Author Topic: New Horizons Pluto Flyby Coverage  (Read 220884 times)


Offline HarrisPeters

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That was a great read! Thanks Chris G!

Offline EE Scott

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Yes, a really enjoyable article. I can't wait to see what this mission turns up. Super exciting!
Scott

Online Comga

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Nice article.
A few nits.

PERSI is an old name for a conceptual UV-Vis-NIR instrument.  These tasks were split between Alice, the UV Imaging Spectrometer, and Ralph, with the MVIC the Panchromatic and color TDI camera detectors and back-up navigation framing array, and the LEISA Imaging Infrared Spectrometer.  Ralph and Alice are named after Ralph and Alice Cramden, the Honeymooners of the famous Jackie Gleason radio and TV series of skits.  The PERSI name is not used on the New Horizons mission.  Likewise I think the PAM name is archaic and not used by the team. 

The article says that "No dust collector instrument has ever operated successfully beyond the orbital bounds of Uranus," but the VBSDC and its student controllers at the University of Colorado have been doing that for a couple of years now.  Just add the word "previous" after "No".  :)

The "spin up and spin down" effected by the small thrusters are, in fact, the method for scanning Ralph and Alice instruments.  Scan mirrors would have been too complex and unreliable for a strongly mass and power limted, ten to fifteen year mission in the cold and dark, as would momentum wheels for the spacecraft.  So all pointing and scanning is done with the little thrusters.

edit:  The RTG was SUPPOSED to provide 250 W at launch.  Due to certain supply limits, it generated more like 210 W at launch. (If you put down a number, this is what happens.  :-)  )

I haven't seen that old New Horizons spacecraft image for a long, long, time.
Try this one.  It is my favorite of the visualized flyby images.
« Last Edit: 01/19/2015 11:29 PM by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Ben the Space Brit

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I'm just worried about how complex and filled with debris the Plutonian system is. With those recently-discovered mini-moons, the area close to the planet could easily have several debris fields (although I would think the area between Pluto and Charon should have been cleared out by their gravity and motion through that space). I know that missions control was looking at ways to minimise collision risk but there has to be only so much they can do, given the probe doesn't have an MPS like Cassini (or, earlier, Galileo).
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Online MATTBLAK

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VERY good article for a mission I can barely wait for! ;) Dawn at Ceres is going to be so cool, too...
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Offline hoku

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Thanks, very informative article.

Another nit-pick:

> During and immediately after the close encounter, the low bandwidth will result in a one-way communication lag of approximately 4.5 hours.

Distance between Earth and Pluto in July 2015 will be about 32 AU, which results in a light (radio) travel time - and hence one-way communication lag - of about 4.5 hours for the first bits of data to arrive on Earth. The low bandwidth implies that it will take a while (how long?) to receive a full image frame at close encounter, and this "while" adds to the 4.5 hours.
« Last Edit: 01/20/2015 11:50 AM by hoku »

Offline Targeteer

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http://nasa3d.arc.nasa.gov/detail/new-horizons

3D Printing

We understand that 3D printing often involves trial and error. If you have to make adjustments or changes when printing these models, please share your experience with us:
arc-special-proj@lists.nasa.gov

If I had one of these lying around I'd try to print it out :)
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Online Sesquipedalian

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Why is bandwidth so much lower at Pluto?  I can't see how the increased lag has anything to do with this.

It seems to me that if New Horizons can transmit at 38 kbit/s from Jupiter, it can transmit at 38 kbit/s from Pluto.  In both cases Earth will receive a 38 kbit/s data stream, the only difference is that in the second case it will receive the stream a few hours later.

Can someone explain why the increased distance affects the bandwidth?

Offline Targeteer

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Best quote heard during an inspection, "I was unaware that I was the only one who was aware."

Offline Ben the Space Brit

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #10 on: 01/20/2015 01:57 PM »
Why is bandwidth so much lower at Pluto?  I can't see how the increased lag has anything to do with this.

Basically, distance. At a further distance, it is harder to detect the digital pulses from a spacecraft and they blur together. The answer to this is to slow the clock speed of the transmitter and thus reduce the bandwidth.
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Offline ugordan

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #11 on: 01/20/2015 02:07 PM »
Why is bandwidth so much lower at Pluto?  I can't see how the increased lag has anything to do with this.

It seems to me that if New Horizons can transmit at 38 kbit/s from Jupiter, it can transmit at 38 kbit/s from Pluto.  In both cases Earth will receive a 38 kbit/s data stream, the only difference is that in the second case it will receive the stream a few hours later.

Can someone explain why the increased distance affects the bandwidth?

Signal strength drops off with the square of the distance and bandwidth scales with received power. Pluto is at around 40 A.U., Jupiter at around 5.2 A.U.

