JSEA Activities

So it started out that I thought maybe I could make a game  on Google Earth to make the space elevator dodge the satellites, but I have become more interested in the actual physics and the details of the calculations behind the actual idea and engineering.  I haven’t finished yet, but it seems pretty accurate what I have done.

For the baseline Space elevator we will need 5 thousand tons of material if we have a 50 GPa ribbon.  This sounds like a lot, but when you compare it to something like the World Trade Center it is nothing.  The WTC weighs about 100 times that much a whopping 500 thousand tons.  In terms of material it is not that much.  But we are talking about hauling it into outer space which still runs about 10,000$/kilogram.  So we are talking about 50 billion dollars.  But then again, lets put that in perspective.  It costs a few billion dollars to build a large skyscraper like the WTC or Taipei 101 or something of that nature.  And we have already launched that much mass into space before.  If you add up all the satellites (30,000 or so) masses, I imagine it is well beyond that figure.  So for me the hard part is still the actual deployment and maintenance of the elevator than the actual lifting of the mass. With next generation heavy-lift rockets, the mass could really be launched in about 100 launches.  It is definitely a big project, but the payoff is phenomenal.

This is still the part of the simulation that I have not completed.  The effect of the moon’s gravity on the motion of the elevator is still unclear.  When making this simulation it is clear to me that breaking things down into components and essentially allowing the computer to be your integration system, it makes the math quite a bit easier to manage.  I read some of the papers about the subject many of which appear to be very well thought out, but I often get bogged down in the math.  The calculations behind the simulation that I have done are fairly simple and fairly accurate.  It gives a decent overall view of the system.

Here is the link to the simulation.  Sometimes it takes a while to load. And it works best in Firefox.  It is a little jumpy when I do the Tether gravity simulation which is what I was working on before I stopped doing anything with it a few months ago.

For the time being everything is set in the Javascript so you cant change the parameters.  But if you are interested in playing around with it yourself, here is the source at the time of writing this post.  It is not really that big, but the 3d models are what takes up the space.  It is the easiest way to get something that looks realistic on Google Earth.  Although things still appear and disappear due to the difficulty of rendering objects quickly on Google Earth.  That may improve at some point.  If you cant see an object you will have to zoom in and out.  And you will have to use your own Google Earth Key if you put it on your server.

So before we can talk about protecting the space elevator from potential debris, we have to understand what we are currently using to protect our satellites already in orbit.  For the purpose of this discussion, the components of the elevator will not significantly differ from the components a satellite is made of.  Both will be impacted by debris travelling at high speeds.  This will have the potential to cause significant damage.

So I previously wrote about the detection mechanisms we currently use to track some 30,000 or so pieces of debris that are greater than about 4cm in diameter, and the detection mechanism is already pretty crude (no better than about a 100m accuracy) for anything a significant distance from earth.  I imagine from statistics and tracking the path for some time this improves quite a bit, but the basic technology which would be able to detect NEW debris that we dont know about and track it until it struck something would be about this (I dont remember the mechanism for the tracking at the moment so don’t quote the 100m).  Anyway, there are some few hundred thousand pieces of debris that are smaller than this.

So the question is what do satellites do currently to avoid this stuff?  Well, they move out of the way which is expensive since the cost of launching fuel is so drastic.  1kg of weight to orbit is still on the order of thousands of dollars which goes for fuel too.

The other thing they have used for smaller objects for the past few decades is a Whipple shield which is just a light-weight shield made of Kevlar or some other high-strength material.  See a sample of one from KIBO here.  And some more info from NASA here.

This would be a potential early application for high-strength Carbon Nano-tubes.

There is a slight difference between the elevator and these Whipple shields though in the fact that only a perpendicular hit on the elevator would cause damage.  I don’t know the research that has been done on this, but basic physics I imagine would show that anything other than a close to perpendicular hit would simply push the space elevator ribbon to one side or the other.

A low impact angle which runs the length of the ribbon would also be dangerous and could be potentially more damaging than a direct perpendicular hit. Again I haven’t thought through the physics of either of these scenarios.

In any case, from just a brief review of existing debris collision shields, it becomes obvious that this would not be a feasible solution to protect the space elevator from existing debris.  It is possible that there would be some way to adapt or pick up a piece of the existing technology, but it would be a stretch I think.  Anyway protecting from a low impact angle which runs the length of the ribbon may require some thought.  I dont believe this would be deflected.  If it hit at a low impact angle in a cross-section of the ribbon, it would spin the ribbon around, but running the length I am not quite sure how it would react.  This is something for further thought.

So what are the existing systems used for keeping track of satellites in a little more detail?

Use this site for a list of satellites.

Here is an open-source project which might be useful.

There a few parts in general that are needed.  One is the automatic adjustment of the orbit.  This includes a communication protocol for the satellite and a guaranteed adjustment acceleration.  Of course we also need a variety of security around this so that not just anybody can adjust the track of the satellite.  In the same protocol, we need a reporting mechanism, which will report everything about its location, speed, etc.  This will of course be double-checked by the radar tracking mechanism, whatever is used for the overall tracking of objects. Another is we will need to keep track of all non-earth objects, but we might as well make it easier on ourselves and make sure all objects launched from Earth have at least a minimal communication and quality standard.

