The 100/10/1 Rule.

richard schumacher wrote:

He will start by dropping the pointless qualifier "unmanned".


I had a thought here... if NASA built something along these lines it
would be spread all over the US:
Engines built here, tankage built over there, electronics somewhere
else, then assembled at yet another place, and taken from there to a
launch site.
But if done commercially...since it doesn't stage, you could build it at
one place, stick the payload on it, and roll it a mile or so away and
launch it. Without staging, one of the main arguments for a seacoast
launch site vanishes, and you now have all sorts of options open to you
as to where you want your launchpad at.
For GEO you still want it as far south as possible, but for polar orbits
you can put it just about wherever you want, so why not right next to
the rocket factory?
You could make it a manned launcher, but NASA would try to get their
hands on it, and it would end up being dragged down to KSC.
If you do it for commercial and military launches, then it might have a
chance of sneaking under the NASA radar.

Pat

In article ,
Pat Flannery wrote:
...keeping the ET's changing center of mass within the
limited gimbal range of the SSMEs absolutely dictated putting the LOX tank
as far away from the SSMEs as humanly possible.

I thought the gimbaling would probably be the main problem... the thing
is already fairly unstable without getting it completely unstable by
sticking the LH2 on top and having it constantly trying to go out of
control.

As I understand it, aerodynamic stability did not end up being an
overwhelming concern, because the SRBs are such a large part of the
stack's mass for most of the atmospheric flight. (Their nozzle gimbals
also handle most of the control then.) By the time they depart, the air
is thinning out fast and the importance of the aerodynamics is dwindling.

The main issue was reducing movement of the center of mass and keeping it
within SSME gimbaling range, so that the off-center SSMEs can always have
their thrust vector pointed toward it. The SRBs and the ET LOX tank
totally dominate the stack's center of mass for most of the flight, so
their centers *had* to be in roughly the same direction, as seen from the
SSMEs.

Was there any particular reason the LOX ended up on top in the Atlas?
Gimbaling limits again?

Gimbal range wasn't an issue with the engines directly under the tanks.
Reducing aerodynamic instability, to go easier on the control system,
might have been. I don't think I've ever seen a discussion of exactly why
Atlas has the LOX on top.

I note that both Jupiter and Thor had it on the bottom.

Designers with different priorities, probably. The Atlas's balloon tanks
minimize the structural-mass penalty of putting the heavy LOX high up, so
the more conventional structures might be expected to encourage putting it
on the bottom. Max Hunter, who was chief engineer for Thor, in later
years was big on saving structural mass by putting the LOX right above the
engines, so that may have been the issue for Thor.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

On Sat, 10 Mar 2007 14:52:12 -0600, in a place far, far away, Pat
Flannery made the phosphor on my monitor glow in
such a way as to indicate that:



richard schumacher wrote:

He will start by dropping the pointless qualifier "unmanned".


I had a thought here... if NASA built something along these lines it
would be spread all over the US:

Before or after the launch?

On Sat, 10 Mar 2007 14:47:25 -0600, in a place far, far away, "Jorge
R. Frank" made the phosphor on my monitor glow
in such a way as to indicate that:

"Paul F. Dietz" wrote in
:

Herb Schaltegger wrote:
On Sat, 10 Mar 2007 00:54:39 -0600, Henry Spencer wrote
(in article ):

Also note that the mass-ratio disparity is not as large as you'd think,
because a dense-propellant SSTO needs less delta-V to reach orbit.

Um, what?

He explained that. What part of the explanation didn't you understand?

He kinda sorta explained that. The actual delta-V required to reach orbit
is purely a function of orbital mechanics and is independent of propellant
density. But the rocket equation does not account for things like gravity
and drag losses, and those things do depend on propellant density. Rather
than expand the rocket equation to explicitly include those terms, the
convention is to apply a fudge factor to the delta-V term. Dense-propellant
SSTOs have lower gravity losses so they need a smaller fudge factor. (They
also typically have lower drag losses since the dense propellants allow
smaller tanks, but that's not as significant as the lower gravity losses.)

