Archive for December, 2013

NASA’s Dawn Plans for Planetary Shores Ahead

Tuesday, December 31st, 2013

By Marc Rayman
As NASA’s Dawn spacecraft makes its journey to its second target, the dwarf planet Ceres, Marc Rayman, Dawn’s chief engineer, shares a monthly update on the mission’s progress.

NASA Dawn spacecraft between its targets, Vesta and Ceres
Artist’s concept of NASA’s Dawn spacecraft between the giant asteroid Vesta and the dwarf planet Ceres. Image credit: NASA/JPL-Caltech

Dear Clairvoydawnts,

Now more than halfway through its journey from protoplanet Vesta to dwarf planet Ceres, Dawn is continuing to use its advanced ion propulsion system to reshape its orbit around the sun. Now that the ship is closer to the uncharted shores ahead than the lands it unveiled astern, we will begin looking at the plans for exploring another alien world. In seven logs from now through August, we will discuss how the veteran adventurer will accomplish its exciting mission at Ceres. By the time it arrives early in 2015 at the largest object between Mars and Jupiter, readers will be ready to share not only in the drama of discovery but also in the thrill of an ambitious undertaking far, far from Earth.

Mission planners separate this deep-space expedition into phases. Following the “launch phase” was the 80-day “checkout phase”. The “interplanetary cruise phase” is the longest. It began on December 17, 2007, and continued to the “Vesta phase,” which extended from May 3, 2011, to Sept. 4, 2012. We are back in the interplanetary cruise phase again and will be until the “Ceres phase” begins in 2015. (Other phases may occur simultaneously with those phases, such as the “oh man, this is so cool phase,” the “we should devise a clever name for this phase phase,” and the “lunch phase.”) Because the tasks at Vesta and Ceres are so complex and diverse, they are further divided into sub-phases. The phases at Ceres will be very similar to those at Vesta, even though the two bodies are entirely different.

In this log, we will describe the Ceres “approach phase.” The objectives of approach are to get the explorer into orbit and to attain a preliminary look at the mysterious orb, both to satisfy our eagerness for a glimpse of a new and exotic world and to obtain data that will be helpful in refining details of the subsequent in-depth investigations. The phase will start in January 2015 when Dawn is about 400,000 miles (640,000 kilometers) from Ceres. It will conclude in April when the spacecraft has completed the ion thrusting necessary to maneuver into the first orbit from which it will conduct intensive observations, at an altitude of about 8,400 miles (13,500 kilometers). For a reason to be revealed below, that orbit is known by the catchy cognomen RC3.

(Previews for the Vesta approach phase were presented in March 2010 and May 2011, and the accounts of its actual execution are in logs from June, July, and August 2011. Future space historians should note that the differing phase boundaries at Vesta are no more than a matter of semantics. At Vesta, RC3 was described as being part of the approach phase. For Ceres, RC3 is its own distinct phase. The reasons for the difference in terminology are not only unimportant, they aren’t even interesting.)

The tremendous maneuverability provided by Dawn’s uniquely capable ion propulsion system means that the exact dates for events in the approach phase likely will change between now and then. So for those of you in 2015 following a link back to this log to see what the approach plan has been, we offer both the reminder that the estimated dates here might shift by a week or so and a welcome as you visit us here in the past. We look forward to meeting you (or even being you) when we arrive in the future.

Most of the approach phase will be devoted to ion thrusting, making the final adjustments to Dawn’s orbit around the sun so that Ceres’s gravity will gently take hold of the emissary from distant Earth. Next month we will explain more about the unusual nature of the gradual entry into orbit, which will occur on about March 25, 2015.

Starting in early February 2015, Dawn will suspend thrusting occasionally to point its camera at Ceres. The first time will be on Feb. 2, when they are 260,000 miles (420,000 kilometers) apart. To the camera’s eye, designed principally for mapping from a close orbit and not for long-range observations, Ceres will appear quite small, only about 24 pixels across. But these pictures of a fuzzy little patch will be invaluable for our celestial navigators. Such “optical navigation” images will show the location of Ceres with respect to background stars, thereby helping to pin down where it and the approaching robot are relative to each other. This provides a powerful enhancement to the navigation, which generally relies on radio signals exchanged between Dawn and Earth. Each of the 10 times Dawn observes Ceres during the approach phase will help navigators refine the probe’s course, so they can update the ion thrust profile to pilot the ship smoothly to its intended orbit.

