Designing Space Science Experiments

Space is a very unusual environment, so the experiments that fly in space face some unusual engineering challenges. This document gives you an overview and introduction to some of these challenges. The aim is to help scientists who want to propose an experiment understand the environment and engineering issues so we accelerate the learning curve.

I'm writing this document based on my understanding of space flight and space science, and the exposure I've had to some of the Soyuz, Mir and ISS science equipment, but I'm not a space engineer. Fortunately we have access to a phenomenal team of very experienced space engineers - possibly the most experienced team in the world - in the form of the Energia corporation. As part of my flight contract we have included the requirement that Energia will assist with the design of our science experiments. They have more time in space than any other country or company.

But we don't want to waste time, so this document serves to brief you on the fundamentals so that you aren't surprised at what can and what cannot be done.

Character of Space Science Equipment

Space science equipment doesn't look very impressive. It looks old-fashioned, and downright simple. That's because it is! Contrary to popular belief, the latest and greatest stuff doesn't often fly in space. Because space is a very tough environment, and because it's so expensive, and because it takes years to design the equipment, and because everything has to be guaranteed to work for many years (15-25) without replacement or repair, the equipment is engineered to be robust, light, SIMPLE, predictable, and accurate.

If you've every worked with cutting edge equipment you'll appreciate this. Think about it! The latest and greatest stuff is usually fragile, temperamental, leaky, needs specialists just to keep it working, doesn't last very well, breaks in unpredictable places and unpredictable ways, and usually isn't particularly compact. So space equipment is extremely well engineered, extremely expensive, but usually not very impressive. Don't be surprised when you read the specs of the equipment that's already there if it doesn't measure the latest gee-whiz parameter or offer the most up-to-date facilities.

The point of space science is to explore qualities of materials that are unique to space. ANYTHING that CAN be done on earth should be done on earth. ONLY stuff that uses the unique properties of space makes sense to do in space.

Engineering Issues

Weight

It costs around $50,000 per kilogram to put anything into orbit. That's just the launch! It costs a lot more to keep it there during the lifetime of the equipment. There are fundamental limits on the amount of mass that a shuttle or Soyuz or Progress can carry, and the ways that mass can be distributed. Experiment equipment should be as light as possible.

Volume

The ISS and all the launch craft are very small. Soyuz can barely fit three adults, ISS is pretty cramped too. Every cubic centimeter of space is accounted for. Equipment needs to be as compact as possible.

Human Interaction

Astronauts work flat out. Every minute in the day is accounted for and planned in advance to the greatest extent possible. Because human time in space is so limited and so expensive the experiments are designed to work with minimal human intervention. An astronaut might switch it on and switch it off. But try to avoid having to have an experiment that needs constant observation. The astronauts tend to be generalists rather than specialists, so experiments need to be able to be operated by people who are new to the field. There's time allocated to science training, but it's limited time since the astronauts also have to handle all the space flight crew training in the lead-up to a launch.

For example, say people want to observe the behavior of a microbe in weightlessness. The astronauts might take up a sealed tube containing a deep-frozen specimen. Once there, the astronaut would thaw the tube by removing it from the freezer and store it in a specified place for a specified time, then freeze it again by putting it back in the freezer. That's it. The frozen sample is returned to earth and only THEN would the tube be opened up and all the observation work done. The sealed tube makes it safer (nothing can leak) and simpler (no interaction required).

Power Supplies

Power is a big issue on the ISS and in space. The station has to carry it's power station along with it. Equipment has to interface to the station power supplies very carefully... you don't want to go tripping power supplies, or potentially damaging other equipment that draws on the same source of power. Ideally, if we design any equipment to fly to the ISS for a short duration flight, it would carry its own source of power (windup? batteries ;-) and not need this interfacing.

Ruggedization

Space equipment has to survive the G-forces (very rapid acceleration causes stresses) of launch and descent. In the Soyuz this can mean man G's (up to 12 in an emergency, but 5 is normal). There's lots of vibration and shudder too. Space equipment might be subjected to jolts and bumps if there is a collision between the station and another craft. And equipment might be banged into other equipment during use. The equipment must be super-rugged and designed to withstand these sorts of stresses.

Even more important, if there are any dangerous chemicals or biological materials on board, these must be contained in such a way that they will not become a problem if there is a catastrophic failure during launch or failure. In other words, don't spray dangerous things around if the rocket blows up or the capsule parachute doesn't deploy.

So space science equipment is very sturdy, very simple in its design. 

Reliability

Equipment that is sent to the station has to survive many years without breaking. The station is designed to last 15 years... Mir was designed to last 5 but flew for 15. So the ISS might end up flying for longer than the planned 15 years... and the equipment is built to last. Knobs and dials are very chunky and robust... they might be switched on or off every day for 15 years and a failure would be extremely expensive and disruptive.

If something does break it is better to fix it in space than to have to schedule a replacement or repair flight. So equipment is designed to make this feasible if it is at all possible. Again, the astronauts aren't necessarily specialists in the field, so it needs to be possible for them to fix as much as possible without that specialized knowledge. That takes a tremendous amount of careful thought during the design of the equipment.

Toxicity

Any space vehicle is a sealed unit - we hope. That means that any leak is effectively trapped and has to be dealt with in place... one can't just open the windows to air the place out. No air. So any leak of gas or fluids can become a major problem. All the air in the station is recycled and there's a limited supply of it, so a poisonous gas leak creates an immediate crisis. Any corrosive liquid will float around until cleaned up.

So any equipment that will contain fluids has to be assessed for safety and the effectiveness of its containment. The simpler and more robust, the better. Almost anything could fly to space, but the containment strategy has to be adequate for the substance, and the level of risk if something goes wrong means that dangerous substances have to pass many years of analysis and bureaucratic hurdles.

Emergency

We hope that all goes well, but emergencies happen. Space equipment needs to be able to behave predictably and safely during an emergency situation. For example, if the capsule or station depressurized, the equipment should not leak or explode or do anything else unexpected. When the station comes down to earth eventually, the equipment inside it will burn up and should not release very dangerous substances such as radioactive dust.