Space Infrastructure Servicing (SIS) is a spacecraft being developed by Canadian aerospace firm MacDonald, Dettwiler and Associates to operate as a small-scale in-space refueling depot for communication satellites in geosynchronous orbit. Intelsat is a requirements and funding partner for the initial demonstration satellite which, as of March 2011[update], was planned to be launched in approximately 2015. MDA put the launch plans on hold in November 2011 pending finding a second launch partner, beyond Intelsat. Such a customer was not found, and Intelsat dropped out of the collaboration in January 2012.  In February 2012, MDA indicated that it was waiting on a possible DARPA contract before shelving the project. In February 2017, DARPA selected MDA's Palo Alto, California company, SSL, as their commercial partner for the Agency’s Robotic Servicing of Geosynchronous Satellites (RSGS) program. 
MDA Corporation announced in early 2010 that a small-scale geosynchronous-orbit refueling project was under development. The design point was to be a single spacecraft that would refuel other spacecraft in orbit as a satellite-servicing demonstration. The 2010 announcement indicated that MDA had already signed an option agreement "with an unidentified satellite fleet operator that has agreed to provide an aging telecommunications spacecraft for a refueling operation as the inaugural customer." Missions contemplated included not only satellite refueling but also space debris mitigation by including the vehicle capability to "push dead satellites into graveyard orbits."
The early technical design point included a fuel-depot vehicle that would maneuver to an operational communications satellite, dock at the target satellite’s apogee-kick motor, remove a small part of the target spacecraft’s thermal protection blanket, connect to a fuel-pressure line and deliver the propellant. In 2010, it was estimated that "the docking maneuver would take the communications satellite out of service for about 20 minutes."
A potential business model for the service, as of March 2010[update], would "ask customers to pay per kilogram of fuel successfully added to their satellite, with the per-kilogram price being a function of the additional revenue the operator can expect to generate from the spacecraft’s extended operational life."
In March 2011, MDA announced that Intelsat was to be their inaugural launch partner and that the SIS vehicle could be ready to launch as early as 2015, with Intelsat providing up to US$280,000,000 over the timeframe that the on-orbit services would be delivered to a portion of the Intelsat satellite fleet.
As of November 2011[update], MDA suspended the satellite servicing mission while awaiting major decisions due soon on the scope and details on planned satellite servicing missions by US government civilian and defence agencies NASA and DARPA. MDA wants to "see the NASA and DARPA bid requests, see what’s in them, whether [MDA] can bid as a Canadian company, or as a U.S. company." MDA Chief Executive Officer Daniel E. Friedmann said "We can’t just go ahead. I know everybody says the government is not a competitor, and yes, literally they are not a competitor. But our whole business is about winning business from the government and then taking that dual-use technology into the commercial market."
In February 2012, MDA said it was awaiting "a decision on a contract bid to the U.S. Defense Advanced Research Projects Agency (DARPA) before deciding whether to shelve its work on a vehicle to service satellites and perform other chores in orbit."
In a June 2012 article in The Space Review, a number of approaches to satellite servicing were discussed and contrasted. The MDA Space Infrastructure Servicing concept is reported to be somewhat more complex than the competitive ViviSat Mission Extension Vehicle, and is considered to be similar to the concepts that NASA is investigating experimentally with a test platform called the Robotic Refueling Mission flying on the International Space Station during the Expedition 29–32 timeframe in 2011-2013. MDA's approach "would use its manipulators to refuel or repair the spacecraft. The original announcement of the SIS by MDA in March of 2011 envisioned using it to deploy stuck [solar] arrays—like the case of [Intelsat] IS-19—or grapple debris. 'Direct refueling, robotically, of a satellite is not trivial, but it’s fully doable.'" By comparison, the DARPA Project Phoenix program has an even more complex mission concept: "cooperatively harvest and re-use valuable components from satellites in orbit that have been retired. DARPA envisions a servicing spacecraft that could remove a solar array, antenna, or other component from a defunct satellite and transport it to another satellite, either a newly constructed spacecraft or one in need or repairs. 'Phoenix is truly all about going up to retired, non-cooperative, non-controlled satellites that have been left for dead in the geosynchronous graveyard orbit, essentially, and see if we can resurrect capability out of those satellites or those satellite components.'"
