Humans make rather poor beasts of burden. Fortunately, nowadays heavy loads are pretty much relegated to machines, saving our spines for recreational activities like donning backpacks and heading into the wilderness. Speaking of which, the suspension system for backpacks-the part that connects the load to our bodies through a series of straps-is relevant to our attempts to keep our muscles and bones from degenerating in space.

To maintain our muscles, bones, and cardiovascular systems, we exercise about two and a half hours each day. These exercises are divided between resistance ("weightlifting" in weightlessness), cycling, and treadmill routines. To run on the treadmill in zero-g requires that your feet stay in contact with the belt, so we wear a backpack harness with adjustable spring-loaded straps.

The loading is important. To reap the full health benefit, the harness is loaded to near (Earth) body weight, which for me is 80 kilograms (176 pounds). It sounds easy, but the technical details of creating a harness add significant complexity to the process of exercise in space. This is another example in spaceflight hardware design where the answers are not in the back of the book.

On Earth, a backpack harness is designed to distribute the load between the shoulders and hips, with the balance between the two usually adjustable. And no one really wants to carry a backpack weighing more than about 80 pounds. I have a minimalist philosophy when it comes to backpacking, and seldom carry more than about 45 pounds.

Now enter the space requirement to carry a load close to your body weight. No backpack I am aware of is designed to do this. And how does one best distribute the load between hips and shoulders? Our bodies are not meant to carry our own weight on our shoulders, so the load has to be distributed more widely. But since the spine has to be loaded, too, the entire weight cannot be placed on the hips. Your hips also have to be free to swing with your stride.

When backpacking with heavy loads on Earth, we seldom work near maximum cardiovascular levels. Backpacking is slow and easy; we take the time to smell the roses along the wilderness trail. In space, we run on a treadmill at 95 percent of our maximum heart rate. At this level of exertion, your chest is expanding and contracting to its full extent while your heart feels like it is going to jump out of your chest. Normal backpacks are not designed to accommodate the required chest expansion at maximum exertion.

These seemingly small engineering details complicate the backpack design enough that we can't just use off-the-shelf equipment. The treadmill harness we use on Space Station was engineered at NASA Glenn Research Center, and so is called the Glenn harness. The engineering was tested on Earth by taking a treadmill and mounting it vertically on a wall.

Then the test subject (I was one of them) is suspended horizontally above the floor with a series of bungees, like in a magician's floating lady act. Now the harness can be tested at near-body-weight loads in normal gravity. It's often necessary to go to such lengths to design and test spaceflight hardware. In that way, a large visionary technology program like Space Station drives numerous small advances that never would have been contemplated (or funded) without the greater driving force.

An Astronaut's Guide to Space Etiquette

How to be civilized on the space frontier, Chapter 6: Having company for dinner.
It does not matter that you've seen the same faces every day for months on end; you'd still like to invite everyone over to "your module" for dinner. With invitations accepted, you prepare for the occasion. But what is the expected etiquette for entertaining in orbit? How do you arrange things so your guests will not think you are gauche? Here are a few space-tested guidelines to help in the preparations.

Have plenty of food, and serve your very best. Now is the time to break out those thermal-stabilized pouches of beef steak that you have been hoarding. Bring out any specialty item from your personal crew allotment (these items arrive on the periodic unmanned resupply spacecraft that visit us). Perhaps you can share a can of smoked anchovies, New Mexico green chili, or a piece of Old Amsterdam cheese. Always serve something special that is not repeatedly eaten on the standard nine-day menu. Being generous now will reap more benefits than eating these delicacies in solitude.

The choice of beverage is rather limited. You can serve the standard ones: coffee, tea, and artificially flavored, artificially colored, sugar-loaded, fruit-replica drinks. All, of course, are served in a bag, and you sip the fluid through a straw. The image of an insect sucking the juices from some lower insect may come to mind, but in space it is considered impolite to give voice to such imagery.

You can provide a special treat if you have access to one of the research refrigerators. In space, all your food is either hot or at room temperature. When you live in an isothermal environment, it can be a real treat to serve your guests a bag of cold water.

For special occasions-perhaps after a space walk or the docking of a resupply vehicle-you can serve your beverages in a "zero-g" cup. This is something you will have to make from scrap plastic sheeting (instructions are in Appendix C). These cups allow you to sip beverages from an open container, like we do on Earth. Zero-g cups, unlike bags with straws, are better for social rituals like toasting, and will bring a smile to the faces of your guests.

It is important to dress up your galley. Have full packets of wet and dry wipes within easy reach on the galley table. Take any partial packets and save them for another time. Empty the trash bins. A full trash bin is problematic; a handful of small things typically float out when new items are added. This rudely interrupts conversation while everyone scatters to collect the floating debris.

It is good to have two trash bins; the standard-sized one for largish items, and an old wet wipe container for small ones. This separation of smaller trash-cutoff pouch corners, food crumbs, and wrappers-helps prevents their release when the lid is opened. Be sure to label this wet wipe container "trash". Newly arrived crew may not be aware of this trash protocol, so it is best to politely demonstrate by example. They will learn quickly enough.

Clean the food scissors. Scissors are needed to open food pouches, as tearing them along the built-in perforations usually results in liberating hot droplets of fatty ooze and other asteroid-like particles. That's why, if the scissors aren't kept clean, they become caked in solidified gravy to the point where they become glued shut (not to mention being slightly repulsive). Such a state is considered rude, so clean your scissors before the guests arrive.

Always have a loaner spoon available. In weightlessness, it is easy to lose things. It is not unusual in a group of six for someone's spoon to have floated off. Having a clean loaner spoon allows for the evening to continue and the conversation to flow. It is rude to give your guest a loaner spoon caked in crud from the last time it was used. The lost spoon is usually found by morning, stuck to a ventilator inlet screen, and your guest will appreciate it being returned.

Always put out new tape. The galley table has multiple spots of Velcro to park packets of food. However, not all packets and pouches have mating spots of Velcro, which means they can't be set down on the table. Several strips of duct tape, carefully folded so the adhesive side is out (see Appendix D for instructions), allows such containers to be parked on the table.

Tape left over from the previous week, while perfectly functional, collects errant crumbs, hairs, lint, and other unsightly things. Displaying dirty tape is exceedingly rude to your guests; always put out new, clean tape.

In space, catching food in your mouth is considered polite. Opening wide and making a clean catch will most always bring cheers from your guests. In one impressive gulp, you can leave them with the image of some sea creature inhaling another. Catching food in your mouth, like belching at the table (considered impolite in most cultures, but a compliment to the chef in others) is rude on Earth but de rigueur in space.

By following these simple rules, you will ensure a delightful evening with your guests. And remember, on the space frontier, the etiquette book is still being written. I encourage you to invent new ways of conducting everyday life, including entertaining. It is one of the reasons we find ourselves here in the first place.