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?

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.

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!

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

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

I also came to that conclusion. But would that mean both have been deployed?

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

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.

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/

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.

Heh, that's what I meant. I worded it wrong

Hm. I thought DCAM1 was already jettisoned... I guess not

http://www.isas.jaxa.jp/home/IKAROS-blog/?itemid=646

Since IKAROS is spinning at only 1.1 rpm, I would assume the deployment of DCAM1 will be much more stable than that of DCAM2...and that IKAROS will be better framed (much more centered) in the DCAM1 images this time around

Thanks ngunn, norm and Tolis (and everyone else) for the great info. Sending IKAROS to Apophis (via one or more flybys) is an interesting idea. I have a hunch that it could be possible for an IKAROS type spacecraft to be captured by Venus or maybe Mercury (solar sails work better closer to the sun - not so good for outer solar system). Someone must have studied this possibility, I'll see what I can google. It would also be interesting to get some idea of the numbers involved regarding possible acceleration, dV, etc.

The complexities involved with attitude control of a (slowly) spin-stabilized flexible sail attached to a rigid "hub", using two different methods (hub thrusters / sail variable reflectivity), are fairly mind boggling. I can imagine the whole thing starting to "ripple" like a flag in the wind, or even just wrap itself up into a ball, if you don't do it right!

Amazing stuff.

Thanks and regards,
Brian

From what I understand of the Google translation of the IKAROS blog http://www.isas.jaxa.jp/home/IKAROS-blog/i....php?itemid=647 it appears that the second camera pod is released today. It is to be jettisoned at a slower relative speed (details of the separation system and separation speeds anyone?) to conduct a longer imaging session from a closer distance.
Anybody knows also how long are the DCAM batteries supposed to last?

I would imagine the batteries last far longer than the RF link budget between DCAM and IKAROS can last.

A previous IKAROS blog stated that the DCAM batteries...at least the one for DCAM2...is designed to last 15 minutes

15 minutes of fame

First picture from DCAM1 released! http://www.jspec.jaxa.jp/ikaros_channel/bn007.html
from much closer to IKAROS than DCAM2

According to today's blog post (6/22) they are adjusting the spin rate to "The spin rate will be selected to operate at optimum balance with light pressure" and they are seeking the optimum spin rate (now at 1.4 rpm). Also the GAP experiment is being activated under the charge of Kanazawa University.

DCAM1 images finally released

http://www.jspec.jaxa.jp/ikaros_channel/bn009.html

I am not very surprised about this. About 15,16 years ago I was chatting to a prof at ISAS about the anntena opeinng of Halca space intereferometry satellite and asked him about the possibility. He simply flatly said that he would be extremely surprised if it did open up.

Apparently, he had seen it fully opended up at Mitsubishi's kamakura factory and never believed it will open up in space, but it did...

Second generation is going up in 2012, and what follows is some info on that.

http://www.jaxa.jp/pr/brochure/pdf/04/sat24.pdf

Of course, opening mechanisms must be different, I think. Halca anntena was built of very fine metal mesh, as I remember. Ikaros anntena must have been a lot easier to open up, I think. After all, it is a membrane, not a metal mesh.

Pandaneko

To continue this line of thought:

What is the possible ultimate fate of Ikaros? Is there a maximum communications range?

Can the inspection camera be also used to image asteroids or comets during a fly-by five or ten years from now, or are they only in the jettisoned pods?? We can still do radio occultation science.

Can it achieve solar system escape velocity?

From the images I've seen, the on-board cameras are wide-angle, not suitable for distant objects.

http://www.jaxa.jp/index_e.html

July 9, 2010 Updated
IKAROS: Acceleration by solar sail confirmed

The small solar power sail demonstrator "IKAROS," which successfully deployed its solar sail, was confirmed to accelerate by solar sail receiving solar pressure.

This proved that the IKAROS has generated the biggest acceleration through photon during interplanetary flight in history.

There's much more info in the Japanese version (Google translate link)

At last a release in English: http://www.jaxa.jp/press/2010/07/20100709_ikaros_e.html

Meanwhile, IKAROS is also doing some science. There is a release today (in Japanese) about the first gamma-ray burst detection

Some gems about the possible future of IKAROS from The Mainichi Daily News http://mdn.mainichi.jp/mdnnews/news/201007...0na012000c.html

Apparently the solar radiation pressure attitude control experiment was successful! we have a true solar sail out there!
release (in Japanese only at the moment): http://www.jaxa.jp/press/2010/07/20100723_ikaros_j.html

Solar Distance : 1.05AU
Earth Distance : 26105537km, ascension =- 141.2 °, declination =- 26.2 °
Venus Distance : 0.75AU
Attitude : spin rate = 1.5rpm, sun angle 22.4deg

For the last few days IKAROS was spun back down and the solar angle increased as JAXA continues to investigate sail trimming. Experiments in ranging are on going and increased emphisis is being given to acceleration. Since the 24th of July all attitude control is being handled by the RCD (LCD panels), a truely stunning breakthrough in propellantless deep space navigation.

According to this animated image, IKAROS will arrive at Venus on December 18 (Japan time)...11 days after Akatsuki does

http://twitpic.com/2g57yr/full

8 / 26 IKAROS
Solar Distance : 1.00AU
Earth Distance : 31401035km, ascension =- 130.8 °, declination =- 28.0 °
Venus Distance : 0.48AU
Attitude : spin rate = 1.3rpm, sun angle = 26.0deg

IKAROS has crossed Earth's orbit and is headed Sunward. The last few weeks have seen experiments with rotation rates going up to 2.0rpm and back down and sun angles reaching as high as 32.2 degrees.

