Mars Terraforming Solar Reflectors - suggestions please?

[JackHiggins]

For an external education project involving Celestia, I have been asked to develop a model of a futuristic Martian Terraformer. The concept is to position a series of these parabolic dish reflector spacecraft above the Martian North and South Poles and reflect sunlight down to the polar ice to melt it, thereby changing the climate, boosting CO2 for the greenhouse effect, increasing humidity on the planet, and changing the atmospheric composition and pressure, to make it more hospitable for life. The concept has been kicking around in planet terraforming circles for years.

The model has turned out very well. It consists of parabolic dish, focusing lens, rocket motors, solar panels, etc. It even has a sunlight beam shining out from the focus. Here are some screenshots:









(If you need any more closeup screenshots to see something more clearly just ask)

I want to make this model as technically realistic & scientifically accurate as possible, so I am looking for suggestions & comments which I could use to improve the craft or its positioning. The plan is to use 12 or so of these craft in a geostationary polar orbit around each pole of Mars (24 total).

Here are the subjects I need your comments/suggestions on:

1. Orbital elements for craft - is it even possible to position the craft in synchronous orbit and still have enough beamed energy to melt any ice, or is it simply not scientifically feasible (too far away)?
2. If synchronous orbit is not possible, what orbital elements could we use to maximize reflective radiation on each pass, using a spacecraft array that is forced to circle Mars every 90 minutes or so?
3. Does the structure of the craft created look reasonable? How big would each dish in meters have to be to make a dent in Mars' polar ice?
4. Is the focusing lens the right way round?
5. Would 12 seem to be a reasonable number of reflectors per pole?
6. If this is possible, what kind of time frame would it take to melt enough ice to affect Mars' climate?
7. How much solar radiant energy could be focused by each dish and what is it measured in (radiants, watts, lumens, candlepower???)
8. Is it possible to make only the beam & reflector "emissive true" without also making the rest of the model glow?

Anything else which would improve the general idea!

Thanks!

[billybob884]

Well, this is just my opinion, but I think it will be a bit tricky to get it to orbit just around one of the poles (in celestia anyway, I don't know about real life), unless it was to be fixed right above one specific spot, which means it would not move at all. But in this case you could still make it rotate on its own axis to 'hit' different spots, but even then it would still spend most of the time facing into space. You might want to seek further help from chris. BTW, who asked you to make this model anyway?

[selden]

Here are the subjects I need your comments/suggestions on:

1. Orbital elements for craft - is it even possible to position the
craft in synchronous orbit and still have enough beamed energy to melt
any ice, or is it simply not scientifically feasible (too far away)?

There are no synchronous orbits that have continuous line-of-sight to
either of the poles. Remember that orbits travel all the way around the
planet.

Synchronous orbits are the ones that happen to have a period
equal to the planet's rotational period. The best you can do are orbits
that are inclined 90 degrees so they pass directly over the poles.
Orbits with large diameters let you see more of the planet at once,
so they let you see one or the other of the poles for a longer time.
Also, a high eccentricity orbit would increase the "loiter" time over
one of the poles when the satellite is near its apocenter.

The satellite also is much further away from the planet then, but that
doesn't really matter -- which is the question you're really asking.

Remember that the solar reflector is a mirror reflecting incoming
sunlight onto a particular place on the surface. That means that
(to first approximation) it's focusing an image of the sun onto the
planet. 1/R^2 does not apply to the reflected light, just to the light
reaching the mirror from the Sun.

2. If synchronous orbit is not possible, what
orbital elementscould we use to maximize reflective radiation on each
pass, using a spacecraft array that is forced to circle Mars every 90
minutes or so?

That short a period is *much* too close and fast.
It'd put the mirror behind the planet and in shadow a lot of the time.

A distance of 200,000 km or more would be more appropriate.
For a circular orbit, that'd give a period of more than a month.

3. Does the structure of the craft created look
reasonable? How big would each dish in meters have to be to make a dent
in Mars' polar ice?

Sorry: no. It's much too massive.
The mirror needs to be many kilometers in diameter in order
to collect enough sunlight. That suggests it should be made
of a very thin film of aluminized mylar or the equivalent.

