Aggiornamento situazione sonda New Horizons - 20.03.06

The PI’s Perspective
Zero G and I Feel Fine
Alan Stern
March 20, 2006

It’s been over three weeks since I last filed a PI’s Perspective, so
there is a lot to catch you up on. We’re more than 60 days into flight
now, and in every respect, New Horizons is doing fine.

As you probably already know, our third and last post-launch Trajectory
Correction Maneuver (TCM-3), a cleanup tweak of about 2.6 miles per
hour, was successfully executed on March 9. TCM-3 featured the first
in-flight closed-loop burn control, in which the onboard navigation
system senses the acceleration of the vehicle and targets the burn
cutoff for a precise change in velocity. This worked entirely as
advertised, and it’s a capability we plan to use in future burns,
than just conducting the burn with a timer.

On the day following TCM-3, the mission control team uploaded the
Command Loss Time Safety Net (CLTSN), which is the autonomy “catcher’s
mitt” code that I wrote about last month. Also this month, we have
continued the in-flight testing of our SWAP and PEPSSI plasma
instruments. SWAP passed a major milestone on March 13 by successfully
opening its launch door - on the first try, I might add. That’s the
second launch door to open, since Alice opened hers in late February.
Still to come are the Ralph and LORRI doors, which will open later in
the year when we are farther from the Sun and these instruments no
longer need such strong protection against accidental Sun pointing.

Another important activity that has been carried out of late is the
just-completed check of the high-gain antenna and its associated
electronics that we’ll rely on very heavily for communications in the
outer solar system.

Also, the Student Dust Counter (SDC) was turned on and commissioned in
its entirety in March. SDC is kind of like an acoustic sensor that
up impacts by micrometeoroids on its surface. But SDC can also hear
background noises on the spacecraft, such as engine firings, thermal
noise (like the popping and cracking sounds you hear from your car when
the engine is hot) and the opening of instrument doors. In fact, SDC
clearly heard the opening of SWAP’s launch door on March 13. The
instrument is now collecting data on tiny impacts occurring along our
route of flight to Jupiter.

In the coming few weeks we plan on additional testing of LORRI camera
and the “first light” (or more properly, “first particle”) observations
for SWAP, as well as the first turn-on of the Ralph
imager/infrared-spectrometer, and the first of two significant updates
of the spacecraft Command and Data Handling (C&DH) software. In a
milestone of sorts, on April 6, we’ll cross the orbit of Mars - that’s
just 10 weeks after launch, folks. By comparison, the Mars
Reconnaissance Orbiter took 5.5 months to get there, arriving
(successfully!) into orbit on March 10.

Meanwhile, the New Horizons science team is finishing up our final list
of Jupiter observing plans, and the ground team is completing a major
upgrade of the mission control software, while simultaneously working
planned software bug-fix upgrades for our onboard Guidance and Control
(G & C) and autonomy systems. These bug-fix type upgrades are normal
a mission in early flight; we’re finding the same kinds of little “this
and that” software anomalies, features and idiosyncrasies that most
missions find when they finally get to operate in the real flight
environment. The autonomy upgrades are planned to be uplinked in May
June. The G&C software will go up late in the summer.

Back over at Pluto, the same Hubble Space Telescope team that found
Pluto’s two small moons last year, measured the color of those moons. I
led that effort. What we found is that both the outer moon, called
S/2005 P 1 (or more colloquially for the time being, “Baltimore”) and
the inner moon, called S/2005 P 2 (or more colloquially for the time
being, “Boulder”), are the same color as one another, and as Pluto’s
larger moon, Charon. The figure below illustrates this, as well as the
fact that Pluto’s color is reddish in comparison to its satellites.
things we do not yet know, but would love to find out in future
observations, are the shapes, rotation periods and overall
reflectivities of Pluto’s small moons. Stay tuned. We’re hoping HST
awards more observing time soon.

Until next time . . .

– Alan Stern