-- Manned Spacecraft Session
Moderators: Stu Loewenthal and Bob Fusaro
1) What are the current space drive resources and issues for Manned Space Craft?
Describe the Current State-of-the-Art
Current state-of-the-art appears to be adequate for current manned projects.
Harmonic Drives used for many applications.
Currently known space drive technology problems are:
Trade off between Performance and Robustness
Space shuttle turbo pumps still a problem
RL-10 idler pump system a problem.
Unknowns exist for manned spacecraft going to Mars
Nuclear propulsion poses mechanisms problems
Current facilities and people working in space drives
No facilities and very little technology research being conducted in space drive area.
Missions where technology problems will be an impact:
Propulsion systems
Manned missions to Mars.
Technology deficiencies are
How do we replace or service drives in space?
How do we qualify and how much qualification is necessary.
There is a need to develop accelerated life test techniques and scale
factors that people can believe in.
What are the life limiting factors?
2) What are the future space drive technology needs and
issues for Manned Space Craft?
Future missions expected & drives needed for these missions.
Space Station
Need improved bearings, lubricants and gears.
Type is dependent on application.
Manned missions to Mars.
Need improved bearings, lubricants and gears.
Type is dependent on the application.
Shuttle flights to space station.
Cryogenic propulsion issues.
Technology barriers for future space drive systems
Qualification testing methodologies inadequate.
Significant technology milestones we should strive for.
Improved accelerated life testing techniques.
Reliable scaling factors.
Improved design methodologies.
Future space drive research facilities needed.
A need for project centers to develop technology.
Facility to develop improved robotic joints.
Facility to develop easily replaceable systems.
Space qualification methods needed for future space drives
A need for developing accelerated life-testing methodologies.
A need for developing scale factors that are accurate.
Synergistic or combined parameter effects on life need to be determined.
A need to reduce the cost of qualification.
Other Issues
A need for a vendors list of approved supply sources.
NASA needs to define the Specifications for spacecraft more precisely.
Centers in charge of NASA Missions need to define the state-of-the-art in technology and insure
that programs are in place to develop enabling technology necessary for success of the mission.
Fracture properties of exotic materials need to be determined.
3) What is the Importance of holding an annual
workshop on space mechanisms and space drives
Is a space drives working group needed?
The general consensus was such a group would be advantageous.
A need for a list of experts to obtain information.
A need for an approved vendors lists.
Other space mechanisms areas that need to be addressed in future workshops.
Bearing Seals.
Vibration isolation both active and passive systems.
High Temperature applications such as found on the X-vehicles.
Lubricant Management (Supply Systems).
Dry Lubricants for gears.
Heat Rejections.
Cryogenic Lubrication.
Space Qualification techniques.
Magnetic Bearings.
How do we communicate?
Yearly workshops.
An extra day at the AMS to deal with new technology.
News Groups or Chat rooms on the Internet.
Teleconference or Video Conference.
-- Unmanned Spacecraft Session
Moderators: Romer Predmore and Wilfredo Morales
Summary of main conclusions reached by the group:
NASA support for mechanisms technology and subsystem mechanism standards
should be established using commercial standards to reduce costs.
NASA should fund the technology for future space mechanisms, including
MEMS devices, under the guidance of industry steering groups.
Unless there is government support for space mechanisms research, there
will be little need for future workshops.
Industry needs to know the future needs of NASA.
One immediate need is flywheel energy storage systems, in lieu of batteries,
for flat spacecraft.
Need much more work in magnetic bearings for use with small momentum
wheels and for improvements in "control electronics".
NASA should define the performance requirements for advanced space mechanisms.
NASA should increase support for MEMS technology and smart materials technology.
Comments: A number of people thought that NASA funding would be
available for mechanisms work. Over 50% of the discussions focused on the
need to establish space mechanisms standards in order to reduce costs. A
number of people were design engineers and not researchers; therefore, future
workshops should be geared towards either research or design. Future
workshops should have a single theme or objective.
-- Planetary Surface Exploration Session
Moderators: Red Whittaker and Fred Oswald
1) Consider current space drive resources and issues.
Technology of today such as on Sojourner rover and the Mars '03 Rover,
(originally called "Athena" or Fido) uses commercial brush-type motors
(by Maxon) with harmonic or multi-stage planetary drives. Typical
transmission ratio: 80:1 to 250:1 Sojourner Mass=11 Kg, Power=10W. Athena / Fido Mass=32 to
60 Kg Power level of typical antenna or solar array pointing mechanism ~ 8 W.
Russian Lunokhod used radioisotope heater/generator and brush type motors in sealed enclosure. The Apollo Moon Rovers used brush motors and harmonic drives operating
in a sealed enclosure with a 7.5 psi nitrogen atmosphere (for heat transfer).
The performance of the Apollo rovers was seriously degraded by dust by
the end of their mission (about three Earth days).
Small positioning mechanisms may use ultrasonic motors. Examples:
camera focus mechanism, robot joints. These employ a polymer that
changes dimension in an electro-static field. This produces wave
motion in a ring, which acts like a motion transducer. For more info.,
contact Hari Das or Paul Schenker at JPL.
MEMS: Micro Electronic Mechanical Systems (solid state switch) can
replace brushes in motors.
Problems:
Life of present motors & transmissions too short for long duration missions.
Dust interferes w/cooling, contaminates seals, and causes wear.
Brushes are no good in vacuum. Current tech. must use pressurized chamber in vacuum.
Extreme temperatures (on Moon, range from ~40K in craters at poles to ~400K
at noon on equator with dark soil.
Present tech. cannot endure heat of day or cold of night on Moon
Present tech. not adequate for long duration missions, especially using solid lubrication.
2) Consider the future space drive technology needs
and issues.
Needs & Problems:
Long duration missions will require new technology. Mars environment is "easy" compared
to Moon & Mercury. However 2-year Mars mission means equipment must be extremely reliable.
Possible mission to Jovian moon Europa may require a submarine.
Mars reference mission calls for power plants ~ 2Km from base.
Laying power cable is a difficult job for rover vehicles.
Burrower robots may be needed on Moon (underground habitat for radiation shielding)
For more info., contact Wilxox at JPL or www.ndeaa.jpl.nasa.gov (limited access to page).
Promising Technology:
Reversed electrostatic field may repel charged dust
Variable reluctance motors provide for start and run power requirements.
For motion measurement: encoders are heavy. Hall effect sensors are an alternative.
Most current actuators do not have torque sensors. They operate in on/off mode.
NASA should issue RFP for studies to identify technology needs.
Need studies to examine tracked vs wheeled vehicles (efficiency & reliability issues)
An interesting concept: The lifetime range of a device is related to
its size (within limits). Consider range of ant vs. deer. However an
elephant's range is comparable to a deer's.
3) Consider holding regular Space Mechanisms
Technology Workshops.
There were only 12 people in this discussion group (the smallest
group). All favored holding regular Space Mechanisms Technology meetings,
possibly every year. We should investigate operating a "list serve"
for ongoing discussions.
The one-day meeting was too short and people did not arrive prepared
to make the best use of the limited time available. Prior communication
(preparation) would help improve the focus of the discussions.
Possible future topics: motors, commutators, wheels, suspensions,
materials, manipulators, antenna / solar array pointing.