OSIRIS-REx is scheduled for lift-off from Space Launch Complex-41 (SLC-41) at Cape Canaveral Air Force Station on September 8, 2016 at 7:05 pm EDT. The daily launch window is almost two hours long, extending to 9:00 pm EDT. The entire launch window is 34 days long, extending through October 11, 2016. We certainly hope we don’t have to wait that long to get into space! Given the outstanding technical performance to date, the most likely cause of a launch delay will be due to the weather. Our ride into space is the Atlas V AV-067 launch vehicle built by the United Launch Alliance. The OSIRIS-REx launch will be the 65th Atlas V mission.
The Atlas V 411 Configuration
Every Atlas V version has a three digit ID-Number:
First Digit: Payload Fairing diameter: 4XX – 4m Diameter; 5XX – 5.4m Diameter
Second Digit: Number of Solid Rocket Motors (0-5)
Third Digit: Number of RL-10A Engines on Centaur (1 or 2)
The 411 designation indicates that we are flying with a 4-meter payload fairing, with 1 solid rocket motor and a single-engine Centaur second stage. In its more than 10 years of service, the 411 rocket has completed three flights. The first launch of an Atlas V 411 occurred on April 20, 2006, when it successfully launched the Astra 1KR commercial communication satellite. The second 411 launch occurred on March 13, 2008 for the NROL-28 reconnaissance satellites. This event was also the first Atlas V launch from Vandenberg Air Force Base. The most recent 411 launch was on April 15, 2011 for the dual NROL-34 reconnaissance satellites.
It has been an amazing experience to watch the assembly of the Atlas V launch vehicle for OSIRIS-REx. There are four main components of the rocket: the payload fairing, the Centaur upper stage, the common core booster first stage, and a single solid rocket motor.
The OSIRIS-REx Spacecraft and Payload Fairing
The OSIRIS-REx spacecraft is encapsulated in the 4-m (14-ft) diameter large payload fairing. The fairing is a two-piece shell that is made of aluminum skin/stringer construction with vertical structural components. The NASA and OSIRIS-REx logos were hand painted on the fairing. The launch vehicle’s height to the tip of the fairing is approximately 189 ft (57.6 meters).
The Centaur Second Stage
The Centaur second stage is 10 feet (3 meters) in diameter and 41.5 feet (12.6 meters) in length. Its propellant tanks are constructed of pressure-stabilized, corrosion resistant stainless steel. Centaur is a liquid hydrogen/liquid oxygen- (cryogenic-) fueled vehicle. It uses a single RL10-A-4-2 engine producing 22,330 pounds of thrust (99,195 Newtons). The cryogenic tanks are insulated with a combination of helium-purged insulation blankets, radiation shields, and spray-on foam insulation. The Centaur forward adapter (CFA) provides the structural mountings for the avionics system and the structural and electrical interfaces with the spacecraft.
The Common Core Booster First Stage
The Atlas V booster is 12.5 feet (3.8 meters) in diameter and 106.5 feet (32.5 meters) in length. The booster’s tanks are structurally rigid and constructed of aluminum barrels, spun-formed aluminum domes, and inter-tank skirts. Atlas booster propulsion is provided by the RD-180 engine system (a single engine with two thrust chambers). The RD-180 burns RP-1 (Rocket Propellant-1 or highly purified kerosene) and liquid oxygen, and delivers 860,200 pounds of thrust at sea level (3.8 million Newtons). The Atlas V booster is controlled by the Centaur avionics system, which provides guidance, flight control, and vehicle sequencing functions during the booster and Centaur phases of flight.
The Solid Rocket Motor
One solid rocket motor (SRM) provides an additional 348,500 pounds of thrust at liftoff (1.6 million Newtons). This booster is 64 feet (19.5 meters) long and 61 inches (155 centimeters) in diameter. The Atlas V SRM was developed by Aerojet Rocketdyne as a low cost strap-on booster for the Atlas V launch vehicle. In a solid rocket, the fuel and oxidizer are mixed together into a solid propellant which is packed into a solid cylinder. A hole through the cylinder serves as the combustion chamber.
How Does the 411 Fly Straight?
Many people have commented on the unusual 411 configuration with only one SRM. At first glance it seems like this configuration should create uneven loading and an off-center thrust. The RD-180 engine (one engine, two thrust chambers, two nozzles) used for the Common Core Booster first stage has the ability to slew its nozzles up to 8 degrees. This capability is more than sufficient to account for the small asymmetry that the additional solid rocket motor creates. In addition, the single SRM is located on the center line between the two RD-180 nozzles, facilitating the ability of the nozzle slew to counteract the moment induced by the offline thrust.
We are 16 days away from the opening of the OSIRIS-REx launch window. It is an honor and a privilege to watch the team members from the NASA Launch Services Program and the United Launch Alliance prepare our ride into space. I know we are in good hands.