OrbitalHub

Credits: KuoShen Choong

This year, the Kalman filter, an essential part of the development of space technology, has its 50th anniversary. To quote from the announcement of the 2008 Charles Stark Draper Prize, the Kalman filter is an “optimal digital technique that is pervasively used to control a vast array of consumer, health, commercial, and defense products.”

In order to understand what a Kalman filter is, we should remember that a water filter is used to remove impurities from water by passing them through strata of sand, charcoal, etc. The modern usage of the term filter though involves more abstract entities than fluids with suspended impurities. In the context of electrical engineering, we can think of a filter in the sense of signal processing.

More generally, and I promise I will try not to make it more complicated than this, a filter is used to estimate the state of a system (whatever we want the system to be) using measurements that are affected by errors. Are you aware of any measurements not affected by errors? Exactly! This is why filters are very useful.

The Kalman filter is able to produce estimates of the true values of the measurements by computing weighted averages of the predicted values and the measurements themselves. Believe it or not, the estimated values produced by the filter tend to be closer to the true values than the original measurements. Many extensions and generalizations of the Kalman filter have been developed. One of them is the unscented Kalman filter (can anyone guess why this variation of the filter is called unscented?).

The Kalman filter is named after Rudolf E. Kalman. Kalman first published his ideas on filtering in two papers in 1960 and 1961: Kalman, R.E., A New Approach to Linear Filtering and Prediction Problems, Journal of Basic Engineering, Trans. ASME, Series D, Vol. 82, No. 1, 1960, pp. 35-45, and Kalman, R.E., and Bucy, R.S., New Results in Linear Filtering and Prediction Theory, Journal of Basic Engineering, Trans. ASME, Series D, Vol. 83, No. 3, 1961, pp. 95-108. A downloadable version of the first paper can be found on Professor Greg Welch’s web page dedicated to The Seminal Kalman Filter Paper at The University of North Carolina at Chapel Hill. If anyone has a downloadable version of the second paper, please let me know. I would be happy to link to it.

As Kalman’s ideas on filtering were met with skepticism in the electrical engineering and systems engineering communities, he published his research results in mechanical engineering. One of the scientists who supported his ideas was Stanley F. Schmidt of NASA’s Ames Research Center. Kalman filters were employed by the control systems used in the Apollo program, and later in the Space Shuttle program.

Credits: Ryan K. Morris/National Science & Technology Medals Foundation

Rudolf Emil Kalman was born in Budapest, Hungary, on May 19, 1930. His father was an electrical engineer. Having decided to follow in his father’s footsteps, he emigrated to the United States and obtained a Bachelor Degree in 1953 and a Master’s Degree in 1954 from the Massachusetts Institute of Technology, and the D.Sci. Degree in 1957 from Columbia University, under the direction of Professor J.R. Ragazzini.

From 1957 to 1958 Kalman worked as a staff engineer at the IBM Research Laboratory in Poughkeepsie, New York. He worked as a research mathematician at the Research Institute for Advanced Study in Baltimore from 1958 until 1964. During this period of time, he made his innovative contributions to modern control theory. He became a professor at Stanford University, where he lectured between 1964 and 1971, and later a graduate research professor in the departments of mathematics, electrical engineering, and industrial and systems engineering at the University of Florida at Gainesville. While at the University of Florida, he established the Center for Mathematical Systems Theory (CMST). Since 1973, he also held the chair for Mathematical Systems Theory at the Swiss Federal Institute of Technology in Zurich.

Rudolf Kalman is the recipient of numerous awards. He was awarded the IEEE Medal of Honor in 1974, the IEEE Centennial Medal in 1984, the Inamori Foundation’s Kyoto Prize in High Technology in 1985, the Steele Prize of the American Mathematical Society in 1987, the Richard E. Bellman Control Heritage Award in 1997, and the Charles Stark Draper Prize of the National Academy of Engineering in 2008. Rudolf Kalman is also a foreign member of the Hungarian, French, and Russian Academies of Science and he is the holder of many honorary doctorates.

