Thrust Oscillation Issue Threatens Ares I Design, Aviation Week

Thrust Oscillation Issue Threatens Ares I Design, Aviation Week
http://www.aviationweek.com/aw/gener...&channel=space

There are lots of bits of actual data in the above article. In particular:

Of particular concern was the effect of the oscillation on the crew.
Based on static ground tests of four-segment boosters conducted
throughout the history of the shuttle program, and some very limited
information extracted from data collected during shuttle flights for
other purposes, the tiger team's "best estimate" for the vibration's
average amplitude at the Orion command module would be 4.3g. But the
Orion specifications set a crew health vibration limit of less than
0.6g rms (root mean square) in any axis over 1 min. during ascent.

"Vibrations beyond 0.6g rms for 1 min. are considered intolerable to
humans," state the "human system integration requirements" for the
Constellation Program, which is developing Orion and Ares I. "It is
expected that internal organs could be damaged if the level of
vibration or the time period for these levels were increased. In
studies, subjects [exposed to] such levels for 1 and 3 min. reported
that they had to exert great effort to finish the test. Pain was
reported primarily in the thorax, abdomen and skeletal musculature.
Varying effects on blood pressure and respiratory rate were also
observed." Getting those figures into spec "could be a significant
design challenge," the tiger team reported. And there is also a
concern that the vibrations will damage fragile hardware in the
cryogenic Ares I upper stage, the avionics ring above it and the
Orion service module that rides behind the crew capsule on top of
the stack.

But the focus team has since calculated that the problem may not be
as severe as originally feared. Nominally the oscillation frequency
of a five-segment booster is 12 Hz. (compared with 15 Hz. for the
four-segment version). But after that it gets complicated.
Translating RSRM ground-test data into accurate forcing function
figures and the stack's response to that force is extremely difficult,
particularly since the upper-stage and Orion designs remain immature
and oscillation data are based on ground tests.

Lyles says oscillation may not be as well-organized-and destructive-as
feared, and may even be random instead of a steady wave that can
resonate with the rest of the vehicle. And even if it isn't, the
vehicle response may not be as severe as possible. The shuttle stack
is "insensitive" to the frequencies generated by its four-segment
boosters, and because of the timing of the oscillations the Ares I
structure may already be robust enough to handle the most serious loads.
That would limit needed fixes to subsystems, which should be easier.

"[These loads come] late in the burn when there's not a lot of other
loads, which is a good place for it to be," Lyles says.

To get better data, Ares project engineers want to mount dedicated
pressure sensors inside an operational shuttle RSRM, probably on a flight
early in 2009, to measure specific changes in pressure inside the motor
as it burns, according to Ares Projects Office Manager Steve Cook. He
says
planning for a flight test is in the early stages, as are discussions
with
the shuttle program.

What scares me the most about this is that NASA will likely keep plowing
ahead with Ares I and Orion without understanding how bad this problem will
be. The pressure data gathered from a shuttle flight in early 2009 would
still apply to the four segment RSRM, not the five segment version planned
for Ares I. That and the design for Ares I upper stage and Orion will have
to "firm up" quite a bit before accurate vibration simulations can be
performed using the pressure data gathered.

In other words, NASA could spend billions developing Ares I only to find out
late in the game that it's fatally flawed, or not.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein

On Jan 29, 7:33 am, "Jeff Findley"
wrote:

What scares me the most about this is that NASA will likely keep plowing
ahead with Ares I and Orion without understanding how bad this problem will
be.

I'd say we should also worry that the potential problem either wasn't
recognized or was wished away when the decision to man-rate an SRB for
Ares 1 was made a while back.

Processes that do that don't inspire confidence in future performance.

"Allen Thomson" wrote in message
...
On Jan 29, 7:33 am, "Jeff Findley"
wrote:

What scares me the most about this is that NASA will likely keep plowing
ahead with Ares I and Orion without understanding how bad this problem
will
be.

I'd say we should also worry that the potential problem either wasn't
recognized or was wished away when the decision to man-rate an SRB for
Ares 1 was made a while back.

Processes that do that don't inspire confidence in future performance.

ATK was pushing "the stick" as "safe, simple, soon". They had to do
something to keep their business going after the shuttle retired. They
were, and are, a bit biased when it comes to the use of large, segmented
solids on manned launch vehicles.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein

In article ,
"Jeff Findley" wrote:

"Allen Thomson" wrote in message
...
On Jan 29, 7:33 am, "Jeff Findley"
wrote:

What scares me the most about this is that NASA will likely keep plowing
ahead with Ares I and Orion without understanding how bad this problem
will
be.

I'd say we should also worry that the potential problem either wasn't
recognized or was wished away when the decision to man-rate an SRB for
Ares 1 was made a while back.

Processes that do that don't inspire confidence in future performance.

ATK was pushing "the stick" as "safe, simple, soon". They had to do
something to keep their business going after the shuttle retired. They
were, and are, a bit biased when it comes to the use of large, segmented
solids on manned launch vehicles.

When are we gonna finally kill this pig? When is the next election?

