The very first test flight for NASA's Orion spacecraft is Thursday December 4th. Here's the nitty-gritty details of how the 4.5 hour test flight will put the service module, launch abort system, heat shield, and parachutes through their paces as the craft launches, completes two orbits, and returns to Earth.

Orion on the launch pad and awaiting its first test flight. Image credit: NASA/Kim Shiflett

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After months of assembling the spacecraft, fuelling and erecting the rockets, mounting the craft onto a seriously big firecracker, and a lot of impatient bouncing around filling time until the final countdown, we're just days away from Orion's trial by fire. While this test flight will be flown remotely with no on-board crew, Orion is being developed as part of the Next Giant Leap to bring humans to Mars.

The plan for Exploration Flight Test-1 is to launch, orbit twice while popping up through the Van Allen radiation belt, come roaring back to Earth, and slow down enough for a relatively gentle landing. The entire test flight will last just 4.5 hours, and will test each of the spacecraft components together as a system for the first time after passing isolated individual tests. Of course, the design crew behind Orion's sleek alphabet book are back with beautifully clean illustrations of what we can expect.

0. Pre-Launch Activities

When reading the anticipated times of events, L- is a time before launch, and L+ is a time after launch. The major prelaunch checkpoints are:

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Launch - 8 hours 15 minutes: First motion of the mobile service tower. The gantry support pulls away from the rocket and spacecraft.
L-4:35 Fuel readiness poll. United Launch Alliance will decide if the rocket is a go/no go for fuelling. If it's a go, fuelling will start five minutes later, filling the boosters with liquid hydrogen and oxygen.
L-3:30 Huston takes over flight control from the pre-flight team.
L-2:35 NASA TV's live streaming coverage begins. We'll be providing coverage highlights on space.io9.com, so you can always catch up with us!
L-1:55 Landing weather briefing on conditions at the splashdown point off the California coast in the Pacific Ocean.
L-0:30 Launch weather briefing on conditions at the launch site in Cape Canaveral, Florida.
L-0:19 Final 15-minute hold. If everything goes according to schedule, Orion will be totally ready for the final 4-minute countdown a full fifteen minutes early. The final Go/No-Go polls take place during this hold.
L-0:16 Final Go/No-Go poll for Orion. Lockheed Martin's spacecraft manager will do final polls of their team to make sure all Orion's systems are ready for launch.
L-0:08 Orion switches to internal battery power. Final Go/No-Go poll for the Delta IV Heavy rocket. United Launch Alliance's rocket manager will do a final poll of their team to make sure all of Delta's systems are ready for launch.
L-0:04 The fifteen-minute hold expires as Orion enters the final launch countdown. This will be the first time the new countdown clock is used at Cape Canaveral.

1. Launch

Time 0:00:00 - Launch

The launch is scheduled for 7:05 a.m. EST on December 4th out of Cape Canaveral in Florida. NASA is currently forecasting 60% chance that weather conditions will be go for launch, with some concern over precipitation or winds. The full launch window is 2 hours, 39 minutes. If the launch can't happen within that timespan, it will be delayed until another day.

While eventually Orion will lift off with a custom-built super-heavy rocket, for now it's hitching a ride on the United Launch Alliance Delta IV Heavy. This rocket has an unnerving habit of gently setting fire to itself during launch, so don't be alarmed when fire spills around the pad and licks up the boosters.

L+00:01:23 Orion and its rocket reach maximum dynamic pressure ("max Q") during the ascent.
L+00:01:25 Orion and its rocket achieve Mach 1, the speed of sound.
L+00:03:56 The side booster engines cuts out, and the boosters ("port and starboard common boosters") are jettisoned from the Delta rocket.
L+00:05:30 The main booster engine cuts out. Three seconds later, the entire first stage of the rocket is jettisoned.
L+00:05:49 The second stage of the rocket engine starts, an 11-minute 50-second burn that carries Orion even further into space.

2. Exposure

Time 0:06:15 Jettison protective coverings from the service module and launch abort system.

Just over six minutes after launch when the spacecraft has reached space, the protective panels will jettison. Once in space, the panels are no longer needed to protect the service module and launch abort system from vibrations and the grasping rip of atmosphere, so ditching them will reduce spacecraft weight.

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L+00:06:20 Five seconds after the panels peel off, the launch abort system will jettison, pulling away from the spacecraft. The launch abort system will only trigger if something goes horribly wrong (like during the recent Antares and Spaceship 2 anomalies) and it needs to blast astronauts to safety. When things don't go wrong, the jettison motors will need to fire a few minutes into flight to peel free of the spacecraft. Right now it needs to be tested to ensure it can separate quickly, cleanly, and powerfully. If it fails, Orion will never land: the launch abort system directly blocks the parachutes from deploying.

L+00:17:36 The second stage engine cuts off, having placed Orion in its initial orbit.

3. Re-ignition

Time 1:57:11 Ignite the upper stage rockets to boost Orion higher for the second orbit.

