Oberg: "The real significance of the ISS thruster test failure"

Pat Flannery wrote:


Again, on the Intermountain Railways model....with the implied proviso
"get ****in real".
(anyone who hasn't built that model hasn't gotten any real idea
exactly _how_ big the original ISS proposal was intended to be. I've
got a Mir; I've got two Salyuts: I've got a Skylab.... that SOB is
gigantic.)



Following that up, NASA's biggest mistake was always showing the scale
of the ISS in regards to a docking Shuttle instead of an EVAing astronaut.
It's ****in' HUGE, as in Saturn V first stage huge.
You know; "how big?" ..reply being "around a city block across".

Pat

Pat Flannery wrote in
:

Jorge R. Frank wrote:

Yeah, I kind of thought so with all the modules sticking out at the
front end.

It's not the modules that make up the bulk of the area; it's the solar
arrays and radiators.

No, looking at the huge model (one of my favorites) you can feather
the solar arrays so that the present minimal drag to the ISS as she
travels forward through space, and the radiators are put in her drag
shadow.

The station can't fly like that all the time; the solar arrays have to be
feathered face-on (and the radiators edge-on) to the sun during orbital
day. *As I said before*, the ballistic number I quoted was an "average"
value over an orbital day, to account for solar array/radiator area.

Of course, that the final configuration actually is seems to change
from month-to-month.

The only major difference in frontal area between the config I quoted
above and the "current" config is the deletion of the Russian Science
Power Platform.

Again, on the Intermountain Railways model....with the implied proviso
"get ****in real".

I have that model... in fact, I have two of them, one at home and one at
work. I've even done a bit of scratch-build on both of them to properly
depict the current config (the IMR instructions only describe how to build
the "assembly complete" config).

Clarifying my earlier statement, I should have wrote "current planned
assembly complete config", not "current config in orbit right now".


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JRS: In article , dated Sat, 13
May 2006 19:05:46 remote, seen in news:sci.space.station, Jorge R. Frank
posted :
"Jorge R. Frank" wrote in
:

The ballistic number of the current config is 166.0 kg/m^2 while
flying in XVV (normal low-beta) attitude. That's a mass/area ratio;
the higher the number, the *less* draggy the station is.

The ballistic number of the station at assembly complete will be 70.02
kg/m^2, which is considerably less draggy than the current config.

Oops - got that backward; the final config is more draggy.

What does the drag amount to in actual Newtons and pounds-of-force, for
a typical or mean attitude? It can hardly be 166 kgf/m^2.


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Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
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Dr John Stockton wrote in news:$n9DF9AxAObEFwW9
@merlyn.demon.co.uk:

JRS: In article , dated Sat, 13
May 2006 19:05:46 remote, seen in news:sci.space.station, Jorge R. Frank
posted :
"Jorge R. Frank" wrote in
:

The ballistic number of the current config is 166.0 kg/m^2 while
flying in XVV (normal low-beta) attitude. That's a mass/area ratio;
the higher the number, the *less* draggy the station is.

The ballistic number of the station at assembly complete will be 70.02
kg/m^2, which is considerably less draggy than the current config.

Oops - got that backward; the final config is more draggy.

What does the drag amount to in actual Newtons and pounds-of-force, for
a typical or mean attitude? It can hardly be 166 kgf/m^2.

Right, the ballistic number is not pressure (force per unit area) but
rather mass per unit area. So 166 kg/m^2 means the station has 166 kg of
mass for every square meter of projected area.

Drag force is F = 0.5*rho*v^2*Cd*A, drag deceleration is a = F/m. The
ballistic number is BN = m/(Cd*A) so drag simplifies to a = 0.5*rho*v^2/BN
or F = 0.5*rho*v^2*m/BN. m is around 185,000 kg, v is around 7700 m/s. I
don't have my atmosphere models handy so plug in your favorite value for
rho and chug away.


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In article ,
Jorge R. Frank wrote:
No, looking at the huge model (one of my favorites) you can feather
the solar arrays ...

The station can't fly like that all the time; the solar arrays have to be
feathered face-on (and the radiators edge-on) to the sun during orbital
day.

There's always an orientation which puts the radiators edge-on to both the
Sun and the air, although perhaps it might be one that ISS can't use
because of something like gimbal limits. To keep the solar arrays edge-on
to the air, alas, you'd have to accept less-than-ideal Sun angles much of
the time, and a penalty on power output as a result. (Mind you, it might
have been preferable to just make the arrays somewhat bigger and plan to
operate this way, to save reboost fuel; there was a nice little paper by
Landis&Yu in 1991 suggesting this.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Mind you, it might have been preferable to just make the arrays
somewhat bigger and plan to operate this way, to save reboost fuel;
there was a nice little paper by Landis&Yu in 1991 suggesting this.

