by Gurbir Singh
SXT was activated on 26 October 2015 and calibrated with an onboard source. On the same day, it looked at its first astronomical object, an active galaxy well known as a strong X-ray source. SXT also observed Tycho, a supernova remnant that was recorded as a naked eye observation from the 14th century before the telescope was invented. Despite the sensitivity of the CCD, SXT requires several hours (at least half a day, accumulated over several orbits) to complete a typical observation.
Ultraviolet Imaging Telescope
The UVIT is one instrument made up of two almost identical telescopes that can operate in three parts of the spectrum. One telescope looks at the visible spectrum (visible 320–550 nm) and Near Ultraviolet (NUV 200–300 nm) using a beam splitter. The second telescope is designed to observe in the range known as the Far Ultraviolet (FUV 130–180 nm). In both UV ranges, a built-in grating is used to disperse the incoming light to conduct a spectroscopic analysis. Both telescopes have an aperture of 375 mm with a focal length of 4750 mm. The imaging sensors used are semiconductor devices that detect individual photons originating from either visible, NUV or FUV.[909] Individual photons are amplified, counted and integrated over the period of the exposure. UVIT is a collaboration between ISRO, TIFR, Inter University Centre for Astronomy and Astrophysics, Indian Institute of Astrophysics and the Canadian Space Agency. The UV photon counting detector was provided by Canada.[910] The lead institution for UVIT is the Indian Institute of Astrophysics.
UVIT’s first target was NGC 18 (object number 18 listed in the New General Catalogue used by astronomers to identify deep sky astronomical objects), an open cluster of about 1,500 stars in the constellation of Cepheus. It was the first object to be observed by UVIT on 30 November 2015, 62 days after launch. Although not an object used for calibration as the Crab Nebula, NGC 18 has been observed from space in the past, so an assessment of UVIT could be made by comparing observations. Since astronomical objects are fainter in UV than visible, the UV photons are first amplified before they can contribute to the detected signal. To avoid interference from background photons and in the interest of sensor safety, UVIT is operated only at night. It has a Moon and Sun avoidance angle of 45° and 12° from the limb of the Earth and can typically make an observation of an optical or UV source of a maximum of 30 minutes at a time.
Cadmium Zinc Telluride Imager
CZTI is not a telescope in the traditional sense but a single solid-state detector divided into four identical and independent quadrants with 16 individual CZTI modules. CZT is an alloy of cadmium, zinc and tellurium that can run as a radiation detector at room temperature. The 64 modules of 256 pixels each produce an image with a resolution 16,384 pixels. All the CZTI modules have built-in collimators providing a field of view of 4.6° by 4.6°. A large radiator plate is used to dissipate the heat produced by the instrument during operation to maintain the nominal operating temperature of 0 to 15°C.
CZTI is located on the same platform as the telescopes so can observe the same object at the same time as the other instruments. It operates in the 10–100 keV range, also known as hard X-ray range. These new energies extend Astrosat’s capacity to study X-ray binaries stars, active galactic nuclei and gamma-ray bursts. It is also expected to reveal polarisation in the hard X-ray part of the spectrum. The CZTI only needs to avoid the Sun when observing, as neither the Moon nor the Earth emits hard X-rays. Once Astrosat arrived in orbit, the CZTI was the first primary scientific payload to be activated on 15 October 2015. The Crab Nebula was used to calibrate the timing capability of the instrument.
Operational Status
Unlike Chandrayaan-1 and MOM, Astrosat did not have far to travel. Consequently, the mass, electrical power and data transmission capacities of its instruments are an order of magnitude larger. The spacecraft and all the instruments are operating in orbit as planned. Two solar panels provide 1,600 watts via two 36 Ah lithium-ion batteries. It has two 120 GB solid state storage devices enough to store data collected in four orbits. Astrosat can generate up to 420 GB of data daily. Typically, Astrosat has a line of sight of ISTRAC in Bangalore for about 10 minutes during 10 or 11 of its 14 daily orbits. Using two X-band carriers, Astrosat can transmit data to Earth at 105 Mb per second. The first six months after launch were used for calibration and performance evaluation, and then, the fully operational mode was activated. Astrosat is reserved for use by Indian institutions only for the second six-month interval. After the first year in orbit, Canada will have 5% and the UK 3% observing time throughout the mission lifetime. In the second year, 10% of the time is set aside for international proposals from nations that have not contributed to Astrosat, which will increase to 20% in the third year.[911]
Scientific experiments make a tangible contribution to a national space programme. They help develop key technical infrastructure and allow scientists and engineers to acquire operational experience through developing and operating leading edge experiments. They also boost morale and enhances job satisfaction while gaining scientific credibility for those involved. Further, the sense of discovery emanating from pure research attracts curious and talented individuals for careers in space. An invigorated and growing space programme can deliver long-term national economic and societal development, national prestige at home and international recognition beyond.
