ISRO's Reusable Launch Vehicles

[AnantS]

^ There will be no saddle back design for future. What US and Soviets had concluded, Big Shuttles are unsafe, move is towards smaller space planes like X-37, which will in future also carry humans in Cargo Bay. India is also following US on the same. If you see designs from ESA, JAXA, US, all are having design in which Spaceplane forms part of last stage of the rocket.

For TSTO, most promising design is Skylon

 

[Indx TechStyle]

Our next plan is to make launch vehicle land in runway: K Sivan, Director, Vikram Sarabhai Space Centre

The next test of the Reusable Launch Vehicle Technology Demonstrator (RLV-TD) will be to land the aerospace vehicle in a runway when it returns from space, said K Sivan, Director, Vikram Sarabhai Space Centre of the Indian Space Research Organisation (ISRO).

On Monday, ISRO successfully tested the indigenously built winged-body aerospace vehicle, which when fully developed can be used multiple times to send satellites in to orbit. At present, a rocket goes waste ever time a satellite is launched, he told newspersons.

On return from space, the RLV-TD landed at the precise location in the sea but got disintegrated. However, the next test is to fully get back the RLV-TD and make it land in a 5-km runway to be built at SHAR, Sriharikota, he said.

A large amount of data has been collected from RLV-TD, a project initiated in 2003. It will be analysed, and if fully satisfied, ISRO will go ahead with the next stage of testing, he said without giving a time frame.

There will be different levels of tests and demonstrations in the next 10-15 years before a full fledged RLV is developed. For instance, the energy to be dissipated on re-entry is large resulting in extreme heat due to aero-dynamic drag experienced by RLV (1800 k surface temperature). The re-entry module must land on a pre-designated landing site without disintegrating due to extreme decelerating loads, he said.

 

[salute]

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[Indx TechStyle]

In fact: After reuse trial, long flight ahead
The excitement over the success of the RLV is deserved, but ISRO has done this twice before. The cost benefits of a reusable launch vehicle remain uncertain, and the challenges before ISRO huge.
WRITTEN BY AMITABH SINHA |PUBLISHED ON:MAY 27, 2016 12:04 AM

While the testing of a prototype Reusable Launch Vehicle (RLV) on Monday is no doubt an important milestone for ISRO, it is easy to see why the space organisation itself has been calling it only a “baby step” towards the objective of acquiring a launcher that can deliver satellites into space just like airplanes transport passengers and cargo.

The RLV technology is at least four decades old, and several nations, and even private space firms, have experimented with it. However, only NASA has put it to any practical use until now, in its much-acclaimed space shuttle programme that ran from 1981 to 2011.

The main rationale for developing a reusable system is to bring down the costs of satellite launch, and to increase the frequency of launches. Satellites and scientific instruments need to ride on rockets to go into space. These are of the use-and-throw kind, which mostly fall into the sea after doing their job, or sometimes float uselessly in space, adding to space debris. Reusable rockets can save the costs of building a new vehicle for every launch, and also the manufacturing time, thus enabling more frequent launches.

Related

• India’s shuttle
• ISRO's RLV test: It's all about lowering the cost of satellite launches
• From Aryabhata to RLV-TD: A history of India’s space journeys

No quick cost cuts

It is estimated that RLV, once fully developed in about a decade, could bring down launch costs 8-10 times. Currently, it costs Rs 6-8 lakh to send a 1 kg payload into a low earth orbit. The PSLV and GSLV carry payloads of 1,000-2,500 kg per flight.

Since no RLVs have been used except in NASA’s space shuttle programme, there is little direct evidence for cost reductions. Besides, the space shuttle programme was driven more by the need to frequently carry astronauts and logistics to the International Space Station than to cut launch costs. In 30 years, the shuttle flew 135 missions — or 4.5 times a year on average. The programme budget was about $ 209 billion (2011 $), making the average mission cost more than $ 1.5 billion (approx Rs 10,000 crore today). This cost included expenses over buildings, salaries and other logistics. And though the shuttle was reusable, albeit only partially, the incremental cost per flight was estimated to be about $ 450 million (approx Rs 3,000 crore). This cost can be an indication of the service, repair and replacements needed before every flight. There is no estimate of how much additional money NASA would have spent if it had used an expendable launch vehicle instead of a partially reusable one.

