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The Robot Operated Materials Processing System (ROMPS) is a space shuttle carried Hitchhiker (HH) payload scheduled to make its first flight on Space Shuttle Discovery, Mission STS-64 in September 1994.
The purpose of ROMPS is to demonstrate commercial methods of processing semiconductor materials in a microgravity environment. The expectation is that ROMPS will improve the properties of materials by processing them in space.
ROMPS can be reflown quickly and easily because of its degree of automation. The second ROMPS flight is expected to take place within a year of the first flight.
ROMPS is the first U.S. robotics system to be used in space. ROMPS is designed to advance microgravity processing by using a robot to transport each of a large variety of semiconductors from the storage racks to halogen lamp furnaces where their crystal structures are reformed in heating and cooling cycles.
ROMPS is managed by the Goddard Space Flight Center (GSFC), Greenbelt, Maryland, for NASA's Office of Advanced Concepts and Technology (OACT), Washington, D.C.
Microgravity processing can reduce semiconductor crystal irregularities caused by convection and sedimentation. Improved crystal structure will increase the performance of many types of semiconductors which can yield higher efficiency devices such as solar cells and computer chips.
The performance, and consequently the commercial value, of most semiconductor materials is highly dependent on their crystalline structure. Gravity-driven connection and sedimentation, which disturb crystal formation, can be eliminated in the microgravity environment of space.
The current robotic design of ROMPS permits it to address a variety of commercial objectives in materials processing and automation technology.
The ROMPS flight hardware will be contained in a pair of Getaway Special (GAS) cans mounted on the HH-G carrier. The first GAS can is a full-size can designated the Processing Can, and will house the samples, sample storage racks (for the pallets containing samples) the robot, two furnaces and some electronics.
The second GAS can is half the height of the first can and is called the System Controller Can. This can will house the control electronics, which is a derivative of a commercial system, and Hitchhiker interface. Each GAS can will be pressurized to one atmosphere using dry nitrogen.
The HH system will provide the ROMPS GAS cans with power and ground links for telemetry and commands. This arrangement allows ground monitoring and control of in-space processing, return of the samples to ground and reflight of the ROMPS system with new samples and modified processing capabilities.
The ROMPS samples will be analyzed on the ground after the shuttle mission, and the results will be compared to samples processed on Earth. These results will also be used to define materials and processing for planned reflights of ROMPS on future shuttle missions.
A long term ROMPS objective is to develop microgravity-processed semiconductor devices with sufficient performance advantages that they can be produced competitively in-space.
There is also a more immediate objective of using microgravity processing to understand better the behavior of semiconductor crystal structures. This better understanding can improve the quality of ground-processed semiconductors. To this end, samples are being provided, for evaluation by universities Government labs and private companies. For instance, F.W. Bell, a maker of Hall Effect magnetic sensors, and Astropower, a solar cell manufacturer, are two contributing companies.
Examples of samples to be flown and their commercial applications are: 1) Indium Arsenide- to improve noise immunity of Hall Effect devices. 2) Doped Zinc Sulfide- enhance color and reduce power in electronic devices. 3) Galium Arsenide- improve optoelectronic devices 4) Silicon Germanium- Improve high speed transistors 5) Silicon semiconductors- higher performance and lower cost solar cells. Another objective of the ROMPS program is to advance automation and robotics for material processing in ways that can lower the costs of developing and manufacturing semiconductors.
The added cost of operations in space creates a need for in-space materials processing to have more advanced automation and robotics to increase productivity. For example, an efficient long term space facility for materials processing not only needs to have robotic materials processing, but the assembly, servicing and upgrading of the facility also needs to be done by robotics. This higher level of automation and robotics needed for in-space materials processing can be applied to improve the operational efficiencies of ground-based semiconductor laboratories and production facilities. ROMPS enhances this process by using elements of commercial hardware and software automation products, which allows for direct "spin-off" to U.S. industry.
A new proximity sensor, called a Capaciflector, developed by Goddard, will be flown to aid in the alignment of the pallets to within a thousandth of an inch. By using the electric field generated by the sensors, proximity of the pallets to the furnace aperture can be measured and perfect alignment can be made without physical contact perturbing the process. Developing such a sensor-based control scheme is key to advancing space automation and robotics.
The ROMPS robot will transfer each of 110 sample pallets from its storage location to a processing furnace and back to the storage location. The robot has three degrees of freedom and a gripper.
The robot's three position axes (elevation, azimuth, radial) and the gripper will be position-controlled and force-limited. Each robot axis incorporates a brushless D.C. motor drive, incremental position encoder, brake, gearing and end-of-travel monitors. The gripper is activated like the robot axes except that it does not have a brake because it is not back-driveable and its position is monitored via sensors. Only one motor at a time is powered during operation.
Transfer time for each sample between the storage rack and furnace is less than two minutes. The robot will be unpowered and braked during heating cycles so as to not disturb the sample being processed.
