New Horizons Update - February 27, 2006

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

The PI's Perspective
Alan Stern
Boulder and Baltimore
February 27, 2006

Last week, details of discoveries and early interpretation of Pluto's
two small moons, formally called S/2005 P1 and S/2005 P2, were
published
in a pair of papers (Weaver et al. 2006 and Stern et al. 2006) in the
scientific journal Nature. Nature is very much the Rolling Stone of the
scientific community, and the discovery and interpretation of "P1" and
"P2" won the cover of Nature. This is probably as close as the nine of
us will ever get to making the cover of Rolling Stone. Although this
was
my 10th scientific publication in Nature, it was a real rush of
accomplishment that vindicated long years of searching the Pluto system
for companions to Pluto and Charon.

In our two back-to-back papers, we described the orbits and sizes of
our
two newly discovered moons, discussed the unique architecture of the
Pluto satellite system, predicted that similarly complex satellite
systems will be found routinely in the Kuiper Belt, predicted that P1
and P2 probably generate ephemeral rings around Pluto, and argued that
P1's and P2's orbits argue strongly that they were born in the
cataclysmic collision of a large Kuiper Belt object into Pluto that
created Charon, billions of years ago. In fact, we believe the presence
of P1 and P2 in Charon's orbital plane is very much the discovery that
checkmates the 20-year-old hypothesis that Charon was born because of a
giant impact onto Pluto.

On the same day (Feb. 23) that Nature published our papers and an
accompanying "News and Views" piece by New Horizons co-investigator
Rick
Binzel, the nine of us on the discovery team also published a
scientific
bulletin called an IAU Circular. This brief communication, edited by
Max
Mutchler and Andrew Steffl, revealed the results of brand-new Hubble
Space Telescope (HST) observations of P1 and P2, made just days before
on Feb. 15. The new Hubble images confirm the discovery (see above for
an image from this run on HST); the new imagery also shows that our
published orbital predictions, made in the fall, were almost bang on.
We
expect to get one more HST observation on March 2, from which we hope
to
further refine the orbits of P1 and P2 and obtain the first
high-quality
color measurements of P1 and P2.

You may have also heard that we're working on official names for P1 and
P2. We hope to submit those to the International Astronomical Union
(IAU) for formal approval this spring. In the meantime, we're referring
to the pair as "Boulder" and "Baltimore," in honor of the hometowns of
eight of the nine people on the discovery team (and, we note, the
respective locations where HST's instruments were built and where HST's
scientific institute is located). S/2005 P1, which is the larger moon,
is the one we call "Baltimore." S/2005 P2, being smaller, is the one we
call "Boulder."

And what about New Horizons? Well, it's halfway to the orbit of Mars
now, and the flight mission is continuing smoothly. Last week, we
conducted the "Launch Plus 35 Day" review of the engineering and
operational aspects of the mission. In this formal daylong review, the
engineering leads and the operations team presented the status and
lessons learned from the first five weeks of flight to a review team
consisting of experienced spacecraft engineers and project managers.

Also last week, we conducted the first testing of instruments in our
scientific payload. In total, three instruments were tested last week:
ALICE, PEPSSI, and LORRI. (And there is no truth, dear reader, to the
rumor that we chose these three to begin with because they spell,
A-P-L.)

Although "first light" for each of these three instruments is still in
the future, the early tests we performed last week proved that all
three
instruments survived launch and have good power and command interfaces
to the spacecraft. Additionally, each instrument put their
microprocessors through various paces, and ALICE unlatched and
successfully tested her front door by opening it to space. All of this
testing went well and we're very happy with the engineering data
returned to Earth by all three instruments.

This week, SWAP and SDC will be turned on and tested similarly to the
work done last week with ALICE, PEPSSI, and LORRI. In fact, SDC will
even begin collecting data, as will PEPSSI. Starting in March, we plan
to use SDC, PEPSSI, and SWAP a great deal during the flight to Pluto in
order to trace out conditions in the interplanetary environment across
the space of 5 billion-plus kilometers from here to the Kuiper Belt.

In March, we will continue instrument commissioning with increasingly
complex testing of our optical and plasma instruments. Additionally,
both copies of our radio science instrument, REX, will receive their
initial checkouts in mid-April.

Also in March, we'll undertake four very important activities with the
New Horizons spacecraft itself. One I've discussed before is a course
correction called TCM-3. This roughly 1.2 meter/second trajectory
correction maneuver will trim up our course to the Pluto "keyhole" at
Jupiter even more precisely than TCM-1A and 1B did. TCM-3 is planned
for
Thursday, March 9. The other major activities for March are an upload
of
a few post-launch fixes to our Command and Data Handling (C&DH)
software, the checkout of our High Gain Antenna (HGA) and the
installation of something called CLTSN.

CLTSN stands for Command Loss Timer Safety Net. It's a new feature of
the spacecraft's autonomous fault detection and protection system
designed to act as a backup ("last ditch") recovery of the mission if
the spacecraft determines it has failed to hear from the ground
controllers for too long a time (about 135 days). If this unlikely
happenstance ever occurs, autonomy's CLTSN switches the entire
spacecraft avionics chain to the backup side, turns the spacecraft back
to a good communications attitude with the HGA dish pointed toward
Earth, sets the downlink beacon to "Red 6" and fires up the receivers
to
await new instructions from Earth.

CLTSN, which we colloquially call the "catcher's mitt," is a new layer
of autonomous spacecraft recovery smarts designed to take over if the
normal autonomous fault detection and recovery procedures have failed
to
recover the mission. This is something I insisted on seeing added to
the
mission before I signed off on launch. I hope we never have to use
CLTSN, because it'll mean we're down to the last play in our playbook.
But I do think it's an important new capability. After all, without
CLTSN, we wouldn't have a last-ditch recovery to take over if some
"unknown, unknown" prevented the normal recovery processes from working
as expected.

Well, you can see the next few weeks are going to be busy for New
Horizons. Pluto, Charon, Boulder, and Baltimore lie ahead.

Until next time.

-- Alan Stern