In March 2016, 'Robotic Servicing of Geosynchronous Satellites' (RSGS) became DARPA's new name for the Phoenix Project. In February 2017, DARPA selected MDA's Palo Alto, California company, SSL, as their commercial partner for the RSGS Program.  In June 2017, SSL announced the formation of Space Infrastructure Services LLC (SIS), its contract to SSL to build SIS's first Robotic Servicing Vehicle, and its first commercial customer, Luxembourg-based satellite owner/operator SES S.A. 
In-space refueling demonstration projects
As of March 2011[update], MDA had secured its first major customer for the initial demonstration project. Intelsat entered into a preliminary agreement to purchase one-half of the 2,000 kilograms (4,400 lb) propellant payload that the MDA spacecraft would carry into geostationary orbit. Such a purchase was projected to add somewhere between two and four years of additional service life for up to five Intelsat satellites, assuming 200 kg of fuel is delivered to each commsat.
SIS was envisioned to carry a toolkit designed to open most of the approximately 40 types of "fueling systems aboard satellites now in geostationary orbit."
The servicing plan for the initial satellite on the demonstration mission was:
- "Intelsat [would] select one of its satellites nearing retirement to be moved into a standard graveyard orbit some 200 to 300 kilometers above the geostationary arc 36,000 kilometers over the equator."
- MDA [was to] "launch the SIS servicer, which [would] rendezvous and dock with the Intelsat satellite, [and attach itself] to the ring around the satellite’s apogee-boost motor."
- Controlled from a ground station, "the SIS robotic arm [was to] reach through the nozzle of the apogee motor to find and unscrew the satellite’s fuel cap."
- "the SIS vehicle [would then] reclose the fuel cap after delivering the agreed amount of propellant and then head to its next mission."
Post-demonstration mission extension
In addition to refueling and servicing geostationary comm sats with the fuel that is initially launched with the vehicle, the SIS vehicle is being designed to have the ability to orbitally maneuver to rendezvous with a replacement fuel canister after deploying the 2000 kg of fuel in the first load, enabling the further refueling of additional satellites after the initial multi-satellite servicing mission is complete.
Technology maturation by NASA
MDA's commercial interest in robotic in-space refueling got a boost in 2013 when NASA completed a demonstration mission doing robotic refueling of satellite hardware that had never been designed for refuel. In January 2013, an extensive series of robotically-actuated propellant transfer experiments on the exposed facility platform of the International Space Station (ISS) were completed by the NASA Robotic Refueling Mission (RRM). The NASA Robotic Refueling Mission was launched in 2011
The set of experiments included a number of propellant valves, nozzles and seals similar to those used on a wide variety commercial and government satellites, plus a series of four prototype tools that could be attached to the distal end of a Space Station robotic arm. Each tool was a prototype of a device that "could be used by future satellite servicing missions to refuel spacecraft in orbit. RRM is the first in-space refueling demonstration using a platform and fuel valve representative of most existing satellites, which were never designed for refueling."
Competitive design alternatives to in-space RCS fuel transfer exist. The ViviSat Mission Extension Vehicle illustrates one alternative approach that would connect to the target satellite in a similar way as MDA SIS, via the kick motor, but will not transfer fuel. Rather, ViviSat will use "its own thrusters to supply attitude control for the target." ViviSat believes their approach is simpler and can operate at lower cost than MDA, while having the technical ability to dock with a greater number (90 percent) of the approximately 450 geostationary satellites in orbit.
In September, 2012, the DLR Space Administration announced a funded development project to build a two-vehicle set of spacecraft to demonstrate several technologies necessary for on-orbit satellite servicing, including spacecraft refuelling, to enable satellite mission extension and also controlled disposal of a defective satellite. The project is entitled "DEOS" (German orbital servicing mission), and consists of "two satellites, a 'client' and a 'servicer'. The client acts as the satellite requiring maintenance or disposal. The servicer carries out the necessary work on the client." The two spacecraft will be launched together into low-Earth orbit of 550 kilometres (340 mi). As of 2012[update], the mission "will be ready for launch in 2018." EADS Astrium Friedrichshafen is the prime contractor for the definition phase of the DEOS project, with a contract value of approximately €13 million.
