Next Call: Mars / Damon Landau and Nathan G. Strange

Adopting ideas from robotic interplanetary reconnaissance missions will make it possible to send astronauts to asteroids and Mars cheaply and quickly as part of a manned space program

* The views expressed in the article are those of the authors, not NASA or JPL.

In October 2009, we, a small group of "geeks" interested in robotic exploration of space, decided to dare and emerge from our comfort zone and brainstorm to find new approaches to flying people into space. We sprang into action after the Augustine Commission, a panel of top experts appointed by President Barack Obama in early 2011 to examine the space shuttle program and its successor, cast doubt on the future of the US manned space program. Since we have experience with the exciting US robotics exploration program, thanks to which humanity was able to reach from the planet Mercury to the outskirts of the solar system, we wondered if we could find technical solutions to some of NASA's political and budgetary challenges.

The ideas flowed like water: using ion engines to fly components to build a base on the moon; sending energy beams to propel robotic all-terrain vehicles across Phobos, one of Mars' moons; high-powered plasma engines to be attached to the International Space Station (ISS) to move it into orbit around Mars; prepositioning rocket boosters along interplanetary orbit so astronauts can pick them up en route; Using patrol cabins like in the movie "2001: A Space Odyssey" instead of space suits; Not sending astronauts to an asteroid, but bringing a (very small) asteroid to the astronauts on the space station. After crunching numbers, we discovered that electric propulsion - using an ion engine or similar technologies - could significantly reduce the launch mass required for manned missions to asteroids and Mars.

We felt like we were back at NASA in the 60s, only without the cigarette smoke. We talked about what we are capable of doing and stayed away from getting bogged down in what we are not capable of doing. After the initial analysis we conducted, we built a short seminar that we gave during the lunch breaks to our colleagues at NASA's Jet Propulsion Laboratory (JPL), in which we weaved together our ideas and calculations. Over the following spring and summer we met with other engineers and scientists who expressed interest in our approach and gave us ideas on how to improve it. We learned about experiments conducted by people at NASA and beyond: from tests of powerful electric motors to models of lightweight, high-efficiency solar arrays. Our discussions branched out and became part of a larger gulf of creative thinking that spread throughout the space agency and the aviation industry.

Currently, we have combined the most promising proposals with tried and tested strategies and developed a plan to send astronauts to the near-Earth asteroid 2008 EV5 as early as 2024, in preparation for the ultimate goal: landing on Mars. This approach was designed to fit within NASA's current budget, and most importantly, it breaks down the overall mission into a series of incremental milestones, so that the space agency has the flexibility to speed up or slow down the program depending on funding. In short, the goal is to apply lessons learned from the robotic scientific research program to modernize manned patrols.

Small steps make a big step

The Augustine Commission's report ignited a tremendous political war, culminating in the decision to transfer a significant portion of the mission to launch astronauts into orbit and hand it over to private companies. NASA can now focus on technologies that can make a difference and advance manned exploration missions to new frontiers. But how could the agency move forward without the political support and resources that were at its disposal during the heyday of the Apollo moon landing missions?

The accepted approach to robotic research missions is gradual: the development of a portfolio of technologies that enables the execution of more and more ambitious missions. Instead of relying on an "all or nothing" development path toward a single goal, the robotic patrol program uses innovative combinations of technologies to achieve a variety of goals. There is no doubt, though, that the robotic program was flawed and ran into its own efficiency problems; Nothing is perfect. But at least it doesn't screech to a halt when the winds change in the administration or when technological innovation starts to falter. The manned program can learn from this strategy. It does not need to start with a "big step" as was the case with the Apollo program. It can launch a series of modest steps, each of which builds on the previous one.

