|Mission type||Venus flyby|
|Operator||NASA / JPL|
|Mission duration||294.5 seconds|
Failed to orbit
based on Ranger Block I
|Manufacturer||Jet Propulsion Laboratory|
|Launch mass||202.8 kilograms (447 lb)|
|Start of mission|
|Launch date||July 22, 1962, 09:21:23GMT|
|Rocket||Atlas LV-3 Agena-B|
|Launch site||Cape Canaveral, LC-12|
Mariner 1, built to conduct the first American planetary flyby of Venus, was the first spacecraft of NASA's interplanetary Mariner program. The spacecraft carried a suite of experiments to determine the temperature of Venus as well to measure magnetic fields and charged particles near the planet and in interplanetary space. Mariner 1 was launched by an Atlas-Agena rocket from Cape Canaveral's Pad 12 on 22 July 1962. Shortly after takeoff, errors in communication between the rocket and its ground-based guidance systems caused the rocket to veer off course, and it had to be destroyed by range safety.
As the closest planet to Earth, Venus presented an appealing spaceflight target in the first years of the Space Race between the two then-superpowers, the United States and the Soviet Union. :172 Every 19 months, Venus and the Earth reach relative positions in their orbits around the Sun such that a minimum of fuel is required to travel from one planet to the other via a Hohmann Transfer Orbit. These opportunities mark the best time to launch exploratory spacecraft as the size of the experiment package can be maximized.
The first such opportunity of the Space Race occurred in late 1957, before either superpower had the technology to take advantage of it. The second opportunity, in and around June 1959, lay on the bleeding edge of possibility, and U.S. Air Force contractor, Space Technology Laboratory, intended to take advantage of it. A plan drafted January 1959 involved two spacecraft evolved from the first Pioneers, one to be launched via Thor-Able rocket, the other via the yet-untested Atlas-Able. The project proved too ambitious, and the launch window was missed. The Thor-Able probe was repurposed as the deep space explorer Pioneer 5, which was launched 11 March 1960 and maintained communications with Earth for 25,000,000 mi (40,000,000 km) as it traveled toward the orbit of Venus. (The Atlas Able probe concept was repurposed as the unsuccessful Pioneer Atlas Moon probes.) No American missions were sent during the early 1961 opportunity. The Soviet Union launched Venera 1 on 12 February 1961, but it stopped transmitting on 26 February, long before it reached Venus on May 19-20.
For the summer 1962 launch opportunity, NASA contracted Jet Propulsion Laboratory (JPL) in July 1960 :172 to develop "Mariner A", a 1,250 lb (570 kg) spacecraft to be launched using the yet undeveloped Atlas-Centaur. By August 1961, it had become clear that the Centaur would not be ready in time. JPL proposed to NASA that the mission might be accomplished with a lighter spacecraft using the less powerful but operational Atlas-Agena. A hybrid of Mariner A and JPL's Block 1 Ranger lunar explorer, already under development, was suggested. NASA accepted the proposal, and JPL began an 11-month crash program to develop "Mariner R" ("R" indicating it being a Ranger derivative).
Three complete Mariner R spacecraft were built: two for launching and one both for testing and to serve as a spare.:174 Aside from its scientific capabilities, Mariner also had to transmit data back to Earth from a distance of more than 26,000,000 mi (42,000,000 km), and to survive solar radiation twice as intense as that encountered in Earth orbit.:176
All three of the Mariner R spacecraft weighed within 3 lb (1.4 kg) of the design weight of 447 lb (203 kg), 406 lb (184 kg) of which was devoted to non-experimental systems: maneuvering systems, fuel, and communications equipment for receiving commands and transmitting data. Once fully deployed in space, with its two solar panel "wings" extended, Mariner R was 12 ft (3.7 m) in height and 16.5 ft (5.0 m) across. The main body of the craft a was hexagonal with six separate cases of electronic and electromechanical equipment. Two of the cases comprised the power system: switchgear that regulated and transmitted power from the 9800 solar cells to the 33.3 lb (15.1 kg) rechargeable 1000 wattsilver-zinc storage battery. Two more included the radio receiver, the three-watt transmitter, and control systems for Mariner's experiments. Case #5 held electronics for digitizing the analog data received by the experiments for transmission. The sixth case carried the three gyroscopes that determined Mariner's orientation in space. It also held the central computer and sequencer, the "brain" of the spacecraft that coordinated all of its activities pursuant to code in its memory banks and on a schedule maintained by an electronic clock tuned into equipment on Earth.:175
At the rear of the spacecraft, a monopropellant (anhydrous hydrazine) 225 N rocket motor was mounted for course corrections. A nitrogen gas fueled stabilizing system of ten jet nozzles controlled by the onboard gyroscopes, Sun sensors, and Earth sensors, kept Mariner properly oriented to receive and transmit data to Earth.:175
The primary "high gain" parabolic antenna was also mounted on the underside of the spacecraft and kept pointed toward the Earth. An omnidirectional antenna atop Mariner R would broadcast at times that the spacecraft was rolling or tumbling out of its proper orientation, to maintain contact with Earth, though its signal was much weaker. Mariner R also mounted small antennas on each of the wings to receive commands from ground stations.:175–176
Temperature control was both passive, involving insulated, and highly reflective components; and active, incorporating louvers to protect the case carrying the onboard computer. At the time Mariner R was built, no test chamber existed to simulate the near-Venus solar environment, so the efficacy of these cooling techniques could not be tested until the live mission.:176