Rudolf Kalman had several Ph.D. students at each of the institutions where he was a faculty member. Among them, Edward W. Kamen (Julian T. Hightower Professor Emeritus at the Georgia Institute of Technology), Yves Rouchaleau (faculty member at the Ecole des Mines de Paris), Patrick Dewilde (member of the Institute for Advanced Study, TU München), and Yutaka Yamamoto (Professor in the Department of Applied Analysis and Complex Dynamical Systems at the Graduate School of Informatics of Kyoto University). The April 2010 issue of the IEEE Control Systems Magazine contains a series of essays written by the above mentioned.

A very good source of information about the Kalman filter is a website maintained by Greg Welch and Gary Bishop, faculty members of the Department of Computer Science at the University of North Carolina at Chapel Hill.

Credits: NASA

Les Johnson is the Deputy Manager for the Advanced Concepts Office at the George C. Marshall Space Flight Center in Huntsville, Alabama.

He recently took the time to answer a few questions for OrbitalHub readers.

Please note: Les Johnson wrote Paradise Regained as a private citizen and the views expressed herein are his own and unofficial.

DJ: You have an engineering background, hold patents, and have contributed to numerous technical publications. Traditionally, in light of the Victorian view of the engineer, who is the superhero taming nature, environmental issues and the impact of human civilization on the environment are not always areas of concern for people with an engineering background. How did you develop your interest in these areas?
Les Johnson: Before I earned my MS in physics, I earned a BA from a liberal arts college (Transylvania University in Lexington, KY). I am a firm believer in a well rounded education — college should provide an education, not just a vocation.
When I first became interested in space exploration, it was all about “going there” or “leaving here.” As I’ve experienced more of life (marriage, children, travel and working with many interesting people from all around the world) my views changed. The world changed. Billions of previously “invisible” people from all around the world are wanting to improve their quality of life and there simply are not enough resources here to sustain six billion people consuming even half as much as the average American. And we don’t have the right to say “we can have a good life but you can’t!” That would be immoral. It would also be immoral to degrade the quality of life of those in the developed world. My worldview doesn’t allow me to think that the quality of human life, all human lives, cannot be improved. My worldview, combined with recent technological advances (in many areas discussed in Paradise Regained), led me to the conclusion that it is more important for humanity to develop space for the benefit of the multitudes here on Earth rather than for the few who will leave the planet to explore the solar system and beyond.

DJ: In his book The High Frontier, Professor Gerard K. O’Neill of Princeton described space colonies located at the Lagrangian points in the Sun-Earth system. He also envisioned solar power stations, mining operations on the moon, and a roadmap for the human settlement of the Solar System. To what extent was the work of Gerard K. O’Neill an inspiration to you?
L.J.: O’Neill was a visionary. He, Von Braun, Clarke and others provided the vision for those of us who came later. I don’t consider myself to be a visionary but rather an implementer. I’ve spent my career at NASA advocating for the development of advanced technologies and their use in space missions. Most of those technologies were actually invented by others — my talent is making things happen.

DJ: Clearly solar power is an alternative to our current power energy sources and a solution for the future. Space solar power is not a new idea, but the technology had to catch up with the concept. Given the costs and the fact that governments lack the necessary funds due to financial difficulties, do you think such developments are still feasible?
L.J.: Can we afford NOT to develop space solar power? As I write, a leak from a single oil well in the Gulf of Mexico is going to cause economic and environmental damage estimated to be in excess of $9B and Iran is enriching uranium from its nuclear power reactors to make bombs. We could develop space solar power for far less than we are spending to maintain access to middle eastern oil, not to mention the money we are sending to countries who then use that money to fund terrorists. To put things into perspective, the United States budget this year totals $3.5 trillion dollars — that’s $3500 billion dollars. The NASA budget is $18 billion dollars. The budget for the Department of Energy is $26 billion. What about the other $3456 billion? We can afford to do the research. It just isn’t considered important enough by those that make budget decisions.
And there is no reason that the cost should be borne by taxpayers alone. Yes, government should probably foster the technologies required to make space solar power possible. Industry should then make the up-front investment to place the satellites in orbit. After all, they will make money for a long time after the satellites are in place and beaming clean power back down to the people of Earth.

