Design of Next-Gen NASA Rocket Showing Flaws

caffiend666 writes "According to an AP news article, NASA engineers are concerned about the design for the new rocket meant to replace the shuttle. Work on the project has revealed that the first few minutes of flight could see 'violent shaking', a serious flaw that might destroy the craft soon after launch. 'NASA officials hope to have a plan for fixing the design as early as March, and they do not expect it to delay the goal of returning astronauts to the moon by 2020. The shaking problem, which is common to solid rocket boosters, involves pulses of added acceleration caused by gas vortices in the rocket similar to the wake that develops behind a fast-moving boat.'

Comments

It's simple to solve this problem

[ThreeGigs]

It's a harmonic vibration issue apparently, and these are generally solved quite easily. Adding or removing stiffness, a spiral wrap of an energy dissipating elastomer, isolation mounts, ading or removing mass (or simply moving mass around)... doesn't look like it's a severe issue at this early of the design stage. Someone's just being alarmist.

Re:It's simple to solve this problem

[corsec67]

Actually the way I read it is the problem is in the gas inside the solid booster having turbulence that leads to vibrations. Thus it isn't dependent on the structure of the booster, but on the way the fuel inside it is shaped, at ignition and during the burn.

But, I am not a rocket scientist.

Re:It's simple to solve this problem

[ThreeGigs]

Yes, it's the gas that causes it, which would ordinarily just be a rumble. However, the frequency of the rumble apparently matches one of the harmonics of the rocket casing or motor, which causes a nasty bit of positive feedback.

Much like bouncing in the middle of a board. Changing the frequency of the input force means you won't go as high, changing the mass (lighter or heavier person) means the resonant frequency changes, making the board out of something stiffer or less stiff changes the optimum rate of bouncing...etc.

Re:Nasa

[wjsteele]

Actually, NASA's ROI is pretty good at about $7 returned for every $1 spent. They also develop a lot of technology that doesn't have a financial ROI, but rather a simple non-tangible benefit to society as a whole. For example, they developed the CCD imager for use in the Hubble Telescope. That technology is now widely used in inexpensive digital cameras but is more importantly also used in medical imagers for detecting breast cancer. It has eliminated something like a half a million unneeded biopsies which not only save that cost, but also the pain from the procedure itself.

Bill

Everything old is new again

[Anonymous Coward]

The first Saturn V rockets for the Apollo program had a similar problem with pogo oscillations. http://www.time.com/time/magazine/article/0,9171,902216,00.html . Engineers were able to solve the problem back then, I'm sure they can come up with solutions again.

Apollo Called: It Wants its Saturn V Back

[segedunum]

Seriously, this was known about forty years ago and are called pogo oscillations. They are generally disastrous, and they were the cause of Apollo 13's fifth engine shut down after liftoff.

In general, I'm pretty non-plussed by NASA's moon landing attempts. Their design is basically Apollo rehashed plus forty years (fifty years if it actually launches - pretty depressing), the vast majority of it isn't reusable (I haven't got a clue how they can call it a shuttle replacement) and it really doesn't get us any further forwards in terms of making getting into space easier, safer and something that can be done on a regular basis.

Re:Apollo Called: It Wants its Saturn V Back

[Chairboy]

Nope, Pogo oscillation was caused by compression waves that affected pump volume in liquid fueled rockets. This was solved in the SSME for the Shuttle by adding a chamber along the fuel feed that acted like a capacitor. Transient pressure waves would back fill the chamber, then the other side of the wave would suck it out. Constant flow, no pogo.

This is a solid rocket, it's a different problem.

Re:Apollo Called: It Wants its Saturn V Back

[prisoner-of-enigma]

Seriously, this was known about forty years ago and are called pogo oscillations. They are generally disastrous, and they were the cause of Apollo 13's fifth engine shut down after liftoff.

They're "generally disastrous" only in the sense that they'll destroy the craft if they aren't addressed. Apollo solved the problem by essentially adding a big bellows to the fuel supply feed, allowing the pressure pulses to be damped instead of allowing the fuel flow to resonate. The Space Shuttle main engines have similar dampers in place, and their design was based on data acquired during Apollo.

