Editing Viking program (section)

===Entry, Descent and Landing (EDL)===
Each lander arrived at Mars attached to the orbiter. The assembly orbited Mars many times before the lander was released and separated from the orbiter for descent to the surface. Descent comprised four distinct phases, starting with a [[Deorbit#Deorbit and re-entry|deorbit burn]]. The lander then experienced [[atmospheric entry]] with peak heating occurring a few seconds after the start of frictional heating with the Martian atmosphere. At an altitude of about {{convert|6|km|mi|abbr=off|sp=us}} and traveling at a velocity of 900 kilometers per hour (600&nbsp;mph), the parachute deployed, the aeroshell released and the lander's legs unfolded. At an altitude of about 1.5 kilometers (5,000 feet), the lander activated its three retro-engines and was released from the parachute. The lander then immediately used [[retrorockets]] to slow and control its descent, with a [[soft landing (rocketry)|soft landing]] on the surface of Mars.<ref name="astro.if.ufrgs.br-viking">{{Cite web |title=Viking |url=http://astro.if.ufrgs.br/solar/viking.htm |url-status=live |archive-url=https://web.archive.org/web/20230813090441/http://astro.if.ufrgs.br/solar/viking.htm |archive-date=August 13, 2023 |website=astro.if.ufrgs.br }}</ref>
{{Wide image|Mars_Viking_12a001.png|800px|First "clear" image ever transmitted from the surface of Mars – shows [[List of rocks on Mars#Viking|rocks]] near the ''[[Viking 1]]'' lander (July 20, 1976).}} At landing (after using rocket propellant) the landers had a mass of about 600&nbsp;kg.