Future Science and Interplanetary Missions
At the present ISRO has ruled out HSF but continues to focus on primarily on development in launch vehicles including reusable technology, infrastructure including a second VAB, potentially another launch pad or even another launch site, return to the Moon, Mars and other goals in the Solar system. It is doing this in the backdrop of the maintaining and enhancing its Earth observation, navigation, weather and communication satellite constellations. Missions in the pipeline include:
Return to Mars
As MOM approached its second year in orbit, ISRO issued a call for proposals to the scientific community and academics for India’s second mission to Mars: MOM-2. It is seeking proposals for scientific objectives to target and the instruments that can deliver them. ISRO’s initial design of MOM-2, also an orbiter, includes a payload of 100 kg (MOM was just 15 kg) designated for the much lower orbit of 5,000 km, instead of MOM’s 77,000 km. One report suggests that the orbit will be 200 by 2,000 km.[912] The date of launch is not established but it is unlikely to be before the 2020 launch window.[913]
Aditya-L1
India’s first science mission in Earth orbit was Astrosat launched in 2015, the second called Aditya-L1 is due for launch in 2019/20 to examine the Sun. Aditya, from the Sanskrit name for the Sun God, was originally designed to observe the Sun’s outer atmosphere, known as the Corona, from an SSPO. The mission was initially proposed in 2008 when Chandrayaan-1 was in final stages of preparation. The initial designs published in 2011, Aditya-1 consisted of a single instrument (a Visible Emission Line Chronograph) on a 400kg spacecraft in an 800 km SSPO.
A polar orbit is not the most convenient for solar observations. The Earth itself is “in the way” and obscures the Sun for half of every orbit. The stability of the viewing platform is also harder to maintain from a spacecraft moving at about 7 km second. The Aditya-1 mission has since been revised to include a larger science payload and a destined for the Lagrangian L1 orbit instead of SSPO and renamed as Aditya-L1. The Earth has 5 gravitationally “neutral” points in space known as Lagrangian points (L1 thru to L5). Here the force of gravity between the Sun and the Earth is equal. L1 is a special point on a line drawn from the centre of the Earth to the Centre of the Sun. The L1 point is 1.5 million km from the Earth towards the Sun. Once the decision was taken to use L1 for Aditya, Aditya was renamed to Aditya-L. Being further away than the 800 km, it will require additional fuel to get to the new L1 orbit. Once a spacecraft arrives in a Lagrangian point, it has a minimal force of gravity acting on it and stays put with little or no station keeping requirements. From L1 Aditya-L1 will have uninterrupted view of the Sun at all times. It will carry a
total of 7 instruments to observe the Sun.
The original Visible Emission Line Chronograph from the Indian Institute of Astrophysics (IIA). It is designed to study the solar corona and monitor Coronal Mass Ejections.
A Solar Ultraviolet Imaging Telescope (SUIT) from the Inter-University Centre for Astronomy & Astrophysics designed to image Solar Photosphere (the visible “surface of the Sun).
Aditya Solar Wind Particle Experiment (ASPEX) from the PRL to study the particles emanating from the Sun.
Plasma Analyser Package for Aditya (PAPA) from VSSC to analyse the composition of the solar wind.
Solar Low Energy X-ray Spectrometer (SoLEXS) from ISAC to monitor solar X-ray flares
High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) from PRL, ISAC and Udaipur Solar Observatory observe and monitor dynamic solar events that can give rise to disruptive space weather effects on Earth
Magnetometer from LEOS and ISAC to measure the variations in Interplanetary Magnetic Field
Venus Orbiter Mission
Reports of an Indian mission to Venus first surfaced in 2012 with a timeline of an orbiter to arrive at Venus in three years later. This announcement was at about the same time that the Mars Orbiter Mission acquired the formal approval. The mission to Venus was then shelved.
