The Regolith Advanced Surface Systems Operations Robot (RASSOR) excavator robot is a teleoperated mobility platform with a space regolith excavation capability. This more compact, lightweight design (<50 kg) has counterrotating bucket drums, which results in a net-zero reaction horizontal force due to the self-cancellation of the symmetrical, equal but opposing, digging forces

Cox, Rachel

Ebert, Thomas

Mueller, Robert P.

Nick, Andrew

Rahmatian, Laila

Schuler, Jason

Smith, Jonathan D.

Wood, James

NASA Technical Reports Server

NASA Tech Briefs, January 2013 17
Mechanics/Machinery
The design of machines that rely on
arrays of servomotors such as robotic
arms, orbital platforms, and combina-
tions of both, imposes a heavy computa-
tional burden to coordinate their ac-
tions to perform coherent tasks. For
example, the robotic equivalent of a per-
son tracing a straight line in space re-
quires enormously complex kinematics
calculations, and complexity increases
with the number of servo nodes. The
conventional method of executing these
calculations is with a PC-style set of elec-
tronics including a powerful CPU (cen-
tral processing unit) microprocessor, op-
erating system, power supply, a number
of peripherals, connectors to support
each servo node, and a web of star-topol-
ogy wiring across the machine (includ-
ing flexing joints), generally exceeding
100 conductors. In industry, the most
common implementation is one or
more dedicated PC cards mounted on
an ISA (Industry Standard Architec-
ture), PCI (Peripheral Com ponent
Interc onnect), or VME bus. These cards
provide the I/O connectors and supple-
ment the CPU to execute the massive
kinematic calculations in real time.
A new high-level architecture for coor-
dinated servo-machine control enables a
practical, distributed transputer alterna-
tive to conventional central processor
electronics. The solution is inherently
scalable, dramatically reduces bulkiness
and number of conductor runs through-
out the machine, requires only a frac-
tion of the power, and is designed for
cooling in a vacuum.
The benefit of this innovation is total
elimination of the central controller and
reducing the heavy web of star-topology
wiring across the machine to four wires
along a shared serial bus. This scalable
innovation results in decreased power
consumption, decreased bulk, and vac-
uum compatibility.
This controller places a digital signal
processor (DSP), instead of a micro-
processor, at each motor axis, each with
its own power supply, conduction cool-
ing, etc. The DSPs communicate via
CANbus over RS-485 hardware, forming
the heart of the transputer.
Features of the device include reduc-
tion in flex wear in serial-articulating
joints, streamlining of robotic structures
(with reduced wire-harness bulk), surviv-
ability in the case of a single-processor
failure, and uniformity in handling vari-
ous types of servos (brushless, brushed,
etc.) and sizes up to 300 W. Brushless
compatibility supports elimination of
brush-life limits and particulate genera-
tion. Power in the 2-wire bus flows di-
rectly between regenerative power
nodes and motive power nodes, rather
than traversing the round-trip star topol-
ogy.
This work was done by Brian Zenowich,
Adam Crowell, and William T. Townsend of
Barrett Technology Inc. for Johnson Space
Center. Further information is contained in a
TSP (see page 1).
In accordance with Public Law 96-517,
the contractor has elected to retain title to this
invention. Inquiries concerning rights for its
commercial use should be addressed to
Barrett Technology Inc.
625 Mount Auburn Street
Cambridge, MA 02138-4555 USA
Phone: (617)252-9000
Fax: (617) 252-9021
E-mail: robot@barrett.com
Refer to MSC-24295-1, volume and num-
ber of this NASA Tech Briefs issue, and the
page number.
Ultra-Compact Transputer-Based Controller for High-Level,
Multi-Axis Coordination
Features include reduction in flex wear, streamlining of robotic structures, survivability, and
uniformity in handling various types of servos.
Lyndon B. Johnson Space Center, Houston, Texas
Regolith Advanced Surface Systems Operations 
Robot Excavator 
This design enables new ways of excavating for resources on planetary bodies. 
John F. Kennedy Space Center, Florida
The Regolith Advanced Surface Sys-
tems Operations Robot (RASSOR) ex-
cavator robot is a teleoperated mobility
platform with a space regolith excava-
tion capability. This more compact,
lightweight design (<50 kg) has counter-
rotating bucket drums, which results in
a net-zero reaction horizontal force due
to the self-cancelation of the symmetri-
cal, equal but opposing, digging forces.  
This robot can operate in extremely
low-gravity conditions, such as on the
Moon, Mars, an asteroid, or a comet. In
addition, the RASSOR system is de-
signed to be easily transported to a space
destination on a robotic precursor land-
ing mission. The robot is capable of tra-
versing over steep slopes and difficult re-
golith terrain, such as an impact crater
on the Moon, and has a reversible oper-
ation mode so that it can tolerate an
over-turning incident with a graceful re-
covery, allowing regolith excavation op-
erations to continue.  
The RASSOR excavator consists of a
mobility platform with tread belts on the
port and starboard sides that are each
driven by electrical motors, but it could
also operate with a wheel system to fur-
ther reduce mass. Two batteries are
https://ntrs.nasa.gov/search.jsp?R=20130009412 2019-08-31T00:06:14+00:00Z