At the time of the Mariner project's inception, few of Venus' characteristics were definitely known. Its opaque atmosphere precluded telescopic study of the ground. It was unknown whether there was water beneath the clouds, though a small amount of water vapor above them had been detected. The planet's rotation rate was uncertain, though JPL scientists had concluded through radar observation that Venus rotated very slowly compared to the Earth, even advancing the (later disproved) hypothesis that the planet was tidally locked with respect to the Sun (as the Moon is with respect to the Earth). No oxygen had been detected in Venus' atmosphere, suggesting that life as existed on Earth was not present. It had been determined that Venus' atmosphere contained at least 500 times as much carbon dioxide as the Earth's. These comparatively high levels suggested that the planet might be subject to a runaway greenhouse effect with surface temperatures as high as 600 K (327 °C; 620 °F), but this had not yet been conclusively determined.:7–8
Mariner would be able to verify this hypothesis by measuring the temperature of Venus close-up; at the same time, the spacecraft could determine if there was a significant disparity between night and daytime temperatures.:331 An on-board magnetometer and suite of charged particle detectors could determine if Venus possessed an appreciable magnetic field and an analog to Earth's Van Allen Belts. A television camera might resolve other outstanding questions.
As Mariner would spend most of its journey to Venus in interplanetary space, the mission also offered an opportunity for long-term measurement of the solar wind of charged particles and to map the variations in the Sun's magnetosphere. The concentration of cosmic dust beyond the vicinity of Earth could be explored as well.:176
Experiments for the measurement of Venus and interplanetary space ultimately included:
- A crystal microphone for measurement of the density of cosmic dust, mounted on the central frame.
- A proton detector for counting low-energy protons in the solar wind, also mounted on the central frame.
- Two Geiger-Müller (GM) tubes and an ion chamber, for measuring high-energy charged particles in interplanetary space and in the Venusian equivalent of Earth's Van Allen Belts (if they existed). These were mounted on Mariner's long axis to avoid the magnetic fields of the control equipment as well as secondary radiation caused by cosmic rays hitting the metal structure of the spacecraft.
- An Anton special-purpose GM tube, for measuring lower energy radiation, particularly near Venus, also mounted away from the central frame.
- A three-axis fluxgate magnetometer for measuring the Sun's and Venus' magnetic fields, also mounted away from the central frame.
- A microwave radiometer, a 20 in (510 mm) diameter, 3 in (76 mm) deep, parabolic antenna designed to scan Venus up and down at two microwave wavelengths (19 mm and 13.5mm), slowing down and reversing when it found a hot spot. The 19 mm wavelength was for measuring the temperature of the planet's surface while the 13.5mm wavelength measured the temperature of Venus' cloudtops. The instrument was mounted just above the central frame.
- Two infrared optical sensors for parallel measurement of the temperature of Venus, one at 8 to 9 microns, the other at 10-10.8 microns, also mounted above the central frame.:9
Not included on Mariner R was a camera for visual photos. With payload space at a premium, project scientists considered a camera an unneeded luxury, unable to return useful scientific results. Carl Sagan, one of the Mariner R scientists, unsuccessfully fought for their inclusion, noting that not only might there be breaks in Venus' cloud layer, but "that cameras could also answer questions that we were way too dumb to even pose."
Flight plan and ground operations
The aim of the Mariner R project was to launch the two operational spacecraft within a 30 day period on slightly differing paths such that they arrived at Venus within the same nine day period, 8-16 December. Taking into account the motion of Earth and Venus, as well as the launch capabilities of the Atlas-Agena and the weight of its payload, JPL engineers determined that there was a 51 day period, between from July 22 through September 10, during which a launch was possible. Only Cape Canaveral Launch Complex 12 was available for the launching of Atlas-Agena rockets, and it took 24 days to ready an Atlas-Agena for launch. This meant that there was only a 27 day margin for error for a two-launch schedule.:174
Each Mariner would be launched into a parking orbit, whereupon the restartable Agena would fire a second time, sending Mariner on its way to Venus (errors in trajectory would be corrected by a mid-course burn of Mariner's onboard engines). Real-time radar tracking of the Mariner spacecraft while it was in parking orbit and upon its departure was provided by the Atlantic Missile Range, with stations at Ascension and Pretoria, while optical tracking was provided by Palomar Observatory. Deep space support was provided by three tracking and communications stations at Goldstone, California, Woomera, Australia, and Johannesburg, South Africa, each separated on the globe by around 120° for continuous coverage.:231–233
The launch of Mariner 1 was scheduled for the early morning of 21 July 1962. The countdown began at 11:33 p.m. EST after several delays caused by trouble in the range safety command system. Concern over the cause of a blown fuse in the range safety circuits caused the launch to be canceled at 2:20 a.m. (T minus 79 minutes to launch). That night, at 11:08 p.m., countdown was reset and proceeded with several holds, planned and unplanned, through the early morning of the next day.