Whenever the spacecraft stops to acquire images with the camera, it also will train the visible and infrared mapping spectrometer on Ceres. These early measurements will be helpful for finalizing the instrument parameters to be used for the extensive observations at closer range in subsequent mission phases.

Dawn obtained images more often during the Vesta approach phase than it will on approach to Ceres, and the reason is simple. It has lost two of its four reaction wheels, devices used to help turn or stabilize the craft in the zero-gravity, frictionless conditions of spaceflight. (In full disclosure, the units aren’t actually lost. We know precisely where they are. But given that they stopped functioning, they might as well be elsewhere in the universe; they don’t do Dawn any good.) Dawn’s hominin colleagues at JPL, along with excellent support from Orbital Sciences Corporation, have applied their remarkable creativity, tenacity, and technical acumen to devise a plan that should allow all the original objectives of exploring Ceres to be met regardless of the health of the wheels. One of the many methods that contributed to this surprising resilience was a substantial reduction in the number of turns during all remaining phases of the mission, thus conserving the precious hydrazine propellant used by the small jets of the reaction control system.

When Dawn next peers at Ceres, nine days after the first time, it will be around 180,000 miles (290,000 kilometers) away, and the pictures will be marginally better than the sharpest views ever captured by the Hubble Space Telescope. By the third optical navigation session, on Feb. 21, Ceres will show noticeably more detail.

At the end of February, Dawn will take images and spectra throughout a complete Ceres rotation of just over nine hours, or one Cerean day. During that period, while about 100,000 miles (160,000 kilometers) distant, Dawn’s position will not change significantly, so it will be almost as if the spacecraft hovers in place as the dwarf planet pirouettes beneath its watchful eye. Dawn will see most of the surface with a resolution twice as good as what has been achieved with Hubble. (At that point in the curving approach trajectory, the probe will be south of Ceres’s equator, so it will not be able to see the high northern latitudes.) This first “rotation characterization,” or RC1, not only provides the first (near-complete) look at the surface, but it may also suggest to insightful readers what will occur during the RC3 orbit phase.

There will be six more imaging sessions before the end of the approach phase, with Ceres growing larger in the camera’s view each time. When the second complete rotation characterization, RC2, is conducted on March 16, the resolution will be four times better than Hubble’s pictures. The last photos, to be collected on March 24, will reveal features seven times smaller than could be discerned with the powerful space observatory.

The approach imaging sessions will be used to accomplish even more than navigating, providing initial characterizations of the mysterious world, and whetting our appetites for more. Six of the opportunities also will include searches for moons of Ceres. Astronomers have not found moons of this dwarf planet in previous attempts, but Dawn’s unique vantage point would allow it to discover smaller ones than would have been detectable in previous attempts.

When the approach phase ends, Dawn will be circling its new home, held in orbit by the massive body’s gravitational grip and ready to begin more detailed studies. By then, however, the pictures and other data it will have returned will already have taught Earthlings a great deal about that enigmatic place. Ceres has been observed from Earth for more than two centuries, having first been spotted on January 1, 1801, but it has never appeared as much more than an indistinct blob amidst the stars. Soon a probe dispatched by the insatiably curious creatures on that faraway planet will take up residence there to uncover some of the secrets it has held since the dawn of the solar system. We don’t have long to wait!

Dawn is 20 million miles (32 million kilometers) from Vesta and 19 million miles (31 million kilometers) from Ceres. It is also 2.42 AU (225 million miles, or 362 million kilometers) from Earth, or 1,015 times as far as the moon and 2.46 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 40 minutes to make the round trip.

› Read more entries from Marc Rayman’s Dawn Journal

Habitability, Taphonomy, and Curiosity’s Hunt for Organic Carbon

Tuesday, December 24th, 2013

By John Grotzinger
This blog entry from John Grotzinger, the project scientist for NASA’s Curiosity Mars rover, was originally prepared for use by the Planetary Society and explains the importance of some of the rover’s findings.

