Spaceflight Insider

NASA’s OSIRIS-REx set for Earth flyby on way to Asteroid Bennu

OSIRIS-REx zips past Earth in this artist's depiction. Image Credit: NASA

OSIRIS-REx zips past Earth in this artist’s depiction. Image Credit: NASA

Traveling at a staggering 19,000 miles (30,758 km) per hour, NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) will fly past its homeworld on its way to the asteroid Bennu. The slingshot maneuver will provide the Lockheed Martin-built spacecraft with a push to an inclination of six degrees – the angle that Bennu orbits the Sun – from Earth’s orbital plane and onward to the rocky leftover from the Solar System’s formation.

The September 22, 2017, Earth Gravity Assist, or EGA, will consist of the spacecraft using the gravity of a larger body in space to act on it, which prevents the expenditure of precious fuel. Gravitational assists can either slow a spacecraft down, or speed it up depending on the direction of the approach of the craft to the body, and that body’s spin direction, spin rate, and mass.

Graphic showing how fast OSIRIS-REx could traverse the U.S. during the EGA. Image Credit: NASA

Graphic showing how fast OSIRIS-REx could traverse the U.S. during the EGA. Image Credit: NASA

Gravitational assists can also be done to shift the trajectory of the spacecraft, which is the same type of maneuver that NASA’s Cassini mission which ended its nearly 20-year journey in space last week (Sept. 15, 2017), used to swing itself around and through the Saturn system for more than 13 years.

In OSIRIS-RExs case, it will slingshot itself around the Earth during its EGA, serving a dual purpose of increasing its speed as well as altering its trajectory. The spacecraft is scheduled to arrive at its destination of Bennu in 2018, but without the EGA that wouldn’t be possible, as the asteroid resides in a slightly off-axis plane. In order for OSIRIS-REx to successfully move into Bennu’s orbital plane, it’s imperative that the EGA be successful so that it can adjust its trajectory by 6 degrees, putting it on an intercept trajectory with Bennu.

Friday’s maneuver is expected to bring the spacecraft to within less than 11,000 miles (17,000 kilometers) of Earth, swinging it over Australia before making its closest approach over Antarctica near Cape Horn, Chile. This will put the craft within the orbital neighborhood of some satellites, but OSIRIS-REx’s flight dynamics team has a maneuver in place that they are prepared to execute in case the vehicle needs to avoid any potential collisions.

During Friday’s EGA maneuver, an expected 50-minute communications blackout will begin about 12:50 p.m EDT (16:50 GMT) due to the spacecraft’s position over Antarctica, placing it out of range of the Deep Space Network (DSN). Once communication has returned, which is expected at approximately 1:40 p.m. EDT (17:40 GMT), the operations team will begin preparations for science observations of Earth and the Moon beginning at 4:52 p.m. EDT (20:52 GMT) in order to calibrate the instruments in anticipation of its arrival at the asteroid Bennu in late 2018.

Bennu is a smaller asteroid and NEO that was chosen from more than 7,000 other near-Earth asteroids based on its size, location, and composition. Bennu is a type B carbonaceous asteroid with an approximate diameter of about 1,614 feet (492 meters) which also has a high probability of impacting the Earth in the late 22nd century.

OSIRIS-REx is the third of NASA’s New Frontiers missions, the first being New Horizons which flew by Pluto and its moons in 2015 and is currently on its way to visit 2014 MU69 – a Kuiper Belt object – on Jan. 1, 2019. The second New Frontiers mission is Juno which is currently orbiting Jupiter and returning fantastic science and images about the largest planet in our Solar System. OSIRIS-REx’s primary objectives are to survey a near-Earth object (NEO) asteroid, sample it, and then return those samples to Earth, giving scientists an unprecedented look at the environment of the Solar System at the time it formed – more than four-and-a-half billion years ago.

As thrilling as that is, those aren’t its only objectives. The mission also plans to study the Yarkovsky effect. The Yarkovsky effect is the force of photons on objects in the vacuum of space which alters their trajectories and spin rates by the transference of momentum from the photons to the objects which they impact. This force is believed to alter the trajectories of asteroids and meteors.

Since Bennu has the potential of striking the Earth in the future, studying the Yarkovsky effect on it could allow astrodynamicists to build better models and factor in the anticipated changes to its trajectory and movement as well as of other objects in space (whether to an asteroid, meteor, or spacecraft). More importantly, this could allow for more accurate modeling of how the Yarkovsky effect will impact trajectories over time.

OSIRIS-REx launched atop a United Launch Alliance Atlas V 411 rocket on Sept. 8, 2016, from Cape Canaveral Air Force Station’s Space Launch Complex 41 located in Florida.

Infographic showing how close OSIRIS-REx will come to Earth during Friday's flyby. Image Credit: NASA

Infographic showing how close OSIRIS-REx will come to Earth during Friday’s flyby. Image Credit: NASA





A native of the Greater Los Angeles area, Ocean McIntyre's writing is focused primarily on science (STEM and STEAM) education and public outreach. McIntyre is a NASA/JPL Solar System Ambassador as well as holding memberships with The Planetary Society, Los Angeles Astronomical Society, and is a founding member of McIntyre is currently studying astrophysics and planetary science with additional interests in astrobiology, cosmology and directed energy propulsion technology. With SpaceFlight Insider seeking to expand the amount of science articles it produces, McIntyre was a welcomed addition to our growing team.

Reader Comments

Are you sure 19,000 mph is correct. That doesn’t sound right. I thought the escape velocity from earth orbit was higher than that.

Sept. 23, 2017

Hello Dave,
Apologies, I provided you with incorrect data. Escape velocity is 25,000 MPH. Please review the NASA infographic in the center of this article as the speed noted is accurate.
Sincerely, Derek Richardson, Managing Editor – SpaceFlight Insider

Hi Derek,
Thanks for the reply. Just to let you know, I was curious and did a few minutes of research and discovered that escape velocity is…… a lot more complicated than I thought. Evidently its 25,000mph on the ground but less the higher you get above the earth. So the Osiris-Rex was traveling at a slower speed when it left earth orbit. Thanks for your effort for this good internet site.

Sept. 23, 2017

Hi Paul,
Your comments were deleted by me. You should review our Commenting Rules before you post again.
Jason Rhian – Editor, SpaceFlight Insider

I read this article apparently after the event, but was confused by the lack of a solid date for the fly-by. Many references to “Friday’s EGA”, but I had to re-read the article several times to figure out which Friday. Perhaps it would be useful to include the date in the first paragraph for those of us that come late to the party. Also, I was puzzled over the comment that Jupiter was the “first” and largest planet in the Solar System. First at what? Editorial comments aside, lots of great information

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