NASA Reschedules Space Shuttle Launch

The launch of
NASA's space shuttle Atlantis will take place no earlier than Saturday, Dec.
8, at 3:43 p.m. EST. Thursday's scheduled liftoff from NASA's Kennedy Space
Center, Fla., was postponed because of a problem with a fuel cutoff sensor
system inside the shuttle's external fuel tank.
   The fuel cutoff sensor system is one of several that protect the shuttle's
main engines by triggering their shut down if fuel runs unexpectedly low.
Launch Commit Criteria require that three of the four sensor systems function
properly before liftoff.
   Space Shuttle Program managers will hold a Mission Management Team meeting
Friday at 2 p.m. to discuss the issue and determine the steps necessary to
start a new launch countdown. A news conference will be held at approximately
5 p.m. after the meeting's conclusion.
   On Thursday morning, two of the four engine cutoff, or ECO, sensors inside
the liquid hydrogen section of the tank failed a routine prelaunch check.
Following the launch postponement, the tank's liquid oxygen and liquid
hydrogen were drained. While the tank was being emptied, engineers monitored
and collected data on the liquid hydrogen sensors that failed. During that
process, another sensor gave a false reading, indicating that the tank was
"wet," when it was dry. All ECO sensors are now indicating dry as they should
be.
   During Atlantis' 11-day mission to the International Space Station, the
shuttle and station crews will work with ground teams to install and activate
the European Space Agency's Columbus laboratory. The new lab will expand the
station's scientific research capabilities.

NASA To Examine Signs Of Degradation On Discovery RCC Tiles

Safety Team Recommends Replacement; Launch Could Be Delayed

NASA will examine a handful of reinforced carbon-carbon (RCC) heating tiles on the wings of the space shuttle Discovery, now at the launch pad in anticipation of an October 23 launch, to determine if the tiles should be replaced.

The Associated Press reports three of the 44 reinforced tiles that line the edges of Discovery's wings show signs of degradation in their outer coating.

The issue has come up before, the space agency says; thermography inspections of the affected tiles have shown no internal defects in the tiles, which gives NASA scientists little clue as to what may be causing the degradation.

Discovery has flown at least twice with the tiles in their present state, according to NASA, with no apparent problems. Still, on Wednesday the NASA Engineering and Safety Center (NESC) recommended replacement of three of the tiles.

Replacement of the tiles would require a trip back to the Vehicle Assembly Building for Discovery... potentially adding weeks to the timetable for launch.

NASA managers wrapped up two days of meetings Wednesday, ahead of next week's Flight Readiness Review. That meeting is planned for October 16, and its unlikely a decision on whether to replace the tiles will be made prior to then.

The issue of whether to replace the tiles is a thorny one for NASA, in light of the 2003 loss of Columbia. A breach of several RCC tiles on the leading edge of that orbiter's left wing -- caused by a chunk of insulating foam that struck the tiles during launch -- led to the shuttle's destruction during reentry.

Tones from Deep Space

"Beep… beep… beep...." That's the sound that marked the beginning of the Space Age fifty years ago. It was a simple radio tone transmitted by the first satellite, Sputnik 1, as it orbited Earth in October 1957.

Since then communication with spacecraft has advanced tremendously. Yet a modern probe on the way to the edge of the solar system is using Sputnik-like tones to send messages back to Earth.

Right: In Oct. 1957, ham radio operator Roy Welch of Dallas, Texas, tunes in to the 20 MHz radio tones of Sputnik. [More] [Larger image]

Why the retro technology? It solves a modern problem: multiplication. Sputnik has so many descendants! There are robots on Mars; spacecraft circling Saturn, Mars and the Sun; probes en route to Mercury, the asteroid belt and even Pluto. All of these missions are trying to talk to Earth, creating a cacophony that threatens to overtax NASA's Deep Space Network. If only these probes could learn to communicate with greater brevity as Sputnik once did.

Enter Beacon Monitor--a device onboard NASA's New Horizons spacecraft that communicates with Earth using only eight simple tones. It leverages the fact that New Horizons doesn't have much to do during its 9-year voyage to Pluto other than report its status to Earth. "I'm okay," sums up a typical weekly transmission.

New Horizons is capable of complex communication. It can transmit detailed images and data streams rich in numerical information. "But when we only need a basic status check, a few simple tones are fine," says Henry Hotz an engineer at NASA's Jet Propulsion Laboratory who helped develop the technology.