Like MOM, the Venus mission would also be launched by a PSLV and enter a highly elliptical orbit (500 x 60,000 km). Details available are tentative and likely to change. It is expected to carry 5 instruments, use a single solar panel providing at least 500 W and have a total mass of around 175 kg. Over time this apogee would be reduced offering closer views of Venus and its atmosphere. In Mid-2017, ISRO formally made an "Opportunity Announcement" for science instruments for a mission to Venus.[914] The opportunity is open only to scientists in India. The mission plan is still at a very early stage what detail is available is tentative. A launch date has not yet been established but expected sometime in the middle of the next decade.
Team Indus
An Indian private sector entity, Team Indus is planning to send a rover to the surface of the Moon. Team Indus is entirely independent of ISRO but has commercially engaged ISRO to launch its rover to the Moon on one of its PSLV. It is participating in the international Google Lunar Xprize competition. The Google Lunar XPrize is a competition designed to foster innovation in low cost development of robotic exploration of the Moon with a prize of $20 million. The $30M Google Lunar XPRIZE is a global competition to challenge and inspire engineers and entrepreneurs to develop low-cost methods of robotic space exploration. To win, a privately funded team must successfully place a robot on the surface of the Moon, travel at least 500 meters and transmits high-definition video and images back to Earth. Competing with Team Indus are 4 other teams from Japan, two from the US and one from Israel.
All the contenders have signed contracts with a launch service provider to transport the rovers from the Earth to the Moon. Following a ride share agreement, one of ISRO’s PSLV will launch Team Indus and the Japanese rovers to the Moon in December 2017. Team Indus is entirely independent of ISRO. The launch to space using ISRO’s PSLV is a commercial arrangement. As part of Chandrayaan-2 mission, ISRO is planning to send a lunar rover to the surface of the Moon. Team Indus is private initiative, and may succeed in that goal ahead of ISRO.
Chapter Sixteen
Space and National Security
I ndia established a nuclear programme long before it embarked on a space programme. INCOSPAR, which later became ISRO, was founded in 1962 under the Atomic Energy Commission, binding India’s space programme to its nuclear programme from inception. The Department of Space did not exist until 1972. The AEC was established in 1948, rather hastily after independence, by Homi Bhabha, a gifted and internationally accomplished physicist. The emergence of the AEC was a product of the unique phase India was passing through when the democratic institutions and the now infamous bureaucratic procedures had not yet been firmly established. India’s space programme has a social and economic development agenda at its heart but military objectives have gradually crept in the space programme has matured.
Space Infrastructure
One of the earliest external threat came from China when it conducted its first nuclear test in 1964. A decade later India responded. On 18 May 1974, a small fission device with a yield of 8 kt (although a larger yield was initially claimed) was detonated underground at the Pokhran Test Range located in the isolated Thar desert region in the state of Rajasthan. With Pokhran-I, India became the sixth nation to join the nuclear weapons club. The detonation was categorised as a Peaceful Nuclear Explosion, an internationally accepted form of nuclear testing.
Pokhran-II came two decades later. On 11 May 1998, India conducted three further nuclear tests, one was a fusion device and the other two, fission. Two days later, two more fission devices were detonated, all underground at Pokhran. Just as India had responded to China’s nuclear test, Pakistan responded to India’s. Between 28 and 30 May, Pakistan tested six devices, also underground, in the Chagai district of the province of Baluchistan. The exclusive club of six nations with the capability to deploy nuclear weapons since 1974 became seven amidst widespread international condemnation. The diplomatic fury was accompanied by economic sanctions formalised by the UN resolution 117 in June 1998. In the resolution, the UN recognised the new threat to international peace and raised its concerns about a potential arms race in South Asia. In 2016, India had around 110 nuclear devices and Pakistan about 140.[915] Neither India or Pakistan has conducted further tests since May 1998.