Also, the cost advantage of a reusable vehicle can become evident only over several launches. That is because the development cost of RLV far exceeds the manufacturing cost of an existing launch vehicle. ISRO has spent about Rs 90 crore on developing the prototype RLV. The likely cost of an operational RLV over the next 10 years is expected to be substantially more than the average cost of a PSLV, which is about Rs 120 crore. A GSLV costs about Rs 170 crore. The development of an experimental fully reusable vehicle called X-33 by NASA, aborted in 2001, cost $ 1.3 billion (about Rs 9,000).

Several studies have compared the costs of a fully reusable system and continued use of an expendable vehicle. The results vary depending on the parameters chosen.

Degree of reusability

The cost advantage also depends on the degree of reusability built into the vehicle. There are different stages to the flight of a launch vehicle. At each stage, a part of the rocket breaks off, while providing thrust to the remainder to keep going. There are designs of Single-Stage-To-Orbit (SSTO) vehicles that would not require booster parts. But most vehicles in use today are multi-stage rockets.

A fully reusable vehicle would deliver payloads into orbits and return to Earth completely intact. Even a Two-Stage-To-Orbit (TSTO) vehicle, which ISRO’s tested prototype was, can be fully reusable if both the parts are made to fly back to Earth. In the case of the prototype tested on Monday, only the second stage, a winged structure that looks like an airplane, re-entered the atmosphere and landed in the Bay of Bengal for possible reuse.

In the NASA shuttle, the final stage, called the orbital vehicle, was reusable while some components of the boost stages were also recovered and reused after servicing. Studies have shown that recovery and reuse of the final stage, or the orbital vehicle, has more cost benefits compared to the boost stages.

On the degree of reusability depends the repairs and servicing required before reuse.

Not the first time

In January 2007, ISRO launched a 555-kg space capsule aboard PSLV-C7 that remained in orbit for 12 days before re-entering the atmosphere and crashing into the Bay of Bengal. In December 2014, ISRO carried out the Crew Module Atmospheric Re-entry Experiment, sending a heavy payload to a height of 126 km on the inaugural experimental flight of GSLV-Mk III, an advanced launch vehicle still under development. The payload separated and re-entered the atmosphere, and fell into the Bay of Bengal after a nearly 21-minute flight.

However, both these re-entries were meant to result in crash landings. The vehicle could be recovered but not reused. The RLV prototype was structurally very different — the winged structure intended to be able to make a soft landing like an airplane, and thus much more challenging. The actual RLV, when it is developed, would have to land on a runway. ISRO has said a 5-km runway, more than double the length of the longest in the country, would have to be built for it.

 

[Indx TechStyle]

Official:
RLV-TD - Indian Space Research Organization

Reusable Launch Vehicle – Technology Demonstrator (RLV-TD) is one of the most technologically challenging endeavors of ISRO towards developing essential technologies for a fully reusable launch vehicle to enable low cost access to space. The configuration of RLV-TD is similar to that of an aircraft and combines the complexity of both launch vehicles and aircraft. The winged RLV-TD has been configured to act as a flying test bed to evaluate various technologies, namely, hypersonic flight, autonomous landing and powered cruise flight. In future, this vehicle will be scaled up to become the first stage of India’s reusable two stage orbital launch vehicle.

RLV-TD consists of a fuselage (body), a nose cap, double delta wings and twin vertical tails. It also features symmetrically placed active control surfaces called Elevons and Rudder. This technology demonstrator was boosted to Mach no: 5 by a conventional solid booster (HS9) designed for low burn rate. The selection of materials like special alloys, composites and insulation materials for developing an RLV-TD and the crafting of its parts is very complex and demands highly skilled manpower. Many high technology machinery and test equipment were utilised for building this vehicle.

Objectives of RLV-TD:

• Hypersonic aero thermodynamic characterisation of wing body
• Evaluation of autonomous Navigation, Guidance and Control (NGC) schemes
• Integrated flight management
• Thermal Protection System Evaluation

Achievements:

RLV-TD was successfully flight tested on May 23, 2016 from SDSC SHAR Sriharikota validating the critical technologies such as autonomous navigation, guidance & control, reusable thermal protection system and re-entry mission management.

Vehicle Configuration

Mission Profile

Tracking of RLV-TD Mission

 

[HariPrasad-1]

______________________________

Can anybody post here the descent diagram?

 

[Indx TechStyle]

Can anybody post here the descent diagram?

Of what?
Please enter a message with at least 30 characters.

