In July 2015, NASA — and the United States — completed the reconnaissance of the planets by exploring the Pluto system with New Horizons. Navigation of the New Horizons spacecraft during approach to Pluto and its satellite Charon presented the following new challenges related to the distance from the Earth and Sun and the dynamics of two body motion where the mass ratio results in the barycenter being outside the radius of the primary body:
* Since the Earth is about 30 astronomical unit (a.u.) from the spacecraft during the approach to Pluto and Charon, the round trip light time is greater than 8 hours making two-way Doppler tracking difficult. 1 Astronomical Unit = 92 955 807.3 miles.
* The great distance from the Sun also reduces the visibility of Pluto since Pluto receives about 1/900 of the solar radiation as the Earth.
* The two body motion involves Pluto and Charon moving in elliptic orbits about each other, and the system mass is a simple function of the period and semi-major axis of the orbit.
* The period can be measured to high precision from Earth based telescope observations and the orbit diameter can be measured to a precision of perhaps 100 km enabling the system mass to be determined within 1 percent.
* The maximum separation of Pluto and Charon on a star background provides a powerful observation of the total orbit size.
* The fly-by mission is characterizing the geology and atmosphere of Pluto and its large moon Charon. At launch, the spacecraft followed a heliocentric trajectory to a Jupiter fly-by for gravity assist in 2007, and then settling into a long 8-year cruise to the outermost planet.
To navigate further into stars beyond our solar system, a rotating black hole might provide additional gravity assistance, if its spin axis is aligned the right way.
General relativity predicts that a large spinning mass-produces frame-dragging—close to the object, space itself is dragged around in the direction of the spin. Although attempts to measure frame dragging about the Sun have produced no clear evidence, experiments performed by Gravity Probe B have detected frame-dragging effects caused by Earth.
In general relativity the gravitational field is encoded in the elliptic geometry of space-time. Much of the conceptual compactness and mathematical elegance of the theory can be traced back to this central idea. The encoding is also directly responsible for the most dramatic ramifications of the theory: the big-bang, black holes and gravitational waves.
Reaching Pluto, the “third” zone of our solar system — beyond the inner, rocky planets and outer gas giants — has been a space science priority for years, because it holds building blocks of our solar system that have been stored in a deep freeze for billions of years. Encoding the geometry of navigating solar system and beyond, we can fix “The Fault in Our Stars”, mitigating risk and uncertainty.
drjohnxwang 