So a dense-propellant SSTO doesn't really need less delta-V to reach orbit,
but you use a smaller delta-V term when modelling one using the rocket
equation.

It depends on how you use the terms. *Ideal* delta V is the same for
all vehicles from a given location, but "actual" is not.

On Sat, 10 Mar 2007 14:47:25 -0600, Jorge R. Frank wrote
(in article ):

"Paul F. Dietz" wrote in
:

Herb Schaltegger wrote:
On Sat, 10 Mar 2007 00:54:39 -0600, Henry Spencer wrote
(in article ):

Also note that the mass-ratio disparity is not as large as you'd think,
because a dense-propellant SSTO needs less delta-V to reach orbit.

Um, what?

He explained that. What part of the explanation didn't you understand?

He didn't really. See Jorge's explanation below.

He kinda sorta explained that. The actual delta-V required to reach orbit
is purely a function of orbital mechanics and is independent of propellant
density.

Yep. Hence my comment/question.

But the rocket equation does not account for things like gravity
and drag losses, and those things do depend on propellant density. Rather
than expand the rocket equation to explicitly include those terms, the
convention is to apply a fudge factor to the delta-V term. Dense-propellant
SSTOs have lower gravity losses so they need a smaller fudge factor. (They
also typically have lower drag losses since the dense propellants allow
smaller tanks, but that's not as significant as the lower gravity losses.)

So a dense-propellant SSTO doesn't really need less delta-V to reach orbit,
but you use a smaller delta-V term when modelling one using the rocket
equation.

Thank you, Jorge.

--
You can run on for a long time,
Sooner or later, God'll cut you down.
~Johnny Cash

Pat Flannery wrote:

:Without staging, one of the main arguments for a seacoast
:launch site vanishes, and you now have all sorts of options open to you
:as to where you want your launchpad at.

Actually, no. You still have all the usual downrange range safety
issues. This is why launches over water are preferred. If something
goes wrong, you're less likely to hit something you don't own.

The real answer to this is to get reliability provably up to the point
where people think no more of the 'range safety' issues for a launch
than they do for those connected with an airplane taking off.

--
"Rule Number One for Slayers - Don't die."
-- Buffy, the Vampire Slayer

Rand Simberg wrote:
Before or after the launch?


You probably want to launch it in some fairly desolate area to be on the safe side.
But you do get the advantage of getting all your engines firing on the pad prior to liftoff, so you can be sure they are operating correctly.
Of course as soon as an engineer sees that they are going to suggest the Atlas engine drop, then suggest dropping the associated tankage as well as the engines, then since that will come to Earth somewhere, it should be on a seacoast... :-D

Pat

Fred J. McCall wrote:

Actually, no. You still have all the usual downrange range safety
issues. This is why launches over water are preferred. If something
goes wrong, you're less likely to hit something you don't own.


I say Polar launches take off from North Dakota and fly over Canada,
then if something goes wrong it won't fall on something _we_ own. :-(

Pat

On Sat, 10 Mar 2007 18:29:15 -0600, in a place far, far away, Pat
Flannery made the phosphor on my monitor glow in
such a way as to indicate that:



Fred J. McCall wrote:

Actually, no. You still have all the usual downrange range safety
issues. This is why launches over water are preferred. If something
goes wrong, you're less likely to hit something you don't own.


I say Polar launches take off from North Dakota and fly over Canada,
then if something goes wrong it won't fall on something _we_ own. :-(

And at worst, it kills a moose, or a polar bear (whose numbers are
apparently increasing).

http://www.telegraph.co.uk/news/main...9/wpolar09.xml

Per the headline, I blame global warming.

Rand Simberg wrote:

http://www.telegraph.co.uk/news/main...9/wpolar09.xml

Classic neocon fascist science : anecdotal evidence from the telegraph.

--
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