Rockoon

Discussions on high/extreme altitude and mach busting rockets.

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joeman
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Rockoon

Postby joeman » Sun Mar 29, 2015 9:23 pm

Hi,
Someone suggested that I start a thread on Rockoons. Wasn't too sure how I should go about, I thought it might be best to quickly introduce the concept of Rockoons (for those who are not familar) and then pose a little problem/question that I have.

Rockoons are where one launches a rocket from a balloon, hence the merging of the words, Rocket and Balloon. They have been done many times before, and there is a WIKI entry on it. http://en.wikipedia.org/wiki/Rockoon
People sometimes refer to the balloon as the First Stage and the actual rocket flight as the second stage.

As we know, the atmosphere provides considerable drag on our rockets, and so by launching the rocket above most of the atmosphere, we can obtain a greater height, not just because the launch already starts ~30km up, but also because the rocket has less drag forces on it, slowing it down. There is obviously practical limitations in the size of rockets that can be hauled up by a Helium balloon and there are other complexities involved with ignition, guidance, balloon launch, flight aborts. But it certainly is an interesting concept.

As a bit of a diversion....One concept I saw is a 'donut' shaped (torus) rocket...then a smaller one inside it...and so on...all the different stages...because their is considerably less air/drag, the need to have a tall, thing rocket is not so critical. One of the perks of having less air to contend with.

Anyhow, back to it...I've been trying to get my head around how to get a rocket to "keep" going 'straight' up...and not veer off to the side. I've thought of using a typical rocket design with the CP below the CG and with some fins...and still use some rod to assist in the guidance of the rocket during the initial acceleration. MY concern is that because the air pressure is less up there(100,000feet), the corrective forces may not be sufficient. Perhaps bigger fins, to lower the CP even further.
When I think about it, many Hobby rockets that are launched are coasting (and slowing down) when they get to high altitudes, like 100,000ft or higher...it is their APOGEE....so drawing a comparison may not be a good thing to do.

Thoughts?

Cheers

Joe
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Re: Rockoon

Postby OverTheTop » Mon Mar 30, 2015 6:53 am

You could spin-stabilise the rocket. That is the conventional approach to stabilising our point-and-shoot rockets at high altitude.

Another possibility is a vertical trajectory system. Not much work been done on these that I have seen lately. It is a long-term goal of mine to make one of these systems.
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Re: Rockoon

Postby joeman » Fri Apr 03, 2015 10:22 pm

ahh, yes a bullet uses spin to help keep it on target.

I'll have to research on how to get it to spin. That sounds like something worth looking at first.

The design of a VTS sounds like a massive project, and a lot of testing.

Thanks
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Re: Rockoon

Postby martymonsta » Fri Apr 03, 2015 11:25 pm

The Eagle Space Flight team from Embry-Riddle Aeronautical University in the USA, which LCO Bryce from Thunda is a leader, have been doing some work using 3D printed fins that are canted at 0.5° which provides a proximity 4Hz of rotation at Mach 1.

I ran a very quick sim in OR on a 75mm MD powered by a CTI M840 and set the launch hight to 100k' and 1 sec after burnout the rocket begain tumbling end over end (it stiĺl went to +200k), I then applied 0.5° of cant to the fins and it resulted in stable flight. This was a sim using FREE HOBBY SOFTWARE and this kind of flight is well outside what the software was designed for. However I'm pretty sure that the Eagle Space Flight team have good reason to expect that it would work as they are planning to take a space shot within 2 years.

Here is a video from their launch featuring this canted fin tech from the other weekend.

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Re: Rockoon

Postby joeman » Sat Apr 04, 2015 5:41 pm

That's awesome Marty.
Thanks.

Just had a bit more of a read around and found this.

http://www.apogeerockets.com/education/ ... ter228.pdf

Might be useful for others too.
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Re: Rockoon

Postby ROCKet STAR » Sat Apr 04, 2015 6:38 pm

I would suggest looking at early sounding rockets for examples of rocket stability at high altitude. You'll probably find that simply using fins will be just fine. Sure the air is very thin above 100,000', but it is still present, and will act upon the vehicle/fins as you pass through it. The Skylark sounding rocket, for example, utilised only its fins for stability in it's earlier configurations, and had an apogee in excess of 200km.
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Re: Rockoon

Postby air.command » Sat Apr 04, 2015 7:23 pm

At the most extreme even the GOCE spacecraft used fins for stabilization at an orbit altitude of 250-270km.
http://www.esa.int/Our_Activities/Observing_the_Earth/GOCE/Satellite
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Re: Rockoon

Postby joeman » Sun Apr 05, 2015 11:18 am

Thanks guys.

