13 MORE Things That Saved Apollo 13, part 8: The Indestructible S-Band/Hi-Gain Antenna

The explosion of a liquid oxygen tank in Apollo 13’s Service Module violently propelled debris and a 13-foot (4 meter) outer panel of the SM out into space.

Later, the crew saw the damage when they jettisoned the SM prior to reentering Earth’s atmosphere. Commander Jim Lovell described the scene:

“There’s one whole side of the spacecraft missing!” Lovell radioed to Mission Control. “Right by the high-gain antenna, the whole panel is blown out, almost from the base to the engine.”

The panel was likely blasted outward and rearward, toward the deep space S-Band radio antenna. The antenna was attached to the outer edge of the module’s rear base via a meter-long strut, and was used for both telemetry and voice communications.

NASA engineer Jerry Woodfill feels this hi-gain antenna was surely struck by the panel and/or schrapnel ejected by the oxygen tank explosion.

“That deep space radio communication was maintained during and after the explosion was almost miraculous,” Woodfill said. “Such a blow should have destroyed that hi-gain antenna. Those of us who watched the telemetry display monitors saw only a momentary flickering of the telemetry, but after a few flickers we continued to receive data.”

Woodfill said it was as though a boxer had taken a devastating punch and continued to stand unfazed.

This video of the severely damaged Apollo 13 service module was taken by the crew after it was jettisoned.

If instead, the antenna had been destroyed, the loss of data would have resulted in an impaired ability to analyze the situation and communicate with the crew.

The moments following the explosion are seared into Woodfill’s memory. On the night of April 13, 1970, 27-year-old Woodfill sat at his console in the Mission Evaluation Room (MER) in Building 45 at Johnson Space Center — next door to Mission Control in Building 30 — monitoring the caution and warning system.

Jerry Woodfill working in the Apollo Mission Evaluation Room.  Credit:  Jerry Woodfill.
Jerry Woodfill working in the Apollo Mission Evaluation Room. Credit: Jerry Woodfill.
“Because I was watching the command ship’s telemetry on a monitor at the moment of the explosion, both the words heard in my headset, “Houston, we’ve had a problem” and the scene I saw of the video monitor have not been forgotten” Woodfill said. “Seconds before I heard the audio of Jack Swigert’s call, I watched the video screen flicker several times.

To this day, Woodfill said he cannot understand how it continued to function following the explosion.

“As an engineer, I have studied the basics of simple machines,” he said. “The concept of the lever arm dictates that when an explosive blow strikes a structure atop an arm, the arm must bend back about its attachment to the supporting structure. In this case, that structure was the command ship’s supply module, the Service Module. Later photos by the crew (below) showed the antenna intact and the conical reflector dishes present with their center probes intact. In my mind, the entire assembly simply should have been severed altogether.”

An Apollo high gain antenna, on display at the Stafford Air & Space Center, Weatherford, Oklahoma.
An Apollo high gain antenna, on display at the Stafford Air & Space Center, Weatherford, Oklahoma.

The Unified S-band (USB) system was a tracking and communication system that combined television, telemetry, command, tracking and ranging into a single system. The high-gain antenna consisted of an 11-inch-diagonal wide-beam horn flanked by an array of four 31-inch-diameter parabolic reflectors. Its multifunctional system simplified operations, and its construction saved on weight.

And obviously, it was very durable.

Woodfill reiterated how important it was that the antenna survived the explosion.

“Later on it wasn’t needed, as the crew used the Lunar Module communication system,” said Woodfill, “but having that initial continuous communication was one of the things that was very important.”

This color view of the severely damaged Apollo 13 Service Module (SM) was photographed with a motion-picture camera from the Lunar Module/Command Module following SM jettison. Credit: NASA.
This color view of the severely damaged Apollo 13 Service Module (SM) was photographed with a motion-picture camera from the Lunar Module/Command Module following SM jettison. Credit: NASA.

And later those in Mission Control and the MER were be able to go back and look at the data that had been transmitted to Earth during that very crucial period of the mission, to help understand what had actually occurred.

