Author Topic: Design a mission to Proxima b  (Read 68894 times)

Offline JasonAW3

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Re: Design a mission to Proxima b
« Reply #80 on: 08/30/2016 05:47 pm »
The problem here, I think, is more along the lines of conventional thinking.

     First off, there is a higher likelihood of something catastrophic happening to a single probe, traveling at 20% the velocity of light than there is of impact on either the Voyager or pioneer probes, which are traveling far slower.

     Thus, using a group of smaller probes, about the gram size and mass and numbering in the hundreds or thousands, networked together to act as a distributed neural network, could allow for a fairly advanced and sophisticated AI system to control the group as a whole.  Losses during transit could be more readily absorbed by a group, than a single probe.

     This configuration also allows for a potential synthetic aperture sensor capability, allowing much more detailed information to be gathered during their transit through the Proxima Centauri system.

     Such a multiprobe approach would also add to the knowledge base of what hazards exist for human starflight at 20% C or higher velocities.
My God!  It's full of universes!

Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #81 on: 08/30/2016 07:42 pm »
Some thoughts:

1) No nation or private group is ever going to commit to a "starship" or probe until more is known about its destination.
This statement is trivially true. There is serious scientific hay to be made by JWST and the 39m E-ELT, instruments already under construction, let alone ones that will be built in the future.
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2) As someone said, a space probe won't work. Unless we can create true artificial intelligence for it to operate itself
Like what? think of a probe as just a sensor. It just needs to receive information and broadcast it.
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it would be increasingly impossible to control,
You pre-program it with instructions, obviously.
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activate (you're not going to let it run its power and fuel out over years)
And why not? Voyager 1 and 2 look like they'll probably last for half a century, which is longer than Breakthrough Starshot will need (for instance).
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or even receive the data it finds because the distance needed to send and receive signals aren't going faster than light (and let's leave the SF out of it until someone invents something truly FTL).
Why does the probe need to receive commands? Just program it to send the right information. It doesn't need "AI" except in the trivial sense that is already used today on Mars.

There's never been a probe that works autonomously. Probes can't anticipate the unexpected or fix issues themselves. From the Dawn probe, JAXA's Akatsuki to MER Spirit, human intervention is eventually required. Now multiply that matter when an issue is reported days, if not months later, and a command is sent to correct an issue when the probe might be pointed the wrong way or dead by the time the command gets there.

Durability of probes isn't my problem. JPL continually makes probes that outlast their mission design by years to decades. Now am I complaining about the versatility of many probes to fix many of its problems on its own. The problem is simply communication to fix what the probes cannot.

Voyager 1 and 2 have completed their missions.

Oh, we should also consider what power source these things would use. RTGs have a good life, but even they might have limits if a mission takes decades, and the scarcity of plutonium is one reason why Juno is using solar panels.

You're still talking years to send or receive anything. That can be managed except for some mission-critical issues that have occurred on missions before. Good planning and innovation might reduce those issues.
These are the easiest problems to solve in the whole mission. All the probe needs to do is collect data and relay it to Earth.

By focusing on these "issues," you're vastly overestimating the difficulty of the propulsion problem. It's absurdly hard.
« Last Edit: 08/30/2016 07:43 pm by Robotbeat »
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Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #82 on: 08/30/2016 07:43 pm »
Falcon 9 is totally autonomous once launched. Sputnik 1 was autonomous.
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Offline gospacex

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Re: Design a mission to Proxima b
« Reply #83 on: 08/30/2016 08:05 pm »
It seems to me that a probe to Proxima b is not a good idea.

Microprobe flybys (e.g. lightsail-propelled stuff) would have hard time collecting useful information: they can snap some pics at best, but how they would transmit the data back? Not trivial, you'd need a HUGE receiving antenna in Sol system.

Macroprobes we don't quite have propulsion for. Need to develop some fusion drive.

Developing a VERY powerful space telescope (interferometry?) can give you about the same information, sooner, with less R&D and mission risk (if something does not work out, you aren't at square one. You can debug it).
And also the 'scope can look and many, many other targets too, whereas probes capable of reaching Proxima will become even less tenable for targets farther away.

Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #84 on: 08/30/2016 08:28 pm »
It seems to me that a probe to Proxima b is not a good idea.

Microprobe flybys (e.g. lightsail-propelled stuff) would have hard time collecting useful information: they can snap some pics at best, but how they would transmit the data back? Not trivial, you'd need a HUGE receiving antenna in Sol system.
Lasers and with a large telescope.

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Macroprobes we don't quite have propulsion for. Need to develop some fusion drive.

Developing a VERY powerful space telescope (interferometry?) can give you about the same information, sooner, with less R&D and mission risk (if something does not work out, you aren't at square one. You can debug it).
And also the 'scope can look and many, many other targets too, whereas probes capable of reaching Proxima will become even less tenable for targets farther away.
Do both.
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Offline hop

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Re: Design a mission to Proxima b
« Reply #85 on: 08/30/2016 08:45 pm »
These are the easiest problems to solve in the whole mission.
It may well be the easiest problem, but it is far beyond anything we've done.

