Tuesday, February 3, 2009

P to N flight

You may recall that I recently posted about an O to N flight to about 50,000 feet. Here is the previous post.

Well the same rocket (or slightly modified perhaps) flew on a P motor staged to an N motor, or an RDH8 P6000BB to an AMW N4000BB to quote the page. This is your optimum stage ratio of 4:1. It was estimated that the peak altitude passed 80,000 feet and the top speed was more than mach 3. But yet again, there was severe burning, blistering, and fraying on the fins. Note that recovery was only partial, the upper stage (sustainer) did a lawn dart. Probably, that was the only way it could have been recovered on the Playa because from 80,000 feet such a small rocket with recovery could have drifted 10 miles. The upper stage crashed within 1.5 miles of the launch, exceptionally close for a flight to 80,000 feet. (Thanks again to the lawn dart recovery.)

This project helps put one of the older CSXT space attempts, also a P to N rocket, into perspective. The CSXT flight failed to stage, and the sustainer hit nearly 80,000 feet as a boosted dart! Obviously CSXT was going to break 100,000 feet, but by how much? 80,000 feet is far from space; why did this flight get such limited altitude? (Yes it feels strange to say that about 80,000 feet.) Firstly, the use of high thrust motors (N4000 for example) is not ideal for altitude. The upper stage was probably scraping the bottom of the hypersonic range, and that is part of the reason for the horrendous fin and airframe damage. There are so few details about the CSXT project, it is hard to really figure out how much this launch can tell us about what it takes to hit space. Professional rockets have made space on less power. But the question is what will it take for an amateur rocket to do the same? Better documentation of all high altitude attempts would be nice, even the failures. The internet makes this into a pretty simple task. The following represents more information by far than I have ever seen about the CSXT attempt. I do know that the CSXT attempt used a much faster P motor, possibly a P 13,500 as I remember. That would not have helped. But either way, a P to N should make space. The key is in timing, as I will discuss at the end of this post.

Recovery was:

3 x #4 shear pins
Drogue=CD3 CO2 deployment & backup 4g BP


And obviously the sustainer system failed for some reason. Here is what the author thinks:

"Looking into altitude temperature data the Troposphere ends around 45,000 feet. Above that point the temperature is -70degF.
So the rocket was exposed to -70degF for over 45seconds.
The electronics in the fiberglass nosecone didn't stand a chance without any insulation."

I wonder if electronics could really cool down so quickly under these conditions. They are fairly well insulated by the airframe (well for a 1 minute exposure that is), and the rocket airframe was also heated to several hundred degrees during flight.  It is very hard to really figure out what happened, though the author does not say if the ejection charge even ignited or not.

The dynamics of this kind of flight really make it hard to ever know what went wrong. But I personally wonder at the power of ejection charges used. Dynamic pressures at high mach speeds, even at 80,000 feet, can combine with cold temperatures and with the shear pins to really lock or even cement (via melting paint) a nose cone into the airframe. CO2 ejection + 4 grams of black powder seems like a lot. But maybe, just maybe, it still was not enough? The fact is, most high altitude flights fail to recover properly. The OuR project, now almost totally lost to the world due to limited records (again the documentation issue), failed to recover after a flight to near space.

Under these flight conditions, my advice would be make sure that either the recovery system ejects properly, or the rocket blows up.

This rocket scientist's name is Robert DeHate. Check out his web page, loaded with tons of great rocket projects and lots of electronics as well. The best has to be his 13mm two stage carbon fiber rocket that can carry what appears to be a sonic beacon or even GPS! I love the look of this little guy.

Robert DeHate

*Update - 2/6/2010

This video below is from Balls 18, it looks like the next attempt at flying this rocket. Mr. DeHate expects it to break 100,000 feet. I understand that he continues to work on ways to protect the airframe from these high mach flights.

It is worth noting that a two stage P to N flight is capable of hitting space (100 km) but only under the right conditions. The best possible mass fractions are needed, and equally important is timing. In the video above, DeHate attempted a 10 second delay in staging. This is a great way to protect the airframe from burning up so much, as well as increase final altitude. The goal of 100,000 feet requires both after the results of 80,000 feet on the first P to N flight. Space would call for the following: Optimizing mass fractions by either lightening the airframe (particularly the upper stage) and/or making the motor casing on the lower stage the airframe. Next, the N could be replaced with the reliable, efficient, and extremely powerful N 5800 motor. Finally, the timing is crucial. The delay must be long enough to let the upper stage ignite as high as possible, but in no case lower than 40,000 feet. If you get the upper stage doing mach 5 at 50,000 feet, space is in the bag. Ideally the P can get the upper stage to 50,000 feet and about mach .8 for the motor burn. That will take more than 10 seconds delay, however. It requires a reliable timer, probably a burst disk in the nozzle, and possibly head-end ignition on the motor. Doing this is harder than it sounds.

Read this post about the possibility of space on two N motors.

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