Introduction
An
important technology that is needed for robotic satellite servicing is
the ability to fly up to a spacecraft and to circle around it to find a
location to grasp and dock. Due to time delays, this needs to
occur autonomously with sensors and computer systems to guide the
servicer onto the right location. One way to test this
technology
is to place a demonstration system onto the Space Station and view the
incoming spacecrafts that are flying up to perform periodic resupply
missions. The benefit of this sensor system to the ISS is the
ability to have a "third-party" verification of the correctness of the
incoming spacecraft's trajectory.

Space craft coming up to the International Space Station being viewed by
a sensor package (orange and yellow cones) to verify their trajectory.
Image from
here.
Raven
Raven
is a project that will fullfill the role that is described above.
My role on this project is the Electrical Lead, responsible
for
the electrical design and its integration into the Space Station
interfaces. The system will have three main sensors:
- The
first, named VNS (Vision Navigation System), is a long wavelength infra
red LIDAR system. It will be able to 'image' the target by
gathering a point cloud of range. This will be especially
useful
to obtain the shape and pose (pointing direction) of the incoming
spacecraft. Our LIDAR unit has flown in space before on the
STS-134 Space
Shuttle mission in 2011.
- The
second is a long wavelength Infra Red imaging sensor, called IRCam.
It is able to see without visible light, and can thus work in
the
shadow of the Earth. This technology has also flown in space
on STS-128
and STS-131. The resolution of this imager is
640x480, and is sensitive from 8-14 um.
- Finally, the third sensor is a
visible light camera with a zoom and focus motor, called RNS (Relative
Navigation Sensor).
The camera has also flown in space before on the final Hubble
Servicing Mission SM-4/STS-125. Originally built by MDA in
Canada, its resolution is 1kx1k in the visible band.
These
three main sensors, and along with an IMU (Inertial Measurement Unit)
will be housed in the RSE (Raven Sensor Enclosure). This
enclosure will be moved by a two-axis motor gimbaling system to provide
pan and tilt control. This will allow the Raven sensors to
continuously track the incoming space craft and keep it in our field of
view at all times.
In addition to the above sensors, the other main components are:
- Our main computer willl be a (now
standard Goddard component) SpaceCube
2.0. It has three Virtex 5 FPGAs for the computing
fabric.
- The motor driver electronics, which
drives the two motors of the gimbal and the two motors in the RNS.
- The AEB (Auxiliary Electronics Box),
which provides interface hardware to unify the entire system together.

Raven will be located on the 'under' side, or Nadir side to view
incoming space crafts.
It will be on ELC-1 (bottom right white circle). ISS travels
towards you in this view.
Development
I
started work on Raven in September 2013. The initial phase
consisted of understanding what sensors we were going to use and
finding a mechanism and motors for the gimbal actuator. By
April
2014, the electrical design was set, and I had my Electrical Peer
Review that
month in front of a review panel. A large part of the design
had
already been tested in various forms. Our project's CDR (Critical
Design
Review) was in May 2014. At that point, we started the flight
construction in earnest, and started system integration of the flight
parts at the end of 2014. We then started environmental
testing
in early 2015.
Construction and test
One
of the first items we received was the two-axis gimbal, and that is
shown below. This is our key mechanism that will position the
Raven Sensor Enclosure (with the cameras above) to keep the target
space craft in view.

The two axis gimbal motor system for the pan-tilt control.
The unit bolts to the base of Raven on the right side,
and the Sensor Enclosure bolts the large circle on the left.
(photo from the vendor website).
Unlike
our previous projects, where we are fastened directly to an ELC
(Express Logistics Carrier) location, we will in this case be perched
on top of another experimental platform called
STP-H5.
The 'bunker' or box for the latter is shown in the image
below.
This mockup allowed us to verify the volume swept of the RSE,
and
would be the wiring mockup that will be used to build the system wiring
harness.
We travelled to
NRL
to check out the wooden mockup of STP-H5.
The aluminum box at the top (being held) is the RSE (Raven Sensor
Enclosure),
and you can see the mockup of the gimbal bolted to it.
In
the image above, you can see the first representation of the RSE, which
is the large grey aluminum box at the top.
The top left square opening is for the RNS. The top
right
for the IRCam, and the bottom two round ones are for VNS.
Closeup of our IR Camera.
Note the beautiful purple color of the lens. Since
it is
only using the IR portion of the spectrum, shorter wavelength light can
be
reflected.
One of the new designs
for this project is the Auxiliary Electronics Box (AEB).
Here it is being bolted onto the vibration table for its strength test
(12/14).
Following vibe test, the
unit is placed inside a vacuum chamber and the temperature
is cycled cold and hot to simulate the effects of being in space
(12/14).
EL ROM
from Edward
Cheung on Vimeo.
Time-Lapse of Range of Motion Test shows the tilt function working.

