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We eport on engineering trades that led to the conceptual design of a laser communications terminal for spacecraft probing Mars. The flight terminal, the ground receiver and the ground transmitter subsystems are described. The flight terminal point design has 0.25 Gb/s downlink data-rate capability from the Mars close distance (0.42 AU). Capability for uplink data-rate of 0.3 Mb/s and ranging with 30 cm precision are also addressed.
The article gives an account of the history of unmanned exploration of the planets of the solar system, including both earthbound exploration and exploration with spacecraft. Examples of images of the Martian surface are presented along with images obtained in Jupiter and Mercury flybys. Data are presented on the growth of US launch vehicle performance capability, navigation performance, and planetary data rate capability. Basic information regarding the nature of the scientific experiments aboard the Pioneer and Viking spacecraft is given. A case is put forward for the ongoing exploration of the planets as a worthwhile endeavor for man.
As the National Aeronautics and Space Administration moves into the 21st century with programs like Space Station Freedom, a manned mission to Mars, and the new Landsat mission, transmission demands on the Tracking and Data Relay Satellite System (TDRSS) will very likely exceed the available bandwidth. The Manual Lujan, Jr. Center for Space Telemetering and Telecommunications Systems (CSTTS) at New Mexico State University (NMSU) is studying techniques for increasing the data rate capabilities of TDRSS. These techniques include the use of advanced bandwidth efficient modulation formats to increase the data rate that can be sustained in a TDRSS transponder and the use of lossless bandwidth compression of the data to be transmitted to lower the data rate required from the user spacecraft. Based upon current technology the most promising bandwidth efficient modulation technique is Trellis Coded Modulation (TCM) operating with Octal Phase shift Keying (8PSK). Trellis Coded Modulation coding with 8PSK carrier modulation has the capability to increase the data rate which can be transmitted through the TDRSS spacecraft by a factor of 2 to 2.5 times that available with todays coded QPSK systems with only a small penalty in link performance relative to the existing systems. However, before NASA can safely employ TCM coding it is necessary to prove that this complex format can perform on the real TDRSS link as it does in labs and simulation studies. This proof-of-concept test over a live satellite channel was the objective of the construction and testing performed under this task of the NMSU NASA grant referenced above. In conjunction with NASA, NMSU's CSTTS has constructed a system to test a new candidate TDRSS modulation scheme, TCM 8PSK, that can enhance the information throughput of the TDRSS spacecraft. The test system for this project which was constructed over a period of 18 months by NMSU consisted of two racks of commercial and univeristy-designed and -built equipment. This project has included modifications of an existing White Sands Ground Terminal (WSGT) High Rate QPSK Demodulator to demodulate 8PSK as well as the construction of other support hardware. Also, two TCM codecs (coder/decoders) have been constructed to implement two levels of bandwidth efficiency. One was designed and built by the research team at NMSU while the other was created by the University of Notre Dame with the University of South Australia. The NMSU codec achieves a 2-to-1 increase in data rate per unit bandwidth with a coding gain relative to QPSK of about 3dB. The Notre Dame/South Australia codec achieves a 2.5-to-1 increase in data rate per unit of occupied bandwidth and a coding gain of about 2dB.
Apollo/Saturn 5 Kennedy Launch Complex 39 /LC-39/ physical characteristics emphasizing high launch rate capability, economy of operation and superior flexibility
Driven initially by the desire for X-ray microcalorimeter arrays suitable for imaging the dynamic solar corona, we have developed a transition-edge-sensor (TES) microcalorimeter optimization that exhibits a unique combination of high spectral resolving power and a wide X-ray bandpass. These devices have achieved spectral performance of dE approximately 1.3 eV FWHM at 1.5 keV, 1.6 eV at 6 keV, and 2.0 eV at 8 keV, using small TESs (e.g., approximately 35 micron x 35 micron) that operate in a regime in which the superconducting transition is highly current dependent. In order to accommodate high X-ray count rates, the devices sit directly on a solid substrate instead of on membranes, and we use an embedded heatsinking layer to reduce pixel-to-pixel crosstalk. We will present results from devices with a range of TES and absorber sizes, and from device wafers with varied embedded heatsink materials. This contribution will focus on count-rate capabilities, including a discussion of the trade-off between count rate and energy resolution, and the heatsinking design. We will also present preliminary tests of array readout using a code-division multiplexed SQUID readout scheme, which may be necessary to enable large arrays of these fast devices.
The lithium-molybdenum disulfide system offers attractive characteristics including high rate capability, successful operation up to 75 C, a very low self-discharge rate, a good cycle life and safety characteristics which compare favorably to those of other lithium cells. Moreover, the materials and manufacturing costs for the system is effectively controlled, so the cells should ultimately be competitive with currently marketed rechargeable cells.
