MIRV (Multiple Independent Reentry Vehicle)

This new model, for both me and Estes is very unique, which is why I wanted to try it. It is a challenge too, with both the construction and the flying being different. I am motivated to fly this one just to show off at the rocket club launch. I’ll be so bummed if somebody else gets one up in the air before me! There are several challenges with this rocket. One is that there is no place for an altimeter on either the booster or any of the second stages without major modifications. Since it uses three second stages it will not be so affordable to fly, although the mini 13 mm motors are a lot cheaper than even a single 24 mm engine. I painted my model different from Estes all-black suggestion, opting for a black booster and magenta, yellow and aqua upper stages, making them colorful and easy to identify each sustainer on first sight.  Lacking time before the next launch, I sent it up without decals, which I intend to place on this model before the next flight.  I lucked out and was the first in my club to launch such a model!

The MIRV is Estes new multi-stage rocket introduced in 2011.  I chose this kit because it is unique, not just in appearance but it represents a whole different method of multi-staging than is commonly done. The first stage boosts as usual, but it then ignites - simultaneously - three independent second stages! That's the concept anyway, we'll see how practical it is.

The booster returns with tumble recovery, the three nearly identical upper stages return with tumble recovery also, after popping off the nose cones. As you can see above in this glimpse from the future, the three upper stages are shaped to form a hexagon when assembled on the booster stage. Each upper stage has three fins. The booster uses a B6-0 or C6-0, while the upper stages use the A10-3T mini-motors.

Estes was not very comunicative with this kit about how it works in their catalog or online, so here's the scoop. The ejection from the 18mm ("standard size") booster stage goes through a pre-molded plastic manifold that is designed to split the ejection charge into thirds, with each 1/3 leading to the nozzle of a 13mm mini-motor.  Each of the three upper stages will then launch from the booster stage which acts as a moving launch base.

The booster has a wooden-dowel version of a launch rod, and the upper stages all have lugs. They fly ahead independentaly while the booster then tumbles to the ground.  Each of the upper stages then fires its own ejection that pops off the nose cone, and the three stages fall / tumble to the ground with the theory that the added drag of the shock cords and seperated nose cone will let the model fall slow enough. I might want to add a streamer to the shock cords, but I'll try this model stock for the first test flight.

I'm skeptical, as I can see trouble getting one motor to reliably ignite three mini-motors with their small nozzles, but it is worth a try. I am hoping to be the first one at the club's launch to fly one of these, so I can get the praise and glory that comes along with poineering such a unique concept.  Apparently this concept is not catching on just yet, as even after a half of a year or so I still don't see any website reviews of this rocket, or even any flight descriptions.

Above, looking down at the manifold designed to hold and then ignite three mini-motors. This is made from plastic. Notice the wooden dowel acting as a launch rod for the second stages.

The booster motor is mounted with a traditional metal clip. Estes recommends a B6-0 or C6-0.  The upper stages have to be friction-fit. Estes only recommends A10-3T motors, I assume because they have a fast-burning, high impulse to get the stages moving faster off of the lower stage so the fins will have enough airspeed to be effective immediately.

The good and bad of this kit is that it uses pre-molded styrofoam pieces, one for the booster and one each for the upper stages. On the booster, it is really helpful to "automatically" align the fins because they are inserted into slots in the foam block. The purpose of the upper stage foam is, I suppose, to make the model appear as a single, six-sided upper stage instead of three discrete tubes.  The top-view outline of the upper stages appears to look like a flattened diamond shape. The three nosecones match this pattern, so when all three are placed together on the booster they form a single, hexagonal shaped nosecone.

This picture here of a single upper stage shows how it is constructed from a small tube with a styrofoam "wrap" which gives it the shape of a flattened diamond.  What's good is that the Styrofoam material is light and produces a shape that would be very difficult to reproduce with paper or cardboard, and is much lighter than that or if it was made of balsa.  What is bad about the foam I found out from building: 1) In shipping, it is very prone to surface dents, scratches and such from the other parts in the bag, and even when painted it is a somewhat fragile surface. 2) You must be careful what primer, paints, glue and fillercoat etc. chemicals you use, because some finishing materials can literally disolve the foam.  Most distressing to me is that the finished surface will still be prone to knicks and dents, I expect this rocket to look pretty beat-up after a few flights.  I had to add wood filler and sand a lot of the dents in the foam just from shipping. I have seen plenty of Estes kits shipped in boxes, so why wouldn't Estes ship this kit in a box is beyond me.