4. Is the focusing lens the right way round?

There's no need for a lens. It just gets in the way.

A very slight concave shape for the reflective mirrors would be
adequate to focus the sunlight onto the planet.

5. Would 12 seem to be a reasonable number of
reflectors per pole?

What matters is the total area of the mirrors, since that determines
the amount of sunlight they'll be intercepting and redirecting.
(See below where I've done the arithmetic)

6. If this is possible, what kind of time frame
would it take to melt enough ice to affect Mars' climate?

dunno. It depends a lot on side-effects -- like what happens to all
the subsurface water that's been detected within the past year.
Some past estimates have been 10s to 100s of years.

7. How much solar radiant energy could be focused
by each dish and what is it measured in (radiants, watts, lumens,
candlepower???)

The units are Watts, and 10s of TeraWatts would be needed.
(1 TW = 10^12 watts) See the papers mentioned below.

Doing the arithmetic:
The sun provides about 600 watts per square meter at the distance of Mars.
If you need 20 TW (20*10^12),
then you need a total surface area of 20*10^12 / 600, or
3*10^10 square meters.
With 12 mirrors, each would have to have an area of 1/12 that, or
25*10^8 square meters.
if the mirrors are square, they'd be 5*10^4 meters on a side:
that's 50 kilometers on a side!

Calculating the radius of a circle with that area is left
as an exercise for the student.

8. Is it possible to make only the beam &
reflector "emissive true" without also making the rest of the model
glow?

I think they'd have to be separate objects, but I suspect that Rassilon
can do a better job of answering that question.

Anything else which would improve the general
idea!

I'd suggest doing some more reading on the topic, especially of the
original research papers. Popularized summaries can be very misleading.

One useful paper is at
http://www.users.globalnet.co.uk/~mfogg/zubrin.htm
It actually answers most of your questions.
http://www.users.globalnet.co.uk/~mfogg/paper1.htm
seems to be a reasonable summary with references to recent research.


I hope this helps a little.

[Rassilon]

8. Is it possible to make only the beam & reflector "emissive true" without also making the rest of the model glow?

Unfortunately...not at this time...It would be nice for the data for specular mapping and self illuminated materials be loaded into Celestia. This would help in making more realistic models. Not to mention internal lighting for spacecraft

Jack looking at the beam coming out of your dish Ive noticed your using something similar to the pulsar ray I made...You might want to consider using a transparency instead...Making a PNG file using an alpha 1 channel should allow you a bit more flexability on looks. Make sure u make it using the Gimp and also setting it up in 3d Studio MAX set the opacity to 99% and use Image Alpha on both Diffuse and Opacity material channels using the same texture...

[julesstoop]

I would use a flat mirror. The sunrays travel almost parallel anyway. With a concave mirror you would focus the colleted energy of your thirty mile mirror to a smaller surface, creating a hotspot.

With a flat mirror it would simply seem that the subject area on the pole was lit by a second sun. In that way you would slowy heat up a larger area which seems to be more effecient per square meter of mirror surface. Why is this? Imo the hotspot could much more easily create atmospherical disturbances (clouds.dustclouds, blocking your radiation) because of the strong winds involved with the larger temperature diferential between the subject area and the rest of the planet. Besides that, you run into he risk that you would heat part of the atmospheric gasses to such an extent that they would simply diffuse away in to open space.

[JackHiggins]

Thanks everyone for your suggestions- it seems like a major redesign is in order for the model no matter what happens, so i'll get started on that right away.

Selden- you've provided a *LOT* of information there it'll take me a few days to get my head round it all!! I had a look at the two research papers, & the "statite reflector concept" seems to be the best idea to implement in a 3d model. A large number of reflectors could speed up the process a good bit, & since there are a greater number they could each be smaller then 1 huge one! Maybe about 30 of them (15 focused on each pole)? I'll have to think about all your ideas & i'll have a new seriously modified model in a few days.

