Ikaros 80,000Ks Venus

[Meanderer]

Hi
I was about to ask if any one had a update, then I found this.

http://mdn.mainichi.jp/mdnnews/news/...na003000c.html

Hope in right spot George

[jjjnettie (Jeanette)]

very cool, thanks

[CraigS]

I find I get a little frustrated when I hear news about this spacecraft.

There is actually very little information around and JAXA seems to control all status information very closely. I don't seem to be able to find out any more detailed info from the JAXA/JSPEC site, and say Wiki doesn't even seem to know much about it. …

For example, I have never seen any information about exactly what acceleration figures the sail has produced and Wiki says it was number 3 on the list of 'key technologies' to measure … so has anyone heard what the measured figures are ??

And, to make things even more perplexing, the follow-up project targetting Jupiter and the Trojan Asteroids, is switching to ion engines, as the primary means of propulsion. Does this mean that solar propulsion as a primary means for deep space exploration missions, is a dead duck ?

Co-incidentally, NASA announced this the other day:

First-ever solar sail a 'momentous achievement'

Whilst this quote is slightly out of context, it seems to at least justify my above question …

"We couldn't get out of FASTSAT," says Alhorn. "It was heart-wrenching—yet another failure in the long and troubled history of solar sails."

As far as strategies are concerned, I feel that solar sail research for deep space spacecraft propulsion, should fall way down the priorities list for funding, unless they can demonstrate some substantial benefits in terms of peak velocities/acceleration.

After all, isn't the primary purpose of deep space spacecraft propulsion, to reduce the flying time over the vast distances ? How can solar sailing ever get us closer to light-speed ?

Comments welcome.

Cheers

[renormalised (Carl)]

Solar sails are just a cute way of getting around the solar system. As far as deep space travel goes, forget it...not worth the effort. They'll never get you up to lightspeed (well, actually nothing will, according to SR). What they maybe good for is as emergency propulsion for manned craft, if their main engines fail for some reason. But it'll be a slow boat home.

[mswhin63 (Malcolm)]

Originally Posted by renormalised

Solar sails are just a cute way of getting around the solar system. As far as deep space travel goes, forget it...not worth the effort. They'll never get you up to lightspeed (well, actually nothing will, according to SR). What they maybe good for is as emergency propulsion for manned craft, if their main engines fail for some reason. But it'll be a slow boat home.

I think they are a good way to maintain a speed once attained. The speed of the solar particle is still quite fast. The next project is to include an ion engine which could be used the build up speed quicker than the sails and yet the energy of the sun or the particles could re-fuel the craft.

So for long term travel could be a good way. The only current method for long term fueling is Nuclear power. I am sure if that is strapped to my back for a very long time I would hope it didn't leak on my trip.

[CraigS]

Ok, so to be fair and challenge my own grouchiness on the topic, I've done some research to find out some facts. Overall, this topic is a complex one with many 'ins' and 'outs' and engineering tradeoffs.

Here goes for the statistics which I can sort of relate with:

1) Solar escape velocity is 618 km/s;
2) The mean velocity of the solar wind is about 145 km/s with a few particles reaching 400 km/s. (So presumably, this would be the primary motivating force behind solar sails … reminder: there is photon pressure, as well .. not sure about its net contribution, though);

3) The termination shock of the Solar system is around about 80 to 100 AU.
4) At 100 AU, a typical solar sailcraft speed would be about 70 km/s, (theoretical figure, and well below escape velocity);

5) The max ion propulsion thrust achieved so far, is about 10 N (flight proven);
6) The max solar sail thrust varies (depending on distance from the sun) between 9 to 230 km/s⌃2 (from 1 AU to 0.2 AU) - theoretical only;

7) The max ion propulsion delta-v is greater than about 100 km/s (flight proven);
8) The max solar sail delta-v is greater than about 40 km/s (theoretical);

It would seem that there are three theoretical ways of getting the solar sailcraft moving fast headed out of the Solar System. The first requires usage of:

an additional propulsion system to send the folded-sail sailcraft to the perihelion of an elliptical orbit; there, the sail is deployed with its axis parallel to the sun-light for getting the maximum solar flux at the chosen distance.

This may be why they are incorporating a secondary ion propulsion system in the next generation of Ikaros. (??)

It seems that the main design issue at the moment is being able to produce a sail light enough to do the job and getting a sail predictably deployed, in situ. At the moment, the goal for the sail mass is about 2 g/m⌃2 which hasn't been achieved yet although, this is not too far beyond present technology constraints.

