Thursday February 21, 2008
Thursday February 21, 2008
Hi guys, it's David from adcs.
I sent out an email last week, and decided to turn it into a blog post (thanks Pradeep).
I started the work (which will hopefully turn into my master thesis) on a Micro Pulsed Plasma
Thruster for statellite stabilization, attitude control and within limits:
stationkeeping and deorbiting. Especially the ability to deorbit seems to bring a certain attention to this project, since it is a real concern for the establishing of small sat missions like the Cubesat project. Well, attention on a project is never bad, especially not from Norad :-), maybe this would be some innovative idea for a secondary payload?
The thruster itself in a few words: it's a device that ablates
teflon through a discharge, ionizes and accelerates it.
We are currently
running testseries to validate our model and to find a suitable geometry for use
in picosatellites such as Cubesats.
Here (http://gallery.seds.org/v/Sedsat+2+PPT/) you can find pictures, sorry for the bad quality, but it's not easy to catch a 10 µsec discharge through a vacuum chamber window. Shown are the two horizontal electrodes (those are strongly oversized for testing purposes), the white teflon in between on the left, and the discharge initiation system above. The plasma formes to the left over the surface of the teflon and is moving to the right along the rails...pictures are shown from a low energy discharge at about 1000V & 3000A.
For those really interested: I wrote some abstract a while ago for the CC, I might still have that...
Have fun,
-David, adcs
Posted by David Krejci in Attitude control at 20080221 Comments[0]
Sunday November 25, 2007
Hello! I'm Steve from Comms!
I thought I'd write a short (and my first) blog post on s-band communications. The problem is that we have these big image files, about a meg in size, to download, and the quicker we can do this, the more often we can take photos. Most other cubesats out there seem to use the 435mhz amateur radio band but this doesn't seem that attractive to me - it is a small band and it's very busy with lots of other VHF communications, other cubesats, amsats etc. However, if we move higher in frequency things get a little less crowded and more bandwidth (= more data rate) is available. What's the catch with this? I'll tell you next week when I've found out.
Monday August 20, 2007
If you check my earlier posts on this channel, you'd find many questioning why scientists and engineers don't blog more often and I was never satisfied with the explanations they provided. I am still trying to prove myself wrong on that point.
Sorry for the long break from this blog. I was engrossed trying to sort out my academic life.
The Structures team now has some fodder to work on. The Interface Tables are slowly beginning to fill (SUB-SYSTEMS: COME ON, FILL UP THE INTERFACE TABLES). So, we now have an idea of what we're trying to design.
We've split the workload among the three team members ( which includes me). Parshati has taken the responsibility for the mass related aspects, Giuditta is doing thermal control and I'm doing the planning of where the equipments need to be or can be (called location).
This week, a few of the team members have been looking at writing the IAC 2007 Paper where we're selected.
Hoping most of you are coming to India for the SEDS International Conference and the International Astronautical Congress.
Posted by Pradeep in Structures at 20070820 Comments[0]
Wednesday August 15, 2007
Some more
information, why the ADCS team is suddenly talking about having the whole team
decide between two possibilities to control the attitude of SEDSat.
Me, the
other ADCS-member besides Michael :-), has been offered to write a diploma
thesis about designing a micro Pulsed Plasma Thruster (µPPT) which should be
commercially used for CubeSats. Therefore, it would be possible to use fly-ready
prototypes of this (for CubeSat) innovative technology (if you classify, like
me, electric propulsion as the most innovative propulsion system there currently
is, at least in use with nano satellites like ours), once they are ready. And
here is problem: This will not be until Fall 2008, which would obviously get in
conflict with a sooner (and currently discussed) launch opportunity.
So, the
deal is: If we decide to use those thrusters, this would also mean to decide
against an earlier launch. Or, if the earlier launch has top priority, attitude
control would have to be done with magnetic torquers, which is a well known
technology for CubeSats.
Here you go, if you have any questions, just ask :-)
David
If you want a discussion going on, just comment there...
