How to intercept an incoming NEO

Joachim Köppen Kiel/Strasbourg/Illkirch February 2002


About the Applet and what it does

The NEOintercept Applet extends the Travels in the Solar System Applet by the possibility to compute (by trial and error) possible ways to intercept an incoming NEO. For the explanations for most features, we refer to its Help Page

The Intercept Page:

We've zoomed in a portion of the x-y-plot, showing only the Earth orbit and the vicinity of some time before the collision. We've chosen to launch an interceptor 0.3 years (about 4 months) before the collision, and with a (heliocentric) speed of 35 km/s in a direction 45 degrees away from the Earth's direction (towards the side opposite to the Sun). The resulting trajectory is shown as a mauve track:

The track is shown only for the intervall between launch and when the collision of the body with Earth would happen. There are three coloured spots: they refer to the positions of Earth (blue), the body (cyan), and the interceptor (black) at the time when both interceptor and body have the same radius from the Sun. This particular try shows that the interceptor will be crossing the body's track too late to make a real interception.

The left hand side panel shows:

situation at Launch
time before coll.
the launch time (positive!)
the initial speed. Note that this is with respect to the Sun, not the departure speed from Earth
as explained for the Orbit Page , 0 degrees means in direction of the Earth's movement, 90 degrees pointing radially outwards from the Sun, 180 degrees is opposite of Earth's movement about the Sun
show track
this button re-draws the trajectory of the interceptor, for example after one has zoomed or cleared the x-y-plot
Hitting the Return key after entering data will cause computation of the track with the currently available data.
situation at Intercept
interception is ...
this is a message about whether the interceptor passes across the body's track too late or too early to make a proper interception
time before coll.
is the time when the interceptor and the body have the same distance from the Sun, i.e. the positions mareks with the coloured dots
distance from Earth
... at the same time
speed w.r.t. Body
is the speed with which the interceptor actually approaches the body ...
direction w.r.t. Body
is the angle between the trajectories of interceptor and body
defl.velocity chg.
is the change in velocity of the body done perpendicular to its flight direction (for maximum effect) to cause a deflection by one lunar orbit radius at the time of collision. This value was taken as a conservative guess, but the values can easily be scaled to other deflection distances, by noting the velocity change depends linearly on the deflection
the change of kinetic energy affected by the above deflection maneuver, given in Megatons of TNT explosive power. This does not take into account any inefficiency in the process of making the velocity change. Note that this value also scales linearly with the velocity change or the deflection

Let us try to aim at a lower angle:

but that resulted in the interceptor crossing the body's trajectory too early, before the body was there. But the solution is evidently in between these two angles, and finally we get this: The applet calls is a "close interception" as it makes only a rough judgement, and does not optimize the trajectoory automatically. Nonetheless, one can use the data displayed on the left hand side which tell about the situation at the intercept. Also, it tells about the velocity change necessary for a successful deflection. Here I demand a deflection by one radius of the lunar orbit, to be on the safe side. If one is content with a smaller deflection, one may scale the velocity change directly by the ratio of the deflection distance. Also, the change of kinetic energy for this deflection maneuver is given:

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