The emblem for this Delta 4 mission depicts the DSCS payload and the Air Force's first use of an EELV rocket. Credit: Boeing

Boeing's Delta 4 rocket enters U.S. military service this weekend to launch a $210 million relay satellite for the government's national security communications network.

Liftoff of the second Delta 4 is scheduled for 6:44 p.m. EST (2344 GMT) Saturday from pad 37B at Cape Canaveral Air Force Station, Florida.

The rocket's 42-minute flight will transport the Defense Satellite Communications System 3-A3 spacecraft into Earth orbit to mark the Air Force's first Evolved Expendable Launch Vehicle mission.

"This is certainly the dawn of a new day for military space programs," said Lt. Col. Tony Taliancich of the EELV Cape Consolidated Task Force. "It culminates our joint efforts with industry to develop a national launch capability that satisfies both government and commercial needs."

The EELV program began in the mid-1990s to create a new generation of American launchers to ensure the Pentagon would have a reliable and economical way of delivering payloads into space through 2020. Boeing's Delta 4 and Lockheed Martin's Atlas 5 boosters were born of the EELV competition, and both families of rockets have successfully completed their maiden flights -- lofting commercial cargos last year.

The Air Force awarded 22 launches to Delta 4 and seven flights to Atlas 5 during the initial round of EELV orders.

An artist's concept of DSCS satellite in orbit. Credit: Air Force

The 6,025-pound DSCS A3 satellite riding atop the Delta 4 this weekend is destined for geostationary orbit 22,300 miles above the Indian Ocean region where it will join a worldwide constellation of sister-craft.

The DSCS fleet is called "the backbone" of the U.S. military's global satellite communications, providing jam-resistant, high-data rate communications between military forces, the White House, U.S. embassies and the intelligence community.

Built by Lockheed Martin, DSCS A3 will replace the B12 satellite launched in July 1992.

The new craft features improvements as part of the Service Life Enhancement Program to increase the tactical communications capability by 200 percent over the B12 satellite.

A Delta 4-Medium vehicle configuration will be used for this launch. The two-stage rocket doesn't sport solid-fuel motors and is the least powerful of the Delta 4 family.

Without solids giving the rocket an extra boost at liftoff, this Delta 4 will have a 1.2 thrust-to-weight ratio, making it slower than the maiden launch last November, said Dan Collins, manager of Boeing's Delta programs.

"This rocket will not leave the pad at the same pace that our inaugural launch did. The thrust-to-weight ratio on the Medium without the solid rocket motors is lower. It will be more similar to what folks saw on the inaugural Atlas 5 launch," Collins explained in an interview Wednesday.

The DSCS A3 spacecraft, enclosed in the rocket's nose cone, is lowered atop the launcher at the pad. Photo: Boeing/Carleton Bailie

Saturday's launch will be the first of four Delta 4s in 2003 -- all Air Force EELV missions.

"We are looking forward to it," said Collins. "We believe that we've been able to do all the right processes, we've gone by the book and we're pretty confident. We really feel good about things."

As is typical for a launch campaign, two minor issues are currently being worked. However, officials expect the glitches to be cleared up soon.

"Neither of them look like they are big issues, just the last couple of engineering points that we are closing out," Collins said.

"The vast majority of the launch team had the weekend off. Everybody looks well rested and prepared. The vehicle is acting very nicely. We started our engineering walkdowns the other day and the engineers are very, very happy with the vehicle. It is very clean."

After the successful debut launch of Delta 4 last November, an extensive review of data from that flight was performed. Boeing and government-sponsored teams analyzed the mounds of information before moving forward with this second Delta 4.

The inaugural Delta 4 rocket blasts off on November 20, 2002. Photo: Boeing/Carleton Bailie

"In general, the first launch was very, very clean -- very nominal response by all the systems, controls was absolutely beautiful, guidance was very, very good," Collins said.

"We did look very hard at a lot of the acceleration data. We saw a little bit of higher vibration from down in the engine section -- the aft end of the (Common Booster Core first stage). So there were a couple of components that we went and qualified to a little bit higher level.

"With the solid rocket motors, we saw a slight exceedance in one area in the buffet loads. So we have gone back and addressed them. Of course, those are not an issue on the DSCS mission, which doesn't have the solid motors.

"But those were the two little things that we saw and we've gone back and adjusted them to account for what we saw. But the vast majority of the data was all very, very clean. We are very pleased with it."

An illustration of the Delta 4-Heavy rocket configuration. Credit: Boeing

Looking beyond the next Delta 4 launch, Boeing and the Air Force plan to launch the final DSCS satellite in July, followed by a demonstration flight of the Delta 4-Heavy triple-body vehicle in September and the first West Coast mission in December to place a classified National Reconnaissance Office cargo into space.

"It is a pretty exciting year," Collins said. "At this time, we are still on schedule to do all of those. But as you can imagine, there is a lot of work between now and then. We think we've identified the risks and have the right risk mitigation plans in the place. But the team is focused and working hard and I think in pretty good spirits.

"These are some pretty important payloads and missions that are being launched. We understand it's key for the nation that we get these payloads up safely. We're focused on meeting the commitments. Above all, we're focused on mission success and making sure we do things right."

A commercial launch of the Estrela do Sul 1 communications satellite, originally envisioned as the third Delta 4 flight, has been scrubbed from the manifest. The Loral-built spacecraft has been transferred to Sea Launch. Delta 4 and Sea Launch offer mutual back-up to each other as part of Boeing Launch Services.