Building Up the Unmanned Rocket Fleet

Feb. 20, 2003
The recent loss of the Space Shuttle Columbia is forcing NASA to rethink its manned space program. Future government payloads and NASA missions could rely more on unmanned commercial launch vehicles.

Building up the unmanned rocket fleet

Senior Editor

A technician checks the cryogenic tanks that will store propellant in the second stage of an Ariane 5 rocket.
About three months ago, the two major launch-vehicle manufacturers, Boeing and the European Aeronautic Defence and Space Co. (EADS), put updated versions of their rockets to the ultimate test: flying satellites into precise orbits. The Boeing launch, the first flight of a Delta IV, carried aloft a W5 communication satellite for Eutelsat S.A. The EADS mission, on the other hand, was the first for a new variant of the Ariane 5, one with a cryogenic second-stage motor. The rocket failed before the new motor ever had a chance of firing, and the two satellites, a Hot Bird 7 for direct-broadcast TV and a French Stentor for communications, were lost.

According to experts, there should be 30 to 35 launches of telecommunication satellites into geostationary orbits per year, but the trend will be toward heavier satellites in the 4.5 to 5.5-ton range. These are the missions the Delta IV and Ariane 5 were built for: getting heavier, sometimes multiple payloads into orbit. And those added capabilities should make them suitable for many of the NASA missions previously scheduled for Space Shuttles.

The Ariane 5 family
The A5E/CA Ariane 5 is the latest in the Ariane family of expendable launch vehicles. It can place a single 5.9-ton payload or two payloads weighing 6.9 tons into geosynchronous transfer orbits (GTO). Its central component is the cryogenic or core stage. It consists mainly of an aluminum alloy tank containing two compartments for extremely cold liquid hydrogen (LH) and liquid oxygen (LOX), which serve as fuel. The two compartments hold 157 tons: 132 tons of LOX and 25 of LH. The core incorporates a thrust frame that handles forces created by the Vulcain 2 engine, and twin solid-propellant boosters.

The Vulcain 2, built in France by Snecma and new on the Ariane CA, develops 303,500 lb of thrust, a 20% improvement over the Vulcain. The improvement is mainly due to a higher oxygen-to-hydrogen ratio and it's enough to let the new Ariane 5 CA increase the payload it can put into GTO by 1,760 lb. The increase in thrust also led to a redesign of the LOX turbopump, combustion chamber, and nozzle extension.

Oxygen and hydrogen turbopumps are powered by hot gas produced in a small gas generator burning hydrogen and oxygen at a low mixture ratio. This ensures the gas isn't too hot. To pressurize the LOX tank, a subsystem carries liquid helium through heat exchangers near the engine where it's converted to a gas and sent to the LOX tank.

Each Vulcain 2 can last through 20 starts and fire for 6,000 sec, which seems like overkill since the Ariane 5 will only need the engine for 575 sec and a single start. The extra capacity, according to Snecma, lets engineers test fire each motor for a few hundred seconds, ensuring each is similarly calibrated. The extra power and reliability could also come in handy for upgrades and to make sure missions have a safety margin.

Each booster holds 240 tons of propellant (ammonium, polybutadiene, and aluminum), and can be steered up to 6* by a nozzle actuation unit. Compared to the previous Ariane 5, the CA 5 uses boosters with slightly larger fuel capacities and lighter engine nozzles. Each booster generates 540 tons of thrust at liftoff, which quickly increases to 600 tons of thrust, as much as an Ariane 4 at lift-off. Boosters remain with the core until it has reached 30 to 45 miles, at which point they detach and follow their own trajectories, burning out after a total runtime of 129 sec and parachuting back to Earth for recovery.

Medium+ launchers are further delineated by a pair of numbers in parentheses. The first is the diameter of the fairing in meters. The second is the number of GEM-60 strap-on boosters it carries
The second stage of the CA 5 uses Snecma's cryogenic HM-7 engine, also burning LOX and LH. It carries almost 12 tons of fuel and throws out almost 15,000 lb of thrust for up to 800 sec. The second stage connects to the payload and faring through the vehicle equipment bay. The bay houses avionics for guidance and telemetry as well as hydrazine boosters for attitude control. Ariane 5 can deploy two satellites simultaneously or sequentially. And to handle a variety of missions, the rocket has three fairings: short, medium, and long.

The Delta IV Family
To match various payloads and mission needs, Boeing builds a variety of Delta IVs: the Medium, three variations of the Medium+, and the Heavy. All are built around a common booster core (CBC), the first stage that carries the new Boeing Rocketdyne RS-68 engine. The engine burns LH and LOX, producing 650,000 lb of thrust. It is 30% more efficient than liquid oxygen/kerosene engines and is also environmentally friendly, generating only steam as a combustion by-product.

The second stage is similar to that used in the Delta III, but with larger fuel tanks for the Pratt & Whitney second-stage RL10B-2 engine. Versions of the P&W RL10 have been used on Delta launchers for more than four decades.

The Delta Medium consists of one CBC and a second stage topped with a faring over the payload. It can take a 9,285-lb payload to GTO. (The Delta III can lift 8,400 lb into GTO, which is twice the payload of the Delta II.) The Medium uses a 4-m (13-ft-diameter) fairing to protect payloads during assembly, launch, and ascent. Once in space, the composite fairing splits in half and falls away. Satellites and other payloads are put on a payload fitting (PAF) and inside the fairing away from the launch pad, which cuts on-pad time to about six to eight days. Like the entire second stage, the Delta IV Medium fairings are follow-ons to Delta III fairings.