Curiosity Selfie

This self-portrait of NASA’s Mars rover Curiosity combines dozens of exposures taken by the rover’s Mars Hand Lens Imager (MAHLI) during the 177th Martian day, or sol, of Curiosity’s work on Mars (Feb. 3, 2013), plus three exposures taken during Sol 270 (May 10, 2013)
› Full image and caption

It was fun for me to catch up with Emily Lakdawalla of the Planetary Society at the American Geophysical Union meeting, and to discuss our new Curiosity mission results. They focus on the discovery of an ancient habitable environment; we are now transitioning to the focused search for organic carbon. What’s great about Emily’s blog is that with her strong science background she is able to take complex mission results and translate these into something that can reach a broader and more diverse audience. I’ll try to do the same here.

Since we first reported our results on March 12, 2013, from drilling in Yellowknife Bay it has been my experience that lots of people ask questions about how the Curiosity mission, and future missions, will forge ahead to begin with looking for evidence of past life on Mars. There is nothing simple or straightforward about looking for life, so I was pleased to have the chance to address some of the questions and challenges that we find ourselves most frequently discussing with friends and colleagues. The Planetary Society’s blog is an ideal place to take the time to delve into this.

I also need to state at the outset that what you’ll read below is my opinion, as Curiosity science team member and Earth geobiologist, and not necessarily as its Project Scientist. And I have only worked on Mars science for a decade. However, I can say that many other members of the Curiosity team share this opinion, generated from their own experiences similar to mine, and it was easy for us to adopt these ideas to apply to our future mission. To a large extent, this opinion is shaped by our experience of having spent decades trying to explore the early record of life on Earth. As veterans of the Mars Exploration Rover and Curiosity missions, we have learned that while Mars has significant differences from Earth, it also has some surprising similarities that could be important in the search for evidence of ancient Martian life - a “paleobiosphere,” if you will. The bottom line is that even for Earth, a planet that teems with life, the search for ancient life is always difficult and often frustrating. It takes a while to succeed. I’ll try to explain why later on.

So here goes….

The Dec. 9, 2013, publication of the Curiosity team’s six papers in Science provides the basis for understanding a potentially habitable environment on ancient Mars. The search for habitable environments motivated building the rover, and to that end the Curiosity mission has accomplished its principal objective. This naturally leads to the questions of what’s next, and how we go about exploring for organic carbon?

To better understand where we’re coming from, it helps to break down these questions and analyze them separately. With future advocacy of missions to Mars so uncertain, and with difficult-to-grasp mission objectives located between “the search for water” (everyone got that) and “the search for life” (everyone wants NASA to get on with it), the “search for habitability” and the “search for carbon” are important intermediate steps. By focusing on them scientists can identify specific materials to study with more sophisticated future missions and instruments, or to select for sample return, or to be the target of life detection experiments.

Note: You can get access to all six of these Science papers here or here. The latter site also has the papers we published back in September. Science has a policy that allows us to post a “referrer link” to our home websites. This redirects the query to AAAS, where the paper can be downloaded without cost.


Let’s start with “habitability.” We reported the discovery of an ancient lake, and one that formed clay minerals. The presence of clays represents more benign environmental conditions than the acid sulfates found by Spirit and Opportunity. However, clays are not the only thing needed to demonstrate habitability. The bar is high: In brief, a mission needs to demonstrate the presence of water, key elements regarded as the building blocks of life (including carbon), and a source of energy. And you need to find them all together, and at the same instant in geologic time. In turn, each one of these must be characterized further to qualify an environment as having been habitable. Finally, it’s never black and white; understanding habitability is part of a broad continuum of environmental assessment, which is why orbiters and earlier rovers and landers are important assets in this process as well.

It is also important to define what group of organisms is being imagined to have inhabited the environments - their requirements will vary. Single-celled microorganisms are a great place to start based on our understanding of the early evolution of life on Earth, which was dominated by microbes for at least the first two billion years of the planet’s history. More specifically, the Curiosity team has been focusing on the conditions of habitability relevant to “chemolithotrophs,” a group of microbes that feeds on chemical energy available in rocks.