Yes, one way light time has nothing directly to do with bandwidth. Of course that increasing distance for a *given* transmitter power will decrease bandwidth, but nothing in principle prevents you from putting a kilowatt transmitter at Pluto and getting back a more reasonable bitrate than the trickle New Horizons will get.

Offline notsorandom

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #12 on: 01/20/2015 02:32 PM »
Why is bandwidth so much lower at Pluto?  I can't see how the increased lag has anything to do with this.

It seems to me that if New Horizons can transmit at 38 kbit/s from Jupiter, it can transmit at 38 kbit/s from Pluto.  In both cases Earth will receive a 38 kbit/s data stream, the only difference is that in the second case it will receive the stream a few hours later.

Can someone explain why the increased distance affects the bandwidth?

Signal strength drops off with the square of the distance and bandwidth scales with received power. Pluto is at around 40 A.U., Jupiter at around 5.2 A.U.

Yes, one way light time has nothing directly to do with bandwidth. Of course that increasing distance for a *given* transmitter power will decrease bandwidth, but nothing in principle prevents you from putting a kilowatt transmitter at Pluto and getting back a more reasonable bitrate than the trickle New Horizons will get.
Additionally with radio bandwidth is pretty much related to the width of the spectrum a signal takes. The wider the signal the more data. However a wider signal needs more total transmitter energy to cover the space it takes. Basically the narrower the signal the more concentrated the transmitter's power. So a narrow signal is more detectable than a wider one for the same transmitter power.

As you get further away the signal strength decreases. There are some pretty big dishes on each end but those can only focus the radio beam so much. The inverse square law is at play here. So if the transmitter power is staying the same and the distance means you are getting a smaller percent of the transmitter signal's power back the only way to keep the signal detectable is to narrow the bandwidth of the signal.

Offline pagheca

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #13 on: 01/20/2015 02:39 PM »
Why is bandwidth so much lower at Pluto?  I can't see how the increased lag has anything to do with this.

It seems to me that if New Horizons can transmit at 38 kbit/s from Jupiter, it can transmit at 38 kbit/s from Pluto.  In both cases Earth will receive a 38 kbit/s data stream, the only difference is that in the second case it will receive the stream a few hours later.

Can someone explain why the increased distance affects the bandwidth?

Moreover, I understand that deep space transmissions are a trade-off between the capability to beam the signal (aka reduce the antenna pattern) and the antenna pointing error. The more you beam your signal, the more power is received, but at some point pointing accuracy and diffraction limits take over.

So, as the communication distance increases, the pointing error becomes more and more relevant on each side, and you cannot beam as the receiver could miss the information.

I haven't done my homework to find if this is true in this condition, but as a general rule I understand this is important.
« Last Edit: 01/20/2015 02:40 PM by pagheca »

Offline ugordan

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #14 on: 01/20/2015 02:53 PM »
So, as the communication distance increases, the pointing error becomes more and more relevant on each side, and you cannot beam as the receiver could miss the information.

That doesn't make sense. Any given directional antenna will focus its signal into a specific cone. As distance grows, the cone footprint at Earth increases so the pointing requirements become *less* stringent, not more.

I don't know much about RF comms, but my understanding was that the radio wavelength chosen is what limits how well the signal can be collimated (to reduce "waste" of the footprint) due to diffraction. That's one of the biggest motives for going with optical comms, not that RF is inherently bad. Optical beams can be collimated so tightly that it really does get to a point where you need to have very precise pointing. For radio, not so much.

Online Comga

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #15 on: 01/20/2015 02:55 PM »
I'm just worried about how complex and filled with debris the Plutonian system is. With those recently-discovered mini-moons, the area close to the planet could easily have several debris fields (although I would think the area between Pluto and Charon should have been cleared out by their gravity and motion through that space). I know that missions control was looking at ways to minimise collision risk but there has to be only so much they can do, given the probe doesn't have an MPS like Cassini (or, earlier, Galileo).

Two of the teams on the mission have opposing goals.  One is to search for new objects with the hope of finding new moons and the conjectured rings.  The other is searching for new objects with the hope of NOT finding new things and proving that the planned route is clear of danger. 

Alan Stern wrote of three possible "Safe Haven Bail-Out Trajectories" which caused our friend Keith Cowing at NASAWatch to pitch a fit about who has authority to optimize the mission for safety over science.  My personal impression is that Dr. Stern liked the acronym, SHBOT, and the team was just engaging in prudent planning, which continues.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline JasonAW3

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #16 on: 01/20/2015 02:58 PM »
Perhaps with the next Pluto probe we can send a Light Sail craft that can use it's li8ght sail to double as an antenna.  Still need a MUCH more powerful power source of a strong signal.  Maybe a Lockheed Martian Fusion Powerplant?