So the rest of this is regarding tracking man-made objects.  I work under the presumption that eventually we expect man-made satellites to outnumber natural satellites in the vicinity of Earth.

First, as far as communication, is there a Wireless communication protocol equivalent to Ethernet/WiMAX in space?

Second, do we have minimum maneuverability standards for the satellites and grades?

Third, what does the existing tracking system consist of and how granular and how accurate is it?

One thing I notice initially about all of these is that they should be one of the top priorities for any Space Advocate.  We have the technology now to enforce this fairly easily if we all agree that this is needed.  Without these standards the launch business as well as any future space development costs will increase.

Ethernet/WiMAX for Space: All satellites must have some sort of communication protocol available to them, because this simply makes economic sense.  I don’t know if all satellites have them but I imagine all modern ones do.  But what we are interested in is a standard protocol, and a standard service which will allow for automatic maneuverability communication.

Deep Space Network telecommunications receivers

They apparently use phase-modulation and the satellite/receiver uses the same Frequency.  Basically it will be Frequency divided like old Cell-phones cell towers.  But we only have a few for all of earth since any signal will not be directed at the receiver very well.  So one downlink could disrupt another downlink I believe.  Theoretically not much different than Mobile CDMA or GSM technology, but the details are somewhat different.  So basically it is just a matter of choosing a standard.  There may be some constraints on standard ethernet which would prevent its use (I don’t know enough about the standard), but you could at least put TCP/IP on top of whatever physical communication is going on.  This would allow us to build on top any service that we wanted into the data control.

This article shows some information about the DTN (Disruption Tolerant Networking) protocol which I suppose is interesting, but I do not believe it is that important.  I believe in reality router logic will eventually take care of this problem.  If one route fails, then we will dynamically change the route, not queue the messages.  All Space routers will have Location information built in, and they should know their closest routes and closest locations, so if there is a communication problem it will be because of something other than a route problem.  I believe this is a better approach.  This constant calculation of location will be built into any “Space Router”, or “Space Network”, since we will eventually have to direct the radar like any normal wireless tower does to ensure that the strongest signal goes to the right spot.  But I guess some people figure this will be a useful addition to the TCP/IP protocol.  And who knows I could be wrong, maybe there will be many dynamic disturbances in space communication.

Manuveurability:What we are interested in the power system and the Attitude control systems.  If these are not sufficient, then it doesn’t matter whether we have an automated system or not.  So these need to be regulated.

Existing tracking system: appears to be run mostly by the Air Force, known as SPACETRACK or the space fence, but the data is shared with other organizations.  And it is primarily used to track known objects.  It is able to detect objects as small as 10cm (four inches) at heights up to 30,000 km (15,000 nautical miles.)  If you dumb it down, I suppose it is just a bunch of RF transmitting and receiving stations.

Distance and velocity measurement by using the electronics delay (doppler effect), is this practical in the long term?  Is there any better way to determine distance and velocity?  Very Long Baseline Interferometry seems like a better approach. But what is the minimal distance that this will work at? We may need both measurements, but if we have a satellite which participates in this measurement, then we can simply use VLBI and forget the other measurement techniques. This has a risk if there is damage to the satellite(s) though.
I read this from the fairly recent HAYABUSA, which shows that we can get down to about 200 mas or milliarc second precision using VLBI.  Still need to read more to see if this is accurate.  To get an idea of how accurate this is, on earth’s surface we have SRTM data which is about 3 arc seconds accurate which is equivalent to approximately 90 meters.  So 200 milliarc seconds would be about 5-6 meter accuracy.  Of course out in space one arcsecond becomes much larger, but then again we will have more space out there.  So this is accuracy for relative position, but how accurately can we track altitude?  I imagine this is basically the same thing, so I would imagine we can track things into about a 200 milliarc second area.  So if this is 5 meters at the earth’s radius (6,000 km), I guess it is about 5*7=35 meters at GEO (42,000 meters).  Does the detection technique degrade with distance though is the question.  I believe it probably does but probably not a linear correlation.  It probably degrades less than that, so we may be able to get accuracy of a bit more like 20 meters or so at GEO.  So we can detect tiny objects 10 cm or so, but we do not know their exact location in space.  So basically whether it is a 10cm object or a 30m object, we still have to leave it 4/3*PI*35*35*35=180,000m^3.  This is the spherical calculation.  So how much space we can actually use in space (no pun intended) is very closely related to how accurately we can locate and track objects.

Can we get any data from the DSN (Deep Space Network)?  After an initial look, it doesn’t appear that we can get any public data.  Will keep looking.

Some laws do exist such as:

As of 2002, the FCC now requires all geostationary satellites to commit to moving to a graveyard orbit at the end of their operational life prior to launch.  There needs to be more done here.