OrbitalHub

Credits: NASA

Dr. Mason Peck, head of the Space Systems Design Studio at Cornell University, answered a few questions for OrbitalHub readers about the Sprite spacecraft. Peck earned a B.S. in Aerospace Engineering from the University of Texas at Austin, and his M.S. and Ph.D. at UCLA as a Howard Hughes Fellow.

A team at the Space Systems Design Studio focuses on Sprite, a simple, feasible design of spacecraft systems printed on small wafers of silicon. This design packages traditional spacecraft systems onto a single silicon microchip.

DJ: Miniaturization brings along quite a few limitations: small payloads and data storage, and much less power available. Why pursue miniaturization when designing a spacecraft?
Mason Peck: In fact, I would disagree with the word–and the concept of–miniaturization. It implies that the goal is to shrink an existing space-system architecture or technology here. Instead, the goals are the following:

– Start from the bottom and work up, i.e. from the level of fundamental technologies, and find out how little it might take to create a space system. If we start by focusing on a mission and consider the problem from the top down, or if we merely try to implement an existing solution at a smaller scale, we miss out on lots of opportunities for innovation.

– Without prejudice, ask how we explore at this small scale? Specifically, how does a very tiny spacecraft exploit the physics of the solar system to navigate, reorient, scavenge power, and the other housekeeping tasks that are fundamental to space exploration.

– And then, with this basic technology concept in place, ask what missions are possible? This approach is known sometimes as “technology push,” where the availability of some new function or performance motivates a new sort of exploration.

So, we expect to discover a kind of parallel universe of exploration possibilities, which has remained hidden from us because of our parochial view of what a spacecraft consists of. I’ll give you some examples in response to your third question.

DJ: How far can miniaturization go?
M.P.: One of our most surprising discoveries is that commercial, off-the-shelf electronics components for mainstream contemporary applications like cell phones and iPods are vastly superior in performance to typical spacecraft electronics. Most people understand that spacecraft electronics are several generations behind the state of the art, and for good reasons such as needing radiation-hard parts, flight-proven reliability, etc. But what’s astonishing is just how far ahead consumer electronics are. We’ll be able to implement GPS-based orbit knowledge, radio communications, and attitude sensing all on about 1 cm^2 of integrated circuitry, using catalog components that anyone can buy. And they’re remarkably cheap, mostly because they’re made in the millions: single-chip GPS receivers, little CMOS cameras, etc. are no more than a few $ each in some cases.

The reliability or survivability of these off-the-shelf components is certain to be much poorer than flight-qualified parts. However, remember that at this scale of size and cost, fabricating and launching thousands or millions is entirely within reach. A single ChipSat may be unreliable, but the cloud of them may offer very high reliability. More than that, a cloud can be understood statistically, with notions like “statistical confidence,” which are very hard to come by when one is building a single, exquisite spacecraft.

A ChipSat will never replace Hubble, but it would not be expected to do so. Instead, ChipSats would form the basis of exploration missions that benefit from a large number of distributed, although coarse, measurements. More generally, this notion of “technology push” introduces a transformative idea for scientists. Instead of posing a science mission that presupposes a spacecraft architecture, let innovation in mission-science objectives couple with engineering innovation. That’s how we’ll do new, remarkable things.

DJ: Can you give some examples of mission scenarios envisioned for swarms of Sprite spacecraft?
M.P.: One of my favorites is that a Sprite may be able to enter a planetary atmosphere without parachutes, rockets, or a heat shield, and yet never burn up. Some of our early work on this problem for Earth’s atmosphere suggests that a 25 micron thick Sprite can reenter without burning up and maintain a cool enough temperature that electronics can continue to operate. So, reentering Sprites can sample the ionosphere, the mesosphere, and on down to the surface of the Earth. We’d get unprecedented measurements of spatial and temporal phenomena like turbulence and particle densities.

