Thank you for visiting the Deep Space 1 mission status log, still ranked as the most popular site among sentient life forms in the Milky Way galaxy for
information on this technology validation mission. This message was logged at 7:00 pm Pacific Time on Saturday, June 12.
The mission of Deep Space 1 continues to go extremely well. The overwhelming majority of the mission's objectives of testing high-risk,
high-payoff new technologies is complete. More tests are being conducted
on many of the technologies however to assess how they fare as they
continue operating in space.
Repeating a remarkable and complex activity conducted in February, the operations team replaced the software running on DS1's main computer this
week. With most of the technology testing behind it, the team's attention
is now turning to preparations for the July 29 encounter with an asteroid
with the haunting, yet descriptive, name 1992 KD. The primary objective of
the event will be to provide the final 5% of the testing of the autonomous
navigation system, known to loyal readers as AutoNav. To conduct the
encounter, new AutoNav features need to be on board, so on Friday, June 4,
the team began the lengthy process of sending new software to DS1.
The software running in DS1's main computer is three quarters of a million lines long. It took nearly 3 days for the Deep Space Network to send the more than 4 megabytes of computer code to the spacecraft. Once the software
and all the supporting files were on board, the spacecraft was reconfigured
to prepare it for rebooting the computer.
To run the new software required stopping the computer and restarting it. The spacecraft responds to restarting of the computer as if it were caused
by a problem, so it automatically follows routines to place the spacecraft
in a safe condition by turning off nonessential devices and pointing to the
Sun, the only easily recognized target from its vantage point in the solar
system. The operations team knew exactly what the spacecraft was supposed
to do, so prior to rebooting the computer, commands were sent to ease the
spacecraft's job by pointing it at the Sun and making other changes.
On Tuesday the computer was stopped and started, and the new software has been running smoothly ever since.
As Deep Space 1 approaches 1992 KD, AutoNav will fine tune the spacecraft's path. Until 2 days before the closest approach to the asteroid, AutoNav
will use the extremely efficient ion propulsion system for these course
corrections. But in the final 2 days, when time is of the essence, it will
use the faster but less fuel-efficient reaction control system, or RCS.
This system burns conventional rocket propellant, known as hydrazine,
through combinations of 8 small thrusters. Normally used to control only
the orientation of the spacecraft, the RCS can also change the flight path
using 4 of the thrusters that together will provide about 60 times as much
thrust as, but use about 15 times more propellant than, the ion engine.
For small maneuvers, that propellant cost is worth it, whereas for the
large maneuvers, the mass of the hydrazine the RCS would consume would
exceed what the rocket that launched DS1 could have carried into space.
The gentle and efficient ion engine easily wins when we can be patient.
Prior to this week, the RCS, had never been used to change DS1's course. So on Thursday, a test was conducted in which the RCS changed the
spacecraft speed by 0.54 meters/second, or a little over 1 mile/hour. The
RCS took just under 2 minutes and 130 grams of hydrazine to make this
change. The ion propulsion system could have done it with only 9 grams of
xenon, but it would have taken 2 hours. The successful test cleared the
way for future maneuvers with the RCS.
On Monday, June 14, AutoNav will make its first complete course correction.
In the past it has corrected its course by modifying the direction and
duration of thrusting that was planned for the ion propulsion system. But
in this case, there is no reference plan for it to change; it has to start
from scratch and decide the direction and duration of thrusting. Based on
its own determination of where it is in the solar system, where 1992 KD is,
and what both of their motions are, AutoNav calculates what changes to make
in its course. And if the needed thrusting is in an orientation in which
the spacecraft is not allowed to thrust (such as with the camera pointed
near the Sun), the on-board system will figure out how to do two separate
ion engine firings in acceptable directions that combine to produce the
desired effect. (Our term for this process is "vectorizing".) So on
Monday AutoNav will fire up the ion propulsion system to carry out its
changes to assure that Deep Space 1 continues to close in on the asteroid.
And don't forget that The Planetary Society and JPL are conducting a contest to select a better name, if that's even imaginable, for 1992 KD.
The contest is at http://www.planetary.org/news/contest-ds1.html, and the
deadline for entering is June 15.
Deep Space 1 is now 98% as far as the Sun and over 380 times farther than the moon. At this distance of nearly 147 million kilometers, or almost 91
million miles, radio signals, traveling at the universal limit of the speed
of light, take over 16 minutes to make the round trip.
Thanks again for logging in!