Construction of the Space probe for NASA's Psyche Mission

[ccdengr]

I mean this linkage next to the Hall-effect thruster.

The thrusters are on gimbals.  See https://theory.pppl.gov/news/Psyche%20talk%20Goebel_June2023.pdf slide 36.

[roma847]

Thanks for this interesting JPL PDF.

Okay, this means that the Hall thruster is mounted on gimbals. But that's not the lateral mount next to the thruster which I mean, or are these the gimbals?

In its working position the thruster is aligned vertically, as one can see in the video, which however differs from the laterally folded position in the photo.

[roma847]

Hello everybody,

in this Official NASA Broadcast video one can see the moment the Psyche space probe is separated from the Falcon 9 rocket. One can clearly see that the thrusters on both sides are not yet in operation and are therefore locked onto the lateral linkage.



This position is only left when the thrusters are to be put into operation and are swung out by the gimbals. I can't imagine any other explanation.

Maybe I'll still try to contact and ask Lead Systems Engineer David Oh.

[roma847]

Hello everybody,

it is probably just a question of the limited space in the Falcon 9's Payload fairing – the cone at the top of the rocket,


Source: flickr.com

which is why the thrusters have to be folded in, as one can also see in the following image, and are only unfolded after separation. Maybe I'll still figure out if this linkage is only a mounting, which is what I suspect.


Source: Jet Propulsion Laboratory (David Oh)

Regardless of this, the blanketing of the probe with the insulating blankets continues, where today it was the turn of the back, on which there are not as many details as was already seen in the last post.



In addition to the X-Band Low Gain Antenna and the two Multispectral Imagers, which should be comparatively easier to scratch-build, the two complex Hall-effect Thrusters (SPT-140) are far more difficult details, as can easily be seen in this true-scaled NASA model.



In contrast, this is a highly simplified model representation that could serve as inspiration for the later Scratch-build construction.


Source: psyche.asu.edu

But first, the insulating blanket for the back, which I have already prepared from crumpled aluminum foil, into whose small recess on the underside the finished Thruster will later be glued. To mark the other parts, I again created several 1:1 templates of the back in MS Word in the tried and tested way.



To ensure that nothing can slip when marking the attachment points of the parts, the aluminum foil was first fixed,



then the template was placed exactly on top of it and also fixed in place. Then I used pins to mark the points on which the X-Band Low Gain Antenna and the two Multispectral Imagers should sit.



After removing the template, the piercing points are clearly visible in the foil.



The bottom three points belong to this leverage next to the Thruster, which has been discussed so far, but which I did not want to simply leave out.





For better visibility, I inserted short round rods into the piercing points.



I've still  postponed gluing the blanket to the back of the probe for a while, because I had considered not leaving the previously 'bare' backs of the solar panels as they were so far, but also refining them with a solar panel structure.



The paper kit only provided gray panels for this, but which does not correspond to the original and I therefore do not like it.



More on the solution to the problem in the next post.

[ccdengr]

I'm 98% certain that the structures you are asking about support the Hall thruster gimbals during launch vibration.  See https://www.flickr.com/photos/nasakennedy/53213102534/in/album-72177720298576586/ and https://www.flickr.com/photos/nasakennedy/53213229385/in/album-72177720298576586/ though the view is partially blocked by the red remove-before-flight covers on the thrusters.

The gimbals aren't to save space but to correctly point the thrusters through the center of mass of the spacecraft, see https://electricrocket.org/2019/192.pdf

[roma847]

Thanks for your reply.

I have now looked into the subject a little more closely and was able to clarify some terms and abbreviations for my better understanding.

Abbreviations are all well and good if you know what they mean, so that we don't compare apples with oranges.

So now I know that SPT means Stationary Plasma Thrusters.

And these SPT are on a Dual Axis Positioning Mechanism (DAPM), and together they make a DSM, or DAPM-Actuated SPT Module.

This is what I've learned from this great NASA photo NASA's Psyche DAPM Deployment and Stow for Launch,


Source: NASA (Kim Shiflett, 2023-08-04)

Because I was, as usual, very interested in such technical details, I continued searching and came across this interesting NASA Video, that goes with this photo, which shows very clearly and slowly how this DAPM-Actuated SPT Module can be moved,

what I've marked in this image by red arrows.



The movement starts at 4:25 and ends after 4:51, whereby in this image one can see, in my opinion, the two location points of the holding device for locking the SPT Module in the folded state.



BTW, I've read the linked article but found no references to your information regarding "... to correctly point the thrusters through the center of mass of the spacecraft, ..." But maybe I've missed the part.

Finally, a nice comparison.

During my further research I came across another great Psyche Video, in which Professor Linda Elkins-Tanton (ASU) has compared the white Thruster DAPM with a white arm:



"The arm has an elbow and a shoulder, so you can move the thrusters in any way that you want relative to the spacecraft." 

[ccdengr]

BTW, I've read the linked article but found no references to your information regarding "... to correctly point the thrusters through the center of mass of the spacecraft, ..." But maybe I've missed the part.

Unlike Deep Space 1 and Dawn, which used the EP gimbals for direct attitude control of two axes while the EP
thruster is operating, the Psyche GN&C uses RWAs for full 3-axis control even while thrusting.  GN&C performs
nominal RWA unloading and momentum control using torques generated by the EP system. The approach is similar
to that used for Maxar's GEO communications satellites. The RWAs provide 3-axis control of the spacecraft attitude
while a low-bandwidth momentum control algorithm positions the EP gimbal to direct the thrust vector near the
vehicle center of mass. Small offsets to the EP thrust vector produce torques that allow near continuous unloading of
two transverse axes of RWA momentum.

I think I ran across a variety of other more detailed references about the Psyche Hall thrusters, but I'll leave you to track those down if you care.

[roma847]

It seems we are talking past each other.

That's why it's enough for me to now know how the main components of the Thrusters are constructed and how they can be moved by the DAPM during being unfolded. And only this unfolded state of the SPTs is what I'll try to scratch-build, after all, they are not supposed to work.

And these special mountings next to it only serves to securely lock the SPTs in the folded position, as one can see in the photos and videos.