Nescorna Rocketworks

I finally did more than remove the bulk of the damage on Bed Knobs and a Broomstick, damaged (very bad zipper, and a gussetted centering ring partially torn) at last month’s NASA Ames launch (see the posting). The zipper on the forward portion of the lower part of the rocket went right down into the coupler that joined the two tubes together. I had expected to have to patch at or slightly forward of that coupler. I looked more closely today, and noticed that some of the remaining body tube had, essentially, delaminated from the tubing coupler. It turned out that the forward body tube itself could be peeled away from the coupler, leaving a pretty clean, intact, standard diameter coupler sticking just the right amount out of the aft body tube.

Instead of having to craft a complicated two-part stepped coupler, it was a very simple matter of taking the new forward body tube and gluing it to the coupler!

Fie on burned-through delays. A pox on them and their progeny!

Bed Knobs and a Broomstick Launch, June 26, 2010, NASA Ames

It was an absolutely beautiful day out at NASA Ames Research Center at Moffett Field for the monthly LUNAR launch. Cloudless, light winds (almost no wind until about 11!), pleasantly warm but not hot, fun people, a good crowd. Paul Pittenger started us off with a triple drag race, including a pair of his styrofoam Sputniks. We had plenty of volunteers, so the expected possibility of flying once, if that, before helping didn’t materialize.

Bad, Bad Zipper for Bed Knobs and a Broomstick

I enjoyed chatting with people as a built the G64-4W for Bed Knobs and a Broomstick’s third launch. The rocket got lots of attention while I waited in the check-in line: Dan’s nosecone really is an eye-catcher. After a minor difficulty with the launch controller, up went the Broomstick! I was just settling in for a nice flight and the tension of the ejection charge’s timing when BAM! went the motor and out popped the parachute, with the rocket doing about 100 meters/second and at maybe 100 meters altitude. The chute deployed fine, but—but—when I recovered the rocket after a reasonably gentle landing, I saw the zipper.

Feh. Feh, feh, and fie on that delay charge! I’m not at all sure why the delay charge just burned right through. The zipper is evident in the picture on the right where the red-orange parachute is showing through.

King Tut’s Pyramid flew twice today: once on a single-use F50-4T for a very nice flight, once on a G77-4R. Again, something odd happened with the delay, and it seemed to burn right through, or perhaps the thrust gasses leaked around the seals. Regardless, ejection occurred during or just after boost. The pyramid’s rear ejection (tossing the entire motor mount aft, with parachute attached) prevented damage, though.

Despite the problematic ejections, it was a wonderful day!

Removal of the vast majority of the damage to the forward portion of the S-II is complete. This entailed cutting around the S-II aft skirt wrap, which is the most complicated of the cylindrical (as opposed to conical) wraps, and probably the most complicated of all the wraps. The S-II aft skirt wrap has a large number of LH2 Feed Line fairings, LH2 Recirculation fairings, the LH2 fail and drain fairing, etc., all of which protrude forward of what would otherwise be the forward edge of the wrap. The plan is to avoid replacing that wrap: it’s complicated and difficult to glue the wrap to the body tube, and the masking and painting is also difficult. (In retrospect, it might have been faster to just cut lower and replace it, but that seems also somehow less, well, elegant.)

One of the unexpected challenges was cutting through the forward thrust ring, a very small piece of tubing that lines the inside of the S-II tube and abuts against the forward side of the motor mount centering ring. I did an awfully good job gluing that thing in, and the yellow glue is resilient stuff! That’s done, though, and the remnants of that thrust ring that were on the inner sides of the fairings are also removed. I believe that it’s now time to begin real repairs and reassembly.

I’ve made the first sets of cuts on the Saturn V.  The rough cut to remove the forward, damaged portion of the S-II is done, the body tube for that has been separated from the S-II tunnel cover, and the forward motor mount centering ring, with its gussets, is removed. I’m documenting the work in a photo album.

I’ve been considering rebuilding the rocket in a way that a mild H motor (H97J, H128W, maybe even H180W). If I do this, I don’t want to add much weight: finesse, rather than brute force, will be the goal. While walking the dog last night, a way to increase strength of the forward MMT CR joint (to the main tube, the 144 mm body tube) hit me, so I spent about 20 minutes writing down my thoughts and creating revision 4 of the repair plans. (What’s wrong with this picture? The repair’s barely begun, and the repair plans are already on R4! Maybe nothing’s wrong with this picture, though, and reflects careful thinking. I hope so!)

