View source for Mars Polar Lander

{{short description|Failed NASA Mars lander (1999)}}
{{Use dmy dates|date=July 2024}}

{{Infobox spaceflight
| name                  = Mars Polar Lander
| names_list            = Mars Surveyor '98 ''Lander''

<!-- image of the spacecraft/mission -->
| image                 = Mars Polar Lander - artist depiction.png
| image_caption         = Artist's depiction of the ''Mars Polar Lander'' on the Martian surface

<!-- Basic details -->
| mission_type          = [[Mars]] lander
| operator              = [[NASA]] / [[Jet Propulsion Laboratory|JPL]]
| COSPAR_ID             = 1999-001A
| SATCAT                = 25605
| website               = [https://science.nasa.gov/mission/mars-polar-lander-deep-space-2/ science.nasa.gov]
| mission_duration      = {{time interval|3 Jan 1999|3 Dec 1999|show=dhm}}<br>{{small|Mission failure}}

<!-- Spacecraft properties -->
| manufacturer          = [[Martin Marietta]]
| launch_mass           = {{cvt|290|kg|lb}}{{r|nssdc1}}
| power                 = 200 W [[Photovoltaic system|solar array]] and [[Nickel–hydrogen battery|{{chem|NiH|2}} battery]]

<!-- Launch details -->
| launch_date           = {{start date|1999|01|03|20|21|10|7=Z}}
| launch_rocket         = [[Delta II]] 7425–9.5<br>D-265
| launch_site           = [[Cape Canaveral Space Launch Complex 17|Cape Canaveral Air Force Station SLC-17A]]
| launch_contractor     = [[Boeing]]

<!-- end of mission -->
| disposal_type         = Communication failure after landing
| last_contact          = {{end date|1999|12|03|20|00|7=Z}}
| declared              = {{end date|2000|01|17}}

| interplanetary        = 
 {{Infobox spaceflight/IP
   |type                = lander_impact
   |object              = [[Mars]]
   |arrival_date        = ~20:15 UTC [[Spacecraft Event Time#SCET versus Earth time|ERT]], December 3, 1999
   |location            = [[Ultimi Scopuli]], {{coord|76|S|195|W|globe:Mars|name=Mars Polar Lander}} (projected)
 }}

 {{Infobox spaceflight/IP
   |type                = impactor
   |object              = [[Mars]]
   |component           = ''[[Deep Space 2]]''
 }}

<!-- Only use where a spacecraft/mission is part of a clear programme of sequential missions.
If in doubt, leave it out -->
| programme         = '''[[Mars Exploration Program]]'''
| previous_mission  = [[Mars Climate Orbiter]]
| next_mission      = [[2001 Mars Odyssey|Mars Odyssey]]
| programme2        = '''[[Mars Surveyor '98]]'''

<!-- mission insignia or patch -->
| insignia              = M98patch.png
| insignia_size         = 180px
| insignia_caption      = ''Mars Surveyor 98'' mission logo
}}

The '''Mars Polar Lander''', also known as the '''Mars Surveyor '98 Lander''', was a 290-kilogram [[uncrewed spacecraft]] [[Lander (spacecraft)|lander]] launched by [[NASA]] on January 3, 1999, to study the [[Martian regolith|soil]] and [[Climate of Mars|climate]] of [[Planum Australe]], a region near the south pole on [[Mars]]. It formed part of the [[Mars Surveyor '98]] mission. On December 3, 1999, however, after the descent phase was expected to be complete, the lander failed to reestablish communication with Earth. A post-mortem analysis determined the most likely cause of the mishap was premature termination of the engine firing prior to the lander touching the surface, causing it to strike the planet at a high velocity.{{r|LossReport}}

The total cost of the Mars Polar Lander was US$165 million. Spacecraft development cost US$110 million, launch was estimated at US$45 million, and mission operations at US$10 million.{{r|AP-19991208}}

== Mission background ==
=== History ===
As part of the [[Mars Surveyor '98]] mission, a lander was sought as a way to gather climate data from the ground in conjunction with an orbiter. [[NASA]] suspected that a large quantity of frozen water may exist under a thin layer of dust at the south pole. In planning the Mars Polar Lander, the potential water content in the Martian south pole was the strongest determining factor for choosing a landing location.{{r|press_kit_1998}} A CD-ROM containing the names of one million children from around the world was placed on board the spacecraft as part of the "Send Your Name to Mars" program designed to encourage interest in the space program among children.{{r|send_name_1998}} <!-- needs expansion -->

The primary objectives of the mission were to:{{r|press_kit_1999}}
* Land on the layered terrain in the south polar region of Mars;
* Search for evidence related to ancient climates and more recent periodic climate change;
* Give a picture of the current climate and seasonal change at high latitudes and, in particular, the exchange of water vapor between the atmosphere and ground;
* Search for near-surface ground ice in the polar regions, and analyze the soil for physically and chemically bound carbon dioxide and water; and
* Study surface [[Geomorphology|morphology]] (forms and structures), geology, [[topography]], and weather of the landing site.

