DJ
David J Taylor
Fri, Sep 20, 2013 4:50 PM
NASA's Deep Space Comet Hunter Mission Comes to an end
The news release includes this paragraph:
"After losing contact with the spacecraft last month, mission
controllers spent several weeks trying to uplink commands to reactivate its
onboard systems. Although the exact cause of the loss is not known,
analysis has
uncovered a potential problem with computer time tagging that could have led
to loss of control for Deep Impact's orientation. That would then affect
the positioning of its radio antennas, making communication difficult, as
well as its solar arrays, which would in turn prevent the spacecraft from
getting power and allow cold temperatures to ruin onboard equipment,
essentially freezing its battery and propulsion systems."
Knowing the membership of this group, does anyone have more insight into
what the "computer time tagging" problem might be?
Thanks,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
NASA's Deep Space Comet Hunter Mission Comes to an end
The news release includes this paragraph:
"After losing contact with the spacecraft last month, mission
controllers spent several weeks trying to uplink commands to reactivate its
onboard systems. Although the exact cause of the loss is not known,
analysis has
uncovered a potential problem with computer time tagging that could have led
to loss of control for Deep Impact's orientation. That would then affect
the positioning of its radio antennas, making communication difficult, as
well as its solar arrays, which would in turn prevent the spacecraft from
getting power and allow cold temperatures to ruin onboard equipment,
essentially freezing its battery and propulsion systems."
Knowing the membership of this group, does anyone have more insight into
what the "computer time tagging" problem might be?
Thanks,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
MC
Mark C. Stephens
Fri, Sep 20, 2013 11:47 PM
Winders?
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of David J Taylor
Sent: Saturday, 21 September 2013 2:51 AM
To: Time-nuts mailing list
Subject: [time-nuts] Space mission comes to an end becuase of a "computer time tagging" problem
NASA's Deep Space Comet Hunter Mission Comes to an end
The news release includes this paragraph:
"After losing contact with the spacecraft last month, mission controllers spent several weeks trying to uplink commands to reactivate its onboard systems. Although the exact cause of the loss is not known, analysis has uncovered a potential problem with computer time tagging that could have led to loss of control for Deep Impact's orientation. That would then affect the positioning of its radio antennas, making communication difficult, as well as its solar arrays, which would in turn prevent the spacecraft from getting power and allow cold temperatures to ruin onboard equipment, essentially freezing its battery and propulsion systems."
Knowing the membership of this group, does anyone have more insight into what the "computer time tagging" problem might be?
Thanks,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Winders?
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of David J Taylor
Sent: Saturday, 21 September 2013 2:51 AM
To: Time-nuts mailing list
Subject: [time-nuts] Space mission comes to an end becuase of a "computer time tagging" problem
NASA's Deep Space Comet Hunter Mission Comes to an end
The news release includes this paragraph:
"After losing contact with the spacecraft last month, mission controllers spent several weeks trying to uplink commands to reactivate its onboard systems. Although the exact cause of the loss is not known, analysis has uncovered a potential problem with computer time tagging that could have led to loss of control for Deep Impact's orientation. That would then affect the positioning of its radio antennas, making communication difficult, as well as its solar arrays, which would in turn prevent the spacecraft from getting power and allow cold temperatures to ruin onboard equipment, essentially freezing its battery and propulsion systems."
Knowing the membership of this group, does anyone have more insight into what the "computer time tagging" problem might be?
Thanks,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
BC
Bob Camp
Sat, Sep 21, 2013 12:12 AM
Hi
Low bid wrist watch used as time base?
I'd bet there is some form of master time tick in their RTOS that keeps everything pumping. Loose the time tick (or the time tick count) and it all goes away…
As the onboard computers accumulate radiation induced faults, there's a lot of software patching that goes on to map around the faulty sections. They may have done one to may patches.
Bob
On Sep 20, 2013, at 7:47 PM, Mark C. Stephens marks@non-stop.com.au wrote:
Winders?
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of David J Taylor
Sent: Saturday, 21 September 2013 2:51 AM
To: Time-nuts mailing list
Subject: [time-nuts] Space mission comes to an end becuase of a "computer time tagging" problem
NASA's Deep Space Comet Hunter Mission Comes to an end
The news release includes this paragraph:
"After losing contact with the spacecraft last month, mission controllers spent several weeks trying to uplink commands to reactivate its onboard systems. Although the exact cause of the loss is not known, analysis has uncovered a potential problem with computer time tagging that could have led to loss of control for Deep Impact's orientation. That would then affect the positioning of its radio antennas, making communication difficult, as well as its solar arrays, which would in turn prevent the spacecraft from getting power and allow cold temperatures to ruin onboard equipment, essentially freezing its battery and propulsion systems."