“It was critical to have that data in those first moments of the explosion to analyze what had happened,” Woodfill said. “Uninterrupted communication was essential to investigating the status of the vehicle. While it may be true that the backup omni-antenna might have provided temporary communication, based on my analysis, the omni-antenna would not have served as ably during the time of greatest initial peril. In fact, to configure its use with the NASA world-wide tracking network would have caused an unfortunate delay.”

Here are some zoomed-in photos taken by the crew of Apollo 13 after the explosion of the S-Band/hi-gain antenna, and Woodfill has noted the parts of the antenna. They show the explosion failed to sever the hi-gain antenna mast and the conical dish receivers as well as the rectangular antenna, and the center probes of the conical dishes appear intact. Considering the force of the explosion, this is remarkable.

At left, a view of the Service Module and the S-Band antenna during a previous Apollo mission. At right is a zoomed in look at the damaged SM and the unfazed S-Band antenna on Apollo 13, taken during SM jettison. Credit: NASA/Jerry Woodfill.
At left, a view of the Service Module and the S-Band antenna during a previous Apollo mission. At right is a zoomed in look at the damaged SM and the unfazed S-Band antenna on Apollo 13, taken during SM jettison. Credit: NASA/Jerry Woodfill.
An annotated closeup of the S-Band/Hi Gain antenna on Apollo 13 after the explosion. Credit: NASA/Jerry Woodfill.
An annotated closeup of the S-Band/Hi Gain antenna on Apollo 13 after the explosion. Credit: NASA/Jerry Woodfill.
Apollo 13 images via NASA. Montage by Judy Schmidt.
Apollo 13 images via NASA. Montage by Judy Schmidt.

Previous articles in this series:

Introduction

Part 1: The Failed Oxygen Quantity Sensor

Part 2: Simultaneous Presence of Kranz and Lunney at the Onset of the Rescue

Part 3: Detuning the Saturn V’s 3rd Stage Radio

Part 4: Early Entry into the Lander

Part 5: The CO2 Partial Pressure Sensor

Part 6: The Mysterious Longer-Than-Expected Communications Blackout

Part 7: Isolating the Surge Tank

Find all the original “13 Things That Saved Apollo 13″ (published in 2010) at this link.

Infographic Shows The Quick-Changing Satellites Of The Early Space Age

It’s not often that one associates a satellite with French folk songs, but this infographic does that and more. Below you will find the major launches of the early space age — from the Soviet Union’s Sputnik to the Czechoslovakian Magion 1 — showing how satellites quickly evolved between 1957 and 1978.

In two decades, satellites changed from simple transmitters and receivers to sophisticated machines that carried television signals and science instruments.

Another striking thing about this Broadband Wherever graphic: the number of participating countries. While we often think of the early Space Age as being dominated by the United States and Soviet Union, you can see other nations quickly rushing their own satellites into orbit: Canada, Italy, Australia, India and more.

Enjoy the sound bites and cute graphics below. Full sources for the information are listed at the bottom of the infographic.

Early History of Satellites

Aesthetics of Astronomy

This Hubble image reveals the gigantic Pinwheel Galaxy (M101), one of the best known examples of "grand design spirals," and its supergiant star-forming regions in unprecedented detail. Astronomers have searched galaxies like this in a hunt for the progenitors of Type Ia supernovae, but their search has turned up mostly empty-handed. Credit: NASA/ESA

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When I tell people I majored in astronomy, the general reaction is one of shock and awe. Although people don’t realize just how much physics it is (which scares them even more when they found out), they’re still impressed that anyone would choose to major in a physical science. Quite often, I’m asked the question, “Why did you choose that major?”

Only somewhat jokingly, I reply, “Because it’s pretty.” For what reasons would we explore something if we did not find some sort of beauty in it? This answer also tends to steer potential follow up questions to topics of images they’ve seen and away from topics from half-heard stories about black holes from sci-fi movies.

The topic of aesthetics in astronomy is one I’ve used here for my own devices, but a new study explores how we view astronomical images and what sorts of information people, both expert and amateur, take from them.