=== ''Deep Space 2'' probes ===
{{Main|Deep Space 2}}
The Mars Polar Lander carried two small, identical [[impactor (spacecraft)|impactor]] probes known as "Deep Space 2 A and B". The probes were intended to strike the surface with a high velocity at approximately {{Coord|73|S|210|W|globe:Mars|name=Deep Space 2}} to penetrate the [[Martian regolith|Martian soil]] and study the subsurface composition up to a meter in depth. However, after entering the Martian atmosphere, attempts to contact the probes failed.{{r|press_kit_1998}}

Deep Space 2 was funded by the [[New Millennium Program]], and their development costs was US$28 million.{{r|AP-19991208}}

=== Spacecraft design ===
The spacecraft measured 3.6 meters wide and 1.06 meters tall with the legs and solar arrays fully deployed. The base was primarily constructed with an aluminum [[Honeycomb structure|honeycomb]] deck, composite [[Carbon-fiber reinforced polymer|graphite-epoxy]] sheets forming the edge, and three aluminum legs. During landing, the legs were to deploy from stowed position with compression springs and absorb the force of the landing with crushable aluminum honeycomb inserts in each leg. On the deck of the lander, a small thermal [[Faraday cage]] enclosure housed the computer, power distribution electronics and batteries, telecommunication electronics, and the capillary pump [[loop heat pipe]] (LHP) components, which maintained operable temperature. Each of these components included redundant units in the event that one may fail.{{r|press_kit_1998|nssdc1|nasa1}}

==== Attitude control and propulsion ====
While traveling to Mars, the cruise stage was three-axis stabilized with four [[hydrazine]] [[monopropellant rocket|monopropellant]] reaction engine modules, each including a 22-[[Newton (unit)|newton]] trajectory correction maneuver thruster for propulsion and a 4-newton reaction control system thruster for [[Spacecraft attitude control|attitude control]] (orientation). Orientation of the spacecraft was performed using redundant [[Spacecraft attitude control|Sun sensors]], [[Spacecraft attitude control|star trackers]], and [[Spacecraft attitude control|inertial measurement units]].{{r|nssdc1}}

During descent, the lander used three clusters of pulse-modulated engines, each containing four 266-newton hydrazine monopropellant thrusters. Altitude during landing was measured by a [[Doppler radar]] system, and an attitude and articulation control subsystem (AACS) controlled the attitude to ensure the spacecraft landed at the optimal [[azimuth]] to maximize solar collection and telecommunication with the lander.{{r|press_kit_1998|nssdc1|nasa1}}

The lander was launched with two hydrazine tanks containing 64 kilograms of propellant and pressurized with [[helium]]. Each spherical tank was located at the underside of the lander and provided propellant during the cruise and descent stages.{{r|press_kit_1998|nssdc1|nasa1}}

==== Communications ====
During the cruise stage, communications with the spacecraft were conducted over the [[X band]] using a medium-gain, horn-shaped antenna and redundant solid state power amplifiers. For contingency measures, a low-gain omnidirectional antenna was also included.{{r|press_kit_1998}}

The lander was originally intended to communicate data through the failed [[Mars Climate Orbiter]] via the [[Ultra high frequency|UHF]] antenna. With the orbiter lost on September 23, 1999, the lander would still be able to communicate directly to the [[NASA Deep Space Network]] through the Direct-To-Earth (DTE) link, an X band, steerable, medium-gain, [[parabolic antenna]] located on the deck. Alternatively, [[Mars Global Surveyor]] could be used as a relay using the UHF antenna at multiple times each Martian day. However the Deep Space Network could only receive data from, and not send commands to, the lander using this method. The direct-to-Earth medium-gain antenna provided a 12.6-kbit/s [[return channel]], and the UHF relay path provided a 128-kbit/s return channel. Communications with the spacecraft would be limited to one-hour events, constrained by heat-buildup that would occur in the amplifiers. The number of communication events would also be constrained by power limitations.{{r|press_kit_1998|press_kit_1999|nssdc1|nasa1}}

==== Power ====
The cruise stage included two [[gallium arsenide]] [[Photovoltaic system|solar arrays]] to power the radio system and maintain power to the batteries in the lander, which kept certain electronics warm.{{r|press_kit_1998|nssdc1}}

After descending to the surface, the lander was to deploy two 3.6-meter-wide gallium arsenide solar arrays, located on either side of the spacecraft. Another two auxiliary solar arrays were located on the side to provide additional power for a total of an expected 200 watts and approximately eight to nine hours of operating time per day.{{r|press_kit_1998|nssdc1}}

While the Sun would not have set below the horizon during the primary mission, too little light would have reached the solar arrays to remain warm enough for certain electronics to continue functioning. To avoid this problem, a 16-ampere-hour [[nickel–hydrogen battery]] was included to be recharged during the day and to power the heater for the thermal enclosure at night. This solution also was expected to limit the life of the lander. As the Martian days would grow colder in late summer, too little power would be supplied to the heater to avoid freezing, resulting in the battery also freezing and signaling the end of the operating life for the lander.{{r|press_kit_1998|nssdc1|nasa1}}

==== Scientific instruments ====
{{Gallery|align=center
|title=Scientific instruments
|file:Mars Polar Lander - MARDI instrument photo - mardi.jpg|Mars Descent Imager
|file:Mars Polar Lander - SSI instrument photo - ssi closeup s.jpg|Stereo Surface Imager
|file:Mars Polar Lander - LIDAR instrument photo - mpl lidar.gif|LIDAR
|file:Mars Polar Lander - RA instrument photo - arm.png|Robotic Arm
|file:Mars Polar Lander - RAC instrument photo.png|Robotic Arm Camera
|file:Mars Polar Lander - MET instrument photo - mettop.png|Meteorological Package
|file:Mars Polar Lander - TEGA instrument photo.png|Thermal and Evolved Gas Analyzer
|file:Mars Polar Lander - Mars Microphone instrument photo - microphone.jpg|Mars Microphone
}}

