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#1 to #160 (Updates)



Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Day 36 - Acceleron III - Multi Stage Progress
The new Acceleron III booster shown assembled. A couple of our early rockets shown for comparison.
A detail of the top of the booster. The TDD is on the left, and the sustainer air supply is on the right.
Test setup for the sustainer air supply. A bottle with a pressure gauge on left tests the non return valve in the booster segment stand-in (below).
We used a couple of smaller bottles instead of the full booster so we wouldn't waste so much air.
Acceleron III with Tachyon sustainer on top. This is work in progress and sustainer elements are likely to change.
Detail of the release mechanism. The rubber bands provide the force to pull back the Gardena release. The yellow bulkheads will mount the flight computer, actuators and parachute. You can see the air supply line running on the left of the pod.
If the sustainer gets any taller, we are going to have to assemble it outside.
Our first symmetrical splice. We will test it in a couple of days to see how well it holds up.
Date: 27th May 2007
Pleasant since it was indoors.
(click the name for rocket details)
Name Capacity Notes
Acceleron III 24.75 L A new rocket expanding on Acceleron II's capacity. It is also our first two stage rocket booster.

Team Members at Event: GK and PK


Although we haven't done an update for a while we have still been busy developing the Acceleron III booster and its staging mechanism.


The Acceleron III booster has 3 segments each with a capacity of 8.25L. The booster segments are attached to a central aluminium tube running the full length of the rocket. Each booster has a 10mm nozzle. The full details of the rocket design including dimensions will be published once the rocket is finished. We are changing the design as we build it so to do the drawings too early would be a waste of time.

The Payload Pod

All the electronics, actuators, camera and parachute will now be mounted inside a pod that sits just above the three booster segments. The pod provides protection for those components from the sustainer spray during release and during landing.

The pod has a PVC pipe running through it to support the sustainer. There are two RC servo actuators inside the pod. One is used to deploy the parachute, and the other is used to release the second stage. The servos will be controlled by version 1.4 of the flight computer.

The bulkheads in the pod are made from corrugated plastic sheets used to make signs. We decided to go with this material because it is relatively stiff, lightweight, water proof and cheap to obtain. The bulkheads are just glued together with a polyurethane glue.

The pod's aeroshell also provides a stabilising anchor point for the sustainer during ascent.

New software is currently under development to support the staging mechanism and parachute deployment sequence.

Staging Mechanism

The staging mechanism is based on a Gardena hose attachment. We removed the spring from it and glued a plastic ring on the outside sleeve. Rubber bands are attached to this ring to provide the pulling force needed to release it. A small latch keeps the sleeve in place and this latch will be controlled by a servo motor inside the pod.

Sustainer Air Supply

The air supply to the second stage feeds through a thin clear plastic hose from the top of one booster segment. The hose is attached to a unit that has a swivel connector as well as a non-return valve in it. The swivel connector is useful for when we remove the cap to fill the segment with water.

We cut off the regular garden hose attachment on the Gardena fitting and glued in an adaptor for the thin hose. The hose passes out of the central tube just above the pod to allow us to remove the pod from the tube for maintenance.

Parachute Deploy

The parachute bay now uses a piece of soft spongy foam to help push the parachute out when the door opens. We decided to go with a sideways opening door this time because it made the parachute bay more streamlined. The hinge is made from a piece of cloth. The door latch is quite simple (and it uses a flexible line to unhook it. The line directly connects to the servo motor.

Staging and parachute deploy sequence

The second stage release timing will be initiated by a device known as a TDD. This was kindly donated by Trevor. It is based on a pneumatic piston inside a cylinder that activates when the pressure inside the rocket drops below a certain pressure. The TDD is connected to a micro-switch that then connects to the flight computer. When the pressure drop is detected a small delay later the second stage is released. The flight computer then starts a second delay, and when that delay is over the parachute is deployed.


The Tachyon sustainer is a new rocket being designed to fit the Acceleron III booster. It is made from two 1.25L bottles joined together with a Robinson Coupling. It will use a 5mm nozzle (our smallest yet). The fins are not complete yet, the ones in the photo are only representative. Tachyon uses version 1.3 flight computer for parachute deployment. For now the deploy delay is time based.

Pressure Testing

We have now completed our pressure tests for all the different components up to 125 psi. (Except the sustainer).

Thanks to the new bigger lids, the three booster segments held up well without leaks up to the maximum test pressure.

We also tested the seal around the TDD. Although up to about 40 psi there was a small leak around the piston, above 40 psi it started sealing properly and went well all the way up to max pressure without problems. Just doing crude tests, the TDD activated in the 10psi range which is pretty good. 

After we assembled the sustainer's air supply we tested it for leaks, and it leaked a little bit. Upon closer inspection we found on the inside of the thin tube that there are three ridges running the full length of it. This is probably the main reason it leaked around where it attaches. We made new rings for the outside that were a much tighter fit and it then it held fine up to the maximum test pressure.

We made a special connector for the top of a bottle that could connect a pressure gauge using a quick release fitting. We put this in place of the sustainer and we performed a test of the non return valve at the end of the thin tube. Using the attached pressure gauge we could see that the valve held the pressure in the sustainer just fine for the minute or two that we observed it.

Other Developments

We also had a go at splicing our first bottles. We used some PL premium kindly donated by Jordan from Team Parental Advisory. We decided to splice them base to base so to speak so that these units can screw together to make longer rockets or be replaced should they get damaged. Thanks also to Damo for advice on splicing. We still need to burst test these. More info on this next time.

Ben Jackson is also working on similar projects with flight computers for water rockets. Here is his deployment system:

Another recent and interesting deployment system from Christian Thomsen is here:

It is still going to be at least a couple of weeks before we get a chance to fly this multistage rocket.

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