During the 1990s, as India developed its domestic space launch capability (the SLV-3, ASLV-3, and the PSLV), it was inevitably seen as a potential delivery mechanism for nuclear weapons. The dual use nature of missile technology, as well as the close connection between the civil nuclear power and nuclear weapons programmes, has helped and hindered India’s space programme. As a nuclear power, India acquired greater political and diplomatic influence on the international stage. The sanctions after Pokhran II held back ISRO’s cryogenic engine programme from which it is still recovering. India’s first explicit use of space for national defence started with the Technology Experiment Satellite (TES). In 1999, the Indian Army supported by the IAF engaged in military action (the Kargil War) to regain positions that Pakistani soldiers and Kashmiri militants had occupied on the Indian side of the Line of Control. The Indian forces would have benefited from satellite imagery, but ISRO at the time did not have such capability. The US had satellites with sufficient resolution capable of assisting the Indian military but refused India’s request for satellite images. The Kargil Review Committee Report highlighted India’s deficiency in space-based high-resolution reconnaissance,[916] and TES was ISRO’s prompt response to this recognition of a shortfall in India’s strategic infrastructure at a critical time.
TES was designed and built in record time and placed in a 568 km SSO on 22 October 2001. With a panchromatic camera designed to provide a resolution of 1 m, it was arguably India’s first instrument with military photo reconnaissance capability.[917] It incorporated a step and stare mode that provided high resolution in a wide field of view.[918] TES was classified, and unlike data from other Indian satellites, TES data was not made commercially available.[919] Before TES became operational, India had purchased images from the IKONOS satellite that made 1-m resolution images commercially available from 1 January 2000. While TES provided high-resolution imagery sufficient for strategic purposes, ISRO was also using it as an experimental test bed for numerous technologies. TES was designed to operate for only three years but returned data for over a decade. On 11 January 2007, China launched a ballistic missile from the Xichang Satellite Launch Centre that intercepted and destroyed one of its non-operational weather satellites, Fengyun-IC, in Earth orbit at an altitude of 863 km. The international community was surprised and alarmed by the demonstration of this military capability. The Indian military and political leaders r
ecognised that they would have to respond. As a signatory to the Outer Space Treaty, India had maintained a strict stance on not weaponising space. Another incident in the following year further highlighted India’s military shortcomings. The sophisticated terrorist attack in Mumbai in November 2008 motivated India to initiate its first dedicated photo reconnaissance satellite called RISAT-2 (Radar Imaging Satellite-2). Since the first INSAT series, RISAT-2 is the only satellite that ISRO has launched and operates but had not built.
RISAT-2 was acquired from Israel Aerospace Industries (IAI) in exchange for providing satellite launch services at a very short notice. It has a mass of 300 kg and is based on the TecSAR mini satellite designed and built by IAI. It was launched on 20 April 2009, six months after the Mumbai attacks, and placed into orbit by PSLV-C12, along with a 40-kg student-built microsatellite Anusat. RISAT-2 was designed to monitor hostile incursions across Indian borders, suspicious vessels at sea and for search and rescue.[920] It uses radar rather than visible or infrared light for imaging and incorporates Synthetic Aperture Radar (SAR) technology that can operate in spot, mosaic and strip imaging modes. The combination of a 3-m communication dish, radar and SAR allows RISAT-2 to provide imaging capability at a resolution of 1 m at any time (day or night) and in any weather (radar can penetrate clouds). Three years after RISAT-2, ISRO completed and launched RISAT-1. It was placed in a 536 km SSPO at an inclination of 41°. RISAT-1 is equipped with a larger data storage capacity (300 GB), higher capacity data transmitter and a battery to cater for the longer periods of an eclipse in the SSPO.[921] Instead of a traditional dish antenna, ISRO produced an unusual 6 m (along-track) x 2 m (cross-track) antenna customised for the SAR function. The orbits of RISAT-1 and RISAT-2 take them over parts of the globe not just India. Most of the data they collect cover countries other than India. Antrix and the National Remote Sensing Centre make this data commercially available on the international market, along with data from other ISRO remote sensing satellites. RISAT-1’s polar orbit brings it over Norway’s Svalbard ground station (SvalSat). Because of its unique geographical position, SvalSat is the only commercial station that can offer images from anywhere in the world an hour after they were taken. In 2015, Antrix entered into a commercial agreement with SvalSat that allows it to directly download data and generate images from RISAT-1.[922]