{{Gallery|align=center
|title=Images of the spacecraft
|File:Mars Polar Lander - spacecraft diagram.png|Annotated diagram of the Mars Polar Lander spacecraft
|File:Mars Polar Lander close-up.jpg|The spacecraft in stowed position just prior to encapsulation
|File:Mars Polar Lander undergoes testing.jpg|Testing performed at the Spacecraft Assembly and Encapsulation Facility
|File:Mars Polar Lander prelaunch.jpg|The ''Mars Polar Lander'' entry capsule, just prior to being mounted to the [[Star 48]] upper stage
}}

; [[Mars Descent Imager#Mars Descent Imager (MARDI)|Mars Descent Imager]] (MARDI): Mounted to the bottom of the lander, the camera was intended to capture 30 images as the spacecraft descended to the surface. The images acquired would be used to provide geographic and geologic context to the landing area.{{r|nssdc2}}
; [[Phoenix (spacecraft)#Surface stereo imager|Surface Stereo Imager]] (SSI): Using a pair of [[charge-coupled device]]s (CCDs), the stereo [[panoramic camera]] was mounted to a one-meter-tall mast and would aid in the thermal evolved gas analyzer in determining areas of interest for the robotic arm. In addition, the camera would be used to estimate the column density of atmospheric dust, the optical depth of [[aerosol]]s, and slant column abundances of water vapor using narrow-band imaging of the Sun.{{r|nssdc3}}
; [[Lidar|Light Detection and Ranging]] (LIDAR): The laser sounding instrument was intended to detect and characterize aerosols in the atmosphere up to three kilometers above the lander. The instrument operated in two modes: ''active mode'', using an included laser diode, and ''acoustic'' mode, using the Sun as the light source for the sensor. In active mode, the laser sounder was to emit 100-nanosecond pulses at a wavelength of 0.88-micrometer into the atmosphere, and then record the duration of time to detect the light scattered by aerosols. The duration of time required for the light to return could then be used to determine the abundance of ice, dust and other aerosols in the region. In acoustic mode, the instrument measures the brightness of the sky as lit by the Sun and records the scattering of light as it passes to the sensor.{{r|nssdc4}}
; [[Robotic arm|Robotic Arm]] (RA): Located on the front of the lander, the robotic arm was a meter-long aluminum tube with an elbow joint and an articulated scoop attached to the end. The scoop was intended to be used to dig into the soil in the direct vicinity of the lander. The soil could then be analyzed in the scoop with the robotic arm camera or transferred into the thermal evolved gas analyzer.{{r|nssdc3}}
; Robotic Arm Camera (RAC): Located on the robotic arm, the charge coupled camera included two red, two green, and four blue lamps to illuminate soil samples for analysis.{{r|nssdc3}}
; Meteorological Package (MET): Several instruments related to sensing and recording weather patterns, were included in the package. Wind, temperature, pressure, and humidity sensors were located on the robotic arm and two deployable masts: a 1.2-meter ''main mast'', located on top of the lander, and a 0.9-meter secondary ''submast'' that would deploy downward to acquire measurements close to the ground.{{r|nssdc3}}
; [[Thermal and Evolved Gas Analyzer]] (TEGA): The instrument was intended to measure abundances of water, water ice, adsorbed carbon dioxide, oxygen, and volatile-bearing minerals in surface and subsurface soil samples collected and transferred by the robotic arm. Materials placed onto a grate inside one of the eight ovens, would be heated and vaporized at 1,000&nbsp;°C. The evolved gas analyzer would then record measurements using a [[spectrometer]] and an [[Electrochemistry|electrochemical]] cell. For calibration, an empty oven would also be heated during this process for differential scanning [[calorimetry]]. The difference in the energy required to heat each oven would then indicate concentrations of water ice and other minerals containing water or carbon dioxide.{{r|nssdc3}}
; Mars Microphone: The microphone was intended to be the first instrument to record sounds on another planet. Primarily composed of a microphone generally used with [[hearing aid]]s, the instrument was expected to record sounds of blowing dust, electrical discharges and the sounds of the operating spacecraft in either 2.6-second or 10.6-second, 12-bit samples.{{r|nssdc5}} The microphone was built using off-the-shelf parts including a [[Sensory, Inc.]] RSC-164 integrated circuit typically used in speech-recognition devices.{{r|tps1}}

