Discussion Developing my first satellite

[RisingFury]

And please don't mention the Mars rover, that really is an appallingly bad mesh :lol:

I had a feeling that just mentioning the rover would make you cringe :lol:

 

[PhantomCruiser]

Everybody has to start somewhere...

 

[MaverickSawyer]

OK, now that the storm has calmed down... I think a set of cheap toy-store sized gyros with servomotors attached would be enough for pointing control. one for each axis. That's all you need, unless you want manuevering ability. In that case, I would suggest a small electric-based thruster. they're small, and low enough in thrust to not send you off at 2 gees! :lol:

As for antennas, the omnidirectional antenna is more of a black-magic design process than most would care to admit. I have seen some that look like a bent paperclip, and have been wonderful for their intended purpose.

 

[RisingFury]

OK, now that the storm has calmed down... I think a set of cheap toy-store sized gyros with servomotors attached would be enough for pointing control. one for each axis. That's all you need, unless you want manuevering ability.

Would it work? Yes, if they're capable of spinning at least at ~1000 RPM for a long period of time.
Would it work reliably and be efficient? No. Gyros only produce torque when they're speeding up or slowing down. So to turn your satellite, you speed up the gyro to turn it one way and slow it down, to turn it the other way. While the satellite is oriented in a specific direction, the gyro has to hold the RPMs constant.

Due to gravity gradients, drag and other influences, the satellite tents to start tumbling over time. it gets angular momentum from outside sources and the gyros need to compensate for it. If the effect of these outside influences isn't averaged out to 0 over time, the gyros will need to spin faster and faster to compensate and obviously the electric motors and bearings have their limits.

Also, another thing to take into account is that the smaller the engine is in terms of power, the less efficient it tends to be. Large engines, in the 5 kW range or more tend to be almost 100% efficient. RC motors in the 1 kW range are typically about 85% efficient and smaller motors drop to about 60% or less.

As for antennas, the omnidirectional antenna is more of a black-magic design process than most would care to admit. I have seen some that look like a bent paperclip, and have been wonderful for their intended purpose.

The simplest "omnidirectional" antenna I could think of, would be a conductive material, bent in two places, to make 3 perpendicular parts...

 

[Tex]

I guess that I won't get that Add-on Dev tag (and that orange name I always wanted) anytime soon.
That's the real reason I wanted to develop.

You will not be granted the Addon Developer tag if this is the only reason you want to develop addons. To be frank, you're setting yourself up for failure right from the beginning with that frame of mind. As I have already mentioned in a previous post; you should only make addons if YOU want to make addons. Again, I am not trying to be mean here or discourage you from making addons, but you do have to understand that your reasoning is flawed if you only seek an addon dev tag and an orange name. The more time you spend on the forum talking about this, the less time you're learning how to make addons. :yes:

So, take some time to reflect on what you REALLY want. If you want to make addons, then do your research. Take notes, plan your project out, put effort and time into it for YOU. Release it to the community only after you have something to share and when you're ready to receive positive and negative feedback and constructive criticism. :idea:

I genuinely hope you really do want to make addons and you invest the time to do it right someday. I think you will find when that day comes, the tag and orange name, will not be so important anymore. :tiphat:

 

[Zatnikitelman]

The simplest "omnidirectional" antenna I could think of, would be a conductive material, bent in two places, to make 3 perpendicular parts...

Actually the easiest omnidirectional antenna is just a single whip with some kind of coutnerpoise (can be the satellite's body). There's a sharp null in the radiation pattern in the direction the antenna tip points, but that's usually not a problem as the null is very very sharp, on the order of a few degrees which would require an extremely high precision orientating system to actually hit. A better idea might be a dipole antenna, you'd have sharp nulls in the directions of the elements, but again, very small.

 

[RisingFury]

Actually the easiest omnidirectional antenna is just a single whip with some kind of coutnerpoise (can be the satellite's body). There's a sharp null in the radiation pattern in the direction the antenna tip points, but that's usually not a problem as the null is very very sharp, on the order of a few degrees which would require an extremely high precision orientating system to actually hit. A better idea might be a dipole antenna, you'd have sharp nulls in the directions of the elements, but again, very small.

