Example of map surrounding a Moon skylight

Example of a point-radius search in the map database

Example of database points (in green) with image points overlaid (in blue), ready for correlation

This graph represents an estimated and actual X and Y trajectory. The red line in this graph represents a simulated trajectory of a lunar lander where the lander is at a constant altitude of 300 meters above the lunar surface and is moving away from a skylight visible at the start of the video. The blue line represents the estimated trajectory of the lander as computed by the software demonstrated in the first half of the video. As the software computes the change in motion based upon its own current position estimate, the drift of the estimated position relative to the actual lander position is compounded over time. This will be corrected by the map registration process to provide an accurate position over time.

Robotic arm sporting the fiducial tracking rig

The simulation of the Moon’s gravity is key in testing the performance of our rovers. On the Moon, an object weighs one sixth of what it does on Earth. The gravity offloader lifts five sixths of the rover’s weight by hoisting the rover from above its center of mass.

Real-time tracking ensures that the lift is always directly over the rover’s center of mass, enabling unfettered mobility. The tracking is currently accomplished using a camera and fiducial markers. These fiducials are unique black and white patterns that are easily printed and mounted on a rover or test rig. The current tracking experiment utilizes a cross-shaped rig mounted to a robotic arm.

A fiducial marker

In this experiment, the robotic arm moves while a stationary camera continuously snaps photos. The photos are processed using tracking software from reacTIVision. The fiducial movement data is then run through motion estimation code, producing a position estimate for the test rig.

These position estimates will control the movements and position of the crane hoisting the rover, enabling the crane to always remain over the rover’s center of mass.

Gravity offload tracking system

The composite swing arm of Polaris was tested to failure. A testing rig was developed from which weight could be hung until the swing arm broke. The test rig is composed of a metal top plate bolted to an L-shaped lower metal plate (figures 1 and 2). Between these two plates is the composite swing arm.

Figure 1: Solidworks model of the test rig

Figure 2: Test rig

The test rig was mounted to a forklift and weight was hung off the rig. In figure 3 a forklift was used to move four 250 lbs. plates used to test the part. In figures 4-7 the test rig is mounted on the forklift. Figure 7-9 show the fracture in the part after it has broken. The test rig is removed from the forklift in figures 10-12. Figure 13 is the composite swing arm after it has been removed from the test rig. In figure 14-16 the actual weight hung from the eyebolts attached to the test rig is determined. The team that conducted the testing is in figure 17.

Figure 3: Four 250 lbs plates are used to test the part

Figure 4: The test rig is mounted to the forklift

Figure 5: Test rig fully mounted to the forklift

Figure 6: Weight is hung from the eyebolts

Figure 7: The part after it has broken

Figure 8: The break is a fracture in the swing arm

Figure 9: Another view of the break

Figure 10: The rig is disassembled

Figure 11: Another view of the disassemling

Figure 12: The rig is removed from the forklift

Figure 13: The swing arm is removed from the test rig

Figure 14: The actual weight of the first test was 505.90 lbs.

Figure 15: The actual weight of the second test was 556.88lbs

Figure 16: The actual weight of the third test was 606.15lbs

Figure 17: The testing team

“Astrobotic seeks the immense resources available on the Moon to both accelerate space exploration and improve life on Earth,” said David Gump, president.  “The lunar path is near term.  We intend a prospecting mission in 2015.”

Astrobotic began development of its lunar excavation robot in 2009 under a series of NASA Small Business Innovation Research (SBIR) contracts that now total $795,000.  The new NASA SBIR Phase 3 follow-on contract is to consider robot refinements for carrying NASA-supplied instruments and a drill.

Recent lunar-orbiting satellites from several nations, and a NASA probe that impacted near the Moon’s south pole, have sensed polar ice composed of water, methane, ammonia, carbon monoxide, hydrogen sulfide and other substances.   These polar resources went undiscovered during the Apollo expeditions which landed near the equator.   The next step is to drill and measure the polar ices directly to see if they are sufficiently concentrated to be useful.

Lunar propellant derived from the ice could fuel spacecraft for long voyages, Earth-return, or maneuvering satellites.  Water and oxygen would be invaluable for life support.  Other elements have immense value for energy, processes, fabrication and habitation.

When seeking resources from planetary destinations, the four-day travel time to reach the Moon enables early return on investment compared to more distant targets.

Astrobotic has reserved a Falcon 9 launch vehicle made by SpaceX to send its spacecraft and robot explorer on a trajectory toward the Moon.  The Astrobotic spacecraft will deliver the prospector to the lunar surface with technology that autonomously avoids landing hazards such as large rocks and craters.  The navigation system is derived from technology developed at Carnegie Mellon University under Dr. William “Red” Whittaker, Astrobotic’s founder.  Dr. Whittaker won the DARPA Urban Challenge with a driverless car able to autonomously navigate through city streets, avoiding other cars and obeying the California traffic code.  The ability to detect hazards and automatically select alternative pathways is the core of Astrobotic’s  automatic lunar landing system.

