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Planetary News: Asteroids and Comets (2005)Hayabusa: JAXA Delays Departure of Injured “Falcon” to 2007
By A.J.S. Rayl |
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 Hayabusa
Artist's depiction of Hayabusa at asteroid Itokawa Color: True color. Created: 2002. Credit: JAXA |
The Japan Aerospace Exploration Agency (JAXA) announced earlier today that it was delaying the return trip of its injured Hayabusa from the asteroid Itokawa until the spring of 2007. If the spacecraft can endure out there, 180 million miles away, and does make it out with the new exit strategy in 2007, it could arrive home in 2010.
Hayabusa had been scheduled to depart in a window that closes in mid-December, but team members were not able to get the spacecraft out of safe mode since anomalies occurred after its second touch-down landing on November 26. Now they are having trouble even communicating with their robotic falcon, and with the exit window closing, they had no other option but to reschedule the departure.
During its ascent away from Itokawa after the second touch-down last month, the redundant chemical rocket [thruster] system onboard Hayabusa sprung a leak in one subsystem and lost thrust in the other subsystem, causing the spacecraft to lose its attitude toward the Sun and communications with its mission control center in Sagamihara, Japan. The leak was fixed but a subsequent “out-gassing” event of fuel vapor from the spacecraft caused a “torque disturbance” last Thursday throwing the spacecraft out of its attitude and out of range for ground communications.
The team believes that the spacecraft’s current attitude does not meet either of the Sun or Earth geometry requirements for power or communication in the coming days. Additionally, Hayabusa’s major systems, including its attitude and communication network, have "significantly deteriorated.”
If Hayabusa’s injuries weren’t enough to handle, the salt in the falcon’s wounds come with new data that now indicate that the spacecraft may not have snatched a sample after all on that last trip down to the asteroid.
The project team has shifted now to a “rescue” phase, Project Manager Jun’ichiro told The Planetary Society via email today, and “the team is still actively working to bring Hayabusa back to “nominal operation in near future.”
Hayabusa is currently hovering in the vicinity of Itokawa in an unstable attitude. Until the team can re-establish communications, they cannot determine the cause(s) or extent of the spacecraft’s troubles, and that, in turn, makes it difficult to take effective measures to regain normal attitude. “It’s bad enough to postpone Hayabusa’s departure, but we will do our utmost to make the probe come back home,” Kawaguchi said during a press conference earlier today.
For the time being, they are not too concerned about losing Hayabusa even though they can’t communicate with it or pinpoint exactly where it is right now. “Presently, Hayabusa is in almost the same position as Itokawa. "Even [given] the uncertainty of the orbit, we can track the vehicle by orienting the Usuda [ground] antenna to Itokawa, and the risk of losing Hayabusa will be minimal,” Kawaguchi informed.
Hayabusa – which means "falcon" in Japanese -- is JAXA’s $170-million-dollar mission to the near Earth asteroid named after the "father" of Japan's rocket program, Hideo Itokawa. The world's first spacecraft to attempt to land on an asteroid, collect samples, and return them to Earth was developed at the Institute of Space and Astronautical Science (ISAS), a space science research division of JAXA. It launched from Japan’s Kagoshima Space Center on May 9, 2003, and arrived in September of this year. On November 20 and November 26, the spacecraft flew down to the asteroid and made touch-down landings, and, according to early data returns, Hayabusa succeeded in snatching a sample during its second flight.
 Hayabusa Spots Target Marker
Left hand side image shows the area named MUSES Sea taken at 4:58 a.m., Nov.20, and right hand side image was taken at 6:24 a.m., Nov.26. A white light spot inside a red circle is the Target Marker with the names of 880,000 people from 149 countries. Credit: JAXA / ISAS |
It was right after that flight that Hayabusa was struck with its life-threatening wounds, as the incidents on spacecraft’s redundant rocket system caused it to fall out of a stable attitude into safe mode after leaving Itokawa. While the team regained control and communications, the accomplishment would be short-lived and the efforts to bring their falcon out of safe mode or to fire-up its rockets did not go well.