"richard schumacher" wrote in message
...
In article ,
"Jeff Findley" wrote:
ATK was pushing "the stick" as "safe, simple, soon". They had to do
something to keep their business going after the shuttle retired. They
were, and are, a bit biased when it comes to the use of large, segmented
solids on manned launch vehicles.

When are we gonna finally kill this pig? When is the next election?

I think that the pig is finally starting to stink bad enough that whoever is
elected as President will want to kill it. At least I hope so. Large
segmented solids are a bad thing on a manned launcher and aren't even such a
good thing on an unmanned launcher.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein

On Jan 31, 8:03 am, "Jeff Findley"
wrote:

Large segmented solids are a bad thing on a manned launcher...

Old softie that I am, I'd back off that and say that large segmented
solids have known properties that should cause concern when
contemplating using one as the sole first stage engine of a manned
launcher. Consequently, a well-considered development/testing program
should have been carried out before committing to use them in
something like VSE.

IMO, since the Shuttle SRBs already exist and are in production, such
a program -- which should have gone through a couple of test flights
-- could have been done relatively quickly.

And, of course, there should have been a Plan B, probably Atlas/Delta,
if the solid program revealed major problems.

On Thu, 31 Jan 2008 09:03:13 -0500, "Jeff Findley"
wrote:


I think that the pig is finally starting to stink bad enough that whoever is
elected as President will want to kill it. At least I hope so ....

Well, it looks as if both Clinton and Obama want to continue with the
Orion Ares 1 design. Republicans, friendlier to the "military
industrial complex" will also do it. The good news is you have a year
to prepare for disappointment.



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On Tue, 29 Jan 2008 08:33:11 -0500, "Jeff Findley"
wrote:

Thrust Oscillation Issue Threatens Ares I Design, Aviation Week
http://www.aviationweek.com/aw/gener...&channel=space

There are lots of bits of actual data in the above article. In particular:

...... But the focus team has since calculated that the problem may not be
as severe as originally feared. Nominally the oscillation frequency
of a five-segment booster is 12 Hz. (compared with 15 Hz. for the
four-segment version). But after that it gets complicated.
Translating RSRM ground-test data into accurate forcing function
figures and the stack's response to that force is extremely difficult,
particularly since the upper-stage and Orion designs remain immature
and oscillation data are based on ground tests.

Lyles says oscillation may not be as well-organized-and destructive-as
feared, and may even be random instead of a steady wave that can
resonate with the rest of the vehicle. And even if it isn't, the
vehicle response may not be as severe as possible. The shuttle stack
is "insensitive" to the frequencies generated by its four-segment
boosters, and because of the timing of the oscillations the Ares I
structure may already be robust enough to handle the most serious loads.
That would limit needed fixes to subsystems, which should be easier.



Bingo.

"[These loads come] late in the burn when there's not a lot of other
loads, which is a good place for it to be," Lyles says.

Another important point. It's not as if Ares 1 will shake itself
apart on liftoff. It's something like 1 minute 40 seconds in before
this might be a problem.


To get better data, Ares project engineers want to mount dedicated
pressure sensors inside an operational shuttle RSRM, probably on a flight
early in 2009, to measure specific changes in pressure inside the motor
as it burns, according to Ares Projects Office Manager Steve Cook. He
says
planning for a flight test is in the early stages, as are discussions
with
the shuttle program.


And from the very end of the article:

'Although the problem isn’t fully understood, none of the NASA
engineers involved in solving it sees it as a show-stopper.

“I hope this is the worst we’ve got to deal with,” says NASA
Adminstrator Michael Griffin.'

What scares me the most about this is that NASA will likely keep plowing
ahead with Ares I and Orion without understanding how bad this problem will
be .....

On the other hand, the guys at NASA were the ones who found the
problem in the first place. If they are competent enough to identify
the problem years before the first Ares 1 flies, might they not be
competent enough to fix it in time?

..... In other words, NASA could spend billions developing Ares I only to find out
late in the game that it's fatally flawed, or not.


Or maybe, just maybe, against all probabilty, they could do the
impossible ... and fix it. Stranger things have happened.



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Michael Gallagher wrote:

On the other hand, the guys at NASA were the ones who found the
problem in the first place.

That's ridiculous, the entire physics community knew about this problem
from day 1. We didn't think anybody was dumb enough to actually try it.

After late September of 2005, I ran a blog which clearly pointed out
these problems, surely you must remember it. You did read it, right?

http://cosmic.lifeform.org (offline)

I guess you didn't read it.

On Feb 2, 1:12�pm, kT wrote:
Michael Gallagher wrote:
On the other hand, the guys at NASA were the ones who found the
problem in the first place.

That's ridiculous, the entire physics community knew about this problem
from day 1. We didn't think anybody was dumb enough to actually try it.

After late September of 2005, I ran a blog which clearly pointed out
these problems, surely you must remember it. You did read it, right?

http://cosmic.lifeform.org(offline)

I guess you didn't read it.

is it possible nasa intentially chose a design they knew wouldnt work?
just to keep the shuttle flying longer..........