Mercury-Redstone 1

Mercury-Redstone 1
Mercury-Redstone 1
Mission insignia
Mercury insignia.jpg
Mission statistics
Mission name Mercury-Redstone 1
Spacecraft mass 2,720 lb (1,230 kg)[1][note 1]
Crew size Unmanned
Launch vehicle Mercury-Redstone
Launch pad Cape Canaveral, Launch Complex 5
Launch date November 21, 1960, 14:00 GMT
Landing November 21, 1960, 14:00 GMT
Mission duration 2 seconds
Number of orbits Suborbital
Apogee 100 millimetres (3.9 in)
Peak acceleration 9.8 m/s² (1 g)
Related missions
Previous mission Subsequent mission
N/A Mercury insignia.jpg MR-1A

Mercury-Redstone 1 (MR-1) was the first Mercury-Redstone mission in the Mercury program and the first attempt to launch a Mercury spacecraft with the Mercury-Redstone launch vehicle. Intended to be an unmanned sub-orbital flight, it was launched on November 21, 1960 from Cape Canaveral, Florida. The launch failed in a peculiar fashion which has been referred to as the "four-inch flight".[2]


Mission background and launch failure

The purpose of the MR-1 mission was to qualify the Mercury spacecraft and the Mercury-Redstone launch vehicle for the sub-orbital Mercury mission. It would also qualify the spacecraft's automated flight control and recovery systems, as well as the launch, tracking, and recovery operations on the ground.[3][4] The mission would also test the Mercury-Redstone's automatic inflight abort sensing system, which would be operating in "open-loop" mode. This meant that the abort sensing system could report a condition requiring an abort, but it would be unable to actually trigger an abort itself. Since the flight did not have a living passenger, this would not pose a safety problem, and it would prevent a faulty abort signal from prematurely ending the flight.[3]

The mission used Mercury spacecraft #2 together with Redstone MR-1;[note 2] its launch location was Cape Canaveral Air Force Station's Launch Complex 5. An early launch attempt on November 7 was canceled due to last-minute problems with the capsule, so launching was rescheduled for November 21.[6][7]

On that day, following a normal countdown, the Mercury-Redstone's engine ignited on schedule at 9:00 a.m. Eastern Standard Time (14:00 GMT). However, the engine shut down immediately after lift-off from the launch pad. The rocket only rose about 4 inches (10 cm) before settling back onto the pad. It wobbled slightly, but stayed upright and did not explode. An odd series of events then took place.[6][8][4]

Immediately after the Redstone's engine shut down, the Mercury capsule's escape rocket jettisoned itself, leaving the capsule attached to the rocket. The escape rocket rose to an altitude of 4,000 feet (1,200 m) and landed about 400 yards (370 m) away. Three seconds after the escape rocket fired, the capsule deployed its drogue parachute; it then deployed the main and reserve parachutes, ejecting the radio antenna fairing in the process.[6][8][4]

In the end, all that had been launched was the escape rocket. Meanwhile, a fully fueled, slightly wrinkled Redstone and its Mercury capsule sat on the launch pad, both with full batteries and live pyrotechnics. Among these pyrotechnics were the capsule's retrorockets and the Redstone's self-destruct system, which was still active. Furthermore, the capsule's main and reserve parachutes were hanging down the side of the rocket, threatening to tip it over if they caught enough wind. Fortunately, the weather conditions were favorable. Technicians had to wait until the next morning, when the flight batteries in the rocket and capsule had run down and the Redstone's liquid oxygen had boiled off, before they could work on the rocket and render it safe.[6][9]

Causes of the failure

Investigation revealed that the Redstone's engine shutdown was caused by two of its electrical cables separating in the wrong order.[6] These cables were a control cable, which provided various control signals, and a power cable, which provided electrical power and grounding. Both cables were plugged into the rocket at the bottom edge of one of its tail fins and would separate at liftoff.[10] The control cable was supposed to separate first, followed by the power cable. However, for this launch, a control cable for the military Redstone missile had been substituted for the shorter cable designed for Mercury-Redstone. This control cable had been clamped to compensate for its greater length. But when the vehicle lifted off, the clamping did not work as planned, and the control cable separated about 29 milliseconds after the power cable did.[11][4]

During this brief interval, the lack of electrical grounding caused a substantial current to flow through an electrical relay which was supposed to trigger normal engine cut-off at the end of powered flight. This relay tripped, causing the Redstone to shut off its engine and send a "normal cut-off" signal to the capsule, which jettisoned its escape rocket as it was supposed to. However, the capsule did not separate from the rocket as it normally would have. The capsule was designed to suspend its separation until the vehicle's acceleration had almost ceased, so that the capsule would not be hit by its own launch vehicle. Because the acceleration sensors in the capsule detected a constant acceleration of 1 g, capsule separation was disabled.[12][4]

