India Shoots for the Moon with New Probe
An Indian-built Polar Satellite Launch Vehicle stands poised to launch the Chandrayaan-1 lunar probe for the Indian Space Research Organization.
Credit: ISRO

BANGALORE, India - Five years after being formally approved and following a series of late delays, India?s first-ever planetary mission is on track to launch the morning of Oct. 22 Local Time, with arrival in lunar orbit scheduled to occur 17 days later.

The Chandrayaan-1 moon mission, featuring Indian, European and U.S. instruments, had been scheduled to launch in April but suffered setbacks including late-arriving payloads and integration issues. But officials with the Indian Space Research Organisation (ISRO), who unveiled plans for the orbiter in 2000 with a target launch date of 2008, are confident those issues are behind them.

?The spacecraft reached the launch site Sept. 30 after completing thermal vacuum, vibration and acoustic testing in Bangalore,? ISRO spokesman S. Satish said Oct. 15. Integration with the launcher was completed Oct. 14 and at press time the rocket was slated to be moved to the launch pad Oct. 18, he said.

?The Chandrayaan-1 spacecraft after successfully completing [thermal vacuum], vibration and acoustic tests, has reached the launch site,? ISRO spokesman S. Satish told SPACE.com sister publication Space News Oct. 8. ?All the operations are going on satisfactorily.?

If all goes well, Chandrayaan - which means moon vehicle in Hindi - will join two other spacecraft that reached lunar orbit roughly one year ago: Japan?s large Kaguya, or Selene, mission, which launched in September 2007, and China?s Chang?e 1, which launched in October 2007. NASA?s Lunar Reconnaissance Orbiter is slated to launch in February, meaning that four spacecraft, each built by a different country, could be in lunar orbit simultaneously.

Built at a cost to ISRO of some $87 million, the fully fueled Chandrayaan-1 will weigh 2,874 pounds (1,304 kg) when it lifts off from the Satish Dhawan Space Centre on Sriharikota Island off India?s east coast. After a countdown lasting 52 hours, the probe will lift off tomorrow at 6:20 a.m. Local Time (Tuesday evening Oct. 21 EDT) aboard a modified version of ISRO?s Polar Satellite Launch Vehicle, or PSLV.

The probe will be India?s first to leave Earth orbit, something that will be accomplished not by a direct transfer typical of lunar missions but rather through a series of Earth orbit-raising maneuvers. In direct transfer missions, a spacecraft is placed into a parking orbit around Earth before on board propulsion systems give it a substantial velocity boost to place it into a lunar transfer orbit with an apogee of 238,550 miles (384,400 km) - roughly the moon?s average distance from the Earth.

?Direct transfer would have required an additional stage to PSLV,? said V. Adimurthy, a scientist at ISRO?s Vikram Space Science Centre, where the rocket was built.

Satish said the PSLV will inject Chandrayaan-1 into an elliptical orbit around the Earth with a perigee of 155 miles (250 km) and an apogee of 14,291 miles (23,000 km). The spacecraft will reach lunar orbit by firing its liquid-fueled apogee motor several times. The first firing will put the spacecraft in a 186- by 22,990-mile (300- by 37,000-km) Earth orbit. Successive firings will raise the apogee to 45,360 miles (73,000 km) and then to the lunar transfer trajectory orbit of 186 by 240,470 miles (300 by 387,000 km).

?It takes about 11 days after launch to establish the lunar transfer trajectory,? Satish said.

Further firings will insert Chandrayaan-1 into a 310- by 3,106-mile (500- by 5,000-km) orbit around the moon. The orbit will then will be lowered to 62 by 3,106 miles (100 by 5,000 km) and finally to the desired 62-mile (100-km) circular orbit, which will take the spacecraft over the Moon?s poles once every 118 minutes.

?If the launch takes place on Oct. 22, the spacecraft is expected to enter the 100-kilometer lunar orbit on Nov. 8,? Satish said.

The Chandrayaan-1 spacecraft itself is relatively small, measuring about 5 feet (1.5 meters) on a side with a dry mass of only 1,153 pounds (523 kg). It carries 11 scientific payloads, including six provided by other nations: two from the United States, and one each from Britain, Sweden, Germany and Bulgaria.

?The real challenge was in accommodating different payloads in specific locations and orientations in a small spacecraft,? Mylswamy Annadurai, Chandrayaan-1 project director, told Space News.

The Indian-built payloads are: the Terrain Mapping Camera; Lunar Laser Ranging Instrument; Hyperspectral Imager; High Energy X-Ray Spectrometer; and the Moon Impact Probe.

The 64-pound (29-kg) impact probe will be released from the orbiter over a selected site once the spacecraft enters its final orbit, Satish said. During its 18-minute descent, the impact probe - with India?s national flag painted on its shell - will take images of the lunar surface. Its impact will kick up a cloud of dust that will be observed and analyzed by the instruments on the orbiter.

Among the international payloads, India collaborated on two: the X-ray Fluorescence Spectrometer with Britain?s Rutherford Appleton Laboratory; and the Sub-keV Atom Reflecting Analyzer with the Swedish Institute of Space Physics. The other international payloads are: a Mini Synthetic Aperture Radar built by the Johns Hopkins University?s Applied Physics Laboratory of Laurel, Md.; Moon Mineralogical Mapper supplied by NASA?s Jet Propulsion Laboratory and Brown University; Near Infrared Spectrometer from Germany?s Max Planck Institute; and Radiation Dose Monitor supplied by the Bulgarian Academy of Sciences.

In addition to mapping lunar surface features and topography, the instrument suite will study the Moon?s elemental and mineralogical composition - in part by measuring reflectance from solar flares that are expected to rise in frequency and intensity over the next few years. ?Water-ice, if present, can be detected by several of these instruments,? ISRO said on its Web site.

In response to questions, Narendra Bhandari, who until recently headed ISRO?s planetary exploration division, listed four main Chandrayaan-1 objectives:

  • Study how volatile elements and compounds - possibly including water - get transported to the poles from the hot lunar surface during the day.
  • Produce a digital elevation map with 5-meter resolution both vertically and horizontally. This will enable scientists to select potential sites for a future base.
  • Produce chemical and mineral maps of the moon. The mineral spectrometer will measure signals up to 3 microns in the near-infra red portion of the electromagnetic spectrum - data that has not previously been collected - giving scientists new information about water and possible organic compounds at the poles.
  • Map subsurface features on the Moon using a synthetic aperture radar.

?Simultaneous photo-geological, mineralogical, and chemical mapping will enable us to identify different geological units, which will test the early evolutionary history of the Moon,? Bhandari said.

He added that the simultaneous presence of four Moon probes will enable coordinated study. For example, he said, one mission may benefit from data collected by another; or one probe could observe as another crashes into the surface after completing its mission.

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