Another idea is to place a cloud of these Sprites between the Earth and the Sun, maybe at a so-called Lagrange point, which would be a sort of orbital equilibrium between the two. Each Sprite in the cloud would have the simple task of transmitting a single bit when solar-wind flux or magnetic flux exceeded some threshold, indicating a solar storm. This data would offer a distributed measurement for science, but at least as important it would provide a new type of advance warning of these storms, which can knock out radio communications on Earth.

Yet another application is a bit of science fiction, but it gets us thinking along new lines. Consider a particle accelerator. On Earth, these systems accelerate charged particles like electrons to relativistic velocities so that physicists can study subatomic phenomena. Now imagine the Sprite as a particle. It would be electrostatically charged, like a toy balloon on a dry day, and in that way resembles a very large electron. Could we build a kind of particle accelerator to launch Sprites out of the solar system at very high speed? The Navy already has a railgun that uses electromagnetic effects to launch large masses. Their recent successes show that the concept is perfectly sound. In fact, if you could direct the energy of their 30 kg railgun into a, say, 30 mg Sprite, that’s a factor of 1000 higher speed. Such a Sprite could be the first interstellar explorer. Michio Kaku and I have discussed the wild notion of a ring-shaped Sprite accelerator on the moon or in Jupiter’s orbit (in fact, the idea appeared on his Sci Fi Science TV show). In principle, such a launch system could send a Sprite to the nearest star system in a few decades.

DJ: The small mass and size of a Sprite spacecraft does not leave much room for radiation shielding. Especially during deep space missions, single events can take a spacecraft out of commission. How can Sprite spacecraft compensate for these inherent hazards of space travel?
M.P.: Absolutely right. Radiation will degrade the Sprite until it stops functioning. The easiest solution is simply to produce a rad-hardened chip. They’re not uncommon, although it’s expensive to design and build them. But it can be done, and amortizing that cost over millions of Sprites would make doing so a lot more appealing than how it’s done now, where we go to all that effort for a relatively small number of chips. But if you don’t want to get into rad hardening, remember that this effect is a statistical one. So, using a large enough number of Sprites for a mission would be a way to ensure that a desired fraction of them survive, even though a large number would fail. Again, we could design in this statistical reliability. And the more you use, the more reliably the mission meets its objectives.

DJ: Sprite is by definition a propellantless spacecraft. What type of propulsion can be employed?
M.P.: I wouldn’t be against trying to implement traditional propulsion at this scale. In fact, it’s been done, with mixed success. But the reason to pursue propellantless technologies is that chemical propulsion does not scale down well.

We find that several approaches do scale well. First, solar sailing is a clear winner. With a thin but still rigid silicon wafer, we can get performance benefits similar to the vast solar sails that have been proposed, but with the important advantage that the sail is not a floppy mess, difficult to deploy and steer around. The acceleration of a solar-sail Sprite increases with 1/L, where L is the length scale. As long as there are no limitations on thickness, a uniformly shrunken solar sail works better than its larger analogue. For example, a 1m solar sail accelerates 10x as fast as a 10m solar sail, as long as the thickness scales proportionately. That proportionate scaling may be tough to achieve, but what’s easy is the stiffness: a 25 micron Sprite is stiff enough that it needs no deployable booms or trusses, and it’s therefore effectively thinner (less mass for the area) than the larger sails.

A little harder to implement but even more intriguing is electrodynamic tether technology. Sprite sends a current through a wire that extends from the spacecraft, grounded in the ionospheric plasma. The current interacts with the Earth’s magnetic field, like the windings in an electric motor, producing a force. That force can accelerate the spacecraft. Just like the solar-sailing example, an ED tether is a lot more convenient when it’s shorter: it’s basically a rod, not a floppy string. The dynamics-related problems that the Space Shuttle tether experiments encountered would not arise here.

DJ: How many Sprite spacecraft are currently deployed and what kind of payloads do they have?
M.P.: There are three prototypes on the outside of the International Space Station. They’re not free-flying. They’re self-powered with solar cells, and they have their own on-board computers, radios, and other circuitry. They are their own payload in the sense that if they communicate, we’ll be able to confirm that Sprite’s unique communications architecture is a valid design. We didn’t have time (and we had no money, in fact) for a science payload per se.

