Rendezvous Spacecraft Research Articles

Optimal impulsive rendezvous for highly elliptical orbits using linear primer vector theory

In this paper, minimum-fuel rendezvous is investigated for the case in which the reference orbit is highly elliptic. To this end, the well-known Tschauner-Hempel equations are used to describe the relative motions between rendezvous spacecraft and the target. Lawden's primer vector theory is then applied on this linear but time-varying system. The analytical solution of the required primer vector for this problem is then derived by using a recently developed method. For the existing non-optimal solutions which don't satisfy the conditions, the methods are further designed to improve the performance by shifting impulses or adding a new one. Finally, two algorithms are developed for free-impulse time-fixed rendezvous problems. The first algorithm can determine the globally optimal trajectory with the optimal number of impulses. The second one enables for fast trajectory planning. The proposed algorithms have been successfully applied to coplanar and three-dimensional rendezvous problems in which the target is flying on highly elliptical orbits.

Time-Synchronized Tracking Control for 6-DOF Spacecraft in Rendezvous and Docking

For the short-rangerelative motion of the on-orbit service spacecraft during rendezvous and docking missions, this article improves control performance with the describable straight line convergence trajectory and reduces energy consumption by proposing and solving the spacecraft time-synchronized control problem. This problem requires that the closed-loop system of the spacecraft is finite/fixed-time stable, all nonzero elements converge synchronously, and the trajectory of the closed-loop system tends to be the describable straight line. Based on the time-synchronized stability (TSS) and fixed-time-synchronized stability (FTSS), this article proposes the TSS and FTSS controllers for the 6-degree of freedom (DOF) spacecraft to solve the problem. For the spacecraft closed-loop system under these optimization-free methods, the derivative of the state is always opposite to the direction of the state, then the system trajectory will tend to a straight line, and the redundant motion components in the direction orthogonal to the state are significantly suppressed (performance improvement), and the excess energy loss is reduced considerably. Conversely, redundant motion components will cause excess transient motion and more energy consumption. Furthermore, this article proposes the linear combination theorem of the ratio persistence property, which further enriches the theoretical tools for the time-synchronized control method. The rigorous theoretical proof and comparative simulation verify the rationality, effectiveness, and advantages of the controllers proposed.

Sailing at the brink – The no-limits of near-/now-term-technology solar sails and SEP spacecraft in (multiple) NEO rendezvous

Near-Earth object (NEO) in-situ exploration can provide invaluable information for science, possible future deflection actions and resource utilisation. This is only possible with space missions which approach the asteroid from its vicinity, i.e. rendezvous. This paper explores the use of solar sailing as means of propulsion for NEO rendezvous missions. Given the current state of sail technology, we search for multiple rendezvous missions of up to ten years and characteristic acceleration of up to 0.10 mm/s2. Using a tree-search technique and subsequent trajectory optimisation, we find numerous options of up to three NEO encounters in the launch window 2019–2027. In addition, we explore steerable and throttleable low-thrust (e.g. solar-electric) rendezvous to a particular group of NEOs, the Taurid swarm. We show that an acceleration of 0.23 mm/s2 would suffice for a rendezvous in approximately 2000 days, while shorter transfers are available as the acceleration increases. Finally, we show low-thrust options (0.3 mm/s2) to the fictitious asteroid 2019 PDC, as part of an asteroid deflection exercise.

