The Indian Space Programme

by Gurbir Singh

  Figure 10‑9 Reusable Launch Vehicle Technology Demonstrator. Credit ISRO

  ISRO’s vision of a RLV is a TSTO space shuttle, like a delta-winged spaceplane. The winged design was the product of almost 4,500 wind tunnel tests. Launched vertically by a single rocket motor (first stage), the RLV is designed to use its onboard engine (second stage) to arrive in orbit. Once the in-orbit operations are complete, the RLV is designed to return to Earth using the same engine to de-orbit and land on a runway as a traditional aircraft. In ISRO’s phased development programme, the RLV did not have engines on-board for the initial series of tests. In May 2016, ISRO conducted its first RLV test. It was launched using a single solid booster from the FLP and returned simulating an unpowered glider approach to a splashdown at sea with no plans for recovery.

  A research paper identified some of the RLV technology objectives “The key aerodynamic and aerothermodynamics design aspects are optimum heat flux, heat load, load factor, less than 4 g deceleration, sufficient payload bay, down-range and cross-range capability, good longitudinal and lateral directional aerodynamic stability and adequate control surface effectiveness.”[574] The reference to a deceleration of less than 4 g is typically associated with human spaceflight. The maximum acceleration of GSLV-Mk3 is also limited to 4 g. While the flight characteristics of RLV design may cater for human passengers, currently all ISRO’s RLV experiments fly completely autonomously without the capacity to support human crew.

  Figure 10‑10 RLV-TD at Launch. 23 May 2016. Credit ISRO

  The first time ISRO publicly displayed the design of its RLV was at the bi-annual Aero India International Aerospace Exhibitions in Bangalore (now Bengaluru) in February 2009. Initially, ISRO intended the first flight to be in 2011, but a series of delays followed. In its annual report in 2014, ISRO outlined its intentions stating “solid booster motor (HS9) has been positioned at Satish Dhawan Space Centre, Sriharikota. Assembly of the vehicle is in progress towards RLV-TD HEX-01(Reusable Launch Vehicle Technology Demonstrator Hypersonic Flight Experiment) mission targeted originally for launch during the first half of 2015.”[575] It took place a year later.

  At 7 am local time on 23 May 2016, ISRO launched a 1.75-tonne 6.5-m long (one-sixth scale) model of its version of a reusable space shuttle from the FLP in Sriharikota. The RLV-TD was launched vertically on a sub-orbital trajectory using a single 9,200 kg solid fuel booster based on the 1 m by 10 m strap-on used on the PSLV. Typically, PSLV boosters achieve a velocity of about 0.8-1 km/s, which is about Mach 3. The one used to launch RLV was a customised version reaching a higher speed before burning out and separating after 91.1 seconds at an altitude of 56 km. The space shuttle had also used boosters, but they were in parallel with the shuttle, whereas the RLV was on top of the booster increasing the overall length and thus the length-to-diameter (L/D) ratio. This was an important parameter that can increase the vehicle’s dynamic instability, but this first and successful flight demonstrated the success of ISRO's calculations, simulations and modelling.

  Figure 10‑11 RLV-TD as Tracked by Ship, Satellite and Ground Station at

  Sriharikota. Credit ISRO

  Directional control during ascent was maintained by the booster’s four fins, as well as the SITVC control system used by ISRO for its solid fuel booster. The SITVC fuel (strontium perchlorate) is usually contained in what looks like a smaller version of the strap-on strapped vertically on the booster, but in this instance, it was stored in a toroidal tank located at the base of the booster. Following the launch, the RLV ascended to 65 km and started its supersonic re-entry at Mach 4.78 (5855 km/h). It did not cross the 100-km boundary considered the threshold for space, so this was not a space mission, which is perhaps why ISRO kept a low profile throughout the mission, publishing its first press release immediately after the mission was complete.

