ISRO: The shape of rockets to come

ISRO: The shape of rockets to come

Subject: Science and technology

Section: Space technology

Context:

• With seven straight successful launches so far, the LVM­3 rocket — which most recently ferried  the 3.9­-tonne Chandrayaan-­3 spacecraft to the drop­off point 180 km above earth — has proved to be a reliable one.

Details:

• Now ISRO is working on upgrading it to carry 6­ tonne payloads right up to the geostationary transfer orbits (GTO).
• ISRO is working on a bunch of rocket technologies. Here is a quick look at a few of them.

Air-breathing rockets:

• These rockets  have scramjet engines that can accelerate by themselves mid flight through the atmosphere, conserving chemical fuels for later use.
• ‘Scramjet’, or supersonic ram jets, have funnel ­like openings, with the mouth of the funnel facing the direction of flight.
• During flight, air enters the funnels at high speeds and becomes compressed as it passes through the thin end of the funnel.
• The compressed air is fed into the combustion chamber, where it meets the vaporise fuel (as in an automobile engine) and self ignites.
• This creates a thrust. In a ramjet, air is fed into the combustion chamber at speeds less than the speed of sound (subsonic); in a scramjet, it happens at supersonic speeds.
• Ramjets and scramjets are commonplace in missile technology.
• India’s Brahmos missile has ramjets; a supersonic variant has a scramjet engine.
• However, scramjets have not been successfully used in rockets, which travel not at supersonic speeds (Mach 1.2­5) but at hypersonic speeds (above Mach 5).
  • One Mach is the speed of sound, roughly 1,225 km per hour.
• Some years ago, ISRO successfully tested an air breathing engine on a sounding rocket, but  is now working on a bigger engine (called air frame integrated air breathing engine) that can sustain for longer durations in flights.
• The engine is under manufacture for testing, but ISRO is already in talks with  industry for producing the rockets.

LOx methane engines:

• Methane engines are taking rocketry to the next level.
• The advantages are:
  • Liquid methane — essentially LNG — is not as potent a fuel as hydrogen. But the temperature at which it is stored in rocket tanks is much higher than in the case of hydrogen —  minus­161 degrees C versus minus­253 degrees C.
  • It does not leak — methane molecules are  much bigger  than hydrogen. And, methane is a lot cheaper and abundantly available.
  • So every space company is eyeing methane rockets, or rather liquid oxygen­methane (LOx) — because you need an oxidiser to burn methane.
• The liquid methane rockets are not commonplace yet, because a few challenges remain unresolved.
  • One is the problem of ‘coking’, or ‘soot deposition’. As the gas approaches the combustion chamber, some of it splits into carbon and hydrogen, and the carbon gets deposited as soot on the insides of the tubes, leading to a host of problems such as combustion instability.
    • Solutions considered include use of soot resistant materials such as ceramics, and  specially designed additives for the fuel to cut soot.
  • Further, industry must be made aware of this technology to inspire confidence and attract investment for manufacturing.
• The first to deploy a methane engine in a space flight was  the Chinese company Landscape, with its  Zhuque­2 rocket.

HAVA — India’s space shuttle:

• ISRO is working on a space shuttle — a vehicle that can deliver payloads to orbit.
• Called HAVA, for hypersonic air­breathing vehicle assembly, it can deliver payloads up to 500 kg to low earth orbit.
• Based on the ‘re­usable launch vehicle’ technology the HAVA is like a space shuttle; it will fly on the back of a ‘geosynchronous satellite launch vehicle’ or GSLV, deliver the payload, and return to land on an airstrip, like an aeroplane.
• A prototype is expected to be ready for testing in a couple of years.
• There are several other technologies, too, that ISRO is working on, such as:
  • Vertical take­off and landing (V­TOL),
  • Electric propulsion,
  • Nuclear propulsion,
  • Additive manufacturing in space, and
  • Research into functional materials.