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Rough Science 4 Death Valley: Ellen McCallie's diary: Spacesuit

Updated Tuesday, 29th August 2006

The team have to devise a system for cooling a spacesuit. Ellen focuses on the copper pipe that will carry water from fridge to suit.

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Day 1

Challenge: To build a pump that will circulate water through tubing. The tubing will initially hold warm to hot water (ambient Death Valley temperature in summer is typically over 45ºC). The pump will push the water through the tubing, which enters a series of coils inside a fridge that Kathy, Mike, and Ian are making. The water in the tubing is then cooled and finally circulated out of the fridge and through our Rough Science "spacesuit" in order to cool the "astronaut".

The key issues:

• The pump has to push or pull the water with sufficient force that it moves through the tubing, which may be quite long.
• The water in the tubing has to be in the fridge long enough to cool off. With the ambient air temperature potentially being very high in Death Valley, the water may need to spend lots of time in the fridge, so we’ll have to coil lots of tubing in the fridge to give it time to cool down.
• The water in the tubing has to stay cool long enough to reach the person in the spacesuit and cool the person down before the water (now warm) returns to the fridge.
• The tubing connecting the fridge and the person should be as short as possible and should be insulated from the ambient air temperature, so it doesn’t warm up too much between the fridge and the person.

Other things to accomplish:

• Make and connect the spacesuit and tubing system.
• Build a wagon for the fridge system that the astronaut can pull.

In terms of the tubing, we know that copper is a great conductor, not an insulator. Thus, we want copper tubing in the fridge system so the hot water entering it cools quickly. We also want copper tubing in the space suit, so the cool water cools the astronaut.

We want tubing that is a good insulator, however, going from the fridge to the astronaut and from the astronaut to the fridge so the water isn't heated up unnecessarily by the Death Valley air. We’ll use plastic tubing for these connections. Though we are pretty confident that the plastic is a better insulator than the copper, we don’t know how good an insulator it is (and really don’t have time to figure this out), so we will place the plastic tubing in a larger plastic tube which is covered with aluminium foil. This will be helpful, first, because the outer tube is much larger than the tube carrying the water. This will allow for an insulating air space. Second, the aluminium foil will reflect sunlight, so the tubing will absorb less heat through solar radiation.

Jonathan is absolutely brilliant, and he has so much experience building things. Based on an idea of his, we had a pump knocked together by mid afternoon. Basically, we used a power screwdriver as the motor. We connected a hex wrench as the bit and put it through a little system we made of wood, copper tubing, and screws that looks like a miniature Ferris wheel. The key parts are the lengths of copper tubing that push the water through the plastic tubing by pushing the plastic tubing, which is stationary, down against a board.

It is hard to explain in words, but obvious when observed. If you haven’t seen the show, try this. Take a piece of tubing or a straw. Put water in it and then squeeze one section while pushing forward. The water moves forward. Basically, the device Jonathan designed and I helped build does the same thing over and over; each time a piece of copper tube reaches the bottom of the wheel, it pushes water forward in the tube by squeezing the tube between the copper section and the board.

Cool. We filled a plastic tube with water, which we dyed red with common food colouring in order to see it better, and turned the screwdriver on. We watched small air bubbles go round and round, which indicated the water must be travelling, too!

Seems like success on day one. Hmm, that’s a bit unusual. I’m not one to be a sceptic, but this may be too good to be true!

Day 2

Yep, there are a couple of catches in the system. First, today is really cold for this area. It is under 32ºC. A cold wave, complete with thunderstorms. We watch a wall of water cross mountains and sheet across desert valleys. Lightning is seen from miles away. Yes, we were told we were coming to one of the hottest and driest places on Earth and I am in a long sleeve shirt under my rain jacket.

The weather is affecting our challenge. The plastic tubing we have is pretty stiff in this temperature. Yesterday, when it was warmer, the tubing was quite malleable. In this “cold”, our motorized pump isn’t strong enough to smush the plastic tubing sufficiently to squeeze the water through it. When we heat the tubing briefly over Mike B's fire, the system pumps the water just fine… it better be warm tomorrow!

We also needed to test to see if the pump was strong enough to force water through a long system of tubing. This is where things get fuzzy - my botany and ecology training don’t provide much insight. (I run into these types of situations regularly, so I have been taking physics-related courses on things like light, sound, electricity, magnetism, and astronomy for the past couple years in order to better understand how the world works. I still didn’t know how to think about this situation, though.)

