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Naked Emperor?

An interesting comment from someone who claims to work on the program, over at Space Politics (it's the sixteenth one), in response to the usual idiocy that everything is fine with ESAS, and that we all have to get behind it, and there are no other choices:

Your interpretation of published Ares I status is overly optimistic to an extreme. For instance, the J-2X ignition tests to which you refer has been done at the igniter level, a far cry from an actual engine test. The J-2X exists only on paper, and still very much at the powerpoint level.

The Ares I-X is also merely a stunt and represents no true progress to an actual flight configuration. It's what we in the business refer to as an "Admiral's Test," looks impressive to the uninformed, but adds no value to the final product.

You'll find that many of us Ares I naysayers actually work on or have involvement with the project. Ask the troops at MSFC and you'll get a completely different story than what you're getting through the NASA propaganda machine.

A lot of us are concerned with what kind of reputation we'll be left with when Griffin leaves and this whole Ares I/ESAS debacle is exposed.

That certainly rings true to me, based on other emails I get from program insiders.

Meanwhile, over at NASA Space Flight, there's a description of proposed solutions to the Ares vibration issue. The first one is the most interesting kludgesolution:

The anti-Thrust Oscillation RCS would be a totally new system, located on the aft skirt of the Ares I booster. Known as Active Pulse Thrusters (APT), documentation shows this system to hold the potential of reducing Thrust Oscillation by around 10 times that which is currently expected.

'Active Pulse Thrusters (RCS TO Damper): First Stage carries most of the design changes (Orion Service Module tanks change required),' noted associated documentation on this concept. 'Could provide 10X reduction in TO. Relatively mature thruster design. Self contained. Relatively mature control system.'

However, it would - as with most of the mitigation options - hold a mass impact on the vehicle, something Ares I has been struggling with since its early design cycles.

'Performance and aft skirt design challenge: (around) 500 lbm (pounds mass) payload impact. Trade required for separation and booster deceleration. Add failure modes. Must survive aft skirt environments.'

The system consists of four pods, located around the aft skirt on the Ares I First Stage. Early graphics of a system - that are bound to mature if accepted as the way forward - show each pod will have a fuel tank, an oxidizer tank, a pressurant tank, and seven thrusters.

The downside of this concept - which is a completely separate system than the roll control system on the interstage - is the addition of failure modes, which would hit Ares I's LOC/M (Loss of Crew/Mission) numbers.

Also on the downside, the concept is a retro thrusting system (negative thrusting) - which would impact on Ares I's performance figures.

OK, if I understand this correctly, this is what I would call the "Bose headphone" approach. Apparently, the plan is to actually fire thrusters in a direction opposite to the main thrust, at a frequency and phase to actually cancel out the vibration of the SRM. The description of the downside of this solution is a little dry, to me. They are introducing a new, complicated, expensive-to-develop-and-test system into the vehicle, which will add weight and (probably weird) potential failure modes, and reduce the net thrust of the vehicle, thus reducing its payload performance, which already has essentially no margin.


Next? Isolation mounts:

'May reduce payload by 1000 lbm. Reduces lateral stiffness unless mitigated in the design. Adds failure modes. Changes system modes for loads and control.'

"...unless mitigated in the design." There is an implicit assumption in that statement that such a mitigation is possible, but it may not be. I suspect that it doesn't just reduce lateral stiffness, but may also reduce stiffness in bending, which means more potential problems as the upper stage wiggles back and forth on top of the SRB, adding to the joy of the ride for the crew, and further complicating the control system's job, in all three axes.

They're right--this one is unlikely to survive the trade study.

Even the third, favored option is a kludge, which "consists of rails and springs under the top plate of the parachute platform on the First Stage. The active system would require a control system and associated battery power supply - all located under the aeroshell that houses the drogue parachute."

"The passive system has a rail attachment on the forward skirt extension of the First Stage providing lateral support. Damping would be provided by springs attached through the ancillary ring."

Rube Goldberg, call your office.

I've probably used this Einstein quote already recently, but it continues to apply: a clever man solves a problem--a wise man avoids it. This is all the result of the strange decision to use a Shuttle SRB as a first stage. That was not a necessary choice, and a good trade study (as opposed to the sixty-day exercise) would have identified these problems up front, and considered them in the trade. Anyone want to bet that it did?