18 NASA Tech Briefs, January 2013
mounted in a “saddlebag” configuration
on either side. Two counter-rotating
bucket drum digging implements are
held by a rotating cantilever mechanism
at the fore and aft ends of the mobility
platform. The cantilever arms are raised
and lowered to engage the bucket drum
into the soil or regolith. A variable cut-
ting depth is possible by controlling the
angles of the cantilever arms. 
The unit has three modes of opera-
tion: load, haul, and dump. During load-
ing, the bucket drums will excavate
soil/regolith by using a rotational mo-
tion whereby scoops mounted on the
drum’s exteriors sequentially take multi-
ple cuts of soil/regolith while rotating at
approximately 20 revolutions per min -
ute. During hauling, the bucket drums
are raised by rotating the arms to pro-
vide a clearance with the surface being
excavated. The mobility platform can
then proceed to move while the soil/re-
golith remains in the raised bucket
drums. Finally, when the excavator
reaches the end-user or dump location,
the bucket drums are commanded to re-
verse their direction of rotation to the
opposite spin from digging, causing the
gathered materials to be expelled out of
each successive scoop. It can also stand
up in a vertical mode to deliver regolith
over the edge of a hopper container. 
The RASSOR can operate with either
side up in a reversible mode and it can
flip itself over. This means the unit can
drive directly off of the deck of a lander
to deploy in low gravity, eliminating a de-
ployment mechanism, which saves mass
and increases reliability due to de-
creased complexity. The RASSOR system
is scaleable and may be mounted on mo-
bility platforms of various sizes, and has
control equipment — wireless signal
router, computer, joystick, E-stop, and
associated software.  
This work was done by Robert P. Mueller,
Jonathan D. Smith, Tom Ebert, Rachel Cox,
Laila Rahmatian, and James Wood of
Kennedy Space Center; Jason Schuler of EASI;
and Andrew Nick of Sierra Lobo. For more in-
formation, contact the Kennedy Space Center
Innovative Partnerships Office at 321-867-
5033. Refer to KSC-13664.
Magnetically Actuated Seal
Design replaces existing pressure-actuated lift-off seals in turbopumps and eliminates low
pressure drains, thereby increasing overall efficiency.
Marshall Space Flight Center, Alabama
This invention is a magnetically actu-
ated seal in which either a single elec-
tromagnet, or multiple electromagnets,
are used to control the seal’s position.
This system can either be an open/
close type of system or an actively con-
trolled system.
A lift-off seal (LOS) is a type of shaft
seal used in a turbopump that does not
allow propellants to enter the turbine
during pre-start operations, such as
when a cryogenic turbopump is being
chilled-in or when the pump is being
primed prior to start. Typically, lift-off
seals are pressure activated and a low
constant pressure in the seal’s second-
ary seal cavity is needed to provide the
delta-P necessary for the seal to open.
This is typically accomplished with an
overboard drain cavity. The LOS must
remain closed during pre-start opera-
tions. This prevents cryogenic liquid
from chilling-in the turbine, which
would result in excessive thermal shock,
and subsequent turbine blade cracking.
During the start-transient, the LOS
must open to prevent propellant gasifi-
cation and sometimes to provide
coolant to the turbine disk. If it opens
too soon, however, the turbine pressure
can be higher than the pump pressure,
and result in hot gas ingestion into the
pump or bearings. If it opens too late,
the seal surface speed becomes exces-
sive, and results in excessive wear and
premature failure of the seal.
The magnetically actuated LOS is
more reliable and requires no low-pres-
sure secondary seal cavity or overboard
drain (thereby improving efficiency).
An electromagnet is used to open and
close the seal at an exact prescribed in-
stant during the transient. Ad d i tionally,
with the magnetically actuated seal, the
particular instant can be different be-
tween the start transient and shut-down
transient. This allows for more desirable
and predictable transient performance
of the turbopump as well as more cer-
tain wear performance of the seal.
This work was done by Alex Pinera of
Florida Turbine Technologies, Inc. for Mar-
shall Space Flight Center. For more informa-
tion, contact Sammy Nabors, MSFC Commer-
cialization Assistance Lead, at
sammy.a.nabors@nasa.gov. Refer to MFS-
32979-1.
A lightweight, cryogenically capable,
scalable, deformable mirror has been
developed for space telescopes. This in-
novation makes use of polymer-based
membrane mirror technology to enable
large-aperture mirrors that can be easily
launched and deployed. The key com-
ponent of this innovation is a light-
weight, large-stroke, cryogenic actuator
array that combines the high degree of
mirror figure control needed with a
large actuator influence function. The
latter aspect of the innovation allows
membrane mirror figure correction
with a relatively low actuator density,
Hybrid Electrostatic/Flextensional Mirror for Lightweight, 
Large-Aperture, and Cryogenic Space Telescopes 
A much lighter-weight structure with higher correction range uses polymer-based 
membrane mirror technology. 
Marshall Space Flight Center, Alabama


Regolith Advanced Surface Systems Operations Robot Excavator

Regolith Advanced Surface Systems Operations Robot Excavator

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