by Gurbir Singh
Chandrayaan-1 X-ray Spectrometer
C1XS, at 5.2 kg, was a sophisticated version of an instrument that ISRO had initially designed in-house. Funded by ESA, C1XS was designed and developed at the Rutherford Appleton Laboratory in the UK. Apart from ISRO, additional support came from Brunel University in the UK and the French National Centre for Scientific Research in Toulouse. C1XS was similar to HEX but sensitive to lower energy X-rays. It used a new, enhanced version of the CCD, a swept charge device that offered a higher resolution and could operate at room temperature. Data from C1XS was designed to help quantify the relative abundance and distribution of elements, such as magnesium, aluminium, silicon, calcium, iron and titanium. With this data, an estimate of the chemical composition of the Moon could be mapped to a resolution of around 25 km. Sodium was detected on the Moon for the first time by C1XS.[848]
Every 11 years, the Sun goes through a cycle of maximum and minimum solar activity, including sunspots, solar flares and coronal mass ejections. Though random, the likelihood of solar flares increases and decreases within a solar cycle.[849] Chandrayaan-1was launched in 2008 when the cycle was at a minimum. However, two months after it arrived in lunar orbit, a weak solar flare initiated a solar wind, and on 12 December 2008, C1XS picked up X-rays generated on the surface of the Moon by this solar wind. It was a weak signal, but Chandrayaan-1 was there to see it.[850]
Sub keV Atom Reflecting Analyser
SARA was also a product of international collaboration. It was jointly designed and developed for the ESA by the Institute of Space Physics, Kiruna, Sweden; ISRO’s VSSC; Japanese Aerospace Exploration Agency (JAXA) in Tokyo and the University of Bern, Switzerland. At 3.5 kg, SARA consisted of three distinct sensors that between them detected and measured low energy neutral atoms generated by particles emanating from the Sun impacting the top-most layer of the lunar surface. In the absence of a magnetic field and an atmosphere, solar radiation can reach and interact with the material of the lunar surface completely unhindered. SARA could measure the protons reaching the Moon from the Sun and those that were reflected. It determined that 20% of the protons absorbed an electron from the lunar surface to create a hydrogen atom. In places, where oxygen atoms were present, they combined to form water. In October 2009, SARA repeated an observation made by CHACE a month earlier that water was present on the Moon.[851]
Near-Infrared Spectrometer (SIR-2)
SIR-2 was an instrument based on SIR-1 carried by the European SMART-1 spacecraft to the Moon in 2003. It was an enhanced version of SIR-1 and jointly developed and funded by the ESA; Max Planck Institute for Solar System Research in Göttingen, Germany; the University of Bergen (UiB), Norway; and the Polish Academy of Science, Warsaw. SIR-2 was one of the smallest and lightest (2.3 kg) of the Chandrayaan-1 payload.
SIR-2 was designed to collect and analyse sunlight reflected by the Moon’s surface. The collected light was directed through an optical fibre to a spectroscope to understand geological and mineralogical details, space weathering and the vertical distribution of crustal material on the lunar surface. By combining SIR-2 data with that from HySI, it was possible to identify and locate minerals, such as olivine and pyroxene, for potential future exploitation of lunar resources.
Miniature Synthetic Aperture Radar
Mini-SAR was also a product of international collaboration. Interestingly, it had a non-civilian contributor. The instrument was led by the US’s Naval Air Warfare Center with support from NASA and Johns Hopkins University in the US. Mini-SAR was built in the UK by three companies, Raytheon, BAE Systems and Surrey Satellite Technology. At 8.77 kg, Mini-SAR targeted one of the mission’s key objectives of discovering the presence of water on the Moon. Measurements in 1994 by the NASA Clementine mission had raised the possibility of water within the Shackleton crater at the southern lunar pole. Mini-SAR was to help provide evidence to confirm that observation.