Rassilon- yes I got the idea on how to do the light beam from your pulsar (great work btw) except mine doesnt look as good because it cant be emissive... I'll pm you in a while to ask more about the details.

julesstoop- the warming effects would not be so dramatic as to cause that kind of effect. A 100km radius reflector would only have a warming effect of 5K, & even with a large number of reflectors raising the temperature by, say, 20K it could not have have an effect like this. Bear in mind the usual *daytime* temperature on mars in "temperate" regions is only about -10 degrees C, so it would already be well below freezing near the poles.

Keep the suggestions coming- i'll have a new model done in a few days incorporating all your suggestions!

Thanks!!

[granthutchison]

A large number of reflectors could speed up the process a good bit, & since there are a greater number they could each be smaller then 1 huge one! Maybe about 30 of them (15 focused on each pole)?

Jack, it'll be an interesting problem working out where to place all those reflectors without them interfering with each other - to be in equilibrium, the statite mirrors have to lie in the plane containing the Sun, the centre of Mars, and the pole they're aimed at, and the angle between Sun and pole must be bisected by the direction from the mirror to the centre of Mars. They're also constrained by the need to "see" the Sun over one pole of Mars, while simultaneously "seeing" the opposite polar region, and they've got to avoid blocking each other's line of sight in either of these directions ...
But I'm pretty sure I can see how to set them in a suitable "orbit" within Celestia (it needs that latitude-offset trick again, in the absence of gravity and light pressure).

Grant

[Guest]

Bloody Hell Jack.. sorry, just got back from the pub...AArrGGhH!!

Regards..bh.

[Don. Edwards]

Hey JackHiggins,
I have joined you and fsgregs on this project and I think I may have a solution. I believe a way around this would be to adopt the model that was used in the Red,Green, and Blue Mars series of books. The author came up with a mirroring system called a soletta. It was discribed as having mirrors that radiated out from the center in kind of a flower like pattern. The mirrors were pointed at Mars' but in the middle was a mirror pointing toward the sun. This center mirror would capture the suns light and focus the light onto the mirrors facing Mars. This had in the book two effects. It nearly doubled the amount of light that reached the surface and of course it would have some heat output as well. The satalite in the book was maintained in an orbit that kept it always on the sunward side of Mars and at a distance that would make it look like the sun itself from the surface at fairly high latitudes. In the book the main use of the satalite was to increase the surface light on the day light side. Also in the book they used much more agressive means to help melt the ice. They used nuclear detonations at the poles to melt the ice. Another thing they did was to dig very deep pits on the surface so that radiant heat from the molten mantle would raise out of these mole holes as they were called and help heat the atmosphere. I was going to try and create a nightside texture that would show the effecct of your satalites on the surface polar regions but if the orbits can't be configured properly I can't make the lightmaps to go along with them. I am however going to try and show a gradual warming effect of the planet and posibly show the water table in the lowlands start to raise over time. The effect would reach the point of the Wet Mars texture I recently made and I would then progress it further to the Blue Mars phase and show some greening in some areas of the planet. But I don't think I would take it anywhere as far as I did in my Green Mars textures. After looking them over again I feel I got a little carried away with the greening of the whole thing. If I can get ahold of my books I will try and find a better discription of the soletta but if someone else has read the books maybe they can confirm or disprove my discription of it. Let me know what you think of this idea.
Don.

[fsgregs]

Don and Grant:

You're contributions here will be invaluable. Thank you for your willingness to help make this project a success. NASA and the visitors to this website will be very pleased at the sophistication of what is being developed here.

I realize some folks have debated the use of nuclear explosions to melt the ice, but I'm unaware of any explosion technique that would not spray the entire atmosphere and meltwater with long-lived radioactive fallout for possibly centuries to come. Likewise, I don't think we have any idea how deep the molten mantle is on Mars. If a scientifically viable proposal exists in terraforming circles to drill into the mantle and release molten material to help melt the poles, we can always include it in the activity as a small hotspot of volcanic activity on the surface near or within the polar ice. It would obviously increase the complexity of the textures that will have to be drawn/revised. We can include it, or just as easily not mention it or worry about it in the Activity. My preference would be to leave it out to save time and complexity, and just stick with the solar reflectors. What do you think?