Here we see the three nosecones after painting, shaped so that when they come together they form a single hexagonal nosecone.

For the upper stages, the core body tube consists of a BT-5 tube which is surrounded on three sides with a molded Styrofoam piece. This piece also provides the advantage of acting as a permanent fin alignment jig, as the fins are glued to each side and one is inserted into a slot in the foam.  The foam on both the lower and upper stages made it difficult to sand the balsa withouth gouging the foam, so I recommend doing all of the sanding - even the balsa filler -  before attaching the fins.  Be sure to leave dry wood at the base for gluing.

I should have used a paper covering layer on the fins, which I now do to all my rockets to avoid the filler-sand-filler-sand-filler-sand routine. Paper makes a nice, clean, flat surface free from wood grain, adds strength, and is much easier and cheaper than balsa sanding sealer or fillercoat. (Use photo-mount ahesive sold in spray cans at craft and office stores).

One aspect of this kit that seemed a bit strange to me was how the fins are built up from two pieces of laser-cut balsa sheets each. While I totally get this for larger fins, or fins with unique shapes or strakes, it didn't make much sense to me because these shapes are basically parallelograms that are swept forward. A single sheet of balsa would have been easier to build for sure. I can only speculate that the offsets of the grain of the two pieces add strength to the fins. After all, it is a tumble recovery rocket and the fins may take a hard hit occasionally.

Most of the work on this kit is fin construction, sanding and painting. Each upper stage has three fins, and the lower stage has three more, for a total of twelve fins.  Below is a close up of the lower stage after painting.

So far in building this kit I made two known mistakes which shouldn't be too serious.  One mistake was with the engine mount for the booster. The motor tube is glued and inserted into the plastic manifold so the ejection is ducted to three upper stage nozzles. I guess I was asleep at the wheel, because after placing the glue where needed, I didn't manage to get the motor mount tube fully inserted into the manafold. It sticks out about an 1/8 or 1/16 inch - no problem, but I hope that added fraction of an inch of length in the ejection manifold will not cause second-stage ignition issues. I pushed and pushed as hard as I could without buckling the motor tube / plastic and foam pieces, but the glue just stuck like glue before the motor tube was in position.

The other mistake is superficial really. On the upper stage's left and right fins (there are 3 each on three upper stages), I forgot to sand the trailing-edge taper before attaching them to the rockets. Not a big deal.  We don't need no stinkin' taper.

Another change I made which I consider an improvement was to substitute Estes silly shock mount method with loops of Kevlar, from which I will attach the shock cords. Just looking at the tiny diameter of the upper stage's BT-5 tubes, I couldn't even imagine fitting my little finger in there much less a glue-soggy paper shock cord mount.  I glued both ends of a one or two inch thread of Kevlar to the inside about an inch down, after fraying the ends to get a better glue surface.

As I was building this model, I was looking for a place where I could add a small payload for an Altimeter One, but I couldn't find a good spot without some major modifications in either the booster or the upper stage MIRVs. I tend to think that this design might be a bit trickier though, and less forgiving of untested changes, so I'm fine just following the directions on this model.  Still, I so desperately want to see real data on these flights I might just tape the altimeter to the side of the rocket!

On the first picture above (left), you can see how the upper stage (aqua) fits into the lower stage's (black)manifold. The other two stages are removed.  The next picture (right) is a lower view of the booster stage showing the hexagonal styrofoam surrounding the motor tube with the fins inserted into the foam.

That's all for now, the model is still in the paint shop right now. I painted the booster gloss black, and the MIRVs three different colors: Aqua, Magenta, Yellow.  That means the supplied decals may not match, but I'll figure something out.

*

This MIRV is just about done.  Two items concern me about this particular design.  I still don't know how I will address them just yet or if I even can.

