Chapter 1 of 5

A long way to the Moon

Launch, a low-energy L1 cruise, lunar orbit insertion and student names

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

CAPE CANAVERAL, Fla.
GRAILWe were twins, built to fly together.
NASA/Jim Grossmann
01I am one of GRAIL’s two identical spacecraft. We launched together on September 10, 2011, on a Delta II Heavy from Cape Canaveral. Each of us was small enough to fit through a classroom door, yet we carried clocks and radios precise enough to listen to gravity.
We took the slow road on purpose.
02Instead of sprinting straight to the Moon, we cruised for about three and a half months on a low-energy path that went near the Sun–Earth L1 point. That gentler route helped our ultra-stable clocks settle and needed less braking fuel than a fast, steep arrival.
NASA twin Gravity Recovery and Interior Laboratory GRAIL spacecraft are lowered onto the second stage of their Delta II launch vehicle.
GRAILA new year began our orbit.
NASA/JPL-Caltech/KSC
03Ebb entered lunar orbit on December 31, 2011. I followed about a day later — NSSDCA lists January 1 for me, while NASA Science’s date table lists January 2. Either way, the twins arrived around the turn of the year and began their careful dance.
Schoolchildren gave us our names.
04Fourth-graders at Emily Dickinson Elementary School in Bozeman, Montana, won a nationwide contest and named us Ebb and Flow. The names came from the tides, which the Moon pulls across Earth — a perfect hint for two spacecraft that would measure the Moon’s own pull.

The big idea

A slower, low-energy route can be smarter than a sprint when clocks must settle and fuel must be saved.

Think about it

Why would a spacecraft take months to reach a place a crewed ship reached in days?

Fact file

Launch
10 September 2011 / 13:08:52 UT
Delta 7920H (D356) from Cape Canaveral SLC-17B.
Source ↗
Ebb orbit insertion
31 December 2011
NSSDCA and NASA Science agree on Ebb’s date.
Source ↗
Flow orbit insertion
NSSDCA: 1 January 2012 / NASA Science: 2 January 2012
The story says about a day after Ebb; the date table difference is retained in the evidence JSON.
Source ↗

In this chapter: Delta II Heavy, low-energy trajectory, Sun–Earth L1 route and lunar orbit insertion burns

Sources: Main record · GRAIL-A (Ebb) · NSSDCA · GRAIL-B (Flow) · NSSDCA

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

Chapter 1 of 5

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