OrbitalHub

Credits: NASA

ARES (or the Aerial Regional-scale Environment Survey) is an autonomous powered airplane. ARES will bridge the gap between remote sensing and surface exploration on Mars.

This new class of science will allow magnetic surveys with an improved resolution, geologic diversity coverage, and in-situ atmospheric science.

ARES method of deployment is unique because the robotic aircraft has to travel to Mars folded inside a protective shell. After the atmospheric entry and the parachute deployment, the heat shield that protects the aircraft during entry is released. Once the heat shield is out of the way, the folded aircraft leaves the protective shell. The unfolded tail will stabilize the tumbling aircraft. Finally, the wings will unfold and the aircraft will pull up from the dive.

It is needless to say that reliability is essential. All the mechanical systems of the aircraft that are involved in this maneuver must perform without any flaws, and that has to happen after spending six to eight months in vacuum at (more than) freezing temperatures. It is hard to imagine that ARES would be able to fly with a folded wing.

Credits: NASA

The ARES design is the result of five years of extensive analysis and testing. Testing has included wind tunnel tests, ejection tests, and flight tests. In order to simulate the Mars environment, the flight tests had to be performed at certain Mach and Reynolds numbers. A 50% scale prototype was released from a high-altitude research balloon. The robust design that resulted will handle the uncertainties in the Mars environment.

ARES could be selected as the next Mars Scout Mission. For more details about ARES you can visit NASA’s website. ARES Principal Investigator, Dr. Joel S. Levine, presented ARES at a TEDxNASA event. If you want to build your own paper-made scale model of the ARES Mars Airplane, you can find the model here.

Credits: NASA

In a nutshell, it is really tough! The higher you go, more bad things can happen to you… the increasingly rarefied air, freezing temperatures, ionized atoms, radiation, and space debris make life challenging. So, besides thinking of how to place spacecraft in orbit, engineers must consider all of the factors mentioned above (and much more) when designing a spacecraft.

The space environment (the vacuum, the radiation, the space debris, etc.) definitely poses big challenges to spacecraft design engineers. From 1971 to 1989, more than 2,700 spacecraft anomalies related to interactions with the space environment were recorded. These interactions with the space environment are called space environment effects and the changes in the space environment define what is called the space weather. Believe it or not, there are dedicated programs aimed at developing the ability to predict these changes in the same way the weather forecasting does for terrestrial weather. The Space Weather program was formed in the mid-1990s by the National Science Foundation (NSF). The Europeans developed a similar program under the umbrella of the European Space Agency (ESA).

The space environment effects can be grouped into several categories. Such categories include: vacuum, neutral, plasma, radiation, and micrometeorid/orbital debris. So, basically, we can discuss the effects of the vacuum environment, the neutral environment, etc. Each one of these environments interact with the subsystems that comprise a spacecraft: the propulsion system that provides the means of maintaining a certain orbit or attitude, the electrical power system that provides power to the rest of the subsystems onboard, the thermal control system, the attitude and orbital determination and control system, etc.

The vacuum environment imposes challenges when it comes to designing the structure, choosing the materials, and defining a strategy for thermal control. The pressure differential between the inside and the outside of a manned spacecraft is tremendous (around 350 km above the surface of the Earth, the pressure is ten orders of magnitude less). The lack of atmosphere translates into the fact that the spacecraft will have to deal with solar ultraviolet (UV) radiation (the UV radiation is energetic enough to degrade material properties). Also, the spacecraft can only cool itself by conduction or radiation.

Credits: NASA

Even if very rarefied, the neutral atmosphere in low Earth orbit is dense enough to cause a significant atmospheric drag force. The atoms can physically sputter material from surfaces and even cause erosion. All these mechanical and chemical interactions depend on the atmospheric density.

In low Earth orbit, the solar UV radiation ionizes the oxygen and nitrogen atoms. This environment, known as the plasma environment, can give rise to very interesting effects, like spacecraft charging and arcing between regions of differing potentials.