 

[Indx TechStyle]

ISRO gears up for next shuttle mission

The next test of the Reusable Launch Vehicle Technology Demonstrator (RLV-TD) will be to land the aerospace vehicle in a runway when it returns from space, said K Sivan, Director of Vikram Sarabhai Space Centre of the Indian Space Research Organisation (ISRO).

On Monday, ISRO successfully tested the indigenously built winged-body aerospace vehicle, which when fully developed can be used multiple times to send satellites into orbit. At present, a rocket goes waste every time a satellite is launched, he told newspersons.

Next target

On return from space, the RLV-TD landed at the precise location in the sea, but got disintegrated. However, the next test is to fully get back the RLV-TD and make it land in a 5-km runway to be built at SHAR, Sriharikota, he said.

A large amount of data has been collected from RLV-TD, a project initiated in 2003. It will be analysed, and if fully satisfied, ISRO will go ahead with the next stage of testing, he said without giving a time frame.

There will be different levels of tests and demonstrations in the next 10-15 years, before a full fledged RLV is developed. For instance, the energy to be dissipated on re-entry is large resulting in extreme heat due to aero-dynamic drag experienced by RLV (1,800 k surface temperature). The re-entry module must land on a pre-designated landing site without disintegrating due to extreme decelerating loads.

The RLV would launch spacecraft, including satellites, into space and re-enter the earth’s atmosphere withstanding extreme pressure and heat conditions and land in an intended spot.

In future, there is going to be a huge demand for ISRO to launch satellites – around 60 in the next five years. This requires RLV, which can return to earth after inserting the payload in to the designated orbit and can be re-used with minor refurbishment. This will ensure fast turnaround time between launches, he said.

While the VSSC designed, conceptualised and tested the RLV-TD, which costs around ₹95 crore, some of the work, including fabrication, was done by private companies, he said.

The US and Russia have developed RLV while Japan has tested a portion of the RLV. The RLV-TD was only one-sixth the size of RLV, he said.

Expandable launch

ISRO’s focus has been mainly on expendable launch systems such as PSLV, GSLV, GSLV-Mk-III and hybrid launch system, which is partly re-usable like Space Shuttle. These systems are expensive to produce and incur high rates per launch.

Typically, the cost of transporting 1 kg of payload to space using expendable launch vehicle is $15,000-20,000. Of this, 80 per cent of the rocket cost is towards engines and structure. If the engines and the structure can be recovered and re-used, there could be a substantial reduction in cost to launch payloads in space, he said.

To break even, the RLV should be used 30-40 times. However, ‘our target’ is to use the RLV for nearly 100 times. We will then spend only 20 per of the present cost, which will be a substantial saving,” he said.

 

[sayareakd]

Yeah, this successful launch has fired us all, we can match with the best, so lets aim higher and reduce the time line. Get to work guys and next time use full scale working shuttle.

Plus take one circle of the earth and then come back collecting one of our old satellite by robotic arm. That will send chill down the spines of few of our neighbours.

 

[A chauhan]

...

Plus take one circle of the earth and then come back collecting one of our old satellite by robotic arm. That will send chill down the spines of few of our neighbours.

Feels like Star Wars ......sci-fi....

 

[Akask kumar]

Yeah, this successful launch has fired us all, we can match with the best, so lets aim higher and reduce the time line. Get to work guys and next time use full scale working shuttle.

Plus take one circle of the earth and then come back collecting one of our old satellite by robotic arm. That will send chill down the spines of few of our neighbours.

thats way too much for a project that has just begun..you cant do all this in one experiment.. all this will happen in series as we have limited budget and resource.. only way to increase the devlopment is to carry all related experiment simultaneously,which wil require much greater logistics than we currently have.For example we had to develop a 5km runway to test the landing gear.. if we already had this runway then a lot of time could have been saved.

 

[LETHALFORCE]

British presses asses are on fire look at recent articles in guardian and others even al jazzera headline says plane tested nothing about the test result

 

[sayareakd]

Feels like Star Wars ......sci-fi....

Yeah all charged up, specially when they can deliver at shoes string budget.

I am also thinking of drdo using astra missile revolver kind of robotic arm at its cargo bay shooting off enemy missiles and satellites in space.

Not bad idea to have these at the time of hostilities.

Let it keep their in space and shoot some Agni 1 RV as test.....then come back after week on runway.

