Saturday, August 30, 2008

Comments on your Comments and Suggestions

Updated: Tuesday, September 2, 7am ET

First of all, I'd like to thank everyone who commented on the video (the original posting is just below this one) and made suggestions for how to improve the experiment.  I will try to address as many of the issues you raised in this posting, and amend it as I get more suggestions.  I'll also be posting about some tests I've already done and how they've evolved the design in a day or so.

James raises some objections about using balloons as deployment devices and suggests some sort of hard container (as do several other people).  Tests I've done indicate there are indeed multiple failure modes with balloons that make them problematic as deployment devices.  The big problem with hard containers is getting the fluid out of the container in microgravity; you can't pour stuff, and surface tension and hydrophilic/phobic effects are going to dominate, so getting the liquid to go where you want it is going to be a complex issue.  Given that you only get one or two shots during a flight to get it right, and you're under significant time pressure, I want to keep things as simple as possible.

Why don't I just pop a mento into a cola bottle? If you look back through the older posts, you can see that this was my original idea.  During the last week before the flight, I simplified the experiment after realizing that if convection was an important factor, nothing much would happen, and it would be hard to see what was going on inside the bottle.  In retrospect, doing it this way would have demonstrated a difference between the two environments better than what I eventually did, but it wouldn't have shown what was going on.

Using a baggie of cola: this might actually work, but it might make it hard to see what is going on.  A variant that uses a flat "slab" of cola in a specially constructed container might work (Ger later suggests a similar idea), but there are several problems that would have to be worked out; getting the cola into the container from the bottle without loosing too much carbonation, and isolating/releasing/moving the mento in zero G.  If those could be dealt with, then it might be a very interesting experiment, in particular if some glitter was added to the cola so the convective flow is more clear. It might work better with a clear diet soda, like Diet Sprite, or perhaps Diet Club Soda. This approach had not occurred to me, and the more I think about it, the more I am coming to like it.

This may well be the way to conclusively demonstrate the difference in convection, because it could also be performed with the same apparatus on the ground. However, it won't look as visually cool as a doing something with a sphere of cola.

Precision measurements: I don't know this if will be feasible given the constraints we have to work under, and our uncertain ability to precisely control the environment.  For this reason, we need something that demonstrates a really clear difference between 1G and 0G.

Cperdue suggests an ingenious deployment method (and Nick later provides a variant).  The main problem with it is that it would have to be scaled down; the biggest cola bottle we're going to have onboard is 10 or 12oz.  Also, the TSA might get a little bit concerned about allowing long pointed sticks aboard.  Finally, there's the issue of clearly seeing what's going on.

Matt suggests chemically popping the balloon.  If popping the balloon were the only issue, this might be interesting to investigate.  There's also the issue of whether Space Adventures will allow a chemical that dissolves rubber onboard.

Rustin suggests I use "aircraft" instead of "plane" in my description of some of the physics of Zero G.  Yeah, I could, but plainly I was trying for an extended play on words.  I did use typography to differentiate the two usages.

An anonymous coward takes issue with my use of "weightless" and "oG".  I didn't use the former term at all, and my opinion of his other quibbling is identical to Winston Churchill's opinion of objections to prepositions at the end of sentences: it is arrant pedantry up with which I will not put. Learn something about frames of reference, go find a lagrange point relative to the entire universe, then come back and argue with me.

Using IR controls: I have come to agree with the very next poster, who contends that servos are overkill.  I am going to take my own advice and keep everything as simple as possible.  Less failure modes that way.

"As long as your ball of soda is floating without hitting anything..." This is easier said than done. Given that most of the passengers on a flight are Zero G virgins, the inside of the main cabin resembles a 3D peopleball machine in multiball frenzy mode.  When someone's paying $5K+ for a ticket to ride (apparently the price just went up), they probably will be a wee bit upset if they get hit in the face by an errant cokeroid.  This is why we did our experiment in the seat section, which is empty during the parabolic segments.  That area has significantly less airspace (so to speak), and any incompletely collected soda is going to splatter somewhere.  This is why all the experiments have to be done in a sealed environment.

The Zero G coaches do release some small bottled-water balls in the main cabin, but these don't cause a lot of mess, and getting rained on is considered part of the fun.

