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发帖数: 29576 | 1 SpaceX的实用F9火箭一千米回收实验
SpaceX plans to recover stages when customers allow
BY STEPHEN CLARK
Encouraged by the soft landing of a Falcon 9 rocket's first stage in the
Atlantic Ocean after liftoff April 18, SpaceX plans a series of stage
retrieval tests over the next few months, but only on missions where the
launcher has enough leftover fuel to accomplish the complicated re-entry
maneuvers required to safely return a rocket to Earth.
SpaceX hopes the experiments will lead to returning a rocket intact to a
engine-assisted touchdown at Cape Canaveral by the end of the year.
Expanding on updates posted to Twitter shortly after the launch, SpaceX
founder and CEO Elon Musk said Friday the first stage flew itself back to
Earth after completing a nearly three-minute burn to start a resupply
mission to the International Space Station.
Data show the first stage, powered by nine Merlin 1D engines, reached the
sea in one piece and under control, apparently softly splashing down in the
Atlantic at near zero velocity, Musk said.
"I'm happy to confirm that we were able to do a soft landing of the Falcon 9
boost stage in the Atlantic," Musk said in a press conference at the
National Press Club in Washington. "All the data we received back shows it
did a soft landing and was in a healthy condition after that."
SpaceX released a video and image frames Tuesday from a camera mounted on
the rocket, and it appears to show the first stage descending toward the
ocean with landing legs deployed as the engine plume kicks up mist from the
sea. SpaceX has asked video experts to try to improve the noisy footage in a
crowd-sourcing effort.
Musk described the soft landing accomplishment as a "huge milestone for
SpaceX and certainly for the space industry."
SpaceX claims the cost for a commercial launch on a Falcon 9 rocket is
approximately $60 million. Musk said a fully reusable rocket, which also
hinges on streamlined refurbishment and quick turnaround between flights,
could cut launch costs a hundred-fold.
But in the next few years, SpaceX is focused on demonstrating the
reusability of the first stage.
"The boost stage is roughly 70 percent the cost of a launch, so if we're
able to reuse it and refly it with minimal work between flights and
customers are comfortable with that -- and it might take a few years for
customers to get comfortable with that -- then obviously there's as much as
possibly a 70 percent reduction from where things are today," Musk said.
"No one has ever soft landed a liquid rocket boost stage before, and I think
this bodes very well for achieving reusability," Musk said. "What SpaceX
has done so far is evolutionary, but not revolutionary. If we can recover
the stage intact and relaunch it, the potential is there for a truly
revolutionary impact in space transport costs."
After pneumatic pushers separated the first stage from the Falcon 9's upper
stage, which continued to accelerate into orbit, it fired its engines again
for two maneuvers to guide the rocket to a landing zone a few hundred miles
northeast of Cape Canaveral, roughly due east of the Georgia-South Carolina
border.
The booster guzzled kerosene and liquid oxygen propellants left over after
the first stage's primary job in the April 18 launch was finished.
But heavy seas in the Falcon 9 recovery zone destroyed the first stage, and
boats stationed nearby only retrieved fragments of the rocket. One piece
mostly recovered was the interstage, which connects the lower and upper
portions of the launcher, Musk said.
"In this case, we were just trying to get the rocket to go to zero velocity
at the water level. We weren't trying hard to get to a precise location,"
Musk said. "Nonetheless, we were within a few miles of our target. We an
certainly tighten it up with a little effort."
On SpaceX's next launch, tentatively scheduled for May 10, engineers will
program the first stage to splash down into the ocean closer to Cape
Canaveral. SpaceX says it is part of an increasingly ambitious series of
recovery tests Musk hopes will be capped by a precise touchdown of a Falcon
9 first stage on land by the end of 2014.
The April 18 soft landing was the most substantial achievement in SpaceX's
decade-long quest for a reusable rocket.
SpaceX initially used parachutes to slow the descent of rocket stages,
similar to the way the space shuttle's solid rocket boosters were recovered.
But that approach never worked, and SpaceX in 2011 announced plans to
switch a rocket-controlled descent concept, in which the Falcon 9's first
stage would return to Earth vertically with landing legs with the accuracy
of a helicopter.
SpaceX first tried the rocket-assisted landing during a launch from
Vandenberg Air Force Base, Calif., in September. The rocket spun out of
control during descent and disintegrated.
According to Musk, the company doubled the power of nitrogen roll control
thrusters and added additional cold gas nitrogen propellant to the system.
The company's next launch will try the experiment again, but Musk said
engineers will be armed with lessons learned from the last flight since the
experiments are part of a leaning process.
"This time, we're going to have much more capable boats," Musk said. "We
kind of got unlucky in that we essentially landed the stage in the middle of
a big storm. Hopefully, this time we will not have to do that. We'll also
be landing in the water much closer to land than the last time."
With up to eight more launches on SpaceX's books for 2014, Musk said SpaceX
has a good chance at returning a Falcon 9 first stage to a controlled
landing at Cape Canaveral by the end of the year.
"With each successive launch, we expect to get more and more precise with
the landing," Musk said. "If all goes well, I'm optimistic we'll be able to
land a stage back at Cape Canaveral by the end of the year. Assuming that
happens, we should be able to refly the main boost stage sometime next year."
Emily Shanklin, a SpaceX spokesperson, said some Falcon 9 missions will not
carry enough extra propellant for the complex first stage re-entry maneuvers
. Some amount of fuel, a quantity not disclosed by SpaceX, must be set aside
to guide the first stage back to Earth after its primary job is complete.
Heavier satellites need more of a boost from the Falcon 9 rocket, requiring
SpaceX to dedicate extra propellant to the mission.
Shanklin declined to say which upcoming launches do not carry enough
propellant margin to attempt recovery of the first stage, but SpaceX
officials previously said the Falcon 9 did not have sufficient leftover fuel
on two missions in December and January to try for landing of the rocket.
Those flights delivered the three-ton class SES 8 and Thaicom 6
communications satellites to geostationary transfer orbit, a type of high-
altitude orbit often used by telecom payloads destined for operating posts
22,300 miles over the equator.
On the Thaicom 6 launch in early January, SpaceX used the little remaining
propellant in the first stage tanks to conduct one of the two burns required
for a soft landing of the rocket in the ocean.
SpaceX has two launches to geostationary transfer orbit planned this summer
for the Hong Kong-based telecom operator AsiaSat.
In the long run, SpaceX's plans for reusability will be limited to missions
where the Falcon 9 rocket's fuel load can accomplish both the launch of the
spacecraft and the return of the first stage.
The limitations could be eased as SpaceX and customers become more
comfortable with the Falcon 9 rocket's lift capacity, industry officials
said.
Launch providers often reserve additional propellant margin on early
missions of a particular rocket, then gradually lift the restrictions once a
launch vehicle establishes a proven track record. An industry source said
SpaceX could also gain additional lift capability by adjusting the
conditions in which the rocket's liquid propellants are stored. |
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