Super-cold rocket fuel will be pumped into Boeing's inaugural Delta 4 rocket at Cape Canaveral's Complex 37 for the first time next week as the company kicks off a sequence of launch pad tests that will culminate with an engine firing at the end of August.

Fitted with a mock payload for testing, the Delta 4 rocket looks just like it will during the maiden flight in a couple months. The real cargo will be installed closer to launch. Photo: Justin Ray/Spaceflight Now

Chilled to Minus-298 degrees F, liquid oxygen will be loaded into the rocket's first and second stages Wednesday to continue checking out the new launcher and pad in advance of the maiden Delta 4 voyage in late September or early October.

Boeing has booked October 9 as the liftoff date for the mission on the Air Force-controlled Eastern Range, which provides tracking, communications and safety services to all Cape Canaveral and Kennedy Space Center launches. But Delta officials say the rocket should be ready to fly by September 25. The problem is the Range will be closed from September 9 through October 4 while upgrades are made.

"I have a choice as the launch director to either go ahead and move the launch date to the 9th (of October) and process appropriately, or maintain the the ability to launch on the 25th (of September) and I've chosen to do that -- I'm still marching to the 25th," said Joy Bryant, Boeing's Delta 4 launch site director at Cape Canaveral Air Force Station.

"We are maintaining the ability to pull it back (to the 25th). Eventually, as you get down there, we are not going to do our last test and then sit for a month. So eventually you will have to commit to which launch date. But right now we are holding steady and could support the 25th if their range conflict moves."

Before the Delta 4 is ready to blast off and deliver a commercial telecommunications satellite into Earth orbit for Paris-based Eutelsat, engineers have to complete a crucial series of fueling tests and conduct two launch countdown dress rehearsals.

Following next Wednesday's liquid oxygen loading, Boeing will then turn its attention to a test that will see liquid hydrogen propellant pumped into both rocket stages.

A later test will see both liquid oxygen and liquid hydrogen loaded on the same day, but with no time limits placed on the team. The final tanking test will run on the countdown timeline with both stages fully fueled per the launch day script.

"We will prove out the system very slow and methodically," said Bryant.

Propellant tests have already been performed at the pad, but not involving the rocket.

"We have done all the cold shocks and flowing through the systems. We have not flowed to the vehicle at this point. We have flowed up to the base of the rocket through the tail service masts."

The rocket is fitted with special instrumentation for the upcoming tests, giving the launch team added insight to such information as the tank fill rates, temperatures and how the equipment chills, Bryant said. In addition to giving engineers practice in fueling the rocket, the tests will also verify all the systems work and computer software limits are set properly.

If all goes well, the first of two full-up countdown simulations will be held on August 12 and 13. The rocket will be loaded with cryogenics again as clocks tick down to a mock liftoff time.

The second dress rehearsal, however, will actually see fire in the flame trench as the Rocketdyne RS-68 main engine roars to life for a brief but dramatic Flight Readiness Firing, or FRF. The countdown is targeted for August 27 and 28, with engine ignition occurring on the morning of the second day.

The firing is designed to ensure all the computer software, rocket and ground systems will work together on launch day as the real countdown goes through the final seconds to liftoff.

The engine will only fire for a few seconds during the FRF, building to 100 percent thrust before being shut down around T+1 second.

Joy Bryant, the Delta 4 launch director at Cape Canaveral, gives reporters a tour of Complex 37. Photo: Justin Ray/Spaceflight Now

"The sequence that is required for FRF is to get the terminal countdown initiation at 8.5 seconds to engine start commit at 5.5 seconds and roll down to minus 1 second with all the valves in the right place, the right firing and we will call that perfect," Bryant explained.

"What we really want to do is to prove out that we can send all the commands to the engine and get through that sequence. Anything from minus 1 second to plus 1 second is gravy. We are just going to go through the sequence and then shut it down."

Inhibits will be in place so the twin solid rocket boosters strapped to the rocket's first stage can't accidently ignite during the FRF. But the command path to the motors will be checked to ensure the ignition order is sent and received correctly.

"We will have them wired to testers. We will send the command through the cables and receive it and validate it comes at the right time, right place, right command," said Bryant.

This week the 330-foot tall Mobile Service Tower at the launch pad was rolled away from the rocket for the first time since the vehicle was fully assembled with the attachment of the solid motors and a nose cone.

The rollback, which provided the first opportunity to see what the 205-foot tall rocket will look like on launch day, allowed the Range to conduct communications checks -- just another test on the road to the debut flight.

"As we have a new facility, new system and a new rocket, we want to check out and make sure the inherent systems of the Eastern Test Range are not, by radiating all the radars, going to cause our vehicle or ground system any problem, any interference," Bryant said.

A similar test was performed Sunday with rocket enclosed within the tower.

The rocket has been on the launch pad since April 30. Although it has seen a couple target launch dates come and go, the rocket remains in good shape, Boeing says.

"There are no design issues. The vehicle is very clean, performing very well," said Bryant, who moved from management in the Delta 2 program to her current Delta 4 job four months ago.

"As I came into this I wanted to look at our sequences and make sure the team was getting everything they needed to get out of each test -- their own knowledge of the system, making sure all the paperwork was updated and validated -- rather than completing a test and running to the next. We want to go slow and steady. And that process has led to say we wanted to make sure we had enough contingency time so we wouldn't get in a hurry."