DJ: The new NASA policies seem to put lunar exploration on hold and focus on more distant objectives like Mars or the asteroid belt. Why do you think the solar-powered mining facilities extracting the Helium-3 trapped in the lunar regolith have lost their appeal?
L.J.: Mining the Moon has never been an official NASA objective. Project Constellation, NASA’s name for the now-canceled plan to return astronauts to the Moon, was all about getting there for science and exploration. There was nothing in the plan that would have lead to using lunar resources like helium-3.
I believe the appeal is still strong among the public. When I speak about Paradise Regained, I discuss lunar mining — and how I’d rather mine the Moon for energy instead of the mountains of Kentucky or West Virginia. People understand this and they support it. They just don’t understand why we aren’t working to make it happen.

DJ: In the same context, do you think such a change of direction can be more beneficial for the long-term human exploration of our solar system?
L.J.: That depends. Today, people ask why we explore space and how space exploration has benefitted them personally. The answer to that question will be self-evident when we are getting clean energy from space, an improving quality of life, and a recovering environment resulting from the use of space resources. And with the development of space for the betterment of Earth will come lower launch costs and more frequent access to space — the necessary ingredients for a robust exploration of the solar system and beyond.

DJ: The new strategy for exploration of the Earth orbit and beyond relies heavily on private companies. Private companies are driven by profit and many of the environmental issues that we have to face in the present are a direct consequence of this fact. How do you think we can avoid a replay of this tragedy when we eventually move some of the industries from the surface of the Earth into space?
L.J.: There is a role for both government and private enterprise in space exploration. Government should fund basic and applied research to advance the technologies needed. Industry should use that technology to explore and then provide goods and services for consumers back home on Earth for a profit. Profit can be a good thing — if it is the result of innovation and effort.
One should note that the worst environmental offenses of the last one hundred years occurred in countries without private enterprise. The Soviet Union and its satellite countries were far less environmentally friendly than their free-world counterparts. Government control and socialism will not necessarily lead to a greener world.
Finally, the space environment is very different from the environment here on Earth. As far as we know, only the Earth has life. The environment that supports life is important and should be protected. If I have a choice between mining the Moon to provide fuel for clean and safe power on Earth versus mining the mountains of West Virginia, then the choice will be clear — mine where we are not harming any life whatsoever. We should preserve and protect this island of blue and green in an otherwise hostile and deadly universe — Earth.

Les Johnson is one of the authors of Paradise Regained – The Re-greening of Earth, a book which describes a scenario for the re-greening of planet Earth. The book explores the ways in which modern human civilization can use the resources of the solar system to benefit the Earth. The authors suggest that one way to minimize the impact we have as a species on the Earth’s ecosystem is to use extraterrestrial energy sources and move polluting industries from the Earth’s surface to space. A review of the book was published by Paul Gilster on Centauri Dreams.

Credits: ESA – P. Carril

In 2007, projections of sea level rise made by the Fourth Assessment Report of the Intergovernmental Panel on Climate Change were in the range of 28–43 cm by 2100, but there are new projections of the sea level rise that are in the order of 1.4 m.

While the trend is quite obvious, it is very important to be able to make accurate predictions.

Cryosat has been designed to measure the ice thickness on land and also at sea, and will provide enough data so that a precise rate of change of the ice thickness can be determined. A better understanding of how the volume of ice on Earth is changing will also be possible.

The declared primary goals of the CryoSat mission are to determine the regional trends in Arctic perennial sea-ice thickness and mass, and to determine the contribution that the Antarctic and Greenland ice sheets are making to mean global rise in sea level. Cryosat will also measure the variations in the thickness of Earth’s polar caps and glaciers. The spacecraft will be operational for a minimum of three years.

Credits: ESA/P. Carril

The spacecraft has a launch mass of 720 kg, of which 23 kg is the fuel required for orbital maneuvers and attitude corrections. The overall size of the spacecraft is 4.6 m x 2.34 m. Two solar panels are attached to the spacecraft’s body and provide a maximum of 800 W of power. As the CryoSat-2 orbit is not Sun-synchronous, providing enough power to the scientific payload has been a considerable challenge.

The operational orbit will be a 717 km non Sun-synchronous orbit with a 92 degree inclination.

