Space Traffic Control

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As more and more objects are launched into space, our ability to precisely plan missions and detect, track and catalog millions of pieces of space debris will become increasingly important.

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If you think about traffic in space, it probably seems like a commuter’s fantasy—an empty void where you can zip straight from point A to point B without traffic lights or objects in the way. Well, this vision may not be entirely accurate.

Last year alone, more than 92 space launches took place, successfully sending 88 objects into orbit—the largest number in more than two decades.

These spacecraft are not entering a deep, dark void, either. According to the United States Space Surveillance Network, more than 21,000 objects larger than 10 centimeters are currently orbiting the Earth. These chunks of space debris can travel in excess of 17,000 miles per hour and can be so damaging that even the International Space Station (ISS) has been moved out of the way to avoid collision.

“The number of small satellites and satellite operators around the world is skyrocketing, rapidly crowding an environment already congested today,” said Lockheed Martin’s Bruce Schafhauser.

To cope with the congestion, researchers are drawing up precise calculations to determine ideal launch windows, controlling flight paths for spacecraft already in orbit, and developing advanced systems to track and classify hundreds of thousands of pieces of space debris. 

Low Earth orbit space is crowded with active satellites and millions of pieces of debris from dead satellites, spent rocket boosters and stray hardware.

Planning a Mission

Similar to planning an airplane’s flight path, before an object is even launched into space, researchers must carefully plan its launch and flight.

These plans factor in considerations like what rockets will be used, where the spacecraft will be headed, how long it will be flying and whether or not it will rely upon the sun for its power.

In the end, the launch window can get highly specific.

Take for example a mission to Mars like the ones envisioned for Mars InSight—the best launch opportunity comes around only once every 26 months.

Handling Traffic

The potential for objects to collide in space is always a consideration in flight planning and controlling.

After years of space exploration, the vast area known as low Earth orbit is crowded with active satellites as well as debris from dead satellites, spent rocket boosters and stray hardware pieces.

“With more than 60 nations operating in space today, the final frontier is far more complex than when space exploration and use started,” said Schafhauser. “With hundreds of thousands of objects in Earth orbit, space debris and the associated risk of potential collisions threaten space-based assets and critical systems that merit protection.”

This debris threatens not only commercial satellites but also military assets that help monitor and protect nations around the world.

Thankfully, the Space Fence program will make 1.5 million observations a day to detect, track, measure and catalog items as small as a baseball—and will support catalog growth to 200,000 objects. This is a ten-fold increase compared to the number of objects tracked today.

Space Fence will make 1.5 million observations a day to detect, track, measure and catalog items as small as a baseball.

Impacts on Air Traffic

Here on Earth, air traffic is generally not disrupted by space vehicles, thanks to reserved airspaces. However, as space traffic is projected to grow, the Federal Aviation Administration is already looking at ways to increase the efficiency and safety of operations.

The NextGen Air Transportation System is making improvements that will tightly integrate the capabilities of the Flight Management System on board the aircraft with automation platforms.

These improvements include integrating time into the 3-D aircraft trajectory. This four-dimensional trajectory, or 4DT, continuously evaluates the aircraft's position in space and time so operators can more efficiently manage operations.

“Today, the timing of space launches, space debris and potential collisions do not directly affect air traffic management systems, but as the traffic of space vehicles increases, there certainly will be an impact,” said Lockheed Martin Fellow Sergio Torres. “The use of four-dimensional trajectories will need to be extended to incorporate these space vehicles into the air traffic system.”

What the Future May Bring

While the ultimate solution to space traffic may be decades away, researchers and technologists are already thinking about technologies that could help us get there.

“Space traffic control will develop from the need for safety—both of our assets and of course, our lives,” said Tim Priser, Mars InSight deputy program manager. “We will see space traffic evolve more and more complex launch and on-orbit operational rules, regulations, laws and enforcement methods.”

This follows the same evolution as traffic here on Earth. As cities grew and we moved from horse and buggy to vehicles, there was also a need to implement rules and regulations to govern traffic flow, such as installing traffic lights or building highways.

Collisions in space could also be mitigated by applying new technologies to the spacecraft design itself. The autonomous hazard avoidance systems used on automobiles, trains and aircraft today can easily be adapted onto launch vehicles and spacecraft of tomorrow.

For any science fiction fan, the most exciting solution for space traffic control may be to actually build a launch complex in space. A geosynchronous space port where we could assemble, test and launch spacecraft.

“We will eventually see the need for these spaceports ‘above the fray,” said Priser. “This mitigates the low Earth orbit congestion problem and enables an endless list of space technologies that are not feasible today.”    

Air Traffic vs. Space Traffic

What exactly does it take to plan a flight here on Earth versus a mission to space?    

Planning When to Launch

For space travel, a launch takes extended planning, with the ideal launch window varying significantly based on several factors, including the Earth’s orbit on its axis and the location of the sun. Pre-planning is also important for air traffic. While flights generally take off on regularly scheduled timetables, the flight plans, aircraft and personnel may be changed up to the last minute. Departure Planning Information technology is particularly useful for relaying real-time information about aircraft departures, leading to better decisions on how to regulate the flow of traffic and account for arrival times.

Determining Where to Fly

A spacecraft’s path must be carefully mapped out—and adhered to—based on its mission. For example, when a spacecraft is launched into orbit around Earth, it must get above the atmosphere, at least 200 miles up, and have a specific speed depending on its orbit. In addition, systems like Space Fence can be used to ensure that operators know which objects are of a size that could potentially cause harm. An airplane’s flight path is designed for a number of factors as well—such as optimizing fuel efficiency or reducing time in air—and can generally change as needed, based on things like the weather. New NextGen technology uses 4-D trajectory models that can predict the path of each aircraft in time and space, providing an ability for the aircraft to fly along the most efficient routes.

Navigation and Guidance

Many spacecraft are sent into space without a pilot, requiring autonomous or partially autonomous operations throughout the mission. Controllers can receive regular status updates—such as their location or instrument performance—and can respond as needed through direct communications with the spacecraft. To support air traffic navigation here on Earth, automated air traffic tools help controllers detect and resolve potential conflicts. With technology like the En Route Automation Modernization program or ERAM, pre-departure reroute and airborne reroute capabilities can automatically transmit re-routing information from the traffic manager to the pilot and dispatcher.

Arriving at a Destination

Space controllers put significant effort into planning a spacecraft’s arrival—whether it is to re-enter the Earth’s atmosphere, enter into orbit or land on a planet. Often, these plans can take years to unfold. For aircraft, flight times are much shorter, so delays become even more noticeable. In planning for arrivals, systems using time-based separation between aircraft can potentially halve delays from headwinds. Real-time wind data is used to calculate the optimum safe time between arriving aircraft.

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