NH at Jupiter, Planning the Jupiter encounter Options

[john_s]

Maybe you folks can help us...

We're now starting to lay out the timeline for the Jupiter encounter, but what we haven't done so far is look for "Kodak moments" as the Cassini imaging folks call them- times when we have scenic alignments or unusual geometries that call for a picture that's motivated by beauty more than science. Anyone want to help us find these moments?

Mark Showalter has now updated his New Horizons ephemeris tools to include the actual spacecraft trajectory through the Jupiter system. So you can download a table of satellite positions as seen from the spacecraft, and see views from the spacecraft of any body in the system at any time. It's probably most efficient to use the "Jupiter Ephemeris Generator" tool to create a table first and use that to find possible interesting alignments (e.g. times when the RA and Dec offsets of two satellites are similar), and then use the "Jupiter Viewer" to check out the view from the spacecraft at that time. The field of view of LORRI, our greyscale telephoto camera, is 5 x 5 milliradians, or 1044 arcseconds (parameters for all instruments are here). Make sure that you are using the "Official Post-Launch" trajectory option, which is the default.

If you find a specific time when you think we should press the shutter, let us know! No guarantees that we'll be able to do so, as there are numerous conflicts and constraints, but we'll give it a try. LORRI images don't take a lot of resources so we can probably spare a few for scenic purposes. MVIC color images are more "expensive", and are likely to have partial saturation except at high phase angles, so we're less likely to use MVIC for this purpose.

Thanks!
John.

[djellison]

The very easiest way for this is if someone can get it into celestia, and we can just run thru the flyby looking for interesting moment

You've opened a big bad can of worms here John Downlink was 2048kbps from Jupiter wasnt it

I'm sure you'll have lots of loonie ideas - but a moon rising or setting from behind Jupiter with possible refraction thru the upper atmosphere could be interesting....

Not sure of exact timing (see attached) if I have the night-side-day-side right, this would see a crecent Io set behind the dark-limb of Jupiter, so it would be squished and squashed as it set, in a way a little similar to this...
http://spaceflight.nasa.gov/gallery/images.../s103e5037.html but without a bright limb of Jupiter to get 'in the way'

Some upper atmosphere refraction has been seen by Cassini...
http://ciclops.org/media/dr/2005/1114_2631_2.png
http://ciclops.org/media/dr/2005/1191_2857_2.png
http://ciclops.org/media/dr/2005/1017_2487_1.jpg

Perhaps something to be learnt about the properties and extent of the upper jovian atmosphere by catching this little event?

I think that the classic Cassini 'mutual' events of transits etc are likely to be uncommon at a range worth imaging (guessing here).

Another potential target that's perhaps half scientific, half Kodak - is a lit side of a moon, being partially occulted by the jovian ring system- not sure how it might look or if it would appear at all, but again, potential for something 'interesting' if not beautiful


Doug

Attached File(s)

 io_set_nh.mov ( 347.05K ) Number of downloads: 252

 

[hendric]

I created a spreadsheet and imported the ephermis for a few weeks around closest approach, for every 20 minutes in the enounter. Best one so far is:
MJD Objects Notes
54161.44 IO & EUROPA Really close pass

Try adding a few hundredths of a MJD either way. When using the Jupiter Viewer, enter MJD as MJD 545161.44.

There are a few others from further away. I want to redo the ephermis +- a day to closest approach to see if I am missing any due to the 20 minute step size.

I'll post the spreadsheet once I'm done, promise!

Attached thumbnail(s)

 

[hendric]

OK, so there were a few additional close Io and Amalthea passes. Looking at the graphs, the majority of passes are Io & Amalthea, with a few others, mostly with Amalthea. The speedy little moon gets around!

MJD Bodies Comments
54149.68056 IO & AMALTHEA Europa is just out of view to the NW, good view of the rings
54149.8888 IO & AMALTHEA Thebe is left of Amalthea, IO is pretty far away
54150.98611 IO & EUROPA Far pass
54157.925 IO & JUPITER Io grazes the north side of jupiter, leaving J disk on dark side
54158.943 IO & JUPITER Io goes behind jupiter on the dark side
54159.365 EUROPA & JUPITER Europa grazes the southern dark side of Jupiter
54160.12 IO & JUPITER Crescent IO in front of dark side Jupiter, emerges few minutes later
54160.12 AMALTHEA & JUPITER Crescent Amalthea in front of dark side of Jupiter, emerges a few minutes later
54161.042 IO & JUPITER Io disappers behind jupiter on the dark side, with the rings visible and in shadow. Encounter with Io and Rings starts earlier
54161.43646 IO & EUROPA Really close pass!!!
54161.85 EUROPA & AMALTHEA Rings are between them
54161.97083 IO & AMALTHEA Rings are between them, with Adrastea possible
54162.85365 IO & AMALTHEA Close pass, rings and Metis visible, long encounter!
54165.125 IO & EUROPA Small crescents for both
54165.70833 IO & AMALTHEA Rings & jupiter, but distance function shows a bump, so could be interesting encounter
54168.70833 IO & EUROPA Pretty far pass, but in the same field
54170.94633 IO & EUROPA Amalthea emerges from behind Jupiter, might make an interesting appearance, all objects showing thin crescents

I had to do a manual search for Jupiter events, and gave up after a bit.