The complex idea suggested by the anonymous non-coward about using a spherical cage that squirts cola into its center would probably not work well.  The cola would have to be precisely synchronized, and its momentum has to go somewhere, so I think the mixing would be turbulent enough for drops to be ejected.  However, I like the general structure of the device, and will keep it in mind the next time I build a device to punch a hole in the space-time continuum.

Richard mentions that the Mythbusters found that removing the coke from the bottle affects the reaction.  My thinking is that the shape of the bottle helps with the convective flow, which was what we were investigating, with limited success, in our original test.  Also, pouring the coke out of the bottle obviously causes some of the CO2 to be released, so a device that does not require the soda to be poured into an intermediate container would be preferable.
Valisk kvetches about my coining of the word menticulation.  I believe that it is an entirely cromulent word, and that its widespread use will embiggen the English language.
Coating the mento with something the coke dissolves: the problem with this is timing.  Keep in mind that you're only in 0g half of the time during the parabolic segment, and for 20-25 seconds at a time.

Alka-seltzer tablet in water: Toby suggested this, and he's not the first; one of the coaches on the flight told me he's always wanted to do this one. However, the situations are not equivalent, because the CO2 is generated by a chemical reaction in alka-seltzer, as opposed to a physical one in DC&M. So as long as water can reach the tablet, the reaction can continue.

The video Toby linked to is just too cool not to embed, so enjoy!

Thursday, August 28, 2008

Menticulation of Diet Coke in Microgravity!

Note: since the appearance of the slashdot story, lots of people are commenting and making suggestions.  Thanks!  I'll reply to them as a group in a day or so.

As I've mention in several prior postings in the blog, the big experiment we wanted to do during the flight was seeing how the Diet Coke & Mentos reaction works in microgravity. If you haven't read those posts, please do so to get an idea of how the experimental apparatus and goals evolved over several weeks. You may also want to check out my Youtube videos for other high-speed videos I've done, including one that shows the reaction at 1200fps on the ground.

Before I go any further, I want to thank everyone at ZeroG and Space Adventures that went the extra mile to make this experiment possible, in particular the science liason, Michelle Peters. And I'd also like to thank the TSA screeners, who arrived on site already totally up to speed on what we wanted to do (they'd even seen my test videos). Whatever you may think about the rules that the TSA enforces (and I agree with Bruce Schneier in that regard), the fact of the matter is that the frontline staff that you deal with have little or no freedom to apply common-sense discretion, and are often placed in situations where they don't have the time, or the background knowledge, to make an informed decision, which means that the default answer is "no". When you couple that with the fact that anyone can be having a horrible day, and some small percentage of people are jerks to begin with (a smaller percentage than most people assume), and multiply by hundreds of thousands of people going through security a day, it's a recipe for horror stories.

But in our case, since the screeners had been pre-briefed, it was easy to demonstrate that everything we wanted to use was well within the TSA rules. The only thing that didn't fly was a tiny ball of modelling clay that we were going to use to mount the mento onto a ziptie with, and the screeners helped brainstorm an acceptable (and better!) mounting method.

As described in a previous post, the hypothesis that we wanted to test was that convection of the soda was an important part of the whole reaction; under normal gravity, bubbles formed around the mentos rise up through the soda, allowing more soda to come in contact with the candy, and thus more bubbles form. However, in microgravity, there's no "up", so any bubbles that form will just stay near the mento, and will in fact keep new cola from reaching it.

So lets get right to the video, and then discuss what we learned.

I'll begin by discussing what went wrong.

Our first problem was that we weren't quite in free-fall, because in order to do the experiment, we had to be strapped into seats next to the emergency exit window (to get the light we needed). If you think about the geometry of the parabolic arcs from the perspective of the actual plane, the true zero-g path forms a parabolic plane, and (I'll try and state this as plainly as possible) the pilot attempts to fly a path that causes the (physical) plane to follow the (geometric) plane.

I say "attempts", because it's humanly impossible for a pilot to do this perfectly. So anything attached to the plane (as we were) is going to experience some small amount of residual gravity, not to mention the effects of any air turbulence.