 

[Indx TechStyle]

British presses asses are on fire look at recent articles in guardian and others even al jazzera headline says plane tested nothing about the test result

Their defense forums are far more pathetic. :biggrin2:

 

[Indx TechStyle]

Prospects and necessities from RLV-TD
The Indian Space Programme has a mandate to focus on its launch- and earth-oriented capabilities. In the past decade, it has attempted some non-conventional experimental projects under the labels “‘low-cost” and “technology demonstrator”. However the effect of these experimental space projects on India’s techno-economic growth will be realised only if the central government gives the project greater status and funding.

On 23rd May 2016, India for the first time in the history of its space programme tested a fixed-wing launch platform – the Reusable Launch Vehicle-Technology Demonstrator (RLV-TD). This miniature vehicle was launched on a modified first stage of the long-retired Satellite Launch Vehicle (SLV), and it rose to an altitude of 65 km into the mesosphere [1]. This momentous first-of-its-kind experiment brings India into a select line-up of nations that are pursuing hypersonic flight and reusable launch platforms simultaneously. The Department of Space (DOS), Government of India, has a limited mandate for research and development (R&D) and the upkeep of its expendable launch systems and earth-oriented communication, navigation, and surveillance satellites.[2]

With its highly reliable Polar Satellite Launch Vehicle (PSLV) and the yet emerging Geosynchronous Satellite Launch Vehicle (GSLV), DOS has given itself some latitude to occasionally undertake non-conventional experimental space projects in the areas of planetary exploration, human space flight, and space-based observatories. These include Chandrayaan-1, the Mars Orbiter Mission (MOM), Astrosat, the Space Capsule Recovery Experiment (GSLV-launched), and the recent RLV-TD. Despite the success of these missions, most of them are executed only as “low-cost” “technology demonstrators” as DOS is unable to seamlessly carry out high-end projects due to the paucity of resources, owing to the clumsy affinity of space policymakers for frugality.

The expressions “technology demonstrators”—also known as prototypes—and “low cost” are really two sides of the same coin. With a prototype, a constructor exhibits its ability to engineer next-generation technology, not in its entirety but with few fundamentally enhanced design and performance elements. A prototype’s fate is largely dependent on its inherent qualities, its urgent need, and the resources invested in it. Prototypes are inexpensive when compared to their production variants. Car manufacturers, for instance, spend only up to 4% of their total revenue on R&D of a concept, or prototype vehicle[3].

Figure 1: Globally-validated Technology Readiness Levels for space technologies[4]

The Indian Space Research Organisation (ISRO), which is governed by DOS, develops its technologies based on a globally-validated R&D maturity sequence known as the Technology Readiness Level (TRL) (see Fig. 1). The sequence includes starting levels of basic research (TRL 1) to ultimately attaining a fully space-proven technology, with its own complete technical manual (TRL 9). ISRO’s technology demonstrators are positioned at TRL 7, where a prototype validates its performance in a real space environment but does not integrate subsystems that have been fully tested to the last bug.

A maximum TRL of 9 demands R&D of highly complex engineering subsystems as well as their incessant analyses, which leads to a longer project lifecycle and necessitates extensive auxiliary infrastructure. TRL 9 thus demands greater monetary and human resources than what the India’s space policymakers are comfortable allocating, given their undue affinity for frugality.

While pursuing the RLV-TD, the Central Government seeks to maximise its technological output by indigenously harvesting high-end capabilities like hypersonic and autonomous space flight, flight stability and control, mission avionics hardware, and next-generation thermal protection materials. With so many potential spin-offs expected, is it then at all rational to fund the RLV frugally and yet expect great returns from it?

RLV: the future scenario in the small satellite market

Both the consistent launch success of PSLV—its ability to carry out multi-orbit missions with varied payloads (1.4 ton to 750 grams) and evolution into an expendable launch system—as well as ISRO’s Antrix Corporation’s competitive pricing strategy, have given PSLV a wide international clientele. However, it must be stated that PSLV is a small satellite launch system (SSLS) (up to 1.5 ton in Geostationary Transfer Orbit) and its success, howsoever impressive, is limited within the SSLS category. PSLV developed in an era when most of its global SSLS contemporaries had retired. Its only actively operational SSLS competitors are Khrunichev’s Rokot and Orbital ATK’s Minotaur, but in terms of their number of launches and assortment of payloads, they lag far behind.

In the recent past, Antrix’s competitive pricing and services have begun to vex its SSLS competitors, especially those from the U.S. space launch industry[5]. When PSLV launched the Lemur cube satellite constellation in 2015 for private U.S. company, Spire Global, it triggered the protectionist nous in the U.S. domestic launch sector: the implication was that India, with its competitive pricing, was distorting the conditions of competition, taking away its potential local customers. This reaction was an indication of how the international SSLS market, with late bloomers in Space like India taking centrestage, is becoming more and more dynamic with every passing day.