The primary payload of the CryoSat-2 spacecraft is the SAR/Interferometric Radar Altimeter (SIRAL). In order to have the position of the spacecraft accurately tracked, a radio receiver called Doppler Orbit and Radio Positioning Integration by Satellite (DORIS) and a laser retro-reflector are part of the payload as well. A global network of laser ranging stations (the International Laser Ranging Service or ILRS for short) will support the mission. Three star-trackers will ensure a proper orientation of the spacecraft.

Using the Synthetic Aperture technique, CryoSat-2 measurements taken by SIRAL will have a 250 m resolution in the along-track direction. The instrument is designed to operate in three measurement modes: Low Resolution Mode (LRM) mostly over the oceans, Synthetic Aperture Radar (SAR) mode over sea-ice areas, and SAR Interferometric (SARIn) mode over steeply sloping ice-sheet margins, small ice caps, and mountain glaciers.

Credits: ESA – AOES Medialab

CryoSat-2 will be placed in orbit by a Dnepr launch vehicle. With a lift-off mass of 211 tons, Dnepr is 34 m long and 3 m in diameter, and has three stages that use hypergolic liquid propellants (N₂O₄ nitrogen peroxide and UDMH unsymmetrical dimethylhydrazine). In addition, there are Dnepr configurations with a third and a fourth stage for missions that require more energy. The launch vehicle is based on an ICMB designated as SS-18 Satan by NATO. The development and commercial operation of the Dnepr Space Launch System is managed by the International Space Company (ISC) Kosmotras. Dnepr can lift 4,500 kg to low Earth orbit (LEO) or 2,300 kg to a 98 degree Sun-synchronous orbit. Among other satellites launched by Dnepr are Demeter, Genesis I, Genesis II, and THEOS. Dnepr, carrying Cryosat-2, will lift off from Baikonur Cosmodrome in Kazakhstan.

The Rockot launch vehicle that attempted the orbiting of the first CryoSat mission, on October 8, 2005, failed to reach orbit. Due to faults in the onboard software, the second stage engine of the launcher did not shut down. The mission was terminated when the launch vehicle exceeded the flight envelope limit. The Rockot second stage/Breeze-KM/CryoSat stack crashed somewhere in the Arctic Ocean.

You can find more information about Cryosat-2 on ESA’s dedicated website. The Cryosat-2 mission EADS team also has a blog on EADS Astrium website. Check out the latest updates from Baikonur brought to you by Klaus Jäger (Astrium Spacecraft Launch Manager) and Edmund Paul (Astrium Spacecraft Operations Manager). A presentation of the SIRAL-2 instrument is available on Thales Group’s website.

Credits: NASA/Goddard Space Flight Center Scientific Visualization Studio

Predictions of space weather are important as the effects of magnetic storms can be very significant: disruptions in radio communications, radiation hazards to astronauts in LEO, and power lines surges, just to name a few. The goal of NASA’s Living With a Star (LWS) Program is to understand the changing Sun and its effects on the Solar System. The Solar Dynamics Observatory (SDO) is one of NASA’s LWS missions.

SDO will take measurements of the solar activity. There are seven science questions SDO will try to answer. Among them, what is the mechanism that drives the cycles of solar activity? How do the EUV variations relate to the magnetic activity of the Sun? Is it possible to make predictions regarding the space weather and climate? The last question, if answered, will make choosing the launch windows for future interplanetary manned missions an easier task.

The spacecraft is 2.2 x 2.2 x 4.5 m and 3-axis stabilized. At launch, it has a mass of 3200 kg (270 kg the payload and 1400 kg the fuel). The solar panels are 6.5 m across, cover 6.6 m², and produce up to 1540 W of power.

Credits: NASA

SDO carries three instruments: the Atmospheric Imaging Assembly (AIA), EUV Variability Experiment (EVE), and the Helioseismic and Magnetic Imager (HMI). The instruments will take measurements that will reveal at a very high rate the variations of the Sun.

The HMI was developed at Stanford University and it will extend the SOHO/MDI instrument. The HMI will help to study the origin of variability and the various components of the magnetic activity of the Sun. The measurements aim at understanding the origin and evolution of sunspots, sources and drivers of solar activity and disturbances, connections between the internal processes and the dynamics of the corona and the heliosphere.

You can find more information about the instrument on the HMI page on Stanford University’s web site.

The AIA will capture images of the solar atmosphere in ten wavelengths every ten seconds. The data collected by the instrument will improve the understanding of the activity in the solar atmosphere. The instrument was developed by Lockheed Martin.

