Tailfins for Ares 1?

[Thunder Chicken]

Just a thought:

The current Ares design has an 'issue' or 'feature' in that it has a wide second stage perched on a tall skinny first stage, so without active control, the rocket aerodynamics are such that it really would rather fly tail-first. The analogy is trying to balance a broomstick in your hand - it can be done if you are constantly correcting, but the system is negatively stable in that orientation without those corrections.

What prompted me to think of this is the recent report on the Columbia crew survival, and the fact that the body flaps went to a free flight condition that caused the orbiter to pitch up when hydraulics failed, overloading the airframe. Had the flap remained in position during the hydraulic failure, the catastrophe (at worst) might have been delayed, and at best, may have permitted extended flight to a point where a survivable bailout might have been possible, depending on whether the left wing held on while maintaining the nominal re-entry AOA (a big if).

I am wondering about failure modes in the Ares 1, and it occurs to me if there is some guidance problem or mechanical failure that precludes control inputs, you then have a bunch of astronauts in a tumbling rocket, and I don't think the escape tower is really going to be much help in this situation unless luck is on their side.

So, in the interests of dumb and easy redundancy, why can't some good old fashioned tail fins be put on the first stage of the Ares 1? Yes, it is some additional weight, but wouldn't it take some of the effort out of the active control system? They would just need to be big enough to ensure that the ship doesn't flip tail first during a first stage guidance failure to ensure safe separation with the escape tower?

P.S. Or is their enough lead shot in the nosecone to prevent this tail-first issue?

 

[Andy44]

The Saturn rockets had small tailfins, but I don't think they would've helped much in the event an engine anomolously gimballed into the hard stops.

To make fins big enough would add lots of weight, and add drag, too. Add to that the mass of all that vibration-damping gear they've been talking about.

My instinct tells me that as the first stage burns off mass, the whole rocket becomes nose-heavy and thus more stable. In the meantime, you've got an LES rocket tower that can be fired if the AoA gets too far away from nominal. I'd say forget the fins. They are for the 1950s.

ETA: while sniffing around astronautix for information on Saturn rocket fins, I ran across this image of a Saturn Ib being used as a launch vehicle for the X-20 Dynasoar. Check out the big fins. Yet another couple of cool space vehicle designs lost to history [sigh]...

 

[garyw]

There is a full discussion on ARES I abort options on www.nasaspaceflight.com

In short, in the event of an out of limits problem the escape tower will fire pulling the capsule away from the rocket. The capsule will then enter and splash down in the Atlantic.

 

[Hielor]

ARES I abort options: Use the escape tower.

The tower takes all of a fraction of a second to pull the capsule away from the rest of the vehicle. In the event that the computer detects a loss of control, it will be fired automatically. The capsule won't be on the end of a "balanced broomstick," since it shouldn't stay on that long.

 

[starbird]

There was a design iteration where they were thinking of using small fins. I think the worry was that the TVC system wouldn't be fast enough to keep the correct end pointing forward.

At some point it was found that the TVC should work, and the fins were dropped.

There should be discussion about the subject somewhere on nsf.com