Send out a big enough probe with a powerful telescope, gravitationally anchor it to Pluto, and you can use the same probe for other purposes besides Pluto observations.  Maybe a Kuiper Belt observation station?  Oort Cloud mapping mission?  Maybe a Synthetic Appature Optical Interferomitter with a 32 AU width?

That far out, it could even be used to assist with extrasolar planetary finding and Observations.
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Offline JasonAW3

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #17 on: 01/20/2015 03:02 PM »
So, as the communication distance increases, the pointing error becomes more and more relevant on each side, and you cannot beam as the receiver could miss the information.

That doesn't make sense. Any given directional antenna will focus its signal into a specific cone. As distance grows, the cone footprint at Earth increases so the pointing requirements become *less* stringent, not more.

I don't know much about RF comms, but my understanding was that the radio wavelength chosen is what limits how well the signal can be collimated (to reduce "waste" of the footprint) due to diffraction. That's one of the biggest motives for going with optical comms, not that RF is inherently bad. Optical beams can be collimated so tightly that it really does get to a point where you need to have very precise pointing. For radio, not so much.

Basic physics;  As the signal is sent down the cone, the strength of the signal falls off as that same power is spread over a larger width, plus, the signal itself looses energy due to gas, dust, EM fields and general RF interference.  Thus, like all forms of radiation, the signal strength falls of with the square of the distance.
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Offline ugordan

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #18 on: 01/20/2015 03:07 PM »
So, as the communication distance increases, the pointing error becomes more and more relevant on each side, and you cannot beam as the receiver could miss the information.

That doesn't make sense. Any given directional antenna will focus its signal into a specific cone. As distance grows, the cone footprint at Earth increases so the pointing requirements become *less* stringent, not more.

I don't know much about RF comms, but my understanding was that the radio wavelength chosen is what limits how well the signal can be collimated (to reduce "waste" of the footprint) due to diffraction. That's one of the biggest motives for going with optical comms, not that RF is inherently bad. Optical beams can be collimated so tightly that it really does get to a point where you need to have very precise pointing. For radio, not so much.

Basic physics;  As the signal is sent down the cone, the strength of the signal falls off as that same power is spread over a larger width, plus, the signal itself looses energy due to gas, dust, EM fields and general RF interference.  Thus, like all forms of radiation, the signal strength falls of with the square of the distance.

Uh, the inverse square law is exactly what I was talking about in my first post on bandwidth above. I don't see what's that got to do with pointing requirements pagheca talked about. A wider footprint caused by greater distance means that you have more of an angular deadband wiggle room before you need to repoint your antenna at Earth.

It is true, though, that you need to keep the Earth within the angular size of the cone at all times and that doesn't change, but you get progressively more and more of the Earth's orbit inside that cone as distance increases. For example for Voyager, the "half-power half-width of the antenna beam was 0.32 degrees at X-band and 1.1 degrees at S-band.". Compared to 0.4 deg FOV of the narrow-angle camera.
« Last Edit: 01/20/2015 03:25 PM by ugordan »

Online Comga

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Re: New Horizons begins Pluto observations ahead of July flyby
« Reply #19 on: 01/20/2015 03:08 PM »
So, as the communication distance increases, the pointing error becomes more and more relevant on each side, and you cannot beam as the receiver could miss the information.

That doesn't make sense. Any given directional antenna will focus its signal into a specific cone. As distance grows, the cone footprint at Earth increases so the pointing requirements become *less* stringent, not more.

I don't know much about RF comms, but my understanding was that the radio wavelength chosen is what limits how well the signal can be collimated (to reduce "waste" of the footprint) due to diffraction. That's one of the biggest motives for going with optical comms, not that RF is inherently bad. Optical beams can be collimated so tightly that it really does get to a point where you need to have very precise pointing. For radio, not so much.

That is correct.  The beam divergence is limited by diffraction, which is set by the size of the antenna, which was limted to what fit on the spacecraft.  The pointing system is sufficiently accurate to take good images with LORRI and Ralph, which have 10 and 20 microradian IFOVs (pixel projections) which are smaller than the radio beam width, and the attitude knowledge from the star trackers is of a similar precision, so those are not the limiters.  It's just distance, with received power dropping as the square of the enormous distance, as mentioned by several other poster. 

This is an issue for the Voyagers, too, at their even greater distance, but they don't have gigabytes of data to send. 

The New Horizons team has extensive plans for prioritizing data for early transmission and freeing memory to maximize the science return.  This is complicated by the simplicity of the spacecraft, which means that it can't do much science, or any imaging, while it points to Earth to transmit.  (That is, however, the optimum orientation for the Student Dust Counter.) The spacecraft will take short breaks from observing to send back some data, particularly compressed, select data soon after the encounter, before resuming the departure observations, and then spending a year or so on a complete download. 
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

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