The water of a habitable environment should be relatively fresh, or at least not contain so much salt that the relative abundance of water is so low (what chemists call “water activity”) that the osmotic pressure on cells would cause them to collapse. My favorite analog here is honey. Yes, it’s an aqueous environment but no, it’s not habitable: The sugar content is so high that microbes can’t live in it. This is why honey doesn’t spoil when not refrigerated. Salt serves the same role as sugar; too much salt inhibits life. Acidity is also important, although microbes have been shown to tolerate an extraordinary range of pH, including the very lowest values encountered in natural environments on Earth. However, more moderate pH favors a greater diversity of microorganisms, and thus more options to explore for emerging life forms. Finally, the water needs to last a long time on the surface; the longer, the better. A flow of water emerging on the surface of Mars from an underground source and boiling off in the presence of Mars’ modern low atmospheric pressure is not a good scenario for life. A stable source, such as a very ancient lake, with associated streams, and water flowing through the ground beneath it, is much better. We envision for the lake/stream/groundwater system that Curiosity discovered at Yellowknife Bay that the water could have existed for millions of years potentially. But even shorter periods are viable - the qualitative point here is that the rocks at Yellowknife Bay record more than a one-time event.

Key building blocks of life.

A conventional list of key elements for life will include “CHNOPS” - carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Previous orbiter and landed missions have provided ample evidence for H, O, and S via observations of sulfate and clay minerals, and P was measured by earlier rovers and landers. Curiosity has done the same. The tricky stuff is N and C and, along with P, they must all be “bioavailable,” which means to say they cannot be bound tightly within mineral structures that water and microbial chemical processes could not unlock. Ideally, we are looking for concentrated nitrogen- and phosphorous-bearing sedimentary rocks that would prove these elements were actually dissolved in the past water at some point, and therefore could have been available to enable microorganism metabolism. But in the interim Curiosity has been able to measure N as a volatile compound via pyrolysis (heating up rock powder in the SAM instrument), and P is observed in APXS data. We feel confident that N was available in the ancient environment, however we must infer that P was as well. Two of the Science papers, Grotzinger et al. and Ming et al., discuss this further.

Carbon is the elephant in the room. We’ll discuss organic carbon further below, but here it’s important to make one very important point: Organic carbon in rocks is not a hard-line requirement for habitability, since chemoautotrophs can make the organics they need to build cellular structures from metabolizing carbon dioxide (CO2). These organisms take up inorganic carbon as CO2 dissolved in water to build cellular structures. Organic carbon could serve as fuel if it was first oxidized to CO2, or could be used directly for biomass, or could be part of waste products. As applied to Mars it is therefore attractive to appeal directly to CO2, presumed to have been abundant in its early atmosphere. Curiosity does indeed see substantial carbon generated from the ancient lake deposits we drilled. The CO2 that was measured is consistent with some small amount of mineral carbon present in those lake mudstones. These minerals would represent CO2 in the ancient aqueous environment. Furthermore, it is possible that Martian organic sources have been mixed with inorganic sources of carbon in the mudstone; however, any organic contributions from the mudstone would be mixed with Earth-derived sources during analysis (see Ming et al. paper).


All organisms also require fuel to live and reproduce. Here it is essential to know which kind of microorganism we’re talking about, since there are myriad ways for them to harvest energy from the environment. Chemolithotrophs derive energy from chemical reactions, for example by oxidizing reduced chemical species like hydrogen sulfide or ferrous iron. That’s why Curiosity’s discovery of pyrite, pyrrhotite, and magnetite are so important (see Vaniman et al. and Ming et al. papers). They are all more chemically reduced than their counterparts discovered during earlier missions to Mars (for example, sulfate and hematite). Chemolithotrophic microbes, if they had been present on Mars at the time of this ancient environment, would have been able to tap the energy in these reduced chemicals (such as hydrogen sulfide, or reduced iron) to fuel their metabolism. If you are interested in more detail regarding these kinds of microbial processes I can strongly recommend Nealson and Conrad (2000) for a very readable summary of the subject.

The next section describes where I think we’re headed in the future. We’ll continue to explore for aqueous, habitable environments at Mt. Sharp, and along the way to Mt. Sharp. And if we discover any, they will serve as the starting point for seeing if any organic carbon is preserved and, if so, how it became preserved.


Now there’s a ten-dollar word. Taphonomy is the term paleontologists use to describe how organisms become fossilized. It deals with the processes of preservation. Investigations of organic compounds fit neatly in that category. We do not have to presume that organic compounds are of biologic origin. In fact, in studies of the Earth’s early record of life, we must also presume that any organic materials we find may be of inorganic origin - they may have nothing to do with biology. Scientific research will aim to demonstrate as conclusively as possible that the materials of interest were biogenic in origin. For Earth rocks that are billions of years old, it’s rare to find a truly compelling claim of ancient biogenic carbon. Here’s why.