Even if the pilot does this perfectly, only those parts of the (physical) plane that intersect the (geometric) plane will be in true free fall. Anything above or below that perfect plane (in the perfectly-flown plane!) will experience a slight amount of residual acceleration, because it's not free to orbit the earth in a free fall path, but is rather being dragged along either slightly faster or slower than it really wants to travel. In practice, of course, this tidal effect is tiny compared to the errors caused by the pilot as he or she attempts to fly the true parabolic path.

So because the experiment was attached to us, and we were strapped into the seats, and the seats were attached to the plane, the entire apparatus was subject to some residual accelerations. In order to eliminate them, the Mark II Menticulation apparatus will have to be free-floating, self-contained, and will have to operate without being touched. This will permit it to freely fall in a zero-g parabola independent of the path of the body of the plane (although there will be some residual effects due to things like air currents in the cabin, of course).

As a side-point, it's interesting to note that on these flights, from the standpoint of the passengers, the pilot doesn't need to fly an absolutely perfect parabola; as long as he or she can fly a path that is, on average, close to the perfect path, nobody inside the plane will really notice the difference.

The second problem we had was that we wanted to create a reasonably sized ball of soda, and then put the mento into it. However, the nozzle we used to control the soda flow was too small, and we couldn't control the exit velocity properly (and so we got all the squirts). On the second parabola (not in the video), we tried removing the nozzle, but we couldn't get a bubble of soda to detach from the bottle, and everything got messy - a blob of soda impacted right on the camera window, obscuring a lot of the view.

In order to fix this, we're going to have to come up with a method that deploys a preformed, properly positioned bubble of soda.

Finally, the video was slightly out of focus. We had to manually set the focus on the camera before doing the experiment, and it was difficult to keep the coke and mento at the correct distance, considering all the other things we were having to do.

Even with all these problems, I think we got some interesting video and results. It's not definitive, but it looks like the reaction is slowed down by the lack of gravity, and we also noticed something we weren't looking for; the cola apparently clings to the mento (likely, it's hydrophilic), resulting in the interesting dynamics when I moved the candy. A followup experiment might be to compare the behavior of some water surrounding a mento vs. a ball bearing.

The Mark II Menticulator - Initial Design

I've spent a few hours thinking about an improved experimental apparatus, and I think I've come up with something that, with a little refinement, will do the trick.

The experiment will be housed in a transparent case constructed of acrylic or lexan panels locked together by t-slotted structural framing. Inside will be a rubber balloon of soda trapped between two spoonlike holders, one above, and one below. A hobby r/c servo will be mounted inside the box, with two arms extending from it, such that if it rotates in one direction, a sharp tip will puncture the balloon, hopefully releasing the soda which will remain between the spoons; then when it rotates in the other direction, a mento will be moved to the center of the bubble of soda.

The servo will be directly controlled (no radios onboard!) by a small hobby microprocessor such as an Arduino. The microprocessor could also have some sensors to collect related telemetry (accelerometers and so forth).

Finally, several strips of high-intensity LEDs will provide the needed light for the Exilim EX-F1 camera.

Tuesday, August 26, 2008

What the Zero G experience is really like

The ZeroG website gives a broad overview of what you get for your $4K, but I thought I'd set down my impressions while they are fresh in my mind.

The whole process takes about 5-6 hours.  You arrive at the meeting place (in our case, an airport hotel) and check in, and you're given your flight-suit, a carry-bag, and a plastic nametag, which, according to long-standing astronaut tradition, is worn upside down if you haven't flown before.   You get introduced to your coach (ours was a former passenger who finagled a job for herself; James' reaction to this news was to inquire if summer jobs were available!), who is overly enthusiastic about what you're about to experience, etc., etc., etc.  It is at this point that you will start thinking they're laying it on a bit thick; in a few hours, you will change your mind.

Each coach handles a group of about 10 people; you get color-coded badges and socks that identify what group (blue, gold or grey) that you're in.

In our case, we also had a meeting with the TSA security team for final approval of our experiments.  They'd been completely briefed on what we wanted to do, so there were no real surprises.

Then you sit down for a light low-protein meal (it helps settle the stomach, and carbs soak up any acid overproduction) and watch a 35-minute video that goes through the details of the flight, safety precautions, and so on.  It's at this point that you take your motion-sickness meds if you've decided to use them; we did, though now that we've done it, in retrospect we probably didn't need to.  On our flight, one person got a little queasy, but only after the actual parabolic segments!

