by Jeff Pollard
All of these drawbacks haven't stopped people from using LH2 in their rockets. But for Kingsley, these drawbacks were of serious concern. That's why he had chosen to use a different fuel. The Arthur engine burned RP-1, a form of kerosene. The main drawback of RP-1 is a much lower exhaust velocity and therefore a lower specific impulse. But using this less effective fuel has several benefits. RP-1 doesn't need to be kept cryogenically cold, which alleviates a need for insulation and coolers, making the rocket lighter. It also is much more dense than LH2, allowing much smaller pressure vessels and therefore a smaller rocket, again, saving weight. Add in that it's nowhere near as good at finding cracks as hydrogen and that it doesn't cause embrittlement, and you've got a fuel that's far easier to work with, especially for a rocket that's meant to be reusable. Kerosene is a good fuel for when you need high-thrust, such as at liftoff, while hydrogen is a good fuel for when you need a lot of delta-V, but don't need that high of thrust, like when performing orbital insertion.
The Saturn V used kerosene in its first stage, and LH2 in its second and third stages when high thrust wasn't as important as a high specific impulse. For the Space Shuttle, they used LH2 from liftoff, but had to augment the thrust of these lower-thrust engines with Solid Rocket Boosters to get the rocket off the ground.
The choices Kingsley makes are different because he values different things. For NASA, getting the highest specific impulse possible was a huge concern, and thus they were willing to try to overcome all the hurdles involved with using LH2. But Kingsley's main goal was a cheap and reusable rocket. And that meant he was willing to sacrifice performance for a cheaper and simpler rocket. That meant no solid rocket boosters that were thrown away, and that meant using a fuel that was easier to work with.
The Eagle 1-3 weighs about 85,000 lbs at liftoff, and a single Arthur engine puts out about 102,000 lbs of thrust. The first stage will burn for just under three minutes, taking the rocket to 90 km high (or around 300,000 feet). At that point, the first stage will run out of fuel. Explosive bolts will sever the first stage and the second stage will turn on. The first stage will fall into the ocean under parachute as they have yet to start to implement the re-usable architecture. The second stage uses a single Draco engine. The Draco puts out only about 7,000 lbs of force, compared to the 102,000 of the Arthur. The second stage will burn for more than 7 minutes, taking the payload from 90 km high and traveling about 2000 mph, to 150 km high and traveling over 17,000 mph horizontally.
The Draco is being developed by SpacEx as the small engine that will be used on their space vehicle, the Griffin capsule, for orbital maneuvering, powered landing, and launch abort. The Draco uses hypergolic fuels, which means the fuels don't need a source of ignition, simply mixing the fuel and the oxidizer, in this case hydrazine and nitrogen tetroxide, causes them to combust upon contact, which is a nice trait in rocket fuel. However hypergolic fuels are toxic, difficult to handle, and have a lower specific impulse than more conventional fuels, which is why they are only used in applications where instant ignition is a necessity, like in landing engines.
Several Draco engines will be mounted on the full sized Griffin capsule. During launch, if a problem is detected, the launch-abort system will trigger, firing the Dracos and lifting the Griffin right off the top of the rocket, getting it away from an impending explosion, which is not a time when you want to fuss with trying to get the rocket lit. Assuming the Griffin doesn't abort and makes it to space, the Dracos can be used for maneuvering the spacecraft. Upon return to Earth, Kingsley plans to have the Griffins not return under a parachute, but rather to make a powered landing to a landing pad at the SpacEx factory in California, eliminating the need for a fleet of ships to recover the capsule after a splashdown, and enabling a faster turnaround time. The Griffin would also carry parachutes as a backup. The Apollo missions used a launch-escape-tower, a contraption fitted atop the massive rocket, containing its own small rockets. If there was a problem, the tower fired its engines, lifting the capsule off the top and saving the astronauts. However, the tower was jettisoned a while into launch, and thus was effectively dead weight, wasted payload since it was discarded when unused. Kingsley's design, using the same engines you would use in space as the launch-abort system, saved weight and made the spacecraft more capable at the same time.