Some believe that the real lesson from the robotic exploration missions may be that it's not worth sending people at all. If NASA's sole purpose is scientific discovery, there is no doubt that robotic spacecraft would be cheaper and involve less risk. But NASA carries more than just science on its shoulders; Science is only one aspect of a broader human drive, the drive to explore. The space exploration missions are so attractive because of the desire that one day the common man will be able to experience this directly. Robotic spacecraft are just the first wave of exploring the solar system. Government funded manned missions will be the second wave. And the third wave will include private citizens seeking adventure and profits in space. NASA's past investments developed the technologies that fuel today's commercial space race, which includes capsules launched to the space station and spaceplanes that fly like an arrow over the Mojave Desert. Now NASA can develop the technology we need to break through further.

The key word: flexibility

Three basic principles stand in the infrastructure of the road we recommended. The first principle is the "flexible track" approach advocated by the Augustine Commission and accepted by President Obama and Congress. Instead of the old insistence on a fixed orbit from Earth to the Moon and then to Mars, the new strategy offers a wide selection of possible destinations. We must start with nearby targets, such as Lagrange points (places in space where the motion of an object balances with the forces of gravity) or asteroids close to Earth.

The flexible route calls us to develop new mobility technologies, in particular electric propulsion. We suggest using plasma engines (a type of ion engine, also known as a Hall effect engine) whose energy comes from solar panels. A similar system powered the "Dawn" spacecraft on its journey to the giant asteroid Vesta, and it is the one that will carry it further in 2015 to the dwarf planet Ceres. Traditional rockets based on chemical propulsion produce a powerful but short burst of gas, while electric motors fire a gentle but steady stream of particles. Thanks to the electric energy, these engines are more efficient, so they use less fuel (like a Toyota Prius, only in space). The price of this increased efficiency is lower drive, so some tasks may take longer. A common misconception is that electric propulsion is too slow for manned spaceflight, but there are ways around this. The idea that came up in our first brainstorming session was to use sort of electrically powered robotic tugboats that would tow chemical rocket boosters to key points on a trajectory, like a trail of breadcrumbs; Once the path is laid, the astronauts will be able to set off and pick up the boosters on their way. In this way, the missions will gain the fuel efficiency of electric propulsion without losing the speed advantage of chemical propulsion.

The decisive consideration is that an electric drive saves money. Because the spacecraft does not need to carry as much propellant, its total launch mass drops by 40% to 60%. As a first approximation, the price of a space mission increases in direct proportion to the launch mass, so a diet that reduces the mass by half will cut the price by a similar rate.

Many space enthusiasts wonder why bother visiting an asteroid when Mars is everyone's favorite destination. But in fact, asteroids are the perfect target for a gradual approach towards reaching Mars. The space between Earth and Mars is littered with thousands of asteroids, which can literally serve as stepping stones to deeper space. Asteroids' gravity is weak, so landing on one of them requires less energy than reaching the surface of the Moon or Mars. Planning a long interplanetary journey, which should last between six and 18 months, is difficult enough even without having to develop complicated vehicles for re-landing and take-off. Missions to asteroids allow us to focus on the problem that in our estimation is the most complex (and still unsolved) that will be faced in any case by the people who dare to sail away from Earth: learning how to protect astronauts from the harmful effects of gravity and radiation in space. If NASA gains experience in dealing with the dangers of deep space, it will be in a better position when it comes to designing vehicles for missions to the surface of Mars.

There are several asteroids of scientific interest that astronauts will be able to visit with flight times ranging from six months to a year and a half, with the help of an electric propulsion system with a power of 200 kilowatts (kW), a conceivable advance compared to our current capability: currently installed on the space station The international has solar arrays that supply it with 260 kilowatts. Such a mission will break the barrier of deep space, and at the same time will take us a decisive step towards a journey to Mars, which will require flights lasting between two and three years and systems of 600 kilowatts.

The second fundamental principle of our program is that NASA does not need to invent completely new systems for everything, as it did in the 60s. It is true that there are systems, especially protection against lack of gravity and against deep space radiation, that will require new research. But we can build everything else from the space travel assets we already have. The deep space vehicle can be built by combining several components specially designed for certain purposes. For example, we can adopt the structure, the solar arrays and the life support systems from models placed in the space station. Apart from that, there are many private companies as well as space agencies of other countries that have specialized in these fields, and NASA could learn from them.