In general, I'm pretty non-plussed by NASA's moon landing attempts. Their design is basically Apollo rehashed plus forty years (fifty years if it actually launches - pretty depressing), the vast majority of it isn't reusable (I haven't got a clue how they can call it a shuttle replacement) and it really doesn't get us any further forwards in terms of making getting into space easier, safer and something that can be done on a regular basis.

Your observation shows a shocking lack of perspective. Just because the design has a capsule on top doesn't mean it's "Apollo...plus forty years." First off, given currently available technologies, a capsule design is the most efficient, most practical way to get people out of orbit. I'll remind you that the Shuttle, for all its supposed advantages, hasn't left LEO and can't leave LEO. It's too heavy. Reusability carries a very heavy penalty (no pun intended).

Speaking of reusability, you've again missed the mark. The capsule itself is designed to be reused a number of times. The ablative heat shield can't be reused like the shuttle tiles, but then again an ablative shield doesn't have the maintenance (and failure) issues of shuttle tiles, either. The solid booster first stage is, unless I'm mistaken, designed for re-use just like current Shuttle SRB's.

Also, don't forget that reusability hasn't proven to be the huge advantage NASA thought it would be back in the 60's when the Shuttle was on the drawing board. Tile inspection and replacement is extremely time consuming and expensive. The Shuttle engines, for all their fantastic performance, are maintenance nightmares. Until we have some radical breakthroughs in materials technology or propulsion, it's actually cheaper to use expendable stages than it is to reclaim, disassemble, inspect, repair, re-assemble, and re-certify a reusable spacecraft or propulsion system. If you doubt this, consider the cost per pound of Apollo launches versus the cost per pound of Shuttle launches; the Shuttle is far more expensive.

When compared with Apollo, the Shuttle actually comes off quite poorly. The Shuttle is far more expensive to fly. It can't launch with the same frequency as Apollo. It has no abort system for most of the launch profile. The abort modes available even after the SRB's detach are extremely hazardous. It can't leave LEO. It can't carry anywhere near as much payload as the Saturn V. Still think that "going back" to Apollo is a bad idea?

In fact, the Shuttle only exceeds the "forty year old" Apollo in two notable areas: it can carry seven astronauts instead of three, and it can return orbiting satellites to Earth. The former ability is useful but with a limited return; seven orbiting astronauts hasn't given us nearly as much of a return as three moon-bound ones did forty years ago. The latter ability -- returning satellites -- has rarely been used. The original idea (thanks, Air Force) was to snag Soviet satellites and return them for intelligence purposes. Beyond that, returning, repairing, and re-launching a satellite makes absolutely no economic sense. The Shuttle is a neat idea. It's been a wonderful test-bed for new concepts. But as a practical, useful, reliable, affordable space truck, it is an abject failure. The Shuttle has taught us what not to build.

In closing, I'll r

Re:Nasa

[MrKaos]

http://freakonomics.blogs.nytimes.com/2008/01/11/is-space-exploration-worth-the-cost-a-freakonomics-quorum/

Ask anyone who has flown on the shuttle

[cozytom]

The first couple minutes really suck. Those SRB's shake bad. Once they burn out, the ride is really smooth. Solid rockets are that way, I am sorry, but you can't have fuel moving up the tube and the flame following it and have a smooth ride. Think of the solid fuel, it doesn't move, only the pressure. The farther it moves up the more the pressure changes here and there. POGO is something else. That is more from liquid fuel sloshing around, not presenting and even pressure. As the fuel is falling it adds more weight causing more thrust, and as the fuel splashes up, then there is less weight and pressure, meaning the engines are working to compensate. Someone will come up with something to make the ride some what tolerable. I don't think I'd ever want to ride that big long SRB into orbit. That will be more jarring 8 minutes of your life! ick.

Not really

[WindBourne]

IANARS, but these do not blow up. Heck even the challenger did not blow up. A seal popped open that allowed the exhaust to hit the fuel tank. The simple fact is that these are VERY safe. It has only several issues; The mix is hard to get right. Considering that it is the same mix that has gone into all 120+ x 2 shuttles, I am not too worried. The second is that once lit, there is no stopping it, and there is no throttling it (other than building it into the mix). This is not like strapping yourself to a fircracker, but to a simple bottle rocket that does not pop.