== Mission profile ==
{| style="float: right;"
! colspan="2" | Timeline of observations
|-
|
{| cellspacing="0" cellpadding="0" align="center" width="100%" style="border:0px solid #e6e6e6"
|-
| colspan="2" |
----
|-
! scope="col" width="75" | Date
! scope="col" width="350" | Event
|-
| colspan="2" |
----
<!-- Main table data-outside collapsible -->
|-
| {{center|1999-01-03}}
| style="background-color:#f2f2f2;" | Spacecraft launched at 20:21:10 UTC
|-
| {{center|1999-12-03}}
|
<!-- Collapsable data header -->
{| class="collapsible collapsed" align="center" width="100%"
! colspan="2" style="background-color:#e9e9e9;font-weight:normal;" | {{pad|2em}} Begin atmospheric entry and landing
|-
| colspan="2" |
----
|- style="background-color:#e0e0e0"
! scope="col" width="75" | Time
! scope="col" width="230" | Event {{pad|6em}}
|-
| colspan="2" |
----
<!-- Collapsable data input-copy for more entries -->
|-
| {{center|'''1999-12-03'''}}
|
|-
| {{center|14:39:00}}
| {{small|Turn spacecraft away from Earth for final stellar data acquisition, signal loss from spacecraft}}
|-
| {{center|14:42:00}}
| {{small|Turn on heaters on descent engine}}
|-
| {{center|17:34:00}}
| {{small|Turn on heaters on descent camera (MARDI)}}
|-
| {{center|18:49:00}}
| {{small|Turn spacecraft back to Earth point, acquire spacecraft signal, acquire health & status}}
|-
| {{center|19:21:00}}
| {{small|Begin Entry, Descent, Landing sequence}}
|-
| {{center|19:26:00}}
| {{small|Pyros fire to pressurize helium tank}}
|-
| {{center|20:00:00}}
| {{small|Guidance system initialization (2210&nbsp;km, 6.2&nbsp;km/s)}}
|-
| {{center|20:03:00}}
| {{small|Turn spacecraft to entry attitude, loss of signal. We won't hear from the spacecraft again until after landing (1426&nbsp;km, 6.4&nbsp;km/s)}}
|-
| {{center|20:05:00}}
| {{small|Cruise ring/Deep Space 2 probes separate from lander (959&nbsp;km, 6.6&nbsp;km/s)}}
|-
| {{center|20:10:00}}
| {{small|Atmospheric entry (142&nbsp;km, 6.9&nbsp;km/s)}}
|-
| {{center|20:11:00}}
| {{small|Descent radar powered on}}
|-
| {{center|20:12:00}}
| {{small|MARDI instrument powered on}}
|-
| {{center|20:13:00}}
| {{small|Parachute deployed (9.0&nbsp;km, 496&nbsp;m/s)}}
|-
| {{center|20:13:00}}
| {{small|Descent imaging begins, heatshield jettisoned (8.0&nbsp;km, 286&nbsp;m/s)}}
|-
| {{center|20:13:00}}
| {{small|Lander legs deployed, descent radar activated}}
|-
| {{center|20:14}}
| {{small|Radar ground acquisition, altitude (2.438&nbsp;km, 80&nbsp;m/s)}}
|-
| {{center|20:14:00}}
| {{small|Lander separates from backshell, powered descent begins (1.628&nbsp;km, 78&nbsp;m/s)}}
|-
| {{center|20:14:00}}
| {{small|Radar ground acquisition, speed & direction (1.425&nbsp;km, 82&nbsp;m/s)}}
|-
| {{center|20:14}}
| {{small|Gravity turn begins (1.394&nbsp;km, 83&nbsp;m/s)}}
|-
| {{center|20:14:00}}
| {{small|Roll to landed orientation (1.307&nbsp;km, 79&nbsp;m/s)}}
|-
| {{center|20:14:00}}
| {{small|Radar cutoff (40 meters, 13&nbsp;m/s)}}
|-
| {{center|20:15:00}}
| {{small|Constant Velocity Phase (12 meters, 2.4 m/s)}}
|-
| {{center|20:15:00}}
| {{font color|red|{{small|'''Touchdown. Mars Polar Lander on Mars surface.'''}}}}
|-
| {{center|20:20:00}}
| {{font color|red|{{small|Lander unfolds solar panels}}}}
|-
| {{center|20:20:00}}
| {{font color|red|{{small|Medium gain antenna pointed at Earth}}}}
|-
| {{center|20:39:00}}
| {{font color|red|{{small|'''Lander begins 1st transmission to Earth (45 minutes). Sends health & status, meteorology & 1 b/w image'''}}}}
|-
| {{center|21:24:00}}
| {{font color|red|{{small|Lander ends transmission to Earth}}}}
|-
| {{center|21:45:00}}
| {{font color|red|{{small|Lander powers down to sleep so it can recharge}}}}
|-
| {{center|22:10:00}}
| {{font color|red|{{small|Start of 1 hour backup downlink opportunity (if spacecraft went into safemode during landing)}}}}
|-
| {{center|'''1999-12-04'''}}
|
|-
| {{center|02:50:00}}
| {{font color|red|{{small|Lander wakes up, receives instructions from Earth}}}}
|-
| {{center|03:25:00}}
| {{font color|red|{{small|'''Begin DS2 microprobe data reception via Mars Global Surveyor relay (15 minute transmission)'''}}}}
|-
| {{center|04:25:00}}
| {{font color|red|{{small|2.5 hour downlink begins, could include lander and descent images}}}}
|-
| {{center|06:25:00}}
| {{font color|red|{{small|Lander shuts itself down until next day. End of Sol 0 activities.}}}}
|-
| colspan="2" | {{center|<small>Items in {{font color|red|'''red'''}} were planned events.</small>}}
|}
|-
| {{center|1999-12-03}}
|
<!-- Collapsable data header -->
{| class="collapsible collapsed" align="center" width="100%"
! colspan="2" style="background-color:#e9e9e9;font-weight:normal;" | Failure to regain communication after landing
|-
| colspan="2" |
----
|- style="background-color:#e0e0e0"
! scope="col" width="75" | Time
! scope="col" width="230" | Event {{pad|6em}}
|-
| colspan="2" |
----
<!-- Collapsable data input-copy for more entries -->
|-
| {{center|'''1999-12-03'''}}
|
|-
| {{center|20:39:00}}
| {{small|First communication from lander missed}}
|-
| {{center|22:04:00}}
| {{small|Second communication from lander missed}}
|-
| {{center|'''1999-12-04'''}}
|
|-
| {{center|04:08:00}}
| {{small|Third communication from lander missed}}
|-
| {{center|'''1999-12-05'''}}
|
|-
| {{center|04:30:00}}
| {{small|Fourth communication from lander missed}}
|-
| {{center|18:50:00}}
| {{small|First attempt to detect automatic fail-safe UHF communication to Mars Global Surveyor failed}}
|-
| {{center|'''1999-12-06'''}}
|
|-
| {{center|06:10:00}}
| {{small|Second attempt to detect automatic fail-safe UHF communication to Mars Global Surveyor failed}}
|-
| {{center|'''1999-12-07'''}}
|
|-
| {{center|08:20:00}}
| {{small|Third attempt to detect automatic fail-safe UHF communication to Mars Global Surveyor failed}}
|-
| {{center|'''1999-12-08'''}}
| {{small|Radio sweeps of the surface by the Deep Space Network failed. Repeat of prior procedures to exhaust all possibilities of regaining contact.}}
|}
|-
| {{center|2000-01-17}}
| style="background-color:#f2f2f2;" | Mission declared a loss. No further attempts to contact.
|}
|}