EVE was developed at University of Colorado at Boulder. EVE will measure the solar extreme ultraviolet irradiance.

The SDO will launch aboard an Atlas V launch vehicle from SLC 41 at Cape Canaveral. SDO will operate on a geosynchronous orbit, which will allow continuous observations of the Sun. The orbit will also allow a continuous contact with a single dedicated ground station. The high data acquisition rate required such a mission profile, as a large on-board storage system would add to the overall complexity of the system.

You can find more information about SDO on NASA’s website.

Credits: ESA – P.Carril

The European Union’s Global Monitoring for Environment and Security (GMES) initiative was born as the result of a growing need for accurate and accessible information about the environment, the effects of climate change, and civil security. GMES uses as its main information feed the data collected by satellites developed by ESA. Data is also collected by instruments carried by aircraft, floating in the ocean, or located on the ground.

GMES provides services that can be grouped into five main categories: land management, marine environment, atmosphere, aid emergency response, and security.

There are five Sentinel missions designed as components of the GMES initiative. These missions will complement the national initiatives of the EU members involved. The missions will collect data for land and ocean monitoring, and atmospheric composition monitoring, making use of all-weather radar and optical imaging. Each of the Sentinel missions is based on a constellation of two satellites.

Sentinel-1 is an all-weather radar-imaging mission. The satellites will have polar orbits and collect data for the GMES land and ocean services. The first satellite is scheduled for launch in 2012. Sentinel-1 will ensure the continuity of Synthetic Aperture Radar (SAR) applications, taking over from systems carried by ERS-1, ERS-2, Envisat, and Radarsat. Sentinel-1 satellites will be carried to orbit by Soyuz launch vehicles lifting off from Kourou.

Sentinel-2 will provide high-resolution multi-spectral imagery of vegetation, soil, and water, and will cover inland waterways and coastal areas. Sentinel-2 is designed for the data continuity of missions like Landsat or SPOT (Satellite Pour l’Observation de la Terre). Each satellite will carry a Multi-Spectral Imager (MSI) that can ‘see’ in thirteen spectral bands spanning from the visible and near infrared (VNIR) to the shortwave infrared (SWIR). The first Sentinel-2 is planned to launch in 2013. Vega will provide launch services for Sentinel-2 missions.

Credits: ESA – P.Carril

Sentinel-3 will determine parameters such as sea-surface topography and sea and land surface temperature. It will also determine ocean and land colour with high accuracy. The first Sentinel-3 satellite is expected to reach orbit in 2013. The spacecraft bus has a three-meter accuracy real-time orbit determination capability based on GPS and Kalman filtering.

Sentinel-4 is devoted to atmospheric monitoring and it will consist of payloads carried by Meteosat Third Generation (MTG) satellites that are planned to launch in 2017 and 2024. Sentinel-5 will be used for atmospheric monitoring as well. The payload will be carried by a post-EUMETSAT Polar System (EPS) spacecraft, planned to launch in 2020. A Sentinel-5 precursor will ensure that no data gap will exist between the Envisat missions and Sentinel-5.

You can find out more about the GMES initiative and the Sentinel missions on a dedicated page on ESA’s website.

Credits: The British Interplanetary Society

Daedalus was a British Interplanetary Society (BIS) project conducted in the 1970’s. The project aimed to design an interstellar probe capable of flying to the Barnard’s star. The Daedalus design was a 54,000 ton two-stage vehicle powered by a D/He3 fusion engine, which could reach a speed of 10,000 km/s. It seems that the motivation behind the Daedalus project was the Fermi paradox.

Among the stated guidelines of the Daedalus project were the use of current or near-future technology and that the spacecraft must reach its destination within a human lifetime. There were interesting aspects to be considered during the design phase, such as infrastructure, propulsion, supporting technologies, and choice of targets.

Icarus, a new theoretical study of a mission to another star, builds on the solid base of the Daedalus project. Icarus aims to crystallize the design for an interstellar probe. Declared goals of the project include generating greater interest for interstellar precursor missions, and motivating a new generation of scientists to design interstellar space missions.

You can find more information about Project Icarus and the team behind the design efforts on the Project Icarus website.