Update: The IKAROS team has not confirmed full deployment of the sail, but does indicate we’ll have an update tomorrow.

The IKAROS solar sail is partially deployed but the complete deployment was delayed while the mission’s engineers tried to figure out why the spacecraft’s spin rate has been increasing. JAXA’s updates are in Japanese, but the Planetary Society’s Emily Lakdawalla seems to be more skilled at untangling Google Translate than I am and has also used a translation from a user on the excellent unmannedspaceflight.com site to come up with IKAROS details. Thus we learn that the sail is currently deployed about five meters. A new update just in from JAXA points to an attempt at full sail deployment just a few hours from now. This video shows the process at work.

From what JAXA says, there is no danger to the spacecraft from the increased spin rate, but the pause in deployment arose simply because the team wanted to pin down an explanation for the behavior before proceeding. I suspect we’re going to run into many a mystery like this one as we get solar sails shaken out on actual missions. The push of solar photons may account for the spin, or we could be looking at the interesting phenomenon of outgassing of sail materials. You may remember that James and Gregory Benford have studied sail outgassing and pondered using such effects for directed propulsion in future sails.

The difference here is that the IKAROS team has evidently not expected this outgassing, if that is what is causing the spin changes, and has been understandably cautious with IKAROS before proceeding to final deployment. The last reported spin rate I’ve seen seems to be a stable 7.4 rotations per minute. This morning, a new post on the IKAROS blog refers to full expansion of the sail scheduled for June 8, listing the event at ‘evening-midnight’ JST, which would make it no later than late morning EST or mid-afternoon UTC today.

ADDENDUM: My mistake. The full expansion the IKAROS blog talks about seems to refer to full extension of the boom structure. JAXA calls this ‘primary development,’ as opposed to the ‘secondary development,’ which is release of the sail material itself. The latter now seems to be scheduled for June 9 — more tomorrow.

Translating IKAROS Tweets

At the same time, the IKAROS team has been sending out tweets in Japanese which Centauri Dreams reader Lionel Ward has been kind enough to translate. Lionel is an amazing linguist, much better than Google Translate. I won’t reproduce all of these, but some of the more recent ones are quite interesting, and you’ll note that some come via the AKATSUKI Venus orbiter team. The times listed are off by about twelve hours, as Lionel passed these along last night:

IKARUSKUN about 13 hours ago
I’m doing fine. I’m having my distance measured (ranging)

about 12 hours ago via web
AKATSUKI: From the Sagamihara control room: Akatsuki is continuating on a steady course towards Venus. At the same time, Akutsuki will from here on be preparing for observations and experiments. During the 3 weeks spanning last week to next week, the ??? (Positioning System?) team has the main role.

about 12 hours ago
AKATSUKI: There is a very slight force being felt from sunbreams, however it will gradually build up and lead to a negative effect upon Akatsuki’s posture (interference/noise). Hence a position which will incur minimal force from sunlight pressure is being searched for.

about 11 hours ago
IKARUSKUN @Akatsuki_JAXA Akatsuki, you are feeling the effects of sunbeams! I wonder if I am

about 11 hours ago
AKATSUKI @ikaroskun
Yes indeed! There is apparently influence upon me from the Sun’s rays. Perhaps you may also be starting to be influenced by the Sun too Ikaros-kun. Once you’ve completely opened your sails, you’ll ride along upon the sun rays! How wonderful…

about 10 hours ago
IKARUSKUN @Akatsuki_JAXA Yes, because my sails are extended into a cross shape, the sunbeams are hitting me and warming me up! The Sagamihara Centre is checking whether it’s caused by the sunbeams or not

about 10 hours ago
IKARUSKUN I’m about 6.7 million km from Earth. And I’m separated from my big brother Hayabusa too…

about 8 hours ago via web
IKARUSKUN Usuda Centre has gone out of view to the opposite side [of earth]. Today we spoke together lots.

about 8 hours ago
IKARUSKUN @Hayabusa_JAXA Yeah, I’m doing well, and trusting in what I’ve been told from Earth, and trying my hardest!

The first-person informality is fun, and Lionel tells me that the ‘kun’ in IKAROS-kun is an affectionate suffix that older people use when calling boys by their names. Let’s hope the sense of good humor persists as the IKAROS team works through the potentially tricky deployment. This is in many ways the most dangerous part of any sail mission, for you’re dealing with remarkably thin films on the one hand (the sail itself) and a structure of spars and struts needed to get the sail into position. What a relief it will be when this is done and we start getting data from an operational sail!