The second stage with it's single Draco engine will push the payload to orbit, if all goes well. Today's payload is a mockup of the Griffin capsule, a 1/4th scale version, about six feet tall and three feet across. The Griffin mockup is equipped with the same computer package that will guide the real Griffin. It even includes the Draco engines that would do the launch-abort on the real Griffin, but again, at 1/4th scale. These mini Dracos are planned to be used as reaction control thrusters, small engines that will keep the spacecraft oriented properly.
Nine minutes after launch, the second stage will cut-off, at 99% the speed needed to make low-Earth-orbit. The mock-up capsule will fire its mini-Dracos and reach a proper orbit. The Eagle 1 system is theoretically capable of putting 1300 lbs of payload into low-Earth-orbit, at a list price of $6 million. That's theoretical because Eagle 1-1 and 1-2 both failed to make orbit, and even if 1-3 does make orbit, it will have cost much more than $6 million. Once SpacEx is fully operational and pumping out engines and rockets on its assembly lines in large numbers, then the per-unit cost of each Eagle 1 to the customer will supposedly be only $6 million. But getting all of the infrastructure up and running costs way more than the cost of one rocket and has SpacEx essentially tapped out.
The countdown resumes at T-minus 10 minutes. The RP-1 fuel and liquid-oxygen are pumped into the rocket. Just before ignition, the turbopumps in the first stage kick in, preparing to feed the single engine with enough fuel and oxidizer to produce 102,000 lbs of thrust (for comparison, an F-16's GE F110 Turbofan jet engine produces around 28,000 lbs of thrust in full afterburner, so each Arthur has about the same force as 4 F-16s on full afterburner). The Eagle 1-3 is clamped down to the pad, the clamps will only release when the computers sense good ignition. Directly beneath the Arthur engine is a cooled duct called a flame bucket. It's a concrete structure that takes in the exhaust and directs it away. The concrete is water-cooled by numerous pipes running through it, otherwise the intense heat would destroy the flame bucket.
Hammersmith and Harding look on through binoculars from the observation deck ten miles away. Kingsley, Dexter, Travis, and the numerous technicians in the Launch Control Room monitor the data from the rocket. Trails of vapor blow away from the cold rocket. At t-minus 4 seconds, water sprinklers turn on, aimed just below the rocket, heading into the flame bucket to further protect it, as well as to dampen vibration from the engine, which would otherwise bounce off the concrete and head back toward the rocket and shake it to pieces.
At t-minus 3 seconds, the turbopumps spin up, and the LOX and RP-1 race through the complex plumbing and meet each other in the combustion chamber. At t-minus 2 seconds, triethlyaluminum (TEA) and tritehylborane (TEB) are injected into the combustion chamber. The TEA and TEB combination is pyrophoric, igniting in contact with air, and burns with an intense green flame. The flash of green light is visible even in the middle of the day. The rocket fuel and oxidizer meet in the combustion chamber where the TEA-TEB combination is burning very hot, causing instant ignition. At t-minus 1 second, the turbopumps throttle up to maximum and the nozzle of the Arthur expands under intense pressure. Between t-minus 1 and t-zero, the computers are given a chance to analyze the data from the rocket. Are the pumps operating correctly? Is the fuel flowing smoothly and in the proper amounts? Is the combustion stable? In that one second, the computer runs its own checklist, like a flight-director calling out the names of a dozen technicians. At t-minus zero, if no alarm has been tripped, the clamps release and the rocket lifts off.
Kingsley watches anxiously as t-zero comes and the Eagle lifts from the pad. The white rocket with SpacEx written down the side in blue and orange letters takes to the sky. Th
e Eagle emits a rippling roar as it quickly gains speed and altitude. Everything is working perfectly. From Kingsley's seat he looks at several video feeds, some pointed up at the rocket, others pointing down from the Eagle.
The clock ticks through t-plus 30 seconds and Kingsley breathes a slight sigh of relief. At least if something goes wrong now, the rocket won't fall back down and destroy the launch pad. Still 139 seconds left in the first stage. Everyone in Launch Control eyes the telemetry, waiting to see if the computer correctly throttles down as the rocket accelerates through the dense atmosphere. The SpacEx employees cheer on their rocket.
