← INDEX — FIG. 00 — 26 SEPTEMBER 2022, 23:14:24 UTC
DIDYMOS · DIMORPHOS · 6.1449 km/s
IMPACT
DART AND PLANETARY DEFENCE
People deliberately changed the motion of a natural body in space.
BEGIN — CHAPTER 01 →CH.01 / 09 — WHY BOTHER
Chelyabinsk was only 19 metres across
Chelyabinsk released roughly 500 kilotons.
Energy grows with the cube of size and square of speed.
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E = ½ m v², stony density 3,000 kg/m³.
CH.02 / 09 — A TEST YOU CAN MEASURE FROM EARTH
Hit the moon, time the moon
DART chose a binary asteroid.
The period was known to half a second.
CH.03 / 09 — THE LAST THREE SECONDS
25 metres from dead centre, between two boulders
DART hit 25 m from the centre of the figure.
LICIACube watched the plume.
CH.04 / 09 — THIRTY-THREE MINUTES
The ejecta pushed harder than the spacecraft
The period changed by −33.0 ± 1.0 minutes.
β is total momentum over the impactor's momentum.
MOMENTUM TRANSFER AND PERIOD CHANGE
ΔvT = f · β m U / M · ΔT / T = 3 ΔvT / v · v = 2π a / T
Geometry factor f = 0.91.
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CH.05 / 09 — TIME IS THE LEVER
Millimetres per second, multiplied by years
The drift is about 3 Δv t.
Discovery matters more than force.
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Linear drift approximation.
CH.06 / 09 — WHAT DART TAUGHT
Rubble piles are easier to push than solid rock
β was well above 1.
A spacecraft can find and hit a 150 m body by itself.
CH.07 / 09 — THE CRIME-SCENE INVESTIGATOR
Hera goes back to weigh Dimorphos
Hera rendezvous in November 2026.
Apophis in 2029.
CH.08 / 09 — FROM AIRBURST TO DEFLECTION
A short history of planetary defence
DART showed that, given enough warning, we could.
CH.09 / 09 — REFERENCES