Extreme space weather is also increasingly perceived as a threat to large old generation satellites while the 2007 anti-satellite missile tests conducted by Beijing agitated the need in many strategic space circles to escalate the process of satellite miniaturisation. Consequently, next-gen satellites are not only undergoing rapid miniaturisation, but will eventually be built with futuristic materials that resist extreme weather like a solar storm.

Increasing demand for miniaturised satellites is galvanising both private and public space contractors to build diversified reusable launch systems. These include aircraft-launched rockets (Orbital ATK’sPegasus), aircraft-launched fixed wing space planes (the People’s Liberation Army’sShenlong), two-stage-to-orbit (Sierra Nevada Corporation’s Dream Chaser, the European Space Agency’s Intermediate Experimental Vehicle, and Boeing’s X-37), and reusable rocket-stage and boosters (Airbus’s Adeline, the cancelled Khrunichev’s Baikal, German Aerospace Center’s Liquid Fly-back Booster,and the United States Air Force’s Reusable Booster System).

PSLV has launched a large number of miniature satellites of domestic and international clients, the Lemur constellation being one of them. Yet, PSLV has launched these only as secondary payloads as DOS realises it would not be an economical platform to launch them as primary payloads. Instead, if pursued appropriately, RLV is expected to become fully operational by the 2030s, by which time, there would be a considerable global shift to miniaturised satellites which would fit the carrying capacity of RLV’s tentative operational variant. Despite its apparent similarity to the Space Shuttle, RLV could become an SSLS, and also has the potential to be a cargo carrier, if India ever attempts building a space station in low earth orbit. Of course, for all this to happen, and given intensified R&D activity in the SSLS sector, the government at the Centre must realise, RLV will not experience the free run as PSLV did and it will have to enter into an aggressively competitive market that is teeming with players.

RLV: potential for an experimental aeronautical complex

India is poised to become the largest aviation market in the world by 2030.[6] Yet, this growth notwithstanding, and barring a few prominent projects, India’s indigenous aeronautical infrastructure is largely limited to R&D in components and subsystems. Apart from a few successful aircraft platforms— for the defence sector—-which have experienced their share of delayed growth, India is largely stuck in either licence manufacturing or purchasing entire aircraft On the other hand, Brazil, which established its government-owned corporation Embraer in 1969, much later than the Indian government-run Hindustan Aeronautics Limited (HAL) (1940) and National Aerospace Laboratories (NAL, 1959), is the third largest aircraft manufacturer in the world today, ranking after Airbus and Boeing.

Embraer benefitted greatly from its privatisation initiated by then Brazilian president Itamar Franco in the early 1990s. Privatisation opened the floodgates of funds for path-breaking R&D and thereafter Embraer’s product portfolio diversified and its revenues increased drastically. Embraer now delivers 35% of the total executive jets sold in India[7] while the NAL-HAL Saras—the only Indian small business jet and still at prototype stage—has exhausted funds with and languishes in a hangar.[8] Once again, the main reason for India’s aeronautical sluggishness has been the past government’s apathy towards privatising HAL.

Better late than never, the Narendra Modi government recently announced there be an initial public offering for HAL by December this year[9]. Over six decades of HAL, the Centre failed to cultivate it as a company that would develop experimental aircrafts indigenously, even though the most successful aeronautical companies of the world invest substantially in building experimental aircrafts regularly. These aircrafts do not always make into production, but their subsystems often aid in the generational advancement of production units.

If the Centre takes RLV seriously and not merely stick to its monotonous frugality chant, RLV could prompt the establishment of an experimental aeronautical complex in India. R&D of the orbital RLV could concurrently serve the hi-tech necessities—for avionics, supersonic flight, and composite materials—of India’s huge suborbital aerospace sector. The Modi government must create robust synergies between government-run R&D facilities, aerospace design groups, and the commercial aeronautical sector of multiple domestic players.

RLV: potential for airport infrastructure

The first RLV-TD was designed to disintegrate in the Bay of Bengal, deemed a virtual landing by ISRO. Upcoming RLV-TD tests and subsequent space-plane require a long, approximately 5 km airstrip to make a real landing. ISRO has proposed to utilise a large land parcel near the existing spaceport at Sriharikota in Andhra Pradesh[10], but having one end-of-mission airstrip is insufficient—spaceplanes require several mission abort airstrips at various locations around the world. Narendra Modi must therefore request friendly nations around the world to make some of their long airstrips available for any emergency aborts of RLV.