DJ: Swarms of hundreds of decommissioned Sprite spacecraft orbiting the Earth could make mission flight control rooms very nervous. Are there any post-mission disposal methods considered for Sprite missions?
M.P.: Yes and no. Space debris is certainly a risk, but Sprites do not have to be debris. In low-earth orbit, their unique flight dynamics mean that aerodynamic drag very quickly pulls them back into the atmosphere. Specifically, a 325 km orbit would decay in about 2 days. Even at 500 km, they would reenter in weeks, at most. If they burn up, that’s that. If they don’t, it’s because they’re so delicate that they would never hurt anyone even if one were to land on a person on the ground. So, they clean up after themselves.

DJ: What are the areas with room for improvement in the design and manufacturing of chip-sized satellites?
M.P.: The next step will be that the design will transition from discrete parts to a single, application-specific integrated circuit (ASIC). That’s the real objective. It would be far lighter, less power-hungry, and more maneuverable than the current prototypes on ISS.

To find out more about the Sprite Spacecraft, Dr. Mason Peck, and his team at Cornell University, please visit the Space Systems Design Studio webpage. Paul Gilster of Centauri Dreams has also covered this topic in ’Smart Dust’ and Solar Sails and Tiny Spacecraft Point to Future Sails.

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: NASA

Software is a key component of present-day aerospace systems. Increased reliability is required from operating systems that host critical software applications.

Wind River’s VxWorks is a real-time operating system that is widely used in the aerospace industry. Missions using VxWorks include the Mars Reconnaissance Orbiter, the Phoenix Mars Lander, the Deep Impact space probe, Spirit and Opportunity Mars Exploration Rovers, and Stardust.

Mike Deliman, Senior Engineering Specialist at Wind River Systems, answered a few questions related to the new VxWorks MILS Platform 2.0.

DJ: What is VxWorks MILS Platform 2.0?
Mike Deliman: VxWorks MILS Platform 2.0 is a platform for creating systems that are evaluatable to high levels of the Common Criteria / Evaluated Assurance Level scale. VxWorks MILS 2.0 separation kernel is currently under evaluation by NIAP labs to an EAL 6+ level. The VxWorks MILS 2.0 Platform contains a separation kernel and technology to allow you to create multi-partitioned software systems where each partition can be evaluated to handle multiple independent levels of security (MILS) or to handle multiple levels of security (MLS). The long-and-short of it is similar to a VxWorks 653 flight OS, you can use a VxWorks MILS 2 platform to design a single platform that is capable of replacing multiple legacy systems. In other words, like a VxWorks 653 flight system, you can create a single modern system to replace multiple legacy systems, reducing Space, Weight and Power (SWaP) requirements.

DJ: What is a separation kernel and how did the concept make its way into software development for the aerospace industry?
M.D.: Separation Kernels allow you to take a single modern high-powered CPU and use it to replace several legacy systems. There are many examples of separation kernels and paradigms for their use. ARINC 653 defines a time and memory-space partitioning paradigm, services, and an API that must be provided (the Application Executive, or APEX). We have a platform – VxWorks 653 – that implements the ARINC 653 APEX separation and API. Separation Technologies are becoming quite popular, many are called “Hypervisors”. There are many Hypervisors out in cyberspace, the “Type 1” Hypervisors can all be thought of as forms of separation kernels. The Aerospace industry is a prime target for separation technologies because of the need to reduce the “SWaP” factors.

DJ: How does the VxWorks MILS separation kernel improve the reliability of aerospace applications?
M.D.: The VxWorks MILS separation kernel could be used to allow a single satellite to fulfill multiple missions. For instance, there may be a number of sensors and experiments on board, some for civilian / educational interests, some for NASA, some for research entities, perhaps some for the USAF. A MILS kernel could be used to collect, encode, and steer data safely, providing assurance that the data will not be mixed until it is in a state deemed “safe” for mixing. A satellite running a MILS separation kernel to handle such data wrangling could combine and satisfy multiple mission masters. If I were to be asked to design such a system, I would most likely recommend a flight computer separate from the science computer. Even if the science and flight SW were to share a single CPU, the separation technology would help ensure that no problems on any science application could affect any of the other science applications or any flight applications. In this way the flight system would be protected from anomalous events in the science packages, and the overall system would benefit from improved reliability.