From punkboi's post above it appears that IKAROS will be passing Venus on the "outside" as would be expected since it has been increasing its orbital speed since deployment.

9 / 9 IKAROS
Solar Distance : 0.96AU
Earth Distance : 32181854km, ascension =- 126.3 °, declination =- 28.5 °
Venus Distance : 0.35AU
Attitude : spin rate = 1.4rpm, sun angle = 29.9deg

I think this means that due to the angle of IKAROS vs location of the Earth IKAROS is losing com. Also they seem to be having troubles at their ground stations. I have seen no comments on when they expect to regain communications.

Does anyone (Emily?) have any further information?

I actually just sent an email to a Japanese contact about this today. I can't quite figure out what these updates mean. I'll post a blog entry if I learn anything.

Aha, it's not as bad as it seems. The problem is that Earth is passing through the sail plane, which is apparently a blind horizon for radio comms. Once Earth has gone through the sail plane to the other side, comms should resume. Today, Earth is within 13 degrees of the sail plane. IKAROS is being configured for autonomous operation during the communications blackout.

Thanks Ms. E.

I was pretty sure that things weren't as bad as my worry wart self thought but my confident self just could not sort out the good data from the noise.

(Nice rant today BTW)

While the folks running IKAROS were acting fairly confident about the four day communications blackout, their relief and joy as IKAROS reestablished com was evident in the 9-18 Blog entry. http://www.isas.jaxa.jp/home/IKAROS-blog/?blogid=12



9 / 18 IKAROS
Solar Distance : 0.94AU
Earth Distance : 31844918km, ascension =- 124.5 °, declination =- 28.5 °
Venus Distance : 0.34AU
Attitude : spin rate = 1.3rpm, sun angle = 29.0deg

The October issue of the French magazine "l'Astronomie" (http://www.saf-lastronomie.com/revue/index.html) has a very interesting article on a French radio-ham who managed to receive the signal from Ikaros during June using a 3.5 m parabola.
unfortunately I don't have a scanner at hand...

Good old Amatuer DSN guys. There's a ham radio group in Germany with a dish that would rival the smaller dishes of the DSN itself.

A report by the French radio ham is available here

IKAROS has spin up today. This is a very long time 2rpm.
A high spin rate, increasing the spin stiffness (as a frame) in space
Try to maintain a constant attitude.
Conversely a low spin rate will be strongly influenced by movements of the solar light pressure.
Adjusting the spin rate means that a balance of both to take advantage of this
I can do to change the direction of the desired position.

The IKAROS 10/18
Solar Distance: 0.84AU
Earth Distance: 28891627km, RA =- 132.6 °, declination =- 23.5 °
Venus Distance: 0.11AU
Attitude: spin rate = 2.1rpm, sun angle = 4.3deg

(Earth Distance 0.19AU)

Sun angle has been decreasing for several weeks now I wonder if they are "coming about" and reversing the "thrust" vector? One of the animations I saw seemed to indicate that might happen as they approached Venus.

The IKAROS 11/05
Sun Distance: 0.77AU
Earth Distance: 33318160km (0.22AU), RA=-146.5deg, Dec=-15.3deg
Venus Distance: 0.06AU (8975880km)
Attitude: Spin Rate=1.7rpm, Sun Angle=16.4deg

Blog entries are becoming sparser and apparently there are fewer communications periods as JAXA increasingly focuses on the Akatsuki Venus mission.

while Akatsuki was being recovered, IKAROS also flew by Venus last 8 December, some 80,000 km away
http://www.isas.jaxa.jp/home/IKAROS-blog/i....php?itemid=786

Interesting... I thought IKAROS wasn't suppose to pass by Venus till December 18

I am posing a very stupid question, I think...

Akatsuki has sped by Venus, right?, and IKAROS has done that, too? That means they are going in the same general direction. My question is this. Can they not direct IKAROS to Akatsuki and take a look at Akatsuki's nozzle skirt? After all, we have another 5 to 6 years.

As I am not sure as to what IKAROS's ultimate goal, I just thought that it can get closer and closer to Akatsuki. Does it have a telephoto lens, bet not...

With future missions we do need engineering cameras!!!

Pandaneko

They passed Venus at very different distances, which means that IKAROS (80000 km) would have been less deflected by the gravity of Venus during the fly-by than Akatsuki (600 km). Add to that that Akatsuki also performed the incomplete injection burn as it passed the planet. As a result, the two would have been on rapidly diverging trajectories after the Venus encounters.

In addition, Ikaros has only engineering cameras designed to monitor sail deployment. They're pretty low-res, and have a very wide field of view that would make getting a good view of Akatsuki very difficult. The danger of a collision between the two spacecraft would be too high.

OTOH, the thought of Akatsuki taking a self-portrait as reflected in Ikaros's sails is truly delightful! But will have to stay just a thought, alas.

Akatsuki should cast a shadow, having IKAROS close by would allow something for that shadow to fall on. You could just image that shadow. I would figure it could be done at a greater separation than would allow for Akatsuki to image its reflection.

You can't be serious H4I, Ikaros and Akatsuki are going to be thousands, probably millions of miles apart.

Oh I know. I thought it was understood we were just throwing ideas out there in a hypothetical situation.