Prismatic HR and LC cells and batteries were built and tested, and they performed well with respect to the program goals of high capacity and high rate capability at specific energies. The HR batteries suffered reduced utilizations owing to dryout at the 2 and 3 A rates for the 50 C tests owing to the requirement for forced convection. The LC batteries suffered reduced utilizations under all conditions owing to the chimney effect at 1 G, although this effect would not occur at 0 G. An empirical model was developed which accurately predicted utilizations and average voltages for single cells, although thermal effects encountered during battery testing caused significant deviations, both positive and negative, from the model. Based on the encouraging results of the test program, we believe that the zinc-air primary battery of a flat, stackable configuration can serve as a high performance and safe power source for a range of space applications.
This paper provides an overview of the results of the JPL/NASA unmanned exploration of all of the planets of the solar system (except Pluto) as well as the telecommunications capability which was developed to enable/support those missions. The telecommunications link improvements will be described to show increases in data rate capability resulting from addition of ground antenna aperture, transmitter power, coding techniques, lower noise receivers, etc. The paper will also describe (briefly), the current and future flight missions.
This paper provides an overview of the imaging results of the JPL/NASA unmanned exploration missions to all the planets of the solar system (except Pluto) as well as the telecommunications capability which was developed to enable/support those missions. the telecommunications link improvements will be described to show increases in data rate capability resulting from the addition of ground antenna aperture, transmitter power, coding techniques, lower noise receivers, etc. This paper will also describe (briefly) the current and future flight missions. The presentation will be supported by a significant number of pictures taken during the planetary encounters as well as pictures of the Deep Space Network antennas.
The status of aircraft multispectral scanner technology was accessed in order to develop preliminary design specifications for an advanced instrument to be used for remote sensing data collection by aircraft in the 1980 time frame. The system designed provides a no-moving parts multispectral scanning capability through the exploitation of linear array charge coupled device technology and advanced electronic signal processing techniques. Major advantages include: 10:1 V/H rate capability; 120 deg FOV at V/H = 0.25 rad/sec; 1 to 2 rad resolution; high sensitivity; large dynamic range capability; geometric fidelity; roll compensation; modularity; long life; and 24 channel data acquisition capability. The field flattening techniques of the optical design allow wide field view to be achieved at fast f/nos for both the long and short wavelength regions. The digital signal averaging technique permits maximization of signal to noise performance over the entire V/H rate range.
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.
A data acquisition system upgrade project, known as AB-DAS, is underway at the NASA Langley Transonic Dynamics Tunnel. AB-DAS will soon serve as the primary data system and will substantially increase the scan-rate capabilities and analog channel count while maintaining other unique aeroelastic and dynamic test capabilities required of the facility. AB-DAS is configurable, adaptable, and enables buffet and aeroacoustic tests by synchronously scanning all analog channels and recording the high scan-rate time history values for each data quantity. AB-DAS is currently available for use as a stand-alone data system with limited capabilities while development continues. This paper describes AB-DAS, the design methodology, and the current features and capabilities. It also outlines the future work and projected capabilities following completion of the data system upgrade project.
State of art ambient temperature secondary lithium cells were evaluated to determine their performance capability and limitations and to assess the present status of the technology of these cells. Li-MoS2, Li-NbSe3 and Li-TiS2 cells were evaluated for their charge/discharge characteristics, rate capability, and cycle life performance. The cells evaluated have a cycle life of 100-250 cycles at moderate discharge rates (C/5). The specific energy of these cells is between 50 and 100 Wh/Kg, depending upon the system. This paper describes the details of the cell designs, the test procedures, and the results of the evaluation studies.
For rendezvous and docking, assessing and tracking relative orientation is necessary within a minimum approach distance. Special target light patterns have previously been considered for use with video sensors for ease of determining relative orientation. A generalization of those approaches is addressed. At certain ranges, the entire structure of the target vehicle constitutes an acceptable target; at closer ranges, substructures will suffice. Acting on the same principle as the human intelligence, these structures can be compared with a memory model to assess the relative orientation and range. Models for comparison are constructed from a CAD facet model and current imagery. This approach requires fast image handling, projection, and comparison techniques which rely on rapidly developing parallel processing technology. Relative orientation and range assessment consists of successful comparison of the perceived target aspect with a known aspect. Generating a known projection from a model within required times, say subsecond times, is only now approaching feasibility. With this capability, rates of comparison used by the human brain can be approached and arbitrary known structures can be compared in reasonable times. Future space programs will have access to powerful computation devices which far exceed even this capability. For example, the possibility will exist to assess unknown structures and then control rendezvous and docking, all at very fast rates. The first step which has the current utility, namely applying this to known structures, is taken.