Cheers

[mswhin63 (Malcolm)]

I would be interesting to see if this solar technology will be used to replace current solar power techniques as well.

[CraigS]

Whilst they are playing around with attitudinal controls by adjusting the reflectance of various parts of the sail at various key times during the flight, I don't believe they are using it to generate the power for the spacecraft. (??)

Cheers

[CraigS]

Now here's an interesting variant …

Magnetic Sails:

The solar wind is a tenuous stream of plasma that flows outwards from the Sun: near the Earth's orbit, it contains several million protons and electrons per cubic meter, and flows at 400 to 600 kilometres per second (250 to 370 mi/s).

The magnetic sail introduces a magnetic field into this plasma flow, perpendicular to the motion of the charged particles, which can deflect the particles from their original trajectory: the momentum of the particles is then transferred to the sail, leading to a thrust on the sail. One advantage of magnetic or solar sails, over (chemical or ion) reaction thrusters, is that no reaction mass is depleted or carried in the craft.

and I may be wrong about the comparative photon pressure vs solar wind pressure issue:

The operation of magnetic sails, using plasma wind, is analogous to the operation of solar sails using the radiation pressure of photons emitted by the Sun.

Although solar wind particles have rest mass, and photons do not, sunlight has thousands of times more momentum than the solar wind. Therefore, a magnetic sail must deflect a proportionally larger area of the solar wind, than a comparable solar sail, to generate the same amount of thrust. However, it need not be as massive as a solar sail, because the solar wind is deflected by a magnetic field instead of a large physical sail.

Interesting.

Cheers

[CraigS]

Chapter 2:

In the case of the (M2P2) system the spacecraft releases gas to create the plasma needed to maintain the somewhat leaky plasma bubble.

The M2P2 system therefore has an effective specific impulse which is the amount of gas consumed per newton of thrust. This is a figure of merit usually used for rockets, where the fuel is actually reaction mass.

Robert Winglee, who originally proposed the M2P2 technique, calculates a specific impulse of 200 kN·s/kg (roughly 50 times better than the space shuttle main engine). These calculations suggest that the system requires on the order of a kilowatt of power per newton of thrust, considerably lower than electric thrusters, and that the system generates the same thrust anywhere within the heliopause because the sail spreads automatically as the solar wind becomes less dense.

However, this technique is less well understood than the simpler magnetic sail, and issues of how large and heavy the magnetic coil would have to be, or whether the momentum from the solar wind can be efficiently transferred to the spacecraft, are under dispute.

Chuckle, chuckle …

Cheers

[mswhin63 (Malcolm)]

Here is a basic site on the craft that mentions Solar power generation

http://www.jaxa.jp/projects/sat/ikaros/index_e.html

[CraigS]

Originally Posted by mswhin63

Here is a basic site on the craft that mentions Solar power generation

http://www.jaxa.jp/projects/sat/ikaros/index_e.html

Ok .. thanks Malcolm .. I stand corrected.

It still isn't all that clear as to whether the present version of Ikaros has an ion drive, or not (?) It seems that they will be powering the ion drive, (is this the second generation sailcraft or the first ?), from the thin film sail solar cells.

Everytime I read this stuff, I get frustrated by their inability to describe the spacecraft and the project phasing … and their progress against the relevant objectives !!


Aarrrghh !!



Cheers

[mswhin63 (Malcolm)]

No there is a version being created now that will include an Ion drive (will go to Jupiter), this one is an experiment in deployment of the sails only.

I read it on another JAXA site but not the one on the link.

[Meanderer]

What is the IKAROS?

The small solar power sail demonstrator “IKAROS” (Interplanetary　Kite-craft Accelerated by Radiation Of the Sun) is a space yacht that gathers energy for propulsion from sunlight pressure by means of a membrane (or a solar sail.) The thin film solar cells are attached to part of the solar power sail to generate large electric power. It realizes a hybrid propulsion system with a solar sail and a high efficiency ion engine activated by electric power generated by the solar cells to enable a more efficient and flexible mission.
The IKAROS mission aims at verifying space navigation by a solar sail and power generation through thin film solar cells for the first time in the world. The IKAROS was launched by the H-IIA Launch Vehicle as a secondary payload with the Venus Climate Orbiter “AKATSUKI.”
http://www.jspec.jaxa.jp/ikaros_chan...images/002.jpg
http://www.jspec.jaxa.jp/ikaros_chan...images/001.jpg