In fact, very few airports within India—at Hyderabad, New Delhi, Begaluru, and the Arrakonam Naval Air Station —have airstrips longer than 4km, so the Indian Air Force often exercises landing its medium-lift and heavy-lift aircraft on the country’s shortest airstrips, at Daulat Beg Oldi in Ladakh, Port Blair in the Andamans, and Juhu Aerodome in Mumbai. In the coming years, with probable far greater inventory of heavy-lift aircrafts, the imminent return of supersonic commercial jets like theConcorde, and space-planes like the RLV, the central government has to overcome the infrastructural limitations of its existing airports.

Potential for a hi-tech spin-off market

The decision to pursue non-conventional space projects has begun to brood spin-offs that could easily spread across different markets. ISRO’s experience with computational fluid dynamics and rare-earth magnets—a part of rocket engine R&D developed indigenously—has resulted in a non-invasive artificial heart[11] which, if if mass produced, can serve India’s cardiovascular prosthetic devices market.

Another ISRO spin-off is an ultra lightweight ‘aerogel’ that can be used for containing oil spills and in the advanced materials, pharmaceuticals and chemicals industries[12]. ISRO has also collaborated with Tata Motors in the development of a hydrogen cell-powered passenger vehicle[13]. ISRO probably foresees applications of aerogels and fuel cells in its manned space flight program as well, and continuing with such non-conventional projects will only equip the Indian Space Programme to engineer far more spin-offs to meet India’s emerging demands.

The government must therefore push its TRL 7 technology demonstrators to grow into TRL 9 missions, and aptly invest further. It must stop cloaking its stunted investment in R&D with glossier and self-placatory terms for frugality and cost effectiveness. RLV’s comparison to the Space Shuttle is an exaggeration, but then it also signifies the nation’s innocuous aspirations for outer space. RLV has the potential to fire up India’s manufacturing and infrastructure sector while propelling the Indian Space Programme further.

 

[pmaitra]

^ There will be no saddle back design for future. What US and Soviets had concluded, Big Shuttles are unsafe, move is towards smaller space planes like X-37, which will in future also carry humans in Cargo Bay. India is also following US on the same. If you see designs from ESA, JAXA, US, all are having design in which Spaceplane forms part of last stage of the rocket.

For TSTO, most promising design is Skylon

Thanks. Please quote next time so that I know.

 

[sorcerer]

ISRO RLV-TD Launch Video from on-board camera

 

[pmaitra]

^ There will be no saddle back design for future. What US and Soviets had concluded, Big Shuttles are unsafe, move is towards smaller space planes like X-37, which will in future also carry humans in Cargo Bay. India is also following US on the same. If you see designs from ESA, JAXA, US, all are having design in which Spaceplane forms part of last stage of the rocket.

For TSTO, most promising design is Skylon

You are correct that the future shuttle missions will probably be tandem configuration. The reason I think is not with size, but with increased chances of debris hitting the heat shield tiles, like what happened with the Challenger. You are probably thinking that saddle-back configuration makes the entire complex unbalanced. While it is true that it is unbalanced, the gimballing capabilities of the boosters can easily overcome that.

Source: http://news.bbc.co.uk/2/hi/science/nature/3019516.stm

Source: http://news.bbc.co.uk/2/shared/spl/hi/americas/03/columbia_disaster/html/1.stm

 

[AnantS]

You are correct that the future shuttle missions will probably be tandem configuration. The reason I think is not with size, but with increased chances of debris hitting the heat shield tiles, like what happened with the Challenger. You are probably thinking that saddle-back configuration makes the entire complex unbalanced. While it is true that it is unbalanced, the gimballing capabilities of the boosters can easily overcome that.

Source: http://news.bbc.co.uk/2/hi/science/nature/3019516.stm

Source: http://news.bbc.co.uk/2/shared/spl/hi/americas/03/columbia_disaster/html/1.stm

Yeah you are correct, the reason was the large number of small heat shield tiles on big shuttles, multiplied the probability of their failure and were difficult to maintain (considering most of the space shuttle incidents are related to some form heat shield tile failure).

 

[pmaitra]

India's Space Shuttle - Space Pod 5/18/16

(retro)