Dissolution of a stationary bubble in a glassmelt with reversible chemical reaction - Rapid forward reaction rate constant
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Weinberg, M. C.↗
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Experimental Results from Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T) Program
The National Aeronautics and Space Administration’s (NASA) Integrated LCRD Low-Earth Orbit (LEO) User Modem and Amplifier Terminal (ILLUMA-T) payload was launched and installed on the International Space Station’s (ISS) Japanese Experiment Module - Exposed Facility (JEM-EF) in November 2023. ILLUMA-T was the first space-based user to communicate with NASA’s Laser Communications Relay Demonstration (LCRD) using free space optical communication to transfer data from the ISS at return rates to Earth of up to 1.244 Gbps and forward rates from Earth of up to 155 Mbps. A 6-month long Experiments Program on ILLUMA-T concluded in June 2024, after which the payload was removed from the ISS and is currently de-orbiting. The Experiments Program was carefully designed to understand and characterize the Pointing, Acquisition, and Track (PAT) process with the new Modular, Agile, Scalable Optical Terminal (MAScOT), optical modem performance, and end-to-end relay performance.
ISS↗
Qualitative differences between on-orbit and transition RCS control
Two separate reaction control system (RCS) digital autopilots (DAPs) evolved from one original Space Shuttle orbital autopilot concept. A computer overload forced this evolution. Part of the overload problem was due to unique performance requirements imposed on the RCS controller during each of several different flight regimes. The two resultant RCS DAPs yield different effector responses because they rely on different sources of sensory input and they process data differently. This paper describes the evolution of the two RCS controllers and illustrates their behavioral differences. The transition autopilot, used in orbital insertion and deorbit, is sensitive to orbiter flexure due to its feedthrough character. The on-orbit autopilot is sensitive to transient rate control degradation from large disturbances due to feed-forward rate estimation. Simulation results and flight data are used to illustrate performance differences between the two autopilots under various conditions. These include computer failures where electronic stringing and procedural reconfiguration differences affect autopilot behavior.
Hattis, P. D.↗
Acoustic Study of a Sweeping Jet Actuator for Active Flow Control Applications
Active flow control for aircraft has been demonstrated to improve aerodynamic performance but generally introduces additional noise sources. This study presents measurements of the acoustic fields of sweeping jet actuators at full- and half-scale compared to the configuration recently demonstrated in ground- and flight-tests of a full-scale rudder. The effects of scale, flow rate, forward speed, and actuator synchronization state on tone and broadband noise directional power spectral density (PSD) levels are presented. The sweeping jet actuator PSD levels in the audio range increases as the second power of actuator flow rate. A fourth power variation of PSD level with flow rate is observed for a comparable non-sweeping actuator. These measurements will be used to develop noise source models for new aircraft configurations utilizing active flow control.
Active Flow Control Noise↗
Forebody vortex control with jet and slot blowing on an F/A-18
A wind tunnel test program was conducted in October, 1992, on a 6-percent F/A-18 model, to determine the most effective methods of forebody vortex control for providing increased yaw control at high angles of attack. A series of circular jet blowing configurations were investigated with variations in blowing rate, fuselage station, circumferential position, and blowing angle. Slot configurations were also tested and included variations in blowing rate, forward fuselage station, and length. The optimum jet and slot configurations were then also tested at -10 deg of sideslip. Yawing moments from both the jet and slot blowing configurations were found to have very good trends with increasing blowing rates and the maximum yaw control available at 50-deg angle of attack (where rudder power had dropped to near zero) was found to be 40 percent greater than the level provided by the rudder at 0-deg angle of attack.
