2017-09-22: Earth gravity-assist flyby



Official website page: NASA'S OSIRIS-REx Spacecraft Slingshots Past Earth

The graph shows the gravity-assist geometry in the geocentric mean equator and equinox of J2000 reference frame.
According to the NAIF's files, the change in the velocity vector was 3.8056 km/s.

The blue line represents the Earth's heliocentric velocity vector, while the yellow line points toward the Sun (both lines lie almost exactly in the J2000 ecliptic plane).

The altitude (shown as "h= ..." when you hover the mouse over a point) is calculated above an ellipsoid with an equatorial radius of 6378.1366 km and a polar radius of 6356.7519 km.
The values obtained for the perigee are:
   time: 2017-09-22 16:51:46.345 UTC
   radius vector: 23591.783 km
   geocentric speed: 8.5198 km/s
   location: 74.7251 S, 88.0949 W
   altitude: 17233.542 km
Here's the flyby in the geocentric mean ecliptic and equinox of J2000 reference frame.

The graph covers 90 days before and after the spacecraft perigee epoch.
The following objects are shown: Earth (single blue dot), OSIRIS-REx, Sun (in the geocentric frame, the Sun orbits the Earth), Bennu, Moon (its orbit is very small in this scale).

Notice how the flyby changed the spacecraft orbital plane to match Bennu orbital inclination.

The graph shows the distance between the spacecraft and the Earth (blue plot) and the spacecraft osculating orbital inclination to the ecliptic plane of J2000 (orange plot).
The green vertical lines represent the Earth sphere of influence (the distance from the Earth where the gravitational acceleration of the Earth and of the Sun are the same).

The spacecraft orbital inclination increased from about 0.15 deg before the SOI to about 6.5 deg after the SOI.
Here's the path across the Earth's surface.

The values obtained for the lowest altitude above the WGS-84 ellipsoid are:
   time: 2017-09-22 16:51:47.924 UTC
   radius vector: 23591.786 km
   geocentric speed: 8.5198 km/s
   location: 74.6944 S, 88.0594 W
   altitude: 17233.539 km
Here's the distance between the spacecraft and the Earth (blue plot) and the spacecraft speed wrt the Sun (orange plot).
The green vertical lines represent the Earth sphere of influence.

The spacecraft heliocentric speed increased from about 29.7 km/s before the SOI to about 31 km/s after the SOI.