=== Launch and trajectory ===
''Mars Polar Lander'' was launched on January 3, 1999, at 20:21:10 UTC by the [[NASA|National Aeronautics and Space Administration]] from [[Cape Canaveral Space Launch Complex 17|Space Launch Complex 17B]] at the [[Cape Canaveral Space Force Station|Cape Canaveral Air Force Station]] in Florida, aboard a [[Delta II]] 7425–9.5 launch vehicle. The complete burn sequence lasted for 47.7 minutes after a [[Thiokol]] [[Star 48]]B solid-fuel third stage booster placed the spacecraft into an 11-month, Mars transfer trajectory at a final velocity of {{cvt|6.884|km/s}} with respect to Mars. During cruise, the spacecraft was stowed inside an [[aeroshell]] capsule and a segment known as the ''cruise stage'' provided power and communications with Earth.{{r|press_kit_1998|press_kit_1999|nssdc1}}{{Clear}}

<!-- Gallery of launch and trajectories at end of section -->
{{Gallery|align=center
|width=175 |File:Mars Polar Lander - launch configuration diagram.png|alt1=Diagram of the configured positions of Mars Polar Lander within a Delta II launch vehicle |{{small|Launch configuration diagram.}}
|File:Mars Polar Lander - launch photo.png|alt2=Launch photo of Mars Polar Lander being lifted into space by a Delta II launch vehicle |{{small|Launch photo of Mars Polar Lander aboard a Delta II launch vehicle.}}
|File:Mars Polar Lander - interplanetary trajectory.png|alt3=Diagram of the interplanetary trajectory of Mars Polar Lander |{{small|Diagram of the interplanetary trajectory of Mars Polar Lander.}}
}}

=== Landing zone ===
The target landing zone was a region near the [[Planum Australe|south pole]] of Mars, called ''Ultimi Scopuli'', because it featured a large number of [[Scopulus|scopuli]] ([[wikt:lobe|lobate]] or irregular [[escarpment|scarps]]).{{citation needed|date=July 2016}}

=== Landing attempt ===
{{further|Exploration of Mars}}
{{multiple image
| footer    = Mars Polar Lander entered the Martian atmosphere with an aeroshell for protection from atmospheric friction.
| image1    = Mars Polar Lander - cruise configuration.png
| width1     = 90
| alt1      = Cruise configuration diagram of Mars Polar Lander.
| caption1  = <small>Cruise configuration</small>
| image2    = Mars Polar Lander - landing diagram.png
| width2     = 102
| alt2      = Diagram of landing procedures of Mars Polar Lander as it would pass through the atmosphere and land on the surface.
| caption2  = <small>Landing procedure</small>
| image3    = Mars Polar Lander - targeted landing sector.png
| width3     = 84
| alt3      = Map of the region targeted for landing by the Mars Polar Lander.
| caption3  = <small>Landing region</small>
}}
On December 3, 1999, ''Mars Polar Lander'' arrived at Mars and mission operators began preparations for landing. At 14:39:00 UTC, the cruise stage was jettisoned, which began a planned communication dropout to last until the spacecraft had touched down on the surface. Six minutes prior to atmospheric entry, a programmed 80-second thruster firing turned the spacecraft to the proper entry orientation, with the [[heat shield]] positioned to absorb the 1,650&nbsp;°C heat that would be generated as the descent capsule passed through the atmosphere.

Traveling at 6.9 kilometers per second, the entry capsule entered the [[Atmosphere of Mars|Martian atmosphere]] at 20:10:00 UTC, and was expected to land in the vicinity of {{Coord|76|S|195|W|globe:Mars|name=Mars Polar Lander}} in a region known as [[Planum Australe]]. Reestablishment of communication was anticipated for 20:39:00 UTC, after landing. However communication was not reestablished, and the lander was declared lost.{{r|press_kit_1998|press_kit_1999|nssdc1}}

=== Intended operations ===
Traveling at approximately {{cvt|6.9|km/s}} and {{cvt|125|km|mi}} above the surface, the spacecraft entered the atmosphere and was initially decelerated by using a 2.4 meter [[ablation]] [[heat shield]], located on the bottom of the entry body, to [[Aerobraking|aerobrake]] through {{cvt|116|km|mi}} of the atmosphere. Three minutes after entry, the spacecraft had slowed to {{cvt|496|m/s}}, signaling an 8.4-meter [[polyester]] parachute to deploy from a mortar, followed immediately by heat shield separation and MARDI powering on while {{cvt|8.8|km|mi}} above the surface. The parachute further slowed the speed of the spacecraft to {{cvt|85|m/s}} when the ground radar began tracking surface features to detect the best possible landing location and determine the vertical speed via the Doppler effect for thrust control.

