Discussion Uranus and Neptune mission concepts

[Nicholander]

I don't exactly know how it looks like, and keep in mind that this isn't really supposed to be the Orbiter mesh. And Urwumpe, I know how RTG's work, but would that 1 RTG be sufficient to keep the thing running for 10 years? Also, would that medium gain dish be suitable for communications at Neptune?

 

[Urwumpe]

I don't exactly know how it looks like, and keep in mind that this isn't really supposed to be the Orbiter mesh. And Urwumpe, I know how RTG's work, but would that 1 RTG be sufficient to keep the thing running for 10 years? Also, would that medium gain dish be suitable for communications at Neptune?

Well, I described the influencing factors above already. Yes, a single RTG can be enough. But then, lets look at the existing options:

A MMRTG would produce 125 W of electrity at the beginning of its life, but only about 100W after 14 years. It weights 45 kg. Now, 100W isn't that much.

For example: if you use only a medium gain antenna, but plan to also have a high data rate, you need a much stronger transmitter to also get a useful SNR at the receiving DSM antenna. And during reception of the week signals from Earth, you also need some signal preamplifiers to get some data rate in the end. Voyager for example launched with a 20 W transmitter, but has only a data rate of 160 bit/s unless you use special reception strategies - one per week, it can transmit data at 115 kbit/s, because the SNR ratio is much worse at such a high data rate and such low power.

So, if you want to transmit more data than that, you need more electricity for the transmitter. But for transmitting data to earth, you also need other subsystems to be powered, like guidance systems, mass storage memory and computers. You see: 100W of electricity available by one RTG means also limits on the communication system already.

Now, I can't say: You need more than one. As I said above, all that decisions depend on your mission design and on other design decisions. A bigger antenna would be heavier and would require more room in the launcher, but it would also allow higher data rates with lower transmitter power.

It depends on power schedules and such stuff. Especially Heaters (which are extremely important in the outer solar system, despite the RTG producing lots of heat). How much power is needed during propulsive maneuvers. Are batteries possible (Remember: Batteries don't like it cold. They also need heaters)

 

[N_Molson]

Are batteries possible (Remember: Batteries don't like it cold. They also need heaters)

Absolutely. :yes: I recently documented myself on the Lunokhod soviet rover and I found it used a radioactive isotope to keep batteries (amongst other stuff) at operating temperature during the 14-days lunar night. Hence the concept of the "cooking pot" (at night they closed the "lid" to preserve heat). So yeah, batteries definitively need an heat source for a mission going as far as the outer planets.

Well in fact, from my short 4-month Canada experience, if you use standard batteries for electronic devices like digital cameras on Earth outdoor by say -15°C, you'll notice that they discharge in no time. In this case using your body as an heat source works quite well. And in any country that has serious icing in Winter, you plug the car battery before going to bed unless you want to have problems the next morning.

 

[Nicholander]

Like I said in my post, it's not supposed to have a large bit rate, It'll transmit the data after the Neptune flyby. So I guess it'll have a bit rate similar to Voyager. Also, could an RTG realistically be that small? Keep in mind it's just 0.5 meters long. (0.55 meters if you include the base).

K_Jameson, could you post an upclose image of the Shakespeare's engine? (And if you can, maybe Efesto's and Galileo II's engines too)

 

[Urwumpe]

See here:

http://en.wikipedia.org/wiki/Multi-Mission_Radioisotope_Thermoelectric_Generator

such a small one is pretty compact

 

[K_Jameson]

K_Jameson, could you post an upclose image of the Shakespeare's engine? (And if you can, maybe Efesto's and Galileo II's engines too)

I'll post Galileo II quad engines, that are identical to the single Shakespeare's engine.

The engine is a simple piece of mesh. The bell is enclosed in a protective cover against micrometeoroids. Here the bell with the cover removed.

 

[Nicholander]

Thanks! Also, just 2 little questions: What are the dimensions of the engine? (How long it is, bottom of nozzle to top, and what is the top's diameter and the bottom of the nozzle's diameter?) And what is the cylindrical truss structure around the engine on the Shakespeare?

 

[K_Jameson]

The truss is not related to the engine. the ring at the base is the interface with the payload adapter. The engine is 45 cm high and 27 cm wide at the base.

It is a 980 N engine; a more classical 400 or 500 N can be somewhat smaller.

 

[Nicholander]

I accidentally pretty much ruined my Sketch-up model. :facepalm: I tried to delete some things on the bottom to make way for the engine, and it also selected everything behind that engine bottom. (The top and half of the side) I saved before I realized what I had done, and Sketch-up has no autosaves.

Well... I guess I could try an actual 3D modeling program, say 3D wings. K_Jameson, what program did you use to make the 3 probe models?

EDIT: I'm currently making a model in 3D Wings.

 

[K_Jameson]

I'm using anim8or.