Size matters - The shell lander concept for exploring medium-size airless bodies

Once addressed as a side topic in planetary exploration, the investigation of small solar system bodies has now become one of the corner stones in the international science community in order to study the formation of the solar system and the evolution of life within. For rendezvous spacecraft, small carry-on landers have proven to be valuable assets, and to have a positive impact on the overall mission cost, by avoiding additional complexity of the main satellite and transferring the risk of close surface maneuvers entirely or at least to some extend to an independent deployable system. However, carry-on landers have been designed currently to land on very small bodies only, but medium-size class objects between diameters of 10–50 km are of great interest as well. In this paper we classify carry-on landers with respect to their touchdown and operational strategy, evaluate the constraints of ballistic deployments for different target bodies as well as identify the niche for using simple honeycomb impact dampers compared to optional retro-propulsion systems. Further, we introduce the system design of an attitude-stabilized Shell Lander using a generic instrument carrier attached to a single ejectable crash-pad with stabilizing capability to protect the instrument carrier from structural damage, limit internal shock loads for sensitive payloads as well as reduce the amount of bounces on the surface. Finally, we present a mission architecture for a reference case to the Martian moon Phobos as well as provide a proof of concept based on laboratory impact tests and a multi-body simulation to analyze touchdown dynamics including terrain interaction, shell-shedding and bouncing.

Deflection of fictitious asteroid 2017 PDC: Ion beam vs. kinetic impactor

Mission scenarios for the deflection of fictitious asteroid 2017 PDC are investigated. Two deflection options, kinetic impactor (KI) and ion beam shepherd (IBS), are studied and compared on the basis of deflection performance, safety, as well as mission schedule and political aspects. Firstly, we propose the launch of a medium-size rendevous spacecraft equipped with at least two ionic thrusters that can serve as propulsion means for the interplanetary trajectory up to rendezvous with the asteroid and as contactless actuators for a possible follow-up deflection mission. The asteroid, whose uncertainty ellipsoid is initially too large to establish whether (and how) it should be deflected, is reached by the rendezvous spacecraft after a low-thrust interplanetary trajectory of reasonable duration. Following rendezvous the spacecraft is placed in the vicinity of the asteroid to estimate its mass, study its structure and composition and, crucially, reduce its uncertainty ellipsoid by ground tracking to confirm or rule out an impact. Assuming that an impact is confirmed two main deflection scenarios are considered based on the actual asteroid size. Ion beam deflection is considered with the possibility of full deflection (the asteroid misses the Earth by a safe margin) or impact location adjustment (the impact footprint is diplaced to the nearest unpopulated region) depending on the asteroid size and the predicted impact location. The launch of a kinetic impactor mission is also considered with the employment of the rendezvous spacecraft to measure the deflection outcome and possibly to refine the deflection in case it is needed. The deflection performance of the two methods is compared.

Single photon laser altimeter data processing, analysis and experimental validation

Spaceborne laser altimeters are common instruments on-board the rendezvous spacecraft. This manuscript deals with the altimeters using a single photon approach, which belongs to the family of time-of-flight range measurements. Moreover, the single photon receiver part of the altimeter may be utilized as an Earth-to-spacecraft link enabling one-way ranging, time transfer and data transfer. The single photon altimeters evaluate actual altitude through the repetitive detections of single photons of the reflected laser pulses. We propose the single photon altimeter signal processing and data mining algorithm based on the Poisson statistic filter (histogram method) and the modified Kalman filter, providing all common altimetry products (altitude, slope, background photon flux and albedo). The Kalman filter is extended for the background noise filtering, the varying slope adaptation and the non-causal extension for an abrupt slope change. Moreover, the algorithm partially removes the major drawback of a single photon altitude reading, namely that the photon detection measurement statistics must be gathered. The developed algorithm deduces the actual altitude on the basis of a single photon detection; thus, being optimal in the sense that each detected signal photon carrying altitude information is tracked and no altitude information is lost. The algorithm was tested on the simulated datasets and partially cross-probed with the experimental data collected using the developed single photon altimeter breadboard based on the microchip laser with the pulse energy on the order of microjoule and the repetition rate of several kilohertz. We demonstrated that such an altimeter configuration may be utilized for landing or hovering a small body (asteroid, comet).

