Problems with attitude system doomed Hitomi
A series of failures in the attitude system on Japan’s X-ray space telescope Hitomi led to its destruction.
The problem started when the satellite’s inertial reference unit detected Hitomi was rotating around its Z-axis at 21.7 degrees per hour. The spacecraft was actually stable at the time, mission managers from the Japan Aerospace Exploration Agency said Friday. The satellite’s attitude control system commanded Hitomi’s reaction wheels, rapidly-spinning devices which control the pointing of the spacecraft with momentum, to counteract the spin. The action caused the satellite to rotate in the opposite direction as the faulty inertial reference unit indicated, officials said. Momentum accumulated inside the reaction wheel system, and magnetic torquers aboard the satellite were unable to unload the building momentum, which neared the reaction wheels’ design limit.
Hitomi’s computers recognized the dangerous situation and put the satellite into safe hold a few hours later. The satellite tried to stabilize using the craft’s hydrazine-fueled rocket thrusters to aim its solar panels toward the sun. But the trouble was not over, and the spacecraft’s solar sensor was unable to find the sun. Struggling to correct the growing spin rate, small rocket firings inadvertently caused Hitomi to rotate faster due to a bad setting in the thruster system, JAXA officials said.
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A series of failures in the attitude system on Japan’s X-ray space telescope Hitomi led to its destruction.
The problem started when the satellite’s inertial reference unit detected Hitomi was rotating around its Z-axis at 21.7 degrees per hour. The spacecraft was actually stable at the time, mission managers from the Japan Aerospace Exploration Agency said Friday. The satellite’s attitude control system commanded Hitomi’s reaction wheels, rapidly-spinning devices which control the pointing of the spacecraft with momentum, to counteract the spin. The action caused the satellite to rotate in the opposite direction as the faulty inertial reference unit indicated, officials said. Momentum accumulated inside the reaction wheel system, and magnetic torquers aboard the satellite were unable to unload the building momentum, which neared the reaction wheels’ design limit.
Hitomi’s computers recognized the dangerous situation and put the satellite into safe hold a few hours later. The satellite tried to stabilize using the craft’s hydrazine-fueled rocket thrusters to aim its solar panels toward the sun. But the trouble was not over, and the spacecraft’s solar sensor was unable to find the sun. Struggling to correct the growing spin rate, small rocket firings inadvertently caused Hitomi to rotate faster due to a bad setting in the thruster system, JAXA officials said.
Readers!
My annual February birthday fund-raising drive for Behind the Black is now over. Thank you to everyone who donated or subscribed. While not a record-setter, the donations were more than sufficient and slightly above average.
As I have said many times before, I can’t express what it means to me to get such support, especially as no one is required to pay anything to read my work. Thank you all again!
For those readers who like my work here at Behind the Black and haven't contributed so far, please consider donating or subscribing. My analysis of space, politics, and culture, taken from the perspective of an historian, is almost always on the money and ahead of the game. For example, in 2020 I correctly predicted that the COVID panic was unnecessary, that the virus was apparently simply a variation of the flu, that masks were not simply pointless but if worn incorrectly were a health threat, that the lockdowns were a disaster and did nothing to stop the spread of COVID. Every one of those 2020 conclusions has turned out right.
Your help allows me to do this kind of intelligent analysis. I take no advertising or sponsors, so my reporting isn't influenced by donations by established space or drug companies. Instead, I rely entirely on donations and subscriptions from my readers, which gives me the freedom to write what I think, unencumbered by outside influences.
You can support me either by giving a one-time contribution or a regular subscription. There are four ways of doing so:
1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.
2. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.
3. A Paypal Donation or subscription:
4. Donate by check, payable to Robert Zimmerman and mailed to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652
You can also support me by buying one of my books, as noted in the boxes interspersed throughout the webpage or shown in the menu above.
http://www.space.com/32630-japan-hitomi-satellite-science-data.html