Don, if the books you reference have a sketch of the flower petal dish array, please post it in your gallery if you can. However, I'm not sure we would need it, since a set of rectangular rows of parabolic mirrors can also bounce sunlight to the surface just as easily. It's just a matter of proper alignment (it seems to me??). Your effort to develop new textures to show transitions on the surface as a spreading pattern of green growing outward from the pole is awesome. It will make the activity not only beautiful but very accurate to take our audience through step by step. I will need to know, however, how best you feel we should sequentially load them via the ssc. I guess the best approach would be to use "beginning" and "ending" for each texture and cel://URL's to bring the visitor to each new future date and time. Would that be the way to go?


Grant, thank you so much for volunteering to tackle the orbital issue. Given Selden's prior comments about dish size and wattage, we may need up to 24 - 36 separate reflectors in orbit to cover enough surface area with the required terrawatts of power, while making each dish a "reasonable" size to build. Even then, they will be many kilometers in diameter each. If we use a flower petal pattern as Don suggests, we can always put several duplicate "flowers" in space. There is also the question of whether a true terraforming project would attempt to melt both poles at once, or would concentrate on only one. If so, which pole would make the better target? This is such a complex ssc project that I would never tackle it without your skilled help.

If we are going to have a terraformed Mars, everyone will of course assume it will be the real Mars, within our own solar system. However, all those ssc extras files are going to muck up present day Mars, unless we place them "far" into the future. Folks who download Celestia from the NASA site and use it on their own, may be in for a strange shock if they run time forward to say the 25th century, and suddently discover that Mars is changing (as our extras ssc's kick in). There is an alternative. That is to place a duplicate of our entire solar system around another g star, and use it for the Activity (with a comment in the readme file that we've done so). What do you think?

Thank you both again for joining this project and for your valuable time and talent.

Frank

[julesstoop]

julesstoop- the warming effects would not be so dramatic as to cause that kind of effect. A 100km radius reflector would only have a warming effect of 5K, & even with a large number of reflectors raising the temperature by, say, 20K it could not have have an effect like this. Bear in mind the usual *daytime* temperature on mars in "temperate" regions is only about -10 degrees C, so it would already be well below freezing near the poles.

Keep the suggestions coming- i'll have a new model done in a few days incorporating all your suggestions!

Thanks!! :D

Well, it all depends on the amount of focussing. If you were to focus the light of one mirror on a spot no larger than a few hundred meters in diameter, I'm pretty sure that spot would heat up by an amount considerably larger than mentioned 5K. Like focussing sunrays with a magnifiing glass.

[selden]

Frank,

Why should there be only one download available?

It seems to me that Celestia can be used in many different activities, each with its own set of ssc files, models, scripts, etc. The terraforming of Mars is just one of many possible projects. Trying to include all of them in one download certainly would make it rather unwieldy.

Also, one should not think of the version that's being developed now as being the final one. It should be expected to change: to incorporate new discoveries about the conditions on Mars, or more modules for advanced credit, or whatever.

So far as control of time and movement is concerned, don't forget scripting. While there are still some significant features that need to be added (like user interaction), Celestia's scripts provide an effective way to tie a presentation together.

Jules,

To expend on your comments somewhat, I'm not at all certain I'd want to be living on the planetary surface while the mirrors are in use. Besides them being very effective weapons, there are many possibilites for accidents.

[granthutchison]

I've been looking at the maths of the Zubrin statite, and it's pretty much one mirror per illuminated location - you can't have multiple mirrors aimed at the south pole, for instance, because the only stable locations for such mirrors lie more or less in a line, one Mars radius above the plane of Mars' orbit, so mirrors farther out would be shaded by those farther in. You could create a ring of statite mirrors, though, one Mars diameter across and a few 100,000 kilometres behind Mars, illuminating one or more rings of locations on the Martian nightside centred around the antisolar point. Pretty.
As I recall, Robinson's magnifying soletta was from an idea by Paul Birch - it would be a large and complicated model to build, consisting of nested rings of tilted mirrors. Sunlight would hit the back of one mirror, be reflected inwards to the front of another mirror, and then carry on towards Mars - a graduated tilt in the relative angles of the mirrors ensures convergence of the solar rays. The whole thing is 10600km across, and it needs to be levitated by a ring-shaped mirror 25000km in diameter and 300km wide, hovering behind Mars.