Knowing the membership of this group, does anyone have more insight into what the "computer time tagging" problem might be?
Thanks,
David
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
Low bid wrist watch used as time base?
---------------------------------
I'd bet there is some form of master time tick in their RTOS that keeps everything pumping. Loose the time tick (or the time tick count) and it all goes away…
As the onboard computers accumulate radiation induced faults, there's a lot of software patching that goes on to map around the faulty sections. They may have done one to may patches.
Bob
On Sep 20, 2013, at 7:47 PM, Mark C. Stephens <marks@non-stop.com.au> wrote:
> Winders?
>
> -----Original Message-----
> From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of David J Taylor
> Sent: Saturday, 21 September 2013 2:51 AM
> To: Time-nuts mailing list
> Subject: [time-nuts] Space mission comes to an end becuase of a "computer time tagging" problem
>
> NASA's Deep Space Comet Hunter Mission Comes to an end
>
> The news release includes this paragraph:
> "After losing contact with the spacecraft last month, mission controllers spent several weeks trying to uplink commands to reactivate its onboard systems. Although the exact cause of the loss is not known, analysis has uncovered a potential problem with computer time tagging that could have led to loss of control for Deep Impact's orientation. That would then affect the positioning of its radio antennas, making communication difficult, as well as its solar arrays, which would in turn prevent the spacecraft from getting power and allow cold temperatures to ruin onboard equipment, essentially freezing its battery and propulsion systems."
>
> Knowing the membership of this group, does anyone have more insight into what the "computer time tagging" problem might be?
>
> Thanks,
> David
> --
> SatSignal Software - Quality software written to your requirements
> Web: http://www.satsignal.eu
> Email: david-taylor@blueyonder.co.uk
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
JL
Jim Lux
Sat, Sep 21, 2013 11:45 AM
On 9/20/13 5:12 PM, Bob Camp wrote:
Hi
Low bid wrist watch used as time base?
I'd bet there is some form of master time tick in their RTOS that
keeps everything pumping. Loose the time tick (or the time tick
count) and it all goes away…
yes and no.
Most spacecraft have a default strategy if everything got reset, so they
don't need to know what time it is. They go into "safe hold" mode.
There's several steps in the strategy. If you have attitude knowledge,
you'll sun/earth point the high gain antenna and wait to hear from the
ground.
If you don't have attitude knowledge, you shift to the low gain omni
antenna, and wait to hear from the ground.
DSN cranks up the Tx power, and they transmit at a very low rate (10
bits/sec) to try and get a command in through the LGA.
If you've totally lost attitude control, and you're slowly rotating, you
still might not get a command it, because there's no such thing as a
truly omni antenna pattern: it has lumps and bumps and nulls.
However, unless there's no attitude control authority (e.g. if you have
wheels and they've failed, or you've run out of propellant), you don't
need to know the time to be able to stabilize the spacecraft in one
attitude. And once you're stabilized, you can get that command in.
So there's some other more complex problem.
As the onboard computers accumulate radiation induced faults, there's
a lot of software patching that goes on to map around the faulty
sections. They may have done one to may patches.
I don't think that is the case with DI. Radiation causes upsets, but
they're usually a transient thing, and rewriting the memory fixes it.
Most of the time it's using EDAC on the memory, and scrubbing.
One can send commands from the ground that will kill it accidentally.
Spacecraft have typically very simple command structures. A lot of
commands are basically "poke this value at this address" and with
knowledge on the ground of which control paramters are stored at which
addresses, you can build your commands. However, if you poke the wrong
address, or send the wrong value, you can command the spacecraft to do
something that is irrecoverable. One of the Mars spacecraft was lost
because of this.
People often ask "why doesn't it have range checking and validation on
the parameters". Well.. that would take more code, and memory is a
limited resource. And, it's not like there's a "command parser" in the
sense of a shell that interprets and validates commands. The spacecraft
checks the checksum on the received message, and does it.
This comes from a long history where spacecraft had very simple control
systems (no computer). You'd have a bunch of relays and the message
that comes up has a bit for each relay or control line. The "command
detector unit" sees the frame sync bit sequence and then just loads the
bits into a big register, and when the checksum is ok, it latches them
all in. It's much like how 1553 works. You assign each word or bit to
some actuator or sensor, and it's more like "remote memory access" than
actual commanding.