When that's all done, you go through TSA screening, get on a party bus (ours had a stripper pole!), and go out to the plane.

Once onboard (through the rear stairs), you get the usual safety briefing. Since the flight operates under the normal airline rules, it has to have a trained flight attendant aboard in addition to the coaches, flight director, and pilots (at least, we think there were some pilots aboard, we never saw them for some reason). While there was a cute comedy moment in the briefing, they need to add something to it along the lines of "in case of sudden loss of cabin gravity, a silly grin will appear on your face."

The seating area is at the rear of the plane, and the floating area is divided into 3 zones, one for each group.

The FAA clears a block of airspace for exclusive use by G-Force One (I still think it should be called G-Force Zero), and it takes about 30 minutes for the plane to get there. Then everyone moves to the floating area for a final briefing.

The floating area is heavily padded, but if you come out of a zero G segment upside down and near the roof, you might bang yourself up, which is why at the end of each segment there's a warning so you can get oriented. The transitions to and from freefall take several seconds so you have plenty of time to set yourself up; you'd really have to work at it to get hurt doing this.

There are no windows in the cabin except for the emergency exit windows; this apparently helps reduce the chances of motion sickness by removing external cues about your orientation. In addition to a photographer who literally floats around taking pictures of everyone, there are 6 HD cameras installed in the floating areas. Several weeks after the flight, you will get an edited video plus all the raw footage.

Each complete parabolic cycle is about 55% 1.8G and 45% 0G (the books have to balance, so to speak). During the 1.8G segments you are advised to lie on your back and stare at a point on the ceiling (another anti-motion-sickness trick). I tried other positions later in the flight with no ill-effects.

Each flight contains 15 parabolic segments, divided into 3 groups of 5. The freefall periods last around 25 seconds; they feel like they are much longer while you are doing them, and much shorter after it's all over. Between each group there are 3-5 minutes of normal flying while the airplane does a 180 to keep within the assigned airspace.  This turned out to be very handy, as during the last break, James and I went into the seated area and got set up for the Diet Coke & Mentos experiment, which we did using the light from the emergency exit porthole.  We did the experiment for two parabolas, then on the next one, we unbelted ourselves and swam back up the aisle and into the main cabin area, a very cool maneuver.

To ease you into things, the first parabola is at 1/3G (Martian gravity) and the next two are at 1/6G (Lunar gravity). You can do all sorts of goofy stuff like one-handed pushups, pushups to standing position, and the lunar "bunny hop" gait that the Apollo astronauts used to get around.

Then you go to full freefall. And I cannot emphasize this enough: in freefall, you do not feel like you are falling! For me this was by far the most surprising aspect of the experience.  I expected it to be like going over a hill on a roller-coaster, or like one of the "drop" rides (which I hate).  It was nothing like that at all!

I can be an eloquent bastard from time to time, but I am having real trouble describing what it feels like, because there simply are no words in any language to describe it. But anyway, here goes: it is not so much a sensation as it is the lack of a sensation, one you've felt all your life, one that is so much a part of your daily experience that you do not notice it. The closest you could come to it without actually going into freefall would be scuba diving, but there's a crucial difference. Even when you're neutrally buoyant underwater, if you focus really hard, you can still feel gravity tugging at your insides, pushing your organs against your muscles. In freefall, even that is gone. Once you experience it, you will know the answer to the famous Zen koan, "What is the sound of one hand clapping?" And you will literally be "enlightened".

During the first 7 freefall segments, there's various activities that typically get done; eating M&M's, playing with water spheres, etc. The last 5 segments are free-format playtime. If I have one regret about the flight, it was that I didn't spend one of those segments just floating in midair, eyes closed, doing nothing. I'll know better next time.

And that brings up a word of caution: you need to understand that this flight doesn't cost $4,000. It costs at least $8,000 -- because once is not enough. The first thing Natsumi said to me when we were sitting down, flying back to the airport, was "We have to do this again!" Yes!  My kind of woman!

After the parabolic flying is done, there's the 30 minute flight back to the airport.  As you descend down the stairs, your badge is ceremonially turned rightside-up by the flight director.  After some photos, it's back to the hotel for a light lunch and the distribution of flight certificates.  You get a nice totebag, and you get to keep your badge and flightsuit.

