Silent Spirit … Long Winter Ahead

[/caption]The Mars rover Spirit has entered her long anticipated low power hibernation mode according to a statement released by NASA’s Jet Propulsion Laboratory late Wednesday (March 31). Spirit skipped her scheduled downlink on Sol 2218 (March 30, 2010) via the Ultra-High Frequency (UHF) relay through the Mars Odyssey orbiter from her location on the Martian surface at Gusev crater. No telemetry was received from Spirit and there was no evidence of a UHF signal.

“Well, we knew it was coming… in fact, I’m surprised it didn’t happen earlier”, Steve Squyres told me today, April 1. Squyres is the Chief Scientist for the Mars rover twins, Spirit and Opportunity.

“The vehicle is all tucked in and ready to hibernate, and we have high hopes that we’ll be back in business come springtime. But it’s gonna be a long winter,” Squyres added.

The team was anticipating Spirit to experience a low-power fault about this time due to declining energy production from the wing-like solar panels. As winter approaches in the Martian southern hemisphere, the daily quantity of sunlight impinging on the power producing panels declines daily.

Energy production from the solar arrays had dropped to only 134 watt-hours on March 22. So, the most likely explanation for the missing downlink is that Spirit did go into that low-power fault taking her batteries off-line, sometime between the last downlink on Sol 2210 (March 22, 2010), and Sol 2218 (March 30, 2010).

In hibernation mode, Spirits master clock keeps on ticking, but communications and other activities are suspended in order to channel all available energy into powering the critical survival heaters necessary to save the rovers electronics as well as to try to recharge the batteries and attempt to wake up. When the battery charge is adequate, the rover attempts to wake up and communicate on a schedule it knows.

“Components within the rover electronic module (REM) inside the rover’s warm electronic box (WEB) are experiencing record low temperatures,” says Doug McCuistion, the director of Mars Exploration at NASA Headquarters in Washington, DC, in an interview about Spirit’s predicament. “So far, the coldest temperatures recorded within the REM by one reached a low temperature of -41.5 degrees Celsius (-42.7 degrees Fahrenheit)”. This occurred just prior to the loss in communications.

“The REM electronics rack is located inside the WEB and is about a half meter cube in size”, McCuistion told me. “The expectation is for the REM hardware to reach -55C at the coldest part of the winter. We have tested the REM down to -55C”.

“Spirit’s lowest power production during a single sol (so far) was during a dust storm in November of 2008. For that one sol, Spirit’s solar arrays produced only 89 watt-hours of energy,” McCuistion said.

“We may not hear from Spirit again for weeks or months, but we will be listening at every opportunity, and our expectation is that Spirit will resume communications when the batteries are sufficiently charged,” said John Callas of NASA’s Jet Propulsion Laboratory who is project manager for Spirit and Opportunity.

Spirit has been stuck at a place called ‘Troy’ since becoming mired in a sand trap of soft soil in April 2009. While driving on the western edge of ‘Home Plate’, she unknowingly broke through a hard surface crust (perhaps 1 cm thick) of water related sulfate materials and sank into hidden soft sand beneath. At Troy she made a great science discovery by finding evidence of the past flow of liquid water on the surface of Mars.

Earlier Mars articles by Ken Kremer:

Spirit Freezing; We Will Move Her if We Can

Spirit Hunkered Down for Winter; Stuck Forever ? Maybe Not !

Phoenix Still Silent as Martian Ice Recedes

If Phoenix Arises, Science could flow quickly

Mars 2016 Methane Orbiter: Searching for Signs of Life