By far, the most dangerous environment in Earth orbit is the radiation environment. In the regions of charged particles, known as trapped radiation belts, particles with energy levels in the order of MeV pass through the surface layer and interact with the materials inside the spacecraft. Present shielding technology cannot protect living organisms inside a spacecraft in these regions.

Micrometeoroids and orbital debris are a cause of great concern to spacecraft design engineers and spacecraft operators as the kinetic energies associated with impacts at orbital velocities are very high. The main effect on spacecraft in this case is the physical damage upon impact. Other effects include surface erosion, ejecta resulted from impacts, changes in thermal control properties, and generation of electro-magnetic impulses (EMIs).

As most of the characteristics of the space environment were determined by remote observations or during short duration missions, one long duration mission was necessary to verify and validate these measurements.

In April 1984, the Space Shuttle Challenger placed into low Earth orbit (LEO) a spacecraft carrying a number of experiments for the purpose of characterizing the low Earth orbit environment. The spacecraft (known as the Long Duration Exposure Facility, or LDEF for short) was a twelve-sided cylindrical structure three-axis stabilized in order to ensure an accurate environmental exposure. The spacecraft was supposed to spend one year in orbit, but just before the planned retrieval, the Space Shuttle fleet was grounded as a result of the Challenger accident on January 28, 1986.

The spacecraft was returned to Earth by the Space Shuttle Columbia in January 1990. After almost six years in low Earth orbit, the results of the experiments onboard the facility contributed a great deal to the understanding of interactions between artificial objects and the environment in low Earth orbit.

You can find all the above in much more detail in Alan Tribble’s book The Space Environment – Implications for Spacecraft Design. Alan Tribble presents an excellent account of the effects the space environment can have on operational spacecraft. The book offers a unique perspective, as it combines the study of the space environment with spacecraft design engineering. .

Alan Tribble spent over ten years designing spacecraft. He is a technical project manager in the International Software Defined Radios group for Rockwell Collins.

Credits: CNES

Since the launch of Sputnik-1, on October 4, 1957, some 4,600 launches have placed more than 6,000 satellites in orbits around Earth.

All these activities have created a cloud of particles orbiting the Earth, which is referred to as orbital debris.

The majority of these particles are fragments from explosions and collisions (such as the Chinese Fengyun-1 ASAT test in 2007, and the collision between Iridium 33 and Cosmos 2251 in 2009). Some of them are spent rocket stages and defunct satellites. The total mass in orbit has been estimated to 5,800 tons.

As the ejecta generated in explosions and collisions have a wide range of velocities, the evolution of the particle cloud following the event can evolve in ways that are sometimes hard to predict, as some of the particles can disperse into orbits that are dissimilar to the original orbits.

Credits: NASA

To make things more complicated, the particles comprising the orbital debris environment are quite hard to detect. Some of them are impossible to detect due to technological limitations (present equipment is capable of tracking only objects larger than 1 cm in diameter in low Earth orbit and larger than 50 cm in diameter in geosynchronous orbit) or simply because they have orbits that are out of the range of tracking stations (such as highly elliptical and high inclination orbits with the perigee situated deep in the Southern Hemisphere – the Molniya orbits).

Even if most of the particles orbiting the Earth at velocities in the range of 8-10 km/s (or 28,800-36,000 km/h) are less than 1 cm in size, the kinetic energies associated with impacts at orbital velocities make them a source of great concern.

Just to get a sense of the effects that even small particles with velocities in the order of 10 km/s can have on space structures, if we assume a density of 1 g/cm³, a particle as small as 0.1 mm can cause surface erosion, and a particle 1 mm in size can inflict serious damage. A 3 mm particle moving at 10 km/s has the kinetic energy of a bowling ball moving at 100 km/h. A 1 cm fragment has the kinetic energy of a 180 kg safe. It is easy to visualize the effects of an impact with such an object on an operational satellite or a space station parked in low Earth orbit.

To find out more about orbital debris you can visit the NASA Orbital Debris Program office website.

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.