Satellites servicing satellites
Space is populated by robots. Mechanical arms have long been used to launch and retrieve satellites in orbit. Images of robots working on other planets or in space may seem commonplace, but to date, they are generally controlled remotely by engineers or locally by astronauts. Tomorrow’s space robots will be autonomous.
The primary function of autonomous space robots could be servicing the thousands of satellites in low Earth orbit, medium Earth orbit, and geosynchronous orbit. Long-term ambitions are to use robots to repair and reuse satellites, assemble larger structures and manufacture off-planet.
The size of artificial satellites is restricted by the payload we can lift. Around 80% of any satellite’s mass and part of its design is solely to ensure it can survive the journey. That means only around 20% of every payload, including fuel, is useful to the mission.
When that mission comes to an end, the satellites die. Sometimes, the mission comes to an end because the satellites die. Replacing them incurs time, cost and risk, as does launching new satellites that may have the same mission. Sustainability in space exploitation and exploration demands better.
Keeping satellites alive longer
All nations now rely on satellites for communications, navigation, defense and weather forecasting. These now form critical infrastructure, but almost all satellites produced to date are expendable, with a lifetime of around five years. When they fail or run out of fuel, they are simply left to move into a lower orbit and burn up in our atmosphere. Those that don’t burn up stay in orbit. Dead satellites create space debris, interfering with future missions.
In-orbit servicing, assembly and manufacturing (ISAM) is becoming an area of interest worldwide. ISAM encapsulates initiatives to change the status quo. Part of the motivation for ISAM is to tackle space debris using robotic cleaners. These roaming robots will live in low Earth or geosynchronous orbit, dealing with satellites and debris that refuse to move out of orbit.
Although NASA has developed technology demonstrators (pictured below), the efficacy of ISAM for low Earth orbit (LEO) satellites has yet to be proven in space. But a growing number of commercial space companies are engaging in active debris removal (ADR) projects. Government contracts are in the public domain, and the sector is looking to jumpstart through private investment. The use of competitive tenders rather than grants is expected to stimulate commercial activity.
The photo shows the On-orbit Servicing, Assembly and Manufacturing (OSAM-1) testbed developed by NASA being tested in the Robot Operations Center (ROC) at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. (Source: NASA/Michael Guinto)
Using robots to service satellites in orbit will follow ADR. Servicing may include refueling satellites to extend mission time. It may also include repairing or upgrading satellites in orbit rather than decommissioning them, so they can continue operating. Currently, if repairs are carried out at all it is by astronauts at significant expense. As many low Earth orbit (LEO) satellites are (relatively) low-cost, the expense of a repair mission would likely be too high. If an autonomous satellite can move into position and make the repair, mission extension could be cost-effective.
Manufacturing in space is also a developing field. The International Space Station regularly hosts scientists studying the benefits of zero gravity. Taking full advantage of these benefits will require larger structures and more of them.
Although there are now examples of reusable heavy-lift space rockets, getting large structures into orbit is complex and expensive. Building large structures off-planet has obvious appeal, but it requires the ability to transport smaller sub-sections into orbit and assemble them in zero gravity. Constructing space stations that can sustain human life and take us farther from Earth will be more viable with ISAM.
The challenges facing ISAM
If designing a fully autonomous, mobile, complex electromechanical system capable of operating in the harsh environment of space isn’t challenging enough, there are other factors this burgeoning market needs to tackle.
The satellite industry was established without servicing in mind. Satellites are expected to have a finite mission lifetime, and their designs do not accommodate the features needed to support mission extension through in-orbit servicing. Without an established customer base, satellite manufacturers are reluctant to develop and launch servicing robots, creating a chicken-and-egg market dynamic.
There is also the question of critical mass. Servicing satellites in space would require enough robots to service all the satellites that might need it. Current estimates put the number of active satellites in orbit at around 10,000. That would mean around 20 LEO satellites for every one geosynchronous Earth orbit satellite in operation.
With nearly 40,000 inactive objects greater than 10cm in diameter being tracked in orbit, it makes sense that ADR is the primary goal for ISAM. Without the influence of ISAM, the cumulative number of LEO satellites forecast to launch over the next 15 years could push the total to well over 150,000 (although some will de-orbit and burn up). With an average expected lifetime of around five years, there could be close to 100,000 dead satellites still in orbit by 2040. ISAM could influence that figure by shifting from single-use satellites to serviceable ones.
Avnet estimated how low Earth orbit satellite launches may be influenced by the adoption of ISAM. The figures are upper and lower estimates based on rapid or slow adoption of ISAM [Sources: The global satellite market is forecast to become seven times bigger | Goldman Sachs, Space Logistics Market Size, Share, Trends, Report, Analysis, Advancing Space Technology for ISAM Maturity and Success]
With a ratio of, say, 100:1, teams would need to launch around 100 robots to service existing working satellites. More will be needed in the future, as the number of satellites scheduled to be launched is only getting bigger.
That figure sounds feasible, but there’s another challenge. Low Earth orbit satellites are unevenly distributed. They do not follow the same flight path or even try to stay in neat clusters. This means the service satellites will need to travel farther to intercept the satellite that needs assistance. That uses more fuel and incurs more risk. Conversely, satellites in geosynchronous orbit tend to follow the equator, but they are much farther away from the earth so, again, more fuel.
A lack of industry standards for things like fuel connections is compounding the challenge of moving from single-use to serviceable satellite design. There are examples of commercial companies making fuel connections for serviceable satellites, and there seems to be a growing consensus across the industry that ISAM is a requirement, so some standardization may not be far away.
A global imperative
Our world is now so reliant on satellites that being good stewards of space is becoming an imperative. The Consortium for Space Mobility and ISAM Capabilities (COSMIC) is the U.S.’s response.
COSMIC is funded by NASA and supported by the U.S. Government Accountability Office (GAO). The GAO recently produced a technology assessment of ISAM for Congress. A copy of the report can be found here. COSMIC now has over 250 members from academia, government and industry.
Other nations are also developing ISAM initiatives, including the UK Space Agency, which recently launched a tender for the country’s first ADR mission, worth £75.6 million. The mission is to safely de-orbit two UK-licensed low Earth orbit satellites.
Space is big, but our part of it is starting to get crowded. Much of that traffic is defunct satellites that need to be removed. The number of satellites being put into orbit is climbing quickly and expected to continue climbing. The problem of space junk isn’t new, but it seems we have arrived at an inflection point.
If you are working in this field and need the support of a trusted partner, take a look at Avnet’s Defense and Aerospace solutions.