Recently ISRO was on the news for conducting the first test of the Reusable Launch Vehicle Technology Demonstrator (RLV-TD), which was crowned by media as India’s own space shuttle, a premature epithet, at best.
The main objective behind developing this spacecraft was to test low cost access to space.
Currently, space launches are very expensive. The cost of transporting just 1 kilogram of payload to orbit using a heavy-lift rocket, like Falcon 9, is about $12500 or 8.4 Lakh rupees. For smaller payloads, ISRO uses relatively less powerful rockets like PSLV, but that too costs about $4500 or 3 Lakh rupees per kilogram. This is primarily because of two reasons:
1. The rockets which are currently in service are not reusable - Most of these rockets have 3 or 4 stages which fall back to earth when the rocket reaches certain altitude. After the payload is delivered to the desired orbit, the remaining part of the rocket is discarded which eventually falls back to earth mostly, or sometimes gets lost in space forever.
2. The rockets of today need a humongous amount of fuel to create enough thrust to leave earth’s gravity. Storing more onboard fuel increases the overall weight of the rocket, which is understandably inefficient.
Following NASA’s Footsteps, then..
To overcome the above two problems, in January 2006, ISRO started developing a reusable spacecraft, that is designed to launch vertically like a conventional rocket and return flying horizontally like a regular aircraft, just like NASA’s current space shuttle. This is to take care of the reusability issue of the current systems.
However NASA’s space shuttles are powered by cryogenic engines which use liquid hydrogen (fuel) and liquid oxygen (oxidizer). A cryogenic engine mixes the fuel and the oxidizer in a combustion chamber and ignites the mixture, generating thrust.
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How a conventional cryogenic engine works[/caption]
A cryogenic engine is very expensive, because producing liquid hydrogen and oxygen are resource intensive processes. Also, the fuel can only be stored in temperature nearing absolute zero, which requires a lot of electricity.
The operating costs of these space shuttles are so high ($450 million, or 3000 crore rupees per launch) that even NASA could not afford it any more. High operating costs was one of the key reasons why NASA shut down the space shuttle program in 2011.
ISRO’s current Technology Demonstrator Vehicle does not have any engines. It was launched using a conventional rocket and was designed to glide back to the Bay of Bengal. The objective of the launch was to test whether the on-board computers could actually enable the shuttle to glide to the pre-designated landing coordinates. The experiment also tested the performance of the heat resistant tiles, that had been used to construct the body of the vehicle. The future RLV experiments will have brand new internal engines.
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ISRO RLV-TD flight stages (Image credit: ISRO)[/caption]
Beyond the Space Shuttle model - the Scramjet Engine
To cut down fuel costs, ISRO will use a completely new type of engine in its RLV. This is called a Scramjet engine. The RLV will be launched using a conventional rocket engine, but when the vehicle reaches supersonic speed atmosphere, the scramjet engine will take over.
In a Scramjet, air enters into the engine through the inlet at supersonic speed. The inside of the engine is shaped in such a way that, the air gets compressed as it passes through the engine. When air is compressed, it heats up. At this point, liquid fuel is injected into the stream of hot and compressed air.
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How a scramjet engine works (Image credit: Wikipedia)[/caption]
This hot and compressed air, when mixed with fuel, becomes highly combustible. This mixture is then ignited and the resulting combustion generates very high amount of thrust.
Since a scramjet engine uses Air from atmosphere for combustion, it does not need an onboard Oxidizer tank, reducing fuel weight by 50%. Moreover, when a scramjet engine is moving through the atmosphere, it can additionally collect and liquefy oxygen from the atmosphere and can store it to use at orbital altitudes outside earth’s atmosphere.
That’s huge - surely, someone else has done it before?
No space or military agency in the world has an operational scramjet powered rocket or aircraft at this moment.
On 28th August 2016, ISRO successfully tested its first scramjet engine, and became the third country in the world after USA and China to successfully test fly a scramjet powered vehicle.
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ISRO’s test of Scramjet engines on 28-Aug 2016. (Image credit: ISRO)[/caption]
So, what next?
ISRO will conduct a series of tests in future before the RLV is ready for actual missions.
The Next mission will be for testing the landing capabilities of the RLV in an actual runway. The RLV will be taken to very high altitude by a regular rocket and will be dropped. The mission of the RLV will be to fly like an aircraft and land safely in a Runway. ISRO plans to build a 4 km long runway in Sriharikota for this purpose.
Followed by the landing experiment (LAX), two more tests will be done to test the return from space capability (REX) and Hypersonic Flight capability (HEX1).
ISRO envisions to make the RLV ready for actual missions by 2030 when it will be able to carry satellites (and even humans) to orbit.
As per ISRO, the RLV will be able to cut down the cost of transporting payloads to space by $500 or 35000 rupees per kilogram. That is nearly 1/10th of the current cost.
Currently no country in the world has a reusable spacecraft, since NASA’s space shuttle retired. Several governments and private organizations are working on their own reusable space program. If ISRO is successful with the RLV project, it will definitely put India at a very competitive place on the Space Race..