Saturday July 21, 2007
Structure Status Report - 20 July
Sorry about this one-liner in Kirk's earlier post on the updates from Structures. I'd like to clarify that this is not because we're not doing anything but because I had just returned after 13 incredulous hours of lectures.
We're trying to make sense of the data that we're getting through the Interface Tables. And, trying to make the work easier for the sub-system giving and recieving this data. The problem was encountered when ADCS and Structure were trying to exchange data on the Interface Table in the wiki. We've asked Kirk to look into it and are also (are you Mike?) trying to figure it out.
When the data comes in, I believed structure should be split into three divisions - mass, heat and location. These three need each other for structure to be complete. So, the three members are working on this together. Parshati has said she is ready to take responsibility for all the mass data thrown at structures. (This is what appeared in the status update yesterday). I am still waiting for word from Giuditta on this one. I believe she's in the middle of her exams. So, I'm managing the location and heat parts of it for now.
We're waiting for all sub-systems to provide their data and request all of them to do so asap. Thanks.
The one-liner was neither Kirk's nor anyone else's fault. Just my fault. Sorry, hope it won't repeat the next meeting.
Posted by Pradeep in General at 20070721 Comments[0]
Status reports: 20 July
Communication
Work done in past week:
None, as we were supposed to work on the link budgets with our advisor and he was out sick all week.
Upcoming work:
Link budgets for the communication subsystem.
Problems that need to be solved:
- Need to find out the sensitivity of the earth station's receiver
- Need to get more weight allocated to the communication subsystem (although exact amount is not known yet)
- Need to find resolution between directional vs. dipole antenna.
Power
This week the power team have started with our requirements and posted them on protoforge. The search for the best batteries and solar-panels has continued with emails to several companies requesting mor information and prices. A very simple schematic has been made to get a better understanding of what components the system must contain. The schematic can be found here : http://i209.photobucket.com/albums/bb307/QuantumP7/SEDSAT2_power1.jpg
In the next weeks we hope to take a final decision on witch solar-panels and batteries to use. Under work is also a more detailed plan over the cuircuts on the cuircut board.
We dont realy have any big problems, except that we dont know what voltages the other teams need. But there is many things that can be done without knowing this.
ADCS
1) e-mailed bryan deloder, asked him for the weight of the rgb sensors. He says that they are almost certainly under 1 gram, he will take them to a jewler for a precise weight. still waiting on him for that.
2) get the weights of magnetic sensors, figure out i2c interfaces and mycrocontrolers and if we need them for adcs, figure out how accurate the magnetic map of leo is and whether we can include it in the memory of the sat.
3) can't think of any except that david (other team member) said he was going away at some point, so I am the only person currently active for adcs. and it is one of 4-5 projects I am working on. I have not heard much from tom about the person who was interested in adcs.
Structure
Parshati is incharge of mass under structure.
Payload
- Work done this week: Been looking at different imagers.(still waiting for a reply from the company that manufactures our #1 candidate)
- Will meet on saturday to discuss further work. Will involve starting to do some experimentation with a camera chip.
- Most of the team members have been unavailable the last month(vacation mostly) or so, this presents a challenge.
Command & Data Handling
I moved last week so I've been unpacking boxes after work whenever I
wasn't too tired, as a result I've been relatively out of touch with all
things SEDSat-2 related.
Requirements will be posted to Protoforge by the end of the day.
Saturday June 23, 2007
Reflections on attitude control
Hello, long time no see... :)
The summer is underway, and schecules for some of us have changed rather dramatically. I am no longer juggling an unicycling furiously every day long into the evening. sigh. Actually, it isn't so bad. I am quite enjoying myself. Actually I have to many things to do for life to get boring. I am working on a glider, thinking about a satellite, playing with a new laptop, setting up a mysql server so I can work on my website -actually it wasent me who set up the server but whatever ;), checking out universities online and applying to them... and mucking out the barn. To be quite honest, that is about it. Specifically "thinking" about the satellite. I have got just about nothing done this week for it... oops... actually, shucks darn is the better way of putting it. Things have been rather busy.
