In this presentation, we discuss the first demonstration of a lasercom downlink from a LEO 1.5U 2.3 kg CubeSat to our optical ground station at The Aerospace Corporation in El Segundo, CA. Two vehicles, AC7-B&C, built under NASA’s Optical Communications and Sensors Demonstration (OCSD) program and described in previous presentations, were launched in November 2017 and placed in a 450-km circular orbit. Following on-orbit checkouts and preliminary pointing calibration utilizing on-board star trackers, we have demonstrated (at the time of this manuscript submission) communications links up to 100 Mbps with bit error rates near 10-6 without any forward error correction. Further optimization of the vehicle pointing and detection electronics and operating the transmitter at its full power capacity should enable performance improvements and potential for higher data rates.
In this presentation, we discuss the first demonstration of a lasercom downlink from a LEO 1.5U CubeSat to our optical ground station at The Aerospace Corporation in El Segundo, CA. Two vehicles, AC7-B&C, were built under NASA’s Optical Communications and Sensors Demonstration (OCSD) which is a flight validation mission to test commercial-off-the-shelf components and subsystems that will enable new communications and proximity operations capabilities for CubeSats and other small spacecraft. As designed, the 1.5 U CubeSats weigh 2.3 kg and consume ~2 W during most of the mission life. During lasercom engagements, ~3 minutes, the spacecraft consumes an additional 10-20 W power depending on the set point of the laser transmitter, which yields 2-4 W at 1.06 m. The transmitter consists of a directly modulated laser diode followed by a Yb fiber amplifier and exhibits an overall wall-plug efficiency ~20%. The AC-7B&C vehicles were launched in November 2017 and placed in a 450-km circular orbit. Following on-orbit checkouts and preliminary pointing calibration utilizing on-board star trackers, we have demonstrated (at the time of this submission) first time communications downlinks up to 100 Mbps from the 7B vehicle using open loop pointing (beaconless) to our ground terminal, which is near sea level. The preliminary link experiments at 50 and 100 Mbps (OOK/PRBS23) using the AC-7B CubeSat were recorded at 100 ms intervals. At 50 Mbps, error rates near 1E-6 were observed with numerous error free intervals. At 100 Mbps we observed BERs approaching 1E-6. At the time of these collects, however, the B vehicle was still exercising a scan pattern since the final alignment had not been completed. Thus, the optical link was not continuous over the entire pass. Link budget estimates indicate that lower BERs should be achievable and we will continue to assess the link performance as the system is optimized.
A pair of 2.2 kg CubeSats using COTS hardware is being developed for a proof-of-principle optical communications demo from a 450-600 km LEO orbit to ground. The 10x10x15 cm platform incorporates a 25% wall-plug efficient 10-W Yb fiber transmitter emitting at 1.06 μm. Since there are no gimbals on board, the entire spacecraft is body-steered toward the ground station. The pointing accuracy of the LEO craft, which governs the data rate capability, is expected to be ~ 0.1-0.2 deg. Two optical ground stations, located at the Mt. Wilson observatory, have receiver apertures of 30 and 80 cm. Launch of the CubeSat pair is anticipated to be mid to late 2015.
MEMS offer ultra-low mass, low-power components which may integrated into a variety of aerospace systems. Aerospace-specific MEMS are limited by the relatively small size of the aerospace vehicle market compared to traditional MEMS markets such as automobiles and home computers. Nevertheless, significant applications such as inertial guidance, micro-vehicle propulsion, and active antennas will drive evolution of existing MEMS technologies to meet these needs. MEMS enable many near-term micro-vehicle concepts, and possible mid-to-far term applications such as aerodynamic skin flow control and active aerospace structures.
The evolution of ever-smaller microfabrication techniques, driven by market demand, has lead to multi-million transistor devices as a single piece part. Complimentary metal oxide semiconductor (CMOS) nanoelectronics will be mass-produced by the year 2004 when lateral structures smaller than 100-nm will become common. Beyond the next ten years the future is less certain, but other technologies such as nanometer-scale single electron transistors provide an idea of what may be possible in 20-to-25 years. Microelectromechanical systems (MEMS), which bring "eyes, ears, noses, and muscles" (sensing and actuation) to electronic systems, are fabricated using similar processes and will benefit from decreasing minimum feature size over time. Nanoelectronics and nanoelectromechanical systems will evolve over the next decade to provide ever-higher levels of functional density per unit area. The continuing increase in functional density will enable decreased spacecraft system size, and ultra-small spacecraft. Examples of prototype microengineered attitude determination and propulsion systems are given.
