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Topic: Simulate Spacecraft GN&C Demo (Read 791 times) previous topic - next topic

JPS002

Jan 12, 2013, 06:36 pm Last Edit: Jan 12, 2013, 06:59 pm by JPS002 Reason: 1
First off I want to say hello!

I am just getting started with my first Arduino project so please ignore my ignorance :)

I am leading my senior design project which is comprised of 15 Mechanical, Aero, and Industrial and Systems Engineering undergrads (actually about 24 when you count our partner universities in SC and Paris France that report to us).  Unfortunately no EE's, and I myself am an ISE so after you crack the inevitable "Imaginary Engineer" jokes :) perhaps you could offer some insight as to the feasibility of my idea for an open house demonstration.

Our mission is to design a spacecraft capable of travelling to and performing science both in orbit and on the surface of Enceladus (a very intriguing moon of Saturn).  After the first semester I feel that the weakest subsystem on my team is Guidance Navigation and Control.  This is essentially used for attitude control of the spacecraft and controlling a soft lander upon descent.  Given our weakness, I figured that that jumping headfirst into some project with which I have NO experience would be a fantastic way to show our abilities!

What I would like to do is have a demo where I could hold a mock spacecraft with LED's where the GN&C thrusters would be located.  I would then like to be able to tilt the spacecraft and power LEDS to display how the thrusters would fire.  

I currently have an Arduino Uno R3 and a basic starter kit.  I have looked at some IMU's (https://www.sparkfun.com/products/11055) and the like but have ZERO experience doing something like this.

Can you guys/gals help point me in the right direction?

Thanks so much!

robtillaart

Welcome in Arduino land,

Just thinking out loud,

The gravity of Enceladus is 90x weaker than earth. Still you might use a sensor that is also used for quad-copters like - https://www.sparkfun.com/categories/163 - to detect the orientation of the spacecraft. Where a quad-copter would increase one of its four motors, the spacecraft would fire one of its engines to stabilize. Think you can modify quad-copter sketches for your demo purpose. By connecting the Thruster LEDS to a PWM port of the Arduino you can get different brightnesses (255 in theory) to simulate more less thrust.

With a ping sensor you could make an altitude meter that works.

A colour sensor could "simulate the geological science", or use RFID tagged stones so your sensor can "recognize minerals" - check sparkfun for sensor ideas.

you could include position info [GPS?] that changes if you move the spacecraft through the demo room.

You could make it complete by including a wireless signal send from the Arduino about al the above to base station Earth (PC + 2nd Arduino?).
e.g. - https://www.sparkfun.com/search/results?term=434mhz&what=products -

Have fun!

If questions remain, please post them.
Rob
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

JPS002

#2
Jan 12, 2013, 10:32 pm Last Edit: Jan 12, 2013, 10:56 pm by JPS002 Reason: 1
Thanks for your response!  Wow, that is making my initial idea sound puny :)

The IMU on our spacecraft is really only for attitude control (6 degrees of freedom) and not descent, but I think it will be fine for the purpose of this demo.  On the "real" mission approximately 20 meters from the surface of Enceladus a laser rangefinder in conjunction with imaging equipment will provide altitude data for the final descent.  20 meters sounds way to close,  but as robtillaart noted the gravity is so low we will be falling more like a feather than a rock.  

My initial idea seems to be pretty well displayed herehttp://www.youtube.com/watch?v=luUpCTFVa6I.

I really like the idea of "communicating with earth" .  In addition to giving visual feed back from the LED's is it possible have real-time positional data streaming on a laptop to simulate mission control?

My constraints on this project will be limited to skill, hours, and mostly money.  I am trying to find sponsorship but if I don't get it I doubt we will have more than $100-150 to put toward this.  Keep in mind I do already have an UNO.  The open house is only 25% of the project so I also need to be careful not to take on something way out of my range, we also have a 150 page paper and 1 hour presentation.  That said are there particular parts list that you guys would suggest?  

Do you think a 3-axis accellerometer will suffice in place of an IMU?  Can you suggest a particular model?

The ping sensor sounds like a good idea, can you suggest one to me?

Also, if I wanted to link to my notebook via bluetooth is there a particular modem you would suggest.  I read some positive things about https://www.sparkfun.com/products/10393 but it calls out models other than the UNO.

Thanks so much!


robtillaart

Quote
In addition to giving visual feed back from the LED's is it possible have real time positional data streaming on a laptop to simulate mission control?

You can also simulate all this data in mission control, but having it interactive is more impressive.

Quote
My constraints on this project will be limited to skill, hours, and mostly money. 

Skill - the forum can help
Hours - when is the deadline? (decrease that with 2 days at least ;)
Money => note that most items can be reused afterwards

* make a priority plan, which functionality you want to have first in your demo?
for me the order would be
1) Leds + resistors to make thusters (5$) -
2) Proximity sensor for landing ($20) - https://www.sparkfun.com/products/242
3) RF Link to Basestation Earth ($10) - https://www.sparkfun.com/search/results?term=434mhz&what=products
4) Second arduino ($25) -
5) Some wiring ($10) -
----------------------------
makes ~ $70

If that all works one could simulate the geo analysis sensors.