“Coming up on first stage separation,” Dexter says. “Twenty seconds.” The rocket shrinks quickly in the video feeds. It's 46 km high and 18 km downrange. “MECO in five, four, three,” Dexter counts down to Main-Engine Cut-Off. Several technicians are poised to give commands to the rocket should the computer fail. They each nervously watch the data, hoping they don't need to do anything. The Range-Safety-Officer has his finger poised over a button that sets off explosives in the rocket. In the event the rocket veers off course, the RSO destroys the rocket while it's still headed out to sea. The explosives are shaped charges aimed at the fuel tanks, designed to cause a massive explosion that dissipates the rocket fuel and oxidizer so those materials don't make it back to Earth in a populated area.
“Two, one, MECO,” Dexter says. The Arthur engine cuts off. The now unpowered rocket begins to be slowed by drag. “First stage sep,” Dexter says immediately after MECO. The explosive bolts fire, separating the first and second stage. Separation is accompanied by flash of light and vapor coming off the rocket as the separation creates a disruption in the super-sonic airflow over the vehicle. But through the flash, it appears the first and second stages are still connected.
Multiple alarms go off in the Launch Control Room. The rocket is still in one piece, continuing upward, no ignition from the small second stage, while something else has happened, a flash, something moving fast. “The second stage didn't light,” Kingsley says. “Override the computer, command the second stage ignition.”
“It's not responding,” Stage-Two says.
“Did we get a clean separation?” Kingsley asks.
“It says we did, just no ignition from stage two,” Stage-Two replies.
“What's the situation,” the Range-Safety Officer asks tensely, finger poised on the button that would blow the whole thing up.
“Control, the launch-abort was triggered,” Capsule says.
“Is it off the rocket?” K asks. He looks to Dexter's panel next to him. Dexter serves as the pilot in this unmanned flight. Should the computer guidance fail, he could steer the rocket to orbit manually. His panels show several views from the capsule as well as all relevant data on the capsule's position, velocity, altitude, etc.
“Oh yeah, she's free,” Dexter says, alarmed. His job as the pilot has gone from theoretical to very very real. With one hand on a joystick and another on a throttle, he steers the capsule away from the rocket.
“I'm gonna trigger the self-destruct,” the RSO says.
“Not yet,” Kingsley barks at him.
“The whole second stage is coming down in one piece,” the RSO argues.
“Not fucking yet!” K says. “Stage-One, trigger the parachutes.”
“It's too high for the chutes,” Stage-One says.
“Trigger the pyros,” K insists. Stage-One hits the button, triggering deployment of the parachutes nestled between the top of stage one and the interstage connecting to stage two. The pyros blow, and the first and second stage finally come apart cleanly, starting to fall separately. The first stage slows rapidly, not weighing much at all. The second stage plummets back into the atmosphere, safely out to sea.
“Okay RSO, just for the second stage, self-destruct,” K says. The Range-Safety Officer opens the glass cover and presses the button. The shaped charges up against the second stage tank explodes, piercing the tank and igniting all the fuel at once. The second stage looks remarkably like fireworks, a mortar shell with a shower of sparks, burning aluminum.
“Dexter, bring her in to the LCF,” K says.
“What?” Dexter asks, as he concentrates on his panel, guiding the falling capsule using the mini-Draco engines throttled low.
“The helipad on the roof, bring her down on the helipad,” K says.
“She's already 20 clicks down range,” Dexter says.
“That little capsule has enough delta-V, I've done it in the simulator, burn towards the LCF while you're still high, then get that heat shield pointed down. You'll be low on fuel after the return burn, but you'll have enough to land it,” K insists.
“But why would we do something that crazy?” Dexter asks.
“Do it or we won't have jobs tomorrow,” K says. “If you can't handle it, I can do it.”
“I got,” Dexter replies, throttling up the mini-Dracos and sending the small capsule back toward land. K gets up and walks toward the elevator.
“Where are you going?” Hannah asks, following K into the elevator.
“Up,” K says simply as he presses the button for the roof.
“To get them away from the helipad?” Hannah asks.
“No,” K replies.
