How to Enter, Fly In, and Exit the A-Train Constellation (original) (raw)
Related papers
An Initial Analysis of the Stationkeeping Tradespace for Constellations
2019 IEEE Aerospace Conference
This paper presents an Orbit Maintenance Module (OMM) for Tradespace Analysis Tool for Constellations (TAT-C), a software package to explore a wide range of tradespaces to design constellations for Earth observation. As the tool is primarily meant for rapid pre-Phase A analysis, it has to be able to estimate trade-offs and overall performance parameters with simplified models on a personal computer in a reasonable time frame. The OMM estimates the secular drift of relative orbital elements between pairs of satellites due to the gravitational 'J2' effects and the drift of altitude due to the atmospheric drag, and computes maneuvers to correct them. The J2 is a predominant term in the gravitational zonal harmonics which, primarily, affects the argument of perigee and the mean anomaly. We estimate the drift of these elements between pairs of satellites using a fourthorder polynomial, which is trained using machine learning and which depends on the inclination, altitude and initial angular separation in true anomaly and right ascension of the ascending node. An analytical model is used to predict the deorbiting rate depending on the initial altitude, the solar cycle, the satellite's mass, drag coefficient and area. In order to maintain the required topology of a constellation, the drift of orbital elements is compensated using emulated orbital maneuvers, when satellites breach a user-defined threshold percentage of their nominal values. We assume simple orbital maneuvers (i.e., orbit phasing and Hohmann transfer) to determine the required delta-V, propellant consumption and frequency of maneuvers. These parameters are provided as outputs of the TAT-C's OMM, which advises the user on trade-offs between performance and maintenance overhead of all enumerated constellation architectures. The maneuver metrics can be used to determine various dependent metrics, such as time available for observations, impact on total satellite mass, and mission cost.
NASA’s A-train satellite constellation
2015
Within the framework of AeroKval project, the use of satellite observations of tropospheric trace gases and aerosols was initiated, and a significant experience in this area has been gained since the start of the project in 2006. So far, we have focused on making use of two specific satellite products, namely Aerosol Optical Depth (AOD) at 500 nm from MODIS instrument onboard Aqua and Terra satellites and NO2 tropospheric column from GOME onboard of ERS-2. In accordance with the plans in AeroKval-2009 (WP3), a strategic review of other satellite products has been carried out and is presented in this Note. The usefulness of satellite measurements for qualitative evaluation of chemical transport models, for air quality related applications, including data assimilation in chemical weather forecast, depends on the inaccuracy of the data. We have based our judgement of satellite products (i.e. data availability, coverage, quality etc.), on a large volume of relevant publications, such as peer-reviewed papers, conference/meeting proceedings and conclusions, product documentation, validation reports etc. NASA's A-train satellite constellation currently consists of four active satellites. Actve: o Aqua, lead spacecraft in formation, launched on May 4, 2002. o CloudSat, runs 2 minutes and 30 seconds behind Aqua, launched with CALIPSO on April 28, 2006. o CALIPSO, follows CloudSat by no more than 15 seconds, launched on April 28, 2006. o Aura, lags Aqua by 15 minutes, crossing the equator 8 minutes behind due to different orbital track to allow for synergy with Aqua, launched on July 15, 2004. Past: o PARASOL, launched on December 18, 2004; moved to other (lower) orbit on 2 December 2009. Failed: o OCO, destroyed by a launch vehicle failure on February 24, 2009, and would have preceded Aqua by 15 minutes. Future: o Glory, due for launch not earlier than in late 2010, will fly between CALIPSO and Aura (closer to the first one).
Large Constellations of Small Satellites: A Survey of Near Future Challenges and Missions
Aerospace
Constellations of satellites are being proposed in large numbers; most of them are expected to be in orbit within the next decade. They will provide communication to unserved and underserved communities, enable global monitoring of Earth and enhance space observation. Mostly enabled by technology miniaturization, satellite constellations require a coordinated effort to face the technological limits in spacecraft operations and space traffic. At the moment in fact, no cost-effective infrastructure is available to withstand coordinated flight of large fleets of satellites. In order for large constellations to be sustainable, there is the need to efficiently integrate and use them in the current space framework. This review paper provides an overview of the available experience in constellation operations and statistical trends about upcoming constellations at the moment of writing. It highlights also the tools most often proposed in the analyzed works to overcome constellation managem...
Orbit constellation safety on the PRISMA in-orbit formation flying testbed
2008
PRISMA will demonstrate Guidance, Navigation, and Control strategies for advanced autonomous formation flying. The Swedish Space Corporation (SSC) is the prime contractor for the project which is funded by the Swedish National Space Board (SNSB). The mission consists of two spacecraft: MAIN and TARGET. The MAIN satellite has full orbit control capability while TARGET is attitude controlled only. PRISMA will perform a series of GNC related formation flying experiments. SSC is responsible for three main sets of experiments: Autonomous Formation Flying, Proximity Operations and Final Approach/Recede Manoeuvres, and Autonomous Rendezvous. Many formation flying scenarios, including experiments on PRISMA, require the use of orbits that are not naturally safe. This includes trajectories that, if nominal orbit control were lost, could result in collision or formation evaporation -secular drift that could eventually cause the loss of relative navigation. This paper will focus on the relative...