Grant

[fsgregs]

Selden:

There are to be many separate activities on the NASA website. An initial set of five are planned, with more to follow. The target audience will be 5th to 8th graders, possibly overseen by their teacher (but not necessarily). Each of the five activities will use different extras, models and add-ons. There is no requirement for a visitor to have to start at Activity 1. If they wish to do Activity 4 first, (Terraformed Mars), they should be able to go to it. However, in each case, they will need not only the Activity instructions, but will also need to download the default Celestia package, plus the add-ons needed for that activity.

How to get the files? There are two main choices:

A) Download the Celestia default package with no add-ons. Then, download and/or open the instructions for Activity 1, separately download the add-ons for Activity 1, have an exe file place them automatically in the Celestia folder, and then open, read and perform the activity. Then, move on to Activity 2. Download the add-ons for activity 2 along with the Instructions, have an exe place them into Celestia folders, and perform the activity, etc. As you can see, the add-ons from Activity 1 will still be in their computer and still be loaded in the Celestia directories. When they launch Celestia for Activity 2, the add-ons for Activity 1 will also load and run, unless we ask them to uninstall them first. That is something I don't want to do. I am also unaware of a way to deactivate ssc file add-ons once they've been put in the Extras folder, short of asking the user to go into the folder and move them out of there. Again, 5th graders may be doing this activity. I don't want to have to ask them to fool with cutting, moving or deactivating files in the Celestia folders.

In the end, this option will result in the add-ons for all five Activities being loaded and run by Celestia, by the time Activity 5 has been launched.

2. A second option is I believe, the easiest and least confusing way for a visitor to set themselves up for all of the activities the website can offer. That is to package all of the Celestia files and add-ons for all activities into one single download and let users download it once. Then, open Activity 1, do it, open Activity 2, do it, etc. That is what I presumed would be the approach and is the one I prefer. That is why I asked about positioning the reflectors above Mars in the future. If all activities are to be available when Celestia is running, they should not conflict with each other. It can obviously be done. For example, for Terraformed Mars, we can set it up to have both the Mars textures and reflectors appear in Celestia using beginning and ending at some distant time in the future, or we can position our terraformed solar system around another fictional but nearby Sol, and take visitors there via a script or cel://URL. They will not notice any difference in celestial position and we won't have to worry about our solar system being messed up if someone wants to just cruise around in Celestia.

I hope this clarifies what I meant in the earlier post.

Regards,

Frank

[granthutchison]

Thoughts on modelling a Zubrin-style statite:
1) Any parabolic component will be negligible at the distances we're talking. As Selden said, they might as well be modelled as flat plates.
2) They'll be thin - effectively 2D structures.
3) It seems likely that control would be by adjusting the mirror configuration, rather than by the use of reaction motors, which wouldn't be useful in manoeuvring something this big and filmy.

So we're talking something that's effectively a light sail - a big reflective sheet with guy-lines converging on a dangling "payload" (which in this case would be the control structure). Plenty images of such imagined objects are available on the web for reference. (The control structure really would dangle - supported against Mars' gravity by the thrust on the mirror.)

Grant

[selden]

Grant,

Actually it was Jules who mentioned that they might as well be flat, which makes a lot of sense, of course.

I've been puzzling over how it might be possible to keep the mirrors flat enough. Since they're so far from the planet, even the slightest ripples (caused by any station keeping accelerations, for example) would divert portions of the light beam way off target. How do you damp them out?

Also, if it's supported only at the edges, a mirror will bulge in the middle due to the light pressure. This would defocus the beam significantly.

For many lightsail applications I'd expect that neither of these effects would be large enough to cause significant problems. It's quite a different matter when they're being used as long focal length mirrors, though.

Frank,

Please consider providing all of the activities as separate, individual downloads, perhaps each in its own ZIP file. These would be in addition to the all-in-one package you're planning.