The reloads that appear potentially viable:

It won’t take much to handle the H97J or the H128W: maximum thrust on the first is less that that of the G64W, that of the second is only (only?) 40% more. Going to the H180W, though, is probably not advisable if I still want to fly on the G motors.

It’s been eight or ten months since the bottom part of my Saturn V crashed. The parachute for the bottom part was not ejected at deployment. In the ensuing crash, one fin was broken, the forward part of the tube and its attached wrap and tunnel cover (half-dowel) were damaged, the tube was kinked down to the next wrap, the forward portion of the motor mount tube was crushed, and the forward centering ring was damaged. Since then, I’ve been contemplating the repairs (and procrastinating about them, too).

It’s time to start repairing.

I’ve made lots of scratch-flown rockets. I never write down the build instructions in advance, nor even while working on the rocket. Occasionally, if I work out a particularly difficult or tricky section of the build, I might jot down a quick note or two, but never anything extensive. For the Saturn repair, I realized, finally, that it was complicated enough to warrant a) working through the details ahead of time, and b) writing the sequence and, in most cases, the detailed steps down. When I first determined a rough approach to the repair I conceptualized the steps as something like this:

1. Remove the damaged parts.
2. Repair the MMT and forward centering ring.
3. Replace the damaged body tube.
4. Replace the damaged wrap.
5. Paint.

I’m now up to about thirty steps, not five.  Some of those thirty steps have some sub-steps. It’s a complicated repair, and I think it’s worth getting it right.

When last we visited Bed Knobs and a Broomstick, the nose cone had just been finished. I am very please to say that the first flights were very successful!

It was a simply gorgeous day at Snow Ranch in Farmington for LUNAR’s May 1st launch. We were treated to lots of wonderful flights: Steve Jurvetson’s Sledgehammer, Jamie Clay’s Mercury Joe, Alan Thym’s Blade of Death, some fabulous TARC flights by Westmont High, and I could go on for a long time. LUNAR’s photo gallery of the launch will give you a good (though mostly static) taste—well, except for Alan Thym’s luscious chili!

Back to Bed Knobs and a Broomstick.

I managed to finish painting the rocket the day before the launch. For construction details, you can view the photo album (there are also some flight pictures there). The build and finishing were not without their challenges.

1. The nose cone was heavier than RockSim calculated. This made the rocket very over-stable. Not a big deal, and ameliorated a bit by the fix to another problem.
2. I built a set of Kaplow Clips for motor retention. Since this is designed as a G-powered rocket, I wanted something pretty solid. I didn’t need the expense of something like an Aero Pak retainer, either. Solution: a pair of blind nuts behind the after motor mount centering ring, anchored in two small pieces of balsa each, with an aluminum window screen retaining clip screwed into each blind nut. The balsa cracked a little, which wasn’t a big problem, certainly not one that couldn’t be overcome with a little epoxy. One of the blind nuts ended up just a little too close to the motor mount tube, because of a minor conceptual error in laying out the hole. No big deal: Moto-Tool to the rescue.
3. I glued the aft cone (the fin substitute) together, then installed all the launch lugs. The aft cone was not yet on the rocket! Hooray for rubber cement, which is what I used to hold the aft cone together: it was easy to peel apart the top 5 cm or so, allowing the aft cone to slide down over the launch lugs.
4. Flight experience says I should have used a single solid launch lug inside the aft cone, instead of two pieces (one at the very aft, one at the front of the cone). It would have made it much easier to get the rocket on the launch rod.
5. It was windy when I painted the body tube. I was running out of time, so I didn’t have much choice, and some family circumstances made it even more difficult to wait until the wind died down a little. After beginning to paint, with the rocket standing on its aft end, I had to leave the rocket. I should have had someone stand watch, or found another way to do what I had to do: the rocket blew over, and landed in just the wrong way. The body tube kinked. After the paint dried (barely enough), I was able to section out the kink and splice the body tube back together with a tube coupler. Minor disaster averted.
6. I should have clear-coated the nose cone a day earlier, to give it longer to dry before handling it to install in the forward end of the rocket.
7. RockSim indicated that a 6¼ second delay would be ideal on an G38FJ. That seemed long, but I went with the closest thing: 7 seconds. I was right, RockSim was wrong: 4 seconds would have been better. Much too long after apogee, the parachute popped out (and I breathed again!), but the rocket was falling so fast that the forward end of the body tube zippered slightly. No big deal, and easy to repair. I used a G64-4W for the second flight, even though RockSim indicated an 8+ second delay. (Turns out the RockSim doesn’t do a good job calculating the C_d for anything unusual [thick fins, cone tails, etc.]. It’s a limitation of the assumptions made in the software.)