First, when the second stages are on all together, they do not stay tight together at the nose. Will this air gap between these rockets cause them to seperate or even rip out when 50-100 mph winds blow down between them during boost? Even if they remain undamaged, it doesn't look very aerodynamic.

I was thinking of using some sort of hooks, but I don't know which of the three stages will launch first, so I considered thread holding them together that breaks at launch. It would be hard to determine the thread strength needed with out a lot of trial and error and ensuing disasters. So then I figured small magnets on the nose or just below it, but I'm not sure they would have enough strength to stick with those hurricane-force winds.

What I finally decided upon was a little bit of tape or adhesive round sticker on the tip of the nose cone. I don't know if that would be strong enough but at least the wind force will keep it pressed against the three noses while going up the ground-based launch rail.  After that, who knows? The first rocket off of the booster will pull the tape off with it. It's worth a try anyway.  Looking at how this thing was designed, I don't understand why they didn't extend the "launch rail" up closer to the tip of the second stages where a second lug could keep the noses tight together. IF the individual rockets have a very big variation in ignition/launch times I could see how they would interfere with each other. It's too late for me to do anything about it now, but in hindsight I would use three much longer launch lugs on a longer wood dowel, so that they would stay together on the booster stage better.

The other item that worries me is the soft styrofoam body tubes. I hoped that the paint would provide a stronger shell to these soft pieces, but as I add spray paint layers to it, it appears to not have much of an effect. I am fairly certian with the short rubber shock cords supplied that those heavy plastic nosecones (yes, they are quite heavy), with sharp angles (they are not very rounded) will punch some deep gashes into the body tubes when they eject and then recoil back to the rocket(s). I could use longer rubber but it would be difficult to put much shock cord in those tiny BT-5 tubes, and it would sure add a lot of weight. Even after that while tumbling down, they'll probably be banging into each other.

Should I trust Estes to have tested and worked out all the problems before shipping this product? I just don't know about that with the way corporations are run these days.  Maybe some higher-up just started yelling "Shut up and ship it!" to meet his quarter projections and not look bad.

In my experience as an engineer (but not as a rocket scientist) this is what good engineering is all about. Looking for potential problems and solving them with open-minded brainstorming before it's too late. Well I don't have any plans or solutions to the above problems just yet. I'll just have to go for that first test flight and see what disaster develops if any (that could be fun for all the spectators).  Certianly there will be a lot of anticipation just prior to the launch. I must remember to breathe during the countdown so I dont' faint and miss the launch.

It's tough being on the bleeding edge, I wish somebody else here would have done this MIRV thing and wrote a reveiw already!



SPECIFICATIONS

Serial number: 25

Number of stages: 1 booster, 3 upper stages

Length, all stages: 24.5"

Body diameter: 1.637"

Booster stage mass: 22.3 grams

Sustainer #1 (aqua) mass: 34.1 grams

Sustainer #2 (magenta) mass: 34.0 grams

Sustainer #3 (yellow) mass: 35 grams

Overall combined mass: 125.4 grams

Motor range, booster: B6-0 to C6-0

Motor range, sustainers: A10-3T

Liftoff mass range: 164.7 - 169.3 grams

Booster motor diameter: 18mm

Booster engine length: 70mm

Booster mounting method: friction

Sustainer motor diameter: 13mm

Sustainer motor length: 45mm

Sustainer mounting method: friction

Payload capability: none

Booster recovery method: tumble

Sustainer recovery method: tumble with augmented drag

Recovery protection method: wadding

Shock cord mount: Kevlar

Nosecone material: Plastic

Booster fins: 3

Sustainer fins: 3 x 3

Fin material: Balsa

Launch lug size: 1/8"

Glue used: Titebond III

Paint used: Testor's Model Master

Kit brand: Estes

Completion date: Spring, 2012

TEST FLIGHT

Today, I actually sent the MIRV up for its first test flight this past weekend: Results and pictures to follow!  This first picture shows the rocket sitting on the launch pad waiting to go up.  I ran short of time but wanted it up anyways, so as you can see I sent it up without any decals.  Some of my concerns were answered, but not all of them, so the test flight was all important. In summary: It works. ...but there are some issues.