They still could do this, couldn't they? At least assuming the next
few assembly flights occur, they'll have more power than they know
what to do with, at least for a while.

Or is there something about the radiator design or something which
precludes it?

Jorge R. Frank wrote:

Again, on the Intermountain Railways model....with the implied proviso
"get ****in real".



I have that model... in fact, I have two of them, one at home and one at
work. I've even done a bit of scratch-build on both of them to properly
depict the current config (the IMR instructions only describe how to build
the "assembly complete" config).



That's a pretty challenging model to build; particularly as to how you
put it down during construction with all that gobblety gook sticking out
of it. It comes in a surprisingly small box given its finished size.
I wonder if that was the only commercial kit ever produced at taxpayer
expense? (NASA funded the design of the kit so that their contractors on
the ISS could have a model to go by to keep everything straight.)

Pat

Pat Flannery wrote in
:

Jorge R. Frank wrote:

Again, on the Intermountain Railways model....with the implied
proviso "get ****in real".


I have that model... in fact, I have two of them, one at home and one
at work. I've even done a bit of scratch-build on both of them to
properly depict the current config (the IMR instructions only describe
how to build the "assembly complete" config).

That's a pretty challenging model to build; particularly as to how you
put it down during construction with all that gobblety gook sticking
out of it.

One technique is not to religiously follow the instructions: go ahead and
glue each module from its parts, and test-fit the modules together
(sanding the connecting pegs as necessary), but don't permanently glue
the modules together. That not only allows you to build different station
configurations, it also makes it easier to put the thing down without
breaking it, since you don't have to keep the more fragile modules
attached while you're assembling the rest of it.

Another technique is to improvise display stands for the intermediate
configs. The IMR stand is really only suitable for the assembly complete
config, since the struts are so far apart. I scrounged together some
parts from a children's construction set toy (don't remember the brand
name, but it's kind of like plastic Tinkertoys in 3D - the hubs are
spherical rather than discs) and built some bases out of those; the pegs
that the IMR model uses to join the modules fit nicely into the holes in
the hubs.

It comes in a surprisingly small box given its finished
size.

I'm impressed by the engineering behind it (which was done at Johnson
Engineering rather than IMR). The modules really do fit together well
with just light sanding on the connecting pegs, and the pegs are strong
enough to carry the loads of the completed config without glue. And I'm
sure you've noticed that the model includes the parts for an Orbiter
Docking System (though the instructions don't mention it) that has a slot
cut in the bottom to accommodate the ribbed payload bay in Revell's 1:144
orbiter model. The kicker is that the ODS will snap into the payload bay
without glue (provided you didn't already glue in the Spacelab module
that comes with the Revell kit) and that the ISS model is strong enough
for you to hang the orbiter model off of it.

I wonder if that was the only commercial kit ever produced at
taxpayer expense? (NASA funded the design of the kit so that their
contractors on the ISS could have a model to go by to keep everything
straight.)

Didn't know that, but it doesn't particularly surprise me given that no
one was exactly stepping up to build a purely commercial model (the last
SSF/ISS model I'm aware of was Revell's model of Boeing's SOC station
concept from 1982 or so). And it was almost certainly less expensive than
commissioning JSC's in-house model shop; they probably would have cost
about as much per-model as the entire design and setup cost for the IMR
kit.


--
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Jorge R. Frank wrote:


One technique is not to religiously follow the instructions: go ahead and
glue each module from its parts, and test-fit the modules together
(sanding the connecting pegs as necessary),

Oh yes, those pegs... it sure would have been nice if all of them and
their mounting holes were the same size.
Looking at them, you assume that is the case; it is not the case.

I'm impressed by the engineering behind it (which was done at Johnson
Engineering rather than IMR).

It's a tough little honker, that's for sure; and it's made out of very
high quality plasic as well.
the really impressive engineering is on the big Canadian remote
manipulator arm- that's a little work of art in itself.

The modules really do fit together well
with just light sanding on the connecting pegs, and the pegs are strong
enough to carry the loads of the completed config without glue. And I'm
sure you've noticed that the model includes the parts for an Orbiter
Docking System (though the instructions don't mention it) that has a slot
cut in the bottom to accommodate the ribbed payload bay in Revell's 1:144
orbiter model. The kicker is that the ODS will snap into the payload bay
without glue (provided you didn't already glue in the Spacelab module
that comes with the Revell kit) and that the ISS model is strong enough
for you to hang the orbiter model off of it.


I have a 1/144th scale Shuttle, but it's attached to its ET and SRBs as
it sits between the Saturn V and N-1 in front of me.
You know what would have been nice for the ISS kit? A couple of EVA'ing
astronauts to give it scale.



