Satellite Servicing Demonstration

After so many successful Hubble servicing missions our project has been tasked with taking this expertise to studying the servicing other Satellites in space.  In the Fall of 2009, we started work on demonstration missions for the International Space Station that evaluate certain important  Satellite Servicing technologies.

The first of our demonstration missions illustrates on-orbit refueling of another spacecraft.  In other words, the refill of the fuel that satellites need to stay in the proper location in their orbit.  This activity is important as many communications satellites have a limited life due to their fuel load at launch.  If they could be refueled in space, it would mean a significant extension of their operating life and savings in operating costs.  This demonstration mission is formally called "Robotic Refueling Mission", or RRM.  My role on this new project is the Electrical Lead engineer responsible for the electronics in the tools and the refueling station.

Our hardware will be flown and installed onto an Express Logistics Carrier (ELC).  Our experiment is the grey box in the image below.


The objective of our RRM mission will be to open up a fuel valve cap  and pass liquid into it via fuel filler hose.  This valve is typical of what satellites use so that we perform the same operations in a faithful manner.  This demonstrates our ability to develop tools and procedures to refuel a satellite in space. 

Since the RRM mission is a demonstration, both halves of the refueling hardware (satellite to be refueled and the tools and filler nozzle) is contained on RRM.  Essentially, we will be pumping fluid in a closed loop.  RRM will include four tools, each of these incorporating electronics and two cameras and lights.  In addition, the refueling station will have pumps and controllers as well as electrical valves and sensors.  My work consists of the design, construction and test of these electrical systems.


The operations that the robot performs in this video are as follows:

1. At 0:39, the Wire Cutter Tool (WCT) is retrieved to cut the safety wire that the personnel at the launch site put on the outer cap.
2. 1:10, a second tool is retrieved to remove the outer Tertiary Cap.
3. 2:10, the WCT is retrieved a second time to cut the second wire on the Safety Cap.
4. 2:31, the Safety Cap Tool is used to remove the inner Safety Cap.
5. 3:29, the WCT is used again to cut another wire.
6. 3:50, finally the EVR Nozzle Tool (ENT) is used connect to the fuel valve and the fuel is transferred.
   

The robot we will use during our refueling demonstration is the Special Purpose Dextrous Manipulator (SPDM) robot that is already on the ISS.  Our first hardware to be tested is the camera interface to the SPDM robot.  This was done at the ISIL facility at the Johnson Space Center in Houston Texas.

Here with Henry Pham one of the engineers that is part of my team, our test with the Space Station ground simulator (ISIL) at JSC (June 2010).  The camera we were using for this test is on the red mat.

In the Fall of 2010, after a year worth of effort to design the system, we finally have the finished Avionics Control Unit (ACU).  This circuitry receives commands from the ELC computer and controls the valves and pumps of the RRM.  In the photo above, we see the ACU on the vibration table.  This test violently shakes the flight hardware to verify its strength and workmanship against the launch environment on the Shuttle.

Once the vibration test is complete, we verify that the hardware can survive the vacuum and temperature extremes of space.  This is done by putting our flight hardware into a steel thermal-vacuum chamber.  All the air is pumped out, and we cycle the temperature hot and cold for many cycles to verify our electronics continue to function under these extreme conditions.

Meanwhile on the tools side, we had also completed the design of the electronics and we were getting ready to assemble 8 cameras and their associated hardware in December of 2010.

The main RRM hardware is the plate that holds the Fluid Transfer System (FTS).  This has the tanks, pumps, valves and associated electronics to accomplish the mission of transferring fluid during the demonstration mission.  This panel is shown below during the build up process.