Sunday, July 20, 2008

Lights! Camera! Danger!

Jimmy Neutron has been busy helping the MSFC boys (and girls) genius design rockets. Or so it would appear from the looks of two decisions that have been made affecting ARES 1.

First, it appears that none of the ARES 1 crowd would be welcome at a Jimmy Buffet concert, as they are going to leave the fins at home. Rather than provide a passive system for maintaining stability during the early stages of ascent, they have opted to leave fins off the vehicle and use the SRB's active gimbal system, which is on the edge of having enough control authority to actually work as it is. They think this solution will keep life cycle costs down, as they won't be breaking fins off, or anything they attach to, when the booster his the water for recovery.

Of course, that decision costs 1100 lbs in extra propellant to keep the ship going straight up. Why so? Well, anytime that gimbal is off-center, thrust is not being generated in the straight up direction, and losses must be accounted for.

And, yes, that 1100 lbs is more than fins would weigh. Thanks for asking.

But that 1100 lbs also detracts from the rocket's overall ability to place the desired payload, ORION, into orbit itself. So enter the next decision in this Rube Goldberg line of reasoning. The second stage is a liquid propellant based system. Right after staging, and before the second stage motor is lit, the liquid oxygen and liquid hydrogen must be forced to the bottom of their respective tanks so that pick-ups can direct the liquids into their turbopumps.

So to get the liquids to the bottom of their tanks, small rockets, called ullage motors, are fired to settle the propellants. Normally these little motors are carried along for the ride after they do their job. But in this case, their extra weight, on top of the 1100 lbs for the finless wonder, also detracts from getting ORION to its intended destination.

You can almost hear our future Italian waiter yell, "I can fix that!" "Jettison the ullage motors!"

So instead of having a passive quick release on the fins as they hit the water, extra propellant is added for the steering motor on the first stage, and a jettison system is added for the second stage propellant settling system. Don't forget redundancy on that! Ooops, that's more weight. Risk accepted. Move on.

But we're not done. As reported here on RandS several weeks ago, three means of damping vibrations in the bladder basher were being considered. Now the program is finally ready to make a recommendation, and its the system we graphically depicted here back then. Small thrusters will be fired to and fro to counteract the oscillations in the SRB pipe organ.

We're not sure, but we think we saw Jimmy working on an Entropy Pump design last week as well. Heaven knows that's one device the minions perfected many years ago.


Mr. X said...

Interesting that you would compare the state of the Ares program to "Jimmy Neutron." It's probably more akin to "The Dark Knight." It takes a Joker to come up with a bad design like Ares I, and it takes an even bigger Joker to endorse the idea of multiple thrusters which will dampen out the oscillations (while increasing your LOM numbers.) Two-Face is busy telling the public that all is well, even though Ares I first flight keeps slipping to the right of the schedule.

In all seriousness, I have to ask about the "1100 pound" figure. Are you saying that 1100 pounds of the existing propellant load is being wasted on thrust vector control? Or will the SRB be stretched to accommodate that extra 1100 pounds? Without a change in moldline, it means another performance hit for a vehicle that already had tight performance margins.

kT said...

Why even bother to ask ANY questions about the Ares I, it was a complete failure ever since day 1, almost three years ago now.

After America spends 30 years dumbing down the populace with Reaganesque educational theories, this is what you get. This is the administration you get. Dumb, dumber and dumbest.

Rocket Man said...

That is correct, a performance hit in the form of 1100 lbs of propellant will go towards thrust vehicle control. The SRB will not be stretched.

Anonymous said...

now if the engineers are any good,
that 110 lbs loss is for worst case steering,
that they need to handle 95 or 99%
windshear and still hit the box.

Fins are a problem because while cheap
if you hit shear they don't help you
steer back into the lane.

now i suppose they may put very tight wind
restrictions to reduce steering needs but
then the vehicle becomes inoperable,
flying a couple days each month

kT said...

What vehicle? There is no Ares I.

It's a fantasy for stupid Americans.