I’ve come to the Kennedy Space Center to witness the final launch of shuttle Endeavour.
George Nelson (bottom-right) attempts to control Solar Max using the MMU
It is due to lift off on Friday. The mission will see the delivery of the $2bn Alpha Magnetic Spectrometer to the International Space Station.
It is a strange time to be here. Shuttle retirement has naturally prompted a lot of discussion about the state of the US human spaceflight programme.
Many people have been recalling their most memorable shuttle moments.
For me, some of the most startling images were those of astronauts using the Manned Maneuvering Unit, or MMU.
The backpack seemed to embody what the shuttle was all about and the things it enabled astronauts to do – to work in space.
I recall George “Pinky” Nelson’s attempts in 1984 to retrieve the malfunctioning Solar Maximum Observatory satellite using the MMU.
Floating untethered from the shuttle, he hung on to Solar Max’s solar wings at one point in an effort to bring the rogue platform under control. It didn’t quite work but that wasn’t a problem related to the MMU.
The satellite was eventually grabbed by the shuttle arm and its electronics payload repaired. Twenty-seven years on and Nasa is still interested in satellite servicing as a concept. I’ve been hearing here details of the final shuttle mission – STS-135 Atlantis – which will be taking up a test rig that will allow the Dextre robot on the space station to practise techniques for re-fuelling satellites.
The rig holds a series of tools Dextre can pick up to show how the fuel caps on spacecraft could be released in orbit to allow propellant tanks to be topped up. You can see a promotional video here.
Dextre and the station’s robotic arm are the products of Canadian ingenuity and, in particular, of MacDonald, Dettwiler and Associates (MDA).
The company itself is already pushing ahead with a commercial proposition of its own known as the Space Infrastructure Servicing (“SIS”) vehicle. This is likely to launch in 2015. It’s basically a robotic tanker.
It will go into near geosynchronous orbit some 36,000km above the planet, where it will service commercial and government satellites in need of additional fuel. Ultimately, MDA hopes SIS vehicles could also find work in moving satellites to new locations, or in carrying out simple maintenance tasks.
The latter might include releasing the antennas on satellites that had become stuck during deployment. Some satellites carry huge antennas that must be packed for launch and they don’t always unfurl correctly when commanded.
But it is re-fuelling that is the primary motivation behind the first mission.
Thierry Guillemin, the chief technical officer of satellite operator Intelsat, told me that shortage of propellant to keep its telecommunications satellites in position is the main reason the company has to retire the platforms:
”That’s what it is for the majority of them; it’s why re-fuelling is attractive. We actually keep decommissioning perfectly healthy satellites just because they run out of the fuel needed to keep them at their orbital location. To give you an example: in the next couple of years, we will decommission several Intelsat 6 Series spacecraft - satellites that were launched at the end of the 80s, beginning of the 90s. These satellites have more than 20 years in orbit and they are perfectly healthy from the standpoint of both their housekeeping function and their communications payload – but they are running out of fuel.”
Intelsat has agreed to purchase about 1,000kg of the fuel in SIS – about half its total load. It is likely government agencies will take up the other half.
You’ll recall that it was Intelsat last year that temporarily lost control of its Galaxy 15 spacecraft. Dubbed “Zombie-sat” by the media as it drifted past other satellites in orbit, it later became “Phoenix-sat” as engineers managed to regain full command of the wayward platform. But the incident illustrated very well how in-orbit servicing could be a very profitable venture in the future. Thierry Guillemin again:
”Even though we did a pretty good job with Galaxy 15 in avoiding any interference with the 15 or so satellites that we had to fly by, it’s true that the geostationary orbit becomes more and more crowded and the removal or towing of objects is yet another area where the servicer might be used. This one has its own challenges of course because depending on the size of the debris and how it is tumbling in space, it may be more or less difficult to grab it and tow it. But once we start using this service in orbit, designs and technology will evolve and we will learn how to deal with anything.”
Nasa and MDA/Intelsat are not the only ones pursuing the concept of in-orbit servicing. The German Space Agency (DLR), for example, has an idea it is developing called DEOS.
The German DEOS demonstration would show how to capture spinning satellites
This is a demonstration mission that will also fly around 2015. It comprises a couple of satellites. One will act as the “servicer” and the other as the “client” spacecraft in need of capture and “repair”.
The purpose of the mission is really to understand how best to approach other objects and practise strategies for grabbing them. This is no trivial matter, Professor Felix Huber, the director of DLR space operations and astronaut training, told me:
”In the longer term, our goal is to be able to capture any satellite with a robotic arm. This might be a satellite that has lost control; it might be spinning or whatever. Usually, if you have a geostationary satellite, you have the apogee engine where you can grab into the nozzle. This is relatively easy. Whereas with DEOS, what we want to demonstrate is that we can grab a satellite anywhere with the robotic hand, even if it is rotating.
"But when you make the grab, what you have to do is un-stiffen the robotic arm - just like when you catch a ball, you kind of decelerate it slowly. Otherwise, if you have a hard touch, it will simply bounce off. Capturing a satellite means that once you have grabbed it, you need somehow to weaken your arm to slow it down gently. You will probably have to rotate the servicer to get rid of the spinning moment, and then you are safe. This will be the future if you have a broken satellite.”
With the space above our heads getting ever more crowded, the long-talked-about proposition of in-orbit servicing has to become a reality sooner or later. And not just servicing, but removing redundant satellites from the sky altogether.
It has been calculated that just removing a few key broken satellites would substantially reduce the potential for collision and a near-exponential growth in space debris over coming decades.
The robotic systems on the space station are key Canadian contributions to the ISS project