It's all going horribly wrong.

[major_clanger]

Proposals made to solve Ares 1 rocket vibration worry

OK, that's the story written, I strongly suspect, from a NASA press release and putting, to say the least, a positive spin on things. Now, here's my take, and to establish my qualifications to pontificate, I have an MSc in space engineering and considerable experience in aerospace engineering analysis.

Ares 1 is not circling the plughole - yet. But this story marks the start of that high-pitched sucking gurgle you get when the bath really starts to drain in earnest. NASA, with good intentions, decided that it could make a new launch vehicle by taking one of the Shuttle's solid rocket boosters (SRBs) and plonking a relatively conventional liquid-propellant rocket stage on top, powered by a derivative of one of the shuttle orbiter's engines. Off the shelf bit A plus easy-to-design bit B equals cheap and simple space launcher.

Except that it was never going to be that simple. Because the shuttle has two SRBs it steers in large part by getting them to differentially swivel their nozzles. (And don't underestimate what a tough job it was to make that work for a solid rocket that size.) This means that of itself an SRB has pitch and yaw control, but no means of making itself roll around its long axis. Or, more importantly, stopping itself rolling, which is something that rockets are prone to do. So Ares 1 needed a roll control thruster system adding, and straight away it's not an off-the-shelf SRB any more.

Then the upper stage design changed. This means that the SRB isn't powerful enough any more, so NASA dusted off some ideas about stretching the SRB to give it more thrust. Now it's definitely not an off-the-shelf SRB any more. Worse, this means that it has a whole new set of vibrational modes, which is where the current problem probably came from. This is awfully hard to design out of a solid rocket, so the solution is to add more systems and thus more weight. This cuts into the performance margin still further, in what to many aerospace engineers is a painfully familiar vicious circle.

The whole point of Ares 1 was that it was meant to be a simple derivation from Shuttle technology. NASA is already about to start rebuilding one of the Launch Complex 39 pads to handle Ares, and is soon to start taking decisions that will commit the Shuttle programme to finishing after 2010. In the mean time the replacement vehicle is slipping in schedule at around twelve months a year and is starting to look more and more as if it just won't have the oomph to get the new Orion spacecraft into orbit - well, not with any useful payload on board.

I mean, the whole thing is a mess. Just look at that diagram; the Ares 1 hasn't been nicknamed 'The Stick' for nothing. That long, thin rocket with a big, relatively light stage on top - I wouldn't like to be the engineer trying to develop the flight control software to take that through wind shear at supersonic speeds.

Right now Ares 1 is putting out the same vibes that Shuttle was circa 1978, as the launch schedule began to look impossibly optimistic and all sorts of problems with flaky protective tiles and misbehaving engines started to show up. Except that back then the hype of how wonderful Shuttle was going to be just carried everyone along for the ride, with even the pessimists assuming that this was merely a temporary setback before those NASA predictions of fifty missions a year came to pass. We all know where that took us, thanks in large part to long-ignored problems with, yes, the SRBs.

The last time NASA transitioned from one manned space vehicle to anther, the interval - Apollo-Soyuz to STS-1 - was five years and eight months. The current schedule has STS-133 landing in June 2010 and Orion 2 flying in March 2015, four years and nine months later. My own prediction: that gap will widen to more than the Apollo-to-Shuttle gap, unless someone (an incoming President Obama?) bites the bullet and declares that Shuttle will keep on flying until at least some credible development milestones for both Ares 1 and Orion have been passed. But that will cost a lot of money, and raise the risk of another Shuttle disaster.

That, however, is the corner that NASA has painted itself into.

Comments

[nmg.livejournal.com]

I can't work out from the news stories whether the vibrations occur at T+110s in the existing 4-segment SRBs, or are projected to appear at that time in the proposed 5-segment stage for Ares I. Any idea?

[sharikkamur.livejournal.com]

I don't think they stand a chance of getting Orion 2 flying before at least 2018, possibly even 2020. As you say, a 12-month per year slip is the current rate and I don't see that changing quickly.

Might I ask for the benefit of your experience and enquire what you thought of the Black Horse SSTO with in-flight refueling concept? I've always thought that might be the way to go if we want to get realistic rapidly reusable craft.

[major-clanger.livejournal.com]

According to this article it's a problem with the SRBs as they exist now, but which doesn't cause issues for Shuttle as the overall vehicle mass there is much larger. The change to 5-segment SRBs complicates analysis though, as it is not clear what the vibrational behaviour of those is going to be until they're tested more thoroughly. (ATK did test-fire a five-segment SRB back in 2003, but I don't know if that was representative of the version being used for Ares 1.)

