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Ground and flight test plans for defining operational capability of ammonia and hydrogen resistojet control system for Manned Orbital Research Laboratory
In 2014 a team at NASA Goddard Space Flight Center (GSFC) studied the feasibility of using active aerocapture to reduce the chemical Delta V requirements for inserting a small scientific satellite into Titan polar orbit. The scientific goals of the mission would be multi-spectral imaging and active radar mapping of Titan's surface and subsurface. The study objectives were to: (i) identify and select from launch window opportunities and refine the trajectory to Titan; (ii) study the aerocapture flight path and refine the entry corridor; (iii) design a carrier spacecraft and systems architecture; (iv) develop a scientific and engineering plan for the orbital portion of the mission. Study results include: (i) a launch in October 2021 on an Atlas V vehicle, using gravity assists from Earth and Venus to arrive at Titan in January 2031; (ii) initial aerocapture via an 8-km wide entry corridor to reach an initial 350X6000 km orbit, followed by aerobraking to reach a 350X1500 km orbit, and a periapse raise maneuver to reach a final 1500 km circular orbit; (iii) a three-part spacecraft system consisting of a cruise stage, radiator module, and orbiter inside a heat shield; (iv) a 22-month mission including station keeping to prevent orbital decay due to Saturn perturbations, with 240 Gb of compressed data returned. High-level issues identified include: (i) downlink capability - realistic downlink rates preclude the desired multi-spectral, global coverage of Titan's surface; (ii) power - demise of the NASA ASRG (Advanced Stirling Radioisotope Generator) program, and limited availability at present of MMRTGs (Multi-Mission Radioisotope Generators) needed for competed outer planet missions; (iii) thermal - external radiators must be carried to remove 4 kW of waste heat from MMRTGs inside the aeroshell, requiring heat pipes that pass through the aeroshell lid, compromising shielding ability; (iv) optical navigation to reach the entry corridor; (v) the NASA requirement of continuous critical event coverage for the orbiter, especially during the peak heating of the aerocapture when the radio link will be broken. In conclusion, although Titan aerocapture allows for considerable savings in propellant mass, this comes at a cost of increased mission complexity. Further architecture study and refinement is required to reduce high-level mission risks and to elucidate the optimum architecture.
The Viking '75 Mission to Mars permits a truly unique opportunity to explore the natural satellites, Phobos and Deimos, from distances measured in the tens of kilometers. Because of the particular orbital geometry currently planned for the Viking Mission, the Viking spacecraft can be maneuvered to make repeated passes very close to Phobos and Deimos during the proposed extended mission phase. Multipass images of both satellites will cover approximately 75% of Phobos and 50% of Deimos. Resolution on the order of 50 meters is possible. Close encounters will permit mass determination to an accuracy of tens of percent. A preliminary feasibility study has been made which shows that the propulsive requirements are nominal, the orbit determination accuracy is adequate, and the satellites are within the scan platform pointing capability during portions of each encounter.
A combination of orbital photographic, selenochemical, and magnetic surveys may elucidate the mechanism by which the lunar surface became magnetized and possibly yield an estimate of the intensity of the ancient magnetizing field and its time variation. The determination of the size and shape of the magnetized regions requires the measurement of the altitude dependence of field, especially at low altitudes (less than 100 km) and with a high enough sampling rate to resolve the profile at the edges of magnetized bodies. The planned Lunar Polar Orbiter may well provide the necessary data.
A significant number of spacecraft are planning to use halo orbits and lunar-swingby trajectories in the next decade. Four spacecraft will be placed into halo orbits around the earth's sunward libration point, while two others will be stationed near the sun-earth L2 libration point in the distant geomagnetic tail. Six spacecraft, including two of the aforementioned halo orbiters, will make use of lunar-swingby maneuvers to fulfill their mission objectives. Thus, a total of ten spacecraft, five from the Soviet Union, two from Japan, two from the United States, and one from the European Space Agency, will employ halo orbits and/or lunar-swingby trajectories in the 1990's. Pertinent facts are presented for each of these missions.
