Centauri Dreams

After yesterday’s meditation on the Voyager spacecraft and their significance in the larger canvas of space exploration, it’s worth recalling that we have just celebrated Voyager 2’s encounter with Uranus — this month marks the 25th anniversary of the event. If your memories of the encounter are fuzzy, you might recall the other major news driver that January, the explosion of the Space Shuttle Challenger, which drove Uranus results off the front page. The national psyche was riveted by Challenger, and understandably so, but what a shame to see analysis of the Voyager flyby all but lost in the coverage of an event so much closer to home.

Voyager 2’s closest approach took place on January 24, 1986. I remember it because I was getting ready for a weekend flight training session in Frederick, Maryland and hoping I wouldn’t miss the subsequent release of Voyager imagery and data. In those days, the small company I was flying for did clinics for the Aircraft Owners and Pilots Association, and if memory serves, this was a weekend when the weather cooperated, with relatively high ceilings and no icing issues. I remember working with students on instrument approaches in the West Virginia mountains the day Challenger blew up (the 28th), trying to concentrate on the job at hand instead of speculating about what could have caused the disaster.

Image: A latitude-longitude grid superimposed on this Voyager 2 false color image shows that Uranus’ atmosphere circulates in the same direction as the planet rotates. Credit: NASA/JPL.

I also remember how hard it was to get Voyager news that night on the television. Only much later would I find out how unusual the results had been, especially the discovery that the magnetic north and south poles on the planet weren’t aligned with Uranus’ rotation at all, but were close to the equator. Moreover, the Uranian poles were more or less the same temperature despite the fact that one would be in sunlight for decades while the other was not. Remember, this is a planet with an almost 90-degree axial tilt, probably the result of a collision early in its life with another large body.

Keeping both poles at the same temperature suggests an unusual heat transport mechanism, but so much about Uranus was strange, including tiny Miranda, which had been expected to be cratered and ancient, but turned out to be filled with valleys and ridges and breathtaking cliffs, indicators of tectonic and thermal activity. There was even some speculation that the moon might be a re-aggregation of material following earlier destruction in a massive impact. Voyager also gave us the first imagery of the Uranian rings and their small shepherding moons.

New Horizons Nears Uranian Orbit

All these Uranus memories remind me that New Horizons, our Pluto/Charon mission, will cross the orbit of Uranus on March 18. So how is our other deep system mission going now that the Voyagers are pushing at the boundaries of the heliosphere? The New Horizons team is celebrating the fifth anniversary of launch, which occurred on January 19, 2006 on an afternoon when clouds cleared just in time for the event. That one was a bit frustrating, too — I remember trying to get launch coverage from NASA TV and finding that the local cable company had inserted a replay of a city council meeting from earlier in the week in place of NASA, with no explanation or apology. Coverage on the Net was available but plagued by bandwidth issues.

Even so, the news coming back from various other Net sources was all reassuring, and the flawless launch has been followed by an exceptionally trouble-free cruise thus far. New Horizons has needed fewer trajectory correction maneuvers than had been anticipated, according to this news release from the JHU/APL site. As of this morning at about 1335 UTC, the mission is at 2,969,429,304 kilometers from Earth, with a light delay of 2 hours 45 minutes. The Planetary Society has published a report by Ted Stryk from the New Horizons science team meeting, held last week at NASA Ames, from which we learn that the spacecraft is awakened from hibernation once a year to test its instruments and conduct science.

Stryk recounts some of the interesting science that has flowed from this:

Over the past few years, LORRI, the high resolution camera on New Horizons, has been making observations from its unique vantage in the outer solar system. It has obtained light curves of Pluto, Uranus, Neptune, Triton, and Makemake, and the data to construct light curves have been obtained for several other Kuiper belt objects. RALPH and MVIC, other cameras aboard New Horizons, have also been studying Uranus and Neptune. ALICE, which studies ultraviolet light, is making observations of the interplanetary medium, and the fields and particles instruments are now being used even during hibernation, with their data stored for downlink after wakeup. The limiting factor on cruise science is the fact that New Horizons cannot transmit data as fast as it used to because of its increasing distance from the Sun. Presently, the data rate is down to 3 kilobits per second.