The third principle is building a plan that will not lose momentum even if one component encounters problems or delays. This principle should be applied to the most controversial component of the space policy adopted by Congress: the launch vehicle that will take the crew and rovers from Earth and carry them up to orbit. Congress directed NASA to build a new heavy-lift rocket, known as the Space Launch System (SLS). As NASA announced in September 2011, it plans to develop this rocket in stages: at first it will have about half the capacity of the Saturn 5 launcher, which was used by NASA in the Apollo program, and it will gradually increase until it reaches just beyond its full launch capacity. The first SLS launcher, along with the Orion manned spacecraft currently in development, will be able to take astronauts on a three-week journey to orbit the moon and the Lagrange points, but will not be able to take them further without the development of a new system.

Fortunately, deep space travel does not have to wait until the SLS is completed. You can start preparations right now and develop the life support systems and the electric drive that we will need on trips beyond the moon. If NASA prioritizes these systems, even while the new rockets are still in development, it will have a better ability to refine the details of the SLS design to better suit deep space missions. There is even the possibility of designing these components to be adapted to commercial or international launchers and assembled in orbit, just as was done with the International Space Station and the Mir space station. The use of existing rockets will help gain momentum towards deep space exploration. With the flexibility this portfolio of options will allow, NASA will be able to squeeze more reconnaissance missions into its increasingly tight budget constraints.

The mission: 2008 EV5

In our plan, NASA's renaissance begins with the construction of the Deep Space Vehicle - the means of transportation that will allow people to travel between the planets. A solar powered ion drive will propel it and a new mobile living unit will provide a safe haven away from home. The most basic deep space vehicle will consist of two units that can be put into low Earth orbit with a single launch of the smallest of NASA's new SLS rockets. Alternatively, three commercially available rockets could do this, two for the vehicle parts and one with a road side.

Ironically, the initial quest is the most boring. For two years, the ship will be driven by remote control, without a crew, along a slow and slow path from low Earth orbit, through the Van Allen radiation belts to high orbit above Earth. Although this journey is very economical in terms of material, it is too long and radioactive for astronauts. Once the spacecraft is placed on the outer rim of the Earth's gravity well, a slight push will be enough to bring it into interplanetary orbit. At this stage, it can conduct flights near the moon and other maneuvers that will allow the trajectory to be redesigned to be suitable for an efficient exit into space. The astronauts will take off from the ground aboard a regular booster with chemical propulsion.

For a test flight, the astronauts will fly the vehicles into an orbit that almost always stays over the moon's south pole. From there they will be able to control a fleet of robotic cruisers and explore the composition of ancient ice deposits in the perpetually dark craters of the Aitken Basin. Such a mission breaks down a long-term journey into small steps, with Earth and the security it offers remaining only a few days away. After the crews return to Earth, the deep space vehicle remains in orbit high above Earth, awaiting refueling and a facelift for its first asteroid mission.

We investigated a wide range of tasks of this type. In some of them, astronauts will be flown to small objects (less than 100 meters wide) located just beyond the moon and will return to Earth in less than six months. Others, more daring, went to large objects (more than a kilometer wide) almost to Mars and back for two years. On the one hand, focusing only on an easier mission could paralyze reconnaissance missions because it would inhibit technological capability. On the other hand, striving for a more difficult mission could create a permanent delay in any meaningful reconnaissance mission, because the goals it would set would be too far from our reach. Our program provides a reference level between these two opposite extremes. It is a one-year round trip, which will be launched in 2024, and 30 days of which will be dedicated to the study of asteroid 2008 EV5. This object, which is about 400 meters long, looks like an asteroid of a type that is of great interest to many planetary researchers: a C-type carbonaceous asteroid, a possible relic from the time of the formation of the solar system and perhaps a representative of the ancient source of the organic matter on Earth.

