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New Horizons Taking Exploration To Edge Of Sol

Alan Stern with the New Horizons spacecraft before it departed for land's beyond beyond. Image credit: SWRI
by Alan Stern
for Southwest Research Institute
Boulder CO (SPX) May 02, 2006
Our spaceship, New Horizons, was paid for by the people of the United States of America. New Horizons is on its way to the very frontier of our solar system: Pluto and the Kuiper Belt. Great nations explore.

Echoing the words of Dave Scott, as he stepped onto the Moon as Commander of Apollo 15, "This is exploration at its greatest!"

With the rush of events surrounding launch over, I am back to writing in this column about once per month. We're more than 100 days into flight now and in every respect New Horizons continues doing fine.

As you know, the New Horizons mission team spent the first couple of months checking out all of the spacecraft subsystems and making our initial post launch trajectory correction maneuvers.

All of that went exceedingly well: We have a very healthy spacecraft flying right on its intended course to the Pluto aim point it must reach at Jupiter on Feb. 27, 2007.

On April 7, we crossed the orbit of Mars, outbound at over 75,000 kilometers per hour (47,000 miles per hour). That was a nice milestone, but the biggest spacecraft event of the month was a new software load for our Command and Data Handling system. This load, called C&DH 3.5, went up and online a few days before we crossed the orbit of Mars � on April 5.

C&DH 3.5 contained a bug fix that we wanted to protect against well before the code is updated in a more extensive way after the summer. That code version, called C&DH 4.0, will include a variety of capability enhancements, including data compression capabilities we'll need for Pluto data downlinking.

I'll have more to say about the C&DH 4.0 load in a few months. For now, just know that the 3.5 load is up and running as expected. To invoke a new C&DH load after it is transmitted up to the "bird," one has to reboot the main spacecraft computer. So, you can imagine how much care, how many design reviews, how much event simulation, and how much nail biting was involved in planning for this.

Of course, the Johns Hopkins Advanced Physics Lab spacecraft and mission ops teams made it look easy on April 5, which is a real sign of the careful advance work put in over several weeks leading to that big day.

New Horizons is doing so well that most of our April activities centered on conducting instrument checkouts. Ralph, our main remote sensing suite, and REX, our radio science experiment, both performed flawlessly in their initial functional checks. These occurred on March 21 and April 19, respectively.

In addition, the SWAP solar wind detector, which opened its launch door on March 13 (the 151st anniversary of Percival Lowell's birthday, no less!), turned on its detectors on March 28 for the first time: All went well.

Meanwhile, the LORRI imaging team has been collecting pre-door-opening calibration images to characterize their detector noise in flight. They are seeing what some additional, nuisance-level noise events over what was seen on the ground.

This is pretty common with instruments in the space environment, and it was something we expected because our spacecraft is carrying an RTG that was installed after the instrument calibrations. In fact, we expect the Ralph and Alice detectors to see the same kind of elevated - but still nuisance-level - noise when they calibrate in May.

Speaking of May, both PEPSSI (on May 3) and Alice (May 20) will soon open their detector doors. Carefully, step by step, both of these instruments will then be fully powered and have their detectors turned on for "first-light" measurements shortly thereafter.

Next up: Ralph's front door will open May 29, but because Ralph's door has a see-through window in it, first light and some early calibrations will be made May 10, looking through the partially transparent window of its launch door. These will each be big milestones: We are opening up our "eyes" to space!

Yet another milestone will be our first "AU crossing," which will occur May 7, when our spacecraft crosses 2 AU and is twice as far from the Sun as the Earth. We'll have 31 more AU to go to reach Pluto, but just 3.2 AU to reach Jupiter.

Some of you have been asking what became of our Atlas's Centaur stage. As background, our Atlas first stage and its solid rocket booster never were intended to make it into Earth orbit, so they are resting at 1 AU, deep under the Atlantic Ocean.

Our uppermost STAR-48 stage, which sent us on our way to Jupiter and Pluto, is headed to Jupiter and the Kuiper Belt, just like New Horizons. But the Centaur, which propelled us into Earth orbit and then out of it, isn't on an escape trajectory from the Sun. Instead, it's on an orbit that takes it from about 1 AU out just over halfway to Jupiter.

The figure below shows the Centaur's path over its first two years of flight.

For you orbital mechanics aficionados, here are the data for our Centaur, which have been carefully calculated by Lockheed-Martin's Brian Lathrop, the lead flight designer of our Atlas launch team:

- Semi-major axis: 3.0046694E+08 kilometers - Eccentricity: 0.51053830E+00 - Inclination: 0.57429941E+01 degree - Argument of perihelion: 1.1910526E+02 degree - Longitude of the ascending node: 5.0774401E+01 degree - Mean anomaly: 0.27115934E+00 degree - True angle: 0.97319138E+00 degree

For those interested only in the basics, the Centaur's orbit is essentially in the plane of the Sun's equator, like the nearby planets, and stretches from 1 AU to 3 AU, with an orbital period of 2.8469 years.

When New Horizons reaches Pluto in July 2014, the Centaur will be on its fourth orbit of the Sun, outbound, just beyond the orbit of Mars.

While we're on trajectory matters, it's worth noting we have just realized that New Horizons itself will be traversing through one of the Trojan regions of Neptune in 2014.

For a long time, astronomers wondered if there are asteroids trapped in Neptune's Trojan regions, but in recent years a few have been discovered. These fascinating bodies probably represent a sample of the most primitive bodies in the solar system, like comets and Kuiper Belt objects. New Horizons will cross through Neptune's trailing Trojan cloud in 2014.

Only a handful of Neptune Trojans are currently known, but more will no doubt be found in coming years. If any of those come close enough to New Horizons to be usefully studied, we want to plan observations.

To see if we can help that exciting prospect along, we've alerted our professional colleagues in the planetary astronomy community and asked for their help searching for new Neptunian Trojans in the region of space where New Horizons will fly as it crosses Neptune's orbit in the summer of 2014.

Last, I just want to point to exciting new prospect for New Horizons at Pluto itself: faster data rates. Our APL-based telecommunication team, led by Chris DeBoy, has worked out a way to use our redundant (opposite polarization) transmitters simultaneously to double our data rates.

This "pump you up" technique will be tested later this year and used from time to time to reduce our need for downlink time on the Deep Space Network on the way to Pluto.

When we reach Pluto, we plan to use the higher data transmission rates to cut the time in half required to send all of our data home � from what was almost nine months to just under 4.5.

Even more impressive, the higher data rate will allow us to send home a "lossy compression" dataset with all of our spectra, all of our images, and all of our other data products within just two or three weeks of encounter!

After all the years of delayed gratification that this mission entails, this is welcome news indeed: After all, everyone will be on the edge of their chairs in the summer of 2015 to see Pluto revealed � scientists and lay people alike!

New Horizons, as it appears in cruise, outboard for the frontier.

That's all for now. Until next time.

Alan Stern

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Xena Poses A Bright Mystery
Pasadena CA (SPX) Apr 13, 2006
Xena, the newly found and unofficial tenth planet, poses quite a mystery for astronomers. The latest images taken by the Hubble Space Telescope and interpreted by astronomers show Xena - whose name also remains unofficial - is about 5 percent larger in diameter than Pluto - which is smaller than expected based on earlier images.

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