In early December, the team initiated a new emergency strategy of replacing the rocket [thruster] propulsion system by programming a “new attitude control” using a method of jetting out xenon gas for the ion engine operation and conducting a test control for spin rate. “It worked,” according to the team’s status report issued this past weekend. “As a result, on December 5, the angle between the +Z axis and the Sun, and the Earth, recovered to 10 to 20 degrees, and the telemetry data reception and acquisition speed was restored to the maximum 256 bits per second through the mid-gain antenna,” the team reported.
Communication between the ground team and Hayabusa continued for another three days. Analyses of the data that was produced during the troubleshooting communications with Hayabusa’s Data Handling Unit (DHU) that ensued then indicated the spacecraft lost its attitude to the Sun because of the propulsion system problem and that resulted in extreme power shortage, consequently nearly draining the battery.
Then last Thursday, December 8, Hayabusa suffered the “disturbance” that the team believes was caused by the “out-gassing” of fuel vapor that came from the fuel leak suffered at the end of November. The control capability using the xenon gas thruster control strategy was not strong enough for the spacecraft to withstand the disturbance and it became unstable in its attitude, dropping into “coning” motions.
“We have had a big problem and are trying to fix it,” Kawaguchi said via email last weekend. “The situation is not optimistic.” One thing seemed certain at that point: Hayabusa was not going to ready in time to meet the mid-December deadline for its planned trajectory home.
Hayabusa has been a real roller-coaster ride and the team members have endured it all – serious white-knuckle moments, moments of sheer inspiration and imagination, uncertainty, blissful jubilation, deep disappointment, and now resignation. With this latest announcement, however, they are emerging with an energized resolve to do everything possible to see the mission through, find the value in the lessons learned, and get on with the next sample return.
South Pole of Itokawa
Hayabusa captured this image of the south pole of asteroid Itokawa in late October 2005. The smooth, partially shadowed area in the center is Muses Sea. Credit: JAXA |
At the moment though they have their injured robotic falcon to tend. The first thing they need to do is re-establish communications with the spacecraft. The good news is that “[a]nalysis predicting the attitude property relating to both the Sun and Earth shows that there will be high possibility for the resumption of the communication from the ground for several months or more ahead,” the latest status report issued today stated.
“We need to send a command from the Earth to [Hayabusa to] switch to operation through low-gain antenna,” Kawaguchi said at the press conference. “However, the wave-receiving range of the low-gain antenna is approximately 60 degrees. With [the present] very unstable axis coning movement, it is impossible [for Hayabusa] to keep receiving commands from the Earth even using low-gain antenna. The coning movement takes about one month to be stabilized enough to regain communication. Now we are waiting for that.”
In this state, Hayabusa’s communication computer enters stand-by mode by shutting down the power, Kawaguchi explained. “This probe is designed to restart from [that] mode with the commands from the Earth. Thus, unless the equipment [is] broken from lower temperature, the probe should be recoverable with commands from the Earth.”
“Since the spacecraft is designed to allow spin-stabilization around its high gain antenna (HGA) axis, there will be a good chance of recovering the communication with the ground during the next half-year to one year,” after convergence of the coning motion, Kawaguchi elaborated in his email interview with The Planetary Society. He put the chance of resumption at about 60% by December 2006 to 70% by spring 2007.
As for the damaged rocket system, “the wiring to the drive shutting valve could be broken by the fuel leak,” Kawaguchi speculated at the press conference. “On the other hand, another wiring for a thermometer running in the same place is still working.”
Of course, the team would like to recover the rocket [thruster] system. “After recovery of communication, we'd like to start recovery for the thruster system,” Kawaguchi said. “But there is a risk of total loss of the vehicle during the recovery process. We must get things going carefully considering the risk,” he added.
Currently, the recovery of the thruster system is not a requirement for the return trip to the Earth, nor is a full battery. “We have a plan [to] return by controlling the attitude with xenon jets after we get the leaked gas out of the probe by heating the vehicle,” Kawaguchi told reporters. “It is still in the planning phase, and we are studying its viability.”
If the team can re-ignite the ion engines by the spring of 2007, “the vehicle will be able to return to Earth on June 2010,” he said. Fuel is not a problem. The amount of xenon gas left is “adequate.”
That said, there is still the reality that some instruments will malfunction when warmed up from the freezing cold temperatures to which they are now being exposed, Kawaguchi noted. Moreover, the spacecraft will probably have to undergo a long-term “baking” cycle before it starts the return cruise operation using the ion engines.