A study was initiated to design and evaluate a new design concept for nickel-hydrogen cells. This concept involved constructing a battery in a bipolar stack with cells consisting of a one plate for each nickel and hydrogen electrode. Preliminary designs at the system level of this concept promised improvements in both volumetric and gravimetric energy densities, thermal management, life extension, costs, and peak power capability over more conventional designs. Test results were most encouraging. This preprototype battery, built with less than ideal components and hardware, exceeded expectations. A total of 2000 LEO cycles at 80 percent depth of discharge were accrued. A cycle life goal of 30,000 cycles appears achievable with minor design changes. These improvements include advanced technology nickel electrodes, insulated bipolar plates and specifically designed frames to minimize shunt currents. The discharge rate capability of this design exceeds 25C. At the 10C discharge rate, 80% of the battery capacity can be withdrawn in six minutes. This data shows that the bipolar design is well suited for those applications requiring high peak power pulses.
Present satellite communications systems normally use separate solar cells and antennas. Since solar cells generally account for the largest surface area of the spacecraft, co-locating the antenna and solar cells on the same substrate opens the possibility for a number of data-rate-enhancing communications link architecture that would have minimal impact on spacecraft weight and size. The idea of integrating printed planar antenna and solar array cells on the same surface has been reported in the literature. The early work merely attempted to demonstrate the feasibility by placing commercial solar cells besides a patch antenna. Recently, Integrating multiple antenna elements and solar cell arrays on the same surface was reported for both space and terrestrial applications. The application of photovoltaic solar cell in a planar antenna structure where the radiating patch antenna is replaced by a Si solar cell has been demonstrated in wireless communication systems (C. Bendel, J. Kirchhof and N. Henze, 3rd Would Photovotaic Congress, Osaka, Japan, May 2003). Based on a hybrid approach, a 6x1 slot array with circularly polarized crossdipole elements co-located on the same surface of the solar cells array has been demonstrated (S. Vaccaro, J. R. Mosig and P. de Maagt, IEEE Trans. Ant. and Propag., Vol. 5 1, No. 8, Aug. 2003). Amorphous silicon solar cells with about 5-10% efficiency were used in these demonstrations. This paper describes recent effort to integrate advanced solar cells with printed planar antennas. Compared to prior art, the proposed WSAC concept is unique in the following ways: 1) Active antenna element will be used to achieve dynamic beam steering; 2) High efficiency (30%) GaAs multi-junction solar cells will be used instead of Si, which has an efficiency of about 15%; 3) Antenna and solar cells are integrated on a common GaAs substrate; and 4) Higher data rate capability. The IA/SAC is designed to operate at X-band (8-12 GH) and higher frequencies Higher operating frequencies enable greater bandwidth and thus higher data transfer rates. The first phase of the effort involves the development of GaAs solar cell MIMs (Monolithically Integrated Module) with a single patch antenna on the opposite side of the substrate. Subsequent work will involve the integration of MIMs and antennas on the same side of the substrate. Results from the phase one efforts will be presented.
The Adaptive Deployable Entry and Placement Technology (ADEPT), a mechanically deployable entry vehicle technology, has been under development at NASA since 2011. As part of the technical maturation of ADEPT, designs capable of delivering small payloads (10 kg) are being considered to rapidly mature sub 1 m deployed diameter designs. The unique capability of ADEPT for small payloads comes from its ability to stow within a slender volume and deploy to achieve a mass efficient drag surface with a high heat rate capability. The low ballistic coefficient results in entry heating and mechanical loads that can be met by a revolutionary three-dimensionally woven carbon fabric supported by a deployable skeleton structure. This carbon fabric has test proven capability as both primary structure and payload thermal protection system. In order to rapidly advance ADEPTs technical maturation, the project is developing test methods that enable thermostructural design requirement verification of ADEPT designs at the system level using ground test facilities. Results from these tests are also relevant to larger class missions and help us define areas of focused component level testing in order to mature material and thermal response design codes. The ability to ground test sub 1 m diameter ADEPT configurations at or near full-scale provides significant value to the rapid maturation of this class of deployable entry vehicles. This paper will summarize arc jet test results, highlight design challenges, provide a summary of lessons learned and discuss future test approaches based upon this methodology.
The X-ray Integral Field Unit (X-IFU) microcalorimeter, on-board Athena, with its focal plane comprising 3840 Transition Edge Sensors (TESs) operating at 90 mK, will provide unprecedented spectral-imaging capability in the 0.2-12 keV energy range. It will rely on the on-board digital processing of current pulses induced by the heat deposited in the TES absorber, as to recover the energy of each individual events. Assessing the capabilities of the pulse reconstruction is required to understand the overall scientific performance of the X-IFU, notably in terms of energy resolution degradation with both increasing energies and count rates. Using synthetic data streams generated by the X-IFU End-to-End simulator, we present here a comprehensive benchmark of various pulse reconstruction techniques, ranging from standard optimal filtering to more advanced algorithms based on noise covariance matrices. Beside deriving the spectral resolution achieved by the different algorithms, a first assessment of the computing power and ground calibration needs is presented. Overall, all methods show similar performances, with the reconstruction based on noise covariance matrices showing the best improvement with respect to the standard optimal filtering technique. Due to prohibitive calibration needs, this method might however not be applicable to the X-IFU and the best compromise currently appears to be the so-called resistance space analysis which also features very promising high count rate capabilities.