The whole process works the same on downlink. In fact, even though we
now use computers, it's still called "decommutation"
On 9/20/13 5:12 PM, Bob Camp wrote:
> Hi
>
> Low bid wrist watch used as time base?
>
> ---------------------------------
>
> I'd bet there is some form of master time tick in their RTOS that
> keeps everything pumping. Loose the time tick (or the time tick
> count) and it all goes away…
yes and no.
Most spacecraft have a default strategy if everything got reset, so they
don't need to know what time it is. They go into "safe hold" mode.
There's several steps in the strategy. If you have attitude knowledge,
you'll sun/earth point the high gain antenna and wait to hear from the
ground.
If you don't have attitude knowledge, you shift to the low gain omni
antenna, and wait to hear from the ground.
DSN cranks up the Tx power, and they transmit at a very low rate (10
bits/sec) to try and get a command in through the LGA.
If you've totally lost attitude control, and you're slowly rotating, you
still might not get a command it, because there's no such thing as a
truly omni antenna pattern: it has lumps and bumps and nulls.
However, unless there's no attitude control authority (e.g. if you have
wheels and they've failed, or you've run out of propellant), you don't
need to know the time to be able to stabilize the spacecraft in one
attitude. And once you're stabilized, you can get that command in.
So there's some other more complex problem.
>
> As the onboard computers accumulate radiation induced faults, there's
> a lot of software patching that goes on to map around the faulty
> sections. They may have done one to may patches.
I don't think that is the case with DI. Radiation causes upsets, but
they're usually a transient thing, and rewriting the memory fixes it.
Most of the time it's using EDAC on the memory, and scrubbing.
One can send commands from the ground that will kill it accidentally.
Spacecraft have typically very simple command structures. A lot of
commands are basically "poke this value at this address" and with
knowledge on the ground of which control paramters are stored at which
addresses, you can build your commands. However, if you poke the wrong
address, or send the wrong value, you can command the spacecraft to do
something that is irrecoverable. One of the Mars spacecraft was lost
because of this.
People often ask "why doesn't it have range checking and validation on
the parameters". Well.. that would take more code, and memory is a
limited resource. And, it's not like there's a "command parser" in the
sense of a shell that interprets and validates commands. The spacecraft
checks the checksum on the received message, and does it.
This comes from a long history where spacecraft had very simple control
systems (no computer). You'd have a bunch of relays and the message
that comes up has a bit for each relay or control line. The "command
detector unit" sees the frame sync bit sequence and then just loads the
bits into a big register, and when the checksum is ok, it latches them
all in. It's much like how 1553 works. You assign each word or bit to
some actuator or sensor, and it's more like "remote memory access" than
actual commanding.
The whole process works the same on downlink. In fact, even though we
now use computers, it's still called "decommutation"
>
> Bob
>
JL
Jim Lux
Sat, Sep 21, 2013 12:11 PM
from JPL
http://www.jpl.nasa.gov/news/news.php?release=2013-275
"Mission controllers postulate that there was an anomaly generated by
the spacecraft's software which left the vehicle's computers in a
condition where they are continuously rebooting themselves. If this is
the case, the computers would not continue to command the vehicle's
thrusters to fire and hold attitude. Lack of attitude hold makes
attempts to reestablish communications more difficult because the
orientation of the spacecraft's antennas is unknown. It also brings into
question the vehicle's electrical power status, as the spacecraft
derives its power from a solar array that is fixed, with its cells
pointing in one direction."
If it gets cold enough (without power from solar cells, it won't
generate enough internal heat to keep warm), it will die. That's
probably what happened to Spirit on Mars. It got cold enough during the
Martian winter, and with not enough solar power, enough things drifted
cold enough that we couldn't get commands in.
BTW, DI uses star trackers for attitude knowledge, so it has the
potential to point very precisely.
If anyone is interested in the gory details of how the telecom system works
http://descanso.jpl.nasa.gov/DPSummary/di_article_cmp20050922.pdf
Page 20 shows the variation in AuxOsc frequency of the SDST radio vs
temperature. That shape will look pretty familiar to list members.
from JPL
http://www.jpl.nasa.gov/news/news.php?release=2013-275
"Mission controllers postulate that there was an anomaly generated by
the spacecraft's software which left the vehicle's computers in a
condition where they are continuously rebooting themselves. If this is
the case, the computers would not continue to command the vehicle's
thrusters to fire and hold attitude. Lack of attitude hold makes
attempts to reestablish communications more difficult because the
orientation of the spacecraft's antennas is unknown. It also brings into
question the vehicle's electrical power status, as the spacecraft
derives its power from a solar array that is fixed, with its cells
pointing in one direction."
