I saw the following sentence in The Space Review, and became intrigued:

Japan’s Hagoromo lunar orbiter, deployed in 1990, reached orbit but ceased transmitting enroute.

If it ceasted transmitting en-route, how did they know it reached orbit? Usually we know where things are by monitoring the doppler profile of their broadcasts (or re-broadcasts), or they simply tell us where they think they are themselves.

Radar maybe? But I learned here that optical detection tends to win at larger distances, since sunlight gives you a kilowatt per square meter to start with.

After googling and wikipedia-ing, I read in Wikipedia's Hiten article:

On the first lunar swing-by, Hiten released a small orbiter, Hagoromo (はごろも, named after the feather mantle of Hiten), into lunar orbit. The transmitter on Hagoromo failed, but its orbit was visually confirmed from Earth.

Is there any documentation of how this "visual confirmation" was actually done? Was there someone who was actually visually looking through a giant telescope and saw this 36 cm diameter precocious nano satellite orbiting the moon about 36 billion centimeters away and shouted "Yep! I see it!" in Japanese, or English, or whichever language they use when they spot a tiny satellite in orbit around the another celestial body?

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above: from Gunter's Space Page

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above: from Jaxa hitorical photos (found by googling "はごろも JAXA"). Hagoromo is the little one on the left, deployed for capture into lunar orbit from Hiten on the right as it passed near the moon in its highly elongated orbit around the earth - quite a cool robotic maneuver for a nano satellite in 1990 (and that's only the beginning of Hiten's story.)

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above: from http://usi.kir.jp/CIA/ISAS/USI_cia_DS.html - models (presumably) of Hagoromo sitting on top of Hiten.


1 Answer 1


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

The ignition of the Hagoromo deceleration rocket was confirmed by ground observation at 20:04:03 UT.

From a few other sites, this was done at the Kiso Observatory in Japan using a 105 cm Schmidt camera. The satellite would have been ~22 magnitude and near the Moon, so hard to see -- except when it was firing its engine. Then it would have been considerably brighter than 22 magnitude.

  • $\begingroup$ Nice! By the way, that technique was first seen in January of 1967. Can you show where the value 22 magnitude comes from - I'm sure the links will be interesting to others besides me, unless you have a reason to withhold them because they are trade secrets or otherwise intellectual property. :-) $\endgroup$
    – uhoh
    Jul 19, 2016 at 7:29
  • $\begingroup$ Actually that link says "...an orbit of 7400 x 20000 km orbit with a period of 2.01 days was estimated, but never confirmed, so it is not known if Hagoromo actually entered lunar orbit." So to address my question, 1) was orbit actually confirmed ever, or not? 2) Was the light from the burn visually confirmed, visually being operative, or was it a measurement using vidicon, PMT, or a photographic plate? Inquiring minds want to know! $\endgroup$
    – uhoh
    Jul 19, 2016 at 10:20
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    $\begingroup$ @uhoh -- The full Moon is magnitude -12.6. The satellite was 40 cm across (diameter of 20 cm). Then it's Wolfram Alpha time . That assumes a low albedo for the satellite. An impossibly high albedo might decrease the magnitude to 21. $\endgroup$ Jul 19, 2016 at 15:03
  • $\begingroup$ @uhoh - I don't know the answer to your detailed questions. There's very little written on the internet Hiten / Hagoromo, and very little of it is in English. $\endgroup$ Jul 19, 2016 at 15:26
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    $\begingroup$ hmm... Here's a very contrived example; A very narrow-band optical transmission filter tuned to some tracer-metal emission line, put in front of a photomultiplier tube might detect a signal indicating solid propellant ignition. That could be called an optical detection, but not a visual detection. A vidicon showing a "dot" appear on a screen could be called visual. I seem to be really curious if there was ever an image, or if someone looked through a telescope and saw it and yelled "Yatta!", maybe that's what I should be asking! $\endgroup$
    – uhoh
    May 2, 2017 at 5:18

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