At 4:21:23 a.m. on 22 July 1962, Mariner 1's Atlas-Agena lifted off from Pad 12. The booster seemed to be performing normally until it began drifting northeast of its planned trajectory. Steering commands were sent to the rocket, but the Atlas-Agena proceeded further off course. By 4:25 a.m., it was clear that if the rocket continued on its course, it might crash into the North Atlantic ocean, endangering shipping or an inhabited area. At 4:26:16 a.m., just six seconds before the Agena second state was scheduled to separate from the Atlas, at which point destruction of the rocket would be impossible, a range safety officer ordered the rocket to self-destruct, which it did.:231–233
Cause of the malfunction
Because of the gradual rather than sharp deviation from its course, JPL engineers suspected the fault lay in the flight equations loaded into the computer that guided Atlas-Agena from the ground during its ascent. After five days of post-flight analysis, JPL engineers determined what had caused the malfunction on Mariner 1: a single error in the guidance computer code. One of the lines contained the symbol "R" (for "radius"). This "R" was supposed to have an line over it ("R-bar" or R̄) indicating that the guidance computer should average (smooth) the data it was receiving and ignore what was likely to be spurious data. In the hand-written code, and then as coded onto punch cards and into the guidance computer, the "R-bar" was listed simply as "R". Astrophysicist Scott Manley pointed out that the error was in the printed form of the specification, which the computer code faithfully followed, so this was not a programming error.
During its ascent, Mariner 1's booster briefly lost guidance-lock with the ground. During this not uncommon occurrence, the Atlas-Agena continued on a preprogrammed course until guidance-lock with the ground resumed. When lock was reestablished, however, the faulty line of code caused the ground computer to determine that the now slightly off course rocket was seriously off course and to send faulty signals in an attempt correct its trajectory. This caused Mariner 1 to veer further off course, necessitating its destruction.
Subsequent popular accounts of the accident often referred to the erroneous character as a "hyphen" (describing the missing component of the symbol) rather than an "R-bar", this characterization fueled by Arthur C. Clarke's description of the malfunction as "The most expensive hyphen in history."
The loss of Mariner 1 constituted an $18.5 million setback for NASA. Nevertheless, Mariner 2 was ready for lift-off just over a month later. On 27 August 1962, Mariner 1's sister spacecraft was successfully launched, passing near Venus on 14 December 1962.:171,177
- J.N.James (1965). "The Voyage of Mariner II". In Harlow Shapley; Samuel Rapport; Helen Wright (eds.). The New Treasury of Science. New York: Harper & Row. pp. 171–187.
- "How do spacecraft use an orbit to move from planet to planet?". Northwestern University. Retrieved 11 June 2021.
- "A Development Plan for 2 Interplanetary Probes" (PDF). Space Technology Laboratories. 14 January 1959.
- "Project Thor Able-4 Final Mission Report" (PDF). Space Technology Laboratories. 25 May 1960.
- Adolph K. Thiel (20 May 1960). "The Able Series of Space Probes" (PDF). Space Technology Laboratories.
- "Venera 1". NASA Space Science Data Coordinated Archive. Retrieved 2019-08-15.
- Jet Propulsion Laboratory (various) (1965). Mariner-Venus 1962: Final Project Report (PDF). Washington, D.C.: NASA. OCLC 2552152.
- "Mariner 1". NASA. Retrieved 11 June 2021.
- "Mariner to Scan Venus' Surface on Flyby". Aviation Week and Space Technology. McGraw Hill Publishing Company. 12 June 1961. pp. 52–57. Retrieved 11 June 2021.
- "Instruments Evolve for Mariner Probe". Aviation Week and Space Technology. McGraw Hill Publishing Company. 5 February 1962. pp. 57–61. Retrieved 28 January 2017.
- Elizabeth Howell (3 December 2012). "Mariner 2: First Spacecraft to Another Planet". space.com. Retrieved 11 June 2021.
- "Venus Mission Fails: New Mariner Readied". Aviation Week and Space Technology. McGraw Hill Publishing Company. 30 July 1962. p. 21. Retrieved 12 June 2021.
- Pasternack, Alex (26 July 2014). "Sometimes a Typo Means You Need to Blow Up Your Own Spacecraft". Vice. Retrieved 1 July 2021.
- Manley, Scott (16 May 2019). How A Tiny Mistake Destroyed America's First Interplanetary Space Probe. YouTube. Event occurs at 8m0s. Retrieved 21 July 2021.
- "Equation Error Cited in Mariner 1 Failure". Aviation Week and Space Technology. McGraw Hill Publishing Company. 6 August 1962. p. 29. Retrieved 12 June 2021.
- Henry Walker (2005). The Tao of Computing. Sudbury, MA: Jones and Bartlett Publishers, Inc. OCLC 864860042.