If it gets cold enough (without power from solar cells, it won't
generate enough internal heat to keep warm), it will die. That's
probably what happened to Spirit on Mars. It got cold enough during the
Martian winter, and with not enough solar power, enough things drifted
cold enough that we couldn't get commands in.
BTW, DI uses star trackers for attitude knowledge, so it has the
potential to point very precisely.
If anyone is interested in the gory details of how the telecom system works
http://descanso.jpl.nasa.gov/DPSummary/di_article_cmp20050922.pdf
Page 20 shows the variation in AuxOsc frequency of the SDST radio vs
temperature. That shape will look pretty familiar to list members.
BC
Bob Camp
Sat, Sep 21, 2013 12:52 PM
Hi
So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.
Bob
On Sep 21, 2013, at 8:11 AM, Jim Lux jimlux@earthlink.net wrote:
from JPL
http://www.jpl.nasa.gov/news/news.php?release=2013-275
"Mission controllers postulate that there was an anomaly generated by the spacecraft's software which left the vehicle's computers in a condition where they are continuously rebooting themselves. If this is the case, the computers would not continue to command the vehicle's thrusters to fire and hold attitude. Lack of attitude hold makes attempts to reestablish communications more difficult because the orientation of the spacecraft's antennas is unknown. It also brings into question the vehicle's electrical power status, as the spacecraft derives its power from a solar array that is fixed, with its cells pointing in one direction."
If it gets cold enough (without power from solar cells, it won't generate enough internal heat to keep warm), it will die. That's probably what happened to Spirit on Mars. It got cold enough during the Martian winter, and with not enough solar power, enough things drifted cold enough that we couldn't get commands in.
BTW, DI uses star trackers for attitude knowledge, so it has the potential to point very precisely.
If anyone is interested in the gory details of how the telecom system works
http://descanso.jpl.nasa.gov/DPSummary/di_article_cmp20050922.pdf
Page 20 shows the variation in AuxOsc frequency of the SDST radio vs temperature. That shape will look pretty familiar to list members.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.
Bob
On Sep 21, 2013, at 8:11 AM, Jim Lux <jimlux@earthlink.net> wrote:
> from JPL
> http://www.jpl.nasa.gov/news/news.php?release=2013-275
>
> "Mission controllers postulate that there was an anomaly generated by the spacecraft's software which left the vehicle's computers in a condition where they are continuously rebooting themselves. If this is the case, the computers would not continue to command the vehicle's thrusters to fire and hold attitude. Lack of attitude hold makes attempts to reestablish communications more difficult because the orientation of the spacecraft's antennas is unknown. It also brings into question the vehicle's electrical power status, as the spacecraft derives its power from a solar array that is fixed, with its cells pointing in one direction."
>
>
> If it gets cold enough (without power from solar cells, it won't generate enough internal heat to keep warm), it will die. That's probably what happened to Spirit on Mars. It got cold enough during the Martian winter, and with not enough solar power, enough things drifted cold enough that we couldn't get commands in.
>
>
>
> BTW, DI uses star trackers for attitude knowledge, so it has the potential to point very precisely.
>
>
> If anyone is interested in the gory details of how the telecom system works
> http://descanso.jpl.nasa.gov/DPSummary/di_article_cmp20050922.pdf
>
> Page 20 shows the variation in AuxOsc frequency of the SDST radio vs temperature. That shape will look pretty familiar to list members.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
MD
Magnus Danielson
Sat, Sep 21, 2013 1:03 PM
On 09/21/2013 02:52 PM, Bob Camp wrote:
Hi
So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.
The environmental perturbations should go quite slow most of the time,
as it glides in the void slowly away and often have a fairly stable
direction with regards to the sun. If they have spin-rotation it
complicates things a bit.
Decent dewar-flask with better background radiation and one major heat
source that you track for the solar panels.
Cheers,
Magnus
On 09/21/2013 02:52 PM, Bob Camp wrote:
> Hi
>
> So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.
The environmental perturbations should go quite slow most of the time,
as it glides in the void slowly away and often have a fairly stable
direction with regards to the sun. If they have spin-rotation it
complicates things a bit.
Decent dewar-flask with better background radiation and one major heat
source that you track for the solar panels.
