The Delta 4 family: (from left) Medium; Medium+ 4,2; Medium+ 5,2; Medium+ 5,4; Heavy. Photo: Boeing

Delta rockets have been flying for more than 40 years, but the new Delta 4 dwarfs its predecessors in sheer size and Earth-shaking power to launch much larger cargos than possible in the past.

Development of Delta 4 began in the mid-1990s, giving the Delta team the chance to create a fleet of heavy-lift rockets that would fly through at least 2020, lofting commercial, military and civilian spacecraft. The Delta 4 family features a brand new first stage and main engine, rebuilt launch pads at Cape Canaveral, Florida, and Vandenberg Air Force Base in California, and a new rocket manufacturing plant in Decatur, Alabama.

"It is an opportunity that I think our whole team realizes doesn't come around every day," said Dan Collins, Boeing's Delta program manager. "You don't get the chance to basically have a clean slate and say 'OK, take all the experience of the space programs of the past and go do it the way you want to and address all those issues.'

"There is challenge to it but you also realize you are in a once in a lifetime position with new engines, new factories, new launch pads. You know, this hasn't happened since the 60s. Those were the glory days. Folks look back on those with fond memories...We are living the same thing on Delta.

"We were given by The Boeing Company an opportunity that will not happen again in our careers and I think folks are realizing that as we are getting through the day to day hassles and challenges. This is neat stuff."

The Delta 4 fleet
There are five versions of the Delta 4 launcher, each incrementally increasing the size or weight of the payload to be placed in space.

All configurations feature a Common Booster Core first stage and Rocketdyne-made RS-68 liquid hydrogen/liquid oxygen main engine and an upper stage with Pratt & Whitney's RL-10B-2 cryogenic engine.

The upper stage and RL-10 have already flown on the Delta 3 rocket, along with the Delta program's proven avionics and Redundant Inertial Flight Control Assembly (RIFCA) guidance computer.

What separates the different variants is the use of either two or four Alliant-made strap-on solid rocket motors and the selection of either a four- or five-meter diameter nose cone to enclose the satellite cargo. The solids are larger, more powerful cousins to the Delta 2 and Delta 3 motors.

The most basic version of Delta 4, known as Delta 4 Medium, is just the two-stage vehicle, no solid motors and a four-meter fairing. It is capable of placing 4,210 kg (9,285 pounds) into geosynchronous transfer orbit.

The configuration flying on the first launch is the Delta 4 Medium+ 4,2. That translates to the two-stage vehicle with a four-meter payload fairing and two strap-on solids. It can deliver 5,845 kg (12,890 pounds) into geosynchronous transfer orbit.

Illustration of the first Delta 4 rocket. Photo: Boeing

The next step up is the Delta 4 Medium+ 5,2 with the five-meter fairing to accommodate larger satellites and two solids to loft 4,640 kg (10,230 pounds) to GTO.

A five-meter fairing with four solids is the Delta 4 Medium+ 5,4 to carry 6,565 kg (14,475 pounds).

The largest of the family, the Delta 4 Heavy, features three Common Booster Cores mounted together to form a triple-body. The massive rocket will be able to launch 13,130 kg (28,950 pounds) to GTO, such as a dual payload of two communications spacecraft.

The Air Force has paid for a test launch of the first Delta 4-Heavy, scheduled to occur in mid-2003. The rocket will carry only a dummy payload in an effort to demonstrate that the rocket works before it blasts off on future flights with critical and expensive satellites for the U.S. government.

Delta 4 rockets will fly to both equatorial and polar orbits, and can inject communications satellites directly into geostationary orbit during much longer missions.

New first stage
As its name suggests, the Common Booster Core is "common" across all Delta 4s. A CBC measures about 150 feet (38 meters) in length, 16 feet (5 meters) in diameter and weighs 54,000 pounds unfueled.

The first Delta 4 on launch pad 37B at Cape Canaveral. Photo: Justin Ray/Spaceflight Now

The stage is what Delta program manager Dan Collins calls "the new kid on the block" for Delta 4.

Looking from the bottom to the top, the RS-68 powerplant and engine section are at the base of the stage. The liquid hydrogen tank accounts for about two-thirds of the stage. That portion of the CBC is covered by orange foam insulation. The white band is the known as the centerbody. The next orange section is the first stage liquid oxygen tank.

Boeing has attempted to paint the orange foam to match the "Delta Blue" color that goes hand in hand with the heritage and marketing of Delta. However, the first tries have not produced good results. Instead of spending too much time on this side project, engineers are focused on preparing for the maiden Delta. But future painting efforts are expected.