“The probability of equipment failures will increase. We have to restart [the instruments] from the almost freezing state,” he acknowledged. The figures I put before does not mean that it can return to the Earth with a ‘70% probability.’ It means that ‘for the 70% probability of communication recovery, we will continue the operation,’" he clarified.
Hayabusa sampling Itokawa
Computer simulation of Hayabusa sampling the surface of Itokawa Credit: Kazuya Yoshida, Space Robotics Laboratory, Tohoku University |
If Hayabusa’s injuries weren’t enough to handle, it now turns out that the spacecraft may not have gotten a sample after all. Apparently, the pyrotechnics control device data show no evidence of the projectile firing which is what would initiate the sample collection process, and they were not able to confirm data showing a successful discharge," the team's status report revealed.
The sample collection device is a cone or stubby megaphone-shaped device positioned on the exterior of the spacecraft. By design, as the spacecraft touches down and the front end of the cone touches the surface, a tantulum pellet is fired into the surface at 300 meters per second and the ejecta from that cratering effect is captured by the device and is then brought into the sample chamber.
Confounding the sample issue however is data that indicate “an incorrectly positioned disarming command that may have activated prior to the touching down,” as the team’s report revealed last weekend. The team members also found inconsistent phenomena in the data that may support the pyrotechnics initiation, such as temperature increase. However, the contradicting data could have been caused by the impact of Hayabusa’s system power reset. The team is currently analyzing the details including the confirmation of the sequence before and after the landing on November 26.
Although there have been contradictions in the data, Kawaguchi rescinded the claim that Hayabusa had snatched a sample, tell The Planetary Society that “[t]he chance of having a successful [firing] of the [device’s] projectile was found to be not high enough.”
No team knows the agony and confusion of contradicting data better than The Planetary Society’s Cosmos 1 team, which also had to deal with conflicting data returns during last summer’s failed launch of its solar sail. Indeed, everyone involved in space exploration knows the bite reality can inflict.
Kawaguchi and his team have reflected on the losses. At the press conference, Kawaguchi admitted the events of the last few weeks have been “very depressing.” He said he expected the achievement of the mission “in good condition” and the 3-year extension “will increase risks and make the operation harder.”
That said, Kawaguchi and the others are choosing to look beyond the losses and focus more on the experience gained with the accomplishments achieved. “We attempted the first sample return in this world,” Kawaguchi told reporters at the press conference. “Space development in the past was nervously carrying out projects with a solid chance of success under close watch [of] the mass media. But we think it is also necessary to take risks and go on forward for the space development to progress. If you build a high tower and climb it you will see a new horizon. Hayabusa has inspired the morale toward building such tower on our own, and I think Hayabusa was meaningful on that account. If there is Hayabusa 2, it would be something that only Japan can do. We look forward to it by all means,” he added.
“The most important technical achievement of the mission is that Japan is now at the position to [propose] another mission of sample return using advanced technology,” Kawaguchi expounded later with The Planetary Society. “No other country is so sure to make it [as] Japan we think. Accessing and making a touch down, plus landing [on] an irregular shaped body and pinpointing the landing site requires [very] sophisticated technology, which we think now we have obtained.”
Still, as with everything in the world, Hayabusa’s delay will cost money. “If the government and citizens think it's not worth their money, we [will] have to abandon the operation,” Kawaguchi told reporters. “But the JAXA committee yesterday did not say we should give up.”
Give up? It seems out of the question – for this spacecraft and for this team. Hayabusa has confronted doom on so many occasions and somehow survived, it seems almost as if this spacecraft really wants to make it home, and given the drive and creativity displayed by the team and its stream of successful work-arounds, no mission could ever be more deserving of getting back.
Hopes turn now to re-establishing communications with Hayabusa, then getting it back online, and returning in the window in the spring of 2007. Even if Hayabusa is recovered, though, the robotic falcon is “full of wounds and the return trip will be very hard,” Kawaguchi admitted. “Yet, if there is any chance, we have a will to give it a try.”
"Hayabusa's mission controllers are once again showing enormous ingenuity and resilience in working this most complex mission,” said Planetary Society Executive Director Louis D. Friedman. “They have provided us with an extraordinary rendezvous and adventure at a near-Earth asteroid; and obviously that adventure will continue."
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