Cheers,
Magnus
JL
Jim Lux
Sat, Sep 21, 2013 1:24 PM
On 9/21/13 5:52 AM, Bob Camp wrote:
Hi
So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.
Yep. The AuxOsc is what is used if you don't want to have the downlink
locked to the uplink.
On 9/21/13 5:52 AM, Bob Camp wrote:
> Hi
>
> So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.
>
Yep. The AuxOsc is what is used if you don't want to have the downlink
locked to the uplink.
JL
Jim Lux
Sat, Sep 21, 2013 1:26 PM
On 9/21/13 6:03 AM, Magnus Danielson wrote:
On 09/21/2013 02:52 PM, Bob Camp wrote:
Hi
So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.
The environmental perturbations should go quite slow most of the time,
as it glides in the void slowly away and often have a fairly stable
direction with regards to the sun. If they have spin-rotation it
complicates things a bit.
Decent dewar-flask with better background radiation and one major heat
source that you track for the solar panels.
Yeah, there's jokes about why are they obsessing about hermetic seals on
components when we're going to be operating in a harder vacuum than you
can easily achieve on earth. The outside of the package probably has a
lower pressure than inside the package.
On 9/21/13 6:03 AM, Magnus Danielson wrote:
> On 09/21/2013 02:52 PM, Bob Camp wrote:
>> Hi
>>
>> So it's a pretty good AT cut crystal without any compensation of heating. Not quite a cheap wrist watch, but not a BVA in a dewar flask either.
> The environmental perturbations should go quite slow most of the time,
> as it glides in the void slowly away and often have a fairly stable
> direction with regards to the sun. If they have spin-rotation it
> complicates things a bit.
>
> Decent dewar-flask with better background radiation and one major heat
> source that you track for the solar panels.
>
Yeah, there's jokes about why are they obsessing about hermetic seals on
components when we're going to be operating in a harder vacuum than you
can easily achieve on earth. The outside of the package probably has a
lower pressure than inside the package.
MD
Magnus Danielson
Sat, Sep 21, 2013 2:17 PM
On 09/21/2013 03:26 PM, Jim Lux wrote:
On 9/21/13 6:03 AM, Magnus Danielson wrote:
On 09/21/2013 02:52 PM, Bob Camp wrote:
Hi
So it's a pretty good AT cut crystal without any compensation of
heating. Not quite a cheap wrist watch, but not a BVA in a dewar
flask either.
The environmental perturbations should go quite slow most of the time,
as it glides in the void slowly away and often have a fairly stable
direction with regards to the sun. If they have spin-rotation it
complicates things a bit.
Decent dewar-flask with better background radiation and one major heat
source that you track for the solar panels.
Yeah, there's jokes about why are they obsessing about hermetic seals
on components when we're going to be operating in a harder vacuum than
you can easily achieve on earth. The outside of the package probably
has a lower pressure than inside the package.
True. The trouble is really what happens prior to reaching that hard vacuum.
You could do a in space pumping by having the thing pressurized and then
heat up a lead-plug until it melts and the pressure shoots out the blob,
gas and eventually the innards decays into hard vacuum. If you do that
early in the mission, the handling the shift is relatively easy as C/N
ratios is favorable.
Cheers,
Magnus
On 09/21/2013 03:26 PM, Jim Lux wrote:
> On 9/21/13 6:03 AM, Magnus Danielson wrote:
>> On 09/21/2013 02:52 PM, Bob Camp wrote:
>>> Hi
>>>
>>> So it's a pretty good AT cut crystal without any compensation of
>>> heating. Not quite a cheap wrist watch, but not a BVA in a dewar
>>> flask either.
>> The environmental perturbations should go quite slow most of the time,
>> as it glides in the void slowly away and often have a fairly stable
>> direction with regards to the sun. If they have spin-rotation it
>> complicates things a bit.
>>
>> Decent dewar-flask with better background radiation and one major heat
>> source that you track for the solar panels.
>>
>
> Yeah, there's jokes about why are they obsessing about hermetic seals
> on components when we're going to be operating in a harder vacuum than
> you can easily achieve on earth. The outside of the package probably
> has a lower pressure than inside the package.
True. The trouble is really what happens prior to reaching that hard vacuum.
You could do a in space pumping by having the thing pressurized and then
heat up a lead-plug until it melts and the pressure shoots out the blob,
gas and eventually the innards decays into hard vacuum. If you do that
early in the mission, the handling the shift is relatively easy as C/N
ratios is favorable.
Cheers,
Magnus