Target selection for a hypervelocity asteroid intercept vehicle flight validation mission

Asteroids and comets have collided with the Earth in the past and will do so again in the future. Throughout Earth׳s history these collisions have played a significant role in shaping Earth׳s biological and geological histories. The planetary defense community has been examining a variety of options for mitigating the impact threat of asteroids and comets that approach or cross Earth׳s orbit, known as near-Earth objects (NEOs). This paper discusses the preliminary study results of selecting small (100-m class) NEO targets and mission analysis and design trade-offs for validating the effectiveness of a Hypervelocity Asteroid Intercept Vehicle (HAIV) concept, currently being investigated for a NIAC (NASA Advanced Innovative Concepts) Phase 2 study. In particular this paper will focus on the mission analysis and design for single spacecraft direct impact trajectories, as well as several mission types that enable a secondary rendezvous spacecraft to observe the HAIV impact and evaluate it׳s effectiveness.

Accurate and Stable Control of Shenzhou Spacecraft in Rendezvous and Docking

Rendezvous and docking is a key operational technology for human beings to explore and use space. In November 2011 and June 2012, China achieved successful automatic and manual rendezvous and docking between Shenzhou-8, Shenzhou-9 and Tiangong-1, respectively. The control difficulty of these rendezvous and docking lies in flexible vibration of solar panels, cross-coupling between attitude and position control, and serious disturbances caused by thrusters’ plume. To solve these problems, an intelligent adaptive control method is proposed based on a characteristic model based intelligent adaptive control theory. Combined with a proper thruster control allocation algorithm, the on-orbit application of this control method has gained a complete success. This paper will concentrate on the basic principle, design method, theoretical analysis and on-orbit application of this intelligent adaptive control method. And the application of this method in future rendezvous and docking tasks and other spacecraft control projects will be discussed.

Multidisciplinary Optimization of Autonomous Rendezvous Spacecraft Using Updated Analytical Target Cascading Method

For the multidisciplinary design optimization (MDO) question of autonomous rendezvous spacecraft, first, the analysis model and coupling relations of payload, propulsion and structure discipline are discussed; then the updated analytical target cascading (UATC) method is introduced and compared with the widely used collaborative optimization (CO). Results prove that the UATC method requires 54.8% fewer average subspace iterations than the CO and is more efficient for practical engineering MDO problem. Finally, based on the UATC method, a MDO problem of autonomous rendezvous spacecraft is solved and gets reasonable and effective results. The process proves the effectiveness of UATC method solving spacecraft MDO problem.

Lorentz Accelerations in the Earth Flyby Anomaly

DOI: 10.2514/1.47413 Mission engineers have detected an unexpected anomaly on six spacecraft during low-altitude gravity-assist maneuvers around Earth. This Earth flyby anomaly involves an acceleration that, to date, researchers cannot account for based on known forces or errors in measurement or modeling. This paper evaluates Lorentz accelerationsassociatedwithspacecraftelectrostaticchargingasapossibleexplanationfortheEarth flybyanomaly. This analysis does not explicitly address plasma physics but, instead, bases its conclusions on fundamental six-state flight dynamics. The analysis focuses on the Near Earth Asteroid Rendezvous spacecraft, because it exhibited the largest anomalous error with the smallest estimated residuals. The analysis takes the form of a boundary-value probleminwhichvector-disturbance timehistoriesarefoundnumerically throughnonlinearoptimizationmethods. The analysis identifies the unknown, but required, acceleration based on a model of the Lorentz-force interaction. The algorithm cannot converge on a solution that fully reproduces the anomalous error in all six orbital states. It is unlikely, based on this analysis, that Lorentz forces cause the flyby anomaly.

Deflection of Earth-Crossing Asteroids/Comets Using Rendezvous Spacecraft and Laser Ablation

Space missions are presented to deflect four fictitious Earth impacting objects by using an advanced magnetoplasma spacecraft designed to deliver a laser ablation payload. The laser energy required to provide sufficient change in velocity is estimated for one long-period comet and three asteroids, and an optimal rendezvous trajectory is provided for each threat scenario. The end-to-end simulations provide an overall concept for solving the deflection problem. These analyses illustrate that the optimal deflection strategy is highly dependent on the size and the orbital elements of the impacting object, as well as the amount of warning time. A rendezvous spacecraft with a multi-megawatt laser ablation payload could be available by the year 2050. This approach could provide a capable and robust orbit modification approach for altering the orbits of Earthcrossing objects with relatively small size or long warning time. Significant technological advances, multiple spacecraft, or alternative deflection techniques are required for a feasible scenario to protect the Earth from an impacting celestial body with large size and short warning time.

