New Horizons update
Posted by Emily Lakdawalla
23-01-2006 8:29 CST
I received a lot of email over the weekend about New Horizons. Many of them were expressing concern about how little news there has been since launch. Have no fear. I can't speak for the people who built and launched the spacecraft but I know I was exhausted by the end of last week just from covering the launch -- I expect people were too busy celebrating their relief that New Horizons was safely on its way in a totally nominal fashion to concern themselves with reporting news over the weekend! They deserve a break.
Anyway, now that it's Monday, I've got some news from Alan Stern, the P.I. on New Horizons. The spacecraft is operating "virtually flawlessly." The next events on the mission are two trajectory correction maneuvers, which will serve to clean up New Horizons' trajectory and line it up for the Jupiter gravity assist. Those will take place on January 28 and 30 and will burn a total of 18 meters per second of New Horizons' delta vee. Since 92 meters per second were budgeted for these maneuvers, 18 represents quite a savings, so Alan is delighted about that.
Yesterday, the spacecraft slowed its spin rate down to 5 rotations per minute from 68 rotations per minute. The higher spin rate was used during the firing of the third stage motor (the STAR-48 engine) -- spinning the spacecraft during a major engine burn helps to average out any teensy inhomogeneities in the direction of the rocket firing and keeps the spacecraft on course. With the spin rate slowed down, they can turn on their star trackers, which will allow them to really fine tune their understanding of their position and trajectory.
The spacecraft is running warm -- always a problem for an outer solar system mission while it is still in the inner solar system. In fact, the spacecraft is still less than 1 astronomical unit from the Sun, because Earth was near its perihelion (closest approach to the Sun) when New Horizons launched, and consequently both Earth and New Horizons are closer to the Sun than 1 AU. New Horizons will cross the 1-AU mark on January 29. It will pass Mars on April 8. Alan notes that this is just after Mars Reconnaissance Orbiter -- which had a 5-and-a-half-month head start -- gets there in March. The comparison isn't really fair though; you have to be going much much slower if you hope to be captured into orbit. New Horizons is going so fast that it couldn't possibly go into orbit around any planet -- in fact it's going so fast that it's not even in orbit around the Sun, it's on an escape trajectory.
Actually, Alan passed along a funny fact about that -- New Horizons isn't the only thing that was just launched that is on an escape trajectory. New Horizons' spent third stage motor is, too -- and furthermore, because of that upcoming trajectory correction maneuver that will slow New Horizons by 18 meters per second, the third stage motor is moving fasterthan the spacecraft. Alan wrote:
Because we have to slow down in TCM-1A and TCM-1B by those 18 m/s, our third stage will beat us to Jupiter. However, because it will not hit the Pluto aim point [at Jupiter], it will not beat us to Pluto (a relief -- can you imagine us having to be the second to Pluto after all this, having been beat by a derelict Boeing upper stage?). In fact, the projected closest approach distance of the third stage to Pluto will be 213 million kilometers (well over 1 AU), occurring on 15 Oct 2015.
I had no idea that the third stage was also on its way out of the solar system. I wonder if there's any other "space junk" besides the Pioneers and the Voyagers that's on its way out of our neighborhood.
Another frequent topic of email this weekend was "is there a 'Where is New Horizons Now?' feature anywhere, similar to the one for MESSENGER?" I asked about this and the answer is that it is coming soon to the New Horizons website -- stay tuned.
The next BIG thing for New Horizons will be its encounter with Jupiter. The closest approach will be at approximately 05:00 UTC on February 28, 2007. Unfortunately, Jupiter's moons will all be on the opposite side of Jupiter right at closest approach, but they will still get very good views of Io and Europa because of their fast orbital periods around Jupiter. John Spencer speaks in this week's Planetary Radio about the initial planning for the New Horizons Jupiter encounter. He says that among other things they'll be looking for active plumes on Io, both along the limb and in infrared on its night side. Should be really cool -- stay tuned for more information about that. Here are some approximate dates John shared about the encounter:
|Date (2007)||Range (km)||Event|
|Feb 28 02:00||2,957,815||Europa closest approach|
|Feb 28 05:00||2,304,575||Jupiter closest approach|
|Feb 28 06:00||3,029,556||Ganymede closest approach|
|Feb 28 06:30||4,153,289||Callisto closest approach|
|Feb 28 22:00||2,260,221||Io closest approach|
Those distances aren't very close, but since it's a fast flyby mission, New Horizons' instruments are specifically designed to be able to do very good science from very long range, so I am really looking forward to the images and data that will result from this encounter.