Computing Asteroid Paths For Future Exploratory, Redirect Missions
July 1, 2014

Computing Asteroid Paths For Future Exploratory, Redirect Missions

Gerard LeBlond for - Your Universe Online

Asteroids are chunks of debris left over from the solar system’s formation. They are a substantial interest to scientists, having possible resources embedded within them. Water, along with other resources found on these asteroids would be a benefit to astronauts traveling into deep space with missions to Mars and even deeper in our solar system.

Currently, NASA is developing methods needed for a 2030s mission to Mars. In the 2020s, NASA will test new technologies to capture an asteroid and direct it to a stable orbit around the moon. Asteroids are being monitored in search of a candidate for the Asteroid Redirect Mission (ARM). The Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) is one of the systems to be used. It was developed and maintained at Goddard Space Flight Center in Greenbelt, Maryland.

This system is fully automated and uses specialized computer algorithms to compute a route for a possible round-trip mission to one of the many Near-Earth Asteroids (NEA) that pass by our planet. This is the first study in the world that investigates and monitors accessibility of human flight to an NEA. In the last two years, NHATS has identified more than 1,000 NEAs, which could be part of missions for robotic and human destinations. Quite possibly, some of these NEAs could be a candidate for the ARM.

“We didn't know what the NEA-accessibility landscape for human spaceflight really looked like until the NHATS was created. As of 1 July, 2014, there are now 1,217 NEAs identified by our project that require less flight time and energy to visit and return from than does a Mars mission,” explained Brent Barbee of NASA Goddard Space Flight Center, NHATS project leader.

These asteroids come in a variety of shapes and sizes -- some as small as a car and others the size of a small moon. Asteroids have weak gravity so they’re prime targets for exploration. Most of them are located in the asteroid belt between Mars and Jupiter, however, there are a considerable amount whose orbit passes close by Earth.

“At present we have discovered 11,180 NEOs of all sizes, and we estimate that there are at least 10,000 NEOs larger than 100 yards in size that we haven't found yet,” said Barbee.

The population of small NEAs are estimated to be in the millions, being only a few yards across. Larger asteroids between 100 and 300 yards across number around 16,000, and almost 5,000 are between 300 to 1,000 yards across. An NEA is classified if its orbit passes by earth 1.3 times the average distance of Earth’s orbit to the sun.

Because an NEA’s orbit is so close to Earth, it is a potential impact threat. Sentry is one of NASA’s programs to detect, estimate the orbit and determine if an NEA is an impact risk. The automated system also identifies comets and other Near-Earth Objects (NEO) for a potential impact risk. The Sentry is located at the Jet Propulsion Laboratory (JPL) in Pasadena, California, and was designed and managed by NASA’s NEO Program.

All information and data of the NEOs are sent to the Minor Planet Center (MPC). Once the orbit of the NOE is determined, the data is sent to the JPL and a more precise orbit is determined. This data is used by the NHATS to find easily accessible asteroids for future missions.

“In a sense, the NHATS system complements hazard tracking. The NHATS system monitors the opportunities offered by NEAs, while the JPL Sentry system monitors the hazards NEAs may pose to Earth,” said Barbee, who developed the NHATS system.

Everyday a list of known NEAs are downloaded and NHATS figures out which ones are newly discovered and which ones have an updated orbit. The NHATS applies the new data to algorithms and computes all the possible round-trip trajectories for spacecraft paths.

There are certain criteria that an NEA must meet for a potential human mission. They include, departure dates no later than 2040, explore the asteroid for at least eight days, a round trip flight of 450 days or less and using less fuel than it would take for a trip to Mars.

“The NHATS criteria were developed by a human exploration committee in September of 2010. The idea was for the criteria to mean that round-trip missions to the NHATS-compliant NEAs would be less demanding than even the least demanding round-trip missions to Mars,” said Barbee.

There is a mailing list maintained by Barbee to help with NEA data.

“Anyone can sign up for the mailing list, but the intent is for astronomers and NEO scientists to sign up so that they receive rapid notification when a NEA is discovered that is particularly accessible. This helps ensure that follow-up observations are obtained in a timely manner,” said Barbee.

“I check the daily NHATS results message as soon as it arrives to see what 'the night's catch' brought in for newly discovered and updated NEAs,” said Lindley Johnson, NASA's NEO Programs Executive. “The information is crucial because it's our first look at opportunities to observe smaller NEAs when they are very close to Earth. Most often we have only a few days after discovery to make follow-up observations, so rapid notification is critical. Follow-up observations are important because they allow us to establish the NEA's orbit around the Sun more accurately, and to learn about the NEO's spin state, size, and composition. All of that information is vital for mission planning.”

The NHATS system began operation in September of 2010 and became fully operational in March 2012.

One of NHATS’ missions is the Origins Spectral Interpretation Resource Identification Security -- Regolith Explorer (OSIRIS_Rex) mission to investigate and return a sample from Bennu (an NEA) scheduled for launch in late 2016. It will reach Bennu in 2018 and return the sample to Earth in 2023.


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