DJ: John Rushby introduced the concept of separation kernel in order to provide multilevel secure operation on general-purpose multi-user systems. Do software applications developed for the aerospace industry (and I have in mind software running on micro-controllers) have the level of complexity that would require a separation kernel?
M.D.: Concentrating on the micro-controller aspect, no, most single (federated) systems running one micro-controller (or even several) do not even need a 32-bit processor dedicated to their operation. However, with a proper separation kernel and time-sliced architecture, you could use one modern high-speed 32-bit CPU to control and monitor a large number of smaller systems, and ensure any faults occurring on those control-and-monitor loops are contained. And as noted above, in a system used to satisfy requirements of multiple masters (agencies), MILS-style data separation may be the only way to keep satellite weight within limits and provide the information assurance the agencies require.

DJ: What features make the VxWorks operating system reliable and secure?
M.D.: Focusing on the VxWorks family of operating systems and the VxWorks OS API, VxWorks has been used in millions of devices over more than two decades of service, in applications as simple as MP3 players and as complex as autonomous space exploring robots, and as life-critical as telerobotic surgeons. There is no way a software company could anticipate the wide range of use that our customers have dreamed up and implemented. The VxWorks family of OSes share a common ancestry of code and all can benefit from bugs discovered and fixed in any of the family line.
 
Focusing on the VxWorks MILS platform, the separation kernel was designed expressly in compliance with the SKPP (the Protection Profile for separation kernels), with a focus on controlling embedded applications that require some degree of real-time control.

DJ: What are the features that make VxWorks a real-time operating system?
M.D.: Determinism is king in the real-time world. The ability to react to events in the real world with a high degree of determinism is what gives VxWorks its hard real-time responsiveness. This hard-determinism is carried over into all of the VxWorks family line, including our separation kernels and VxWorks SMP.

DJ: What toolchain is shipped with VxWorks? What programming languages are supported by the toolchain?
M.D.: Depending on the VxWorks package, one or more toolchains may be supplied and supported. For the most part, various versions of the Wind River Complier (formerly “Diab”), and various versions of the Gnu tools are supplied / supported with VxWorks. For the VxWorks MILS 2 platform we use a couple of versions of the GNU tool chains, specially modified for the parts they are used to build.

DJ: What hardware is targeted by the platform? Is an actual board necessary for development of applications or is an emulated target environment available for software engineers?
M.D.: Specifically, chips we are targeting include the following:
– Freescale 8641D (CW VPX6-165)
– Freescale 8548 (Wind River SBC8548)
– Intel Core 2 Duo (Supermicro C2SBC-Q)
– Freescale P2020, P1011, P4080 (future)
– Intel Atom, Nehalem (future)
We currently support Simics as the only simulation environment available for the VxWorks MILS platform.

Wind River Systems was founded in Berkeley, California in 1981. Intel bought Wind River Systems for a reported $884 million in July 2009. VxWorks real-time operating system is one of the Wind River flagship products.

Credits: NASA

NASA’s GRAIL mission will be one of the few missions to utilize the chaos associated with the subtle gravitational forces between planets in order to reach lunar orbit. The mission is scheduled to launch in 2011 and will use a low-fuel trajectory to the Moon.

Ed Belbruno, the first to use weak stability boundary theory to design trajectories for space missions, has agreed to answer some questions for OrbitalHub readers.