Dan Bennett wrote:

I'm not an engineer, so that's probably why I'm confused by something here. This damping system is going to fire against the thrust of the main engine, canceling out the moments of peak thrust to give a smoother ride. Why not point them the other way and smooth out the ride by increasing the moments of least thrust? Then at least they're helping a little and not retarding the process.

Rand Simberg wrote:

Well, I am an engineer, and that's a good question. There's not adequate explanation of the theory here.

Phil Fraering wrote:

First, I thought I remembered from conversations with Gary Hudson (among many others) that control systems based around the throttling of liquid fueled engines had a lag on the order of half a second to a second (although I think they measured it in hertz, and don't remember the exact figure) and were therefore not very useful for use in steering.

It's amazing that their first solution is going to produce a system with all the costs and drawbacks associated with liquid fuels combined with the same for solid fueled rocket engines.

They could have just bought delta-iv engines off the shelf and clustered some tankage together.

anon wrote:

A structural engineer said that the Ares I stack is like a piece of spaghetti (1st stage) pushing a balloon (second stage) with a lead weight on top (Orion).

ken anthony wrote:

Too bad these guys don't play poker or they'd know that sometimes the best bet is to fold and play a new hand. Then again, if we let them lose instead of giving them more government money maybe some of the other players can win.

Edward Wright wrote:

Mark Whittington has his usual comedic response.

After claiming to be a professional novelist, a journalist, and a space policy analyst, Mark now says, "I simply cannot accept postings that frankly could have been made by anyone who might or might not be who they say they are."


Kelly Starks wrote:

I was shocked when I first heard of the idea. All the shuttle reports and cockpit camera footage shows that 8 segmengs of SRB, shakes 1000 tons of orbiter adn filled ET like [quote from astrounauts] "..a long running train wreck.." You don't need a engineering degree to think the light upper stage, SM, and CM are going to get shaken VERY badly on top of 5 segments.

Doug Jones wrote:

A possible answer to Dan Bennett's question: if the thrust fluctuations are not simple sinusoids, but come in the form of a series of spikes in thrust, then only the _excess_ thrust during the spikes can be usefully compensated (by firing upward to cancel them). The liquid thrusters could fire downward, but filling in the broad "troughs" in thrust would require a liquid booster with total impulse comparable to the solid.

Rube Goldberg is spinning in his grave (powered by a hamster wheel, a bowling ball, and a pigeon pecking at corn).

Doug Jones wrote:

A possible answer to Dan Bennett's question: if the thrust fluctuations are not simple sinusoids, but come in the form of a series of spikes in thrust, then only the _excess_ thrust during the spikes can be usefully compensated (by firing upward to cancel them). The liquid thrusters could fire downward, but filling in the broad "troughs" in thrust would require a liquid booster with total impulse comparable to the solid.

Rube Goldberg is spinning in his grave (powered by a hamster wheel, a bowling ball, and a pigeon pecking at corn).

Ed Minchau wrote:

Each of these kludges lists an impact on the payload mass (not the mass of the system itself, which makes sense but can be deceiving if you're not paying close attention - I missed it the first time). A 500 lbm reduction is basically reducing the crew size by one (along with his life support requirements).

The Ares was supposed to take 6 to orbit or 4 to the moon, so drop that number by one or two depending on the solution chosen: now it's 4 or 5 to orbit and 2 or 3 to the moon. Epic fail.

And that's without even considering that the added complexity of the system increases the number of possible failure modes. My corollary to Murphy's law: doubling the complexity of a system quadruples the number of failure modes; your mileage may vary.

As far as I can tell, the only trade studies are being done outsde of NASA, by SpaceX and DIRECT and others. Every time more news comes out about Ares it just looks worse and worse.

Mike Puckett wrote:


When you do your math, remember, the anti-shake device need only travel with the 1st stage. If it is 1K on the SRB, that should decrease the payload to orbit aroun 100lbs if memory serves.

Ed Minchau wrote:

Yeah, Mike, that's what I thought at first, too, until I realized that the masses they were talking about were not the masses of the fixes but rather the impact on the payload mass. The kludges weigh significantly more than 500, 1000, and 1000 pounds respectively.

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This page contains a single entry by Rand Simberg published on April 30, 2008 7:03 AM.

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