Colour variability of asteroids in the Sloan Digital Sky Survey Moving Object Catalog

We report a detection of statistically significant colour variations for a sample of 7531 multiply observed asteroids that are listed in the Sloan Digital Sky Survey Moving Object Catalog. Using five-band photometric observations accurate to ∼0.02 mag, we detect colour variations in the range 0.06-0.11 mag (rms). These variations appear to be uncorrelated with the physical characteristics of the asteroids, such as diameter (in the probed 1-10 km range), taxonomic class and family membership. Despite this lack of correlation, which implies a random nature for the cause of colour variability, a suite of tests suggest that the detected variations are not instrumental effects. In particular, the observed colour variations are incompatible with photometric errors, and, for objects observed at least four times, the colour change in the first pair of observations is correlated with the colour change in the second pair. These facts strongly suggest that the observed effect is real, and also indicate that colour variations are larger for some asteroids than for others. The detected colour variations can be explained as being due to inhomogeneous albedo distribution over an asteroid's surface. Although relatively small, these variations suggest that fairly large patches with different colour than their surroundings exist on a significant fraction of asteroids. This conclusion is in agreement with spatially resolved colour images of several large asteroids obtained by the Near Earth Asteroid Rendezvous (NEAR) spacecraft and the Hubble Space Telescope (HST).

Depletion of sulfur on the surface of asteroids and the moon

Abstract— Data from the X‐ray and γ‐ray spectrometers onboard the Near Earth Asteroid Rendezvous (NEAR) spacecraft were used to constrain the chemical and mineralogical composition of asteroid 433 Eros (McCoy et al. 2001). The bulk composition appears to be consistent with that of L to H chondrites (Nittler et al. 2001). However, there appeared to be a marked depletion relative to ordinary chondritic composition in the S/Si ratio (0.014 ± 0.017). We investigate space weathering mechanisms to determine the extent to which sulfur can be preferentially lost from the surface regolith. The two processes considered are impact vaporization by the interplanetary meteoroid population and ion sputtering by the solar wind. Using impact data for Al projectiles onto enstatite, we find that the vaporization rate for troilite (FeS) is nine times as fast as that for the bulk of the regolith. If 20% of the iron is in the form of troilite, then the net vaporization rate, normalized to bulk composition, is 2.8 times faster for sulfur than for iron. Sputtering is equally efficient at removing sulfur as impact vaporization.

Applying successful near mission operations approaches and refining for contour mission operations

On February 17, 1996, the first NASA Discovery Class Mission to launch, the Near Earth Asteroid Rendezvous (NEAR) spacecraft, began its journey to the asteroid Eros. NEAR is the first planetary spacecraft to be designed and operated by the Johns Hopkins University Applied Physics Laboratory (JHU/APL). In July 2002, the comet nucleus tour (CONTOUR) spacecraft, the second planetary spacecraft to be built and operated at JHUAPL and the 6th in the series of NASA Discovery Class Missions, will be launched. Both NEAR and CONTOUR share ambitious “Faster, Better, Cheaper” goals. Furthermore, with both missions being developed and operated at the same institution, a unique opportunity exists to refine CONTOUR designs and operational practices based on 5 years of NEAR operational experience. This paper provides an overview of designs and operational practices implemented by JHU/APL to safely and effectively conduct the NEAR mission. This paper discusses how these will be applied to the CONTOUR mission and what improvements are planned. It also discusses the unique challenges CONTOUR possesses for operating a 4 year mission with widely varying operations activity levels at low cost.