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All the probe needs to do is collect data and relay it to Earth.
Not if you want to collect useful data. It needs to autonomously identify and select targets, select appropriate observations, and execute the observations with incredible speed, precision and reliability.

Falcon 9 is totally autonomous once launched. Sputnik 1 was autonomous.
That is not a reasonable comparison. You need to look at the amount of human time and effort that goes into planning real spacecraft observations. This is nothing like an LV flying a preprogrammed trajectory with some closed loop guidance. Even those "autonomous" LVs get a huge amount of human analysis and planning before the launch.

Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #86 on: 08/31/2016 12:14 am »
New Horizons, when it entered flyby phase, was entirely autonomous for the same reason as a probe to Proxima b would be. It was given all its instructions of where to look beforehand.

You're making a mountain of a molehill. The real challenge is getting there.
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Offline hop

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Re: Design a mission to Proxima b
« Reply #87 on: 08/31/2016 02:08 am »
New Horizons, when it entered flyby phase, was entirely autonomous for the same reason as a probe to Proxima b would be. It was given all its instructions of where to look beforehand.
No, it was preprogrammed, not autonomous. The amount of autonomy was very limited, basically consisting of rebooting and continuing the sequence at a reasonable point. The sequences were developed through many person-years (decades, centuries?) of effort, and with human input up to a short time before the encounter. That human input was based on analysis of earlier data obtained from the spacecraft.

In any realistic scenario, knowledge of the Proxima system and the location of the probe will not be sufficient to have to develop the sequences in advance. To get much useful data, the probe will need to do the equivalent of planning the sequences itself. That is hard. Not as hard as some of the other problems, but nowhere near as easy your comments suggest.

An analogous New Horizons mission would be if it had been completely under spacecraft control after launch. It would carry out all the TCMs, navigate it's way to Pluto with no DSN, discover the moons that weren't known before launch, refine the orbits of Pluto and Charon beyond what was known at launch, do the analysis to decide the safe trajectory, plan all the specific observations based on its chosen trajectory, and execute it all perfectly without going into safe mode and phoning home for help (unlike the real New Horizons)
As hard as that would be, it would be much easier than doing the equivalent in a different star system.
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You're making a mountain of a molehill. The real challenge is getting there.
Disagree. You are completely failing to grasp the amount of analysis and effort that goes into real spacecraft operations, and how much would have to be done by the spacecraft given a multi-year time lag and limited knowledge of the targets.
« Last Edit: 08/31/2016 02:10 am by hop »

Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #88 on: 08/31/2016 02:13 am »
New Horizons, when it entered flyby phase, was entirely autonomous for the same reason as a probe to Proxima b would be. It was given all its instructions of where to look beforehand.
No, it was preprogrammed, not autonomous....
Sure, that works.
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Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #89 on: 08/31/2016 02:14 am »
...
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You're making a mountain of a molehill. The real challenge is getting there.
Disagree. You are completely failing to grasp the amount of analysis and effort that goes into real spacecraft operations, and how much would have to be done by the spacecraft given a multi-year time lag and limited knowledge of the targets.
disagree? You ignored the second sentence right there. nothing compared to the challenge of getting there.
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Offline hop

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Re: Design a mission to Proxima b
« Reply #90 on: 08/31/2016 02:33 am »
No, it was preprogrammed, not autonomous....
Sure, that works.
Except it doesn't work for an interstellar mission.  That's the whole point. You cannot apply anything like the approach used by New Horizons or any other real space mission to date.

And yes, the disagree was only intended to apply to the mountain vs molehill ;) I fully agree that propulsion is an even bigger mountain :D

Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #91 on: 08/31/2016 03:38 am »
No, it was preprogrammed, not autonomous....
Sure, that works.
Except it doesn't work for an interstellar mission.  That's the whole point. You cannot apply anything like the approach used by New Horizons or any other real space mission to date.

And yes, the disagree was only intended to apply to the mountain vs molehill ;) I fully agree that propulsion is an even bigger mountain :D
But the molehill thing IS applying to propulsion as well.

This thing you keep talking about is /trivial/ compared to propulsion. I mean absolutely trivial. It's just ridiculously hard to get there. MUCH harder than we're used to thinking about.
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Offline rdheld

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Re: Design a mission to Proxima b
« Reply #92 on: 08/31/2016 11:33 am »
it sounds to me you need enough fuel to slow down and have the main craft orbit Proxima?

Offline Stormbringer

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Re: Design a mission to Proxima b
« Reply #93 on: 08/31/2016 01:22 pm »
The US is re-establishing plutonium production. A small batch pilot program is over and it was successful. Plans are already afoot to scale it up to the needed levels. We will have all we need to make as many RTGs as we need as big as we need them to be.
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Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #94 on: 08/31/2016 02:21 pm »
it sounds to me you need enough fuel to slow down and have the main craft orbit Proxima?
Not all concepts bother to slow down. And those that do often find ways to slow down without fuel.
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Offline whitelancer64

Re: Design a mission to Proxima b
« Reply #95 on: 08/31/2016 03:14 pm »
No, it was preprogrammed, not autonomous....
Sure, that works.
Except it doesn't work for an interstellar mission.  That's the whole point. You cannot apply anything like the approach used by New Horizons or any other real space mission to date.