Wouldn't folding the antenna prevent that sharp null area?
In general, a dipole antenna's signal strength has a function of Sin[x]^2, where x = 90° would mean parallel to the antenna.

 

[Zatnikitelman]

It depends on how you fold it, but you're likely to have nulls in one direction anyways. Remember when I talk about directivity, I'm generally talking about within a plane. The radiation pattern may be perfectly circular on a place perpendicular to the axis of the antenna elements, but on a plane parallel to the elements, you see the nulls in the radiation pattern off the ends. Because the nulls are so sharp, for a cubesat, particularly one that may be tumbling somewhat, the nulls don't cause much of a problem. Us Ham radio operators regularly talk though satellites with that kind of configuration, and a handheld "walkie talkie" radio and handheld directional antenna with no problems, so I don't think a dedicated mission control center presumably with at least a satellite-tracking antenna mount, and automatic doppler-compensation, would have any problems with pattern nulls.

 

[RisingFury]

So if I understand you correctly, a cubesat won't need any antennae for typical operations?

In any case, modeling them in an add-on, with unfolding animation would be nice.

 

[Pipcard]

So if I understand you correctly, a cubesat won't need any antennae for typical operations?

In any case, modeling them in an add-on, with unfolding animation would be nice.

What I'm actually wondering about is the hinge for the folding/unfolding.

 

[RisingFury]

What I'm actually wondering about is the hinge for the folding/unfolding.

Forget it. Don't model it. Just make a small cylinder in place of the hinge, to hide the end of the antenna.

Focus your detail on other parts of mesh, especially if you're only learning.

Also, don't neglect texturing. Details in textures are far more powerful than details in polys!

 

[Pipcard]

Also, don't neglect texturing. Details in textures are far more powerful than details in polys!

Of course, just a six-sided cube won't work.

 

[PhantomCruiser]

Hey dude. I found something that you might be able to use as a reference.
http://www.nasaspaceflight.com/2011/10/pslv-launch-megha-tropiques-for-india/
http://www.isro.org/pslv-c18/Imagegallery/satellite.aspx#6
http://srmsat.in/
http://amsat.org/amsat-new/satellites/satInfo.php?satID=139&retURL=/satellites/status.php


I saw VesselSat-1 and thought "Hey, that's Pipcard's build!" The SRMSAT is pretty close also.

 

[Pipcard]

The [ame="http://en.wikipedia.org/wiki/Lunar_Prospector"]Lunar Prospector[/ame] is about the same size as my satellite (without its booms). It has a dry mass of 158 kg (wet mass - 296 kg). It needs hydrazine (22 N) thrusters for attitude control.

Those cold-gas propellants are only for something as small as a 0.1 m x 0.1 m x 0.1 m satellite I guess.

 

[garyw]

Those cold-gas propellants are only for something as small as a 0.1 m x 0.1 m x 0.1 m satellite I guess.

not true. The X-38 was going to have cold gas jets for RCS stlye actions.

 

[Pipcard]

What do you think about the texture work here?

 

[PhantomCruiser]

Looks pretty good. :thumbup:

 

[MaverickSawyer]

Looking nice!

 

[Pipcard]

For anyone who was wondering, I got the foil from CG Textures, and the solar panels were originally from here:

(I searched for "cubesat solar panels")

I might make the individual cells even smaller. (so it is an 8 x 16 array as opposed to 4 x 8)

 

[Pipcard]

Small ion thrusters?; also, solar panel wattage

-Can you make an ion drive that can function as the main engine (not attitude control) of a 1.3^3 m^3 satellite, and what are the thrust, isp, as well as wattage requirements?

However, I have seen this in which the "the propellant is pre-charged on the ground, and placed in small needles."

-Also, what is the average wattage per cm^2 of solar panel?