The most efficient way to get there involves using the Earth's gravitational field for an old trick known as the Oberth effect. This trick is the reverse of the orbital entry maneuvers performed by routine robotic spacecraft. To prepare for this, mission controllers will equip the deep space vehicle with a high-thrust chemical rocket unit, which will be flown from Earth by an electrically powered supply spacecraft that will act as a sort of tugboat. After the unit is attached to the deep space vehicle and the crew gets on board, it will begin a free fall from a place near the moon almost up to the earth's atmosphere to gain tremendous speed. Then, at just the right moment, the high-thrust unit will kick in and the vehicle will be released from Earth's grip within minutes. This maneuver works optimally at the moment when the craft is moving at peak speed near the Earth, because the amount of energy the spacecraft accumulates is directly proportional to the speed at which it is already moving. While ion engines are generally more efficient than chemical rockets, the Obert effect is that exception; High and fast thrust is needed if we are to fully utilize the momentum provided by Earth's gravity, and only high-thrust rockets can provide this. When you combine the helical orbit in ion propulsion with the Oberth effect in chemical propulsion, it is possible to cut the amount of fuel needed to escape the Earth's gravitational field by 40%, compared to a system based solely on chemical propulsion.

As soon as the astronauts escape the Earth's pull, the plasma engines will be ignited and will push the vehicle at a constant rate to its destination. An ion engine provides continuous thrust, so it allows for flexibility. The mission planners can develop a stable system of abandonment routes in case a malfunction occurs at some stage of the mission. (The Japanese robotic asteroid mission, Yabusa, has been able to recover from several mishaps thanks to its ion engine.) If budget or technical issues prevent us from getting the deep space vehicle ready in time to reach asteroid 2008 EV5, we can choose another destination. Also, if we encounter technical difficulties, we can improvise. For example, if it is too difficult to cache the high-performance page materials in deep space, we can switch to the low-performance page materials and rewrite the task accordingly. Every detail of the mission can be changed.

Advantages of the tour booths

In our plan, the astronauts have a full month to tour the asteroid. Instead of wearing space suits, they will be able to learn from the diving chambers used to explore the depths of the sea and use special reconnaissance chambers. Basically, spacesuits are just big balloons, and the astronaut has to constantly fight the air pressure for every little movement, so spacewalking becomes hard work and the range of things that can be done is reduced. Not only does a patrol cabin with robotic operating arms alleviate this problem, but it also provides a place to eat and rest. In such a cabin the astronaut could run around in the field for several days at a time. NASA is already developing a Space Exploration Vehicle (SEV), which can be used as a reconnaissance cabin on asteroids. In the distant future it will be possible to adapt this model and become an all-terrain vehicle for tours on the moon and Mars.

The astronauts will carry out a comprehensive survey of the asteroid, looking for unusual mineral deposits and intriguing places where it is possible to look for samples from the early days of the solar system. NASA would like to send a team that is half Indiana Jones and half Montgomery Scott, the engineer of the Enterprise: astronauts with the scientific background required to locate precious samples hidden in the dust, and also the engineering background required to correct malfunctions that occur along the way.

At the end of the month, the ion engine will propel the deep space vehicle, detach it from the asteroid and send it on a six-month orbit back home. A few days before the team arrives on Earth, they will enter a capsule, detach from the main ship and set off on a trajectory that ends up landing in the sea. The empty deep space vehicle will remain in orbit around the Sun. It will perform a flight on the surface of the Earth and will continue to use the thrust of its ion engine to lower its energy relative to the Earth-Moon system, so that when it returns to Earth a year later it will be able to use a flight maneuver on the surface of the Moon to re-enter an orbit high above the Earth and await its mission the next It will be possible to use the ion engine and its living unit several times.