DJ: You graduated in mathematics from New York University, and received your PhD in mathematics from New York University’s Courant Institute. As a mathematician, how did you develop an interest in celestial mechanics?
Ed Belbruno: I was always interested in space since I was very young, going back to 4 years old. When I went to undergraduate school, also at NYU, I was a joint chemistry and mathematics major. At that time I was also interested in astrochemistry. When I got my BS, I went on to the Courant Institute and immediately wanted to get involved in an area of mathematics involved with space. I asked around, and found that there was a very famous mathematician there who was considered to be one of the leaders in the world in the subject, Juergen Moser. I learned that he was also a leader in a field called theoretical celestial mechanics. So, I asked to work with him and he agreed. For me it was great because I loved mathematics and I loved space. I am also an artist, and my early paintings involved a lot of space scenes. My being drawn to celestial mechanics was a natural thing.

DJ: I think of celestial mechanics as a precise discipline… the word CHAOS from the titles of the presentations you are giving would make any aerospace engineer nervous. Is this a misnomer or it is really the foundation for the new class of trajectories you designed?
E.B.: When I arrived at JPL in 1986, I was previously an assistant professor of mathematics at Boston University. I arrived at JPL and found myself at a leading space center – to work on the following missions: Galileo, Cassini, Magellan, Ulysses. My job was to do trajectory design. I noticed that all these missions and all the others I saw in the past, relied mainly on Hohmann transfers which are straightforward trajectories found using algebra. They are very well behaved and linear in nature. There was nothing chaotic about them. I noticed that in the field of astrodynamics, which designs trajectories for spacecraft, that advanced mathematical techniques using a general subject called dynamical systems theory, which includes chaos theory, was never used. I figured if you could incorporate that into astrodynamics, new exciting low fuel trajectories could be found. No one at JPL really believed me, but in 1986 I started investigating whether or not one could use the subtle gravitational interactions between the Earth and Moon to get a spacecraft into orbit about the Moon without the use of rocket engines – that is, automatically. This had never been done before. I also found that chaos methods had to be employed to do this since the gravitational interactions between the Earth and Moon give rise to chaotic motions for a spacecraft. I succeeded in 1986 and found a way to do this for a mission study at JPL called LGAS – Lunar Get Away Special, where I found a 2-year route to the Moon with automatic capture at the Moon that was chaotic. This was the first time chaos was used for a lunar capture for a spacecraft – or capture at any planet. It was the first systematic use of chaos in astrodynamics as far as I know. The LGAS design was eventually used by the European Space Agency for their SMART-1 lunar mission in 2004. In 1991 I found a 3-4 month route to the Moon using automatic chaotic capture for Japan’s Hiten mission. This transfer first moves out to 1.5 million kilometers from the Earth, then falls back to the Earth-Moon system and into automatic ballistic capture about the Moon. This same transfer type is going to be used for NASA’s GRAIL mission in 2011. All these trajectories that go to automatic capture at the Moon are chaotic since they are very sensitive to small changes.

DJ: Was there any resistance from the scientific community when you first published the results of your research?
E.B.: Yes. When I first started designing routes to the Moon that employed automatic capture (or ‘ballistic capture”) back in 1986-1990 at JPL, that employed chaos as described above there was a good deal resistance, in spite of publishing papers and demonstrating actual trajectories via computer simulations. This is because no one had ever heard of this before, and also, chaos was a not a term that was desired to be associated with space travel. In 1990 I had a disagreement at JPL over this and found myself looking for another job. Luckily, soon, a couple of months after that while still at JPL, ready to leave for another job, I was able to take part in the rescue of a Japanese lunar mission, and get its spacecraft, Hiten, successfully to the Moon on one of these new transfers employing ballistic capture, that vindicated my work – and saved my career.

DJ: Are there any computational challenges that make the class of trajectories you designed difficult to compute? Is the lack of computational power the reason they are a recent development in celestial mechanics?
E.B.: Yes, they require more accuracy than is typically used since the motions involved are very sensitive in nature. So, different methods, other than classical optimization methods, have to be employed. These methods involve using ideas from chaos theory and dynamical systems and making use of regions that support chaotic motions called weak stability boundaries. Once the motions in these regions were better understood, then the methods have been refined and the trajectories can be more easily generated. More powerful computers were/are not necessary. What was necessary were new numerical methods.

