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View Full Version : How does spacecraft sleep for 9 years, then awake ?


davida03801
12-02-2014, 06:47 AM
Headline from ABC news today that I just read:
Spacecraft Bound for Pluto Set to Awake Nine Years After Launch
Per this news article this craft has been napping for periods of 36 to 202 days all this time, and checking in once a week also.
Just how do they do that ?

Captain Amazing
12-02-2014, 06:57 AM
They turn it off and then back on.

Isilder
12-02-2014, 07:03 AM
Headline from ABC news today that I just read:
Spacecraft Bound for Pluto Set to Awake Nine Years After Launch
Per this news article this craft has been napping for periods of 36 to 202 days all this time, and checking in once a week also.
Just how do they do that ?


The minimal amount that would have to be powered on would be an alarm clock. The alarm would then trigger a relay that turns on the main computer...


But that doesn't make a lot of sense, probably the main computer can be in low power mode but running all the time, and they are messing around with what sleep means... They just meant they let it follow trajectory and had no reason to use any instruments or anything.

Grey
12-02-2014, 08:02 AM
The New Horizons is powered by an RTG giving off between 250 to 200W of power. Now you're getting that energy whether you want it or not so hibernation mode, where instruments are powered down, and communitcaion is minimal, is primarily about extending instrument life. It also means you don't have to have the Deep Space Network receiving continual streams of empty data.

Hail Ants
12-02-2014, 08:53 AM
The New Horizons is powered by an RTG giving off between 250 to 200W of power. Now you're getting that energy whether you want it or not so hibernation mode, where instruments are powered down, and communitcaion is minimal, is primarily about extending instrument life. It also means you don't have to have the Deep Space Network receiving continual streams of empty data.An RTG by the way is a radioisotope thermoelectric generator (https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator) (otherwise know as a nuclear battery)...

Xema
12-02-2014, 09:39 AM
In the context of electronics, 'sleep' has no precise meaning. It has the general sense of a state in which only a small subset of the full set of functions are powered up. One that obviously must be included is a clock that can tell when next to 'wake up'.

Chronos
12-02-2014, 10:04 AM
More to the point about RTGs, you can't just "turn them off". Once they're made, they're decaying, no matter what you do. Now, the probe probably also has batteries that it can use when it's doing its really power-intensive functions, and those are probably being trickle-charged from the RTG right now, but not being drawn from. So "awake" might just mean "drawing from batteries".

Nanoda
12-04-2014, 02:17 AM
There's a decent chance your desktop computer can do pretty much all that *right now*. A few desktops at our office can be programmed to turn on at a certain time (never use it, but I know it's there). Alternately, holding down the spacebar or sending a properly formatted ethernet packet to your network card (which you'll note has flashing lights even when your PC is "off") will turn it on.

Once turned on, your monitor kicks in shortly afterwards... you can optionally turn on your webcam without touching it, or print a document and have your printer wake up. If they're even slightly mid-range and made in the last 5 years, you can probably turn on your TV and sound system from your PC too.

Smeghead
12-04-2014, 06:43 AM
It also means you don't have to have the Deep Space Network receiving continual streams of empty data.

"It's still dark. And cold."

kanicbird
12-04-2014, 08:50 AM
For landers/rovers it does seem possible for them to go totally off (as the batteries run down) and they have the capability to restart themselves when light is restored to the solar array. At least the mission controllers always seem hopeful that this will happen (but it also seems like it usually does not).

So in this case is really totally 'off' or does it have some watch battery somewhere that keeps just enough alive to have it restart?

Grey
12-04-2014, 09:25 AM
New Horizon transmits back to earth it's current state, its RTG is continually providing heat and electricity but most of the instruments are powered down.

http://pluto.jhuapl.edu/news_center/news/20141113.php

In hibernation mode much of the spacecraft is unpowered; the onboard flight computer monitors system health and broadcasts a weekly beacon-status tone back to Earth. On average, operators woke New Horizons just over twice each year to check out critical systems, calibrate instruments, gather science data, rehearse Pluto-encounter activities and perform course corrections when necessary.

New Horizons pioneered routine cruise-flight hibernation for NASA. Not only has hibernation reduced wear and tear on the spacecraft’s electronics, it lowered operations costs and freed up NASA Deep Space Network tracking and communication resources for other missions.

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