For an overview of the RS-68 main engine, see our separate story.

Solid rocket motors
To provide additional thrust at liftoff, the Delta Medium+ rockets will sport either two or four solid-fueled strap-on boosters. The 43-foot tall motors are attached to the first stage by a ball-and-socket design.

The first of two solid rocket motors is positioned for attachment to the first Delta 4 on launch pad 37B. Photo: Boeing video/Spaceflight Now

Manufactured by Alliant Techsystems, these third-generation graphite-epoxy motors are advanced and larger versions of the boosters developed for Delta 2 and Delta 3 rockets.

The Delta 4 motors are dubbed GEM-60 because they are 60 inches (1.55 meters) in diameter.

They can fly with nozzles that are either fixed or can swivel. For the first Delta 4 launch, the rocket will have two solids, both with nozzles that gimbal to help steer the rocket in flight.

The average thrust produced by each booster is 195,000 lbf at vacuum.

Top of the rocket
For the Delta 4 Medium and Medium+ 4,2 rockets, an interstage adapter that tapers from the five-meter first stage to the four-meter upper stage is used to join the two stages of the rocket. The Medium+ and Heavy rockets with five-meter upper stages have a straight barrel-like interstage.

The upper stage has been launched three times on the trio of Delta 3 rocket flights. The first launch in 1998 exploded shortly after liftoff and the upper stage was never used. In 1999, the upper stage engine malfunctioned during the second of two firings due to a manufacturing defect. The third flight successfully demonstrated the stage's full use in 2000.

The four-meter version of the stage is nearly identical to the Delta 3 configuration. The RL-10B-2 engine, equipment shelf and liquid oxygen tank are hidden within the rocket's interstage during launch. Once the first stage has completed firing, it and the attached interstage are jettisoned to reveal the RL-10. As seen on the launch pad, the top orange band of the rocket is the upper stage liquid hydrogen tank.

The stage carries about 20,400 kg (45,000 pounds) of propellant for a total burn time of around 14 minutes. A normal mission to geosynchronous transfer orbit features two firings.

Illustration shows the two versions of the Delta 4 upper stage. Photo: Boeing

For the bigger members of the Delta 4 family -- Medium+ 5,2; 5,4; and Heavy -- the stage is enlarged to five-meters in diameter in order to carry more propellant. The oxygen tank is lengthened by a half-meter and the hydrogen tank goes from four to five meters in diameter. The total fuel load is increased to 27,200 kg (60,000 pounds), extending the stage's firing time to nearly 19 minutes.

The RL-10B-2 engine -- developed by Pratt & Whitney on more than three decades of RL-10 heritage -- has the world's largest carbon-carbon extendible nozzle that drops into place just after the first stage falls away. The cryogenic engine produces a thrust of 110 kN (24,750 pounds) and a specific impulse of 465.5 seconds. It has a total service life of 3,500 seconds and 15 starts, including ground testing.

Atop the upper stage sits the payload attach fitting and the satellite cargo enclosed within the fairing. The nose cone can either be a four-meter composite shroud as used on Delta 3, the new five-meter composite fairing or a five-meter aluminium fairing that Boeing already builds for the Titan 4 rocket.

Rocket-making factory
To manufacture Delta 4 rockets, Boeing has built a mammoth, 1.5 million-square-foot plant in Decatur, Alabama. It is considered the largest and most state-of-the-art facility of its kind in the world.

"We've been taking everybody through there. We've taken our competition through there and watched their jaws drop," remarked Collins.

The Delta 4 factory in Decatur. Photo: Boeing

"Raw materials, raw aluminium comes in one end, goes through machining, processing, state-of-the-art welding, friction stir welding, proof testing, turns the corner, we put the insulation on it, put the tanks together...out of the other end of this 1.5 million-square-foot facility comes a Delta 4.

"A rocket travels 2.1 miles in this plant. In our previous manufacturing for Delta 2, the tanks would travel over 6,200 miles during their process and being built into a rocket. We took 6,200 miles, several facilities, all that transportation, all the chances for problems to happen and combined one very controlled 2.1 mile track through one factory."

To date, Decatur has churned out one test rocket used in static firings of the first stage and the first two flight rockets.

"Before the rocket ever leaves the factory, the common booster is fully assembled and checked out. So we know when we deliver to the launch site we have a high quality product, greatly reducing the chances of getting out to the launch pad and finding a problem because we have found everything, if it existed, back in the factory. The people with the right tools, right knowledge can make sure what's leaving their factory doors is absolutely high quality."