STS-51-D was the 16th flight of NASA's Space Shuttle program, and the fourth flight of Space Shuttle Discovery.^[2] The launch of STS-51-D from Kennedy Space Center (KSC), Florida, on April 12, 1985, was delayed by 55 minutes, after a boat strayed into the restricted Solid Rocket Booster (SRB) recovery zone. STS-51-D was the third shuttle mission to be extended.

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STS-51-D

The crew attempt to activate Syncom IV-3 via a "flyswatter" device attached to Discovery's Canadarm
Names	Space Transportation System-16
Mission type	Communications satellite deployment
Operator	NASA
COSPAR ID	1985-028A
SATCAT no.	15641
Mission duration	6 days, 23 hours, 55 minutes, 23 seconds (achieved)
Distance travelled	4,650,658 km (2,889,785 mi)
Orbits completed	110
Spacecraft properties
Spacecraft	Space Shuttle Discovery
Launch mass	113,802 kg (250,890 lb)
Landing mass	89,818 kg (198,015 lb)
Payload mass	13,039 kg (28,746 lb)
Crew
Crew size	7
Members	Karol J. Bobko Donald E. Williams Margaret Rhea Seddon S. David Griggs Jeffrey A. Hoffman Charles D. Walker Jake Garn
EVAs	1
EVA duration	3 hours, 6 minutes
Start of mission
Launch date	April 12, 1985, 13:59:05 UTC
Rocket	Space Shuttle Discovery
Launch site	Kennedy Space Center, LC-39A
Contractor	Rockwell International
End of mission
Landing date	April 19, 1985, 13:54:28 UTC
Landing site	Kennedy Space Center, SLF Runway 33
Orbital parameters
Reference system	Geocentric orbit[1]
Regime	Low Earth orbit
Perigee altitude	300 km (190 mi)
Apogee altitude	452 km (281 mi)
Inclination	28.45°
Period	94.40 minutes
Instruments
American Flight Echo-cardiograph (AFE) Continuous Flow Electrophoresis System (CFES-III) Getaway specials (GASs)Phase Partitioning Experiments (PPE)
STS 51-D mission patch Back row: S. David Griggs, Charles D. Walker, Jake Garn Front row: Karol J. Bobko, Donald E. Williams, Rhea Seddon, Jeffrey A. Hoffman Space Shuttle program ← STS-51-C (15) STS-51-B (17) →

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On April 19, 1985, after a week-long flight, Discovery conducted the fifth shuttle landing at KSC. The shuttle suffered extensive brake damage and a ruptured tire during landing. This forced all subsequent shuttle landings to be done at Edwards Air Force Base, California, until the development and implementation of nose wheel steering made landings at KSC more feasible.

During STS-51-D, the shuttle crew deployed two communications satellites: Telesat-I (Anik C1) and Syncom IV-3 (also known as Leasat-3); both were Hughes-built satellites. Telesat-I was attached to a Payload Assist Module (PAM-D) motor and successfully deployed. Syncom IV-3, however, failed to initiate antenna deployment and spin-up, or ignite its perigee kick motor upon deployment. The mission was consequently extended by two days to ensure that the satellite's spacecraft sequencer start lever was in its proper position. Griggs and Hoffman performed an unscheduled Extra-Vehicular Activity (EVA) to attach homemade "Flyswatter" devices to the shuttle's Remote Manipulator System (Canadarm). Seddon then engaged the satellite's start lever using the RMS, but again the post-deployment sequence did not begin.^[4] The satellite was subsequently retrieved, repaired and successfully redeployed during the STS-51-I mission later that year.

Discovery's other mission payloads included the Continuous Flow Electrophoresis System III (CFES-III), which was flying for sixth time; two Shuttle Student Involvement Program (SSIP) experiments; the American Flight Echo-cardiograph (AFE); two Getaway specials (GASs); a set of Phase Partitioning Experiments (PPE); an astronomical photography verification test; various medical experiments; and "Toys in Space", an informal study of the behavior of simple toys in a microgravity environment, with the results being made available to school students upon the shuttle's return.^[5]

During the shuttle's landing at KSC on April 19, 1985, extensive brake damage was suffered, and a landing gear tire ruptured. This prompted future shuttle flights to land at Edwards Air Force Base, California, until effective nose wheel steering could be implemented to reduce risks during landing.

NASA began a tradition of playing music to astronauts during the Project Gemini, and first used music to wake up a flight crew during Apollo 15. Each track is specially chosen, often by the astronauts' families, and usually has a special meaning to an individual member of the crew, or is applicable to their daily activities.^[6]

• Telesat-I during deployment
• Syncom IV-3 during deployment
• Hoffman and Griggs attach the flyswatter device to the end of the Canadarm.

• List of human spaceflights
• List of Space Shuttle missions