them.  (And as a result, it didn't need five docking ports any
more...)
--
NASA is to spaceflight as            |  Henry Spencer @ U of Toronto Zoology
the Post Office is to mail.          | {ihnp4,decvax,uunet!mnetor}!utzoo!henry

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

Date: 18 May 88 16:43:46 GMT
From: thumper![e-mail]  (Phil R. Karn)
Subject: Re: Yet again the advantages of Mir over Skylab

Glenn Chapman's detailed comparison of Skylab and Mir is interesting,
but especially so because it omitted any mention of what each
accomplished in the way of practical applications (including meaningful,
PUBLISHED scientific research).  Just to keep things fair, we ought to
compare each to the contributions of unmanned spacecraft while we're at
it.

I suppose as an engineer I really ought to care about "whose is bigger"
and who is currently ahead in our hi-tech flagpole-sitting contest, but
as a taxpayer I want to know how effectively my money is being spent on
accomplishing the goals originally used to justify these expenditures in
the first place. Don't forget that these programs are means to an end,
not ends in themselves.

Phil

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

Date: 19 May 88 17:09:11 GMT
From: ulysses!terminus!rolls!mtuxo!mtgzy![e-mail]  (Evelyn C. Leeper)
Subject: Re: Yet again the advantages of Mir over Skylab

You missed the most basic and important one: Skylab is debris scattered
over the Australian desert; Mir is still up there.

                    Evelyn C. Leeper
                    201-957-2070
                UUCP:    mtune!mtgzy!ecl or [e-mail]
                ARPA:    [e-mail]

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

Date: 19 May 88 21:47:25 GMT
From: ulysses!terminus!rolls!mtuxo!mtgzz![e-mail]  (XMRP50000[jto]-d.l.skran)
Subject: Re: Yet again the advantages of Mir over Skylab


Detailed comparisons of research output from MIR/Salyut and Skylab
are probably impossible -- I strongly doubt the Soviets make
public any significant number of their real breakthroughs.

Dale

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

Date: 20 May 88 19:23:40 GMT
From: [e-mail]  (Richard the Nerd)
Subject: Mir predictions

Hi there!

Another evening visibility window for Mir is coming up, so I thought I'd
post some predictions for SF as usual.  Now, I am going home to Toronto
tomorrow, and won't be back for a week.  With all the manouevres that
folks think are likely occur, the predictions might be WAY out by the
28th, but, alas, I can't help it now.  Good luck anyways!  BTW, ignore
the magnitude predictions.  I have the wrong size data stored for Mir
and I did not bother to change them yet.  Actually, if you want
reasonable predictions just subtract about 4.5 from each predicted
value.

This is a message largely for folks on the mailing list.  (People on
this list get predictions for a few requested satellites, calculated for
their own locations.  If you'd like to be on this, drop off a note
including your latitude, longitude, sea level elevation, time zone, name
of town, and the satellites you would like to see, and I can put you on
it.)  Anyways, for those that asked to be on the list but did not
receive anything, please drop off a note - I have no clue whether the
predictions are reaching you, but I am making every effort to send them
successfully.

So, here are the predictions for SF:


   Prediction for:  San Francisco CA
   Lat:  37.800000  Lonw:  122.400000  Ht:    0.   Zone:   8.00000  DST:  1.0
   Satellite: Mir                     16609   Age:   17.5 days   Unc:   171 sec
   Local Date: 1988  5 28

     TIME      MAG  ILL   AZ  EL   R.A.   DEC   RANGE  VANG
   --------  -----  ---  ---  --  -----  -----  -----  ----
   22:27:40    5.3   37  260  29  09:44   10.7    626  0.47
   22:28:00    5.0   36  269  37  09:52   21.6    526  0.65
   22:28:10    4.8   35  277  41  09:57   28.5    485  0.76
   22:28:20    4.7   34  286  45  10:03   36.5    452  0.87
   22:28:30    4.6   34  299  49  10:12   45.5    428  0.96
   22:28:40    4.5   34  314  51  10:25   55.3    416  1.02
   22:28:50    4.5   34  331  51  10:46   65.2    416  1.02
   22:29:00    4.5   35  346  49  11:29   74.4    428  0.96
   22:29:10    4.6   36  358  45  13:26   81.6    452  0.87
   22:29:20    4.7   37    8  41  17:28   82.4    485  0.76
   22:29:30    4.9   38   15  37  19:34   77.7    526  0.65
   22:29:40    5.1   39   20  33  20:19   72.5    574  0.55
   22:29:50    5.2   40   25  29  20:41   67.8    626  0.47



   Prediction for:  San Francisco CA
   Lat:  37.800000  Lonw:  122.400000  Ht:    0.   Zone:   8.00000  DST:  1.0
   Satellite: Mir                     16609   Age:   18.4 days   Unc:   190 sec
   Local Date: 1988  5 29

     TIME      MAG  ILL   AZ  EL   R.A.   DEC   RANGE  VANG
   --------  -----  ---  ---  --  -----  -----  -----  ----
   21:15:50    4.5   84  172  27  13:07  -24.3    657  0.56
   21:16:00    4.4   86  166  29  13:29  -21.4    622  0.62
   21:16:10    4.2   89  159  31  13:52  -18.0    594  0.68
   21:16:20    4.1   92  151  33  14:17  -14.3    573  0.73
   21:16:30    4.1   93  142  34  14:42  -10.2    561  0.76
   21:16:40    4.0   95  133  34  15:08   -5.9    558  0.76
   21:16:50    4.1   95  124  33  15:33   -1.6    565  0.75
   21:17:00    4.1   95  115  32  15:57    2.4    580  0.71
   21:17:10    4.2   94  107  31  16:20    6.1    604  0.66
   21:17:20    4.4   92  100  29  16:42    9.4    636  0.59
   21:17:30    4.5   90   95  26  17:02   12.3    673  0.53



   Prediction for:  San Francisco CA
   Lat:  37.800000  Lonw:  122.400000  Ht:    0.   Zone:   8.00000  DST:  1.0
   Satellite: Mir                     16609   Age:   19.4 days   Unc:   212 sec
   Local Date: 1988  5 30

     TIME      MAG  ILL   AZ  EL   R.A.   DEC   RANGE  VANG
   --------  -----  ---  ---  --  -----  -----  -----  ----
   21:38:20    5.5   29  258  29  09:06    9.8    620  0.46
   21:38:40    5.2   28  268  37  09:15   20.6    520  0.65
   21:38:50    5.0   28  275  42  09:21   27.6    478  0.76
   21:39:00    4.9   28  284  46  09:28   35.6    444  0.88
   21:39:10    4.7   28  297  50  09:38   44.8    419  0.98
   21:39:20    4.6   29  313  53  09:53   54.6    407  1.04
   21:39:30    4.6   31  331  53  10:18   64.6    407  1.04
   21:39:40    4.5   33  347  51  11:07   73.8    419  0.98
   21:39:50    4.6   36    0  46  13:10   80.6    443  0.88
   21:40:00    4.7   38    9  42  16:43   81.1    477  0.76
   21:40:10    4.8   40   16  37  18:41   76.6    519  0.65
   21:40:20    4.9   42   22  33  19:28   71.6    567  0.55
   21:40:30    5.1   44   26  29  19:53   67.0    619  0.47


Good luck once again!

Rich Brezina

[e-mail]    (most nets, thank whomever)

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

End of SPACE Digest V8 #237
*******************