Kramer, Brian R.↗
Integrated Network Architecture for NASA's Orion Missions
NASA is planning a series of short and long duration human and robotic missions to explore the Moon and then Mars. The series of missions will begin with a new crew exploration vehicle (called Orion) that will initially provide crew exchange and cargo supply support to the International Space Station (ISS) and then become a human conveyance for travel to the Moon. The Orion vehicle will be mounted atop the Ares I launch vehicle for a series of pre-launch tests and then launched and inserted into low Earth orbit (LEO) for crew exchange missions to the ISS. The Orion and Ares I comprise the initial vehicles in the Constellation system of systems that later includes Ares V, Earth departure stage, lunar lander, and other lunar surface systems for the lunar exploration missions. These key systems will enable the lunar surface exploration missions to be initiated in 2018. The complexity of the Constellation system of systems and missions will require a communication and navigation infrastructure to provide low and high rate forward and return communication services, tracking services, and ground network services. The infrastructure must provide robust, reliable, safe, sustainable, and autonomous operations at minimum cost while maximizing the exploration capabilities and science return. The infrastructure will be based on a network of networks architecture that will integrate NASA legacy communication, modified elements, and navigation systems. New networks will be added to extend communication, navigation, and timing services for the Moon missions. Internet protocol (IP) and network management systems within the networks will enable interoperability throughout the Constellation system of systems. An integrated network architecture has developed based on the emerging Constellation requirements for Orion missions. The architecture, as presented in this paper, addresses the early Orion missions to the ISS with communication, navigation, and network services over five phases of a mission: pre-launch, launch from T0 to T+6.5 min, launch from T+6.5 min to 12 min, in LEO for rendezvous and docking with ISS, and return to Earth. The network of networks that supports the mission during each of these phases and the concepts of operations during those phases are developed as a high level operational concepts graphic called OV-1, an architecture diagram type described in the Department of Defense Architecture Framework (DoDAF). Additional operational views on organizational relationships (OV-4), operational activities (OV-5), and operational node connectivity (OV-2) are also discussed. The system interfaces view (SV-1) that provides the communication and navigation services to Orion is also included and described. The challenges of architecting integrated network architecture for the NASA Orion missions are highlighted.
Bhasin, Kul B.↗
Per-Pixel, Dual-Counter Scheme for Optical Communications
Free space optical communications links from deep space are projected to fulfill future NASA communication requirements for 2020 and beyond. Accurate laser-beam pointing is required to achieve high data rates at low power levels.This innovation is a per-pixel processing scheme using a pair of three-state digital counters to implement acquisition and tracking of a dim laser beacon transmitted from Earth for pointing control of an interplanetary optical communications system using a focal plane array of single sensitive detectors. It shows how to implement dim beacon acquisition and tracking for an interplanetary optical transceiver with a method that is suitable for both achieving theoretical performance, as well as supporting additional functions of high data rate forward links and precision spacecraft ranging.
Farr, William H.↗
AMELIA CESTOL Test: Acoustic Characteristics of Circulation Control Wing with Leading-and Trailing-Edge Slot Blowing
Aeroacoustic measurements of the 11 % scale full-span AMELIA CESTOL model with leading- and trailing-edge slot blowing circulation control (CCW) wing were obtained during a recent test in the Arnold Engineering Development Center 40- by 80-Ft. Wind Tunnel at NASA Ames Research Center, Sound levels and spectra were acquired with seven in-flow microphones and a 48-element phased microphone array for a variety of vehicle configurations, CCW slot flow rates, and forward speeds, Corrections to the measurements and processing are in progress, however the data from selected configurations presented in this report confirm good measurement quality and dynamic range over the test conditions, Array beamform maps at 40 kts tunnel speed show that the trailing edge flap source is dominant for most frequencies at flap angles of 0deg and 60deg, The overall sound level for the 60deg flap was similar to the 0deg flap for most slot blowing rates forward of 90deg incidence, but was louder by up to 6 dB for downstream angles, At 100 kts, the in-flow microphone levels were louder than the sensor self-noise for the higher blowing rates, while passive and active background noise suppression methods for the microphone array revealed source levels as much as 20 dB lower than observed with the in-flow microphones,
Horne, Clifton↗
Vector plotting as an indication of the approach to flutter
A binary flexure-torsion analysis was made to check theoretically a method for predicting flutter which depends on plotting vectorially the amplitudes of response relative to the exciting force and extracting the relevant damping rate. The results of this calculation are given in graphs both of the vector plots themselves and of the estimated damping rate against forward speed. The estimated damping rates are compared with calculated values. The method has the advantage that in a flight flutter test damping can be estimated from continuous excitation records: the method is an extension of the Kennedy and Pancu technique used in ground resonance testing.
