Long-Distance Spacecraft Engineering *** Posted From Centauri Dreams

Posted: 30 Dec 2014 09:08 AM PST

I find few things more fascinating than remote fixes to distant spacecraft. We’ve used them surprisingly often, an outstanding case in point being the Galileo mission to Jupiter, launched in 1989. The failure of the craft’s high-gain antenna demanded that controllers maximize what they had left, using the low-gain antenna along with data compression and receiver upgrades on Earth to perform outstanding science. Galileo’s four-track tape recorder, critical for storing data for later playback, also caused problems that required study and intervention from the ground.

But as we saw yesterday, Galileo was hardly the first spacecraft to run into difficulties. The K2 mission, reviving Kepler by using sophisticated computer algorithms and photon pressure from the Sun, is a story in progress, with the discovery of super-Earth HIP 116454 b its first success. Or think all the way back to Mariner 10, launched in 1973 and afflicted with problems including flaking paint that caused its star-tracker to lose its lock on the guide star Canopus. The result: A long roll that burned hydrazine as thrusters tried to compensate for the motion. Controllers were able to use the pressure of solar photons on the spacecraft’s solar panels to create the torque necessary to counter the roll and re-acquire the necessary control.

The Messenger spacecraft also used pressure from solar photons as part of needed course adjustment on the way to Mercury, and now comes news of yet another inspired fix involving the same craft. Messenger was on course to impact Mercury’s surface by the end of March, 2015, having in the course of its four years in Mercury orbit (and six previous years enroute) used up most of its propellant. But controllers will now use pressurization gas in the spacecraft’s propulsion system to raise Messenger’s orbit enough to allow another month of operation.

The helium in question was used to pressurize the propellant tanks aboard the spacecraft. Let me quote Stewart Bushman (JHU/APL), lead propulsion engineer for the mission, on just what is going on here:

“The team continues to find inventive ways to keep MESSENGER going, all while providing an unprecedented vantage point for studying Mercury. To my knowledge this is the first time that helium pressurant has been intentionally used as a cold-gas propellant through hydrazine thrusters. These engines are not optimized to use pressurized gas as a propellant source. They have flow restrictors and orifices for hydrazine that reduce the feed pressure, hampering performance compared with actual cold-gas engines, which are little more than valves with a nozzle.”

Bushman adds that stretching propellant use is not the norm:

“Propellant, though a consumable, is usually not the limiting life factor on a spacecraft, as generally something else goes wrong first. As such, we had to become creative with what we had available. Helium, with its low atomic weight, is preferred as a pressurant because it’s light, but rarely as a cold gas propellant, because its low mass doesn’t get you much bang for your buck.”

MESSENGER_Year_Review

Image: A compilation of Messenger images from Mercury in 2014. Next April, Messenger’s operational mission will come to an end, as the spacecraft depletes its fuel and impacts the surface. However, the last few months of operations should be rich, including science data obtained closer to the planet’s surface than ever previously accomplished. Credit: JHU/APL.

So we gain an extra month to add to Messenger’s already impressive data on the closest planet to the Sun. The spacecraft’s most recent studies, begun this past summer, have involved a low altitude observation campaign looking for volcanic flow fronts, small scale tectonic effects, layering in crater walls and other features explained in this JHU/APL news release. Growing out of this effort will be the highest resolution images ever obtained of Mercury’s surface.

The additional month of operations will allow a closer look at Mercury’s magnetic field. “During the additional period of operations, up to four weeks, MESSENGER will measure variations in Mercury’s internal magnetic field at shorter horizontal scales than ever before, scales comparable to the anticipated periapsis altitude between 7 km and 15 km above the planetary surface,” says APL’s Haje Korth, the instrument scientist for the Magnetometer. Korth also says that at these lower altitudes, Messenger’s Neutron Spectrometer will be able to resolve water ice deposits inside individual impact craters at the high northern latitudes of the planet.

That’s a useful outcome and it grows out of sheer ingenuity in using existing resources. What’s fascinating in all these stories is that when we send a spacecraft out, we have frozen its technology level while our own continues to expand and accelerate. Think of the Voyagers, still operational after their 1977 launches, and imagine the kind of components we would use to build them today. The trick in resolving spacecraft problems and extending their missions is to keep the interface between our latest technology and their older tools as robust as possible. That involves, it’s clear, not just hardware and software, but the power of the human imagination.

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2014 in review

Writing Is Hard Work

The WordPress.com stats helper monkeys prepared a 2014 annual report for this blog.  I didn’t do half bad!

Here’s an excerpt:

The Louvre Museum has 8.5 million visitors per year. This blog was viewed about 100,000 times in 2014. If it were an exhibit at the Louvre Museum, it would take about 4 days for that many people to see it.

Click here to see the complete report.

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Put it in writing and kick butt in 2015

Live to Write - Write to Live

A New Year is just around the corner.

happy New Year hat 4I do for the upcoming year what I also do for my birthdays. I don’t set resolutions, instead I set life goals. I write down what I want to work on and see accomplished in the next 12 months. New Year’s isn’t a time for me to party as much as it is a time for reflection.

First, I start with general goals grouped into categories under:

  • Health/Fitness
  • Career
  • Fun/Hobbies
  • Home

Then I identify major goals in each category. For example, in the career category, I am going to focus my writing on parenting this year. (Don’t worry, I’ll still write about my chickens.) I plan on pitching articles to, and writing for, national parenting magazines.

I also have *two* manuscripts that need to get brushed off, spiffed up and sent out for review. Enough is enough. Time to kick those little…

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Character Interview Number Twenty-Three Ronan – Shifter

Library of Erana

Tell Us About Yourself

Name (s) Ronan

Age: I appear to be about twenty five.

I live primarily in the Atlantic ocean, but roam extensively as a shape shifter. I make frequent visits to Ireland as I have a deep appreciation for the landscape. As a shifter and a creature of the water, I realize I can be very fickle. I don’t think this hurts the people around me, I think they just need to accept it.

Do you have a moral code? If so what is it? I often come across to humans as having no morals at all, but that’s just not true. Just because I don’t share human morals doesn’t mean I have none.

Would you kill for those you love? I wouldn’t be opposed to it.

Would you die for those you love? Probably not, but who knows? My moods and feelings can change quite drastically.

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Winter’s Frost

Chronic Conditions & Life Lessons

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Stepping into the black of frosty night fingers lose warm mittens

Calling me hither to view magic sights more to see tomorrow will be

A yawn before dawn, God’s breath blankets all with freezing air

Below the moon of white glowing above so high and bright

There lies a patio table covered for winter with a frozen top

Patterns glisten in blinking lights below inky skies above

Where air stops to rest on camel-colored cloth

Stand back to get a better view

Snowflakes sparkle upon a frozen surface leaving

Speckled dust of diamonds shaved and carved to perfection

Diminutive sizes mirroring heads of straight pins in shining silver

Once draping fabric folds to dance within windy music stiffen to the touch

Brushing along one side, an unusual sound is heard

Kind of crunching, more of moaning, not quite frozen.

Morning light with sky of blue begins anew

Frost is sprinkled like powdered sugar everywhere

Wrought iron…

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2014 in review

Xao Thao

The WordPress.com stats helper monkeys prepared a 2014 annual report for this blog.

Here’s an excerpt:

A San Francisco cable car holds 60 people. This blog was viewed about 660 times in 2014. If it were a cable car, it would take about 11 trips to carry that many people.

Click here to see the complete report.

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