right|thumb|300px|A Mercury-program emlékműve a [[Kennedy Űrközpontban]]
A '''Mercury-program''' az első amerikai emberes űrprogram. kapszulákat indítottak Atlas rakétákkal Föld körüli pályára. A Freedom 7 űrhajóval Alan Shepard volt az első amerikai aki eljutott a világűrbe, a Friendship 7 űrhajóval John Glenn az első amerikai Föld körüli pályán. A szovjetek a Vosztok-programmal megelőzték az amerikaiakat az emberes űrrepülések terén is.

==Az űrhajós csoport==
right|thumb|350px|A Mercury-űrhajósok [[1962-ben (Grissom, Shepard, Carpenter, Schirra, Slayton, Glenn, Cooper)]]

A NASA 1959-ben választotta ki a légierő berepülőpilótái közül a következő hét embert, akik a Mercury-program űrhajósaivá váltak:

* Scott Carpenter
* Gordon Cooper
* John Glenn
* Virgil Grissom
* Walter Schirra
* Alan Shepard
* Donald ''(Deke)'' Slayton

Közülük hatan jutottak fel a program keretein belül a világűrbe (Slayton szívproblémák miatt 1962-ben kikerült a csoportból).

{| border="2" cellpadding="4" cellspacing="0" align="right" width="310" style="margin:  0 0 1em 1em; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 95%;"
!colspan="3" cellspacing="0" cellpadding="2" bgcolor="skyblue"|McDonnell Mercury capsule
|-
|colspan="3" align="center"|285px|<br><small>The Mercury capsule with escape tower</small>
|-
!colspan="3" cellspacing="0" cellpadding="2" bgcolor="skyblue"|Description
|-
|width="150" colspan="1" |'''Role:'''||width="150" colspan="2"| Suborbital and orbital spaceflight 
|-
|width="150" colspan="1" |'''Crew: '''||width="150" colspan="2"| one, pilot  
|-
!colspan="3" cellspacing="0" cellpadding="2" bgcolor="skyblue"|Dimensions
|-
|'''Height:'''|| 11.5 ft || 3.51 m
|-
|'''Diameter:'''|| 6.2 ft || 1.89 m
|-
|'''Volume:'''|| 60 ft³  || 1.7 m³
|-
!colspan="3" cellspacing="0" cellpadding="2" bgcolor="skyblue"|Weights (MA-6)
|-
|'''Launch:'''|| 4,265 lb || 1,935 kg
|-
|'''Orbit:''' || 2,986 lb || 1,354 kg
|-
|'''Post Retro:''' || 2,815 lb || 1,277 kg
|-
|'''Reentry:''' || 2,698 lb || 1,224 kg
|-
|'''Landing:''' || 2,421 lb || 1,098 kg
|-
!colspan="3" cellspacing="0" cellpadding="2" bgcolor="skyblue"|Rocket engines
|-
|'''Retros''' (solid fuel) x 3:|| 1,000 lbf ea || 4.5 kN
|-
|'''Posigrade''' (solid fuel) x 3:|| 400 lbf ea || 1.8 kN
|-
|'''RCS high''' (H<sub>2</sub>O<sub>2</sub>) x 6:|| 25 lbf ea || 108 N
|-
|'''RCS low''' (H<sub>2</sub>O<sub>2</sub>) x 6:|| 12 lbf ea || 49 N
|-
!colspan="3" cellspacing="0" cellpadding="2" bgcolor="skyblue"|Performance
|-
|''' Endurance:'''|| 34 hours || 22 orbits 
|-
|''' Apogee:'''|| 175 miles || 282 km
|-
|''' Perigee:'''|| 100 miles || 160 km 
|-
|''' Retro delta v:'''|| 300 mph || 483 km/h 
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!colspan="3" cellspacing="0" cellpadding="2" bgcolor="skyblue"|''' Mercury capsule diagram'''
|-
|colspan="3" align="center"|285px|<br><small>Mercury capsule Diagram (NASA)</small>
|-
!colspan="3" cellspacing="0" cellpadding="2" bgcolor="skyblue"|McDonnell Mercury capsule
|-
|}

'''Project Mercury''' was the first human spaceflight program of the  United States. It ran from 1959 through 1963 with the goal of putting a man in orbit around the Earth. The Mercury-Atlas 6 flight on February 20, 1962 was the first Mercury flight to achieve this goal.
Early planning and research was carried out by the Mercury, a Roman mythological god who is often seen as a symbol of speed. Mercury is also the name of the innermost planet of the solar system, which moves faster than any other <!--Yes, among the planets Mercury has the highest orbital speed--> and hence provides an image of speed, although Project Mercury had no other connection to that planet. 

The Mercury program cost around $384 million, or about $2.7 billion in 2007 dollars. 

==Spacecraft==<!-- This section is linked from Astronaut Hall of Fame -->
left|150px|thumb|''Mercury program monument''
Because of their small size it was said that the Mercury spacecraft capsules were not ridden, but worn. With 1.7 cubic meters of habitable volume, the capsule was just large enough for the single crew member. Inside were 120 controls: 55 electrical switches, 30 fuses and 35 mechanical levers. The spacecraft was designed by Max Faget and NASA's Space Task Group.