Astrobotic has won $12 million in nine NASA lunar contracts, covering topics from simulating lunar gravity on Earth to discovering ways to robotically explore the Moon’s volcanic caves.  Lunar satellites recently spotted potential entrances to these caves, which can provide shelter to robot and human explorers from the radiation, micrometeorites and extreme temperature swings of the lunar surface.

Astrobotic’s commercial expeditions carry payloads for space agencies and generate exclusive media content for television and Web portals.  Corporate sponsors will give their customers direct access to the robot’s frontier-building activities through competitions and custom internet feeds.

Astrobotic is a spinout from the Robotics Institute at Carnegie Mellon University, which carries out lunar research funded by Astrobotic.  More information is available at www.astrobotictech.com.

Figure 1: Carbon fiber sheet and strips

Figure 2: Resin is applied to the carbon fiber strips

Figure 3: Work area where carbon fiber is coated in resin

Next, the sheets are laid up against the foam mold (figures 4 and 5). The mold consists of two long foam pieces on either side of a metal piece (figure 6). The mold is constructed in this way so that the metal piece can easily be pulled out and the mold separated non-destructively from the carbon fiber after it has been baked. The carbon fiber strips are wrapped on the part at 30 degrees and 150 degrees so that the unidirectional fibers provide extra strength.

Figure 4: First carbon fiber strip is placed on mold

Figure 5: Carbon fiber strips placed on mold

Figure 6: Polaris swing arm mold

Last, the part is covered in plastic (figure 7 and 8). Tape is applied to seal the air in. A hole is put in the plastic so that the air can be sucked out of the plastic. When all of the air has been removed, the part is put in the oven (figures 9 and 10).

Figure 7: Mold and carbon fiber is vacuum-sealed

Figure 8: vacuum sealed part is ready for oven

Figure 9: swing arm mold and carbon fiber is in oven to cure

Figure 10: Composite and mold bakes

The final piece is in the picture below (figure 11).

Figure 11: final swing arm

It is important to simulate and analyze the cruise correction process to (1) insure correction for imperfect injection, (2) insure stability and convergence, and (3) insure propellant margin for any eventualiity. The method employed here is to (1) pre-compute viable earth-moon trajectories, (2) simulate trajectory errors, (3) plan corrections, (4) simulate correction errors, and (5) compute statistics, since this is a probabilistic process. Position/velocity coordinates created by each source of error are modeled as a normal distribution. The first distribution is the set of actual position/velocity coordinates possible due to the error of the thrusters. The distribution is centered on the desired trajectory. The second distribution is the set of estimated position/velocity coordinates. These coordinates are centered about the actual position/velocity computed during the cruise simulation.

M1&2 represent mid-course corrections along the desired path. LOI is the maneuver that injects the lander into lunar orbit.

Polaris Rover

Polaris (shown in the picture above) prospects for water at the lunar poles by using a drill to sample lunar soil and scientific instruments that detect water. The rover is capable of driving and avoiding obstacles autonomously including traverses into dark regions in the lunar pole’s long shadows. Polaris suspension includes raise and lower capability to vary chassis ground clearance to lower for drilling and raise for driving on rough terrain.

CAD Model of Polaris

The Polaris Rover actuates a swing arm at each corner to raise, lower, and tilt the chassis. This vastly improves the ability to drive, work, and get out of trouble. Each swing arm is cut from a rectangular composite tube described in this blog.

Swing arm cut from composite tube (left) and CAD drawing of mold (right)

Fabrication of the swing arm requires a high temperature cure resin, which limits the mold selection to metal or a high-temperature, high-density foam. Metal (aluminum) releases easily, creates a good surface finish, can produce many parts, but is expensive. Foam is cheap, easy to machine, but cannot withstand higher temperatures and will produce fewer parts as a result.

Foam swing arm mold

Thus, a 3-part mold was designed which consists of 2 foam blocks with a metal insert in the middle (shown in the picture above). The metal insert is removed after the part cures in the oven which provides space to extract the foam blocks.

In the picture below the high-density foam for the Polaris swing arm mold is machined on a 3-axis CNC machine.

High-density foam is CNC'ed for the swing arm mold

The mold is sanded to remove waviness caused by the CNC bit, cleaned, and coated with two thin layers of 5-minute epoxy. Next, it is baked at 150 degrees F for an hour to fully cure the resin. Afterwards, the epoxy layer is sanded down to create a very smooth surface. The mold is cleaned again with mold cleaner or acetone and sealed with a mold sealant. Finally, multiple layers of release agent are applied to the surface of the mold to prepare for the composite layup. The release agent prevents the resin from sticking to the surface of the mold. The next step is to test the composite swing arm to determine what force must be applied in order for the part to fail.

Astrobotic is featured in the April issue of Scientific American. Read the full article by Michael Belfiore online through our link on the Astrobotic Facebook Page.

The Pittsburgh Post Gazette covers Astrobotic’s new rover and mission:

Company with Local Roots Aims for the Moon
David Templeton, Pittsburgh Post Gazette