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On The Road To Pluto At Last

by Alan Stern
Baltimore MD (SPX) Jan 24, 2006
New Horizons is en route to Pluto. I was told at a post-launch party down in Cocoa Beach that our launch came 5 years to the day from the date NASA released the Pluto-Kuiper Belt mission Announcement of Opportunity (AO) that resulted in our selection to build and launch New Horizons. Amazing!

Even more amazing, given all the political and technical hurdles, we managed to launch onto the earliest arrival flight time trajectory we could have possibly launched onto�just 9.5 years, from Earth to Pluto. As you know, we were faced with possible arrival times as late as 2020 for launches even a few weeks late and as late as 2021 if we had slipped to a 2007 launch date. What a team of dedicated, hard working people can do when they have a challenge is just magic. And the New Horizons team is magic.

Now that we are launched and safely on our way, we know that our journey will take precisely 3462.7 days, i.e., from 1900 UT on 19 Jan 2006 to 12:00 UT 14 July 2015 to reach Pluto. Encounter science ops will begin about 150 days before we reach Pluto.

New Horizons is currently headed to Jupiter and was at this position outbound yesterday.

As I write this, on flight day 4, we have roughly 0.1% of the journey behind us. In those 4 days, the spacecraft team has been conducting subsystem checkouts and designing the trajectory correction maneuvers planned to trim up our route of flight to the precise aim point we need to thread 2.5 million kilometers from Jupiter, at approximately 05:41 UT on 28 Feb 2007.

On Sunday we completed the spacecraft's planned spin down to 5 RPM (was 68 RPM for the STAR-48 firing, is now 19.2 RPM after an open-loop burn on launch day). Once we did that, we did the initial star tracker turn on. Until then, we're still relying on the sun sensors and IMUs for attitude reference - both of which performed very well.

Because of the extremely accurate launch that our Atlas V plus STAR-48 launcher combination provided, we only need to expend or provide an 18 meter/second correction in order to thread that needle. Pre-launch predicts had allowed for maneuvers 5 to 10 times that size. We're all very happy to only have a small correction to make, since this saves propellant for future science mission use. The 18 m/sec correction is planned to be conducted in two parts: a 5 m/sec increment on 28 Jan and a 13.3 m/sec increment on 30 Jan.

We split the maneuvering up into two parts in order to calibrate our propulsion system with a small first burn before going for the majority of the correction. This strategy will allow us to thread the needle more accurately than a single larger burn would have.

A couple of other tidbits you may be interested in:

About the heliocentric distance, we will be inside 1 AU until late on 29 Jan UT. That makes us officially an inner planet mission for the first 10 days, I guess.

We will pass the orbit of Mars on 8 April, just a little after MRO gets there, and it had a 5.5 month head start.

The C/A to Jupiter is going to be at approx 6 hrs UTC on 28 Feb 2007. A better number will be forthcoming, but that is good to an accuracy of better than an hour already. C/A is at 32 RJ. Because we have to slow down in TCM-a 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, 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, because the third stage cannot trim up its trajectory it will not cross Pluto's orbit until 15 Oct 2015, and when it does, it'll be about 200 million kilometers (roughly the distance from the Sun to Mars) from Pluto.

We're beginning to think seriously now about specific planning for Jupiter, and I will have more to say about that soon.

Related Links
Pluto at JHU

The PI's Perspective 24 Hours After Launch: It Worked!
Boulder CO (SPX) Jan 23, 2006
"It Worked." Those are the words that form the last entry in my project notebook for the day of launch. Now, a day later, the spacecraft is already undergoing checkouts, and has been de-spun from its launch rotation rate of 68 RPMs to just under 20 RPMs.







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