- Orbital Express — a 2007 U.S. government-sponsored mission to test in-space satellite servicing with two vehicles designed from the start for on-orbit refueling and subsystem replacement.
"Intelsat Picks MacDonald, Dettwiler and Associates Ltd. for Satellite Servicing". press release. CNW Group. Archived from the original on 2011-05-12. Retrieved 2011-03-15.
MDA plans to launch its Space Infrastructure Servicing ("SIS") vehicle into near geosynchronous orbit, where it will service commercial and government satellites in need of additional fuel, re-positioning or other maintenance. ... MDA and Intelsat will work together to finalize specifications and other requirements over the next six months before both parties authorize the build phase of the program. The first refueling mission is to be available 3.5 years following the commencement of the build phase. ... The services provided by MDA to Intelsat under this agreement are valued at more than US$280 million.
de Selding, Peter B. (2011-03-14). "Intelsat Signs Up for Satellite Refueling Service". Space News. Retrieved 2011-03-15.
if the MDA spacecraft performs as planned, Intelsat will be paying a total of some $200 million to MDA. This assumes that four or five satellites are given around 200 kilograms each of fuel. ... The maiden flight of the vehicle would be on an International Launch Services Proton rocket, industry officials said. One official said the MDA spacecraft, including its 2,000 kilograms of refueling propellant, is likely to weigh around 6,000 kilograms at launch.
- de Selding, Peter (2011-11-01). "MDA Puts Satellite Servicing on Hold; Reports Core Businesses Doing Well". Space News. Retrieved 2011-11-05.[permanent dead link]
de Selding, Peter B. (2010-03-03). "MDA Designing In-orbit Servicing Spacecraft". Space News. Archived from the original on 2013-01-05. Retrieved 2011-03-14.
MDA has signed an option with an unidentified satellite fleet operator that has agreed to provide an aging telecommunications spacecraft for a refueling operation as the inaugural customer ... the refueling vehicle would dock at the target satellite’s apogee-kick motor, peel off a section of the craft’s thermal protection blanket, connect to a fuel-pressure line and deliver the propellant. MDA officials estimate the docking maneuver would take the communications satellite out of service for about 20 minutes. ... The servicing robot would have an in-orbit life of about five years, and would carry enough fuel to perform 10 or 11 satellite-refueling or orbital-cleanup missions.
- Fate of Canadian Satellite Servicing Project Awaits DARPA Decision, Space News, 1 Mar 2012.
- Foust, Jeff (2012-06-25). "The space industry grapples with satellite servicing". Space Review. Retrieved 2012-07-04.
de Selding, Peter B. (2011-03-18). "Intelsat Signs Up for MDA's Satellite Refueling Service". Space News. Archived from the original on 2012-03-21. Retrieved 2011-03-20.
more than 40 different types of fueling systems ... SIS will be carrying enough tools to open 75 percent of the fueling systems aboard satellites now in geostationary orbit. ... the SIS spacecraft is designed to operate for seven years in orbit but that it is likely to be able to operate far longer than that. Key to the business model is MDA’s ability to launch replacement fuel canisters that would be grappled by SIS and used to refuel dozens of satellites over a period of years. These canisters would be much lighter than the SIS vehicle and thus much less expensive to launch.
- Clark, Stephen (2013-01-25). "Satellite refueling testbed completes demo in orbit". Spaceflight Now. Retrieved 2013-01-26.
Morring, Frank, Jr. (2011-03-22). "An End To Space Trash?". Aviation Week. Retrieved 2011-03-21.
ViviSat, a new 50-50 joint venture of U.S. Space and ATK, is marketing a satellite-refueling spacecraft that connects to a target spacecraft using the same probe-in-the-kick-motor approach as MDA, but does not transfer its fuel. Instead, the vehicle becomes a new fuel tank, using its own thrusters to supply attitude control for the target. ... [the ViviSat] concept is not as far along as MDA.
- "Astrium wins DEOS contract to demonstrate in-orbit servicing". Press Release. EADS Astrium. 2012-09-13. Archived from the original on 2012-10-16. Retrieved 2012-09-25.