When the spacecraft had slowed to {{cvt|80|m/s}}, one minute after parachute deployment, the lander separated from the backshell and began a powered descent at {{cvt|1.3|km|mi}} aloft. Vertical speed was intended to drop to 2.4 meters per second at 12 m height and then be constant until touchdown. Below 40 meters, the radar would become unreliable by raised dust and was switched off already at that height; for the final seconds, the thrust would be controlled by inertial sensors. A function to switch off the thrust immediately at touchdown was also armed at 40 meters. Touchdown was expected at 20:01 UTC, given as 20:15 ″Earth-received time″.{{r|press_kit_1998|press_kit_1999|nssdc1|nasa1}}

Lander operations were to begin five minutes after touchdown, first unfolding the stowed solar arrays, followed by orienting the medium-gain, direct-to-Earth antenna to allow for the first communication with the NASA Deep Space Network. A 45-minute transmission was to be broadcast to Earth containing 30 landing images acquired by MARDI. Arrival of that signal of a successful landing was expected at 20:39 UTC. The lander would then power down for six hours to allow the batteries to charge. On the following days, the spacecraft instruments would be checked by operators and science experiments were to begin on December 7 and last for at least the following 90 [[Timekeeping on Mars#Sols|Martian Sols]], with the possibility of an extended mission.{{r|press_kit_1998|press_kit_1999|nssdc1|nasa1}}

== Loss of communications ==
On December 3, 1999, at 14:39:00 UTC, the last [[telemetry]] from ''Mars Polar Lander'' was sent, just prior to cruise stage separation and the subsequent atmospheric entry. No further signals were received from the spacecraft. Attempts were made by the [[Mars Global Surveyor]] to photograph the area in which the lander was believed to be. An object was visible and believed to be the lander. However, subsequent imaging in September 2005 resulted in the identified object being ruled out. ''Mars Polar Lander'' remains lost.{{r|skytel1|nasa20051017}}

The cause of the communication loss is not known. However, the Failure Review Board concluded that the most likely cause of the mishap was a software error that incorrectly identified vibrations, caused by the deployment of the stowed legs, as surface touchdown.{{r|youtube1}} The resulting action by the spacecraft was the shutdown of the descent engines, while still likely 40 meters above the surface. Although it was known that leg deployment could create the false indication, the software's design instructions did not account for that eventuality.{{r|Leveson_2004}}

In addition to the premature shutdown of the descent engines, the Failure Review Board also assessed other potential modes of failure.{{r|LossReport}} Lacking substantial evidence for the mode of failure, the following possibilities could not be excluded:

* Surface conditions exceed landing design capabilities;
* Loss of control due to dynamic effects;
* Landing site not survivable;
* Backshell/parachute contacts lander;
* Loss of control due to center-of-mass offset; or
* Heatshield fails due to [[micrometeoroid]] impact.

The failure of the Mars Polar Lander took place two and a half months after the loss of the [[Mars Climate Orbiter]]. Inadequate funding and poor management have been cited as underlying causes of the failures.{{r|spaceref-20000314}} According to Thomas Young, chairman of the Mars Program Independent Assessment Team, the program "was under funded by at least 30%."{{r|PBS-20000414}}

{| class="wikitable" style="margin:1em auto;"
! Quoted from the report{{r|LossReport}}
|-
| scope="col" width="750" |
"A magnetic sensor is provided in each of the three landing legs to sense touchdown when the lander contacts the surface, initiating the shutdown of the descent engines. Data from MPL engineering development unit deployment tests, MPL flight unit deployment tests, and Mars 2001 deployment tests showed that a spurious touchdown indication occurs in the [[Hall effect|Hall Effect]] touchdown sensor during landing leg deployment (while the lander is connected to the parachute). The software logic accepts this transient signal as a valid touchdown event if it persists for two consecutive readings of the sensor. The tests showed that most of the transient signals at leg deployment are indeed long enough to be accepted as valid events, therefore, it is almost a certainty that at least one of the three would have generated a spurious touchdown indication that the software accepted as valid.

The software—intended to ignore touchdown indications prior to the enabling of the touchdown sensing logic—was not properly implemented, and the spurious touchdown indication was retained. The touchdown sensing logic is enabled at 40 meters altitude, and the software would have issued a descent engine thrust termination at this time in response to a (spurious) touchdown indication.

At 40 meters altitude, the lander has a velocity of approximately 13 meters per second, which, in the absence of thrust, is accelerated by Mars gravity to a surface impact velocity of approximately 22 meters per second (the nominal touchdown velocity is 2.4 meters per second). At this impact velocity, the lander could not have survived."
|}

[[Planum Australe]], which served as the exploration target for the lander and the two [[Deep Space 2]] probes,{{r|AMS-20190106}} would in later years be explored by European Space Agency's [[MARSIS]] radar, which examined and analyzed the site from Mars' orbit.{{r|Orosei_2018|NYT-20180725|eureka1|bbc1}}

== See also ==
{{Portal|Spaceflight}}
{{div col|colwidth=30em}}
* [[Mars Surveyor 2001]], similar design lander, mission cancelled. Lander used for Phoenix.
* [[Phoenix (spacecraft)|''Phoenix'' lander]], 2008
* [[Exploration of Mars]]
* [[ExoMars]] rover
* [[List of missions to Mars]]
* [[Mars Science Laboratory]] rover
{{div col end}}
* [[List of software bugs#Space|List of software bugs]]