Medium+ launchers also have the CBC and second stage, but to accommodate heavier payloads, Boeing straps two or four booster motors to the CBC. And to house larger payloads, the Medium+ uses a 5-m (16.6-ft-diameter) fairing as well as the 4-m one. A Medium+ launcher can place between 10,230 and 14,475 lb in GTO.

Technicians check filament-wound containers that will either carry fuel or be used to pressurize the cryogenic fuel for Ariane launch vehicles.

The strap-on booster engines, built by Alliant Techsystems, Magna, Utah (, consist of a machine-wound graphite fiber and epoxy casing, rocket engine, and solid propellant. Unlike the main and second-stage engines, solid-propellant motors cannot be stopped and restarted, nor can the thrust be controlled. It's either firing and generating thrust or it's off. Alliant builds several strap-on GEMs (graphite epoxy motors) for Delta launchers, including the GEM 40 and GEM 46 (the number is the diameter of the motor in inches). The Medium+ uses two or four of the new 42.5-ft-tall GEM 60s, depending on payload and mission requirements. A GEM 60 weighs a little over 73,000 lb, carries almost 66,000 lb of fuel, and generates 191,000 lb of thrust for about 90 sec. The engine, little more than a carefully shaped nozzle and combustion chamber, can be fixed, or adjusted in flight to control the direction of thrust.

The Delta IV Heavy, the big kid on the block, combines three CBCs and a second stage, along with three 5-m fairing options to lift up to 28,950-lb payloads into GTO. The composite fairings vary in length and can handle single or multiple payload missions.

Experience counts

It seems that successful launch vehicles never die, and they don't fade away either. Take the current Russian Soyuz rockets, for example. They're direct descendants of the Semyorka, which put Sputnik in orbit in 1957. By 1960, Semyorka had acquired a third stage for putting heavier payloads into orbit and a larger faring for carrying bulkier satellites and spacecraft. About that time, it was also renamed the Vostok. Adding yet another stage and more thrust to the Vostok created the Molnya in 1961, which the Soviets used for interplanetary launches. By 1963, Soviet engineers had optimized Molnya for lunar missions and putting objects in Earth orbit, and renamed it Soyuz.

Today, after more than 40 years, the Soyuz is still around. It has been used on more than 1,100 manned and unmanned flights, racking up a success rating of 98.2%. At their space-faring peak, Soviets were able to build more than 60 Soyuz launchers per year and send them into space from one of six launch pads -- two at Baikonur and four at Plesetsk. They've been used to put satellites in orbit, as well as servicing the Mir and International Space Stations.

Boeing's Delta family of launchers also has roots stretching back to the mid-1950s. The first Delta rocket was based on the Thor intermediate-range missile. The Delta's first mission was to carry the Echo 1A satellite into space in August 1960. The satellite, little more than a metal balloon, let NASA experiment with bouncing communication signals off objects in space, a precursor to today's satellite communication networks.

Over the years, the Delta spawned the Delta II, III, and IV, with capacities that range from putting 100-lb payloads into low-Earth orbits (LEO), to putting several payloads totaling 50,800 lb into different LEOs, or 28,900 lb into a geosynchronous transfer orbit (GTO). (LEO is between 230 and 1,240 miles above the Earth's surface; GTO is 22,236 miles high).

There was a slight hitch in the Delta's evolution between 1981 and 1989. During those years, NASA demanded that all its satellite launches would use the new Space Shuttle, thereby shutting down the Delta assembly line after 24 years. The line was restarted in 1986 when President Reagan decided the Shuttle would no longer carry commercial payloads.

The relative new kid on the block when it comes to building rockets is the Launch Vehicle Division of the European Aeronautic Defence and Space Co. (EADS). It got its start in 1973 when the 11 countries in the European Space Agency decided to develop their own space programs and industries. France provided 63% of the total funding.

The Ariane 1 first flew successfully from Kourou, French Guiana, in December 1979. Today, the Ariane 4 has captured about 60% of the commercial launch market. EADS is also the largest stakeholder in Starsem, a consortium of companies and Russian entities that manufacture, update, and commercialize Soyuz rocket launchers.

One successful launcher that never spawned any direct spin-offs was the Saturn V built by The Boeing Co. and Douglas Aircraft Co. When completed and loaded for an Apollo moon mission, it stood 364-ft tall, weighed 6.1 million lb, and generated 7.5 million lb of thrust. That was enough to take a 285,000-lb payload into orbit, or a 107,000-lb load all the way to the moon.

The first stage of the three-stage launcher used turbopumps to force 15 tons of fuel per second into its five rocket engines. The program to design the Saturn V began in 1961, its first flight was in 1967, and it took men to the moon by 1969.

However, NASA abandoned plans for manned interplanetary flight in 1973, dooming the Saturn V to an unnaturally short life. The Saturn V flew for the last time in 1973, ferrying Skylab into orbit. Fifteen Saturn Vs were built, and thirteen flew missions. The last two are now static displays at NASA museums in Cape Canaveral and Huntsville, Ala. A third was cobbled together from test components and placed on display at NASA's Houston facility.

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