The study was conducted by a group formed in 2008 known as The Aesthetics and Astronomy Group. It is comprised of astrophysicists, astronomy image development professionals, educators, and specialists in the aesthetic and cognitive perception of images. The group asked to questions to guide their study:

1. How much do variations in presentation of color, explanatory text, and illustrative scales affect comprehension of, aesthetic attractiveness, and time spent looking at deep space imagery?

2. How do novices differ from experts in terms of how they look at astronomical images?

Data to answer this question was taken from two groups; The first was an online survey taken by volunteers from solicitations on various astronomy websites and included 8866 respondents. The second group was comprised of four focus groups held at the Harvard-Smithsonian Center for Astrophysics.

To analyze how viewers viewed color, the web study contained two pictures of the elliptical galaxy NGC 4696. The images were identical except for the colors chosen to represent different temperatures. In one image, red was chosen to represent hot regions and blue for cold regions. In the other version, the color scheme was reversed. A slight majority (53.3% to 46.7%) responded saying they preferred the version in which blue was assigned to be the hotter color. When asked which image they thought was the “hotter” image, 71.5% responded that the red image was hotter. Since astronomical images are often assigned with blue as the hotter color (since hotter objects emit shorter frequency light which is towards the blue end of the visible spectrum), this suggests that the public’s perception of such images is likely reversed.

A second image for the web group divided the participants into 4 groups in which an image of a supernova remnant was shown with or without foreground stars and with or without a descriptive caption. When asked to rate the attractiveness, participants rated the one with text slightly higher (7.96 to 7.60 on a 10 point scale). Not surprisingly, those that viewed the versions of the image with captions were more likely to be able to correctly identify the object in the image. Additionally, the version of the image with stars was also more often identified correctly, even without captions, suggesting that the appearance of stars provides important context. Another question for this image also asked the size in comparison to the Earth, Solar System, and Galaxy. Although the caption gave the scale of the SNR in lightyears, the portion that viewed the caption did not fare better when asked to identify the size revealing such information is beyond the limit of usefulness.

The next portion showed an image of the Whirlpool galaxy, M51 and contained either, no text, a standard blurb, a narrative blurb, or a sectionized caption with questions as headers. Taking into consideration the time spent reading the captions, the team found that those with text spent more time viewing the image suggesting that accompanying text encourages viewers to take a second look at the image itself. The version with a narrative caption prompted the most extra time.

Another set of images explored the use of scales by superimposing circles representing the Earth, a circle of 300 miles, both, or neither onto an image of spicules on the Sun’s surface, with or without text. Predictably, those with scales and text were viewed longer and the image with both scales was viewed the longest and had the best responses on a true/false quiz over the information given by the image.

When comparing self-identified experts to novices, the study found that both viewed uncaptioned images for similar lengths of time, but for images with text, novices spent an additional 15 seconds reviewing the image when compared to experts. Differences between styles of presenting text (short blurb, narrative, or question headed), novices preferred the ones in which topics were introduced with questions, whereas experts rated all similarly which suggested they don’t care how the information is given, so long as it’s present.

The focus groups were given similar images, but were prompted for free responses in discussions.

[T]he non-professionals wanted to know what the colors represented, how the images were made, whether the images were composites from different satellites, and what various areas of the images were. They wanted to know if M101 could be seen with a home telescope, binoculars, or the naked eye.

Additionally, they were also interested in historical context and insights from what professional astronomers found interesting about the images.

Professionals, on the other hand, responded with a general pattern of “I want to know who made this image and what it was that they were trying to convey. I want to judge whether this image is doing a good job of telling me what it is they

wanted me to get out of this.” Eventually, they discussed the aesthetic nature of the images which reveals that “novices … work from aesthetics to science, and for astrophysicists … work from science to aesthetics.”

Overall, the study found an eager public audience that was eager to learn to view the images as not just pretty pictures, but scientific data. It suggested that a conversational tone that worked up to technical language worked best. These findings can be used to improve communication of scientific objectives in museums, astrophotography sections of observatories, and even in presentation of astronomical images and personal conversation.