[major-clanger.livejournal.com]

It was a very interesting and ingenious design (and I'm not just saying that because I know the originator, Mitch Burnside Clapp). My feeling was that a true orbital version of Black Horse would have posed huge development challenges, but that the proposed suborbital development version, which could have placed small payloads into orbit via an upper stage, would have been a very worthwhile development. Unfortunately, it came along just as (a) the potential market for huge constellations of small comsats was evaporating (once it became clear that there was little real demand for middle-of-nowhere mobile phone capability) and (b) the Clinton administration was reining in what were seen as some of the more extravagant space power aspirations of the US Air Force.

Black Horse was taken forward as Pioneer Rocketplane, but underwent several major changes. Mitch left some years ago, and the current version has little to do with his concept, essentially being an aspiring competitor to Virgin Galactic in the suborbital space tourism business.

[sharikkamur.livejournal.com]

The in-flight refueling always struck me as a particularly elegant solution to the weight problem. It also seemed the sort of short-cut that the USAF might take. I'm very surprised that there has been so little military spaceflight development from the major powers.

[vicarage.livejournal.com]

I thought one issue with the Ares-1 is that you had to make the Orion spacecraft overweight to ensure that the astronauts didn't pull too many G at the end of the launch, as the unthrottleable SRB was generating too much thrust. Has all that cushion of power gone now?

[daveon.livejournal.com]

As I've read it, they quickly lost all the weight advantages as they had to fiddle with the basic design. Now, as MC says, they're in danger of lacking necessary thrust for the Orion to do what it was meant to even if they cut weight out.

The alt.space crew see this as a great opportunity for Falcon 9 and Musk's boys to come and show NASA how it's done with the Dragon...

I rename deeply cynical about that one too.

[non-trivial.livejournal.com]

[...]this means that it has a whole new set of vibrational modes, which is where the current problem probably came from. This is awfully hard to design out of a solid rocket

Just out of interest, is there any reason that a solid rocket is trickier vibrationally than a liquid one? I'm guessing that in a solid one most of the innards are the fuel, and so you don't have much wiggle room to move stuff around?

[major-clanger.livejournal.com]

The 'engine' - i.e. the void left as the fuel burns - changes shape radically over the burn time of the motor. Also, you can't really throttle a solid rocket as its approaches a resonant frequency, you just have to push through it. True, liquid rocket stages also have vibration problems (POGO oscillations in the engines, slosh modes of fuel) but there is a bit more scope for control.

These issues have generally been accepted until Ares 1 because solid rockets have either been used on unmanned vehicles or as add-on boosters to larger rockets. Ares 1 is the first man-rated vehicle that uses a solid rocket as its solitary first stage.

[major-clanger.livejournal.com]

Apparently the blueprints are all on file - but they're of limited use as the materials and in particular components are all more than forty years out of date. Building a Saturn V from the original designs would be like trying to assemble a VC-10 from scratch.

Now, if the Saturn V had been kept in production and progressively updated, in the manner of Atlas or Delta, things would be very different.

[major-clanger.livejournal.com]

There's a simple reason for this. Despite numerous studies trying to find one, there just isn't a mission for a spaceplane. Recce? If you can afford a spaceplane, you can afford spy satellites. Nuclear strike? If you can afford a spaceplane, you have ICBMs. Conventional strike? Interesting idea, but the payload is so small that you don't really have much advantage over a cruise missile. Anti-satellite? Can be done far more cheaply with modified ICBMs or even SAMs, as the Chinese and US Navy have recently demonstrated.

What might happen is that if commercial spaceplanes are developed, even limited ones like Virgin and Scaled Composites SpaceShip 2, then people might start to look at military applications for them. I suggested in a Staff College presentation that such a vehicle might make an attractive innocent-looking alternative to ICBMs for aspiring nuclear powers. Even so, the counter to such vehicles won't be a 'space fighter', it will be a conventional strike against their launch facilities.

[major-clanger.livejournal.com]

http://www.astronautix.com/lvs/saturnv.htm

[non-trivial.livejournal.com]

If you're an aspiring nuclear power with the tech base to build a spaceplane that can accurately deliver a bucket of sunshine, you've presumably got the tech to develop a 'commercial space launch' capability that's accurate enough to achieve the same result more cheaply?

[major-clanger.livejournal.com]

My thought was more along the lines of considering the implications of vehicles such as SpaceShip 2 becoming commercially available. If you're an up-and-coming member of the Axis of Evil (TM) then developing your own missile capability might earn you unfriendly comments at the UN, or worse, and it's not the sort of thing you can readily buy without attracting attention. But if we get to the situation where aerospaceplanes are as available as high-end executive jets, it might be a lot harder to stop them from ending up with the sort of people who might want to stick a nuke in the hold and point it our way at Mach 8.