NASA's Mission to Pluto and the Kuiper Belt
Our Aim Is True
January 31, 2006
New Horizons is nearing completion of its second week in
flight, and all continues to go well. As Project Manger Glen
Fountain is proud of saying, New Horizons is now safely away
from Earth, in the cold vacuum she was born to thrive in.
In the past week, our spacecraft team, led by Alice Bowman
and Nick Pinkine at the Johns Hopkins Applied Physics Laboratory,
continued their checkouts of spacecraft subsystems, and conducted
Trajectory Correction Maneuver (TCM) 1 with great success.
As a result, the error in New Horizons' trajectory, which
was already small, has been reduced by a factor of almost
The purpose of TCM-1 was both to commission our propulsion
system for trajectory changes, and to null out launch injection
errors. Fortunately, our launch was so accurate that only
about 40 miles per hour of trajectory change needed to be
made; this is less than one quarter of our post-launch trajectory
correction budget. Compare that 40 miles/hour number to our
36,254 mile-per-hour exit from Earth, and you'll see just
how fantastic a job our Atlas V/STAR-48 launcher did. This
allows us to bank the difference in fuel as savings for future
Jupiter, Pluto and Kuiper Belt Object encounters.
TCM-1 was split into two parts, called 1A and 1B. TCM-1A
was a 5 meter/second test and calibration firing conducted
on Saturday, January 28; TCM-1B was a 13.3 meter/second maneuver
conducted on Monday, January 30. Both maneuvers were successful.
We plan to trim out the small (about 4%) residuals from the
two TCM-1 burns, and to correct to the much better orbit solution
we will have from another couple of weeks of tracking by the
Deep Space Network (DSN) in TCM-2. This burn, which is likely
to be the smallest of the three post-launch maneuvers, is
scheduled for Wednesday, February 15.
TCM 1A and 1B were conduced "open loop," by pointing
the spacecraft in the correct direction for the burn, stabilizing
it like a spinning top, and making a timed burn. In contrast,
TCM-2 will be conducted in "closed loop" fashion,
with the spacecraft three-axis stabilized and using its onboard
gyros in the loop to cut the burn off when the precise targeted
velocity change (Delta V) is achieved. As such, TCM-2 should
produce an even closer-to-spec burn than TCMs 1A and 1B. As
you can see, we wanted to "walk before we ran" in
terms of TCM complexity, which is why TCM-1 used the simpler
but less accurate technique described above.
As we gain flight experience with our spacecraft, we are
coming up the learning curve and seeing some of its idiosyncrasies.
This is something all spacecraft teams benefit from in early
flight. For example, careful tracking has shown that New Horizons
is still slowly outgassing some absorbed water it took on
during its construction and testing on Earth. This outgassing
produces tiny puffs of gas from time to time, particularly
when a spacecraft surface that has only been in shadow is
exposed to sunlight, which vaporizes the water in it. Although
the forces at work due to water vaporization events are incredibly
tiny, less than 10-7 Gs, we are able to detect
them from tracking data. Another idiosyncrasy we are seeing
is a few radiation-induced single-bit upsets in the spacecraft
memory each day. Although these are occurring at a somewhat
higher than predicted rate, they are no problem and are corrected
automatically onboard the spacecraft when it does its once-per-minute
New Horizons Mission Operations Manager Alice
Bowman (right) and Deputy Mission Ops Manager Nick Pinkine
(left) on launch day in the New Horizons Mission Ops Center
(MOC) at APL, in Laurel, Maryland.
(Click on the image for a larger version.)
New Horizons Flight controllers at work in the MOC at APL.
(Click on the image for a larger version.)
For those of you interested in the question "Where
is New Horizons?" -- our Web site now has a feature
here) that gives you both graphical location and trajectory
displays, some distances to Earth, Jupiter, and Pluto, and
other information too. As I write these words, the spacecraft
has just passed the 12-million kilometer range from Earth.
For those of you interested in our now-derelict third stage,
we decided not to include it in the "Where is New Horizons?"
feature, but I can tell you that orbit extrapolations tell
us that our third stage is now about 15,000 kilometers from
New Horizons. By the time it reaches Jupiter, the defunct
stage will be about 400,000 kilometers away from our spacecraft.
Owing to it missing the Pluto aim point at Jupiter by this
amount, the third stage will miss Pluto by about 200 million
kilometers — which is about as far as the average distance
from the Sun to Mars.
Finally, for this week, I'll remind you that this coming
Saturday (February 4) will be the 100 th anniversary of Clyde
I'll be helping Clyde 's home state, Kansas, celebrate
that occasion with some events in Lawrence, Kansas, this
weekend. If you have a moment to reflect on this when Saturday
comes, give some thought to the fact that Clyde's hard work
resulted in the discovery of not just a new planet, but also
the Kuiper Belt, and with it, a huge and unexpected new piece
of the geography of our home solar system.
-- Alan Stern