One of the things that makes space applications so expensive is the fact that we cannot service satellites once they get to orbit. The moment a satellite leaves the ground it is destined to survive, or not survive, based solely on what it is carrying and how well it operates. If all of the subsystems work properly, then its expect performance is realized for as long as its propellant lasts. Once the propellant is depleted, the mission is over.

At least this has been the way space operations have worked since 1957. We all have thought about the advantages of being able to repair and refuel these satellites. If only we had a service station in orbit for fixing and refueling spacecraft, the overall cost of using space could drop dramatically.

Now, NASA is developing the technology to build Earth-orbiting 'service stations' that may one day use robotic technology to repair and service satellites. After 55 years of space flight experience, it is about time someone took on this serious and important challenge.

Engineers at the Kennedy Space Center are working with the Goddard Space Flight Center to develop concepts that will lead to high-technology "gas" pumps, robotic mechanics and "tow" trucks for satellites in space. This capability is particularly attractive for servicing large geostationary satellites.

These spacecraft represent a number of space applications including communications relays that serve tens of millions of customers around the world. They are very complex and extremely expensive to build and launch.

Typical lifetimes run up 15 years, but when the propellant is depleted, their usefulness usually ends. If there were a service station in geostationary orbit, satellite lifetimes might be extended for a fraction of the cost of replacing these birds.

The idea of providing such services has been around for decades, but little has been accomplished so far. NASA and private sector companies are now trying to advance the technologies and systems that will hopefully lead to the reality of space servicing. There is plenty of incentives for both NASA and aerospace companies to forge ahead.

If an economical solution can be found, there should be a great deal of business for a satellite servicing system. The key is to find a solution that represents low-cost-per-satellite-services, i.e., a cost that is much lower than the cost of replacing satellites.

Remember, satellites that need servicing are usually those that have been in orbit for some time, thus, representing reduced value as compared to a new satellite that contains the latest technology and capabilities. So, one will have to make a compelling argument for servicing versus replacement.

The key to a successful satellite servicing business seems to be the capacity to service multiple satellites with a single repair/refueling satellite, because each servicing satellite will likely cost about as much as a satellite that is to be serviced.

The most important servicing function appears to be refueling geostationary birds. There are roughly 200 active such birds. Approximately 15 of these run out of propellant each year. If these 15 could be refueled, then lifetimes can be greatly extended.

This is good business for a refueling company, but bad news for satellite manufacturers. Nevertheless, competitiveness, innovation and the profit incentive will surely find a winning solution, sooner or later.

NASA appears to have the most active servicing program at the moment. Preliminary work on a technology demonstrator, called the Robotic Refueling Mission (RRM), is underway on the International Space Station. Space Shuttle Atlantis delivered it during the shuttle program's last mission.

The RRM was designed by the same team that developed instruments and astronaut tools for Hubble servicing missions. The RRM has four tools that cut and manipulate wires, unscrew caps, open and close valves and transfer fluids.

NASA's next step is to study and develop Technology Readiness Levels, (TRLs), for a fully robotic maintenance vehicle that could service satellites, including those that were not originally intended to be serviced. Eventually, NASA hopes to create specific servicing spacecraft with their own navigation systems, enhanced robotic arms, tools and a supply of propellant.