My worries that there was nothing to keep the upper stage motors in place was solved by re-reading the kit instructions: securing the motors to the upper stage body tube by wrapping masking tape OUTSIDE the tube, whereas I always friction-fit my motors using masking tape around the motor INSIDE the tube.  Need to think "outside the tube".

This method does two things, first it secures the motor to the rocket, and second it provides a bit of friction fit to the plastic manifold underneath it, so the motor stays in place long enough to ignite.

After my first test flight though, I have a problem with that. First of all, one of my upper stage motors ejected itself anyway, so the tape on the outside is not 100% fail-proof.  I find it hard to control and test the friction force with this method, whereas with the inside-the-tube method I can keep adding or removing tape until the friction "feels just right".  With the tape outside, it is difficult for me to peel the tape away from the body tube if I apply it tight.

The other problem I had with the outside-the-tube method is that some of the tape on one of the upper stages was burned by the other upper stage's exhaust. The burned tape left a sticky, stainy, burned residue on the finish of the body tube that can't be easily removed.  So although it may be a bit more complicated, I'll stick to friction-fitting the upper stage motors using tape on the motor casing, up inside the body tube, and add a controlled amount of tape on the end of the motor casing tube to friction fit it to the booster stage's plastic manifold.

To keep all the upper stage nose cones together for better aerodynamic control, I used a bit of clear celophane tape on the tip of the nosecones, it didn't look too noticeable and it kept the nosecones together well enough to carry and load the rocket and at least clear the launch rod OK.  And no, the stages did not rip apart during the booster stage burn.

As for the softness of the styrofoam body sections, maybe I was lucky, but I did not notice any significant dings on the new paint finish from the ejection.  That's a good thing because I wanted to fly this thing right away, so I didn't even get a chance to put any decals on it yet.  I'll do that soon, but I have a lot of soot on the booster stage to clean off first.

Of course the first test flight of this MIRV has shown me other problems that I didn't consider, but have to be addressed.  I'll discuss these next.

Here we see the MIRV at the very instant of ignition, the first wisps of smoke comming out of the B6-4 motor.  Nothing I can do now but just stand and watch!

A fraction of a second later, the MIRV begins its first-ever flight.

MIRV 1 has cleared the launch rod and is away!

MIRV is now accelerating with the thrust of the B6-0 motor.  So far all is well.  The tricky part is coming up.

The booster is blown off just as the B6 motor runs out of propellant.  All three second stages are now hopefully igniting.

Success! All the upper stages ignite with a puff of smoke as they begin to pull away from the expended booster.

Now free from the booster, the upper stages each travel on their own, however they appear to be continuing up as a single object.

Finally, after each rocket flew off on its own and then ejected the nosecone, they all return safely to the launch area.

 

FINISHED MODEL

After applying the decals, I now present the three different sides of the MIRV.

And here is a closer view of the tail sections.

FLIGHT LOGS

2012, June 30: Indiantown Gap, Moderate but erratic wind

B6-0 booster, Three A10-3T sustainers:  This was the first ever flight of this new and very different rocket. I used the lower-power booster motor as recommended by Estes. I did not apply any decals for this first flight, I simply ran out of time to get them on and dry for the club launch the next morning. I wasn’t too worried of the breezes, since the B6 is a strong booster even for a rocket that is 124 grams, and the A10’s on a 33 gram rocket would do well. (Note that these weights are a bit lighter than the overall weight published by Estes, I presume because I didn't use a seperate primer.) It did take quite a bit of time to prepare four motors and then stuff three wiggly shock cords into the tiny BT-5 tubes.

The boost phase was as good as can be expected and all parts stayed together. The boost was fairly straight, only slightly turned by the winds. The rocket rotated slowly clockwise as seen from below.

Almost too fast to be seen, the three next stages with higher impulse and less mass were able to rapidly leave the booster behind. Because of the speed increase, I lost them on the video camera. Fortunately all of them lit. All three stages were flying high and sailed up almost out of sight. So it turns out Estes got that part right.

The second stages all continued up and didn’t wander far from each other as they flew in a tight cluster. They seemed to stay together during the upper stage burns, perhaps because of the bit of tape on the nosecone, so I’ll try the next flight without the tape.