DJ: I believe solar sails would match the profile of low-energy space missions. Have you ever considered applying the weak stability boundary theory in order to design trajectories for spacecraft propelled by solar sails?
E.B.: I agree that solar sails would be a great thing to use with these low energy trajectories. I have considered them and made some designs actually, but never designed any missions using them.

DJ: Considering your experience in designing low-cost trajectories for lunar missions, have you been contacted by any Google X-Prize team for assistance? How feasible would it be for a Google X-Prize team to use such a trajectory (costs aside, they would have to launch at least three months before any other team in order to make an attempt to win the prize)?
E.B.: Yes, I was on the so-called ‘Mystery team’ for the Google X-prize from latter 2007 to latter 08. The base design was to use one of these low energy transfers to the Moon of the type that Hiten used, described earlier, and that GRAIL is planning to use. I don’t know how feasible it would be to use this trajectory – certainly no more or less feasible than using a direct Hohmann transfer. It ultimately depends on the launch vehicle, which are very expensive. I don’t think the three months flight time is a factor since it is very unlikely that there will be that kind of time pressure considering how difficult it is to send something to the Moon for a private company.

DJ: What other space missions are you currently involved in? Can you provide a brief description?
E.B.: I am involved, indirectly, with NASA’s STEREO solar science mission in the sense that they have recently redirected that mission to do an excursion to L4, L5 of the Earth-Sun to try and verify a theory of Richard Gott and myself on the origin of the Moon. This theory was published by Gott and myself in 2005 (see http://www.edbelbruno.com) in the Astronomical Journal entitled, Where Did the Moon Come From? In that paper we hypothesized that the giant Mars-sized impactor that is thought to have hit the Earth to form the Moon, billions of years ago (that Hayden has a fabulous show on), actually originated at special locations in space. These locations are called Earth-Sun equilateral L4, L5 points, 93 million miles from the Earth in either direction, on the Earth’s orbit. The impactor is called Theia. It is felt that if our theory is correct that residual material and perhaps asteroids exist near L4, L5. To verify this, the STEREO mission, consisting of two spacecraft, are being redirected to go to these points to investigate the possible remains of the mysterious planet called Theia that may have been there long ago. The NASA press release explains this in detail. The spacecraft are due to arrive at L4, L5 in September, October this year and are currently approaching these locations.

DJ: It is not often you meet someone who is both an artist and a mathematician. How do these roles complement each other?
E.B.: When I do paintings, I find that I have to completely turn off any logical mathematical way of thinking and work on a subconscious level. This is exactly the opposite of working mathematically where you have to be very logical and work mostly with the conscious part of your mind. These two processes are totally different. There is a little subconscious thought when doing mathematical/scientific work, of course, but you have to pay close attention to deductive reasoning. In doing a painting, especially abstract expressionist painting, you have to avoid as much as possible deductive reasoning and be very spontaneous without thinking, which would ruin the painting. I have found it challenging to work in these two different ways – but now I can do it fairly easily.

Credits: Linda Gambone

If you happen to be in New York on July 20, 2009, you can attend the presentation A New Path To The Moon and Beyond Using Gravitational Chaos, at the Hayden Planetarium Space Theater, American Museum of Natural History.

Ed Belbruno will present the weak stability boundary theory and the alternative approach to space travel he developed in the 1980s.

Credits: SETI Institute

SETI stands for Search for Extraterrestrial Intelligence. Initially a program supported by NASA, SETI is now a privately funded institute that conducts research activities to detect intelligent extraterrestrial life.

SETI Institute is currently collaborating with the Radio Astronomy Laboratory at UC Berkley to develop the Allen Telescope Array, which is a specialized radio telescope array designed for SETI studies.

Seth Shostak, senior astronomer at the SETI Institute, kindly answered a few questions related to the search for extraterrestrial intelligence.

DJ: Why did you choose to work for SETI?
Seth Shostak: It probably sounds too easy, and thoroughly trite, but I’ve been interested in the idea of extraterrestrial intelligence since I was ten years old. When, quite by chance, the opportunity arose to work for the SETI Institute, it was like finding that a dream was suddenly reality.