By transmitting and subsequently receiving reflected radio waves, Mini-SAR was to map both lunar poles for water ice by measuring properties of reflectance, roughness and polarisation. In the absence of sunlight in the craters at the poles, deposits of water ice could survive for millions of years. During each sweep over the poles, Mini-SAR collected data in 8-km wide swaths with a resolution of 150 m. It was switched on for ten-minute intervals every orbit as it passed over the poles, above 80° latitudes. It was switched off at other times.
The NASA spacecraft Lunar Reconnaissance Orbiter (LRO) in lunar orbit at the time also carried a Mini-SAR instrument. A joint experiment was scheduled for 20 August 2009 to help detect surface (frozen) water. LRO Mini-SAR was configured to receive radio signals transmitted by Chandrayaan-1 Mini-SAR.[852] It was a novel and technically challenging experiment as both spacecraft were to target the crater Erlanger, only 10 km in diameter while moving at 1.6 km/s. The experiment was conducted as planned with both spacecraft looking at crater Erlanger for at least 35 seconds, but subsequent analysis indicated that Chandrayaan-1 had lost the capability to point with the precision required due to hardware failure. A further attempt was being planned a week later when further hardware deterioration ended the Chandrayaan-1 mission.
Radiation Dose Monitor
RADOM was developed by the Solar Terrestrial Influences Laboratory of the Bulgarian Academy of Sciences in Sofia, Bulgaria. At about 0.1 kg, it was the smallest and lightest of all the eleven science instruments onboard Chandrayaan-1. RADOM was a miniature dosimeter-spectrometer designed to measure energetic radiation present in the environment through which Chandrayaan-1 travelled and operated. It was the first instrument to be switched on, just two hours after launch, and it collected data while in Earth orbit, en-route to the Moon, during the initial series of lunar orbits and the designated 100-km and subsequent 200-km lunar orbits.
RADOM collected data throughout the Chandrayaan-1mission, from 22 October 2008 to 31 August 2009. Measurements of radiation intensity around the Earth were in line with the measurements of similar experiments on-board the ISS. The radiation that RADOM detected came from various sources, cosmic radiation from the cosmos reflected by the Earth or Moon, the steady stream of radiation from the Sun, as well as instances of increased radiation from high solar activity, such as solar flares. On 13 March 2009, RADOM recorded increased radiation resulting from a small magnetic storm on the Sun.[853]
Science from Chandrayaan-1
The primary mission objectives of Chandrayaan-1were to create a high-resolution three-dimensional atlas of both the near and far side of the Moon, including the Polar Regions, and to conduct a chemical and mineralogical mapping of the entire lunar surface. Before the termination of the mission, the M3 instruments had covered 90% of the lunar surface, but the TMC had managed only around 50%, though most of that included the important Polar Regions not covered in detail before.[854] The relative concentrations and locations of aluminium, magnesium and silicon, along with iron-bearing minerals, such as pyroxene, were integrated into a 3D map by combining data from TMC, LLRI and C1XS.
Chandrayaan-1’s data revised three key assumptions about the Moon:
The Moon was not dry. Data, primarily from M3 but also MIP and Mini-SAR, recorded evidence of water and hydroxyl molecules with quantities increasing towards the poles. On 14 November at 20:31 IST, MIP impacted in the lunar south pole. During its journey from the 100-km orbit to the surface, MIP collected images and data. The data from the CHACE instrument independently verified M3’s detection of water in the region of lunar South Pole through which it descended.
Solar wind protons were not absorbed by the Moon. The SARA instrument measured that around 20% of the solar wind protons arriving on the Moon were reflected back into space as neutral energetic hydrogen atoms. These protons were integral to the process of making water on the Moon.
The Moon was geologically active. Hydrated magma indicated episodic explosive volcanic events. M3 data revealed spectra of magma flows around Lowell and Bullialdus craters. The TMC and HySI instruments identified u
ncollapsed lava tubes, which could be used in the future for human habitation.
The planned two-year mission was declared prematurely over at 01:30 IST on 29 August 2009 after 312 days of operation when Chandrayaan-1 finally lost its ability to transmit. The early termination of the mission was caused by the spacecraft’s inability to regulate its internal temperature. On arrival in lunar orbit, Chandrayaan-1 found itself in a temperature regime of +100°C on the day side and -100°C on the night side of the Moon. Designed to operate at 40°C or lower, Chandrayaan-1 was frequently in excess of 50°C, and at one stage, 80°C.