All three successfully popped their nose cones, and they all seemed to come down together in a tight group, one after the other. The heavy nose cones seemed to lead the way with the rocket body fluttering behind them. The swaying, swinging dance of the three sisters tumbling down was an interesting sight. The silver paint of the nosecones glinting in the sun made them easier to see in the air and on video. The tumble/drag recovery worked fine and all three independent rockets landed within 20 or 30 feet of each other.

It first appeared like the soft-ish foam bodies did not suffer any recoil dings, but closer inspection showed a deep triangular puncture in the #3 upper stage. I suspect there will be a lot more of these with continued flying. The above photo compares the ding and the sharp corner of the nosecone.

There was no altimeter on board so no detailed data could be obtained. Stage separation appeared to be at about 150 feet, while the upper rockets may have reached about 350 feet. Post-flight inspection revealed some interesting anomalies though.

First, the booster landed on the top of the launch control tent. It was broken (re-kitted actually). The two plastic parts of the ejection ducting manifold had separated at the glue joint – so much for Estes recommendation to not use too much glue here. I recommend you use a lot of glue! Just don't cover the tiny vent holes on the sides. It likely broke when it struck the canvas tent top and not in flight, since both parts were found together.

As can be seen above, the normally gloss-black booster stage was all quite sooty from those three exhausts, and will require a good cleaning after each flight.

I will look into the glue type I used for the seperated manifold, which was plastic cement. It may not have been the best kind of glue for that plastic. Plastic cement is designed to basically "melt" polystyrene and let it re-harden together (sort of like welding).  If this is (and it appears to be) a different type of thermo-setting plastic, then it would probably work better with CA glue, epoxy or another kind of cement.

As for the upper stages, #3 had ejected its engine casing, although the motor did eject the recovery device just fine before it went away by itself.  The #1 (upper) stage appeared quite sooty in the back.

As seen above, the rocket's finish also had a burn-through to some of the masking tape which Estes recommends to be used to hold the motor in. The balsa fin was burned a bit too. I might repaint the inside back ends with a high-temperature paint. I actually can't imagine how the backs of the upper rockets would NOT get burned.

The above two pictures shows how Estes recommends the motors be held in place. That worked OK for these two sustainers.  However, I will use internal tape for friction fitting, so no tape will be on the outside to burn. 

As can be seen here, this method does not always work!  Maybe I’ll add a little strip of masking tape around the motor casing in the end to keep them tight in the booster manifold.

My substitution of the Estes shock cord mount with simple Kevlar loops glued to the inside of the tube worked well again.  I've tried this before without trouble, not only is it simpler, lighter, but it also allows for untying and changing out the rubber for a new piece or a longer or shorter one. 

I was forced to ground this rocket with the plastic manifold broken, but I will need to fly this again but using the other recommended booster, the double-powerful C6-0 motor.  Should be a great flight, but the upper stages will probably fly beyond visual range if I fly on a hot hazy day again.  They didn't appear to drift very far at all even though it was a windy day, so I wouldn't worry about loosing them, they should all end up near the launch pad.  As for the upper motors, Estes recommends A10's only.  It appeared the booster was going quite fast while staging occurred, so I imagine that A3 motors might work also.

So in summary, it appears this multi-stage odyssey does work, it flies well and was a bit of a curiosity to even the old-timers.  But this "new technology" has some bugs to be worked out.  The cons for me would be the considerable prep time (4 motors), the cleaning required afterwards (not only the booster fins etc., but Estes recommends that the manifold interior needs to be swabbed out to prevent soot and burned-chunks buildup.).

The soft foam body needs to be delt with.  Also, the burning of the stages needs to be addressed.  If doing this again I would paper-cover all the fins before attaching, and I would prefer to fill in and coat the styrofoam with a thinned layer of white glue for a harder finish.  I would also consider using a longer dowel for the launch lug, but these options will certianly add to the weight.

Stay tuned some day for the MIRV tweeks and the next test flight with decals and a C6-0 booster...