An experiment has been conducted to compare the ignition energy of an existing digital thruster design between a pulsed electrical and laser excitations. A 355nm Nd-YAG pulsed laser is used to ignite the stored lead styphnate propellant charge. Given the device design, roughly 800 μJ is necessary to ignite a 180 μg charge volume with a 90% probability of ignition. This energy value is considered an upper limit. Under equivalent conditions, roughly 2.4mJ of electrical energy is required to ignite the same volume. The digital thruster concept is one approach to provide a valveless, slap-on propulsion capability for small (1kg mass class) and large satellites (1000kg mass class) to help maintain attitude or control the damping of low frequency oscillations in extended surfaces.
A pulsed UV laser volumetric direct-write patterning technique has been used to fabricate the structural members and key fluidic distribution systems of a miniature 100 gm mass spacecraft called the Co-Orbital Satellite Assistant (COSA). A photostructurable glass ceramic material enables this photo-fabrication process. The COSA is a miniature space vehicle designed to assist its host ship by serving as a maneuverable external viewing platform. Using orbital dynamics simulation software, a minimum (Delta) V solution has been found that allows a COSA vehicle to eject from the host and maneuver into an observation orbit about the host vehicle. The result of the simulant show that a cold gas propulsion system can adequately support the mission given a total fuel volume of 5 cm3. A prototype COSA with dimensions of 50 X 50 X 50 mm has been fabricated and assembled for simulation experiments on an air table. The vehicle is fashioned out of 7 laser patterned wafers, electronics boards and a battery. The patterned wafers include an integrated 2-axis propulsion system, a fuel tank and a propellant distribution system. The electronics portion of the COSA vehicle includes a wireless communication system, 2 microcontrollers for system, 2 microcontrollers for system control and MEMS gyros for relative attitude determination. The COSA vehicle is designed to be mass producible and scalable.
Miniaturization technologies such as Micro-Electro-Mechanical Systems (MEMS) have been used to fabricate a prototype 100-gm class cold gas propulsion system suitable for use on a Co-Orbiting Satellite Assistant (COSA). The propulsion system is fabricated from bonded layers of photostructurable glass (Foturan glass; the design is based on fabricating integrated modular parts. Thus, the propulsion system is mass producible, expandable, expendable (low unit cost), and highly integrated.
By definition Nanosatellites are space systems that can weigh 1010 kg and can perform unique missions (e.g. global cloud cover monitoring, store-and-forward communications) acting either in constellation of distributed sensor-nodes or in a many-satellite platoon that flies in formation. The Aerospace Corporation has been exploring the application of microelectronics fabrication and advanced packaging technology to the development of a mass-producible nanosatellite. Particular attention is being directed at M3 (Micromachining/MEMS/Microsystems) technology which appears to be important in the integration and manufacturing of these satellites. Laser direct-write processing techniques are being applied for rapid prototyping and to specific 3D fabrication steps where conventional microelectronics fabrication techniques fall short. In particular, a laser based technique has been developed that combines the rapid prototyping aspects of direct-write and the low cost/process uniformity aspects of batch processing. This technique has been used to develop various fluidic components and a microthruster subsystem in a photostructurable glass/ceramic material.
A pulsed UV laser based technique has been developed which permits the transfer, by direct-write exposure, of 3D image into a photosensitive glass/ceramic material. The exposed latent image volume is developed via temperature programmed bake process and then etched away using HF in solution. The height of the 3D microstructures is controlled by the initial laser wavelength used during the exposure and the time duration of the etching cycle. Using this technique we have fabricated large arrays of microstructures which have applications to microfluidics, microelectromechanical systems and optoelectronics. The resulting master copy can be used either as is or by use standard injection modeling techniques converted into a metallic or plastic copies. We present these results and others which have specific applications to miniature 1Kg class satellites - nanosatellites.
An overview of the micro-nanotechnology field is presented with application toward future space systems. Specific discussions are presented on the insertion of MEMS, MOEMS and quantum effect nanoelectronic devices into both current and future space systems. Silicon satellites, based on batch-fabricated microengineered systems are also discussed.
The direct-write laser machining technique has been used to process a lithium-alumosilicate glass (FoturanTM) for an application which requires 3D patterned microstructures. Using two UV laser wavelengths (248 nm and 355 nm), microcavities and microstructures have been fabricated for the development of microthrusters for attitude and orbit control of a 1 kg class (10 cm diameter) nanosatellite. In addition, experiments have been conducted to define the processing window for the laser patterning technique. The results include a measure of the change in Foturan strength after a required program bake cycle plus HF etching rates as a function of the laser repetition rate for the two UV wavelengths.