Active debris removal (ADR) is a potential means to remediate the orbital debris environment in low Earth orbit (LEO). Massive intact objects, including spent upper stages and retired payloads, with high collision probabilities have been suggested as potential targets for ADR. The challenges to remove such objects on a routine basis are truly monumental. A key piece of information needed for any ADR operations is the tumble motion of the targets. Rapid tumble motion (in excess of one degree per second) of a multiple-ton intact object could be a major problem for proximity and docking operations. Therefore, there is a need to characterize the general tumble motion of the potential ADR targets for future ADR planning. The NASA Orbital Debris Program Office has initiated an effort to identify the global tumble behavior of potential ADR targets in LEO. The activities include optical light curve observations, imaging radar data collection, and laboratory light curve simulations and modeling. This paper provides a preliminary summary of light curve data of more than 100 upper stages collected by two telescope facilities in Colorado and New Mexico between 2011 and 2012. Analyses of the data and implications for the tumble motions of the objects are also discussed in the paper.
This study provides a summary of future cryogenic space payload users, their currently projected needs and reported planning for space operations over the next decade. At present, few users with payloads consisting of reactive cryogens, or any cryogen in significant quantities, are contemplating the use of the Space Shuttle. Some members of the cryogenic payload community indicated an interest in flying their future planned payloads on the orbiter, versus an expendable launch vehicle (ELV), but are awaiting the outcome of a Rockwell study to define what orbiter mods and payloads requirements are needed to safely fly chemically reactive cryogen payloads, and the resultant cost, schedule, and operational impacts. Should NASA management decide in early 1990 to so modify orbiter(s), based on the Rockwell study and/or changes in national defense payloads launch requirements, then at least some cryo payload customers will reportedly plan on using the Shuttle orbiter vehicle in preference to an ELV. This study concludes that the most potential for possible future cryogenic space payloads for the Space Transportation System Orbiter fleet lies within the scientific research and defense communities.
The magnetospheric ion population of Jupiter is dominated by the 1000 kg/s of iogenic material constantly ejected by IO volcanism as neutral gas (approx. 1 kg/s goes out as high speed dust grains), subsequent atmospheric losses to the IO torus, and radial transport of torus ions throughout the magnetosphere. As that magnetosphere is greatly distended in radial size by the iogenic plasma loading, so are surfaces of the other Galilean moons also significantly, and perhaps even dominantly, affected by iogenic plasma bombardment, e.g. at the level up to 0.2 kg/s heavy ions (mostly O and S) onto Europa as per local plasma ion measurements. In comparison, cometary impacts onto IO deliver about 0.02 kg/s of impact ejecta to Europa via ballistic transfer through the Jupiter system. The magnetosphere of this system operates as a powerful engine to produce and transport ions from the IO source to the surfaces of these other moons, and any future orbiter missions to these moons must account for surface distributions of the iogenic material and its chemical effects before real assessments can be made of sensible chemical materials otherwise arising from primordial formation and subsequent evolution of these moons. This is a fundamental problem of space weathering that must be addressed for all planetary bodies with thin atmospheres and direct surface exposure to their space plasma environments. Long-standing debates from Galileo Orbiter measurements about the origins of hydrate sulfates at Europa present examples of this problem, as to whether the sulfates arise from oceanic minerals or from iogenic sulfur chemistry. Any orbiter or landed mission to Europa for astrobiological investigations would further need to separate the potential chemical biosignatures of life or its precursors from the highly abundant background of iogenic material. Although no single ion carries a tag identifying it as of iogenic or other origin, the elemental abundance distributions of ions to be measured throughout the jovian magnetosphere and in the local moon environments can act as tracers if we know from direct measurements and models the distributions at the mostly likely sources, i.e. at IO. However, our knowledge of these abundances are very limited from earlier in-situ and remote measurements, mainly confined to major (S, O) and some minor (Na, K, Cl) species with abundances at or above a few percent relative to O. Future in-situ plasma measurements by the planned Jupiter Europa Orbiter and Jupiter Ganymede Orbiter missions should extend the abundance coverage to minor and even trace elemental species. For Europa astrobiological investigations it is also important to specify iogenic inputs and surface processing of isotopic species. We discuss the range of abundance distributions arising from models for IO hot volcanic emissions, and from the subsequent dynamics of ion injection, magnetospheric transport, and icy moon surface bombardment.