MIRV is fixed up and ready for another test flight.  I cleaned off all the soot from the previous flight.  I re-glued the plastic ejection manifold using much more glue this time, making sure not to block the main air way and the small, almost non-visible vent ports on the sides. I scraped off all the burned masking tape glue, sanded down the charred balsa and paint from the back of the one upper stage.  Next I treated all three upper stages with a spraying of high-temperature silver paint on the rear insides of the tail section, and the inside surface of the fins. This is mostly not seen when the rocket is together.  I did this to hopefully protect the rocket's interior areas from the rocket flame of the other ajacent stages.  The high-temperature paint should resist a 1000-degree temperature just long enough for the rockets to fly apart, at least that is the hope.

I also added all the Estes supplied decals, and a few more.  Now the rocket looks sharp and much less like a playskool toy.  If I had painted this black I assume it would look quite bad (good).  I added some pictures showing the "final product". These are just above this Flight Logs section.

I did not do anything to address the dings on the body tubes yet.  If I get any more I will use much longer shock cords, possibly replacing the rubber with much lighter Kevlar string.

All done, the total finished weight of my particular model is still surprisingly less than Estes spec'd for the kit.

2014, May 24: Fort Indiantown Gap, 5-10 mph winds, 70 degrees

C6-0 booster,  Three A10-3T sustainers: The MIRV was not scheduled to fly today, I had plenty of other important test flights to do, but for some reason I just wanted to see the MIRV up there again, so after completing my camera flights, I sent the MIRV up in this “a-bit-windy-but-I-don’t-care” weather.

MIRV during boost.

As usual, prep time was considerable:  Friction fitting three little motors, stuffing shock cords into those tiny BT-5 tubes, and friction fitting the three stages into the booster manifold.

MIRV staging has just started.

The first test flight used a B-powered booster, this flight was to use a C – loaded with twice the black powder. I thought maybe it would really, really go up there.  While the booster didn’t go as high as I imagined, the sustainers certainly did nearly disappear.

MIRV upper stages starting to pull off of booster.

Of course there is no room on the MIRV stages for an altimeter (a shame), so I only have visual impressions to recall.

MIRV upper stages now cleared from booster.

The boost seemed slow, but powerful.  Almost before I was ready, the staging occurred and the three upper motors all lit up.  It appeared to be about 250-300 feet up. The acceleration of the upper stages again took me by surprise and I completely lost track of them with the camera, but a short time later I distinctly heard the three “pop” sounds of the ejection charges.  “Whew!”

MIRV booster slows and falls away while upper stages begin stronger acceleration.

At that point I turned my attention to the booster, which was tumbling back to earth and heading in my direction.  Luckily it landed just a short distance from me and would be easy to find later.  At least it didn’t land on the launch tent and snap in two.

MIRV staging has completed successfully!

It didn’t take too long to re-acquire the uppers, and they were quite high up, perhaps 400 to 500 feet.  I watched the blue and yellow stages return, but lost sight of the red stage.  If I didn’t think so before, I now think I should put a bright streamer on each nose cone.

MIRV upper stages rocket out of view in a tight cluster.

Again I noticed and video confirmed that the uppers continue to fly together as a cluster and not separate under thrust. Maybe it was because I tape the nose cones together a bit.

MIRV is visually re-acquired only after ejection and separation of upper stages.

At ejection they finally separated, but returned to earth in a relatively small cluster.  They fortunately did not wander off to all parts of the sky.

MIRV's three intact reentry vehicles. All systems nominal.

I was a bit bummed that the #2 motor casing (in the red upper) was missing.  It must have blown itself out the rear, although fortunately it was after the nose cone separated.  The upper stages all landed about 350 feet upwind, but very near each other.

Tracking reentry vehicles #1(left) and #3 (right). #2 appears to have separated from the group by a little bit.

I was quite over-joyed that there appeared to be no burn damage on any of the rocket parts.  It appears the new taping method and the hi-temp paint did its job.  Still, the booster stage was again very sooty. I would continue to recommend painting it with a high-gloss black finish, to make it a bit harder to see the soot and easier to clean it off after flight.

MIRV uppers #1 and #3 just before landing. The magenta #2 is close by.

Maybe this MIRV concept can work well.  The next flight I will attempt a flight while not tack-taping the three nose cones together.  I will likely prefer using the B6-0 booster though, to keep the staging low enough to experience and photograph it well.