  The RLV-TD mission verified the protection provided by the 1,200 thermal tiles against the 1,000°C temperature during re-entry. Onboard sensors collected a variety of data, including load, acceleration, temperature, air speed and pressure. There probably were cameras onboard, too, but ISRO has not released any in-flight images from RLV-TD.[576] During the flight, RLV-TD was tracked using a C-band beacon installed in the vehicle. Data was transmitted in real time using the onboard S-band transmitter to the ground stations at the Sriharikota. ISRO was assisted by the Indian coast guard, and the National Institute of Ocean Technology’s research vessel Sagar Manjusha provided ship-borne data relay along the flight path.[577]

  RLV-TD was tracked to 800 m above sea level by ship-borne telemetry at 2 MHz and also at 1 KHz data from INSAT right up to the point of impact.[578] All mission objectives were successfully completed. As RLV-TD was not expected to survive the impact unlike SRE-1 in 2007 and the LVM3-X/CARE mission in 2014, no recovery was planned. The vehicle, however, did survive landing on the water, and ISRO reported that it was intact and floating.[579] Images of the vehicle floating on the sea were captured by helicopter 20 minutes after touchdown but were not published. Had provisions for recovery been in place, RLV-TD could have been recovered (at least some of the larger parts. It is unlikely the vehicle survived the impact intact) and returned to VSSC for further analysis.[580] In this first flight, the RLV-TD had no onboard engine, so during the return journey, it operated as a glider, just as the US space shuttle design. The onboard navigation and guidance systems controlled the descent autonomously from 40 km altitude down to a gentle splashdown. RLV-TD had two vertical tail planes offset from the centre and canted (like the US’s secret X37B unmanned spaceplane).

  The space shuttle had just one fin and a split-rudder assembly doubling as a speed brake. The descent profile was controlled by operating the rudders on the canted tail planes, the elevons on the trailing edge of the wings and an RCS. Although there was no runway in this instance, the glide path simulated an airstrip approach that will be used in future missions when a runway is available. Twelve minutes and 50 seconds after launch, the vehicle splashed down in the Bay of Bengal, 412 km from the launch site. In the post-flight press release, ISRO confirmed mission success stating that “autonomous navigation, guidance & control, reusable thermal protection system and re-entry mission management have been successfully validated.”[581]

  ISRO planned to develop its RLV systematically through four distinct phases using its scaled-down experimental delta-winged RLV. The hypersonic flight experiment (HEX) of the first phase has now been completed. This will be followed by a landing experiment (LEX), return flight experiment (REX) and the scramjet propulsion experiment (SPEX).

  The second phase, the landing experiment, involves landing on a runway and recovering the vehicle for the first time. This would not be a sub-orbital launch but a release from a mother aircraft from high altitude. The third phase, return flight experiment, combines the first two, a sub-orbital launch followed by a return to Earth and landing on a runway. The fourth phase, the scramjet propulsion experiment (SPEX), involves an active scramjet propulsion to get to Earth orbit before returning to a runway landing. Through these tests, ISRO intends to master hypersonic aero-thermodynamic characterisation of winged re-entry body, along with autonomous mission management to land at a specified location.

  The RLV-TD was built by about 500 ISRO engineers at the VSSC over five years at an estimated cost of about $15 million (Rs.99.5 crore). Despite the success of the first test in May 2016, the TSTO concept based on a reusable spacecraft is still more than a decade away. The next key stages of RLV require two critical elements that ISRO is yet to fully develop, scramjet engine technology and a 5-km runway at Sriharikota. The next three tests of landing on a runway, refurbishment and reuse, this can only take place once the runway for the RLV is available. ISRO has no runway although there is ample space to build one. A detailed report for the construction of a 5-km runway at Sriharikota was completed in 2011, but the work is yet to start.[582] The other critical dependencies are special types of combustion engines that operate only at supersonic speed,
ramjet and scramjet engines.

  Scramjet

  Most of the mass of a rocket at launch pad is in the propellant required to acquire the high speed to achieve orbit. The propellant in all its forms, solid, liquid or cryogenic, consists of an oxidiser and fuel, which are brought together for combustion. Typically, rocket fuel mixture ratio has more oxidiser than fuel, and the oxidiser is the heavier of the two. For example, the huge propellant tank used by the space shuttle contained 100 tonnes of LH2 and 629 tonnes of LOX. If an engine were to use oxygen from the air, it could reduce launch weight significantly. Even though there is no oxygen in space, the first 50 km of Earth’s atmosphere has sufficient oxygen, and it is this oxidiser supply that is used by ramjet and scramjet engines. Since atmospheric oxygen is available during ascent and descent, ramjet and scramjet technology lends itself for reusable space launch vehicles. Because oxygen is picked up from the atmosphere during flight, the total mass at launch is considerably reduced. Instead of using, for example, four stages of PSLV to get to orbit, a design using a ramjet/scramjet combination can do it with just two stages.

