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Old 11-18-2008, 04:34 PM
Jeff Walther Jeff Walther is offline
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Default Gap Staged Booster Recovery System?

If one wants to gap stage a rocket and have a streamer or parachute on the booster are there any methods available besides the following two:

1) Use the escaping gasses and clever design of the engine mount to blow it ('chute or streamer) out the rear of the booster.

2) Leave room in the sustainer between the main tube and engine tube for it and pack it in there, so it's pulled out as the booster separates.

I'm planning a booster stage with a tail cone, so #1 is out. And #2 seems a bit clunky.

While I'm near the topic, what causes the stages to separate in a gap staged system? The gasses are vented, so gas pressure is much reduced. I guess the gasses from the ignited sustainer might be enough all by themselves, but I remember some tape-staged rockets not separating in my youth, in which the sustainer just blasted down the spent cartridge of the booster. Is separation generally reliable? Should one be careful that any coupler between the stages is especially loose? Does the forward centering ring of the booster need any special heat-proofing?

Finally, a question which has been drifting through my skull for a while--Why is the upper stage called a "sustainer"?

Thank you for any helpful or humorous responses.
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Old 11-18-2008, 04:48 PM
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Boosters are traditionally very high thrust and short duration solid motors, burning just a few seconds at most, while sustainers burn several minutes, sustaining or gaining airspeed from the boost phase. Reference most of the rockets in the USA's sounding rocket program, such as the IRIS, Aerobee, etc. and the US military's various Nike missile systems.

The gap stage booster needs to be almost loose enough to fall off by itself so that it won't stick and get burned through like a torch. However, you don't want it too loose or it will allow misalignment and some other issues.

Yes, you need to take some precautions if you plan to use the booster repeatedly. Stine's handbook has some good information. Roll up a piece of paper and slip it inside the booster's body tube to keep it from getting cooked.

This is the ultimate gap staging....open air gap staging. As you can see by the bondo on the booster, we learned just how loose the booster needs to fit so that it falls away quick enough not to be torched by the sustainer.






Last edited by tbzep : 11-18-2008 at 05:58 PM.
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Old 11-18-2008, 04:58 PM
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I always understood the terminology to be that a booster "boosts" the rocket off the launch pad, and a sustainer "sustains" the thrust applied to the main rocket after the booster has finished it's job. I don't know if it is more complicated than that, but if it is I suspect someone will educate us around here.
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Old 11-18-2008, 05:56 PM
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Quote:
Originally Posted by STRMan
I always understood the terminology to be that a booster "boosts" the rocket off the launch pad, and a sustainer "sustains" the thrust applied to the main rocket after the booster has finished it's job. I don't know if it is more complicated than that, but if it is I suspect someone will educate us around here.


I thought I took care of that in my previous post. BTW, the sustainer doesn't always take over after the booster has finished. Some of the Iris and Aerobee series liquid fueled rockets ignited their sustainer motors before launch and both motors burned together at liftoff.
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Old 11-18-2008, 06:34 PM
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Quote:
Originally Posted by tbzep
I thought I took care of that in my previous post. BTW, the sustainer doesn't always take over after the booster has finished. Some of the Iris and Aerobee series liquid fueled rockets ignited their sustainer motors before launch and both motors burned together at liftoff.



Good point.
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Old 11-18-2008, 06:42 PM
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Quote:
Originally Posted by tbzep
Boosters are traditionally very high thrust and short duration solid motors, burning just a few seconds at most, while sustainers burn several minutes, sustaining or gaining airspeed from the boost phase. Reference most of the rockets in the USA's sounding rocket program, such as the IRIS, Aerobee, etc. and the US military's various Nike missile systems.

The gap stage booster needs to be almost loose enough to fall off by itself so that it won't stick and get burned through like a torch. However, you don't want it too loose or it will allow misalignment and some other issues.

Yes, you need to take some precautions if you plan to use the booster repeatedly. Stine's handbook has some good information. Roll up a piece of paper and slip it inside the booster's body tube to keep it from getting cooked.

This is the ultimate gap staging....open air gap staging. As you can see by the bondo on the booster, we learned just how loose the booster needs to fit so that it falls away quick enough not to be torched by the sustainer.


You just got to love those pictures.......
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Old 11-19-2008, 08:51 AM
Eagle3 Eagle3 is offline
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Quote:
Originally Posted by Jeff Walther
If one wants to gap stage a rocket and have a streamer or parachute on the booster are there any methods available besides the following two:


You could blow the tail cone off or transition using a modified version of #1

Quote:
While I'm near the topic, what causes the stages to separate in a gap staged system?


The ignition of the sustainer. When I did the R&D for the two methods you mentioned it was clear that the internal pod needed to be very loose in the booster airframe. The pod socketed onto the end of the sustainer motor. Once the sustainer lit it literally blows that pod right out the back.

Quote:
The gasses are vented, so gas pressure is much reduced.


It's still more than enough to blow everything out. In all the tests I performed the only problem I had was the streamer didn't unfurl all the way from the pod on one flight. That was due to a prep issue. The shockline was inadvertently wrapped over the streamer instead of under it.

Quote:
Is separation generally reliable? Should one be careful that any coupler between the stages is especially loose? Does the forward centering ring of the booster need any special heat-proofing?


Yes, yes, and not really, but it couldn't hurt.

Quote:
Finally, a question which has been drifting through my skull for a while--Why is the upper stage called a "sustainer"?

Thank you for any helpful or humorous responses.


It sustains the flight after the booster has done it's job and fallen away.

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Old 11-19-2008, 08:55 AM
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One thing I forgot. Since you can't get B4-6 motors anymore you really need to clean out the nozzle and throat if you use a B6. Most staging problems I've seen lately whether it's gap or butt stage has been with B6 sustainers not lighting.
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Old 11-19-2008, 09:18 AM
Jeff Walther Jeff Walther is offline
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Quote:
Originally Posted by barone
You just got to love those pictures.......


Yes, those photos are jaw-droppingly beautiful. It's difficult to benefit from the helpful text that came with them, because I can't drag my eyes off of the photos. :-)
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Old 11-19-2008, 10:02 AM
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Quote:
Originally Posted by Jeff Walther
If one wants to gap stage a rocket and have a streamer or parachute on the booster are there any methods available besides the following two: (snip)
Jeff,

My take on this is that trying to use a booster motor to both light the sustainer and deploy a booster recovery system will be marginal at best. For reliability, I would either use a timer for sustainer ignition in conjunction with a short delay motor in the booster (eg, C6-3) , OR, use a cluster in the booster wherein one motor, a -0, lights the sustainer, while another motor, with a delay and proper ejection charge, deploys the chute.

Doug...thinking that I now need go build one of these myself

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