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IKAROS JAXA Solar Sail mission
Tom Tamlyn
post Jun 16 2010, 02:09 AM
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Great picture of the fully deployed sail here (in case there's anyone at umsf.com who doesn't check Emily's blog several times a day.)

Are there any specs on how long the camera is expected to remain within wireless range? And what's the plan for the second camera? I like punkboi's suggestion of "a wide shot of IKAROS in deep space, with Venus in the background."

TTT
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nprev
post Jun 16 2010, 02:18 AM
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I've been wondering how long they'll stay near IKAROS as well. Also, do those things have some sort of attitude control? Can't figure out how they made sure that IKAROS stayed in the camera's FOV unless it was very precisely ejected.


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punkboi
post Jun 16 2010, 04:08 AM
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Naw, the cameras don't have attitude control... They're gonna drift off into deep space after being released from IKAROS. Check out the Youtube link below... The DCAM floats off in a spiral fashion after it is ejected from IKAROS...which would explain why the spacecraft is off-center in the image (which I'll provide below...despite Tom helpfully providing a link to the TPS blog smile.gif)

http://www.youtube.com/watch?v=7_6HOqBkP2o...player_embedded
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nprev
post Jun 16 2010, 04:28 AM
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Oh, okay, I get it now: The camera's actually spin-stabilized upon ejection. Thanks, PB!


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tolis
post Jun 16 2010, 03:01 PM
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Hi Brian,

I am not involved with the project myself, so someone should confirm the following:

If IKAROS is following (more or less) the same trajectory as Akatsuki, then it is not possible to insert in orbit around Venus.
The problem is that, although solar sails can in principle affect "large" changes in their speed (DV), they cannot do so quickly.
They are a bit like ion drives in that respect: they thrust gradually but continuously. To go into orbit around a planet,
you would need to gradually modify the sail's orbit around the sun using the solar radiation pressure force (SRPF)
until it is essentially identical to the planet's. I would imagine that, SRPF being quite flimsy a force, that process will take many years.

By the same token, however, the sail should flyby Venus at around the same time as Akatsuki enters orbit, probably at a distance
of several hundred thousand km or more. It could also be maneuvered to encounter near-Earth objects (asteroids or comets)
although I imagine that, for now, the technology demonstration objectives take priority over any other activity.

Regards,

Tolis.


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Norm Hartnett
post Jun 16 2010, 03:48 PM
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Hopefully some kind person here will be willing and able to explain how IKAROS is going to be able to maneuver using its LCD panels. I understand that by darkening and lightening the panels IKAROS can increase or decrease the light pressure (terminology?) thus increasing or decreasing its ‘thrust’ in relation to the sun. I also understand that, depending on its angle in relation to the sun, it can either slow or accelerate in relation to its orbit. What I have a great deal of difficulty envisioning is how it can change its attitude, pitch and yaw if you will. Given that the satellite has to rotate to maintain rigidity how can the LCDs modify its angle to the sun? Can they modify its rotation rate?


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fredk
post Jun 16 2010, 05:37 PM
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This is just a complete guess, but I would think that they could control the LCD panels on different sides of the sail independently. Darkening/lightening the panels on one side would provide a torque that presumably would change the orientation of the sail to the Sun.
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ugordan
post Jun 16 2010, 05:39 PM
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QUOTE (Norm Hartnett @ Jun 16 2010, 05:48 PM) *
What I have a great deal of difficulty envisioning is how it can change its attitude, pitch and yaw if you will. Given that the satellite has to rotate to maintain rigidity how can the LCDs modify its angle to the sun?

Perhaps they plan to alternate the LCDs to on/off and time it depending on rotational rate so that always the same "side" of the spacecraft relative to the sun is dark. This would over time slowly nudge the rotational axis in one direction.

EDIT: fredk beat me to it!


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Schillrich
post Jun 16 2010, 05:45 PM
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Hello,

I once found one abstract on the project page telling that it is indeed possible to change the rotation rate via the solar pressure on areas of the sail, or better that it will be part of the experiment to verify this technique. The idea behind that it not "simply" brightening and darkening of areas, but to switch between diffuse and specular reflection.

I also have one question (because the google translation of Japanese leaves me quite clueless):
Is there a difference between the 2 DCAMs (something about 'separate antennas' and 'only one has a receiver' comes out of google's translation attempts)? Has only one been deployed so far?

source: http://www.jspec.jaxa.jp/ikaros_channel/bn006.html


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Paolo
post Jun 16 2010, 05:58 PM
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QUOTE (Schillrich @ Jun 16 2010, 07:45 PM) *
I also have one question (because the google translation of Japanese leaves me quite clueless):
Is there a difference between the 2 DCAMs (something about 'separate antennas' and 'only one has a receiver' comes out of google's translation attempts)?


I think I understand that only DCAM1 has a receiving antenna on its housing on IKARUS, and DCAM2 uses that of DCAM1


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Schillrich
post Jun 16 2010, 06:03 PM
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I also came to that conclusion. But would that mean both have been deployed?


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punkboi
post Jun 16 2010, 06:52 PM
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QUOTE (Norm Hartnett @ Jun 16 2010, 08:48 AM) *
What I have a great deal of difficulty envisioning is how it can change its attitude, pitch and yaw if you will. Given that the satellite has to rotate to maintain rigidity how can the LCDs modify its angle to the sun? Can they modify its rotation rate?


IKAROS uses its thrusters to position the main spacecraft bus in a certain attitude...which in turn tugs on the tethers attached to the sail membrane and causes the membrane to be pulled and positioned into different angles. There's a computer animation of this towards the latter part of the video below

http://www.youtube.com/watch?v=7_6HOqBkP2o...player_embedded



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Norm Hartnett
post Jun 16 2010, 11:44 PM
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Thanks punkboi, Schillrich, ugordan, and fredk, it becomes clearer to me now. IKAROS is a remarkably dynamic craft and I hope we get some detail on how its trip goes.

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punkboi
post Jun 17 2010, 06:27 PM
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IKAROS' spin rate has decreased from 2.5 rpm to 1.1 rpm to allow better stability of the sail membrane as it gets tested for attitude control

http://www.isas.jaxa.jp/home/IKAROS-blog/


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Schillrich
post Jun 17 2010, 07:28 PM
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Actually I understand it that way that it was decreased in order to allow attitude control experiments by reducing the angular momentum of the spinning craft.


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