DJ: Besides listening for transmissions in the microwave range of radio frequencies, which methods do you think are most likely to prove successful for SETI?
S.Shostak: I happen to be a big fan of so-called Optical SETI, as well as traditional radio SETI. In other words, look for laser flashes that might be sent our way by extraterrestrial societies trying to get in touch. This would be a great way to initiate contact, as the transmitting civilization could “ping” many thousands — indeed, many millions — of star systems in short order, and then do it again. This would be a sort of endless ping to so many star systems that it might reliably generate some reaction. In any case, I think we need to expand our search for these quick flashes in the sky.

DJ: Is SETI looking only for carbon-based ET? Are there any other possibilities to consider when searching for extraterrestrial intelligence?
S.Shostak: SETI searches are agnostic when it comes to the biochemistry of the aliens. After all, from our point of view, what makes them “intelligent” is their ability to build a radio transmitter or a powerful laser. The details of their construction are of no consequence for the search — except insofar as they might not be living on planets surrounding an ordinary star. If they are machine intelligence, they may have migrated away from their natal solar system, and of course that WOULD affect our search strategies.

DJ: Do new discoveries made by astronomers using space telescopes (for example, discovery of exo-planets, detection of their atmospheres, and the study of the composition of these atmospheres using spectral lines, etc.) have any implications for the way SETI conducts searches? Is SETI using this information to fine-tune the search?
S.Shostak: One of the first SETI experiments planned for the Allen Telescope Array is to examine star systems that are known to have planets (the work of astronomers during the past dozen years). Of course, we would like to know which star systems have HABITABLE planets, but that information still eludes us. NASA’s Kepler Mission will give us invaluable insight into what fraction of the cosmos might be suitable for life — and life of the intelligent variety, as well.

DJ: How do you see a two-way communication with ET? What concepts can be considered universal so that they can be used for such communication?
S.Shostak: Given the likely distance between societies, I don’t think that two-way communication is very likely or practical. But there’s still the problem that any deliberate transmissions should be encoded in such a way that the recipients can figure out what is being said. Lots of thought has gone into this problem — should the aliens send dictionaries, mathematics, music, or just a lot of pictures? In general, I figure that the more information they send, the greater the chance that we’ll understand at least some of it.

DJ: Can you make a prediction as to when an ET radio transmission could be picked up by terrestrial receivers? Besides the pace at which terrestrial technology is evolving, what other factors should be considered when making such a prediction?
S.Shostak: The most important parameter affecting SETI success these days is money: do we have sufficient funds to keep up the search? But if the money is forthcoming, then technical developments in the coming decades will allow us to examine a million or more star systems by 2025 or so. I think a million star systems is the right number to expect success, so that’s my prediction — we’ll find ET by 2025. Otherwise, I’ll be disappointed and slightly embarassed.

Seth Shostak’s new book, Confessions of An Alien Hunter: A Scientist’s Search for Extraterrestrial Intelligence, tells the true story of SETI. The book contains answers to many questions about SETI: what frequencies are monitored, where the antennas are aimed, how we should respond if a signal is received, etc. By reading this book, I have learned a great deal about the search for extraterrestrial intelligence.

Paul Gilster of Centauri Dreams has posted a review of the book. I invite everyone to read it.

Credits: NASA/MSFC

Solar sails have emerged as a revolutionary propulsion system for space travel. Due to increased interest in both theoretical and experimental research, the benefits of solar sailing have become clear and compelling.

Two leading experts in solar sail propulsion, Gregory Matloff and Les Johnson, have agreed to share their knowledge about this exciting topic with OrbitalHub readers.

Gregory Matloff teaches physics at the New York City College of Technology and consults for NASA’s Marshall Space Flight Center. Les Johnson is a physicist at NASA’s Marshall Space Flight Center, where he serves as the Deputy Manager of the Advanced Concepts Office.

