Editing Ranger 3 (section)

== Mission ==
[[File:1964 71392L.jpg|thumb|Artist's concept of Ranger 3 in space]]
This was the first American attempt to achieve impact on the lunar surface. The Block II Ranger spacecraft carried a TV camera that used an optical telescope that would allow imaging down to about 24&nbsp;kilometers above the lunar surface during the descent. The main bus also carried a 42.6&nbsp;kilogram instrument capsule that would separate from the bus at 21.4&nbsp;kilometers altitude and then independently impact on the Moon. Protected by a balsa-wood outer casing, the capsule was designed to bounce several times on the lunar surface before coming to rest. The primary onboard instrument was a seismometer.

The mission was designed to boost towards the Moon by an Atlas/Agena, undergo one mid-course correction, and impact the lunar surface. At the appropriate altitude, the capsule was to separate and the retrorockets ignite to cushion the landing. A malfunction in the booster guidance system resulted in excessive spacecraft speed.<ref>{{cite news |title=US racing with the Moon; but Ranger goes too fast |url=https://news.google.com/newspapers?id=544jAAAAIBAJ&sjid=z50FAAAAIBAJ&pg=3565%2C4220174 |access-date=December 30, 2015 |agency=[[Associated Press]] |publisher=The Gazette |date=January 27, 1962 |location=Montreal, Quebec |page=1}}</ref>

Reversed command signals caused the spacecraft to pitch in the wrong direction and the TM antenna to lose earth acquisition, and mid-course correction was not possible. Finally, a spurious signal during the terminal maneuver prevented transmission of useful images. Ranger&nbsp;3 missed the Moon by approximately 36,800&nbsp;km on January&nbsp;28 and was now in a [[heliocentric orbit]]. Some useful engineering data were obtained from the flight.<ref name="nssdc1962-001A" />

===Preparation for launch===
Preparation for Ranger&nbsp;3 was complicated by developmental issues with the Agena&nbsp;B stage, which had failed to operate correctly on Rangers&nbsp;1-2. Agena was primarily the domain of the [[U.S. Air Force]], who intended to use it for military payloads, and NASA had originally assumed it would begin flying in late 1960 or early 1961 by which time any developmental issues with the stage could be weeded out. However, Agena&nbsp;B ended up taking longer to put into service than originally anticipated and its performance also turned out to be somewhat less than expected, which forced some of the planned experiments on the [[Ranger program|Block&nbsp;II]] Rangers to be cancelled.

While the Thor-Agena&nbsp;B had begun flying in October&nbsp;1960, the Atlas-Agena&nbsp;B did not make its maiden voyage until July&nbsp;1961, meaning that Ranger&nbsp;1 was only the second time this launch vehicle combination had been flown. This delay was explained by the fact that Air Force programs such as [[Midas (satellite)|MIDAS]] were taking much longer to develop than Ranger. In addition, as 1961 ended, Agena&nbsp;Bs had malfunctioned no less than seven times (the two Ranger launches and five Thor-Agena launches).

Major General [[Osmond J. Ritland]], Commander of the Air Force Space Systems Division in [[Inglewood, California]], promised NASA that all problems with Agena would be corrected and, because they also affected [[United States Department of Defense|DoD]] programs, the issue was being taken "quite seriously". Among other changes made would be a thorough review of all Lockheed field operating equipment and procedures. In addition, an effort would be made to ensure that checkout procedures on [[U.S. Air Force]] and NASA Agenas were identical and any differences in them eliminated.
[[File:Erection of Missile 121D.jpg|thumb|Erection of Atlas 121D on 12/21/1961]]
In mid-December&nbsp;1961, Atlas&nbsp;121D and Agena&nbsp;6003 arrived at [[Cape Canaveral]] and were erected on [[Cape Canaveral Air Force Station Launch Complex 12|LC-12]]. On January 18, 1962, Ranger&nbsp;3 was stacked atop the booster, but the following day attempted fueling of the Atlas went awry when a tear was found in the intermediate bulkhead separating the LOX and RP-1 tanks. This would mean that the launch vehicle would have to be taken down from the pad for repairs, delaying the launch an entire month. However, Air Force and Convair officials instead suggested the novel solution of doing the repairs right there on LC-12. The Atlas's sustainer engine was removed and lowered into the flame deflector pit and wooden scaffolding installed so that technicians could go up into the RP-1 tank, remove the damaged intermediate bulkhead, and replace it. By January&nbsp;26, repairs were completed.

===Equipment malfunctions and trajectory errors===
[[File:Launch of Ranger III with Agena.jpg|thumb|Launch of Ranger 3]]
Liftoff took place at 3:30&nbsp;PM EST on January&nbsp;26, an hour and 15&nbsp;minutes before the launch window closed, after which Ranger&nbsp;3 could not have been launched for another month.

At T+49&nbsp;seconds into launch, the pulse beacon on the Atlas guidance system ceased operating, which prevented the transmission of any steering or cutoff directions for the remainder of the launch. Backup commands from the missile programmer were used to perform booster jettison and Agena separation, but without the guidance program, it was impossible to perform the necessary fine-tuning maneuvers to put the Atlas on the correct flight path. Second engine cut-off occurred due to fuel running out, rather than a programmed cut-off command, causing the Agena and probe to be accelerated higher and faster than planned.

Even worse, equipment at a Florida tracking station malfunctioned and picked up Ranger&nbsp;3's orbital parameters 5&nbsp;minutes late. Meanwhile, the Agena restarted and sent the probe out of Earth orbit, but another error in its guidance program resulted in yet another trajectory error. As a consequence, the spacecraft reached the Moon 14&nbsp;hours early and on January&nbsp;28 missed striking the Moon by 36,793&nbsp;kilometers (22,862&nbsp;miles).

The trajectory errors made impact with the Moon impossible, but Ranger&nbsp;3 could still have been used for deep-space studies. So the flight controllers issued commands to unfurl the camera boom, and on January&nbsp;28 an amended computer program was uploaded. However, midway through the upload, the probe's signal strength began to weaken and the onboard computer system failed completely. Without a functioning computer, the spacecraft was not able keep its high-gain antenna aimed at the Earth, which impeded communication with controllers on the ground.

===Mission failure, propellant exhaustion, and cancellation===
The TV camera did transmit images, but since the antenna was now pointed away from Earth, the received images were extremely weak and noisy. It was possible to see the reference crosses on the camera lens, illuminated by reflected sunlight from the probe's chassis, but the Moon was not visible.

With the computer dead, Ranger&nbsp;3 became completely unresponsive to any ground commands and the Earth and Sun sensors were rendered useless. The gyroscopes continued to maneuver the probe and ground controllers momentarily reacquired a lock on the antenna, but without stable attitude control, they could not hold it steady. As they were unaware of the computer failure, they continued sending commands to Ranger&nbsp;3 in vain. Sporadic tracking of the probe continued until January&nbsp;31 when the attitude control thrusters exhausted their propellant supply, at which point the mission was officially terminated.<ref name="nssdc1962-001A"/>