On a planet that teems with life, one would presume these discoveries would be ordinary. But they aren’t, and that’s why fossils of almost any type, including organic compounds (so-called “chemofossils”), are so cool - it’s because they are rare. That’s also why taphonomy emerged as an important field of study. We need to understand how biologic materials become recorded in Earth’s rock record. It’s important in understanding modes of organism decomposition, to interpret ancient environmental conditions, and in reconstructing ancient ecosystems. But there also is one other reason that is particularly relevant for early Earth, and even more so for Mars: If you want to find something significant, you have to know where to look.

To explore for organics on Mars, three things have to go right. First, you need to have an enrichment of organics in the primary environment where organic molecules accumulate, which is large enough so that your instrument could detect them. Second, the organics have to survive the degrading effects associated with the conversion of sediment to rock. Third, they must survive further degradation caused by exposure of rock to cosmic radiation at Mars’ surface. Even if organics were once present in Martian sediment, conversion to rock and exposure to cosmic radiation may degrade the organics to the point where they can’t be detected.

Organics degrade in two main ways. The first is that during the conversion of sediment to rock, organics may be chemically altered. This generally happens when layers of sediment are deposited one on top of the other, burying earlier-deposited layers. As this happens, the buried sediment is exposed to fluids that drive lithification - the process that converts sediment to rock. Sediments get turned into rocks when water circulates through their pores, precipitating minerals along the linings of the pores. After a while the sediment will no longer feel squishy and it becomes rigid - lithified.

During the process of lithification, a large amount of water may circulate through the rock. It can amount to hundreds, if not thousands, of times the volume of the pore space within the rock. With so much water passing through, often carrying other chemicals with it, any organics that come into contact with the water may be broken down. Chemically, this occurs because organics are reduced substances and many chemicals dissolved in water are oxidizing. Those two chemical states don’t sit well together, and this tends to drive chemical reactions. Simply put, organics could be broken down to the point where the originally organic carbon is converted into inorganic carbon dioxide, a gas that can easily escape the lithifying sediment. Water on Mars may be a good thing for habitability but it can, paradoxically, negatively affect the preservation of organics.

Now, if any organics manage to escape this first step in degradation, then they are still subject to further degradation when the rock is exhumed and exposed to the surface of Mars. There it will be bombarded by cosmic radiation. I won’t go into the details here, but that is also bad news for organics because the radiation tends to break apart organic molecules through a process called ionization. The upper few meters of a rock unit is the most susceptible; below that the radiation effect rapidly dies away. Given enough time the organics could be significantly degraded.

The Hassler et al. paper just published in Science reports that the surface radiation dose measured by Curiosity could, in 650 million years, reduce the concentration of small organic molecules, such as amino acids, by a factor of 1000, all other factors being equal. That’s a big effect - and that’s why we were so excited as a team when we figured out how to measure the cosmogenic exposure age of rocks we drilled (see Emily’s blog and the Farley et al. paper). This gives us a dependable way to preferentially explore for those rocks that have been exposed for the shortest period of time. Furthermore, it is unlikely that organics would be completely eliminated due to radiation effects and the proof of this is that a certain class of meteorites - the carbonaceous chondrites - have been exposed to radiation in space for billions of years and yet still retain complex organics. This provides hope that at least some types of organics should be preserved on Mars.

Being able to account for the radiation history of rocks that Curiosity might drill is a very big step forward for us in the search for organic molecules. It is a big step forward in learning how to explore for past life on Mars (if it ever existed there). Now we have the right tools to guide the search for rocks that might make the best targets for drilling. Coupled with our other instruments that measure the chemistry and mineralogy of the rocks, to help select those that might have seen the least alteration of organics during burial, we have a pretty good sense of what we need to do next. That’s because we have been through this before on Earth.

Magic Minerals

Over the years Emily has written many blogs dedicated to the discovery of interesting minerals on Mars. There are many reasons for this, but I’ll suggest one more that may grow in importance in years to come.

Believe it or not, the story starts with none other than Charles Darwin. In pondering the seemingly instantaneous appearance of fossils representing complex and highly differentiated organisms in Cambrian-age rocks (about 500 million years ago), Darwin recognized this as a major challenge to his view of evolution. He explained the sudden appearance of fossils in the record by postulating that Cambrian organisms with no known antecedents could be explained by “record failure” - for some unknown reason, older rocks simply didn’t record the emergence and evolution of life’s beginning. Conditions weren’t suitable to preserve organisms as fossils.