Broadbent, E. G.↗
Measurement of solar gravitational oblateness with gravity gradiometers
A very high sensitivity rotating gravity gradiometer onboard the spacecraft is described for measuring the gravitational oblateness of the Sun during a solar probe mission. The proposed instrument would be a self-contained structure in a thermal-vacuum-magnetic shield in the shape of a cross, with a mass of 20 kg and arm length of 1.0 m and thickness of 0.1 m. The sensor inside would have a resonant frequency of 1/30 Hz, a mechanical Q of one million and would use gravitational radiation antenna technology to achieve a sensitivity of 6 x 10 to the minus 8th power Eotvos, which would provide a measurement of the solar oblateness to an accuracy of 1.5 to 6 x 10 to the minus 8th power. The gravity gradiometer will require a spinning spacecraft, so that it will not sense the spacecraft gravity fields, but the gradiometer does not need to be at the spacecraft center of mass, or even on the spacecraft spin axis. Major problem areas to be addressed are demonstration of the instrument sensitivity prior to flight and the measurement and compensation for any residual spacecraft angular rates.
Forward, R. L.↗
Influence of maneuverability on helicopter combat effectiveness
A computational procedure employing a stochastic learning method in conjunction with dynamic simulation of helicopter flight and weapon system operation was used to derive helicopter maneuvering strategies. The derived strategies maximize either survival or kill probability and are in the form of a feedback control based upon threat visual or warning system cues. Maneuverability parameters implicit in the strategy development include maximum longitudinal acceleration and deceleration, maximum sustained and transient load factor turn rate at forward speed, and maximum pedal turn rate and lateral acceleration at hover. Results are presented in terms of probability of skill for all combat initial conditions for two threat categories.
Falco, M.↗
Space and Earth Terminal Sizing for Future Mars Missions
NASA is investigating potential communications architectures to support future missions to Mars, with a time horizon out to about 2040. We examined a wide range of Earth-surface, Earth-orbiting, Mars-orbiting, and Mars-landed assets with both radio frequency and optical capabilities, and estimated the size, weight, power, and comparative cost of spacecraft telecommunications subsystems along with their comparative costs. Link attributes needed to achieve a fixed set of desired data rate capabilities were derived, assuming a planned set of Earth stations. For the trunk link from Mars to Earth, the required return data rates considered were 50, 75, 125, and 250 Mbps, and the required forward data rates considered were 30 and 50 Mbps. For proximity links, the required forward and return data rates (symmetric) ranged from 0.36 Mbps to 100 Mbps. The communication channels considered were UHF (75 cm wavelength) for proximity links only, and X-band (3.6 cm wavelength), Kaband (0.81 cm wavelength), and optical (808, 976, 1064, and 1550 nm wavelength) for both proximity and trunk links. Optical solutions provided substantial size and spectrum constraint advantages, but mixed advantages and disadvantages on mass and power. System cost was lower if the RF capability of space assets was increased to permit the number of arrayed RF Earth stations to be limited to two.