The jettison of the escape rocket activated the capsule's parachute recovery system. Since the altitude was below 10,000 feet (3,000 m), this system was triggered by its atmospheric pressure sensors and followed its usual sequence, with the drogue parachute deploying first, followed by the main parachute. But because the main parachute was not supporting the capsule's weight, the parachute system did not detect any load on this chute, so it acted as if the chute had failed and deployed the reserve parachute.[12][4]

Since the Redstone's automatic inflight abort sensing system was running in open-loop mode, the engine shutdown did not trigger an abort. However, the system did report an abort condition, so it did function properly.[13][8]


The Redstone had suffered some minor damage from falling back on the pad, but it could still be used after refurbishment, so it was returned to Marshall Space Flight Center in Huntsville, Alabama, and was held in reserve. A new mission was scheduled, Mercury-Redstone 1A (MR-1A), which would use a new Mercury-Redstone rocket, numbered MR-3. MR-1's Mercury spacecraft, #2, was undamaged, so it was reused for MR-1A, together with the escape rocket from spacecraft #8 and the antenna fairing from spacecraft #10.[14][15][4]

To prevent a failure like MR-1 from happening again, subsequent Mercury-Redstones added a grounding strap about 12 inches (30 cm) long to electrically connect the rocket to the launch pad. This strap was designed to separate from the rocket well after all other electrical connections to the ground had been severed.[12][15][4]

Mercury engineers were also concerned that MR-1's failure had allowed a "normal cutoff" signal to reach the capsule and trigger the premature jettisoning of the escape rocket, since in an actual emergency this might remove the only escape mechanism for the astronaut. To prevent this, the Mercury-Redstone was altered so that it could not send a "normal cutoff" signal to the capsule until 129.5 seconds after liftoff, about 10 seconds before the expected time of the Redstone's actual engine cutoff.[12][16]

MR-1 was never used for another mission after its return to Huntsville. It was eventually put on display at the Space Orientation Center of Marshall Space Flight Center.[13]

Current location

Mercury spacecraft #2, used in both the Mercury-Redstone 1 and Mercury-Redstone 1A missions, is currently displayed at the Exploration Center at NASA Ames Research Center, Moffett Federal Airfield, near Mountain View, California.[17] A Mercury-Redstone rocket is currently on display at the U.S. Space & Rocket Center in Huntsville among other locations.



  1. ^ This is the weight of the spacecraft after separation from the launch vehicle, including all spacecraft consumables. It excludes the escape tower, which would be jettisoned before spacecraft separation, and the spacecraft-launch vehicle adapter, which would remain attached to the launch vehicle. Note that Mercury spacecraft #2 lacked some of the equipment present in the spacecraft used on the manned Mercury flights.
  2. ^ NASA used the prefix "MR-" both for Mercury-Redstone missions and for launch vehicle numbers. Sometimes, as in this case, the mission and launch vehicle numbers were the same, but not always.[5] Some later sources use the prefix "MRLV-" for launch vehicle numbers, but this form does not seem to have been used by NASA.


  1. ^ Korando, R. D. (February 6, 1961) (PDF). Mercury Capsule No. 2 Configuration Specification (Mercury-Redstone No. 1). St. Louis, Missouri: McDonnell Aircraft Corporation. pp. 7–9. Report number NASA-CR-137390. 
  2. ^ "MR-1: The Four-Inch Flight", p. 293.
  3. ^ a b The Mercury-Redstone Project, p. 8-2.
  4. ^ a b c d e f g h NSSDC Master Catalog page.
  5. ^ The Mercury-Redstone Project, p. 6-3, 8-1.
  6. ^ a b c d e The Mercury-Redstone Project, p. 8-3.
  7. ^ "MR-1: The Four-Inch Flight", pp. 293-294.
  8. ^ a b c "MR-1: The Four-Inch Flight", p. 294.
  9. ^ "MR-1: The Four-Inch Flight", pp. 294-296.
  10. ^ The Mercury-Redstone Project, p. 4-6, 4-47.
  11. ^ The Mercury-Redstone Project, p. 8-3, 8-5.
  12. ^ a b c d The Mercury-Redstone Project, p. 8-5.
  13. ^ a b The Mercury-Redstone Project, p. 8-6.
  14. ^ The Mercury-Redstone Project, p. 8-5, 8-6.
  15. ^ a b "MR-1: The Four-Inch Flight", p. 296.
  16. ^ "MR-1: The Four-Inch Flight", p. 296-297.
  17. ^ "NASA Ames Exploration Center". NASA Ames Research Center. Retrieved 2009-05-14. 

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