During the launch phase of the mission, the Mercury spacecraft and astronaut were protected from launch vehicle failures by the Launch Escape System. The LES consisted of a solid fuel, 52,000 lbf (231 kN) thrust rocket mounted on a tower above the spacecraft. In the event of a launch abort, the LES would fire for 1 second, pulling the Mercury spacecraft and the astronaut away from a defective launch vehicle. The spacecraft would then descend on its parachute recovery system. After booster engine cutoff (BECO), the LES was no longer needed and was separated from the spacecraft by a solid fuel, 800 lbf (3.6 kN) thrust jettison rocket that fired for 1.5 seconds.  Unfortunately, as with the later Apollo and Gemini programs, the scientists believed that if there was a catastrophic failure with the launch vehicle, then the possibilities of survival were minimal even with the tower in place.  There simply wasn't enough time between the detection of the problem and the resulting consequences.  There was never a problem during launch that caused the firing of the tower, and in Project Gemini, Gemini 6 misfired but was aborted before any trouble arose.  

To separate the Mercury spacecraft from the launch vehicle, the spacecraft fired three small solid-fuel, 400 lbf (1.8 kN) thrust rockets for 1 second. These rockets are called the Posigrade rockets. 

The spacecraft was only equipped with yaw, pitch, and roll), supplied from two separate fuel tanks - one automatic and one manual. The pilot could use any one of the three thruster systems and fuel them from either of the two fuel tanks to provide spacecraft attitude control. 

The Mercury spacecraft were designed to be totally controllable from the ground in the event that something impaired the pilot's ability to function.  

The spacecraft had three solid-fuel, 1000 lbf (4.5 kN) thrust retrorockets that fired for 10 seconds each. One was sufficient to return the spacecraft to earth if the other two failed. The firing sequence (known as ripple firing) required firing the first retro, followed by the second retro five seconds later (while the first was still firing). Five seconds after that, the third retro fired (while the second retro was still firing).

There was a small metal flap at the nose of the spacecraft called the "spoiler". If the spacecraft started to reenter nose first (another stable reentry attitude for the capsule), airflow over the "spoiler" would flip the spacecraft around to the proper, heatshield-first reentry attitude, a technique called 'Shuttlecocking'. During reentry, the astronaut would experience about 4 g-forces.

Initial designs for the spacecraft suggested the use of either heat-sink ablative shield. Extensive testing settled the issue - ablative shields proved to be reliable (so much so that the initial shield thickness was safely reduced, allowing a lower total spacecraft weight), easier to produce (at that time, beryllium was only produced in sufficient quantities by a single company in the US) and cheaper.

NASA ordered 20 production spacecraft, numbered 1 through 20, from McDonnell Aircraft Company, St. Louis, Missouri. Five of the twenty spacecraft, #10, 12, 15, 17, and 19, were not flown. Spacecraft #3 and #4 were destroyed during unmanned test flights. Spacecraft #11 sank and was recovered from the bottom of the Atlantic Ocean after 38 years. Some spacecraft were modified after initial production (refurbished after launch abort, modified for longer missions, etc) and received a letter designation after their number, examples 2B, 15B. Some spacecraft were modified twice; for example, spacecraft 15 became 15A and then 15B.

A number of Mercury Boilerplate spacecraft (including mockup/prototype/replica spacecrafts, made from non-flight materials or lacking production spacecraft systems and/or hardware) were also made by NASA and McDonnell Aircraft.  They were designed and used to test spacecraft recovery systems, and escape tower and rocket motors. Formal tests were done on test pad at Langley and at Wallops Island using the Little Joe and Big Joe Atlas rockets.<ref>[http://grin.hq.nasa.gov/BROWSE/mercury_program.html NASA Mercury History] Sections #44 and #47 </ref>

==Boosters==
thumbnail|100px|Mercury Atlas 9.
The Mercury program used three boosters: 

*Little Joe - 8 suborbital robotic flights, 2 carrying monkeys. Launch escape system tests.
*Redstone - 4 suborbital robotic flights, 1 carrying a chimpanzee; 2 piloted suborbital flights.
*Atlas - 4 suborbital robotic flights; 2 orbital robotic flights, 1 carrying a chimpanzee; 4 piloted orbital flights.

Little Joe and a Mercury Boilerplate<ref> [http://aesp.nasa.okstate.edu/fieldguide/pages/address/a-f/airpower.html A Fieldguide to American Spacecraft]</ref> was used to test the escape tower and abort procedures.<ref>[http://www.astronautix.com/project/mercury.htm Mercury Boilerplate Tests] </ref>  Redstone was used for Jupiter missiles were also considered as suborbital launch vehicles for the Mercury program, but were cut from the program in July, 1959 due to budget constraints. The Atlas boosters required extra strengthening in order to handle the increased weight of the Mercury capsules beyond that of the nuclear warheads they were designed to carry.  Little Joe was a solid-propellant booster designed specially for the Mercury program.
The Titan missile was also considered for use for later Mercury missions; however, the Mercury program was terminated before these missions were flown. The Titan was used for the Gemini program which followed Mercury.

The Mercury program used a Scout booster for a single flight, Mercury-Scout 1, which launched a small satellite intended to evaluate the worldwide Mercury Tracking Network. The rocket was destroyed by the Range Safety Officer after 44 seconds of flight.
<br clear=all>

thumb|right|200px|Mercury Control - Cape Canaveral, Florida. (NASA)

==Unmanned flights==
The program included 20 robotic launches. Not all of these were intended to reach space and not all were successful in completing their objectives. Four of these flights included non-human primates, starting with the fifth flight (1959) which launched a Rhesus macaque named Sam (after the Air Force's '''S'''chool of '''A'''viation '''M'''edicine). The Mercury program's complete roster of non-human space-farers is given below:

* Sam, a Rhesus macaque, launched December 4, 1959 on Little Joe 2 to 85 km altitude.