Atlas V 551 Rocket

The 5.4-meter (17.7-foot) wide payload fairing is an aero-dynamic shell that encloses the spacecraft at the beginning of its journey. The payload fairing protects the spacecraft from weather and contamination on the ground prior to launch and from friction with the atmosphere during flight. The fairing encapsulates both the Juno spacecraft and the Centaur upper stage in two halves similar to a clamshell. About 3 minutes 40 seconds into flight, once the rocket has reached a height above most of Earth’s atmosphere, the payload fairing splits in half and falls away, landing in the ocean.

The Centaur upper stage sits on top of the common core booster. The Juno spacecraft rides on top of the Centaur. The Centaur is fueled with approximately 21,000 kg (46,000 pounds) of liquid oxygen and liquid hydrogen propellant. After the common core booster is jettisoned, the Centaur ignites.

The Centaur’s engine will fire up three times. The first burn will place Juno into a parking orbit, or coast, around the Earth. At the proper point in the coast orbit, the Centaur will restart for its second burn. The second burn will place Juno on a trajectory to escape Earth’s gravity and begin its journey to Jupiter. Before it separates from Juno, the Centaur will fire a set of thrusters that will give the spacecraft its spin. Finally, to prevent the upper stage from following Juno, the Centaur will start a third time, after separation, to place it on a trajectory that will take it harmlessly away from the spacecraft.

The “551” in the rocket’s name is actually a code that provides three important characteristics of the Atlas V: 

• The first digit provides the width of the payload fairing in meters.
  
• The second digit tells the number of solid rocket boosters attached to the rocket.
  
• The third digit gives the number of Centaur upper stage engines.

So according to the code, Juno’s Atlas V has a 5-meter (16-foot) wide payload fairing, 5 solid rocket boosters, and 1 Centaur upper stage. Juno has to be protected so that it can reach space in one piece.

ATLAS V-551 LAUNCH VEHICLE:
The Atlas sheds weight as it heads toward space by dropping pieces that have spent their fuel or are no longer needed.

PAYLOAD FAIRING:
The rocket's "nose cone" which protects the spacecraft in the lower atmosphere.

UPPER STAGE:
After the fuel in the main stage is spent, it drops away, leaving the upper stage to carry the spacecraft into orbit.

MAIN STAGE:
The largest part of the rocket contains hundreds of thousands of gallons of liquid propellants.

MAIN ENGINE:
Part of the rocket's main stage, the RD-180 engine burns for about four and a half minutes.

SOLID ROCKET BOOSTERS:
The five booster rockets burn for the first minute and a half, then detach and fall away.

The Atlas common core booster consists of the main engine and fuel tanks for the launch vehicle. This booster provides most of the thrust needed to propel Juno into space. The common core booster burns all of its 284,000 kilograms (626,000 pounds, or more than 300 tons) of liquid oxygen and kerosene propellant very quickly and is then jettisoned about 4 minutes 40 seconds into flight, while the upper stage and spacecraft keep going. The common core booster then falls into the ocean.

The Atlas rocket was first developed in the 1950s as an Air Force Intercontinental Ballistic Missile, or ICBM. The Atlas has since evolved into a family of rockets to become a highly reliable launch vehicle. Hundreds of spacecraft, for commercial, military and space exploration purposes, have been launched aboard the various Atlas rocket designs. The Atlas V is the model currently in service, and is the rocket used to launch Juno to Jupiter. The most recent members of the Atlas family are shown here.

ATLAS IIA

The Atlas IIA was in service from 1993 to 2002. It included a 3.3- 4.2 meter wide payload fairing (or nose cone), an upper Centaur rocket stage with two engines and a 3.1 meter wide core booster (or main rocket stage).

ATLAS IIAS

The Atlas IIAS was in service from 1993 to 2004. It added solid rocket boosters to enhance the rocket’s performance.

ATLAS III

The Atlas III was in service from 2000 to 2005. Its Centaur booster had just one engine. This model also introduced the Russian designed RD-180 rocket engine currently used by the Atlas V on its main rocket stage. The Atlas III also introduced a slightly taller Centaur Booster that is currently in use on the Atlas V.

ATLAS V 400 SERIES

The Atlas V 400 series has a larger, 3.8 meter, core booster for its main rocket stage. It has a 4.2-meter wide payload fairing, from zero to three solid rocket boosters and a single- or dual-engine Centaur upper stage booster. The first Atlas V 400 series rocket was launched in 2002.

ATLAS V 500 SERIES

The Atlas V series provides a variety of vehicles capable of launching a wide range of spacecraft and satellites. It has a 5.4- meter wide payload fairing, from zero to five solid rocket boosters and a single- or dual-engine Centaur upper stage booster. The first Atlas V 500 series rocket was launched in 2003. NASA’s Pluto- bound New Horizons spacecraft was launched by an Atlas V 551 in 2006.

Five strap-on solid rocket boosters are attached around the aft end of the Common Core Booster. The five solid boosters assist the common core booster and give Juno the additional thrust required to start its journey into space. The five rocket motors ignite at the beginning of the launch and burn out about 1 minute 30 seconds into flight. The solid rocket boosters are then jettisoned and fall into the ocean.

Three types of rocket engine boost the Atlas V into orbit, and each burns a different type of propellant to produce thrust. The two stages (the Common Core Booster and the Centaur) each use liquid propellants that burn and produce thrust when combined. The Common Core Booster, or main stage, burns a combination of liquid oxygen and RP-1, which is a refined form of kerosene. The Centaur upper stage burns liquid oxygen and liquid hydrogen. The strap-on rocket boosters use a solid fuel that contains powdered aluminum – a form similar to the foil wraps in your kitchen – mixed with oxygen provided by a chemical called ammonium perchlorate.