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To the question

Hagoromo was a ~36cm nano satellite that was deployed by Hiten while Hiten was in a highly elliptical orbit around the earth, in 1990.

From there, Hagoromo was able to enter into an orbit around the moon. Also see this question and any answers that may be there.

How was this done exactly? Was it purely ballistic capture (which still requires a tiny amount of thrust I think?) or more of a propulsive maneuver to enter into a lunar orbit?

What kind of propulsion and attitude control (if any) did Hagoromo actually have?

the answer is:

From the NASA Space Science Data Coordinated Archive entry on Hagoromo,

A solid propellant (KM-L) retrorocket with a mass of 4 kg was mounted inside the spacecraft for orbit insertion.

Question: How could a tiny 36 cm nanosatellite with a 4 kg solid propellant rocket inside maintain attitude control throughout the burn in order execute an orbital insertion?

enter image description here enter image description here

above left: from http://usi.kir.jp/CIA/ISAS/USI_cia_DS.html - models (presumably) of Hagoromo sitting on top of Hiten. right: from Gunter's Space Page Muses A (Hiten)

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Looking at the pictures of Hiten and Hagoromo on Gunter's Space Pages, it appears that the subsatellite was positioned along the central axis of the mothership. According to the same source, Hiten was spin-stabilized at 10-20 rpm.

I assume that Hagoromo was released while Hiten was spun-up, so it would have the same spin-stabilization. Since the burn would likely be short, and the resulting orbital parameters probably not that critical, no additional attitude control would be required.

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  • $\begingroup$ I've added two photos for reference. It's about 1/3 the radius, I don't know if that matters or not. I assume powered flight puts a lot more demands on gyroscopic stabilization than just floating idle in space, things can happen quick with such a tiny craft. It must have been very balanced and a good quality solid rocket motor. $\endgroup$
    – uhoh
    Commented Jan 7, 2019 at 7:36
  • $\begingroup$ From here Hiten was ~197 kg, Hagoromo ~ 11kg and I think that includes the 4 kg of solid propellant. Not sure if what's good for the goose is good for the gander (was that spin rate sufficient for 1/3 diameter 1/20 mass) under propulsion?) i.sstatic.net/Hi65x.jpg There may be something in this PDF but I can't even select the text properly to paste into a translator isas.jaxa.jp/j/isasnews/backnumber/1994/ISASnews154.pdf it grabs only clusters of characters then skips some. $\endgroup$
    – uhoh
    Commented Jan 7, 2019 at 8:00
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    $\begingroup$ @uhoh - along with the gyroscopic effects spinning also gives stability to solid rocket burns by rotating any off axis forces. As long as you are spinning fast enough that the force does not tumble you completely in one rotation the off axis forces (hopefully) cancel out and are only a problem due to the energy they wasted and the residual from the last turn. So an interesting question here is how many 3-6 second rotation periods the burn took. $\endgroup$
    – GremlinWranger
    Commented Jan 7, 2019 at 8:42
  • $\begingroup$ @GremlinWranger I am angular momentum-illiterate so while I'm imaging that a craft with thrust pointing slightly off the CM will go instantly bonkers, perhaps that's not the right way to think about it. I hope to ask a separate question on this, but will have to think about it a few days. $\endgroup$
    – uhoh
    Commented Jan 7, 2019 at 8:54
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    $\begingroup$ @uhoh - Will admit to being cautious on this - it certainly works in Kerbal space program to deal with the results of computational rounding or design errors producing asymmetric mass but KSP is only a vague approximation of reality. $\endgroup$
    – GremlinWranger
    Commented Jan 7, 2019 at 9:14

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