What is the subject of the paper/presentation?

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

liudr

Maybe one thing at a time. The hardest thing I see is radiation hardening. Anything you write in arduino will be erased and rewritten by cosmic radiation. But if you are doing a demo, forget that.

I'm thinking about balloons that get inflated for soft landing. I wonder if that applies here. This project sounds very big but budget-wise sounds too small. Any way to tell us the exact requirement for finishing the project?

JPS002

Paper and presentation are also on the same mission.  Essentially it is a response to an academic announcement of opportunity published by NASA.  We are to put forward a fairly refined concept of how we suggest the mission be carried out.  We are operating with an imaginary budget of 3 billion US dollars. 

I am simply trying to showcase some of the concepts behind the mission and I thought this would be a good opportunity to
1 Use my Arduino
2 Have something more interesting that the posters you always see at these open house type events

Sorry if there was any confusion. 

My priority is to have a model of our orbiter, lander, or both.  Then to be able to hold the model in my hand, tilting it to light LEDs to show how the GNC system would work to correct the flight pattern.

I now believe I can accomplish this with a 3 axis sensor.  I will try to accomplish this first and come back when I am ready to complicate things again. 

Thanks a ton!

michinyon

If you are going all the way to Enceladus,  I'd be more worried about navigation than attitude control.

michinyon

To address your other issues:

you refer to attitude control as 6 degrees of freedom ...  actually,  it is 3 degrees of freedom.

and then later, you ask if a 3-way accelerometer is sufficient?  No, it isn't.   

To maintain the orientation ( attitude ) of the spacecraft,  you need to detect its rotation,  and for that you need a 3-axis gyroscopic sensor or equivalent 3-axis MEMS device,  plus some means of accounting for the integration error ( drift ) resulting from the sensor readings.  On earth the normal way to do this,  is to use an accelerometer to deduce the reference direction of gravity,  or alternatively a magnetic field sensor, which indicates the direction of the earths magnetic field.   Usually both of these are required to prevent the attitude of the vehicle from drifting around some axis or another.   

You can also detect changes in the orientation of the craft if you have enough accurate accelerometers at the extremities of the craft to enable you to detect rotating motions,  but that is unnecessarily difficult.

JPS002

#8
Jan 13, 2013, 03:38 am Last Edit: Jan 13, 2013, 03:48 am by JPS002 Reason: 1

To address your other issues:

you refer to attitude control as 6 degrees of freedom ...  actually,  it is 3 degrees of freedom.

and then later, you ask if a 3-way accelerometer is sufficient?  No, it isn't.    

To maintain the orientation ( attitude ) of the spacecraft,  you need to detect its rotation,  and for that you need a 3-axis gyroscopic sensor or equivalent 3-axis MEMS device,  plus some means of accounting for the integration error ( drift ) resulting from the sensor readings.  On earth the normal way to do this,  is to use an accelerometer to deduce the reference direction of gravity,  or alternatively a magnetic field sensor, which indicates the direction of the earths magnetic field.   Usually both of these are required to prevent the attitude of the vehicle from drifting around some axis or another.    

You can also detect changes in the orientation of the craft if you have enough accurate accelerometers at the extremities of the craft to enable you to detect rotating motions,  but that is unnecessarily difficult.


You are absolutely correct, I wouldn't try to send a spacecraft to Enceladus with an Arduino and a 3-axis accelerometer :)

However, are you telling me that the 3-axis accelerometer is not going to be able to sense me tilting a model and thus send a signal which will light my LED's.  

I am just looking for simple way to highlight the basic concepts of attitude control.  Yes, the real spacecraft will have control for degrees of freedom, IMU's, startrackers, and a suite of avionics equipment but I am just looking for a simple demonstration.  

I was originally thinking I needed an IMU and not just a 3-axis accelerometer, maybe I was just being hopeful because the accelerometer's are so affordable.

Thanks for the help...and patience.

liudr

The 3-axis accelerometer will tell you, not accelerations in 3 orthogonal directions, but force experienced in 3 orthogonal directions. Whoever coined the name was lacking basic physics concept. Think of the accelerometer as a weight on a spring. If you are level, there is only force in the straight downward direction, downward compared with your lander axes. You will read -1 (g) or +1 (g) if you orient the accelerometer upside down. If your lander is tilted from vertical down, this vector force will no longer show its entire magnitude in lander -z but components in -z, x, and y. You use the sqrt(x^2+y^2+z^2)=1g, and cos(tilt angle)=x/1g, assuming small acceleration during descent. You may find out your tilt angle with the downward direction. There is an additional angle you can find, but not very useful unless you have a thruster to decelerate. You will still miss one angle, which is given by magnetic field on earth. So search some data for the moon you intend to land on and see if there is a way to tell one more direction, magnetic field, whether the moon is tidally locked to the planet (finding where the planet is will give you another angle), etc. You don't have to demonstrate these but having the concept on the poster will show you really worked the physics. Get a physics/astrophysics student on board. This project will benefit from that student.

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