At nearly two hours after launch, Orion will have completed a full orbit. The second stage of the rocket will re-ignite to boost the spacecraft up to 5,800 kilometres (3,600 miles) altitude for its second orbit. This will carry Orion to a higher altitude than any crewed spacecraft has gone in the past forty years.

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L+01:55:26 Second stage engine re-ignites, a 4-minute, 45-second burn to boost Orion into a higher orbit.
L+02:00:09 Second stage engine cuts off.
L+02:05 Orion will enter the lower Van Allen Belt, exposing it to high radiation. Its cameras will shut down to protect them from damage.
L+02:20 Orion will rise above the Van Allen Belts, exiting the high radiation zone. Its cameras will turn back on.
L+02:40 The Reaction Control System will activate, preparing to steer Orion once it separates from the Delta second stage.
L+03:05 Orion reaches peak altitude at 5,800 kilometers, the farthest it will get from the Earth during the test flight.
L+03:09 Orion manoeuvres into position to shed the remains of the Delta rocket.

4. Separation

Time 3:23:41 Peel off the crew module in preparation for re-entry.

Extra weight is a pain when trying to slow down, so once again Orion will shed no-longer-needed parts by separating the crew module from the upper stage and service module. Only the crew module will undergo controlled re-entry; the other pieces will be abandoned in a decaying orbit to crash and burn in the atmosphere.

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The service module is connected to the crew module with a zero insertion force connector. The electrical connector holds the modules together using a lever mechanism and very little force, reducing the risk of bending pins or damaging circuits. The connector is severed when the modules are separated prior to reentry.

L+03:23:41 Jettison the Delta second stage and the service module.
L+03:30 Orion will reenter the lower Van Allen Belt, exposing it to high radiation, and again shutting down its cameras.

5. Orientation

Time 3:57:00 Fire control jets to reorient crew module for re-entry.

Orion's control jets will fire up, reorienting the crew module for re-entry. Although for now the module is occupied only by imaginary astronauts, it is never too early to practice keeping the crew chamber pointed in the right direction to help squishy humans survive the tremendous accelerations.

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L+03:57:11 Reaction Control Systems fire for 10 seconds, reorienting the shortstack spacecraft for reentry.
L+04:05 Orion passes back out of the Van Allen belts, exiting the region of high radiation and turning its cameras back on.

6. Heating

Time 4:13:41 Re-entry begins with the crew module hitting the atmosphere.

Orion slams into the atmosphere at about 32,000 kilometers per hour (20,000 miles per hour), testing out the last few system components. The heat shield takes a beating, heating as the spacecraft drops back to Earth. The heat shield backshell has 970 tiles to protect the crew module from the scorching burn of re-entry.

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L+04:13:35 Orion reaches the upper limits of the Earth's atmosphere, which reduces the spacecraft's speed.
L+04:13:31 Superheated plasma forms around the spacecraft, creating static and knocking Orion out of communication with mission control for 2 minutes, 30 seconds.
L+04:15:03 Orion reaches peak heating, scorching the heat shield to an anticipated 2,200°C (4,000°F).
L+04:19:29 Protective coverings on the forward bay jettison, exposing the parachutes. The Forward Bay Cover jettisons through a combination of pyrotechnics, thrusters, and drag from three parachutes attached directly to the cover. The parachutes will slow it down for splashdown in the ocean.

7. Deploy

Time 4:20:22 A sequence of eight parachutes begin deploying to use drag to further slow the crew module.

Atmospheric friction drops Orion's velocity by orders of magnitude down to a mere 480 kilometres per hour (300 miles per hour), but that's still way too fast for a safe splashdown. That means it's time for the deployment of a series of parachutes, adding drag to slow the spacecraft down to a less bone-breaking and teeth-rattling 32 kilometres per hour (20 miles per hour) before impacting the ocean.

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Only a few of the eight parachutes will be deployed at a time, with the full sequence staggered to most efficiently slow the crew module before splashdown. The three main parachutes are large enough to cover an entire football field.

L+04:19:31 The first two parachutes deploy.
L+04:20:40 Three pilot ("drogue") parachutes deploy, pulling out three massive main parachutes. The main parachutes slow Orion from 160 kilometres per hour (100 miles per hour) to 32 kilometres per hour (20 miles per hour).

8. Landing

Time 4:24:46 Orion splashes down in the Pacific Ocean for recovery.

Although it's a bit counter-intuitive to use "landing" to describe a capsule splashing down in the ocean, that's what will happen next. A remotely-piloted Ikhana will be in the area to provide a live-feed of the splashdown. The target splashdown area is 16 kilometers (10 miles) across.

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Orion will splashdown 965 kilometers (600 miles) west of the coast of Baja California in the Pacific Ocean, in the same broad region where crews coordinating with the Navy have been practicing splashdown recovery tests. If the launch was on-time, splashdown will be at 8:26 am Pacific time.

L+04:23:29 Orion splashes down in the Pacific Ocean off the coast of Baja California. Recovery operations begin to collect the spacecraft.

Orion recovery test. Image credit: NASA

Want to know more? Read the full Exploration Test Flight press kit here, or explore this First Flight interactive.