“Isn't there something like crashing into the helipad with toxic fuel any second.”
“You're such a pessimist...” Kingsley tries to remember her name.
“Hannah,” Hannah interjects.
“I knew that,” K replies. Kingsley and Hannah exit the elevator on the roof of the LCF. The observation deck is to one side of the roof, the other side is a helipad that is currently empty.
“Sorry old boy, terrible luck,” Harding says. Brittany's eyes try to hide her feeling of utter defeat.
“What are you talking about, it went perfectly!” Kingsley says excitedly.
“Have you gone mad? It exploded!” Harding replies.
“That was just the second stage,” Kingsley says dismissively, “that's just a mock-up. The first stage, the Arthur, it worked flawlessly, we got the data we need, we can move on to the Eagle 5 now. In fact, this test went better than perfect. When the second stage didn't light, the launch-abort kicked in automatically and lifted the capsule right off the top of the rocket to safety. So not only did we just successfully demonstrate the Arthur, we also proved the launch-abort system!”
“If there were people in that thing they'd be scrambled eggs,” Harding replies.
“Are you sure about that?” K asks. K looks over Harding's shoulder, scanning the sky for the tiny capsule which should be coming their way, assuming Dexter followed his orders.
“Your idea of success is alarming,” Harding replies, looking to Hammersmith, flummoxed.
“K,” Brittany says, “are you feeling alright?”
“I'm just excited about the successful test of the launch-abort system, that proves the safety of our rocket,” K says, his eyes appear shifty as he looks over their shoulders, scanning the sky.
“You say that as if it was planned,” Harding replies. “This wasn't a planned test of the abort, was it?”
“We've got to prove the launch-abort works sometime,” K replies with a smile. “So Mr. Harding, are you prepared to invest in SpacEx?”
“How on Earth you're going to convince anyone to ride that rocket is beyond me,” Harding says, offended. Hannah stiffens up, alarmed. Kingsley keeps his poker face on. Hannah wants to back away as this falling rocket approaches, K puts his hand on her back and keeps her from moving.
“Lindsey, do you have my phone?” K asks Hannah. She takes a tentative step back, staring up at the incoming capsule. “Lindsey?” K asks more insistently. Hannah finally catches on that he's talking to her.
“What?”
“Phone, do you have my phone?” K asks.
“Yeah, it's right in here,” she digs into her purse, looking away from the capsule plummeting towards them and pulls out his smart phone.
“Thanks,�
� K says. K turns on the video camera on his phone and aims it at the mini-Griffin. Hannah takes a careful step back. The low rumble of the throttled down Dracos alert Hammersmith and Harding, who quickly turn around and look up, finding the mock-up Griffin falling toward them.
“Jesus,” Hammersmith says, rushing to the railing, getting away from the capsule.
“Is this safe!?” Harding asks as the mini-Griffin descends towards the helipad, perched delicately on a column of rocket exhaust, wavering from side to side, as if it might lose control and fall out of the sky at any moment. While the main thrusters are throttled low and keeping the capsule from falling, the translational thrusters flash on with bursts of thrust to steer her in.
“It's perfectly safe, these autopilot computers are amazing,” Kingsley says without moving toward safety. He stands his ground bravely, filming the hopefully successful landing, praying that Dexter's as good a pilot as he thought when he hired him.
Four landing legs emerge from the rim of the heat shield, and the mini-Griffin comes in for a picture perfect landing in the center of the heli-pad.
Harding is amazed.
“My word!” Harding says, walking towards the rocket. Kingsley puts his arm around Harding, keeping him from approaching the capsule. A moment later a burst of gas from a vent sprays toxic fuels into the sky. Harding doesn't know it, but the hypergolic hydrazine and nitrogen tetroxide fuels used for that landing are highly toxic. Fortunately the mini-Dracos weren't at full throttle. K holds on to Harding, hoping the light breeze will dissipate the fumes. “Is that the capsule?”
“That's it indeed. Just imagine one four times the size and you've got the real Griffin we're working on. No clumsy splashdown or airbag crap. Powered landing, on landing legs with suspensions. Soft touchdown at an exact spot. How's that for a demonstration?”