  Figure 10‑12 NASA X-43 Scramjet versus Traditional Jet Engine. Credit NASA

  Ramjet and scramjet engines are combustion engines with no moving parts and operate at supersonic (at least 324 m/s or Mach 1) and hypersonic (Mach 5 and beyond) speeds. The difference between a ramjet and scramjet is the speed at which it operates. The air in a ramjet combustion chamber is slowed to sub-supersonic speed before combustion, but in a scramjet, combustion occurs with air at supersonic speed. A scramjet (Supersonic Combusting Ramjet)) is a ramjet that operates in a higher speed regime than a ramjet.

  Ramjet technology has been in use for decades employed mostly in military missiles worldwide. India already deploys ramjet technology in its Brahmos and Akash missiles. However, operationalising ramjet and scramjet technologies for space vehicles is a major engineering challenge.[583] These engines rely on the enormous pressures created by their supersonic speed to compress the air entering the combustion chamber. ISRO is developing a ramjet-scramjet combination in a Dual Mode Ramjet (DMRJ) for its RLV.

  Once built, it will operate between Mach 3 to Mach 9. ISRO has been developing its ramjet and scramjet technologies in the Air Breathing Propulsion Project for several years using sounding rockets. On 3 March 2010, ISRO conducted its first advanced technology vehicle (ATV-D01) experiment. A pair of passive scramjets were attached to the second stage of a two-stage sounding rocket. Launched from Sriharikota, the ATV-D01 solid fuel booster with a launch mass of 3 tonnes reached the intended speed of just over Mach 6 at an altitude of 46 km. ATV-D01 sustained the critical hypersonic speed of Mach 6 for seven seconds during the four-minute experimental flight.

  A second development flight, ATV-D02, was conducted on 28 August 2016. This time, two active scramjets were attached to the side of the second stage of the RH-560, which operated during the hypersonic flight phase of ATV-D02. During the second stage burn of the RH-560, both scramjet engines were generating thrust by using oxygen from the atmosphere for combustion. Albeit for just five seconds, achieving combustion at hypersonic speed is a significant technological feat.[584]

  An RLV can have a profound impact on reducing the cost of placing satellites in orbit. Broadly, 85% of the cost of a space launch is the launch vehicle, 5% is fuel, and 10% is the payload. Reusing the launch vehicle offers the best option in cost-saving. If successful with RLV technology, ISRO will be able to reduce the cost of space launches by at least a magnitude, from $20,000 (Rs.0.13 crore) per kg to Earth orbit to $2,000 (Rs.1.3 lakh). This is the ultimate ambitious objective for ISRO’s RLV design.

  RLV is the first stage in ISRO’s ultimate goal of developing a TSTO spaceplane. While the RLV is a civilian ISRO project, a separate but similar spaceplane called Avatar is being developed by the DRDO. Ultimately, Avatar is designed to be an autonomous single-stage-to-orbit-vehicle with the capability of launching from a runway, placing its payload into orbit and returning to Earth, on the same runway. Organisationally, ISRO and DRDO are separate organisations. However, transfer of technology between the two would not be unusual as similar arrangements are practised in other countries. Other space agencies have attempted to or are planning to make use of spaceplane technology.[585]

  Figure 10‑13 Advanced Technology Vehicle Development Flight. One of the Two Passive Scramjets Can Be Seen in the Middle of the Launch Vehicle. 3 March 2010. Credit ISRO

  NASA’s space shuttle was retired after 135 missions, primarily because of the high-risk nature of its flight regime, but also because it did not bring the cost-savings initially envisaged. ESA, Russia, Japan and China have also experimented with spaceplanes, but none have shown significant commitment to the routine deployment of spaceplanes in the near future. Scramjet technology is still highly experimental. Although further scramjet tests are planned, ISRO, too, is not 100% committed to the RLV or scramjet technology.[586] Private industry. innovations from, for example, Skylon in the UK and Dream Chaser in the US may change this.