The Odyssey spacecraft has been in Mars orbit since October 24, 2001 and has nearly completed 61,490 orbits. Navigation operational objectives include the following: Control the local mean solar time for science observations; for most of the mission, this varied from 3:45 pm to 5:20 pm. Currently, an orbit trim maneuver planned for November 10, 2015 will place Odyssey at 6:45 pm/6:45 am at equator crossings in order to observe early morning ground frost, fog and clouds. Initially, Odyssey was late by 42 minutes for an over-flight of the critical seven minutes of Phoenix's entry, descent and landing (EDL). Odyssey was successfully positioned for this over-flight using the Delta V from angular momentum desaturations (AMD). Similar results for the Mars Science Laboratory's EDL and Comet Siding Spring's minimum risk location will be presented. Odyssey has and continues to relay significant quantities of rover data. Navigation successfully models frequent AMD Delta Vs in order to generate accurate sixty-day trajectory predictions; a typical timing error is 25 seconds after 60 days. However, unexpected events, such as safe-mode entries with their larger and more frequent thrusting, severely impact that trajectory accuracy. Impacted trajectories can have timing errors ranging from a few minutes to ten-to-fifteen minutes after sixty-days. Other analyses (briefly stated) include: a) the offset of the orbital ground track pattern after an initial cycle of 30 days or 362 orbits and b) an operations environment of continuous thrusting if/when one of the three remaining reaction wheels fails.
The paper discusses the plans for the stability and control aspects of the Space Shuttle orbital flight testing. The first flight plan calls for the design of trajectory, cg, and trim schedules which are as tolerant as possible with regard to all the constraints and aerodynamic uncertainties. Vehicle configuration control and downmoding switches will be used to provide capabilities to handle the off-nominal conditions that might be encountered. Measured trim conditions will provide information on the control effector characteristics and provide an early estimate of the control boundaries.
An experimental investigation was performed in the Langley Research Center Unitary Plan Wind Tunnel (Test 0A70) to obtain the detailed effects that RCS jet flow interactions with local orbiter flow field have on supersonic stability and control characteristics of the space shuttle orbiter. Six-component force data were obtained through an angle-of-attack range from 15 to 35 degrees at angles of sideslip of 0, +5, and -5 degrees. The test was conducted with yaw jet simulation at free-stream Mach numbers of 2.5 and 4.6, simulating SSV re-entry flight conditions at these Mach numbers. In addition to the basic force measurements, fuselage base pressures and pressures on the non-metric RCS pods were obtained.
This slide presentation reviews the planning for the Mars Exploration Program. This includes information on the Mars Science Orbiter, the 2016-2018 planning teams, and updates to the Mars Exploration Analysis Group.
The ARTEMIS mission, part of the THEMIS extended mission, is the first to fly spacecraft in the Earth-Moon Lissajous regions. In 2009, two of the five THEMIS spacecraft were redeployed from Earth-centered orbits to arrive in Earth-Moon Lissajous orbits in late 2010. Starting in August 2010, the ARTEMIS P1 spacecraft executed numerous stationkeeping maneuvers, initially maintaining a lunar L2 Lissajous orbit before transitioning into a lunar L1 orbit. The ARTEMIS P2 spacecraft entered a L1 Lissajous orbit in October 2010. In April 2011, both ARTEMIS spacecraft will suspend Lissajous stationkeeping and will be maneuvered into lunar orbits. The success of the ARTEMIS mission has allowed the science team to gather unprecedented magnetospheric measurements in the lunar Lissajous regions. In order to effectively perform lunar Lissajous stationkeeping maneuvers, the ARTEMIS operations team has provided orbit determination solutions with typical accuracies on the order of 0.1 km in position and 0.1 cm/s in velocity. The ARTEMIS team utilizes the Goddard Trajectory Determination System (GTDS), using a batch least squares method, to process range and Doppler tracking measurements from the NASA Deep Space Network (DSN), Berkeley Ground Station (BGS), Merritt Island (MILA) station, and United Space Network (USN). The team has also investigated processing of the same tracking data measurements using the Orbit Determination Tool Kit (ODTK) software, which uses an extended Kalman filter and recursive smoother to estimate the orbit. The orbit determination results from each of these methods will be presented and we will discuss the advantages and disadvantages associated with using each method in the lunar Lissajous regions. Orbit determination accuracy is dependent on both the quality and quantity of tracking measurements, fidelity of the orbit force models, and the estimation techniques used. Prior to Lissajous operations, the team determined the appropriate quantity of tracking measurements that would be needed to meet the required orbit determination accuracies. Analysts used the Orbit Determination Error Analysis System (ODEAS) to perform covariance analyses using various tracking data schedules. From this analysis, it was determined that 3.5 hours of DSN TRK-2-34 range and Doppler tracking data every other day would suffice to meet the predictive orbit knowledge accuracies in the Lissajous region. The results of this