MacNeal, Bruce↗
Addressing the High-Rate Deep Space Communications Shortfall in NASA’s Space Technology Mission Directorate's Envisioned Future
NASA’s Space Technology Mission Directorate (STMD) has identified key technologies needed for future crewed and robotic exploration and science missions. STMD is helping to build the civilian technology base by working with other NASA Mission Directorates, other United States government agencies, commercial industry, and academia to identify technology shortfalls and to develop plans to address them. One critical area of shortfalls lies with deep space communications and navigation. While NASA had huge success to date with the Deep Space Network (DSN), recent studies have shown that without enhancements to current systems, the DSN will be unable to support the anticipated increases in the pace of space exploration or the expected higher data rates from deep space needed soon without severely impacting other missions. High-rate communications from the Moon and beyond is needed to enable future exploration and science missions currently being developed or under consideration. For example, a robust communications infrastructure will be needed to support a sustained human presence on the Moon and its eventual industrialization. High data rate trunk lines between the Earth and the Moon are needed to reduce the number of individual links. The human exploration of Mars will also require high-rate communications between Earth and Mars. Return data rates to Earth from Mars for a single link, for example, are anticipated to be greater than 100 Mb/s; forward data rates to Mars, based on experience from the International Space Station, are anticipated to be greater than 20 Mb/s. Future deep space science missions will also require higher data rates than possible with today’s technology and the current capabilities of the DSN. To support future exploration and science needs, it will be necessary to upgrade the DSN to enhance its radio frequency (RF) capabilities. In addition, it is envisioned that NASA will gradually introduce optical communications to augment its RF systems. Optical communications will enable new science and exploration missions by providing high data rates and better navigation over long distances. This paper will briefly describe STMD’s envisioned future for deep space communications in the 2030+ timeframe and the technology roadmaps being developed for both radio frequency and optical systems.
Bernard Edwards↗
Adaptive data rate control TDMA systems as a rain attenuation compensation technique
Rainfall attenuation has a severe effect on signal strength and impairs communication links for future mobile and personal satellite communications using Ka-band and millimeter wave frequencies. As rain attenuation compensation techniques, several methods such as uplink power control, site diversity, and adaptive control of data rate or forward error correction have been proposed. In this paper, we propose a TDMA system that can compensate rain attenuation by adaptive control of transmission rates. To evaluate the performance of this TDMA terminal, we carried out three types of experiments: experiments using a Japanese CS-3 satellite with Ka-band transponders, in house IF loop-back experiments, and computer simulations. Experimental results show that this TDMA system has advantages over the conventional constant-rate TDMA systems, as resource sharing technique, in both bit error rate and total TDMA burst lengths required for transmitting given information.
Sato, Masaki↗
Unsteady turbulent boundary layers with flow reversal
A theoretical study is carried out to search for the appearance of a singularity in a family of time-dependent turbulent boundary layers with embedded reverse-flow regions and determine the conditions necessary for its appearance. Further insight is gained into the development of unsteady turbulent boundary layers. The calculations performed for a family of prescribed external velocity distributions in which the relative importance of the effects of time-dependence, compared to those of spatial diffusion, are controlled by a given parameter. The conditions necessary for the appearance of a singularity appears to involve the existence of an appropriate relationship between the dominant velocities in the reversed-flow region and the rate of forward movement of the flow reversal point. The results support the hypothesis that a singularity will exist in the flow if and only if the typical reversed-flow velocities exceed the rate of penetration of the reversed flow into the oncoming boundary layer.
Patel, V. C.↗
Initial Thrust Measurements of Marshall's Ion-ioN Thruster