Actually, despite what I just wrote, this post is not about how I have got nothing done on the sat. Actually, an idea for attitude determination that has been tickling me for a while has finally managed to lodge itself in my mind as a viable strategy. That is, it uses a minimum of hardware, a minimum of computing power, and is really simple. How can you beat that? But first for some background. Here is an exert from a report recently sent to our advisors:
"For the satellite ADCS, we are thinking along the following lines:
i.
Determine position via either GPS or NORAD or both, measure the local
magnetic field using a 3 axis magnetometer (say, from Honeywell), and
compare this to a magnetic field model at the determined location to
establish the orientation of the satellite. Then use onboard magnetic
coils interacting with the local magnetic field to control the
orientation of the satellite.
ii.
The other method for ADCS is to measure the power generated by each of
the solar panels to determine the direction of the sun, and determine
the direction of the earth using up to 6 (and perhaps more) optical
sensors (less than half a cubic cm, provided by DALSA). These will tell
us nothing of our position, but will help us point the sat. It should
be noted that as CMOS sensors, these are supposed to have a greater
radiation tolerance than CCD sensors, but that they have not been
tested in the space environment or a space-like environment, and so
should perhaps be treated more as a secondary technological payload.
iii.
A concept that has been used on some NASA spacecraft involves computing
(rather than measuring) the spacecraft's position in 3D space using
data such as the spacecraft's predicted orbit, what time it is and
attitude information derived from solar panels. Corrections to the
spacecraft's 3D position could be up-linked periodically as they are
necessary and available ? this would take some CPU cycles, and
potentially on-board orbital dynamics, but also could be as simple as a
lookup table.
iv.
Because we may not actually know the spacecraft?s orbit accurately, the
idea of computing position (mentioned above) would necessitate further
effort, such as the following:
-
In order to determine our orbit accurately, we can start out with the
preliminary estimate of our orbit and then upload actual TLEs provided
by NORAD once the satellite is inserted. This idea will work provided
we will actually get those TLEs. It might also be possible to get this
information from GPS.
-
In order to control our orbit precisely, we would require propulsion
systems for general orbital insertion as well as for precision orbital
insertion (station keeping). Including thrusters on our satellite would
mean a radical deviation from the way we are currently considering
doing ADCS. We would abandon all the magnetics, and go with
micro-(pico)-thrusters, and the horizon sensors (maybe from DALSA).
- We are also still considering a gravity gradient boom, although it would be pointed away from the earth as opposed to toward it, if we do not want to obstruct the camera image."
We have realized that we can use the power readings from the solar pannels to detect the direction of the sun. The new idea is this: The sat could be pointed in any one of the directions perpendicular to the axis connecting the satellite and the sun. 360 degrees of freedom in the plane. But, if the sat were rotating, we would instead get readings along a line of lattitude. We would also (by the instantanious power readings), know the sun's exact position relative to us. In principle we also know the the sat's position relative to the earth by virtue of the predicted (and corrected thank's to norad) orbit. We (from earth) would also know the position of the sun. This information could be used to create a 3-D orbital model, telling us where the sat is relative to the earth and the sun, and how it's position is changing. This, plus the angle information gained using the mechanism described above, could be used to determine the instantanious direction of the earth relative to the sat. All that would be left to do would be to stop the spinning of the sat in such a way that it is left facing the earth. If there were enough mass left to the subsystem after installing magnetic torkers and a magnetometer, we could install a gravity boom, and deploy it at that time.
Welcoming comments from all and sundry,
Cheers, Mike.
Wednesday June 20, 2007
As we have been discussing already for some weeks we are now recruiting new members for two teams. We see a gap in Marketing and PR, so this is an essential leverage point for the public success of our project. We're promoting these opportunities at different universities and schools right now, using our existing network of advisors and contacts.
The second team that will need to aquire members is Ground Control.
Besides this, Systems Engineering is now working on two things - to figure out our environmental constraints and facts and to elaborate the ground control interface tables together with the Communication Subsystem.
