OrbitalHub

Credits: NASA

The adventure started on October 4, 1957, when the former Soviet Union successfully launched the first artificial satellite, Sputnik-1, using a rocket that was a modified Intercontinental Ballistic Missile (ICMB). Even if the political implications at that time were very important, as the launch ignited the Space Race within the Cold War, we can argue that the scientific accomplishments were more significant.

These accomplishments relied upon the theoretical work of scientists like Hermann Oberth and Konstantin Tsiolkovsky.

What followed this event, as mentioned above, was a race.

Explorer-1, the first American artificial satellite, was launched on January 31, 1958. Yuri Gagarin was the first human in outer space and the first to orbit the Earth on April 21, 1961. He was followed closely by Alan Shepard, who became the first American to travel into space onboard the Freedom-7 capsule, on May 5, 1961.

On August 19, 1964, the first geostationary communication satellite, Syncomm-3, was placed in orbit over the International Date Line. Syncomm-3 was used to relay the television coverage of the 1964 Summer Olympics in Tokyo, Japan, to the United States. The first to propose the concept of a communication satellite was Arthur C. Clarke, who in October 1945 published an article in the British magazine Wireless World that described the fundamental concepts behind the development of artificial satellites used to relay radio signals.

The first space station, Salyut-1, was launched on April 19, 1971. Even if the space station had a short operational life, as it re-entered the Earth atmosphere on October 11, 1971, it tested elements of the systems required on a space station and conducted scientific research and experiments. The construction of the first international research facility in Earth orbit, the International Space Station (ISS), began in 1998. The station is still under construction and it will be operational until at least 2015.

Where are we now, after 53 years of exploration of the space in the proximity of Earth? Since the launch of Sputnik on October 4, 1957, some 4,600 launches have orbited more than 6,000 satellites. All of these activities have created a cloud of orbiting particles around Earth. This new environment is referred to as space debris or orbital debris. Even if most of these particles are small in size (less than 1 cm), they are a source of great concern as the kinetic energies associated with impacts at orbital velocities, which are in the range 8-10 km/s or 28,800-36,000 km/h, are very high. It has been estimated that the total mass in orbit is 5,800 tons.

Credits: NASA/ESA/A.Zezas/JPL/Caltech/GALEX Team/J.Huchra et al.

One thing that I find fascinating about astronomy is the ingenious ways astronomers have come up with to solve the puzzles laid out in the skies. You cannot travel to distant stars and galaxies to study them… so what do you do? Well, you use all of the knowledge that mathematics and physics give you and find out anything you want to know (or pretty much everything) about them.

Eratosthenes (276-194 BC) was the chief librarian of the Library of Alexandria (the same library that Julius Caesar burned to the ground in 48 BC). He knew that every year on June 21 at noon the Sun was 7.2 degrees off the vertical in Alexandria, while in Syene the Sun stood directly overhead. Knowing the distance between the two locations and using basic geometry, he was able to determine the circumference of the Earth to be around 40,000 km. Pretty amazing for that time, don’t you think?

Closer to our time, the astronomer Edwin Hubble (1889-1953) has devised methods for finding distances to other galaxies. Hubble was also able to measure the radial velocities of galaxies using the redshift in their spectral lines. His findings proved not just that the Universe is expanding, but also determined that it all began about 13.7 billion years ago.

Have you ever been able to visualize in terms of relative size or scale the planets and the moons of our solar system? How big do you think the Earth is compared to Mercury or Mars? Which one do you think is a bigger moon, the Earth’s Moon or Saturn’s Titan? How many times do you think the Grand Canyon would fit inside the Valles Marineris on Mars? How big is, let us say, the asteroid Itokawa compared to the International Space Station? Is our own Milky Way galaxy bigger than Andromeda?

I found many other interesting stories and had the above questions answered in a new book, Sizing Up The Universe. I would say that the unifying theme of the book is size comparison. Numerous charts capture a fresh vision of the Universe, introducing an original way of comparing objects in the heavens.

Browsing through Sizing Up The Universe, I could not help thinking about my high school astronomy textbook. The author of the textbook was definitely not into visual arts, as the pages were flooded with math formulas and only a few sketches were present here and there. I did not mind it at that time, but I realize now that stunning images of planets, stars, and galaxies, such as those found in Sizing Up The Universe, would make the learning process much more enjoyable. Moreover, the real stories behind groundbreaking discoveries in astronomy that are sprinkled throughout the text make it captivating and easy to read.

The authors of Sizing Up The Universe are J. Richard Gott III and Robert J. Vanderbei. J. Richard Gott III is professor of astrophysics at Princeton University. He has written articles for Time, Scientific American, and New Scientist. He is also the author of Time Travel in Einstein’s Universe. Robert J. Vanderbei is professor and chair of the Department of Operations Research and Financial Engineering at Princeton University. He is an amateur astronomer and has taken from his own backyard many images of astronomical objects, some of which can be found in the book.

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.