And yes, the disagree was only intended to apply to the mountain vs molehill ;) I fully agree that propulsion is an even bigger mountain :D
But the molehill thing IS applying to propulsion as well.

This thing you keep talking about is /trivial/ compared to propulsion. I mean absolutely trivial. It's just ridiculously hard to get there. MUCH harder than we're used to thinking about.

Trivial??  No it isn't.

Propulsion will be a challenge, indeed as you say, more difficult than anything we've ever done, but it is comparatively straightforward.

The Proxima b probe will need to have a level of AI far beyond anything we've ever been able to make. It will have to be able to detect new astronomical features, decide what they are, change its mission profile, calculate new trajectories, and so on. All on its own. It won't be able to receive new instructions from Earth like New Horizons repeatedly did.
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Offline Paul451

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Re: Design a mission to Proxima b
« Reply #96 on: 08/31/2016 03:20 pm »
So if you want to track a moving target (such as an orbiting planet), then - to skew the view - you need to physically move the telescope laterally to the direction of travel.
Depends on the field of view of the telescope.

How?

It'll already need a wide FoV to observe the entire Einstein ring around our sun. To change what object is "projected" onto that Einstein ring (or to track a moving object), it will need to physically move (not tilt, but move) laterally.

Yes, Proxima b's orbital diameter is only about 7 million kilometers. At about 40,000 million kilometer distance.

40 billion km is 266AU. What "distance" are you measuring?

[edit: It only registered later than you meant 40 trillion km. 4.3ish lightyears.]
« Last Edit: 08/31/2016 04:27 pm by Paul451 »

Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #97 on: 08/31/2016 03:30 pm »
So if you want to track a moving target (such as an orbiting planet), then - to skew the view - you need to physically move the telescope laterally to the direction of travel.
Depends on the field of view of the telescope.

How?

It'll already need a wide FoV to observe the entire Einstein ring around our sun. To change what object is "projected" onto that Einstein ring (or to track a moving object), it will need to physically move (not tilt, but move) laterally.
...
Image the entire system as an object. The distance b orbits from Proxima is about 1000 Earth radii.

Kepler, for instance, has 42 CCDs each ~2000x1000 pixels. So if the whole orbit was in view, you should have many pixels of resolution of the exoplanet. And of course, we could have 1000 CCD arrays instead of just 42.
« Last Edit: 08/31/2016 03:45 pm by Robotbeat »
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Offline Paul451

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Re: Design a mission to Proxima b
« Reply #98 on: 08/31/2016 04:11 pm »
Image the entire system as an object. The distance b orbits from Proxima is about 1000 Earth radii.
Kepler, for instance, has 42 CCDs each ~2000x1000 pixels. So if the whole orbit was in view, you should have many pixels of resolution of the exoplanet. And of course, we could have 1000 CCD arrays instead of just 42.

That's not how Einstein rings work.

At 700AU (so the focal angle is far enough away from the sun for the Einstein ring to be visible beyond the sun's atmosphere) the FoV of an Einstein ring is around 1.5 arcseconds. AIUI, in practice, the useful FoV will be about a tenth of that: 0.15 arcseconds.

A 14 million km orbit in the target system will have an apparent width of around 13 arcseconds. Nearly two orders of magnitude too wide to image from a single location.

To slew from one side of Prox-b's orbit to the other requires a lateral shift by the observer of about 37,000 km.

[edit: At 550 AU, the FoV is 1.7 arcseconds, the useful FoV is 0.17". In case you thought I was cheating by going to 700AU.]
« Last Edit: 08/31/2016 04:26 pm by Paul451 »

Offline Robotbeat

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Re: Design a mission to Proxima b
« Reply #99 on: 08/31/2016 04:17 pm »
Image the entire system as an object. The distance b orbits from Proxima is about 1000 Earth radii.
Kepler, for instance, has 42 CCDs each ~2000x1000 pixels. So if the whole orbit was in view, you should have many pixels of resolution of the exoplanet. And of course, we could have 1000 CCD arrays instead of just 42.

That's not how Einstein rings work.

At 700AU (so the focal angle is far enough away from the sun for the Einstein ring to be visible beyond the sun's atmosphere) the FoV of an Einstein ring is around 1.5 arcseconds. AIUI, in practice, the useful FoV will be about a tenth of that: 0.15 arcseconds.

A 14 million km orbit in the target system will have an apparent width of around 13 arcseconds. Nearly two orders of magnitude too wide to image from a single location.
No it won't. The orbit will be .05AU away from the star, and it's 4 light years away. That's 0.04 arcseconds. Do the math. That's well inside even the "useful" FoV.

https://www.google.com/search?q=.05AU%2F(4+lightyears)+radians+in+arcseconds
« Last Edit: 08/31/2016 04:19 pm by Robotbeat »
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