Image (above): The New Horizons Long Range Reconnaissance Imager (LORRI) observed Neptune on June 23, 2010 as part of a test of the critical optical navigation Annual Checkout (ACO)-4. In this 100-millisecond exposure, taken when the spacecraft was 23.2 astronomical units (about 2.15 billion miles) from Neptune, the planet appears slightly larger than a star. At the time of this observation, the solar phase angle (the spacecraft-planet-Sun angle) was 34 degrees and the solar elongation angle (planet-spacecraft -Sun angle) was 95 degrees. Only New Horizons can observe Neptune at such large solar phase angles, which can be used to study the light-scattering properties of Neptune’s atmosphere. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

We continue to reap the benefit of New Horizons’ flight through the Jupiter system, which provided not only exceptional imagery but useful data on Jupiter’s magnetotail, all of which resulted in six papers on the magnetotail thus far. Science team co-investigator Fran Bagenal says the New Horizons work at Jupiter “provoked a new way of looking at solar wind interaction with the Jovian magnetosphere.” So things have not exactly been quiet during the cruise to the edge of the Solar System, particularly during the Jupiter encounter, and remember that after the Pluto/Charon flyby, we still have interesting possibilities re observing Kuiper Belt objects. Let’s hope the results can be analyzed in an atmosphere less disaster-laden than the Challenger winter of 1986.

Another comet looms, but first, some sail news. If everything went well, NanoSail-D opened its sail at 0255 UTC this morning, and indeed @NanoSailD in a tweet not long after the supposed deployment time said the satellite had sent data confirming the sail was open. We’re now waiting for ground-based tracking to confirm the fact, so patience is in order. Meanwhile, reports from hams tracking the satellite’s beacon on 437.270 MHz are still welcome and should be sent to the NanoSail-D2 Mission Dashboard. Henk Hamoen (PA3GUO) in the Netherlands put together the video below showing his tracking of NanoSail-D. The sail should be visible once deployed — check Heavens Above for visible pass predictions (thanks to @MarkGStacey for the tip).

Later: This from an MSFC news release:

Friday, Jan. 21 at 10 a.m. EST, engineers at NASA’s Marshall Space Flight Center in Huntsville, Ala., confirmed that the NanoSail-D nanosatellite deployed its 100-square-foot polymer sail in low-Earth orbit and is operating as planned. Actual deployment occurred on Jan. 20 at 10 p.m. EST and was confirmed today with beacon packets data received from NanoSail-D and additional ground-based satellite tracking assets. In addition, the NanoSail-D orbital parameter data set shows an appropriate change which is consistent with sail deployment.

Back to Tempel 1

But today’s other mission news involves a more distant object, and a cometary rendezvous scheduled for Valentine’s Day. The target is a familiar one, comet Tempel 1, to which the Deep Impact spacecraft delivered an impactor back in July of 2005. This time the spacecraft is the same Stardust vehicle that collected cometary particles from comet Wild 2 in 2004, along with samples of interstellar dust. After the dust collection (and subsequent return of samples to Earth in 2006 via a capsule that ejected from the spacecraft), controllers changed the craft’s trajectory. The mission was subsequently re-named Stardust-NExT and Tempel 1 became the target.

Tim Larson is project manager for the mission at JPL, and he’s understandably proud of the spacecraft’s performance in its different roles:

“You could say our spacecraft is a seasoned veteran of cometary campaigns. It’s been half-way to Jupiter, executed picture-perfect flybys of an asteroid and a comet, collected cometary material for return to Earth, then headed back out into the void again, where we asked it to go head-to-head with a second comet nucleus.”

It’s an interesting comet, too, given that this is the first time we’ll be able to look at the changes to a comet’s surface that have accumulated after an orbit around the Sun. Data on the material being emitted into the coma, its distribution and composition, should offer us useful information about Jupiter-family comets and their growth. The latter are short-period comets with periods of less than twenty years and aphelia that reach as far as the vicinity of Jupiter’s orbit. Jupiter family comets tend to have longer active lifetimes than long period comets, many of them surviving up to 1000 revolutions before the volatiles in their nuclei evaporate away.

Image: An artist’s impression of Tempel 1 and the Deep Impact spacecraft in 2005. Deep Impact sent a 370-kg impactor into the comet in July of that year, but the resulting dust obscured its view of the newly formed crater. Credit: NASA/JPL/UMD/Pat Rawlings.

It will be fascinating to see whether the high-resolution images that should come from this encounter will include the crater created by the Deep Impact collision, which was obscured by dust after the 2005 impact. 72 images are scheduled in all, with raw imagery sent back to Earth for processing on February 15. The current plan is for the images to be made available within hours. Stardust-NExT, having made eight flight path correction maneuvers and one Earth gravity assist since 2007, will fly past Tempel 1 at a distance of roughly 200 kilometers.

With twelve years of space travel (and four circuits of the Sun since the beginning of the Tempel 1 mission alone), Stardust-NExT has logged almost six billion kilometers since its 1999 launch. We’ve gotten our money out of this one, and Tempel 1 should be its last destination, for the spacecraft is nearly out of fuel. The spacecraft is already imaging Tempel 1 to create the data needed to update predictions of the comet’s trajectory. In just 24 days, we’ll be able to see the comet up close (again), and will be able to measure the dust properties of a second comet with the same instrument used on the Wild 2 dust measurements. As we’ve seen before, re-purposing a spacecraft gives us a low-cost way to stretch our technology in the form of a useful extended mission.