Editing Mars Reconnaissance Orbiter (section)

=== Engineering instruments and experiments ===
In addition to its imaging equipment, ''MRO'' carries three engineering instruments.  The [[Electra (radio)|Electra]] communications package is a [[Ultra high frequency|UHF]] [[software-defined radio]] that provides a flexible platform for evolving relay capabilities.<ref name="Electra">{{cite web |title=The Electra Proximity Link Payload for Mars Relay Telecommunications and Navigation |author1=Charles D. Edwards Jr. |author2=Thomas C. Jedrey |author3=Eric Schwartzbaum |author4=and Ann S. Devereaux |author5=Ramon DePaula |author6=Mark Dapore |author7=Thomas W. Fischer |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/7832/1/03-2150.pdf  |archive-url=https://web.archive.org/web/20130502170707/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/7832/1/03-2150.pdf |archive-date=May 2, 2013 }}</ref> It is designed to communicate with other spacecraft as they approach, land, and operate on Mars. In addition to protocol controlled inter-spacecraft data links of 1&nbsp;kbit/s to 2&nbsp;Mbit/s, Electra also provides Doppler data collection, open loop recording and a highly accurate timing service based on an [[ultra-stable oscillator]].<ref name=":1">{{Cite web |date=March 2006 |title=Mars Reconnaissance Orbiter Arrival Press Kit |url=https://mars.nasa.gov/files/mro/mro-arrival.pdf |access-date=January 20, 2023 |website=NASA |archive-date=December 10, 2022 |archive-url=https://web.archive.org/web/20221210105536/https://mars.nasa.gov/files/mro/mro-arrival.pdf |url-status=live }}</ref><ref>{{Cite web |last1=Taylor |first1=Jim |last2=Lee |first2=Dennis K. |last3=Shambayati |first3=Shervin |date=September 2006 |title=Mars Reconnaissance Orbiter Telecommunications |url=https://descanso.jpl.nasa.gov/DPSummary/MRO_092106.pdf |access-date=January 20, 2023 |website=JPL DESCANSO |archive-date=January 20, 2023 |archive-url=https://web.archive.org/web/20230120201350/https://descanso.jpl.nasa.gov/DPSummary/MRO_092106.pdf |url-status=live }}</ref> [[Doppler effect|Doppler information]] for approaching vehicles can be used for final descent targeting or descent and landing trajectory recreation. Doppler information on landed vehicles allows scientists to accurately determine the surface location of Mars landers and rovers. The two Mars Exploration Rover (MER) spacecraft utilized an earlier generation UHF relay radio providing similar functions through the Mars Odyssey orbiter. The Electra radio has relayed information to and from the MER spacecraft, ''Phoenix'' lander and ''Curiosity'' rover.<ref>{{Cite web |title=Electra |url=https://mars.nasa.gov/mro/mission/instruments/electra/ |access-date=January 20, 2023 |website=NASA MARS Reconnaissance Orbiter |archive-date=September 28, 2022 |archive-url=https://web.archive.org/web/20220928104722/https://mars.nasa.gov/mro/mission/instruments/electra/ |url-status=live }}</ref>

[[File:Phobos by MRO.jpg|thumb|An image of [[Phobos (moon)|Phobos]] taken by HiRISE on March 23, 2008, from a distance of around {{convert|6,800|km}}<ref>{{Cite web |date=2008-04-09 |title=PIA10368: Phobos from 6,800 Kilometers (Color) |url=https://photojournal.jpl.nasa.gov/catalog/PIA10368 |url-status=live |archive-url=https://web.archive.org/web/20230723221437/https://photojournal.jpl.nasa.gov/catalog/PIA10368 |archive-date=July 23, 2023 |access-date=July 16, 2023 |website=photojournal.jpl.nasa.gov}}</ref>]]
During the cruise phase, the ''MRO'' also used the {{Ka band}} Telecommunications Experiment Package to demonstrate a less power-intensive way to communicate with Earth.<ref>{{Cite web |title=Ka-band – NASA |url=https://mars.nasa.gov/mro/mission/instruments/kaband/ |access-date=2023-08-21 |website=mars.nasa.gov |language=en |archive-date=August 21, 2023 |archive-url=https://web.archive.org/web/20230821210310/https://mars.nasa.gov/mro/mission/instruments/kaband/ |url-status=live }}</ref>

The Optical Navigation Camera images the Martian moons, [[Phobos (moon)|Phobos]] and [[Deimos (moon)|Deimos]], against background stars to precisely determine ''MRO''<nowiki/>'s orbit. Although this is not critical, it was included as a technology test for future orbiting and landing of spacecraft.<ref name="Spacecraft Parts: Optical Navigation Camera" /> The Optical Navigation Camera was tested successfully in February and March 2006.<ref name="Optical Navigation Demonstration Near Mars Multimedia Feature" /> It was subsequently turned off, but was turned back on in 2022 to collect data for a potential [[NASA-ESA Mars Sample Return]] mission.<ref name=":8" />{{Rp|page=11}}

Two additional science investigations are also on the spacecraft. The Gravity Field Investigation Package measures variations in the [[Gravity of Mars|Martian gravitational field]] through variations in the spacecraft's speed. Speed changes are detected by measuring doppler shifts in ''MRO''<nowiki/>'s radio signals received on Earth. Data from this investigation can be used to understand the subsurface geology of Mars, determine the density of the atmosphere and track seasonal changes in the location of carbon dioxide deposited on the surface.<ref name="Spacecraft Parts: Gravity Field Investigation Package" /> Due to decreased budgets, data collection ended in 2022.<ref name=":8" />{{Rp|page=8}}

The Atmospheric Structure Investigation used sensitive onboard [[accelerometer]]s to deduce the ''in situ'' atmospheric density of Mars during aerobraking. The measurements helped provide greater understanding of seasonal wind variations, the effects of dust storms, and the structure of the atmosphere.<ref>{{Cite web |title=Accelerometers – NASA |url=https://mars.nasa.gov/mro/mission/instruments/atmosaccel/ |access-date=2023-08-18 |website=mars.nasa.gov |language=en}}</ref>