New Horizons: The PI's Persective - May 1, 2006

http://pluto.jhuapl.edu/overview/piP...ve_current.php

The PI's Perspective
"Exploration at Its Greatest"
Alan Stern
May 1, 2006

Our space ship, 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
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 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
February 28, 2007.

April included our crossing the orbit of Mars, outbound at over
75,000 kilometers an hour (47,000 miles/hour), on April 7. That was a
nice milestone, but the biggest spacecraft event of the month was a new
software load for our Command and Data Handling (C&DH) system. This
load, called C&DH 3.5, went up and on line a few days before we crossed
the orbit of Mars - on April 5. C&DH 3.5 contained a fix for a bug that
we wanted to protect against well before we update the code 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 downlinking Pluto data.

I'll have more to say about the C&DH 4.0 load in a few months. For now,
I just want to say 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 Applied
Physics Laboratory (APL) 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.

With the spacecraft doing well, most of the activities of April
centered
on instrument checkouts. Ralph, our main remote-sensing suite, and
REX,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 (on 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 on May 29. But since Ralph's door has a
see-through
window, first light and some early calibrations will be made on May 10.
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
on May 7 when our spacecraft crosses 2 Astronomical Units 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 go to reach Jupiter.

Where Is the Centaur Rocket?

Some of you have been asking what became of our Atlas' 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; and our uppermost, STAR-48 stage that
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
for the over its first two years of flight.

For you orbit mechanics aficionados, the orbital elements of our
Centaur
have been carefully calculated by Lockheed Martin's Brian Lathrop, the
lead flight designer of our Atlas launch team. Here they a

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

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 2015, the Centaur will be on
its
fourth orbit of the Sun, outbound, just beyond the orbit of Mars.

A Trojan Course?

And while we're on trajectory matters, it's worth noting that 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 were 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.

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.

Faster Communications

Finally, I just want to point to an 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 (DSN) on the way to Pluto.

When we reach Pluto, we plan to use the higher data transmission rates
to cut the time required to send all of our data home in half - from
what
was almost 9 months, to just under 4.5 months. Even more impressively,
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
laypeople alike!

Well, that's all I have for now. So until next time . . .

-- Alan Stern


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 some additional, nuisance-level noise events over what was
seen on the ground. This is common when you get your instrument into
the
space environment, and something we expected since our spacecraft is