There are lots of little things in this rocket that aren’t part of your typical Estes-style kit.

• A couple of the centering rings and the nose section bulkhead have gussets for added strength. These are pieces of card stock (same stuff as the centering rings) glued perpendicular to the surface of the ring (or bulkhead), and glued to the inner and outer tube.
• The shock cord mount uses a yoke wrapped around an inner tube (stuffer tube, for example) and then through small notches on either side of the centering ring. (There are pictures of these details.) The shock cord mount is very strong.
• The Kaplow Clips are very easy to use, easy to install, inexpensive, and light. A screwdriver appropriate to the screws is all I need during prep to secure the motor.

There was lots of interest in the rocket at the launch. People noticed the nose cone, people noticed the aft cone. Some people got the idea of “bed knobs and broomstick” right off the bat (others saw, well, something else). Steve Jurvetson titled his picture of the first launch, “Nimbus FJ lost its rider”!

I’m glad the winds cooperated: the rocket is definitely over-stable, but not as badly as I expected. This is probably another simplifying assumption in RockSim, and I’m guessing the CP was somewhat further forward that RockSim calculated. It flew well, though, and I think it benefits from a reasonably quick kick off the pad.

Unless we get an increase in our altitude waiver at Ames, this one will only be flying elsewhere. On the G64, it made about 500 meters.

A Black Jack or Fast Jack propellant looks very, very cool!

May 1, 2010 launch of Mercury Joe, a 7 foot tall scale model of MR-3 by Jamie Clay (photo from LUNAR gallery)

May 5, 1961 launch of Freedom 7 atop MR-3 (photo from NASA archives)

Freedom. A fitting name for the second small step.

Freedom 7.

The second small step for the inhabitants of this planet to leave this planet.

On May 5, 1961, Alan Shepard climbed aboard Freedom 7, atop a Redstone booster, admonished his support team to “light this candle” (after they had given him the go to “do it in the suit”!) and become the second person in space, the first American astronaut. Today marks the 49th anniversary of that flight, that very short flight, that second small step.

(Thanks to Jamie Clay for Mercury Joe.)

I spent a bunch of time this weekend at my friend Dan’s. He has a wood lathe and is pretty accomplished with it. A few months ago, the conversation turned to woodworking and nose cones and balsa. Though he had no experience with balsa and its very low density, he was willing to give it a try. That left me free to design a pretty odd fantasy nose cone: a bed knob. Thus, the inspiration for the current project.

It happened that I had a nice piece of balsa in my parts bin: certainly much bigger than we needed (10 cm diameter cylinder, about 30 cm long; we needed all the length, but a 7 or 8 cm diameter would have sufficed). Despite a few interesting challenges, like when the piece let go (i.e., broke) at a thin spot that required repairing and then some reworking, Dan produced a very cool piece. It looks just like a turned bed knob!

Much of the rest of the construction is complete; more on that later.

In my recent blog entry that mentioned the C5-3 CATO, I said I’d post some pictures of the CATO. With thanks to Ryan Coleman, fellow LUNARtic who sent them over, and Shaina Pierce, his friend who took the pictures, here they are.

The recovery parachute and the upper portion of the rocket are intact; the lower portion (the part housing the motor mount tube) is not. You can see the Nomex^® parachute protection blanket and the parachute in the pictures; if you look closely, you can pick out the Kevlar^® shock cord and even the parachute’s shroud lines.

I started working on a new rocket a couple of days ago. It’s a combination of a few designs, including one whose C5-3 CATOed at LUNAR‘s Ames launch last Saturday. (It was a pretty cool CATO, even if it was a maiden flight. Who ever heard of an 18mm black powder motor CATOing? Yeah, it happens, but not so often. Motor lit, rocket cleared the tower, and about 10-ish meters up, motor blew. I’ve still not yet done the dissection.) Ryan Coleman has a couple of pictures he’s sent over of that CATO; I’ll post those soon.

New rocket: Bed Knobs and a Broomstick. I’ll start getting some pictures and post a build blog.