Near-IR Reflectance Spectroscopy of 433 Eros from the NIS Instrument on the NEAR Mission: I. Low Phase Angle Observations

From February 13 to May 13, 2000, the near-infrared spectrometer (NIS) instrument on the Near Earth Asteroid Rendezvous (NEAR) spacecraft obtained more than 200,000 spatially resolved 800- to 2500-nm reflectance spectra of the S-type asteroid 433 Eros. An important subset of the spectra was obtained during a unique opportunity on February 13 and 14, when the NEAR spacecraft flew directly through the 0° phase angle point between Eros and the Sun just prior to the orbital insertion maneuver. This low phase flyby (LPF) dataset consists of ∼2000 spectra of the northern hemisphere of Eros, obtained from 1° to 47° phase angle and at spatial resolutions of between 6×12 km to 1.25×2.50 km per spectrum. The spectra were calibrated to radiance factor (I/F, where I=observed radiance and πF=solar input radiance) and then photometrically corrected to normal albedo. The average northern hemisphere spectrum of Eros is similar to the asteroid's unresolved telescopic spectrum and exhibits absorption features near 1000 nm (Band I) and 2000 nm (Band II) consistent with an orthopyroxene to orthopyroxene+olivine (opx+ol) mixing ratio of approximately 0.38±0.08. The ensemble of NIS LPF spectra falls primarily within the S(IV) to upper S(III) fields of the Gaffey et al. (1993) S-asteroid classification scheme and exhibits Band I and Band II properties similar to those of ordinary chondrite meteorites. While some small spatially coherent spectral variations have been detected, neither the opx/opx+ol) mixing ratio nor other spectral parameters vary spatially by more than ∼1σ across the entire northern hemisphere of the asteroid, suggesting a remarkable homogeneity of the composition and mineralogy of the uppermost regolith. Spectral mixture modeling suggests that the presence of glass and/or a reddening agent like nanophase iron, likely formed from exposure of the regolith to the space environment, is a component of the surface of Eros. Reddening and darkening components could also explain the dissimilarity in overall spectral slope and albedo between Eros and other S(IV) asteroids and ordinary chondrite meteorites. The largest (but still weak) spectral variations across the surface are seen in the depths of Band I and Band II, which are greatest in and around the largest craters and at the 0° longitude “nose” of the asteroid, and in the Band II/Band I area ratio between the large impact craters Psyche and Himeros. These subtle NIS spectral variations are usually associated with albedo and surface slope variations seen in NEAR imaging and topographic data and appear to be related to downslope movement of regolith materials.

Inflight Calibration of the NEAR Multispectral Imager: II. Results from Eros Approach and Orbit

During the Near-Earth Asteroid Rendezvous (NEAR) spacecraft's investigation of asteroid 433 Eros, inflight calibration measurements from the multispectral imager (MSI) have provided refined knowledge of the camera's radiometric performance, pointing, and light-scattering characteristics. Measurements while at Eros corroborate most earlier calibration results, although there appears to be a small, gradual change in instrument dark current and flat field due to effects of aging in the space environment. The most pronounced change in instrument behavior, however, is a dramatic increase in scattered light due to contaminants accumulated on the optics during unscheduled fuel usage in December 1998. Procedures to accurately quantify and to remediate the scattered light are described in a companion paper (Li et al. 2002, Icarus155, 00–00). Acquisition of Eros measurements has clarified the relative, filter-to-filter, radiometric performance of the MSI. Absolute radiometric calibration appears very well constrained from flight measurements, with an accuracy of ∼5%. Pointing relative to the spacecraft coordinate system can be determined from the temperature of the spacecraft deck with an accuracy of ∼1 pixel.

Result of Remote Pilot Rendezvous Experiment by ETS-VII.

