New Horizons: A Summer's Work, Far From Home

http://pluto.jhuapl.edu/overview/piPerspective.php

The PI's Perspective: A Summer's Work, Far From Home
Alan Stern
July 14, 2009

The work is fun, no doubt there; but it never ends on this mission of
exploration - particularly in the summer, when we conduct our annual
spacecraft checkouts.

We awakened New Horizons from its record-setting 202-day electronic
hibernation just last week, on July 7. We're now almost 14
astronomical
units from the Sun
(the official crossing date will be July 27), and nearing the halfway
point between the orbits of Saturn and Uranus. And we're going to be
conducting an activity that we call Active Checkout Three ("ACO-3").
ACO-3 has been months in the making, and for the remainder of July and
almost all of August - it's show time!

As you likely know, our general cruise-to-Pluto plan is to hibernate
our
spacecraft most of each year but wake her up each year for an ACO. As
its name implies, ACO-3 is the third of our eight ACOs on the way to
Pluto.

ACO-3 is also - by design - the simplest, least cluttered and least
complex ACO we have ever conducted. We purposely simplified ACO-3 to
free up time for our small operations team to plan and test our Pluto
core encounter, which we are on the hook to NASA to finish by the end
of
this year.

To simplify ACO-3, we put off a trajectory correction maneuver until
2010, avoided flight software updates, all but eliminated cruise
science, and told our instrument payload teams that we would not
conduct
pointed calibration observations as we have in past years. Instead,
they
must get by with the testing and instrument calibrations that could be
conducted while the spacecraft is in spin mode (which is how we fly
during hibernation). These restrictions pay off for us by shortening
the
planning and execution time of the ACO. Consider: ACO-3 took two
months
to plan, design, and test, and will take just under two months to
execute. By contrast, ACO-2 took four months to plan, design, and
test,
and 4 months to execute.

But ACO-3 is still a busy time. Among the activities we will perform
a

* Functional checkouts of all seven scientific instruments.
* Brief science data collections for SWAP and PEPSSI to monitor
the
heliospheric space environment around New Horizons.
* Checkouts of every spacecraft subsystem - including both the
prime
and redundant hardware in each subsystem.
* Two months of careful tracking to improve our trajectory
knowledge.
* Uploading instructions to take us through the next few months of
hibernation, which we'll initiate on August 27.

As we glide across the vast vacuum of space between Saturn and Uranus,
the recent telemetry collected from New Horizons shows that our bird
remains healthy, though we are studying two spacecraft issues very
carefully.

The first is the still unexplained set of command and data handling
computer reboots that occurred in 2007 and 2008, but have not
re-occurred on New Horizons since. We've begun to study similar
reboots
that have taken place in the New Horizons ground simulator as a way of
sleuthing out what's behind these mysterious off-nominal events, but
so
far, we haven't cracked the case and found a root cause.

The other issue, which we first noticed in telemetry taken in late
2008,
is a series of 10-20 percent over-currents in our radio system's
transmitter circuit card when it powers up. These over-currents are
sporadic - sometimes they occur a minute or tens of minutes after we
power up the board - and sometimes they do not occur at all when we
power up. We've seen them on both the primary and backup radio
transmitters in New Horizons. Although our engineering team is
convinced
they are not harmful, the fact that they began after almost three
years
of flight and are not explained, has prompted us to add extra testing
of
the transmitters to ACO-3.

I'll report what we find out in the fall, but it's worth stressing
that
these two issues are more cautions than deep concerns. In the big
picture, our spacecraft is among the most healthy in the solar system.

Now let's look to what comes next. After ACO-3, New Horizons will
hibernate most of the time from September 2009 through May 2010. But
we'll awaken it twice for about 10 days at a time to correct its
antenna
pointing, collect tracking data, and conduct spacecraft maintenance
activities. These wakeups will occur during November 9-20 and then
again
during January 4-15. Following this next hibernation we'll conduct
ACO-4, which will be as chocked full of activities as ACO-2 was in
2008,
and will include a small trajectory correction burn, another upgrade
to
our fault protection and autonomy software, some Pluto encounter
tests,
and a series of instrument calibrations and cruise science
observations.

All of this, of course, comprises just one year of the long, nine-year
road trip to the ninth planet and its moons, on the frontier of the
solar system. It's our job to treat each year's activities as
carefully
as we did the first, and to be good stewards of the spacecraft we've
built, guarding against what New Horizons science team member Rick
Binzel once termed as the fate of Charlie Brown, when Lucy stole his
football just before he could kick it to score a goal in the old comic
strip Peanuts by Charles Schultz.

So every day, we plan, we test, and we constructively critique
ourselves
as diligently as we can. We have more than 1,270 days of safe
spacecraft
operations behind us on the way to Pluto, Charon, Nix and Hydra, but
we
still have almost 2,100 days to go before reaching that goal. Constant
vigilance remains our best friend in conducting every step of this
3-billion-plus mile journey.

That's my update for now. Thanks for following our journey to a new
frontier. I'll be back in touch in September, after we complete ACO-3.
In the meantime, keep on exploring, just as we do!