The accuracy of the three positioning axes at the tool tip is ±0.020 inches (.050. centimeters). ROMPS can accommodate robot positioning inaccuracies of up to about ±0.200 in. using a compliance device on the robot and guides and tapers on pallets and objects which the pallets contact.
The robot will grip a support to provide extra stiffness during launch and descent. In this position the robot harnessing also will be held taut for minimum vibration.
The robot support structure attaches to the GAS can lid. The robot assembly lower plate, on which is also mounted the majority of the GAS can electronics, will be snubbed to the canister walls.
The ROMPS furnaces, made in-house at Goddard, have tungsten halogen lamps and elliptical reflectors. These reflectors give the furnace an equivalent of 5000 watts of energy and permit the samples to be raised to 2550 degrees Fahrenheit (1400 degrees centigrade)
There are two identical furnaces to provide lamp redundancy and they are mounted to the GAS can lid. This configuration conductively will couple to the radiator to reject the furnace power.
Each furnace is about 6.5 in. (16.5 cm) diameter x 8.0 in. (20 cm) long and weighs less than 5 lb. (2 kg). The furnaces also provide a mechanical and electrical interface to the sample pallets.
This mechanical interface, consisting of two tapered pins, serves to align a pallet with respect to the lamp focus. The electrical interface is for the calibration pallets which are equipped with sensors to measure lamp output.
Each sample pallet has a special holder which is sealed so that samples can be heated to a vapor phase without causing contamination. Sample materials, substrates, environments inside sealed sample holders, processing times and temperatures can be varied for each sample, thus allowing a wide range of materials research to be conducted using the same equipment.
In addition to the robot and furnace, the processor GAS can also contains electronics for power control, motor power and furnace control. The power controller interfaces with the Hitchhiker and the ROMPS subsystems.
The power controller provides the first level of Hitchhiker to ROMPS power-line filters, the fusing for safety power distribution to ROMPS subsystems and the power distribution for safety interlocks and experiment operation.
The motor control provides the power for the servo motor and switching to direct this power to whichever one of the four motors is selected by the system controller.
The furnace controller provides the power going to the furnace lamps and controls this power to a level specified by a digital input signal from the ROMPS system controller.
The ROMPS System Controller Can interfaces with the HH avionics and controls all experiment operations. Control functions include robot servo control, furnace profile control and command and telemetry formatting and control.
The systems controller also monitors the sensors and the conditions of other subsystems, and it formats telemetry to provide housekeeping data to the ground station. ROMPS will be commanded from the ground when the need arises for changes to the mission profile.
The controller contains a predetermined program for autonomous experiment operation once initiated by the proper ground commands. The first part of this predetermined program is a power up sequence to test the experiment subsystems. After successful testing, the experiment will execute the preprogrammed sequence of experiment samples at predescribed temperatures and exposure times.
The gripper will be positioned to take the appropriate sample from the storage rack and will position the sample in the furnace. After the heating process, the sample is returned to its position in the rack, and the next sample will be processed.
To get the lowest possible microgravity levels, the samples will be processed during crew rest periods when shuttle vibrations will be at a minimum.
Because of the number of samples and the possibility of lengthy heating times for certain samples, processing probably will extend over more than one crew rest period. As a result, the processing sequence will shutdown ROMPS at the end of each crew rest period as required.
Ground command will restart the processing at the beginning of the next crew rest period. This will occur until all samples have been processed. The processing will be done automatically, with ground control used to monitor progress and intervene if unexpected situations develop.
The system controller will monitor outputs from temperature, position, force and current sensors, as well as telemeter them to the ground station.
The system controller will stop the experiment if it detects problems or receives a shutdown command from the ground operator.
If anomalies occur, the ground crew will diagnose the problem, develop alternate procedures, send up new command sequences and reinitiate processing.
ROMPS is sponsored by the NASA Office of Advanced Concepts and Technology (OACT) as part of its mission to develop commercially-relevant techniques for in-space materials processing.
Goddard developed the ROMPS mechanisms and control electronics. Two NASA-sponsored Centers for the Commercial Development of Space (CCDS's) are involved in the project.
The CCDS's are the Consortium for Commercial Crystal Growth at Clarkson University in Potsdam, New York, and the Space Automation and Robotics Center (SpARC) in Ann Arbor, Michigan. Other participants are, George Mason University, Fairfax, Va., and the Naval Research Laboratory, Washington, D.C.
Goddard provides experience with autonomous space flight technology, space robotics and the HH/GAS system. GSFC also manages the project. The two CCDS's are supported by OACT and are contributing the technical expertise and commercial linkages they have in their respective areas of responsibility.
SpARC is developing the ROMPS control system, and the Clarkson CCDS is leading the materials processing work. The bulk of the Clarkson CCDS work is being done by its University of Florida member.
ROMPS Mission Manager is Lloyd Purves, Goddard. Principal investigators are Dr. Tim Anderson, University of Florida, and Dr. Eric Cole, George Mason University. Co-Principal investigator is Kevin Jones, University of Florida.