Good news arrived me today - Juan, living and studying in Spain, notified me that through his local network he has received the promise to be able to use two ground control stations in Spain free of cost for commanding our CubeSat and up/download data to/from it.
Great job, Juan! :-)
Sunday June 17, 2007
I think perhaps the foremost thing on everyone's mind has been the Interface Tables. There was one tentative deadline, and then a firmer deadline, and it seems that everyone's pulled through. Yes, there was initial confusion, as was bound to be the case, but discussion sorted it out, just like discussion can sort anything out. We decided that it would be simpler to have the interface tables as interface bullets instead, and it seems to have worked. Not to mention that Kirk did an amazing job of wiki-magic and everything ties together so well that it's easy to go back and reference. I think that formatting or structuring of information is really underestimated. It makes all the difference, in my opinion, and I think that it adds to the motivation of the members. Or perhaps it is just that I am obsessive compulsive about such things.
Anyway, I digress. There has been amazing progress made by the Power, ADCS and Payload teams, especially in terms of the interface tables, which right now, seems to be a direct indication or measure of how far a subsystem has progressed in terms of design. There is very specific and quantitative information by these three subsystems, which in turn will help the others progress even further. The Command and Data Handling, upon talking to the subsystem leader, have a clear idea of the progression of data in their subsystem. Communications, having undergone restructuring is a little bit behind in terms of quantitative data, but we're picking up speed and we should be on par with the rest very soon. Structures can make very little progress until all the subsystems have made very significant progress in their designs and decisions of components, and therefore this is limited right now to the specifications provided by the CubeSat program. Still, there has been active discussion on this front, which has gotten the others in other subsystems thinking on ideas for the structure that will best suit their subsystem. For example, Nikko from Communications, has suggested that there be only one circuit board onto which everything be mounted/slotted, in order to save space. This is still open for discussion, however.
Now, the steps that face us immediately are: getting started on the paper to present to the IAC this September (I believe we have enough to fuel the start of it) and deciding on a ground station/subsystem. The main trouble with this has been resources, but then again, with a team this resourceful, I have no doubt that this trouble will be resolved soon.
PS: I forgot to mention a couple of things. We have a coordinator for all our advisors, which in my opinion is a great thing as it will keep all teams very much abreast and keep the advisors, an integral part of the team, involved. Further, Tom assures me that progress has been made for a marketing team--also another great development--which will help us with sponsorship.
It has been quite a while since I've written here last, but that is mostly because I was restructuring the team. This project will take commitment and dedication, and in working with the people who had originally applied, I realised that they didn't grasp the gravity of the project (no pun intended). Not to mention that at our university, with a trimestral system, each term is a dose of craziness, and it was more and more apparent that these students would not be able to give this project the time it deserved, and they themselves admitted it. There were other factors, but these are more subtle.
In any case, I trimmed down the team to those completely dedicated and willing to give everything they can. Way I see it, this will help more than hinder, since two dedicated people can do more than eight listless ones. All that remains of this trimming are Nikko Torcita and I, and a possible new member, Bryan Chug. We have also weighed the contributions of our advisor and decided to ask someone else to take over this job, and this new advisor is Mr Mappatao.
We have had a serious meeting about this new team, and where we're going and I have a very good feeling about this. The advisor seems to be providing both initiative and direction, and with his specialisation in communications, I have faith that we will pick up momentum in no time at all. There is renewed life in this subsystem team, and I believe that this is worth a celebration.
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Recent Entries
- Pulsed Plasma Thruster
- Comms thoughts
- Structures - Here we are
- µPPT
- Structure Status Report - 20 July
- Status reports: 20 July
- Reflections on attitude control
- Further Recruitment
- Interface Tables
- Restructuring
- A potential change of plans
- Analysis, Analysis, Analysis
- End of year
- Michael's Post
- Exam Challenges
- Voting starting with a bitter taste
- *** Voting's on! ***
- OScar
- Recomendation for the team
- And another payload concept