The excessive radiant heat from the lunar surface was higher than what the ISRO engineers had anticipated. A series of innovative workarounds were employed that included re-orientating the spacecraft, operating some of the instruments only on the night side of the orbit or at times switching them off altogether to reduce internally generated heat. To move to a lower temperature environment, on 21 May 2009, ISRO decided to increase the orbit from a 100-km to a 200-km altitude.[855] This decision reduced the spatial resolution of the data collected by some of the instruments. In addition to resolving thermal problems, the engineers also came up with innovative solutions using the onboard gyroscopes to maintain spacecraft attitude control when initially one, and then both, star sensors failed. Intervention and monitoring on a 24/7 basis by ISRO engineers was required to allow all onboard instruments to operate and continue to collect data.
The loss of the mission was eventually identified to be a hardware failure of five individual DC/DC converter components used to convert and send telemetry data from the onboard systems and instruments to Earth. The manufacturer of the component “expected operating lives that exceed ten years” on unmanned spacecraft in a space environment.[856] One report suggested that ISRO had “underestimated temperatures around the Moon, so the probe had been overheating for months.”[857] Despite the premature end, a probe committee reviewing the mission formally concluded in its report that the Chandrayaan-1mission was “quite successful”. During the 3,400 orbits, Chandrayaan-1 collected over 7,000 images, including images of the Earth from an Earth orbit of 7,000 km and a full Earth image from lunar orbit (400,000 km) using TMC. TMC and HySI had also covered 50% of the lunar surface and M3 90%. ISRO concluded that Chandrayaan-1 had completed 95% of its mission objectives.[858] The mission’s success was also recognised internationally with high profile awards from the International Lunar Exploration Working Group, the American Institute of Aeronautics and the Astronautics and National Space Society. Apart from meeting its chief scientific objectives, Chandrayaan-1 will be remembered for three other key achievements. The strong international collaborative spirit it engendered, the wealth of experience many young ISRO engineers gained in managing and operating a spacecraft in lunar orbit and the recognition that ISRO as an organisation had the capability to successfully undertake complex space science missions beyond Earth orbit.
Figure 15‑5 Polar Region of the Lunar Surface Captured by Chandrayaan-1.
15 November 2008. Credit ISRO
ISRO engineers calculated that the Moon’s tenuous atmosphere would decay Chandrayaan-1’s orbit and it, like the MIP, would crash land on the Moon by around 2012. But it did not. Surprisingly, Chandrayaan-1 no longer operational was discovered using Earth based radar, still orbiting the Moon in 2017.[859]
Chandrayaan-2: Journey to the Lunar Surface
On 12 November 2007, a year before Chandrayaan-1 arrived at the Moon, ISRO signed an agreement with Russia for Chandrayaan-2, a joint mission to the Moon in 2011 or 2012.[860] It would have three elements: an orbiter, lander and rover. Russia had agreed to contribute the lander and rover. India would supply the PSLV launch vehicle and the orbiter. Subsequently, the launch date slipped to 2013, and India agreed to provide the rover, as well as the orbiter. PSLV was replaced by GSLV. Russia was expected to provide the lander which would deliver the rover to the lunar surface. However, in November 2011, a Russian rocket Zenit-2SB carrying two spacecraft to Mars, one Russian and the other Chinese, failed to leave Earth orbit, with the loss of both spacecraft. The resulting agency-wide review forced Roscosmos to first delay and then withdraw from the planned joint mission with India to the Moon.[861] Initially, ISRO sought to find alternative partners in NASA or ESA but then decided to go solo making it a wholly Indian mission.