I wonder if that was the only commercial kit ever produced at
taxpayer expense? (NASA funded the design of the kit so that their
contractors on the ISS could have a model to go by to keep everything
straight.)



Didn't know that, but it doesn't particularly surprise me given that no
one was exactly stepping up to build a purely commercial model (the last
SSF/ISS model I'm aware of was Revell's model of Boeing's SOC station
concept from 1982 or so).

Revell of Germany also makes a ISS in 1/144th:
http://www.starshipmodeler.com/real/jc_iss.htm
http://www.explorermagazin.de/modelle/miriss.htm
I like their cutaway truss structure; although this doesn't look as
tough as the IR one which was designed to be disassembled for easy
transport.
The Revell one is also cheaper than the IR one.
http://www.spacetoys.com/proddetail.php?prod=MST11

Pat

And it was almost certainly less expensive than
commissioning JSC's in-house model shop; they probably would have cost
about as much per-model as the entire design and setup cost for the IMR
kit.

Pat Flannery wrote in
:

Jorge R. Frank wrote:

One technique is not to religiously follow the instructions: go ahead
and glue each module from its parts, and test-fit the modules together
(sanding the connecting pegs as necessary),

Oh yes, those pegs... it sure would have been nice if all of them and
their mounting holes were the same size.
Looking at them, you assume that is the case; it is not the case.

All things being equal, I'd agree. At least they generally erred on the
side of making the pegs too big; it's a lot easier to sand them down than
to putty them up.

I'm impressed by the engineering behind it (which was done at Johnson
Engineering rather than IMR).

It's a tough little honker, that's for sure; and it's made out of very
high quality plasic as well.

Yes. Give credit to IMR; it's the type of plastic you typically see on
model railroads rather than model airplanes. And it's a clean injection
molding; no "flash" on the sprues.

the really impressive engineering is on the big Canadian remote
manipulator arm- that's a little work of art in itself.

I was impressed that all seven joints work. It makes me annoyed that none
of the shuttle model manufacturers have ever bothered to make an SRMS
that works half as well, even at 1:72 scale.

Perhaps you've also noticed that the sprues are almost exactly the right
diameter to fit into the SSRMS end effectors, just in case you need to
improvise "load-bearing" grapple fixtures as opposed to the decorative
ones that come with the overpriced "enhancement kit". :-)

I have a 1/144th scale Shuttle, but it's attached to its ET and SRBs
as it sits between the Saturn V and N-1 in front of me.
You know what would have been nice for the ISS kit? A couple of
EVA'ing astronauts to give it scale.

I scavenged one from my Boeing SOC model... :-)

I wonder if that was the only commercial kit ever produced at
taxpayer expense? (NASA funded the design of the kit so that their
contractors on the ISS could have a model to go by to keep everything
straight.)

Didn't know that, but it doesn't particularly surprise me given that
no one was exactly stepping up to build a purely commercial model (the
last SSF/ISS model I'm aware of was Revell's model of Boeing's SOC
station concept from 1982 or so).

Revell of Germany also makes a ISS in 1/144th:
http://www.starshipmodeler.com/real/jc_iss.htm
http://www.explorermagazin.de/modelle/miriss.htm

Right, but that one wasn't available at the time NASA contracted with
Johnson/IMR. It also has some annoying inaccuracies, such as a Soyuz
docked to Zarya *zenith* - when Zarya doesn't even *have* a docking port
on the zenith side. They can't use "changes in the station
configuration" as an excuse for that one; Zarya was *in space* before
this model was produced!

I like their cutaway truss structure; although this doesn't look as
tough as the IR one which was designed to be disassembled for easy
transport.

Although more intricate, it's also less accurate; most of the truss is
covered with thermal blankets. Though the IMR model isn't completely
accurate either - it has thermal blankets even on the front panels of P1,
S0, and S1, while the real ISS has open trusswork there.

http://spaceflight.nasa.gov/gallery/images/shuttle/sts-
114/html/s114e6378.html

If I had the patience, I'd paint the truss: aluminum girders, leave the
thermal blanket white, and paint the front of the truss black where the
open trusswork is supposed to be.

And easy transport isn't the only reason the IMR model is designed to be
disassembled; it also makes it capable of intermediate assembly
configurations. It even includes extra endcaps for the truss segments
(for example, the trapezoidal caps for the S1/P1 for the current
configuration). Though again, annoyingly enough, none of this is
mentioned in the instructions. If you build the model per the
instructions, you'll wind up with an "assembly complete" config and a
bunch of leftover parts in the box that the instructions don't mention.

--
JRF

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