From Wikipedia, the free encyclopedia
Safe mode
is an operating mode of a modern uncrewed
spacecraft
during which all non-essential systems are shut down and only essential functions such as
thermal management
, radio reception and
attitude control
are active.
[1]
Safe mode is entered automatically upon the detection of a predefined operating condition or event that may indicate loss of control or damage to the spacecraft. Usually the trigger event is a system failure or detection of operating conditions considered dangerously out of the normal range.
Cosmic rays
penetrating spacecraft electrical systems can create false signals or commands and thus cause a trigger event. The
central processor electronics
are especially prone to such events.
[2]
Another trigger is the lack of a received command within a given time window. Lack of received commands can be caused by hardware failures or mis-programming of the spacecraft, as in the case of the
Viking 1
lander.
The process of entering safe mode, sometimes referred to as
safing
,
[3]
involves a number of immediate physical actions taken to prevent damage or complete loss. Power is removed from non-essential subsystems. Regaining attitude control, if lost, is the highest priority because it is necessary to maintain thermal balance and proper illumination of the solar panels.
[1]
A tumbling or cartwheeling spacecraft can quickly roast, freeze or exhaust its battery power and be lost forever.
[4]
In safe mode
[
edit
]
While in safe mode the preservation of the spacecraft is the highest priority. Typically all non-essential systems, such as science instruments, are shut down. The spacecraft attempts to maintain orientation with respect to the
Sun
for illumination of
solar panels
and for thermal management. The spacecraft then awaits radio commands from its
mission control center
monitoring for signals on its low-gain
omnidirectional antenna
. Exactly what happens while in safe mode is dependent on the spacecraft design and its mission.
[2]
Recovery from safe mode involves reestablishing communication between the spacecraft and mission control, downloading any diagnostic data and sequencing power back on to the various subsystems to resume the mission. The recovery time can be anywhere from a few hours to days or weeks depending on the difficulty in reestablishing communications, conditions found on the spacecraft, distance to the spacecraft and the nature of the mission.
[5]
Overriding normal safe mode behavior
[
edit
]
Normal safe mode operation can sometimes be overridden. A spacecraft's ability to enter safe mode may be suppressed during crucial spacecraft operations (such as the
orbit insertion
maneuver of the
Cassini
spacecraft
at
Saturn
), during which ? if a critical failure were to occur ? most, if not all, of the mission objectives would be lost anyway.
[3]
On occasion, a spacecraft is placed in safe mode deliberately by mission control, as the
Spirit rover
was on
sol
451.
[6]
Modern incidents
[
edit
]
- 2005
- 2007
- Cassini?Huygens
download of the
Iapetus
flyby data was interrupted by a safing event September 10, 2007.
[3]
- New Horizons
entered safe mode March 19, 2007 due to an uncorrectable memory error in the primary Command and Data Handling (C&DH) computer.
[5]
- Odyssey
has broken the communications link between the
Mars Exploration Rovers
and Earth during several sudden safing events.
[7]
[8]
- 2009
- The
Mars Reconnaissance Orbiter
(MRO) entered safe mode on August 26, 2009 for the second incident in a month, the fourth in 2009 and the eighth since launch in 2005.
[9]
[10]
The spacecraft was kept in safe mode until December 8, 2009.
[11]
- Kepler
entered safe mode on June 15 and again on July 3, 2009. Both cases were triggered by an on-board processor reset.
[12]
- Dawn
entered safe mode due to a programming error during its February 17, 2009
Mars
flyby.
[13]
- MESSENGER
entered safe mode during its third flyby of
Mercury
on September 29, 2009.
[14]
- 2014
- The
Philae
lander
entered safe mode on 15 November 2014, after its batteries ran down due to reduced sunlight and an off-nominal spacecraft orientation at its unplanned landing site.
[15]
- 2015
- New Horizons
entered safe mode on July 4, 2015, ten days before its closest approach to
Pluto
, after a
timing problem
in a command sequence. Some scientific data was lost, but with only minimal impact on mission objectives.
[16]
- 2016
- Juno
entered safe mode on 18 October 2016, just prior to a planned
maneuvering burn
using its main engine to lower its orbit.
[17]
The spacecraft's on-board computer was rebooted, and subsequent check-out of its scientific research systems showed no major malfunctions. The exact cause remains under investigation.
[18]
- 2018
- The
Opportunity
rover
entered safe mode on 13 June 2018 during the
2018 Mars dust storm
. The opacity of the atmosphere was such that almost all sunlight was blocked and the rover's solar panels were unable to recharge its batteries even for minimal maintenance and communications.
[19]
[20]
It was hoped it would reboot once the atmosphere cleared in October, but it did not, suggesting either a catastrophic failure or that a layer of dust has covered its solar panels.
[21]
On February 13, 2019, NASA officials declared that the
Opportunity
mission was complete, after the spacecraft had failed to respond to over 1,000 signals sent since August 2018.
[22]
- The
Hubble Space Telescope
entered safe mode on October 5, 2018, after one of its three active
gyroscopes
failed. The failing gyro had been exhibiting end-of-life behavior for approximately a year, and its failure was not unexpected. Hubble had six new gyros installed during Servicing Mission 4 in 2009 (
STS-125
). The spacecraft usually uses three gyros at a time, but can continue to make scientific observations with just one.
[23]
[24]
- 2021
- NASA announced that
Hubble Space Telescope
went into safe mode after experiencing synchronization issues with internal spacecraft communications. Science observations were temporarily suspended.