Most of that story goes on in the direction of evolutionary biology, and we’ll skip that, rather focusing instead on learning more about taphonomy. What is important for Mars was the discovery of minerals that could preserve evidence of early microorganisms on Earth. (For a good read on Precambrian paleobiology, try Andy Knoll’s “Life on a Young Planet: The First Three Billion Years of Evolution on Earth.”)

We now know that pre-Cambrian time represents about 4 billion years of Earth’s history, compared to the 540 million years represented by Cambrian and younger rocks that Darwin had studied. (See Emily’s blog on the Geologic time scale.) We also know now that the oldest fossil microbes on Earth are about 3.5 billion years old, and that in between there is a compelling, but very sparse record of the fossil organisms that Darwin had anticipated. However, what’s even more remarkable is that it took 100 years to prove this. And this was with hundreds, maybe thousands, of geologists scouring the far corners of the Earth looking for evidence.

The big breakthrough came in 1954 with the discovery of the “Gunflint microbiota” along the shores of Lake Superior in southern Canada. A University of Wisconsin economic geologist, Stanley Tyler, discovered microscopic threads of what we now understand to be fossil bacteria in a kind of rock called “chert”. Chert is a microcrystalline material formed of the mineral quartz, or silicon dioxide, which precipitates very early in waters that contain microbial colonies. It forms so early that it turns the sediment almost instantly into rock, and any microbes become entombed in a mineral so stable it resists all subsequent exposure to water, and the oxidizing chemicals dissolved in water, for billions of years.

As it turned out, this was the Rosetta stone that helped decipher the code to the field of pre-Cambrian paleontology. It took almost 10 years for the discovery to be fully appreciated (the initial report in Science was viewed with much skepticism), but once it was confirmed, in the mid-1960s, the field exploded. Once geologists and paleontologists knew what to search for, they were off to the races. Since that initial discovery, other magic minerals have been found that preserve ancient microbes, sometimes with spectacular fidelity. But chert is still the mineral of choice, and I never pass by it in the field without collecting some.

We don’t know yet what magic minerals exist on Mars that could have trapped and preserved organics. Clays and sulfates hold promise, and that’s why we’re so interested in them. Silica, perhaps similar to terrestrial chert, has been observed from orbit at a few places on Mars, and in Spirit rover data from Gusev crater. The great thing about Gale crater as a landing site is that we have so many choices in this trial-and-error game of locating a mineral that can preserve organic carbon.

The figure below provides some sense of the impact of this discovery. It is modified from a similar figure published in a very nice summary by Bill Schopf, a Professor of Paleontology at UCLA. Bill also was a very early participant in this race for discovery and has made a number of very significant contributions to the field.


In studying Mars, the importance of this lesson in the search for life preserved in the ancient rock record of Earth cannot be overstated. Curiosity’s discovery of a very Earth-like ancient habitable environment underscores this point. With only one or two rovers every decade, we need to have a search paradigm: something to guide our exploration, something to explain our inevitable failures. If life ever evolved on Mars, we need to have a strategy to find it. That strategy begins with the search for organics, and regardless of their origin - abiotic or biotic, indigenous to Mars or not - they are important tracers for something more significant. Curiosity cannot see microfossils, but it can detect organic compounds. And just as with microfossils on Earth, we first have to learn where organics on Mars might be preserved. So that’s what we’re going to try and do.

Slice of History: Spin Test

Monday, December 9th, 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

Spin Test
Spin Test — Photograph number 355-1272B

In August 1964, this test fixture was used by the Spacecraft Design Section at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., to study spin stabilization of spacecraft - in this case, Rangers 8 and 9 (part of the Ranger Block 3 design). Many spacecraft had used spin stability for attitude control during acceleration or thrust, and it was found that a slower spin provided better stability for the coasting phase. One method of decreasing the spin of a spacecraft, or de-spinning, was the deployment of yo-yo devices. Weights were attached to rigid or stretch cords, then released while the fixture was spinning. The cords would unwind, like the arms of a figure skater extending to slow a spin, and then the cords were released. In this photo, the cables and weights can be seen, attached to the outside of the white circle. The test fixture is surrounded by what appear to be bales of paper and trash to absorb the impact of the weights when they were released from the spinning test fixture.

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