Satellite Servicing Capabilities Office

Flexible Fuel Hose Investigation



Introduction
Following on the success of the Phase 1 of the Robotic Refueling Mission, our project continues work on studying technology to perform the repair and upgrading of satellites in space.  One key technology for this kind of mission is how to handle a flexible fuel hose.

Concept for satellite servicing mission
Conceptual satellite servicing mission.  The top satellite is the one we repair by
flying up to it with a vehicle with two robotic arms.  Image from here.

fuel hose in space
Closeup of the refueling nozzle attached to the satellite.  The fuel hose that
is the subject of my investigation can be seen here in light yellow.

In our initial handling of a sample hose, we realized that it could be easily damaged if handled incorrectly.  We decided to test technology and procedures associated with handling such an item, and I came to head up various parts of this work, including the project to fly a sample hose on a zero gravity flight to truly see how this object behaves in the environment of space.  

Investigation of the Flexible Hose
We started the investigation in the Spring of 2012 by using a robot in our lab equipped with its force-torque sensor to better understand how to handle the hose without breaking it.

Initial hose handling
Initial experiments with a flexible fuel hose and its
storage mechanism (not visible on left).

Hose handling in the robot lab
Moving into the robot lab, we built a structure to mimic the overal shape and size of the
satellite to be serviced and moved the robot to the fuel valve location.

Robotic fuel hose handling
Robot is here pulling out the fuel hose and heads to the fuel valve to mimic a servicing operation.

Perhaps not surprisingly, these initial tests, called "Test 5.2" inside our organization, showed us that the gravitational pull of the weight of the hose really affects how the hose handles.  In order to investigate further if our handling procedures work correctly, we needed to offload this gravitational force.  Just like in astronaut training, which occurs in a large water tank, we decided to take our next steps in water.

small Atlantis
During this time period, I attended
the retirement ceremony for Atlantis.

For tests in the bouyancy benefits of water, we went to the nearby University of Maryland Space Systems Laboratory in early 2013.  The internal name for these round of tests was "Test 5.7".  In order to perform the tests we modified the frame above to only include the start and endpoints of the hose, rather than emulate the volumetric space of the two vehicles.

SSL team
The diving and operational crew for our tests in the water tank at Univ of MD.
Divers were Matt Sammons, Mike Oetken and Phil Kalmanson.

SSL at UMD
The water tank at Univ of Maryland where students build and test underwater robots.  The Hubble project also used this tank for tests in the past.

rig being lifted into the water tank
Our rig that holds the hose for the test is being craned into the water tank for tests.

divers in the water with the test rig
Photo of divers under water handling fuel hose.  You can see the foam floaters at regular intervals to make the hose neutrally bouyant.

Control station on top deck
This is our control station for the test.  We ran the procedures from here and talked the divers through the test while we watched the data from the motion capture and force-torque sensor.

Our conclusions with the 5.7 test were partially hampered by the damping effects of the water.  So in order to address this problem we were granted a series of test flights on the zero gravity plane from gozerog.com.  This flight was funded by NASA's Office of Chief Technology via the Flight Opportunities Program.

approval letter from OCT
Approval letter informing us that we were selected for a Zero-G flight.

In order to perform the tests on the zero gravity airplane, we further shrank the fixture holding the hose.  From the large frame representing the entire two satellites in 5.2, to the smaller one showing only the start and end point in the water test of 5.7, to now a minimal fixture as shown below. The reason is that the plane is flown down the zero G parabola by the pilot, and you only experience true zero gravity if you are floating in the plane.  So our fixture needs to 'free float', and as a result needs to be as small and light as possible.

fuel hose arrives
Fuel hose arrives from Kennedy Space Center.

first iteration of zero G rig
Our first cut at the fixture that will hold the hose in the Zero G flight.

In order to gather data on the behavior of the hose, the fixture has a mechanism that gives it a 'push', and we then use motion capture cameras to capture the resulting motion of the hose.

Main flight team
This is the main flight crew on the night before we pack everything up for shipment to Ellington field.  Syrus Jeanes and Matt Sammons are here along with me.
From SSCO Facebook page.

fixture inside shipping container
The main flight fixture packed into its custom shipping container.
The entire shipment weighed about 600 lbs, and we shipped by
overnight air, which costs the government about $1/lb.

Next page: arrival at Ellington field and zero gravity flight.


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