GSAT-18

{{Short description|Indian communications satellite}}

{{Infobox spaceflight |auto=all

| name = GSAT-18

| image = File:GSAT-18.png

| mission_type = Communications

| operator = INSAT

| COSPAR_ID = 2016-060A

| SATCAT = 41793

| website = [http://isro.gov.in/Spacecraft/gsat-18 GSAT-18]

| mission_duration = Planned: 15 years
Elapsed: {{time interval|5 October 2016 20:30|show=ymd|sep=,}}

| spacecraft_bus = I-3K{{cite web |url=http://www.isro.gov.in/sites/default/files/article-files/right-to-information/annual_report-15-16.pdf |title=Annual Report 2015-2016 |publisher=Indian Space Research Organisation |format=PDF |page=28 |date=December 2015 |url-status=dead |archive-url=https://web.archive.org/web/20160705060034/http://www.isro.gov.in/sites/default/files/article-files/right-to-information/annual_report-15-16.pdf |archive-date=2016-07-05 }}

| manufacturer = ISRO Satellite Centre
Space Applications Centre

| launch_mass = {{convert|3404|kg|lb|abbr=on}}{{cite web |url=http://www.isro.gov.in/sites/default/files/flipping_book/GSAT-18/files/assets/common/downloads/GSAT%2018%20-%20Brochure.pdf |title=GSAT-18 |publisher=Indian Space Research Organisation |access-date=2017-06-12 |archive-date=2016-12-13 |archive-url=https://web.archive.org/web/20161213050343/http://www.isro.gov.in/sites/default/files/flipping_book/GSAT-18/files/assets/common/downloads/GSAT%2018%20-%20Brochure.pdf |url-status=dead }}

| dry_mass = {{convert|1480|kg|lb|0|abbr=on}}

| dimensions =

| power = 6,474 watts

| launch_date = {{start-date|5 October 2016}}, ≈20:30 UTC{{cite news |url=https://www.nasaspaceflight.com/2016/10/ariane-5-sky-muster-ii-gsat-18-launch/ |title=Ariane 5 launches Sky Muster II and GSAT-18 |work=NASA Spaceflight |first=Chris |last=Bergin |date=5 October 2016 |access-date=6 October 2016}}

| launch_rocket = Ariane 5 ECA, VA-231

| launch_site = Guiana Space Centre ELA-3

| launch_contractor = Arianespace

| entered_service =

| orbit_reference = Geocentric

| orbit_regime = Geostationary

| orbit_longitude = 74° E

| orbit_periapsis = {{convert|35750|km|mi|0|abbr=on}}

| orbit_apoapsis = {{convert|35822|km|mi|0|abbr=on}}

| orbit_inclination = 0.0616°

| orbit_epoch = 11 June 2017 01:46:00 UTC{{cite web |url=http://heavens-above.com/orbit.aspx?satid=41793 |title=GSAT-18 - Orbit |work=Heavens-Above |date=11 June 2017 |access-date=12 June 2017}}

| apsis = gee

| trans_band = 24 × C band
12 × extended C band
12 × K_u band
2 × K_u beacon

| programme = GSAT

| previous_mission = GSAT-15

| next_mission = GSAT-9

}}

GSAT-18 is an Indian communications satellite. Built by ISRO and operated by INSAT, it carries 24 C-band, 12 extended C-band, and 12 K_u-band transponders.As of 2025, 6 transponders in the spacecraft are kept in idle, as GSAT-14 covers their spectrum.they are expected to be online in early 2027.{{Cite web |date=2025-03-27 |title=GSAT-18 cost: PAC tells space dept to be economically prudent |url=https://indianexpress.com/article/india/gsat-18-cost-pac-tells-space-dept-to-be-economically-prudent-9908053/ |access-date=2025-06-09 |website=The Indian Express |language=en}}

The satellite was launched on 5 October 2016 at approximately 20:30 UTC aboard an Ariane 5 ECA rocket from the Guiana Space Centre in Kourou, French Guiana.{{cite news |url=http://www.business-standard.com/article/pti-stories/india-s-communication-satellite-gsat-18-launched-successfully-116100600381_1.html |title=India's communication satellite GSAT-18 launched successfully |work=Business Standard |agency=Press Trust of India |date=6 October 2016 |access-date=6 October 2016}} The launch vehicle inserted the satellite into a geosynchronous transfer orbit, and once in service it will occupy the orbital slot at 74° East longitude.{{cite web|url=https://spaceflightnow.com/launch-schedule/ |title=Launch Schedule |work=Spaceflight Now |date=4 October 2016 |archive-url=https://web.archive.org/web/20161005082318/http://spaceflightnow.com/launch-schedule/ |archive-date=5 October 2016 |url-status=dead }} The total cost of the satellite and launch services was about {{US$|153 million}}.{{cite news |url=https://spaceflightnow.com/2016/10/05/ariane-5-goes-on-test-run-after-launching-two-satellites/ |title=Ariane 5 goes on test run after launching two satellites |work=Spaceflight Now |first=Stephen |last=Clark |date=5 October 2016 |access-date=6 October 2016}}

GSAT-18 was originally scheduled to launch on 12 July 2016 alongside Japan's Superbird-8 satellite, but a shipping mishap which damaged Superbird-8 forced a delay in the launch schedule.{{cite news |url=http://spacenews.com/japans-dsn-1-military-communications-satellite-damaged-during-transport-to-launch-base/ |title=Japan's DSN-1 military communications satellite damaged during transport to launch base |work=Space News |first=Peter B. |last=de Selding |date=20 June 2016 |access-date=10 September 2016}}{{cite news |url=http://www.thehindu.com/todays-paper/tp-national/deferred-gsat18-awaits-october-launch-at-kourou/article8829906.ece |title=Deferred GSAT-18 awaits October launch at Kourou |work=The Hindu |first=Madhumathi |last=D. S. |date=10 July 2016 |access-date=10 September 2016}} Arianespace later paired GSAT-18 with Australia's Sky Muster II for a 4 October 2016 launch.{{cite web |url=http://www.arianespace.com/mission-update/sky-muster-satellite-delivered-for-flight-va231/ |title=Sky Muster II comes to French Guiana for launch on Ariane 5 |publisher=Arianespace |date=31 August 2016 |access-date=10 September 2016}} The launch was delayed 24 hours to 5 October due to excessively high crosswinds at the launch site.{{cite news |url=http://www.hindustantimes.com/india-news/bad-winds-delay-isro-s-launch-of-communications-satellite-gsat-18-by-a-day/story-edkq5GVmwYVTBl1t2xxp3M.html |title=Bad weather delays Isro's launch of communications satellite GSAT-18 |work=Hindustan Times |agency=Press Trust of India |date=5 October 2016 |access-date=5 October 2016}}