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  Chapter Eleven

  Struggle with Cryogenic Technology

  N ational space programmes are designed to provide specific space-based services but, in practice, serve a more subtle and complex role. They are an expression of national prestige, advance strategic capability and offer a potential for geopolitical influence. In addition, they play a role in the national economy and also offer an opportunity to compete on the fast growing international commercial space market, which was worth close to $7 billion (Rs.20,300 crore) in 1993[587] and has grown to $323 billion (Rs.2,041,038 crore) in 2015.[588] Half a century after its inception, India’s space programme still operates a single launch site, relies primarily on a single operational launch vehicle with low launch capacity and still turns to ESA to launch all its large communication satellites. Why has India’s space programme not advanced at the pace envisioned by its founders?

  The answer may lie in ISRO's troubled history with cryogenic-engine development. The absence of this key technology and the resulting lack of heavy-lift launch capability has held back the pace of its space programme. In its absence, ISRO struggles to meet its domestic demand for transponders, is limited in its ability to take on challenging science missions and can offer only a restricted range of commercial launch services. Notwithstanding ISRO's sustained progress over the last decade, it would have made greater strides more quickly with a heavy-lift launch capacity. For example, ISRO launched the first of a series of seven IRNSS satellites in 2013 and the last in 2016. The first satellite in the constellation was already a quarter of the way through its shelf life before the constellation was complete.

  With a cryogenic-engine powered heavy launch vehicle, ISRO could have launched two or more IRNSS satellites on a single launch vehicle. An operational heavy launch vehicle is also a prerequisite for India to progress with its lunar lander and rover missions and its human spaceflight programme. Further, having only a single launch site (Sriharikota), two launch pads, one VAB (SVAB is due to come online in 2018) and predominantly a single operational launch vehicle, the PSLV, determines an upper limit to ISRO's operations. The construction of an additional VAB is already underway, but developing a heavy launch vehicle has been one of ISRO's messy and enduring challenges.

  In October 1990, the Space Commission approved the heavy-lift launcher GSLV complete with a Cryogenic Upper Stage (CUS) to launch the heavy INSAT satellites that ISRO was building. Since then, it has made slow progress and is finally expected to have an operational heavy-lift vehicle by about 2020. However, even when India's heavy-lift launch vehicle is finally complete, it will still only deliver around 4 tonnes to GTO, a launch capability that is at least a decade old. Currently, ESA's two decades old Ariane 5 can place 6.5 tonnes in GTO, and the proposed Ariane 6 (scheduled for 2020) has a capacity twice that.[589]

  Cryogenic Engine Technology. Buy or Build?

  Engines using cryogenic propellants are much m
ore efficient than rocket engines powered by solid or liquid propellants. They require the least amount of propellant to deliver a spacecraft of a given mass to a predefined orbit[590] and provide the highest thrust through sustained combustion of LH2 and LOX. Cryogenic engines have almost 200% efficiency over liquid-fuel engines typically using UDMH and N2O4.

  However, the very low-temperature engineering required (for example, storage tanks, pipes, pumps, valves) to handle LOX at -183°C and LH2 at -253°C is a major technical challenge. Developing such technology from scratch is not only costly but can take decades to develop and operationalise. Bhabha and Sarabhai had recognised the value of international collaboration with technologically advanced nations when developing new technologies to avoid having to start from scratch. Such collaborations had led to close connections between India and the USSR, US, Japan and France, and India benefited from these connections in the development of sounding rockets, multi-staged launch vehicles, satellites and solid and liquid propulsion systems. A similar arrangement for cryogenic-engine technology transfer with a country that already had it was a natural solution for India. The US, Japan, China, France and Russia have developed and successfully deployed cryogenic engines for their launch vehicles. Approximately 18 cryogenic engine types have been developed across the world, but only seven have been fully tested in flight.[591] The US had developed large cryogenic engines (C-100) capable of delivering a thrust of 100 tonnes (approximately 1,000 kN) for the Apollo missions in the 1960s. Later, CE-200 engines were developed for the space shuttle main engines. When the Viking liquid engine agreement concluded in 1978, France offered the cryogenic technology as used in HM-7 to ISRO with a price tag of Rs.1 crore ($150,000).[592] ISRO declined the offer, a decision that even ISRO's far-sighted and visionary chairman at the time, Satish Dhawan regretted. Later Japan, the US and after that initial offer France, too, refused to engage in a commercially viable deal that included cryogenic-engine technology transfer to India.