Posts Tagged ‘moon missions’

Slice of History: Ranger Impact Limiter

Monday, November 4th, 2013

By Julie Cooper

Each month in “Slice of History” we feature a historical photo from the JPL Archives. See more historical photos and explore the JPL Archives at

Ranger Impact Limiter
Ranger Impact Limiter — Photograph number 292-41A

This photo was taken in November 1960 to show the lightweight balsa wood impact limiter that was to be used in the NASA Jet Propulsion Laboratory’s Ranger Block II spacecraft design (Rangers 3, 4, and 5). The woman holding the sphere is Systems Design secretary Pat McKibben. The sphere was 65 cm in diameter, and it surrounded a transmitter and a seismometer instrument that was designed by the Caltech Seismological Laboratory. The sphere would separate from the spacecraft shortly before impact and survive the rough landing on the moon. The capsule was also vacuum-filled with a protective fluid to reduce movement during impact. After landing, the instrument was to float to an upright position, then the fluid would be drained out so it could settle and switch on.

Due to a series of malfunctions in 1962, these three Ranger spacecraft either crashed without returning data or missed the moon. In July 1964, the first successful Ranger spacecraft, Ranger 7, reached the moon and transmitted more than 4,000 images to Earth.

This post was written for “Historical Photo of the Month,” a blog by Julie Cooper of JPL’s Library and Archives Group.

Lunar Eclipse, the Moon’s Interior, and the Holy GRAIL

Wednesday, December 15th, 2010

By Sami Asmar

Earth's moon

In addition to the awesome views they offer, lunar eclipses have always provided scientific clues about the moon’s shape, location and even surface composition. Although there will continue to be opportunities for observers to examine and reflect on fundamental concepts about the moon, such as its origin and interior structure, more modern tools are aiding these observations.

When it comes to understanding what a moon or a planet is made of remotely — short of touching it or placing seismometers on its surface or probes below the surface — classical physics comes to the rescue. By measuring the magnetic and gravitational forces that are generated on the inside and manifested on the outside of a planet or moon, we can learn volumes about the structure of its interior.

A spacecraft in the proximity of the moon can detect these forces. In the case of gravity, the mass of the moon will pull on the spacecraft due to gravitational attraction. If the spacecraft is transmitting a stable radio signal at the time, its frequency will shift by an amount exactly proportional to the forces pulling on the spacecraft.

This is how we weigh the moon and go further by measuring the detailed distribution of the densities of mountains and valleys as well as features below the moon’s surface. This collection of information is called the gravity field.

In the past, this has lead to the discovery mascons on the moon, or hidden, sub-surface concentrations of mass not obvious in images or topography. If not accounted for, mascons can complicate the navigation of future landed missions. A mission, human or robotic, attempting to land on the moon would need to have a detailed knowledge of the gravity field in order to navigate the landing process safely. If a spacecraft sensed gravitational pull higher than planned, it could jeopardize the mission.

GRAIL spacecraft

The Gravity Recovery and Interior Laboratory (GRAIL) mission, scheduled to launch in September, is comprised of twin spacecraft flying in formation with radio links between them to measure the moon’s gravity field globally. This is because a single spacecraft with a link to Earth would be obstructed when the spacecraft goes behind the moon, leaving us with no measurement for nearly half of the moon, since the moon’s far side never faces the Earth. The GRAIL technique may also reveal if the Moon has a core with a fluid layer.

So as you go out to watch the lunar eclipse on the night of Dec. 20, think about how much we’ve learned about the moon so far and what more we can learn through missions like GRAIL. Even at a close distance from Earth, the moon remains a mystery waiting be uncovered.