Don't forget that many of the less affluent as well as rural school systems have only dialup lines and cannot get broadband connections. This means that download files need to be kept as small as possible. Also, many schools have Macintosh systems, not PCs, so they won't be able to use the Windows version of Celestia.

[julesstoop]

What about short focal length concave mirrors, that translate the collected energy into another form of energy e.g: microwaves, and send that to planets surface?

You could than actually use the light pressure (by keeping them pointed straight towards the sun) to give them the right shape. As the material stretches you could easily adjust the position of the recieving focal point As well, with a shorter focal length, rippling wouldn't be as much of a problem. The focal point would contain the energy converter as well as a seperate guiding mechanism to point the beam of microwaves in the right direction.

Okay, it's getting more complicated, but imo more feasible as well.

By the way: of course the focal point shouldn't be an actual 'point' to avoid overheating.

[selden]

Jules,

One answer: cost. I don't think frequency conversion elements working at the power levels needed could possibly be as cheap as "simple" mirrors.

Also, remember we're talking about TeraWatts of power. Spread out over a significant fraction of a planetary surface, it'll produce a temperature rise of only a few degrees--just enough to evaporate CO2. "Short focal length" optics will promptly vaporise *anything* near the focal point.

[julesstoop]

Jules,

One answer: cost. I don't think frequency conversion elements working at the power levels needed could possibly be as cheap as "simple" mirrors.

Also, remember we're talking about TeraWatts of power. Spread out over a significant fraction of a planetary surface, it'll produce a temperature rise of only a few degrees--just enough to evaporate CO2. "Short focal length" optics will promptly vaporise *anything* near the focal point.

I agree with the cost argument, not with the short focal length one. I never said anything about focussing the secondary beams of microwaves: as you said yourself, I suggested flat mirrors in the first place (for the same reasons). In my brainstorm one would just have a short focal point to the primary sunlightmirror, focussing the rays to the (unfortunately overexpensive) converter, which is only about 2r away from the mirror (having a radius == r). The microwave emitter would emit a slightly diverging beam to cover a large enough surface area on mars.


New idea?:

Okay, but what about stil using the light-pressure to shape our primary mirrors? Simply let the reflecting beam overconverge. Once through the focal point, the reflected light would start to diverge again. One would have some large, sunlight shaped overconverging (=relatively short focal length) mirrors pointed towards the sun, alowing them to approximately keep their shape. Somewhere near their focal point (not exactly in the middle of it for overheating reasons, but a sperical mirror wouldn't have a single focal point anyhow) there are a spacecraft with smaller more manageble, flat secondary mirrors to be found (about say a few hundred meters across) which reflect the light from the primary mirror to the right area on the Mars surface. A flat mirror would not change the con- or divergance of the beam, and the light would reach Mars as a pretty large diverging beam, covering a pretty large surface area.

- There is never any overheating involved, not for the spaceships, nor for the Mars-surface.
- No expensive frequency conversion.
- Expensive guiding systems and difficult flat mirrors, keeping the beam pointed at the right spot, are in the smaller spacecraft.
- Large mirrors keep their shape thanks to the sunlight they receive and could easily be aimed at the sun by the same passive system that keeps a parachute from not going berserk when falling down (a hole in the middle).
- Both mirrors of each pair would need quite some rocketpower to keep them in their respective orbits to counterbalance the light-pressure effect, but one would need that anyhow (in any system we came up with). This energy could probably be obtained by converting part of the same sunlight that pushes them away.

[selden]

Jules,

I was referring to the light coming from the optical mirrors vaporizing the optical-to-rf converters. Sorry I wasn't clear.

FWIW, fear of the RF frying things if the beams ever wander away from the ground stations is one of several reasons why solar power satellites haven't been deployed here on Earth. They were proposed many years ago.

Don't forget that we're talking about handling TeraWatts of power. Concentrating that much energy into any "reasonable" volume introduces many problems. I certainly don't have the slightest idea how they could be handled. For example, reflective materials are not 100% efficient. That means they absorb some of the light and turn it into heat. Even if it's only 1 part in 1,000, that's hundreds of MegaWatts.