Image: Nozomi
An artist's illustration shows the Japanese Mars probe known as Nozomi ("Hope"). The spacecraft went off-course after its launch five years ago.
By NBC News space analyst
NBC News

Despite discouraging reports about Japan’s Mars probe, one Japanese space official has assured his American colleagues that the Nozomi spacecraft still had a chance of completing its trouble-plagued mission.

Quoting officials from the Japanese Aerospace Exploration Agency, the Tokyo newspaper Yomiuri Shimbun had originally reported that the probe would be unable to enter its planned survey orbit when it reached Mars on Dec. 14. Unless it were steered aside, the probe would crash onto the planet and possibly contaminate it with earthly microbes, the newspaper said.

But on Friday, the California-based Planetary Society quoted Ichiro Nakatani, the Nozomi spacecraft manager, as saying that “the probability of hitting Mars is about 1 percent even without any orbit corrections.”

Other space navigation specialists told MSNBC.com privately that navigational uncertainties along the probe’s route would make it impossible to predict a precise impact on Mars. The only reliable results would be a probability calculation such as Nakatani’s, which they found plausible.

Nakatani also said that ground controllers planned to fire Nozomi’s steering engines on Dec. 9. The most critical rocket firing would then come six days later, as the probe passes about 560 miles (900 kilometers) above the planet and tries to enter orbit around it.

The Japanese space official — the first expert to speak publicly about the probe’s status in months — explained that they would continue work on “fixes” to problems in the power control circuits, but he did not discuss the issue of inoperative tank heaters that are needed to keep the liquid fuel from freezing. According to the Planetary Society, Nakatani said the power problems only affected “the various onboard instruments that collect and transmit data.”

Japan’s first Mars probe is approaching the target planet along with three other spacecraft. The European Space Agency’s first Mars probe will attempt to land the British-built Beagle 2 robot laboratory on the surface on Christmas Eve, and NASA is aiming to put two rovers on the surface in January.

Blastoff in 1998
Nozomi blasted off on July 4, 1998, and was supposed to reach Mars by the end of the following year. On board were a camera and several other instruments to study the Martian atmosphere from orbit.

Once in space, the craft remained in an elongated Earth orbit as it stored up energy through several swing-by maneuvers with the moon. On Dec. 20, 1998, in the midst a high-speed dash to within 600 miles (960 kilometers) of Earth, Nozomi fired its main engine to thrust itself towards Mars.

But something went wrong with the rocket firing, and the probe wound up so far off track that two corrective burns had to be made the next day. By the time the probe was back on its proper course, its remaining fuel wasn’t enough to brake itself into the desired survey orbit once it arrived at Mars.

So when Nozomi reached Mars in October 1999, it flew right on past. Back in Japan, space navigators had worked out a flight plan that could bring it back to Mars again, but at a gentler approach speed. But this would require four more years of coasting through space and making a pair of Earth fly-by maneuvers (in December 2002 and last June 19).

Crisis upon crisis
During this long detour, another crisis hit. On April 21, 2002, Nozomi was hit by a massive solar flare, and its power control system was knocked out. Far from the sun without heaters, the craft’s hydrazine fuel tanks froze. Later, when the probe swung closer to the sun, the tank thawed enough to use the fuel for a rocket firing to keep it on course. But mission managers in Japan recognized that the fuel would freeze again before Nozomi arrived at Mars this December.

To restore the power control system, engineers cycled the on-off switch several hundred times just after the last Earth fly-by, when the probe was nearest the sun and receiving the greatest electrical power. But as month followed month into the autumn, there was no happy announcement from Japanese space officials, and observers grew suspicious that the flaw had not been fixed.

Japanese space officials did not respond to e-mailed inquiries from MSNBC.com. However, they appear to have been prompted by the newspaper story to provide a small amount of new information.

James Oberg, space analyst for NBC News, spent 22 years at the Johnson Space Center as a Mission Control operator and an orbital designer.

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