---------- Post added at 10:52 AM ---------- Previous post was at 06:49 AM ----------

I started to work on the mesh of my aerocapture probe. With various project already done (at least on the modeling side), I have a pretty large database of mesh elements that can be quickly reused, reducing drastically the drawing time. For example, the high gain umbrella-like antenna of this new probe is mounted on top of an articulated arm that is exactly a scaled up version of the "direct sampling mast" of the Salviati europa lander, developed for the Galileo II mission.

The new probe is slightly smaller than Shakespeare/Pope and will be enclosed in a lifting-body aeroshell similar to this:

but without the SEP stage and the atmospheric subprobes.

The provisional list of the instruments is: Visual and near infrared mapping spectrometer, mapping camera, laser altimeter, subsurface radar, magnetometers, neutron and gamma ray spectrometer.
The same concept can be used in first istance for Titan and used as dress rehearsal for the Neptune/Triton mission, although the conditions are much different and far less severe. The Titan variant can have a lighter aeroshell, saving weight for additional instruments as a neutral mass spectrometer/gas chromatograph, crucial for sampling the moon's atmosphere (for Titan, the gamma ray/neutron instrument is useless and will be removed).

Maybe, this evening i can produce some screenshots.

 

[Nicholander]

Interesting! I like your aerocapture probe idea. Anyway, I see that you're using anim8or, so is that easy to learn? (I'm currently trying to make my model in Wings 3D, so also, is Wings 3D a good choice for modelling stuff in Orbiter?)

 

[K_Jameson]

Interesting! I like your aerocapture probe idea.

The upper aeroshell can have inlets for atmospheric sampling (that requires a neutral mass spectrometer) and for temperature/pressure sensing. These measurements can be performed during the aerocapture maneuvre and the data stored on the spacecraft for subsequent transmission, when the main 4.3 meters antenna is deployed.

Anyway, I see that you're using anim8or, so is that easy to learn? (I'm currently trying to make my model in Wings 3D, so also, is Wings 3D a good choice for modelling stuff in Orbiter?)

IMHO, is pretty easy. In FOI all the spacecrafts are drawed with Anim8or, except for the internals (Vittorio, our interior designer, use a different program).
I don't know Wings 3D...

 

[Nicholander]

Cool! I can't wait to the afternoon to see those images! Anyway, I'm still working on the cruise stage, hopefully the model will be finished by the tomorrow.

 

[K_Jameson]

An image of the raw model (antenna and magnetometer stowed):


Size comparison with Shakespeare (all antennas stowed on the two models):


The required aeroshell must have around 3 meters of diameter.

 

[Nicholander]

Looks fantastic K_Jameson! Anyway, I feel really stupid for this, but I figure can't out how to make the RTG panels, engine, and medium gain communications dish. I've tried, and I just can't figure it out. So, though I really hate to ask, could you quickly just add those 3 little things? I have the file, it's in 3ds format. (Anim8or can import 3ds files, right?). I also would like it if you could have 6 RTG panels. I'm really sorry to bug you, but judging from that you managed to make the Neptune orbiter mesh is less than a day, I think you can do it. Here's the file: https://www.mediafire.com/?vij5oap2rwlqgbg

 

[K_Jameson]

Don't be fooled: that mesh is essentially made of parts already done in several other projects... for this motive I was able to make it so quickly. And needs other work.

I'll take a look to your mesh later this day.

---------- Post added at 05:14 PM ---------- Previous post was at 07:54 AM ----------

I'll take a look to your mesh later this day.

The 3ds appears empty!

---------- Post added at 06:17 PM ---------- Previous post was at 05:14 PM ----------

A conceptual image of the Neptune/Triton orbiter (Le Verrier) in flight configuration:



the large T-shaped antenna is the subsurface sounding radar, identical to the one mounted aboard the Galileo II spacecraft.

 

[Nicholander]

The 3ds appears empty!

WHAT!?!? When I tried importing the 3ds mesh I exported in Wings 3D, it was right there! Hmm... However, there are some options that Wings 3D brings up when you export to 3ds, these are them:

(Should I adjust them, perhaps? Maybe that will make it work)

In the mean time, I'll try exporting it with the "Export selected" tool, while selecting all the parts that make up the spacecraft.

EDIT: Here's the new 3ds file download link: https://www.mediafire.com/?vij5oap2rwlqgbg By the way, keep in mind that the whole thing is just 1.08 meters tall.

 

[K_Jameson]

OK, i have it. Tomorrow i'll add the antenna, the engine and the RTG.
The engine must be of the same type of the Shakespeare's one? Or less powerful?

 

[Nicholander]

Same type, as I don't think there's a way to increase the isp even with a smaller thrust engine. Also, include the micrometeorite protector on the engine.

 

[K_Jameson]

First hypothesis for the aeroshell:



the base diameter is 2.85 meters. Length around six meters.
I found that with the repositioning of RTGs and magnetometer boom, the size of the aeroshell can be reduced significantly.