Questions:

1. Does the length of tubing, thus the length of the water column, affect the amount of force needed to make the water circulate?
2. What matters more, the total volume of water in the loop or the length of the water column?
3. Is there a critical tube diameter for which water adhering to the tube will over take cohesion of water molecules, thus keeping the water from moving?
4. Does the system need “priming”? In other words, is an exceptional amount of force needed to start the water circulating, compared with the amount of force needed to maintain the system once it is started?
5. How many air bubbles are too many? How much air in the system is too much?

Unless someone just knows the answers to questions like these while we are doing the project, we have to experiment to find out. We dealt with question 1, which quickly lead to others...

We didn’t know if the pump could circulate water through a long length of tube, so we mocked up a long tube, about 10 m, and tried to completely fill it with water. With Kate at our side we turned the pump on. Nothing. The pump wheel went around, but the water didn’t move. There were lots of air bubbles, however. Some were quite large. Jonathan wondered if an airlock was preventing water movement. We took the connecting piece out of the loop. It was easy to suck water through the tube, but quite hard to get the water moving by blowing into the tube. Our pump was equivalent to blowing into the tube.

We refilled the tube, this time ensuring as few air spaces as possible by keeping the funnel feeding water into the tube constantly full and having one of us sucking on the other end of the tube. (Don’t ever put your mouth on something unless you are sure of what it is and where it’s been. In this case, we were using tubing we had washed. We were filling it will drinking water and food colouring, so we felt it was safe.) We basically flushed water through the tubing until the person sucking on the tube encountered no more air spaces. We also inspected the tubing, which was intentionally transparent, for air bubbles. We ended up with one air bubble about two centimetres long. Good enough. Having one relatively small air bubble allowed us to easily determine if water was moving through the system when the pump was on. Yes, indeed, with a full tube of water and a warm tube, the pump circulated water without issue. So we learned if we minimised the amount of air in the tube, our pump was forceful enough to pump water through a long tube (about 10 meters of tubing).

We then tested to see if tight coils restricted water circulation—they didn’t as long as flow was restricted. We also tested to see if the pump could pump water upwards against gravity. The water would, after all, have to travel against gravity at least a couple of feet as I am 6 feet tall before heading back down into the fridge. No problem.

As we ended up with a working system, we didn’t delve much farther into our questions or try to tease out the different components. There just wasn’t time.

With extra screwdriver batteries recharging, we went on to design the actual tubing system for the fridge and spacesuit. We ended up with a long series of copper tubing coils in the fridge, so the water would have lots of time to cool. We connected this by short sections of clear plastic tubing covered by a second plastic tube wrapped in aluminium foil to a set of zigzagging copper tubing designed to cool the astronaut’s body core - the trunk. We chose the core of the body because the extremities have a lot of surface area and thus release heat to the atmosphere quite quickly anyway. Plus, it is the body core that really needs to function effectively to keep the astronaut alive and well. If you take a look at how we positioned the zigzags, we avoided areas of fat and concentrated contact between lean parts of my body core and the cooling system. This should make the cooling system more efficient, because fat is a great insulator and that’s not what we want in this situation.

Also, if the fridge had been likely to produce freezing temperatures, we would have probably set the system up differently and cooled the core slowly by reducing the heat in the body extremities first. But since the fridge wasn’t working at all as a fridge at the end of day two, we weren’t particularly worried about shocking the astronaut’s system or causing hypothermia. Though Kathy, Iain, and Mike had a good vacuum seal and honest-to-goodness zeolite, no real cooling is taking place in the fridge.

(I was chosen as the astronaut to test the spacesuit and cooling apparatus merely because I fit into the spacesuit materials we were given. Who planned this? Thus, I am wondering if I should be slightly concerned about keeling over with heat stroke in Death Valley tomorrow. I am counting on K, I, and M to figure out something!)

Day 3

Wow! It worked. I must admit I had little faith (make that no faith at all) that I was going to do anything but boil in that spacesuit in Death Valley. Remember when Kate said that in space your blood could boil when the sun shines on you?