Despite its seeming simplicity, the beacon is sophisticated. New Horizons has many systems and all of them must be checked. Onboard software boils down the entire situation into a succinct "diagnosis." The system then uses a low-power antenna to transmit the diagnosis as one of eight simple radio tones. One means I'm okay while the other seven signify calls for help ranging in urgency from Help me soon to Help me now to Red Alert! I'm in big trouble.

Above: Sputnik (left) and New Horizons (right).

This approach has many advantages. "Simple tones from a distant probe are much easier to detect on Earth than an ordinary data transmission," explains Hotz. "If you miss part of a complex data stream the information is lost, but any part of a simple tone can tell you its frequency, thus revealing the message." The simpler transmission means that the beacon can use less of the probe's limited power (New Horizons operates on less power than a pair of 100-watt household light bulbs), and mission scientists can use smaller dishes to receive the signal. "Both of these advantages cut costs and make a mission more feasible."

Beacon Monitor was first tested onboard Deep Space 1, an experimental spacecraft flown in 1998 by NASA's New Millennium Program. The raison d’etre of Deep Space 1 was to test a suite of cutting-edge technologies (e.g., an ion engine, a smart autopilot, super-solar arrays and a back-to-the-future status monitor) for possible use on future missions. "Beacon Monitor passed with flying colors and was later installed on New Horizons."

So, as the Space Age began, it continues, to Pluto and beyond. Close your eyes. Can you hear the tones?

The Sun Rips Off a Comet's Tail

On April 20, 2007, the comet had just dipped inside the orbit of Mercury, perilously close to the sun, when a solar eruption struck and literally tore the comet's tail off. This surely has happened to comets before, but for the first time in history a spacecraft was watching. NASA's STEREO-A probe recorded a fantastic movie of the collision. To play it, click on the image:

"We were speechless when we saw this," says Angelos Vourlidas of the Naval Research Lab in Washington, D.C. "I kept playing the movie over and over."

Vourlidas is part of a team of NRC researchers who built the Heliospheric Imager telescope onboard STEREO-A that recorded the event. He's also the lead author of a paper reporting the collision in the Oct. 10 issue of the Astrophysical Journal Letters.

The eruption that hit Encke was a CME or "coronal mass ejection." Sky watchers on Earth are familiar with CMEs because of the auroras they create when they occasionally hit our planet. CMEs are fast-moving and massive, packing billions of tons of solar gas and magnetism into billowing clouds traveling a million-plus miles per hour.

Actually, it is a little surprising that a CME succeeded in ripping off a comet's tail. For all their mass and power, CMEs are spread over a large volume of space. The impact of a gossamer CME exerts little more than a few nanoPascals of mechanical pressure—softer than a baby's breath.

The ripping action must have been something else.

"We believe the explanation is 'magnetic reconnection,'" says Vourlidas. Magnetic fields around the comet bumped into oppositely directed magnetic fields in the CME. Suddenly, these fields linked together--they "reconnected"--releasing a burst of energy that tore off the comet's tail. A similar process takes place in Earth's magnetosphere during geomagnetic storms powering, among other things, the aurora borealis.

"In a sense, the comet experienced a geomagnetic storm," says Vourlidas. "It is the first time we've ever witnessed such an event on another cosmic body."

"Although STEREO is primarily designed to study CMEs and their impact on Earth, we hope this CME strike on Encke will provide insights to scientists studying comets as well," adds Mike Kaiser, STEREO project Scientist at NASA's Goddard Space Flight Center.

Right: STEREO-A monitors a solar eruption, an artist's concept. [More] [Larger image]

Among astronomers, Encke is one of the most famous and important comets. It was only the second comet named, after Halley itself, and it is the shortest-period comet known. Encke loops around the sun once every 3.3 years compared to, say, once every 75 years for the more typical Halley.

Encke's short period combined with its trajectory inside the orbit of Mercury means it may have been blasted by CMEs more often than any other comet routinely observed by astronomers. Could this have some effect on the comet's nature and evolution? "We don't yet know."

Vourlidas' team is only beginning to study all the data gathered by STEREO. The spacecraft carries a suite of five different telescopes (collectively known as SECCHI) each optimized for a different kind of observation ranging from wide-angle views of CMEs at visible wavelengths to pinpoint maps of sunspots through high-resolution ultraviolet filters. The Heliospheric Imager movie represents just a fraction of the total dataset. In the months ahead, "we're going to be looking at the CME-comet interaction in much greater detail to understand the processes at work," says Vourlidas.

Encke may not know what hit it, but NASA scientists soon will.