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Atlas (rocket)

From Academic Kids

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Mercury_Atlas_9.jpg
Mercury Atlas 9 rocket and capsule on pad

The Atlas is a venerable line of space launch vehicles built by Lockheed Martin. Originally designed as an ICBM in the late 1950s, the Atlas is today used as a launch platform for commercial and military satellites, and other space vehicles.

Contents

History

The Atlas, first tested in 1959, was the United States' first successful ICBM (Intercontinental Ballistic Missile). It was a "1.5 stage", liquid-fueled (LOX and RP-1) rocket, with three engines producing 1,590 kN of thrust.

The missile was originally given the military designation "XB-65", thus making it a bomber; from 1955 it was redesignated "SM-65" and, from 1962, it became "CGM-16". This letter "C" stood for "coffin" or "Container", the rocket being stored in a hardened container; it was prepared for launch by being raised and fueled in the open. The Atlas-F (HGM-16) was stored vertically underground, but launched after being lifted to the surface. The Atlas never was used in a missile silo, deep underground. From the mid 1960s, the Atlas (and its 'bigger brother', the Titan) were phased out in favour of the LGM-30 Minuteman, a solid-fuelled rocket which could be stored for long periods and launched, without fuelling, at the turn of a key.

Though never used in combat, the Atlas was used as the expendable launch system for the Mariner space probes used to study Mercury, Venus, and Mars (1962–1973); and to launch ten of the Mercury program missions (1962–1963). The Mercury-Atlas missions resulted in the first American to orbit the earth (Lt. Col. John H. Glenn Jr.) in February of 1962. (Major Yuri A. Gagarin, a Soviet cosmonaut, was the first human in orbit on April 12, 1961.) Atlas launched the Agena Target Vehicles used during the Gemini program. Direct Atlas descendants continue to be used as satellite launch vehicles into the 21st century.

Atlas was suggested for use by the United States Air Force in what became known as Project Vanguard. This suggestion was ultimately turned down, however, as Atlas would not be operational in time and was seen by many as being too heavily connected to the military for use in the U.S.' IGY satellite attempt.

Atlas, named for the Atlas of Greek mythology, got its start in 1946 with the award of a Army Air Forces research contract to Convair for the study of a 1,500 to 5,000 mi. (2,400 to 8,000 km) range nuclear armed missile. This was the MX-774 or Hiroc project. The contract was canceled in 1947 but the Army Air Forces allowed Convair to launch the three almost-completed research vehicles using the remaining contract funds. The three flights were only partially successful. However they did show that balloon tanks, and gimbaled rocket engines were valid concepts.

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Atlas ICBM launching from semi-hardened bunker.


Mercury-Atlas Three (Orbit Flight Events- April 25, 1961)