Engineering Test Satellite-VII (ETS-VII) is the test satellite to demonstrate and verify rendezvous docking technology. After success in an autonomous rendezvous docking in the 1st and 2nd experiment flights in 1998, we performed remote pilot rendezvous experiment by ETS-VII in Oct. 1999. In the experiment, ETS-VII was controlled by a ground pilot via Tracking and Data Relay Satellite (TDRS). To overcome long time delay and poor information on thruster acceleration, the ground pilot predicted the changes of position and velocity after thruster firing, and controlled the Chaser satellite. In this paper, we present the result and evaluation of the remote pilot experiment. It could be shown that remote pilot was very useful to control rendezvous spacecraft with long time delay and/or with unknown control characteristics.

Calibration of Radiometric Data for Relativity and Solar Plasma During a Solar Conjunction

The round trip propagation time of a radio signal passing close to the Sun is affected by the charged particle environment of the solar plasma and the increased path length associated with the curvature of space predictedby general relativity. It has been difficult to separate estimates of the individual contributions to the signal delay. In January 1997, the Near Earth Asteroid Rendezvous (NEAR) spacecraft passed through a deep solar conjunction. For a month before and after conjunction, the spacecraft was pointed at the Sun and attitude operations were suspended. Since the NEAR spacecraft is equipped with two way X-band Doppler and range and the spacecraft attitude was favorable, a high precision spacecraft ephemeris was obtained. Data from the solar conjunction period of the NEAR mission is used to solve explicitly for the total electron content of the solar plasma along the signal path by using the signal delay in the range data to calibrate the signal advance in the Doppler data. The result is a precise estimate of the general relativity delay, and of the total electron content along the signal path, which can be used to improve models of the plasma emanating from the Sun. The general relativity parameter y is determined to less than 0.5 percent, which is competitive with the most accurate current verifications of general relativity.

Spectral analysis and compositing techniques for the Near Earth Asteroid Rendezvous (NEAR Shoemaker), X-ray and Gamma-Ray Spectrometers (XGRS)

An X-ray and Gamma-Ray Spectrometer (XGRS) is on board the Near Earth Asteroid Rendezvous (NEAR) spacecraft to determine the elemental composition of the surface of the asteroid 433 Eros. The Eros asteroid is highly oblate and irregular in shape. As a result, analysis methodologies are in many ways a divergence from comparable techniques. Complex temporal, spatial and instrument performance relationships must be accounted for during the analysis process. Field of view and asteroid surface geometry measurements must be modeled and then combined with real measurements of solar, spectral and instrument calibration information to derive scientific results. NEAR is currently orbiting 433 Eros and is in the initial phases of its primary data integration and mapping phases. Initial results have been obtained and bulk chemistry assessments have been obtained through specialized background assessment and data reduction techniques.

In-Flight Calibration of the Near Earth Asteroid Rendezvous Mission's Near Infrared Spectrometer: I. Initial Calibrations

The Near Infrared Spectrometer (NIS) instrument on the Near Earth Asteroid Rendezvous (NEAR) spacecraft performed a comprehensive series of in-flight tests to validate its preflight radiometric characteristics and to characterize instrument stability, pointing, and co-alignment with other instruments under flight conditions. The results of these tests form the basis of the NIS data reduction and calibration procedure and will support the ability of NIS to achieve its science goal of spectrally mapping NEAR's target asteroid, 433 Eros. Key results include the following: (i) Radiometric calibration of NIS has been confirmed to be accurate to within 4–10%, based on NIS measurements of the Earth and Moon and comparisons to radiances derived from other (NEAR and non-NEAR) optical instruments; (ii) The radiometric response has been demonstrated to be stable on the scale of months; (iii) Gradual, expected detector sensitivity decay of 1–3% over 2 years of operations in space has been characterized; (iv) Temperature dependencies of detector response are identified and characterized; (v) The co-alignment of NIS with the Multi-Spectral Imager (MSI) and with respect to other NEAR instruments has been determined; (vi) A calibration program (NISCAL) that applies appropriate functions and algorithms to convert raw instrument data to analyzable spectra has been developed; (vii) Remaining unresolved instrument calibration and characterization issues have been identified, to be resolved with the help of approach and orbital observations from the main mission.