Electronegative ion thrusters are a variation of traditional gridded ion thruster technology differentiated by the production and acceleration of both positive and negative ions. Benefits of electronegative ion thrusters include the elimination of lifetime-limiting cathodes from the thruster architecture and the ability to generate appreciable thrust from both charge species. While much progress has been made in the development of electronegative ion thruster technology, direct thrust measurements are required to unambiguously demonstrate the efficacy of the concept and support continued development. In the present work, direct thrust measurements of the thrust produced by the MINT (Marshall's Ion-ioN Thruster) are performed using an inverted-pendulum thrust stand in the High-Power Electric Propulsion Laboratory's Vacuum Test Facility-1 at the Georgia Institute of Technology with operating pressures ranging from 4.8 x 10(exp -5) and 5.7 x 10(exp -5) torr. Thrust is recorded while operating with a propellant volumetric mixture ratio of 5:1 argon to nitrogen with total volumetric flow rates of 6, 12, and 24 sccm (0.17, 0.34, and 0.68 mg/s). Plasma is generated using a helical antenna at 13.56 MHz and radio frequency (RF) power levels of 150 and 350 W. The acceleration grid assembly is operated using both sinusoidal and square waveform biases of +/-350 V at frequencies of 4, 10, 25, 125, and 225 kHz. Thrust is recorded for two separate thruster configurations: with and without the magnetic filter. No thrust is discernable during thruster operation without the magnetic filter for any volumetric flow rate, RF forward Power level, or acceleration grid biasing scheme. For the full thruster configuration, with the magnetic filter installed, a brief burst of thrust of approximately 3.75 mN +/- 3 mN of error is observed at the start of grid operation for a volumetric flow rate of 24 sccm at 350 W RF power using a sinusoidal waveform grid bias at 125 kHz and +/- 350 V. Similar bursts in thrust are observed using a square waveform grid bias at 10 kHz and +/- 350 V for volumetric flow rates of 6, 10, and 12 sccm at 150, 350, and 350 W respectively. The only operating condition that exhibits repeated thrust spikes throughout thruster operation is the 24 sccm condition with a 5:1 mixture ratio at 150 W RF power using the 10 kHz square waveform acceleration grid bias. Thrust spikes for this condition measure 3 mN with an error of +/- 2.5 mN. There are no operating conditions tested that show continuous thrust production.
Caruso, Natalie R. S.↗
Coded throughput performance simulations for the time-varying satellite channel
The design of a reliable satellite communication link involving the data transfer from a small, low-orbit satellite to a ground station, but through a geostationary satellite, was examined. In such a scenario, the received signal power to noise density ratio increases as the transmitting low-orbit satellite comes into view, and then decreases as it then departs, resulting in a short-duration, time-varying communication link. The optimal values of the small satellite antenna beamwidth, signaling rate, modulation scheme and the theoretical link throughput (in bits per day) have been determined. The goal of this thesis is to choose a practical coding scheme which maximizes the daily link throughput while satisfying a prescribed probability of error requirement. We examine the throughput of both fixed rate and variable rate concatenated forward error correction (FEC) coding schemes for the additive white Gaussian noise (AWGN) channel, and then examine the effect of radio frequency interference (RFI) on the best coding scheme among them. Interleaving is used to mitigate degradation due to RFI. It was found that the variable rate concatenated coding scheme could achieve 74 percent of the theoretical throughput, equivalent to 1.11 Gbits/day based on the cutoff rate R(sub 0). For comparison, 87 percent is achievable for AWGN-only case.
Han, LI↗
Advanced technology satellite demodulator development
Ford Aerospace has developed a proof-of-concept satellite 8 phase shift keying (PSK) modulation and coding system operating in the Time Division Multiple Access (TDMA) mode at a data range of 200 Mbps using rate 5/6 forward error correction coding. The 80 Msps 8 PSK modem was developed in a mostly digital form and is amenable to an ASIC realization in the next phase of development. The codec was developed as a paper design only. The power efficiency goal was to be within 2 dB of theoretical at a bit error rate (BER) of 5x10(exp 7) while the measured implementation loss was 4.5 dB. The bandwidth efficiency goal was 2 bits/sec/Hz while the realized bandwidth efficiency was 1.8 bits/sec/Hz. The burst format used a preamble of only 40 8 PSK symbol times including 32 symbols of all zeros and an eight symbol unique word. The modem and associated special test equipment (STE) were fabricated mostly on a specially designed stitch-weld board although a few of the highest rate circuits were built on printed circuit cards. All the digital circuits were ECL to support the clock rates of from 80 MHz to 360 MHz. The transmitter and receiver matched filters were square-root Nyquist bandpass filters realized at the 3.37 GHz i.f. The modem operated as a coherent system although no analog phase locked (PLL) loop was employed. Within the budgetary constraints of the program, the approach to the demodulator has been proven and is eligible to proceed to the next phase of development of a satellite demodulator engineering model. This would entail the development of an ASIC version of the digital portion of the demodulator, and MMIC version of the quadrature detector, and SAW Nyquist filters to realize the bandwidth efficiency.
Ames, Stephen A.↗