Incidents resulting in spacecraft loss or near loss
[
edit
]
- SOHO
entered safe mode and was nearly lost on June 25, 1998. Normal operations were eventually restored after a gap of four months.
[4]
[25]
- NEAR
entered safe mode, tumbled out of control and was nearly lost during the first attempt of
Eros
orbit insertion
on December 20, 1998.
[26]
- Mars Global Surveyor
entered safe mode and was lost when its batteries were overheated and destroyed by incorrect solar orientation on November 2, 2006.
[27]
- ISEE-3
was lost on September 16, 2014, during a civilian reboot effort.
[28]
It is believed that the 36-year-old spacecraft entered safe mode due to a drop in power from its solar panels.
[29]
The
crowdfunded
project has been unable to re-establish contact.
References
[
edit
]
- ^
a
b
Bokulic, R. S.; Jensen, J. R. (November?December 2000).
"Recovery of a Spacecraft from Sun-Safe Mode Using a Fanbeam Antenna"
.
Spacecraft and Rockets
.
37
(6): 822.
Bibcode
:
2000JSpRo..37..822B
.
doi
:
10.2514/2.3640
.
- ^
a
b
Bayer, Todd J. (18?20 September 2007).
"Planning for the Un-plannable: Redundancy, Fault Protection, Contingency Planning and Anomaly Response for the Mars Reconnaissance Orbiter Mission"
.
AIAA SPACE 2007 Conference & Exposition
. Retrieved
January 28,
2023
.
- ^
a
b
c
Cassini Spacecraft Safing
Archived
2009-07-09 at the
Wayback Machine
- ^
a
b
"SOHO Mission Interruption Preliminary Status and Background Report"
. July 15, 1998
. Retrieved
2006-08-17
.
- ^
a
b
"The PI's Perspective: Trip Report"
. NASA/Johns Hopkins University/APL/New Horizons Mission. 2007-03-26
. Retrieved
2016-10-19
.
- ^
a
b
"Spirit Updates 2005"
. NASA/JPL. Archived from
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on 2007-08-23
. Retrieved
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.
- ^
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on 2007-08-23
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- ^
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on 2009-04-13
. Retrieved
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.
- ^
Tariq Malik (August 8, 2009).
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. Retrieved
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.
- ^
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on 2011-06-11
. Retrieved
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.
- ^
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. NASA/JPL. December 8, 2009. Archived from
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on 2011-06-11
. Retrieved
2009-12-23
.
- ^
"2009 July 7 Mission Manager Update"
. NASA. 2009-07-07. Archived from
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on 2009-06-11
. Retrieved
2009-07-08
.
- ^
"Dawn Receives Gravity Assist from Mars"
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the original
on 2004-10-16
. Retrieved
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.
- ^
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. MESSENGER Mission News. September 30, 2009. Archived from
the original
on May 10, 2013
. Retrieved
2009-09-30
.
- ^
Brumfield, Ben; Carter, Chelsea J. (18 November 2014).
"On a comet 10 years away, Philae conks out, maybe for good"
.
CNN
. Retrieved
28 December
2014
.
- ^
Gipson, Lillian (6 July 2015).
"NASA's New Horizons Plans July 7 Return to Normal Science Operations"
.
National Aeronautics and Space Administration (NASA)
. Retrieved
6 July
2015
.
- ^
Feltman, Rachel (20 October 2016).
"Juno spacecraft slips into safe mode, putting science on hold"
.
Washington Post
. Retrieved
20 October
2016
.
- ^
"Juno Spacecraft in Safe Mode for Latest Jupiter Flyby; Scientists Intrigued by Data from First Flyby"
.
NASA JPL
. 19 October 2016
. Retrieved
20 October
2016
.
- ^
Opportunity Hunkers Down During Dust Storm
. NASA. 12 June 2918.
- ^
NASA Staff (13 June 2018).
"Mars Dust Storm News - Teleconference - audio (065:22)"
.
NASA
.
Archived
from the original on 2021-12-21
. Retrieved
13 June
2018
.
- ^
"Mars Exploration Rover Mission: All Opportunity Updates"
.
mars.nasa.gov
. Retrieved
2018-02-10
.
- ^
"NASA's Opportunity Rover Mission on Mars Comes to End"
.
NASA
. February 13, 2019
. Retrieved
February 13,
2019
.
- ^
Chou, Felicia (2018-10-08). Garner, Rob (ed.).
"Oct. 8, 2018 - Hubble in Safe Mode as Gyro Issues are Diagnosed"
.
NASA
. Retrieved
2018-10-23
.
- ^
"Hubble on Twitter"
.
Twitter
. Retrieved
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.
- ^
Nancy G. Leveson (2004).
"The Role of Software in Spacecraft Accidents"
(PDF)
.
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41
(4): 564?575.
Bibcode
:
2004JSpRo..41..564L
.
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10.1.1.202.8334
.
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.
- ^
"The NEAR Rendezvous Burn Anomaly of December 1998"
(PDF)
. Final Report of the NEAR Anomaly Review Board. November 1999. Archived from
the original
(PDF)
on 2011-06-14
. Retrieved
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.
- ^
"Report Reveals Likely Causes of Mars Spacecraft Loss"
(Press release).
NASA
. 13 April 2007
. Retrieved
2009-07-10
.
- ^
Geraint Jones (3 October 2014).
"Space, the financial frontier ? how citizen scientists took control of a probe"
.
The Conversation
. Retrieved
16 January
2016
.
- ^
Keith Kowing (25 September 2014).
"ISEE-3 is in Safe Mode"
.
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. Retrieved
15 January
2016
.
See also
[
edit
]