T+ Time Event Description
T+00:00:00 Liftoff Mercury-Atlas lifts off, onboard clock starts.
T+00:00:02 Roll Program Mercury-Atlas rotates along its axis 2.5 deg/s from 30° to 0°.
T+00:00:16 Pitch Program Mercury-Atlas begins a 0.5 deg/s pitch from 90° to 0°.
T+00:00:30 Radio Guidance Lock General Electric-Burroughs guidance system locks onto radio transponder in Atlas booster to guide the vehicle until orbit insertion.
T+00:01:24 Max Q Maximum dynamic pressure ~980 lbf/ft (~0.47 bar -47 kPa)
T+00:02:10 BECO Atlas Booster Engine Cutoff. Booster engines drop away.
T+00:02:33 Tower Jettison Escape Tower Jettison, no longer needed.
T+00:02:25 Atlas Pitchover After tower separation, vehicle pitches over further.
T+00:05:20 SECO Atlas Sustainer Engine Cutoff, capsule reaches orbit, velocity 17,547 mph (7,844 m/s)
T+00:05:24 Capsule Separation Posigrade rockets fire for 1 s giving 15 ft/s (4.6 m/s) separation.
T+00:05:25 5 Second Rate Damping ASCS damps capsule rates for 5 seconds in preparation for turnaround maneuver.
T+00:05:25 Turnaround Maneuver Capsule (ASCS) system rotates capsule 180 degrees, to heat shield forward attitude. Nose is pitched down 34 degrees to retro fire position.
T+00:05:30
T+04:30:00
Orbital Operations Orbital operations and experiments for 3 orbits.
T+04:30:00 Retro Sequence Start Retrofire in 30 s. (ASCS) checks for proper retro attitude −34° pitch, 0° yaw, 0° roll.
T+04:30:30 Retrofire Three retro rockets fire for 10 seconds each. They are started at 5 second intervals, firing overlaps for a total of 20 s. Delta V of 550 ft/s (168 m/s) is taken off forward velocity.
T+04:35:45 Retract Periscope Periscope is automatically retracted in preparation for reentry.
T+04:36:15 Retro Pack Jettison One minute after retrofire retro pack is jettisoned, leaving heatshield clear.
T+04:36:20 Retro Attitude Maneuver (ASCS) orients capsule in 34° nose down pitch, 0° roll, 0° yaw.
T+04:42:15 .05 G Maneuver (ASCS) detects beginning of reentry and rolls capsule at 10 deg/s to stabilize capsule during reentry.
T+04:49:38 Drogue Parachute Deploy Drogue parachute deployed at 22,000 ft (6.7 km) slowing descent to 365 ft/s (111 m/s) and stabilizing capsule.
T+04:49:45 Snorkel Deploy Fresh air snorkel deploys at 20,000 ft (6 km). (ECS) switches to emergency oxygen rate to cool cabin.
T+04:50:15 Main Parachute Deploy Main parachute deploys at 10,000 ft (3 km). Descent rate slows to 30 ft/s (9 m/s).
T+04:50:20 Landing Bag Deploy Landing Bag Deploys, dropping heat shield down 4 ft (1.2 m).
T+04:50:20 Fuel Dump Remaining hydrogen peroxide fuel automatically dumped.
T+04:55:30 Splashdown Capsule lands in water about 500 mi (800 km) downrange from launch site.
T+04:55:30 Rescue Aids Deploy Rescue aid package deployed. The package includes green dye marker, recovery radio beacon and whip antenna.



Design

Atlas is almost unique in its use of balloon tanks for fuel, made of very thin stainless steel with minimal or no rigid support structures. Pressure in the tanks provides the structural rigidity required for flight. An Atlas rocket will collapse under its own weight if not kept pressurized. The only other known use of balloon tanks at the time of writing is the Centaur high-energy upper stage.

Atlas also has a unique and somewhat odd staging system. Most rockets stage by dropping both engines and fuel tanks. However, when the Atlas missile was being developed, there were considerable doubts as to whether or not a rocket motor could be ignited in space. Therefore, the decision was made to ignite all three of the Atlas' engines at launch - later, two of the engines would be discarded, while the third continued to burn. Rockets using this technique are sometimes called stage and a half boosters. This technique is made possible by the extreme light weight of the balloon tanks. The tanks make up such a small percentage of the total booster weight that the weight penalty of lifting them to orbit is not offset by the technical and weight penalty required to throw half of them away mid-flight. Depending on how you look at it, this makes Atlas a single-stage-to-orbit booster (though most call it a 1.5 stage to orbit).

Current Atlas Family

The Atlas II series had 63 successful flights with the last launched August 31, 2004, it is considered the most reliable launcher in the world.

The newest version of Atlas, the Atlas V, is an Atlas in name alone as it contains little Atlas technology. It no longer uses balloon tanks nor 1.5 staging, but incorporates a rigid framework for its first stage booster much like the Titan family of vehicles. Ironically, given Atlas's origin as a military weapon, the Atlas III and Atlas V use Russian-designed engines.

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Atlas EELV family of launch vehicles (US Govt)
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Atlas launch vehicle evolution. (USAF)


External links

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Related content

Comparable missiles: SM-68 Titan

Designation sequence: MGM-13 - MIM-14 - RGM-15 - CGM-16/HGM-16 - PGM-17 - MGM-18 - PGM-19

Designation sequence: SM-62 - XGAM-63 - SM-64 - SM-65 - B-66 - GAM-67 - XB-68/SM-68

Related lists: List of missiles


Lists of Aircraft | Aircraft manufacturers | Aircraft engines | Aircraft engine manufacturers

Airports | Airlines | Air forces | Aircraft weapons | Missiles | Timeline of aviation

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