One of my thoughts is that if I'm concerns about the ability to guide it in the tenuous atmosphere, it would better to launch say at 25km up, where there is a bit more air.

I really do like the idea of the fin cant or fin tabs.

Cheers!

Joe
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Re: Rockoon

Postby martymonsta » Sun Apr 05, 2015 3:44 pm

joeman wrote:Thanks guys.

One of my thoughts is that if I'm concerns about the ability to guide it in the tenuous atmosphere, it would better to launch say at 25km up, where there is a bit more air.

I really do like the idea of the fin cant or fin tabs.

Cheers!

Joe



martymonsta wrote:I ran a very quick sim in OR on a 75mm MD powered by a CTI M840 and set the launch hight to 100k' and 1 sec after burnout the rocket begain tumbling end over end (it stiĺl went to +200k), I then applied 0.5° of cant to the fins and it resulted in stable flight. This was a sim using FREE HOBBY SOFTWARE and this kind of flight is well outside what the software was designed for.


I modified the sim and tried launches at 75k' and 120k' both canted and non canted fins. Interestingly at 120k the non canted fins still resulted in stable flight, at 75k' non canted fins resulted in tumbling post burnout. Not what I would have predicted and possibly incorrect.

I've been thinking about the article by Tim Van Milligan in Peak of Flight and I'm not sure that I agree that all spinning rockets fly lower, and now I want to experiment with canted fins to find out.

I'm interested to see the difference in achieved altitude between straight fins and canted fins. From my understanding a canted fin will want to maintain 0° AoA and once the rocket has spun up drag should be about the same as a straight fin. A fin with spin tabs will have a constant AoA plus the drag caused by the tab itself. So would the altitude gained from a straiter flight dispite the marginally additional drag from canted fins be less then the height of an identical flight with straight fins that weather cocks more and thus loses potentially altitude? A heap of real world testing to find out I think.
Many years ago the great British explorer George Mallory, who was to die on Mount Everest, was asked why did he want to climb it. He said, "Because it is there."
Well, space is there, and we're going to climb it

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Re: Rockoon

Postby jase » Mon Apr 06, 2015 2:50 pm

Great thread, nice work joeman.

As Chris said, hard to look past the US sounding rocket program for state of the art.

This document in particular, http://sites.wff.nasa.gov/code810/files/SRHB.pdf

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Re: Rockoon

Postby martymonsta » Mon Apr 06, 2015 6:18 pm

jase wrote:As Chris said, hard to look past the US sounding rocket program for state of the art.

This document in particular, http://sites.wff.nasa.gov/code810/files/SRHB.pdf

8)


That is one good looking document Jase. Think I'll go do some light reading.
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Well, space is there, and we're going to climb it

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Re: Rockoon

Postby rocket_troy » Wed Apr 08, 2015 3:12 pm

martymonsta wrote: I'm interested to see the difference in achieved altitude between straight fins and canted fins. From my understanding a canted fin will want to maintain 0° AoA and once the rocket has spun up drag should be about the same as a straight fin.

True in theory *if* the velocity was constant (or more correctly - not increasing). With rockets, it's generally not constant unless the propulsion profile is a somewhat regressive -which is quite likely to some extent for pressure fed systems like hybrids or some solid grain geometries.
There are some tricks to help overcome modest drag increases from canted fins - like reducing the number of fins - like to 2 :)

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Re: Rockoon

Postby OverTheTop » Wed Apr 08, 2015 4:07 pm

If you think about the spinning rocket it probably becomes effectively "longer" when you spin it. Consider a particle of air: As the rocket slides past it traces a longer line around the spinning rocket than one flying without spin.
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Re: Rockoon

Postby citizenspace » Sun Aug 30, 2015 8:43 am

Did a quick sim on OpenRocket... Rockoon to over 100km... The fins weren't that big. 4 of them canted to 8 degrees was good enough for a straight flight. Although this is OpenRocket, so let's not take that without skeptisim.
My only question is (and this might sound stupid): How do you release the rocket without it colliding into the balloon platform above? Releasing it from a tow, then using nitrogen gas thrusters (powerful ones) to correct angle to 12 degrees of the balloon, fire motor, then correct back to straight after 25m or something would do it, but that seems overly complicated.

How is it done?
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Re: Rockoon

Postby jase » Mon Aug 31, 2015 8:41 am

Most weather balloons 'pop' between 80,000 and 120,000 feet - you want to get to 300,000...

Maybe get in touch with these guys http://wotzup.com/

Re your question, the rocket goes straight through the balloon - it is only latex...

Rockoon is theoretically possible, has been done plenty of times before, but the practical 'in reality' stuff for amateurs is virtually impossible...

Even if you could work out the practical side, how are you going to keep the rocket in a safe and predictable recovery cylinder?
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