Editing Luna 4 (section)

==Spacecraft==

The Ye-6 spacecraft consisted of a stack of three cylindrical modules, with a height of {{cvt|2.7|m}} and a launch mass of {{cvt|1422|kg}}. The first module was the Isayev rocket module, which held the main engine, used for mid-course correction and the descent to landing, four thrusters for attitude control, and two cruise modules. The main engine propellant was [[hypergolic]], consisting of [[nitric acid]] and [[amine]] and producing a thrust of about 45,000 [[Newton (unit)|N]]. The four thrusters were mounted on outriggers and could produce 245 N each. A {{cvt|5|m}} boom would be deployed from the bottom of the spacecraft, used to trigger the final landing sequence. The second module was a hermetically sealed pressurized compartment that held the propellant and oxygen and contained communication, attitude orientation, an altimeter, and the onboard control system ("I-100").<ref name=nssdc/>

Luna 4 carried an astronavigation system so that it could autonomously change course midflight. This device (SAN) was derived from similar systems developed for aircraft. The spacecraft's autonomous control system, gyroscopes, control and logic circuits were all combined in the {{cvt|80|kg}} I-100 package that also controlled aspects of the Molniya rocket's third and fourth stages; this was a weight-saving measure that, nevertheless, was conducive to failures, as had occurred when similar solutions had been applied to the [[Mars program|Mars]] and [[Venera]] spacecraft.<ref name=ranp3/>{{rp|379}}

The third module was the lunar lander, a {{cvt|58|cm}} diameter sphere protected by two hemispherical airbags. The {{cvt|105|kg}} sphere had a hermetically sealed compartment that held communications apparatus, batteries, thermal control systems, a timer, and the science experiments. The top of the sphere had four petals, which would open up on landing, allowing deployment of four {{cvt|75|cm}} whip antennas and the lander camera turret. Control of the lander was done by the timing device onboard or by communication from Earth. The batteries were designed to operate for a total of 5 hours over about 4 days.<ref name=nssdc/> 

The scientific payload comprised an imaging system and an SBM-10 radiation detector.<ref name=nssdc/> The latter was a [[Geiger counter|gas-discharge counter]], {{cvt|50|mm}} long and {{cvt|10|mm}} in diameter, heavily shielded on one side. Radiation counts were telemetered continuously with a statistical accuracy of about 0.1%.<ref name=study>{{cite journal|author=S. N. Vernov, A. Ye. Chudakov, P. V. Vakulov, Ye. V. Gorchakov, Yu. I. Logachev, G. P. Lyubimov, A. G. Nikolayev|title=Investigation of Radiation with the Flights of the "Mars 1" and "Luna 4" Interplanetary Automatic Stations|journal=Cosmic Research |volume= 2 |issue= 4 |year=1964 |language= Russian|url=https://apps.dtic.mil/dtic/tr/fulltext/u2/605513.pdf|archive-url=https://web.archive.org/web/20190426223255/https://apps.dtic.mil/dtic/tr/fulltext/u2/605513.pdf |archive-date=April 26, 2019 }}</ref>

The mission plan was to initialize the landing sequence at an altitude of about {{cvt|8300|km}}. At {{cvt|70|km}} to {{cvt|75|km}} altitude the cruise modules would be jettisoned, the main engine would start, the radar altimeter would be activated, and the lander airbags would inflate. At {{cvt|250|m}} to {{cvt|265|m}} altitude the main engine would shut off and the four thrusters would ignite. The {{cvt|5|km}} meter boom would touch the surface first, causing the ejection of the lander, which would hit the surface, cushioned by the airbags, at about {{cvt|15|m/s}}. The airbags would deflate, the petals would open, causing the sphere to be oriented correctly, and the antennas and instruments could be deployed.<ref name=nssdc/>{{PD-notice}}