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.
RRM as installed onto an ELC-4 once it is on the International Space
Station
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.
Artist conception of how we will look once on Space Station
on the Express Logistics Carrier (ELC) and working with
the Dextre robot (right).
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:
- 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.
- 1:10, a second tool is retrieved to remove the outer
Tertiary Cap.
- 2:10, the WCT is retrieved a second time to cut the second
wire
on the Safety Cap.
- 2:31, the Safety Cap Tool is used to remove the inner
Safety Cap.
- 3:29, the WCT is used again to cut another wire.
- 3:50, finally the EVR Nozzle Tool (ENT) is used connect to
the
fuel valve and the fuel is transferred.
Lab test of the RRM project. The robot holds a refueling
tool. The grey box in the previous image is represented by
the
one covered in gold foil.
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.
Yanci Viegas and Giovanni Munguia instrumenting the ACU for the thermal
vacuum test.
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 eight flight video cameras (small black right angle units) along
with the lights (white cone at top), along with their housings and
cables.
Here is one Tool Electronics Box (TEB) assembled with its two cameras
and lights. The SPDM robot grabs this box and connects
electrically to it.
Four completed tool avionics assemblies. The LED housings are
now
covered with protective red covers.
Henry holding up one functioning unit. Note the white LED
lights!
After assembly, we placed the four tool avionics unit into a thermal
vacuum chamber.
This is a steel chamber that has all the air pumped out during the test,
and the temperature is cycled from cold to hot.
The person in the middle is Raymond Witcher, our Quality
Assurance engineer (photo: Chris Gunn).
Part of the test team for the TEB Thermal-Vacuum test. You
can
see the monitor showing
the image of the four cameras under the orange light.
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.
The FTS holds pumps, valves and tanks to accomplish the fluid transfer
of the mission.