Chapter 3 of 5

Two impacts, one experiment

Separating the Centaur and observing its impact

Told in LCROSS’s imagined voice · the events are real · source

CAPE CANAVERAL, Fla.
LCROSSOn October 9, I let my heavy partner travel ahead.
NASA/Dimitri Gerondidakis
01At 01:50 UT, the Centaur and shepherding spacecraft separated. A braking maneuver created time between our arrivals. My instruments could watch the first impact before my own mission ended.
The Centaur's motion supplied the punch for the experiment.
02It struck Cabeus near 11:31 UT, at approximately two and a half kilometers per second. The deliberate impact excavated lunar material. We were using the energy of a moving rocket body to expose material from beneath the surface.
The Lunar Reconnaissance Orbiter and Lunar Crater Observation and Sensing Satellite are bound for the moon after a flawless liftoff Thursday, June 18, 2009, from Cape Canaveral Air Force Station in Florida aboard an Atla
LCROSSDifferent instruments watched different parts of what happened.
NASA/Bill Ingalls
03The payload's cameras, spectrometers and photometer observed the impact and its aftermath. Debris rising into sunlight could be studied for composition; thermal views offered information ordinary visible-light pictures could not.
The time between the impacts was my chance to send the evidence home.
04I followed the Centaur and observed the plume while transmitting data to Earth. These were short, carefully planned observations. The later scientific results would come from analysing those records—not from the size of a televised splash.

The big idea

Timing is part of instrument design. Separating the impactor from the observer made a destructive event into a brief scientific experiment.

Think about it

Why did the spacecraft carrying the instruments need to arrive later?

Fact file

Separation
9 October 2009 / 01:50 UT
The shepherd then performed a braking maneuver to arrive later.
Source ↗
Centaur impact
9 October 2009 / approximately 11:31 UT
Cabeus crater. The catalog gives 11:31:19.5 UT and an approximate speed of 2.5 km/s.
Source ↗
Observation interval
Approximately four minutes
Time between impacts, not a claim of four minutes inside a uniform cloud.
Source ↗

In this chapter: Separation mechanism, braking thrusters, Centaur stage and payload cameras

Sources: Main record · LCROSS · NSSDCA Master Catalog · Flight Operations for the LCROSS Lunar Impactor Mission · What is LCROSS? · NASA Ames

Machine illustration: AI-made. Photos: NASA Image and Video Library, credited on each picture.

Chapter 3 of 5

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