Satellite Servicing Capabilities Office

Raven logo
The Raven Project


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.

Approaching Space Station
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.

Location of Raven on ISS
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.  

EH25 Gimbal from Sierra Nevada Corporation
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.

First mockup
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.

IR camera
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.

Auxiliary Electronics Box AEB vibe
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.

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

IR image
This second image from the IR Camera.

LIDAR image after color map
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.

Thermal cycling test of SC2EM
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.

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

In vibration cell at NASA/GSFC
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.

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

into chamber
View through the personnel access door.

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

tvac
View through the access door.

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

staffing
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.

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

Drilling the Raven baseplate
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.

Apollo MOCR JSC Building 30
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.

Raven on STP-H5
Photo of the STP-H5 payload with Raven on top.
Publicly image available from here.

TVAC test at Langley Research Center
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.

Updates coming...

Launch
Raven will launch as part of the STP-H5 experiment on SpaceX-10 / CRS-10, no earlier than November 2016.



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