The Techsat-21 Autonomous Sciencecraft Constellation Demonstration
2001
The Autonomous Sciencecraft Constellation flight demonstration (ASC) will fly onboard the Air Force’s TechSat-21 constellation (an unclassified mission scheduled for launch in 2004). ASC will use onboard science analysis, replanning, robust execution, modelbased estimation and control, and formation flying to radically increase science return by enabling intelligent downlink selection and autonomous retargeting. Demonstration of these capabilities in a flight environment will open up tremendous new opportunities in planetary science, space physics, and earth science that would be unreachable without this technology.
New Scientific Capabilities Enabled by Autonomous Constellations of Smallsats
2007
Several scientific missions exist that require hundreds to thousands of near-simultaneous measurements at widely distributed locations within the earth's magnetosphere. The current paradigm of individually building, designing, launching, and operating satellites is not capable of performing these missions. An autonomous constellation of smallsats and nanosats, developed as an ad hoc network of distributed wireless sensors will enable real-time, distributed, multi-point sensing of relevant phenomena. A low-cost and mass-producible solution to support this new class of space missions has been designed [1] and this paper addresses the significant system issues driven by this revolutionary technology. The constellation uses smallsats in the ~ 100 kg class as communication and computation nodes and multiple ~5 kg nanosats as distributed sensors to continuously measure plasma parameters in the ionosphere as part of a global space weather monitoring system. The constellation is comprised of separate orbital rings that consist of one or two nodes and between ten and fifty nanosats. Each of the nanosats is a distributed sensor and routing device that generates data messages and routs neighboring data to the nodes. The nodes maintain both an instantaneous data map of the entire orbit distribution of sensors and a time history of all measurements. NOMENCLATURE Distributed sensor satellite = DSsat = A single adhoc sensor node. Communication & Computation Node satellite = CCsat = A single hub satellite for one orbit ring in the network. Ad-Hoc Network = A self-configuring network of mobile routers. Platform Design = A design that can be easily modified for different missions.
The Skybridge Constellation Design
Space Technology Proceedings, 1998
The SkyBridge space segment, based upon Low Earth Orbit satellites, had to face a challenge: though using the same frequency band as various geostationary systems in order to profit by wellproven and cost-efficient techniques-i.e. Ku Band-, SkyBridge satellites must not in any way interfere with geostationary satellites. This "frequency sharing constraint" forces SkyBridge satellites to stop emitting (resp. receiving) towards (resp. from) any portion of the ground as soon as they are seen in alignment with the geostationary orbit from the point of view of this earth portion. The paper focuses on how the coverage requirements, coupled with frequency sharing constraint, has led to a new original concept of satellite constellation design: in this concept, orbital planes are grouped by pairs, and within "doubleplanes", satellites are also grouped by pairs. Thus, the whole 64 satellite constellation is in fact subdivided into two 32 satellite sub-constellations, and relative phasing between the two subconstellations has been numerically optimized to provide the best coverage performance.
Design of Constellations for Earth Observation with Intersatellite Links
Journal of Guidance Control and Dynamics, 2017
Satellite constellations are used for navigation purposes since long. Connecting the satellites in a constellation by intersatellite links (ISLs) offers a full range of new possibilities. Ranging and time synchronization information can be exchanged between the satellites to improve the in orbit SC positioning knowledge. Besides ranging and time synchronization, ISLs can be used for service channel purposes or to distribute SW updates for the spacecrafts in a short period of time. ISLs improve the navigation constellations autonomy properties being less vulnerable to ground station unavailabilities. For ISLs, radio frequency (RF) and optical technologies have been investigated. Due to the shorter wavelength, a better ranging resolution can be achieved with optical than with RF ISL solutions. Optical ISLs (OISLs) offer a very attractive solution for intersatellite links in terms of size, weight and power while providing multi gigabit per second data rate capabilities. In addition, optical communication links offer high operational security and immunity to interference sources while benefitting from a non-regulated optical frequency spectrum. For those reasons, optical intersatellite links for navigation constellations have been investigated in several studies supported by DLR and ESA. TESAT with partners have investigated the benefit of OISLs for navigation systems and on the Galileo OISL Terminal design. In this paper, the results of these studies will be presented. Various OISL connection schemes in a navigation constellation are compared. The key design parameters of a Laser Communication Terminal for navigation systems will be given. Furthermore, the results of a lab demonstration showing the parallel distribution of ranging and communication data will be summarized. The focus of the investigation is on the Galileo navigation constellation.
2021
The high number of objects in the LEO is a risk that collisions between sub-orbital or escape velocity objects with an orbiting object of satellites occur when two satellites collide while orbiting the earth. One of the approaches to avoid collisions is a robotic configuration of satellite constellations. Satellite constellations should not be confused with satellite clusters, which are groups of satellites moving in close proximity to each other in nearly identical orbits; nor with satellite series or satellite programs, which are generations of satellites launched successively; nor with satellite fleets, which are groups of satellites from the same manufacturer or operator that operate an independent system. CfEOS constellations designed for geospatial applications and Earth observation. Unlike a single satellite, a constellation can provide permanent global or near-global coverage anywhere on Earth. CfEOS constellations are configured in sets of complementary orbital planes and c...