== References ==
{{Reflist|refs=

<ref name="AMS-20190106">{{cite news
| author1= B. Evans
| title= 'Could Not Have Survived': 20 Years Since NASA's Ill-Fated Mars Polar Lander
| url= https://www.americaspace.com/2019/01/06/could-not-have-survived-20-years-since-nasas-ill-fated-mars-polar-lander/
| work= AmericaSpace
| date= 6 January 2019
| access-date= 15 April 2022 }}
</ref>

<ref name="AP-19991208">{{cite news
| title= Mars Polar Lander Mission Costs
| url= https://apnews.com/article/0520e4b6fa628215ee93b0d3c74d6ce2A
| newspaper= [[Associated Press]]
| date= 8 December 1999
| access-date= 30 September 2020
| archive-date= 17 February 2022
| archive-url= https://web.archive.org/web/20220217151317/https://apnews.com/article/0520e4b6fa628215ee93b0d3c74d6ce2A
| url-status= dead }}
</ref>

<ref name="bbc1">{{cite web
| author1= M. Halton
| title= Liquid water 'lake' revealed on Mars
| url= https://www.bbc.com/news/science-environment-44952710
| work= [[BBC News]]
| date= 25 July 2018
| access-date= 15 April 2022 }}
</ref>

<ref name="eureka1">{{cite web
| title= Huge reservoir of liquid water detected under the surface of Mars
| url= https://www.eurekalert.org/pub_releases/2018-07/aaft-hro072318.php
| work= EurekAlert
| date= 25 July 2018
| access-date= 15 April 2022 }}
</ref>

<ref name="Leveson_2004">{{cite journal | author1= N. G. Leveson
| title= The Role of Software in Recent Aerospace Accidents
| url= http://sunnyday.mit.edu/accidents/issc01.pdf
| journal= Journal of Spacecraft and Rockets
| volume= 41
| issue= 4
| date= July 2004
| doi= 10.2514/1.11950 }}
</ref>

<ref name="LossReport">{{cite web
| title= Report on the Loss of the ''Mars Polar Lander'' and ''Deep Space 2'' Missions
| url= ftp://ftp.hq.nasa.gov/pub/pao/reports/2000/2000_mpl_report_1.pdf
| publisher= [[NASA]] / [[Jet Propulsion Laboratory|JPL]]
| archive-url= https://web.archive.org/web/20151213144413/ftp://ftp.hq.nasa.gov/pub/pao/reports/2000/2000_mpl_report_1.pdf
| archive-date= 2015-12-13
| url-status= dead
| date= 22 March 2000
}}
</ref>

<ref name="nasa1">{{cite web
| title= Mars Polar Lander / Deep Space 2 - NASA Science
| url= https://science.nasa.gov/mission/mars-polar-lander-deep-space-2/
| website= science.nasa.gov
| publisher= [[NASA]]
| access-date= 12 March 2011 }}
</ref>

<ref name="nasa20051017">{{cite web
| title= Mars Polar Lander NOT Found
| url= https://www.msss.com/mars_images/moc/2005/10/17/
| website= www.msss.com
| publisher= [[NASA]] / [[Jet Propulsion Laboratory|JPL]]
| date= 17 October 2005
| access-date= 22 April 2009
| archive-url= https://web.archive.org/web/20081207053229/http://www.msss.com/mars_images/moc/2005/10/17/
| archive-date= 7 December 2008
| url-status= live
| id= MGS-MOC2-1253 }}
</ref>

<ref name="nssdc1">{{cite web
| title= Mars Polar Lander
| url= https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1999-001A
| website= nssdc.gsfc.nasa.gov
| publisher= [[NASA]]
| access-date= 1 December 2022 }}
</ref>

<ref name="nssdc2">{{cite web
| title= Mars Polar Lander: Mars Descent Imager (MARDI)
| url= https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1999-001A-02
| website= nssdc.gsfc.nasa.gov
| publisher= [[NASA]]
| access-date= 17 March 2011 }}
</ref>

<ref name="nssdc3">{{cite web
| title= Mars Polar Lander: Mars Volatiles and Climate Surveyor (MVACS)
| url= https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1999-001A-01
| website= nssdc.gsfc.nasa.gov
| publisher= [[NASA]]
| access-date= 17 March 2011 }}
</ref>

<ref name="nssdc4">{{cite web
| title= Mars Polar Lander: Light Detection and Ranging (LIDAR)
| url= https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1999-001A-03
| website= nssdc.gsfc.nasa.gov
| publisher= [[NASA]]
| access-date= 17 March 2011 }}
</ref>

<ref name="nssdc5">{{cite web 
| title= Mars Polar Lander: Mars Microphone
| url= https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1999-001A-04
| website= nssdc.gsfc.nasa.gov
| publisher= [[NASA]]
| access-date= 17 March 2011 }}
</ref>

<ref name="NYT-20180725">{{cite news
| author1= K. Chang
| author2= D. Overbye
| title= A Watery Lake Is Detected on Mars, Raising the Potential for Alien Life
| url= https://www.nytimes.com/2018/07/25/science/mars-liquid-alien-life.html
| date= 25 July 2018
| work= [[The New York Times]]
| access-date= 15 April 2022 }}
</ref>