Unfortunately, the spreadsheet is over 20 MB, so I can't post the full thing. Here is a PDF of the charts, and a cut-down spreadsheet that you can enter the data in yourself. Some notes:

1. You have to modify the RA so that it is monotonic. What does that mean? When scrolling down, if you get to a set of entries that go from +~24 to ~0, then you need to change the RA(corr) column to (RA+24) to keep it linear.
2. RA is multiplied by 15, to get something vaguely representing degrees.

Any other questions, or if you want the full spreadsheet, feel free to ask.

Attached File(s)

 ephem_jup_5946.pdf ( 868.6K ) Number of downloads: 153

 

[hendric]

Here's the reduced spreadsheet.

Attached File(s)

 cut_down_ephem_jup_5946.zip ( 155.31K ) Number of downloads: 222

 

[Bart]

Any word yet on the possibility of imaging Himalia?

Bart

[mcaplinger]

I am sure there is a good reason for not doing this, but I have always wondered why these ejectable lens covers aren't made of lexan.

Lexan isn't a good choice due to outgassing and optical quality. It's fairly hard to make a cover that doesn't screw up optical performance, especially for a fixed-focus system.
That said, the Galileo SSI did have a transparent cover (I'm guessing it was glass). All of the systems I've worked on (MOC 1&2, THEMIS, CTX, MARCI 98&05) had no covers at all -- we were too mass-constrained.

This post has been edited by mcaplinger: Feb 9 2006, 05:57 PM

[ljk4-1]

Lexan isn't a good choice due to outgassing and optical quality.  It's fairly hard to make a cover that doesn't screw up optical performance, especially for a fixed-focus system.
That said, the Galileo SSI did have a transparent cover (I'm guessing it was glass).  All of the systems I've worked on (MOC 1&2, THEMIS, CTX, MARCI 98&05) had covers at all -- we were too mass-constrained.

If only they had been as thoughtful with the antenna on Galileo.

Could they have put Galileo into orbit around Europa? Or was the radiation just too much for the probe towards the end of its life?

[djellison]

Did you mean to say 'no covers at all' ?

As thinking back to imagery from the KSC gallery - I certainly dont remember any covers on the instruments you mention.

Doug

(PS - Galileo was basically knackered - electronics exposed to huge ammounts of radiation - and certainly not enough fuel to go into Europan orbit - the reason for crashing it into Jupiter as I understand it was that they didnt expect to have enough fuel for manouvering on board to keep control of the vehicle, and they wanted to dispose of it whilst still in control of it.)

[ugordan]

If only they had been as thoughtful with the antenna on Galileo.

As someone already said, unfolfing HGAs were used numerous times before, with no difficulties unfolding. It was a proven concept. What got Galileo in the end was all that trucking around the country, waiting to be launched literally for years.

Could they have put Galileo into orbit around Europa?  Or was the radiation just too much for the probe towards the end of its life?

That's an even worse situation than trying to put Cassini into orbit around Titan. There's just too much delta-V needed for it to be anywhere near feasible. Galileo was "running on fumes" at the end of its life with practically no propellant left.
It also wasn't really designed to stand up to prolonged heavy radiation doses a Europa orbit would guarantee so that scenario wouldn't work in real life.

[dvandorn]

And, the final nail in the Europa-orbit coffin was that Galileo wasn't completely sterilized (although you'd think that the Jovian radiation belts would have finished *that* job*), and there was a perceived contamination risk if it were to crash onto Europa. The easiest and most certain way to make sure that never happened was to ensure that Galileo was destroyed well away from Europa -- hence it was flown to its destruction into Jupiter itself.

-the other Doug

[JRehling]

If only they had been as thoughtful with the antenna on Galileo.

Could they have put Galileo into orbit around Europa?  Or was the radiation just too much for the probe towards the end of its life?

A qualitative guide to delta-v calculations:

Let's use an object at infinity (from, say, Jupiter) as the baseline. Zero energy.

The next thing is to put it into a very distant orbit. That's one step away from zero.

Then put it into an orbit with a distant apojove but a decently close perijove. That's a big energy step from the last one. It's also the easiest science orbit to achieve. Almost all orbiters of all other planets have been in that category, besides the ones that have used aerobreaking to help. By the way, the energy is proportional to the mass of the object, so it's about 3000 times more delta-v at Jupiter than Mars.

Then it's a big step to pull in that apojove. Roughly 20% of escape velocity. That's what it would have taken to get Galileo into a jovian orbit near Europa.

At that point, stop thinking about Jupiter and consider getting the thing at infinity for Europa, and bring it down in the same steps (much easier, because of Europa's lower mass).

Basically, that 20% of Jupiter's escape velocity is a killer.

[john_s]

Here's the reduced spreadsheet.

Just a quick note to say thanks, hendric, for all your work on this- I haven't had a chance to look at the details yet but I'll do so soon.

John.

[tedstryk]

One thing I remember reading in the early 1990s, before the stuck antenna problem was known, is that the idea of ending the mission with a Ranger-like kamikazee into Io. That would have been cool, but of course with the antenna being stuck, there was no way to transmit the data from such an even.

[Rob Pinnegar]

One thing I remember reading in the early 1990s, before the stuck antenna problem was known,  is that the idea of ending the mission with a Ranger-like kamikazee into Io.

Yeah, straight into one of the calderas and *SPLASH*!