The provisional mission design consists of a lander, at 1.25 tonnes with four instruments and a 20-kg rover with two instruments. Although small, the rover will have about twice the mass of NASA’s rover Sojourner, which operated on the surface of Mars for about three months in 1997. The power and range of the transmitters on the rover and lander are not sufficiently strong to communicate directly with the Earth, so the orbiter is used as a relay. The orbiter is configured to carry 5 instruments. Each of the three components, orbiter, lander and rover, has a distinct collection of science packages designed to make the best use of its local environment. Unlike Chandrayaan-1, Chandrayaan-2 does not involve international collaboration.
Chandrayaan-2’s journey from the Earth to the Moon will be similar to that of Chandrayaan-1. Following launch, Chandrayaan-2 will first orbit the Earth in increasingly larger orbits through eight Earth bound orbits extending the orbit each time. The ninth burn (Trans Lunar Injection) will extend its orbit to intersect with that of the Moon’s orbit. Once in lunar orbit, a series of four lunar bound manoeuvres will result in the desired 100 x 100 km lunar orbit. It is from here that the lander containing the rover will separate from the orbiter on its journey for a soft landing on the surface of the Moon.
Orbiter
Origin
Purpose
TMC-2
SAC, Ahmedabad
Generate a map of the lunar geology and mineralogy. Terrain Mapping Camera-2
Imaging Infra-Red Spectrometer
SAC, Ahmedabad
Locate, identify and study the minerals and water molecules on the lunar surface from orbit.
Synthetic Aperture Radar
SAC, Ahmedabad
Locate and identify the chemical constituents in the first few metres under the lunar surface. This will include water and water ice including in areas that are not in permanent shadow.
CHACE-2
Space Physics Laboratory, Thiruvananthapuram
Study the lunar exosphere (100 km). Chandra’s Altitudinal Composition Explorer (CHACE-2, a neutral mass spectrometer)
X-Ray monitor
Spectrometer from ISAC and X-ray Monitor from PRL
Large-scale mapping of specific elements across the lunar surface. Chandrayaan-2 Large Area Soft X-ray Spectrometer and Solar X-ray Monitor
Lander
Origin
Purpose
Seismometer
LEOS
Monitor moonquakes. Laboratory for Electro Optics Systems, Bangalore
Thermal Probe
Space Physics Laboratory, Thiruvananthapuram
Measure temperature at the landing site for the duration of the mission.
Langmuir Probe
VSSC
Measure electrons released by the interaction between high energy solar radiation and lunar surface particles.
Rover
Origin
Purpose
Laser Induced Breakdown Spectroscopy
LEOS
Qualitative and quantitative elemental analysis of lunar surface material.
Alpha Particle Induced X-ray Spectroscope
PRL, Ahmedabad
Identify the elemental composition of the lunar surface material. The spectroscope carries a small source of alpha particles to which the source material is exposed. A measurement of the resulting X-rays helps to identify the source.
Table 15‑3 Overview of Chandrayaan-2 Science Payload. Credit ISRO
The Chandrayaan-2 orbiter is designed for a mission of one year, and the lander/rover are expected to operate for about two weeks. The temperature on the lunar surface ranges from a maximum of about 100�
�C at midday to a minimum of -180°C at night. A day on the Moon lasts 28 earth days. Chandrayaan-2 is not designed to survive the extreme range of temperatures it will experience in one lunar day. There was a proposal to provide Chandrayaan-2 with a nuclear power source to sustain it through the 14 days of a lunar night when the solar panels receive no sunlight, but ISRO is no longer pursuing that option.[862]
Testing on several elements of the Chandrayaan-2 mission, including soft landing on the surface, the lunar rover exiting the lander and the rover traversing the lunar surface has been completed. These tests have been conducted in the open air within the perimeter of Bangalore’s HAL airport and ISRO Satellite Integration and Test Establishment, which is a part of ISAC, also in Bangalore. Chandrayaan-1 with a mass of 1.3 tonnes was launched using a PSLV-XL. Chandrayaan-2’s mass is expected to be twice that so will be launched using a GSLV Mk2. By March 2015, ISRO had used a third of the allocated Rs. 603 crore ($90 million) for the mission,[863] and in February 2016, the ISRO chairman asserted “ISRO is ready for Chandrayaan-2” for launch in 2018[864] or early 2018.[865]