The series of first successful images. This one from the
visible light camera (RNS).

This second image from the IR Camera.

Finally, this one from the LIDAR. The images are fuzzy
because the focus
of the system is for distant objects. This last image took a
week to obtain
because of a software issue. After much troubleshooting the
problem was
located and it was very meaningful.
Images shot in January 2015.

While we test the main part of Raven, we also put the computer
(SpaceCube2) into its own thermal cycling test (2/15).
The unit under test can be seen inside the open door.

At the end of February 15, we left the cleanroom and boarded the
elevator to go
downstairs to the vibration test chambers.

The moment Raven is craned onto the vibration table for its test.
The table shakes the hardware so violently that you must wear
hearing protection to be in this room when the test is going on.

Image from Craig Huber. He was shooting this behind me.

After vibe, we transferred to the Thermal Vacuum Chamber (Facility 238).

View through the personnel access door.

Raven inside the chamber divided into two zones. Raven Minus
and SpaceCube (covered with gold foil on right).

View through the access door.

We use a lot of GN2, and it looks like I am walking through a cloud of
it.

Fuzzy preview image from my GoPro of the console operators at GSFC TVac
tests.
After
Thermal-Vacuum testing at GSFC, Raven was shipped to Johnson Space
Center to be integrated onto STP-H5 in May 2015. This latter
mission is our host on the ELC platform, and has over a dozen other
experiments integrated onto it. As you can see in the diagram
below, Raven sits on the very top of the module, and represents their
flagship payload. As you can also see in the bottom image,
Raven
is meant to view down onto the Earth and will be able to view incoming
resupply vehicles.

Diagram of payloads on STP-H5. The Earth's surface is in the
direction
of the "Nadir" direction. Image from
here.

A problem was found during our installation of Raven onto STP-H5.
Due to an error
in a drawing, the Raven baseplate would not fit onto the walls of the
STP bunker.
The
best way to solve the problem was to redrill the baseplate.
To
check our new locations, we used a calibration system shown here as the
silver
arm with the word "EDGE" on it.

Our integration lab at the Johnson Space Center happened to be on the
top floor of
the Building 30 Mission Control Center. It was just down the
hall from the
historic Apollo Control Room.
Called
the MOCR, it has been preserved
historically.

Photo of the STP-H5 payload with Raven on top.
Image from
here.

We were then shipped to Langley Research Center for system-level
Thermal-Vacuum test in October 2015. You can see Raven on
top of the blanketed STP-H5 chassis in the opening of the chamber.
It was here that a second problem was found. More on this
below.

After
that, the entire payload was shipped to the Kennedy Space Center for
launch site integration at the Space Station Processing Facility in
November 2015.
Image from
here.
Launch
Raven launched as part of the
STP-H5
experiment on
SpaceX-10 / CRS-10 on 2/20/2017. I was planning on seeing
this event, but unfortunately, we suddenly lost our cousin
Dr.
Chee Mun Lum and I went to Canada to attend his funeral.
SpaceX-X (aka CRS-X)
launched from the historic Apollo and Shuttle pad 39A.
I was at this pad years ago for the
final
Shuttle mission.
The above is a post from Elon Musk about the test firing
of the engines days before launch.

Launch of CRS-X from LC-39A the historic Apollo and Shuttle pad.
This
is the image of Raven (bottom) sitting on top of STP-H5, sitting inside
the CRS-X capsule. This view taken from the booster as its
separates from the capsule.
During
the first week of March 2017 we did our first Ops in space.
That
included the first power on of SpaceCube 2 and checking its telemetry.
Then a few days later, we fired the launch locks that hold us
down for launch and then lifted the sensor head out of the hibernate
position. We then took our "first light" image.