Which, of course, you'll need when you go on your next flight.

Sunday, August 24, 2008

3.. 2.. 1.. Ignition

We just got back from the ZeroG flight.  We managed to do 3 experiments onboard; the hard-drive gyro, karate, and Mentos&Diet Coke.

I will post later when I have looked at the video, but it looks like we got some cool high-speed video.

Everyone had a great time, and the most surprising thing was this - when you are in free-fall, you do not feel like you are falling.  You feel like you are floating.  It is a totally alien sensation.  Other participants noted this also; it is nothing like what you would expect from taking a drop ride at a theme park.  The general consensus was that the reason for this are the visual cues provided by the cabin, and the fact that you transition from 1.8G to 0G over a period of seconds.

Saturday, August 23, 2008

Practice makes Perfect

The rollercoaster ride that is the runup to the rollercoaster ride we want to take threw us for another loop when, the night before we planned to drive from Las Vegas to Los Angeles, we got a call that "G-Force One" (shouldn't it be G-Force Zero?) had a mechanical issue that needed repairing, and the Saturday flight was cancelled. There was, however, a chance that it could be rescheduled for Sunday.

After 24 hours of angst, we got the word that all was well and we could indeed fly on Sunday. So we are now skulking in a secret lair in Gendale CA (we were promised a stimulating hive of scum and villiany; so far, not so much), counting down the hours, and half-expecting that a massive earthquake will devastate Burbank Airport overnight.

In the meantime, we did several practice runs of the several experiments we are going to attempt. Here you can see James and I running through our core experiment, "Menticulation of Aspartame-sweetened Cola-flavored Carbonated Beverages in a Microgravity Environment".

After much thought, we have decided not to repeat the prior experiments that have been done in 1G, but instead do something that can only be done in ZeroG.

Prior research by Hyneman, Savage, et al. and others has demonstrated conclusively that menticulation is largely a physical reaction. The mentos, when introduced to the cola, provide a large number of nucleation sites because they are quite rough on the microscopic level, and thus permit the rapid growth of bubbles of carbon dioxide, which is in solution in the soda. In addition, the aspartame sweetener used in diet soda, as well as some other ingredients, reduce the surface tension of the liquid, making it easier for the bubbles to form.  The result is the pressurized shower of slightly minty soda that we all know and love.

However, there may be another important process that takes place during menticulation that has not been addressed by prior research -- convection. Consider than when the bubbles are formed, they will naturally rise to the top of the bottle (since they are less dense than the soda), and more importantly, this will draw more cola into contact with the mentos. But in ZeroG, there is no up and down, and so the bubbles have no inherent tendency to rise. So what will happen? Will the process continue, but at a slower rate? Or will the initial bubble formation effectively cut off the reaction entirely by isolating the mentos from the cola? Might we even end up with a thick skin of cola surrounding a bubble of CO2?

So it seems that the cola and mentos idea has gone from just being a cute stunt to being real science. If we get an interesting effect, we will be discovering something that nobody knew before, and adding, in a small way, to the sum of human knowledge.

In the above photo, you can see our experimental apparatus. We are using a plastic glove-bag to contain any spills, and have added an 8x10 acrylic window to it with heavy duct-tape. Taped to the window is a wide-angle rubber camera sunshade that we can screw the camera into.  Inside the bag are several ziplock sub-bags that will contain our materials. The cola is contained in a small plastic bottle with a nipple attachment that will allow me to dispense small amounts of soda in front of the camera port, at which point I will insert a mento into the cola using a ziptie with a small blob of artist's clay on the end.

Depending on how the first trial works, we'll try it again using a bigger blob of cola, and think of something on the spot to do.

On a side note, recent pictures I have seen of G-Force One indicate that the main cabin does have some windows.  If so, we should be able to get enough natural light to film at 300 frames per second!

Wednesday, August 20, 2008

Holy Ground

Subsequent to our interesting discoveries at Hoover Dam, we continued eastward on our scientific pilgrimage to check out other sites of interest.

First up was Meteor Crater, the best preserved impact crater on Earth...