analysis are presented. Both GTDS and ODTK have high-fidelity environmental orbit force models that allow for very accurate orbit estimation in the lunar Lissajous regime. These models include solar radiation pressure, Earth and Moon gravity models, third body gravitational effects from the Sun, and to a lesser extent third body gravitational effects from Jupiter, Venus, Saturn, and Mars. Increased position and velocity uncertainties following each maneuver, due to small execution performance errors, requires that several days of post-maneuver tracking data be processed to converge on an accurate post-maneuver orbit solution. The effects of maneuvers on orbit determination accuracy will be presented, including a comparison of the batch least squares technique to the extended Kalman filter/smoother technique. We will present the maneuver calibration results derived from processing post-maneuver tracking data. A dominant error in the orbit estimation process is the uncertainty in solar radiation pressure and the resultant force on the spacecraft. An estimation of this value can include many related factors, such as the uncertainty in spacecraft reflectivity and surface area which is a function of spacecraft orientation (spin-axis attitude), uncertainty in spacecraft wet mass, and potential seasonal variability due to the changing direction of the Sun line relative to the Earth-Moon Lissajous reference frame. In addition, each spacecraft occasionally enters into Earth or Moon penumbra or umbra and these shadow crossings reduche solar radiation force for several hours. The effects of these events on orbit determination accuracy will be presented. In order to plan for upcoming stationkeeping maneuvers, the maneuver planning team must take the current orbit estimate, propagate it forward to the planned maneuver time, and determine the optimal maneuver to maintain the Lissajous orbit for one or more revolutions. The propagation is performed using a Runge-Kutta 7/8 integrator and typically the position and velocity uncertainty increases with propagation time, increasing the overall uncertainty of the orbit state at the maneuver execution time. The effect of orbit knowledge uncertainty on stationkeeping operations will be presented.
Digest of advanced planning reports on orbiter missions and flyby flights to outer planets
Solids, liquids, and gases emit at microwave wavelengths measurable amounts of black-body thermal radiation. Receiver sensitivities readily approach 0.01 K, and permit accurate measurements of land, sea, and atmospheric temperatures. Sea and land temperature measurements must be corrected for the effects of surface emissivity, but these effects can often be measured or estimated. Observations near the 5 mm wavelength 02 resonances can yield atmospheric temperature profiles with an approximate accuracy of 2 K for altitudes 0-80 km. Such measurements from balloons and aircraft suggest that the planned earth-orbital satellite experiments will yield data valuable for numerical weather prediction. Ground-based radio telescopes and planetary-probes have yielded similar information about the surfaces and atmospheres of other planets.
It is seen that a Shuttle laboratory will provide a facility for meeting the continuing need for planning frequency and orbit utilization and specialized radio interference measurements. The Shuttle could be used for placing communications and navigation satellites into the desired orbit, and also for conducting laser communications tests with the aim of developing the required technology and acquisition techniques for space-to-space and space-to-ground telecommunications. Other uses include the proof-testing of large spacecraft antenna structures and their erection mechanisms, and the testing of high-voltage high-current communications satellite components and subsystems.
Space habitats are considered, with attention given the evolution of space station systems, space station habitability, space settlement planning methodology, and orbital assembly. Various aspects of the Space Transportation System are discussed, including Shuttle booster/propulsion growth concept, advanced earth orbital transportation systems technology, single-stage-to-orbit vehicles and aeromaneuvering orbit transfer vehicles. Materials processing in space is examined, with emphasis on biological materials, metallurgical materials, the uses of space ultrahigh vacuum, and extraterrestrial mining and industrial processing. Solar space power is investigated, with attention given the potential of satellite solar power stations, thermal engine power satellites and microwave power transmission to earth. Individual items are announced in this issue.
Microwave beaming of satellite-collected solar energy to earth for conversion to useful industrial power is evaluated for feasibility, with attention given to system efficiencies and costs, ecological impact, hardware to be employed, available options for energy conversion and transmission, and orbiting and assembly. Advantages of such a power generation and conversion system are listed, plausible techniques for conversion of solar energy (thermionic, thermal electric, photovoltaic) and transmission to earth (lasers, arrays of mirrors, microwave beams) are compared. Structural fatigue likely to result from brief daily eclipses, 55% system efficiency at the present state of the art, present projections of system costs, and projected economic implications of the technology are assessed. Two-stage orbiting and assembly plans are described.