DJ: From the whole range of space technology-related fields of research, why was it that solar sails attracted your attention?
Gregory Matloff: I was attracted to solar sailing because it is an example of space propulsion that requires no fuel. As such, it has the potential to achieve higher velocities at less cost.
Les Johnson: They are simple, elegant and very practical in that they do not require any fuel. We are extremely limited in our exploration of space because of our lack of efficient propulsion. Sails, which require no fuel, will enable some science and exploration missions that are currently impossible (using only chemical rockets).

DJ: In the Solar Sails book, you have presented the problems and limitations of chemical, nuclear, and ion rocket propulsion. Why do you think that, despite these limitations, the solar sail has not yet been adopted as a means of propulsion for interplanetary robotic missions?
G.M.: Solar sails have been slower to achieve operational readiness for a number of reasons. First, space agencies have developed vast rocket-based infrastructures. We simply have more experience with rockets. Second, rockets work on Earth as well as in space. We needed a lot of in-space experience before sail testing in space could begin. Third, space-mission planners are a conservative lot. They (correctly) will not risk their payloads to a sail until the technological readiness of solar sailing is sufficiently advanced.
L.J.: The reasons are simple. 1) Any mission conducted in space is expensive. When you are the owner of a multi-million dollar spacecraft, you tend to become very conservative and risk averse. Even though there are many benefits to be gained from using a solar sail, it is new and therefore risky. We’ve flown hundreds, if not thousands, of rocket engines and not a single solar sail. Would you risk your investment on a new (risky) propulsion system? 2) Anytime you use a new technology, the first flight will be more expensive. If you are paying for a space mission and your budget is limited, you must often choose between what is best (like a solar sail) and what is good enough (like the tried and true rocket engine). Tried and true seems to be the choice right now.
Let me be clear. This may be penny wise but it is pound foolish. If solar sails become an “off the shelf” option like some rocket engines, then we will be going new places and learning things that we simply cannot otherwise accomplish with “tried and true” technologies.

DJ: How many solar sail designs have been considered to date, and which one do you think will prove to be the most successful in the future?
G.M.: There are six or seven different sail designs. These include rectangular (or square), spinning-disc, heliogyro, parachute, hollow-body, parabolic and hoop sails. All these and various other configurations may find application to different missions.
L.J.: There is no clear answer here. NASA and DLR selected the square, 3-axis stabilized approach. The Russians, with their Znamya, appear to prefer a spinning solar sail. Others prefer the heliogyro. All appear to be feasible.

DJ: How well suited is the solar sail for manned space missions?
G.M.: Unfurled near Earth, solar-sails are slow to accelerate but can reach high velocities. Current Earth-launched sail designs could be uprated and enlarged to carry freight to support manned interplanetary expeditions. Future thinner, heat-tolerant and radiation resistant solar sails manufactured in space could result in faster interplanetary transfers and even slow interstellar travel.
L.J.: Any solar sail that we can foresee building in the near term will be useful only for robotic missions. These sails will be big enough — some nearly half a mile on a side! To get the materials and sizes required for a human mission will require advances in materials technology that are difficult to imagine happening anytime soon. Though I am optimistic that they will eventually occur, we prefer the incremental approach. We should begin with using sails to propel robots and move toward a capability for humans.

DJ: How do you think space propulsion systems will evolve in the near future? To what extent will they include solar sails?
G.M.: Future solar-sail evolution requires advances in space infrastructure — notably in-space manufacturing, and materials science. More theoretical work on space environment effects and theories of devices such as the perforated solar sail is also required. Also, space-based solar-pumped lasers could be developed to allow sail acceleration farther from the Sun.
L.J.: I believe we won’t be giving up chemical rockets anytime soon. We will see more and more flights of solar electric propulsion after the (assumed) success of the DAWN mission, which is currently enroute to asteroids Ceres and Vesta. THEN we might see the use of solar sails begin.

Les Johnson and Gregory L. Matloff are two of the co-authors of the book Solar Sails: A Novel Approach To Interplanetary Travel. A good review of the book was written by Paul A. Gilster of Centauri Dreams. I invite everyone to read it.