Stage Separation using Hot Staging for a Sounding Rocket

[Alan Offer]

Hi everybody , I'm planning to make a two stage sounding rocket that will go to 38km high and I'm analysing options for booster separation . I'm using two 98mm stages with an O3400 motor for the booster and a N1100 for the sustainer. I wanted to know if somebody has already made an hot staging using those kind of motors and if it was safe to do so. The body tubes are made out of fiberglass and the bulkhead in aluminium. I was also thinking of cutting the fiberglass tubes to make something like the starship mechanism where the flames are coming out on the side.

You will find in the photo, a quick schematics of the stage separation mechanism that I thought, where an aluminium conical support goes in the nozzle of the 98mm Cesaroni motor. Don't hesitate to ask me for information if you need.

If anybody has experience in two stage rocket this size, I would really appreciate any advices. Thank you in advance,

Alan Offer, founder of IMF.Rockets

 

[MClark]

The upper stage is a Kosdon M3700.
Look below transition there are six 3/4” vent holes.
Airframe is all aluminum.
Thirty years ago.

 

[MClark]

The inter-stage needs to be vented or the sustainer motor will blow before coming off.
I wouldn’t put any load against the nozzle

 

[Alan Offer]

The upper stage is a Kosdon M3700.
Look below transition there are six 3/4” vent holes.
Airframe is all aluminum.
Thirty years ago.

View attachment 650730

Thank you for the response, I see, do you think fiberglass will do the job ?

 

[Alan Offer]

The inter-stage needs to be vented or the sustainer motor will blow before coming off.
I wouldn’t put any load against the nozzle

Thanks for the advice, I'm trying to figure out how to build the separation mechanism for two stages that have the same diameter and with the sustainer having a minimum diameter 98mm motor. I think I will put some sheer pins coupled with some vents holes but I'm trying to figure out how to embed the sustainer into the booster. Do you have some advices ?

 

[MClark]

Assuming the fiberglass airframe is over the motor.
Motor can be used as the coupler, I like 1.5x the diameter. Shear pins are not needed, if it separates after burnout all the better. Use head end ignition or if through nozzle have attached to sustainer.
Fiberglass will work. Just don’t use minimum size fins on booster. If it goes straight coupler won’t fail, if not going straight the game is already over.
Extra drag doesn’t matter in reality because it’s only there for a few seconds, going straight and not oscillating is more important.

Electronics in motor nozzle to go with sustainer. This gets covered.
Remember, 30+ year old tech.

 

[MClark]

Where are you planning on launching? Not much open land in Monaco.

 

[Alan Offer]

Where are you planning on launching? Not much open land in Monaco.

I'm planning to come to FAR to launch it. Otherwise I will try to get a NOTAM to launch the rocket in the middle of France or Italy. A sea launch on the coast of Monaco would be awesome but it adds to much complexity to the project !

 

[Alan Offer]

Assuming the fiberglass airframe is over the motor.
Motor can be used as the coupler, I like 1.5x the diameter. Shear pins are not needed, if it separates after burnout all the better. Use head end ignition or if through nozzle have attached to sustainer.
Fiberglass will work. Just don’t use minimum size fins on booster. If it goes straight coupler won’t fail, if not going straight the game is already over.
Extra drag doesn’t matter in reality because it’s only there for a few seconds, going straight and not oscillating is more important.

Electronics in motor nozzle to go with sustainer. This gets covered.
Remember, 30+ year old tech.
View attachment 650918

I will try to figure out if I can make the nozzle as the coupler. I'm using a N1100 98mm motor from Cesaroni with a burn time of 12s and the nozzle will look something like this (see the link from Cesaroni website) Do you know if the Cesaroni motors can make a head end ignition ? I was thinking of putting sheer pins because I was want to have the electronics compartment for ignition in the booster. Because on the upper stage I was thinking of making a dual separation of the sustainer (for drogue and one for the main chute ) to reduce complexity. So I would have to pass the ignition wire through the drogue compartment. What do you think ?

http://www.pro38.com/pdfs/Pro98_dimensions.pdf

For the avionic, to light up the motor, I was thinking of having a flight computer of my own creation and a Blue Raven for redundancy. I would put two ignition wires in the motor. Is that safe ? Or it's a bad idea ?

 

[cls]

I think it's an interesting tradeoff, hot staging vs coasting ... For as long as you dare.

SpaceX does hot staging because they want velocity for orbit. Just going for altitude, theoretically it's better to go slower through the denser (lower) part of the atmosphere.

Have you run some simulations?

 

[Alan Offer]

I think it's an interesting tradeoff, hot staging vs coasting ... For as long as you dare.

SpaceX does hot staging because they want velocity for orbit. Just going for altitude, theoretically it's better to go slower through the denser (lower) part of the atmosphere.

Have you run some simulations?

I've done some simulations on Open Rocket, you can see the picture below. I've tried other combinations of motors and this gives me the highest apogee with mach 3.1 and a max acceleration of 135m/s^2. My goal is to say that I left the lower part of the atmosphere so that's why I have an apogee of 38km. I calculated the fluttering speed of the fins using Apogee Newsletter number 411 and for the booster and sustainer they are way above the maximum speed attained. I choose to use a calliper of 2.21 cals because I saw that a calliper higher than 2 was going to reduce roll lockout probability. I think that a calliper higher than 3 was too much. What do you guys think ?

 

[cls]

The screenshot of the 2D layout doesn't answer the question, what altitude is staging?

Consider using a burst disk to help pressurize the sustainer motor.

I've burned several N1100s. Look carefully at the thrust. Yeah they make noise for many seconds but only significant thrust for about half of it

In the same rocket (Mongoose 98), AT N1000s went 8% higher than CTI N1100s.

 

[Alan Offer]

The screenshot of the 2D layout doesn't answer the question, what altitude is staging?

Consider using a burst disk to help pressurize the sustainer motor.

I've burned several N1100s. Look carefully at the thrust. Yeah they make noise for many seconds but only significant thrust for about half of it

In the same rocket (Mongoose 98), AT N1000s went 8% higher than CTI N1100s.

Staging is happening at 3000m at 8s. Sorry what do you mean about the burst disk to pressurise the sustainer ? Is it better to have a lower thrust but higher burn time of higher thrust and shorter burn time for the sustainer ?