The official story is that Meteor Crater is the result of the impact of a very small asteroid (approximately 50m across).  Of course, the official story is a total crock.  Meteor Crater was created in 1873 as a demonstration of the power of a super-weapon created by one of my personal heroes, the terribly misunderstood Dr. Miguelito Quixote Loveless.

Needless to say, that weapon, or a version of it, is what we found under Hoover Dam.

Monday, August 18, 2008

Pretty Dam Impressive

Since the Zero-G scheduling snafu has given us some extra days in the southeast, we're making lemonade by visiting important sites that might possibly be incorporated into our diabolical schemes. First up, Hoover Dam.

Now, you might think that the dam is just an incredibly impressive feat of engineering that provides tons of electricity and tames the wild Colorado river.  That's what they want you to think! However, a closer observation reveals the true purpose of the structure.

Consider this, which they claim to be one of the diversion tunnel spillways under the dam...

Oh, so innocent.  However, while #2 son distracted the tour guide, #1 son found the hidden control panel that activated the device's true function...

We have made a note that our plans for World Domination must not involve anything that gets within line of sight of Hoover Dam!

Saturday, August 16, 2008

Vegas, we have a problem...

We were literally waiting for the cabin doors to be closed on our flight to Vegas when we got a call from Zero-G with some bad news; this weekend's flight had been cancelled at the last minute.

Apparently, they'd done some modifications to the plane related to a NASA contract, but the needed FAA paperwork had not been completed in time, so they couldn't fly.

A seriously bummed Team Mad Overlord arrived in Las Vegas Thursday night, checked in (to room 321!) and went into bigtime logistical reconfiguration mode.  We finally determined that we could reshuffle work and school obligations sufficiently to permit us to extend our vacation through next weekend, allowing us to fly the next scheduled Zero-G flight in LA.  So we're going to run around the southwest visiting places like the Grand Canyon and Meteor Crater.

Meanwhile, we're doing Vegas'y things, like taking in the excellent Penn&Teller show and a little indoor skydiving...

In one of the great ironies of modern entertainment, Teller, the guy who never speaks onstage, actually has a much better voice than Penn -- probably because he never wears it out on stage...

Wednesday, August 13, 2008

Packing up and Heading out!

After much discussion with the folks at Zero-G, we're ready to head off and do some experiments!  The big news is that they've figured out a way to let us do Diet Coke & Mentos!!!  The solution turned out to be doing the experiment inside a portable glove-box.  This means we will be able to definitely answer the important question of "when the hero traps you outside your space fortress, can you rocket your way back to the airlock using only your favorite diet soda and minty candy?"

Above you see the complete experimental loadout.  The hard-disc gyroscope consists of a 7200 rpm drive unit that contains the platters from several dead hard drives.  The enclosure is a cheap USB enclosure that has the virtue of needing only a simple 12v power supply.  Testing showed that the best batteries to use were a set of 10 1.2v 2000mah NiMH cells; regular alkaline cells simply cannot source the required amperage, and even high-discharge lithium cells are borderline.

As a backup to the hard drive, we're also taking along a manual PowerBall gyroscopic hand exerciser.  Attached to the red pull-cord of the PowerBall are a 0.500" spherical rare-earth magnet and a matching ball-bearing.  These will be used both for pendulum experiments at 1/3 and 1/6G, as well as perhaps some ZeroG sillyness, using a blowtube (not in picture) to fire one past the other.  Both have one hemisphere painted red to make their rotational motion more evident on video.

For the Diet-Coke and Mentos experiment, a series of tests, some of them spectacularly unsuccessful, have resulted in the development of a deployment system that should work in Zero-G.  After the Diet Coke is uncapped and the gas pressure is allowed to equalize, a plastic sheet from a ziplock bag is placed over the mouth of the bottle, and a Spangler Geyser Tube is screwed on.  The Mentos are then inserted into the tube, and the first one in has a thumbtack affixed to it with modelling clay. The restriction nozzle of the Geyser Tube having been previously removed, deployment is achieved using a short length of plastic water pipe to ram the Mentos into the Coke.

Here is a video of the final test of the deployment system, filmed at 300fps using the Exilim camera.

Finally, last but not least, I have packed 4 pairs of Peril Sensitive Sunglasses. We won't need them, of course, but the Zero-G staff might!