<ref name="Orosei_2018">{{cite journal
| author1= R. Orosei
| author2= S. E. Lauro
| author3= E. Pettinelli
| author4= A. Cicchetti
| author5= M. Coradini
| author6= B. Cosciotti
| author7= F. Di Paolo
| author8= E. Flamini
| author9= E. Mattei
| author10= M. Pajola
| author11= F. Soldovieri
| author12= M. Cartacci
| author13= F. Cassenti
| author14= A. Frigeri
| author15= S. Giuppi
| author16= R. Martufi
| author17= A. Masdea
| author18= G. Mitri
| author19= C. Nenna
| author20= R. Noschese
| author21= M. Restano
| author22= R. Seu
| display-authors= 5
| title= Radar Evidence of Subglacial Liquid Water on Mars
| date= 25 July 2018
| journal= [[Science (journal)|Science]]
| volume= 361
| issue= 6401
| pages= 490–493
| doi= 10.1126/science.aar7268
| arxiv= 2004.04587
| pmid= 30045881
| hdl= 11573/1148029
| doi-access= free
| bibcode= 2018Sci...361..490O }}
</ref>

<ref name="PBS-20000414">{{cite news
| author1= J. Kaye
| title= NASA in the Hot Seat
| url= https://www.pbs.org/newshour/bb/science/jan-june00/nasa_4-14.html
| format= transcript
| work= NewsHour with Jim Lehrer
| publisher= [[PBS]]
| date= 14 April 2000
| access-date= 22 April 2009
| archive-date= 26 December 2013
| archive-url= https://web.archive.org/web/20131226075519/http://www.pbs.org/newshour/bb/science/jan-june00/nasa_4-14.html
| url-status= dead }}
</ref>

<ref name="press_kit_1998">{{cite press release
| title= 1998 Mars Missions
| url= http://www.jpl.nasa.gov/files/misc/mars98launch.pdf
| publisher= [[NASA]] / [[Jet Propulsion Laboratory|JPL]]
| date= December 1998
| access-date= 12 March 2011
| archive-date= 30 April 2020
| archive-url= https://web.archive.org/web/20200430120208/https://www2.jpl.nasa.gov/files/misc/mars98launch.pdf
| url-status= dead
| format= Press Kit }}
</ref>

<ref name="press_kit_1999">{{cite press release
| title= Mars Polar Lander/Deep Space 2
| url= http://www.jpl.nasa.gov/files/misc/mpl-ds2hq.pdf
| publisher= [[NASA]] / [[Jet Propulsion Laboratory|JPL]]
| date= December 1999
| access-date= 12 March 2011
| archive-date= 23 December 2016
| archive-url= https://web.archive.org/web/20161223235619/http://www2.jpl.nasa.gov/files/misc/mpl-ds2hq.pdf
| url-status= dead
| format= Press Kit }}
</ref>

<ref name="send_name_1998">{{cite news
| author1= B. Huh
| title= Kids' Names Going To Mars
| url= http://articles.sun-sentinel.com/1998-03-03/lifestyle/9803020131_1_martian-surface-robotic-arm-space-program
| work= Sun Sentinel
| date= 3 March 1998
| access-date= 30 May 2013
| archive-date= 2 December 2013
| archive-url= https://web.archive.org/web/20131202235239/http://articles.sun-sentinel.com/1998-03-03/lifestyle/9803020131_1_martian-surface-robotic-arm-space-program
| url-status= dead }}
</ref>

<ref name="spaceref-20000314">{{cite report
| author= T. Young
| title= Mars Program Independent Assessment Team Summary Report
| version= Draft #7
| publisher= House Science and Technology Committee
| url= http://www.spaceref.com/news/viewpr.html?pid=1444
| date= 13 March 2000
| access-date= 22 April 2009
}}
</ref>

<ref name="skytel1">{{cite news
| title= Mars Polar Lander Found at Last?
| url= http://skyandtelescope.com/news/article_1509_1.asp
| work= [[Sky & Telescope]]
| date= 6 May 2005
| access-date= 22 April 2009
| archive-url= https://web.archive.org/web/20080723233112/http://skyandtelescope.com/news/article_1509_1.asp
| archive-date= 23 July 2008
| url-status= dead }}
</ref>

<ref name="tps1">{{Cite web
| title= Projects: Planetary Microphones -- The Mars Microphone
| url= http://www.planetary.org/programs/projects/planetary_microphones/mars_microphone.html
| work= [[The Planetary Society]]
| archive-date= 18 August 2006
| archive-url= https://web.archive.org/web/20060818152601/http://www.planetary.org/programs/projects/planetary_microphones/mars_microphone.html
| url-status= dead }}
</ref>

<ref name="youtube1">{{YouTube
| id= YJ6pbCHpXEI
| title= NASA 3: Mission Failures }}
</ref>

}}

== Further reading ==
{{Commons category}}
* {{cite journal | author=Michael C. Malin | title=Hidden in Plain Sight: Finding Martian Landers | journal=Sky and Telescope | volume=110 | issue=7| date=July 2005 | pages=42–46 | bibcode=2005S&T...110a..42M | issn=0037-6604}}

{{Mars}}
{{Features and artificial objects on Mars}}
{{Mars spacecraft}}
{{Orbital launches in 1999}}
{{Jet Propulsion Laboratory}}

[[Category:Missions to Mars]]
[[Category:NASA space probes]]
[[Category:Derelict landers (spacecraft)]]
[[Category:Mare Australe quadrangle]]
[[Category:Spacecraft launched in 1999]]
[[Category:Spacecraft launched by Delta II rockets]]
[[Category:Space accidents and incidents in the United States]]
[[Category:Attached spacecraft]]
[[Category:1999 on Mars]]