After several year-long asteroid missions, gradual improvements in life support systems and radiation shielding will pave the way to Mars. The first Mars mission may not actually land on the planet's surface. Instead she might tour its two moons, Phobos and Deimos. Such a journey is essentially an asteroid mission that stretches into a journey of two and a half years. At first glance, traveling all the way to Mars without landing on it may seem silly, but in fact such a landing would add enormous complexity to the mission. Missions to the moons of Mars will allow astronauts to get used to traveling in interplanetary space before taking on the challenge of landing on the Martian soil, walking across it and taking off from it.

Engineers have already come up with various ideas that would allow maximum flexibility and minimal cost for a space mission on Mars. The most appealing idea involves pre-positioning living units and exploration systems, so that the astronauts have a base ready when they arrive. This equipment will be able to be sent in a slow spaceship (with ion propulsion). As soon as it gets there, it will produce the propellant on Mars itself, either by distilling carbon dioxide from the atmosphere and mixing it with hydrogen, which will be imported from Earth to create methane and oxygen, or by creating liquid hydrogen and oxygen through the electrolysis of water extracted from the frozen ground. If the mission planners launch an empty rocket that can be refueled on Mars and used to return, they will significantly reduce the launch mass from Earth.

The relative motion of Earth and Mars gives astronauts about a year and a half (Earthly) on the surface before the two planets realign with each other, so they will have plenty of time for research. At the end of their stay, they will board a launch vehicle filled with locally produced fuel, jump into orbit around Mars, rendezvous with a deep space vehicle previously used in the series of asteroid missions and return to Earth. It would even be possible to place the vehicle on a circular orbit that would travel back and forth between Earth and Mars with gravity assist maneuvers providing all thrust for free.

Even if we pre-place some of the equipment on Mars, rockets that are supposed to land on Mars and take off again are very heavy and will need the largest SLS launchers to send them on their way. But the first deep space missions can be built from smaller parts to be launched on the first SLS or even on existing rockets. The phased approach recommended by us will provide the program with maximum ability to adapt to changes and will allow NASA to focus on solving the really difficult problems, such as radiation protection.

Today, NASA has the best opportunity in a generation to refocus on new types of spacecraft that will reach interplanetary space. The biggest barriers facing space exploration are not technical but related to the question of how to do as much with as little as possible. If NASA plans a gradual series of technological developments and increasingly ambitious missions, manned space flights will finally be able to break free, after 40 years, from low Earth orbit and enter the most exciting era they have ever experienced. With flexible planning, NASA can pave a path for those who want to wander among the wandering stars.

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About the authors

Damon Landau is an exoplanet mission analyst at NASA's Jet Propulsion Laboratory (JPL). He helped plan the trajectory of the recently launched Juno spacecraft to the planet Jupiter and worked on the agency's survey of near-Earth asteroids that astronauts might visit.

Nathan G. Strange is a mission architect at JPL. He was a member of the navigation team of the Cassini-Huygens spacecraft to Saturn and participated in the planning of the spacecraft's gravity assist orbit between Saturn's moons. He worked on technical drafts for future manned missions.

And more on the subject

Plymouth Rock: An Early Human Mission to Near Earth Asteroids Using Orion Spacecraft. J. Hopkins et al. Presented at the AIAA Space 2010 Conference & Exposition, August 30– September 2, 2010. http://tinyurl.com/PlymouthRockNEO

Target NEO: Open Global Community NEO Workshop Report. Report of a workshop held at George Washington University, February 22, 2011. Edited by Brent W. Barbee. July 28, 2011. www.targetneo.org

Near-Earth Asteroids Accessible to Human Exploration with High-Power Electric Propulsion. Damon Landau and Nathan Strange. Presented at the AAS/AIAA Astrodynamics Specialist Conference, Girdwood, Alaska, July 21–August 4, 2011. http://tinyurl.com/ElectricPath

300-kW Solar Electric Propulsion System Configuration for Human Exploration of Near-Earth Asteroids. JR Brophy et al. Presented at the 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, San Diego, July 31-August 3, 2011. http://tinyurl.com/300kWSEP

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