Well, the skies cleared and the sun was shining when we arrived in Death Valley. Not as hot as is typical for Death Valley, but when I put the suit on and zipped it up with hood in place, I felt my body temperature soar. The blasted thing didn’t breathe at all! Why wasn’t it made of one of those high tech breathable fabrics! In any case, I was trying to figure out how I could be stoic about this without falling over, when Jonathan turned on the pump. The vacuum had worked and Kathy had rigged an evaporative cooling system on the car roof by covering a container of water with the red long-johns, which thankfully I wasn’t required to wear, and t-shirt, both soaked in water. As Kate drove us to the test site, the water in the container cooled as wind evaporated the water from the clothing covering the container, thus drawing heat energy out of the water in the container. And Mike had come up with a chemical way of cooling the water too. Brilliantly successful!

Sometimes the low tech solution to a problem is the only one that reliably works! Hurrah! So, Kathy put this cool water, about 20ºC, in the fridge container, which we now called a cooler, not a fridge, and then kept it cooled under vacuum. Thus all the effort making the fridge/cooler was not wasted.

It took a mere second or two for me to feel the cool water hit the space suit. Wow! What a difference. It was terribly exciting—almost confusing as I just hadn’t expected us to have both cool water and a working pump. The pump had been too easy, too simply built to work. Again, the simple, relatively low-tech solution worked.

So, I dragged the cart with the fridge along a course in Death Valley. The weak link turned out to be something we hadn’t focused on much--the cart, whose wheels started to splay as soon as I began to drag it over the rough playa. The ground was rugged and dissected by evaporated salts, which we hadn’t expected at all. At one point, I tripped and skinned my hand and knee on the stuff. It was amazingly sharp.

I monitored the temperature in the spacesuit, which continued to drop as the water cooled, thus indicating we had ended up with a reasonable proportion of time the water was in the cooler cooling down compared to time the water was circulating around the suit cooling me off (and warming up before heading back in to be cooled again).

The ironic bit was that just as I had completed the challenged and planted the flag (they convinced me that even I could plant a Union Jack as I was a member of a British team), the pump stopped circulating water. The water in the tubing had cooled the tubing so much that it was no longer malleable enough for our little pump to compress it and force the water forward. Our success in cooling had led to an ultimate breakdown in the system. We hadn’t even considered this as a potential problem even when we faced cold weather issues on day two.

This just drove home the point that NASA and the companies it contracts, heck, everybody that ever makes something, really has to test it in all conditions and changing conditions, because even though we try, we can rarely predict all the issues involved, even the seemingly obvious ones. It also reinforces “Safety first—always”.

Reflections on Death Valley

You know it is hot when:

• You drive with a bag of ice on your lap and the cold of the ice never reaches your skin
• You open the door of your car that has been sitting in the intense sun for over an hour and it is cooler than the air outside
• Water, when poured over ice in a cup, melts all the ice before the cup is full
• The sign on the road says not to run your car air conditioner for fear the car will overheat
• When walking, you want to get into the shade of the shade in order to get cool
• Your skin looks similar to that of a lizard because it is trying to get away from itself

Death Valley reached 53ºC yesterday at 5pm, about the hottest part of the day. The thin, hot wind makes one’s skin stand up like scales trying to get as far apart from each other as possible. I’m slathered in sunscreen and covered with a hat and sunglasses that set close to my face. It’s windy; at least it seems so. The trees seem to blow in slow motion, picking out leaf by leaf for motion. The hat is good, the sun doesn’t feel like it’s beating me down. It is as if the light and heat go directly to the ground. Thin air, no moisture. I breathe through my nostrils to filter dust and to reduce moisture loss. Every so often the back of my nose and mouth become so dry they reflexively close up as if ocean water has gone up my nose. I open my mouth with a quick gasp before returning to nostril breaths.

As I walk, it is almost as if the air parts before me. I am aware that the air is dry. It is so hot that I can’t tell if it is hot. I almost expect a flame as I enter new patches of air. My skin has a burning sensation, like it is trying to release heat to the atmosphere immediately around it.

Two plants dominate the area, two hundred feet below sea level: honey something and desert holly. The carcass of a dead bird sits dry on the ground. The canyon through which I walk shows signs of mud flows through it. Layers of variously textured sediments indicated lake bottom, alluvial fans, and other deposits. I didn’t look for fossils.