Human beings have been launching spacecraft since World War 2. Rocketry, in principle has not changed much from the early days of rocketry in ancient China to Von Braun who invented the worlds first rockets like the V-2 capable of sub-orbital flight and atmospheric reentry. Chemical rockets are rather simple in concept. A generally explosive fuel + oxidizer mixture forms the propellant, which is burnt in a controlled fashion in a reaction chamber. The hot gases exit a nozzle providing a large amount of thrust to the rocket.
Since then we’ve done several fancy things to a rocket. We’ve put a space capsule on the top, making it possible for man to travel out of earth’s orbit. We’ve attached airplanes to the rocket body which we lovingly knew as a space shuttle. Space shuttles were not a NASA creation alone. The Soviet Union created its own version of the space shuttle called ‘Buran’. Buran completed one unmanned spaceflight in 1988 which was an unmanned test flight. The program ended shortly due to budget cuts arising from the collapse of the Soviet Union. NASA’s space shuttle programme was however the successful and ambitious effort in human spaceflight till date.
NASA’s Space Shuttle Atlantis
The space shuttle was a a marvelous piece of engineering. Not only it put humans in orbit. It also had a massive payload capacity. Powered by two giant solid booster rockets and cyogenic engines, the shuttle could lift a total payload mass of 27 tonnes to low earth orbit. The shuttle programme also pushed the frontiers of spacecraft reentry technology. The shuttle on atmospheric reentry slams into the atmosphere at a speed in excess of Mach 25. For the new reader thats 25 times the speed of sound or 8.7 Km/s. Normally for small objects, the reentry shield is a carbon-ablative material. Ablative materials were used by early spacecraft like Apollo and Gemini programmes. They are also used in ballistic missile payloads. In simple talk these are shields made out of carbon. As the material heats up, it slowly burns off, keeping the payload relatively cool. However these things are difficult to fabricate for larger objects. Another problem with the ablation system was that once the temperature fell in a zone where shielding was needed but low enough to prevent the ablation, they would cease to function making them somewhat unreliable.
The space shuttle introduced a different type of heat shielding. This strategy is called “thermal soak”, where the shield has an enormous capacity to trap heat. You could heat the substance to over a 1000 degrees in one end, and still hold it with your fingers at the other
Super Insulators like this ceramic cube is red hot inside, but cool enough to be lifted by bare hands
This strategy is wildly popular and used by all space programs. However there have been issues with tiles in how they are integrated onto the spacecraft. The ceramics are usually brittle and many times have caused serious problems. The Columbia space shuttle disaster in 2003 is a typical example where a piece of insulating foam from the main external tank hit the leading edge of the shuttle’s wing, destroying some of the tiles. This was enough to cause the orbiter to burn up during atmospheric reentry and instantly kill the crew. Losing a few tiles had been a common occurrence on previous shuttle missions too, the risk associated with losing this critical thermal protection was well known too. However since then NASA has taken a lot of measures to ensure that such accidents would not happen on future missions.
In recent years, space programs have had to face major budgetary cuts all over the world. NASA’s budget fell from 1% of US GDP to approximately 0.5% of the GDP. For comparison this number was about 4.4% at the peak of the Cold War. The Russian space program has also seen similar cuts for a variety of reasons, both political and economical. In times of financial crisis governments usually trim funding for space programs. For mankind’s space ambition to survive, it could no longer afford to be a drain on large amounts of cash. So a concept of reusable launch vehicles was conceived. Bulk of the spaceflight industry comprises of launch systems that put satellites in orbit. It made sense, if we could find a way to do it cheaper and faster.
RLV technology is not that novel. The US operates unmanned spacecraft routinely. The X-37 is a reusable unmanned spacecraft that is boosted into orbit by chemical rockets, but lands back on the ground like a conventional plane.
One of the biggest pioneers of reusable technology is South African capitalist, Elon Musk’s SpaceX Corporation. SpaceX has been able to make significant strides in space technology in a rather small amount of time. In the man’s own words
“If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred. A fully reusable vehicle has never been done before. That really is the fundamental breakthrough needed to revolutionize access to space”
This is no longer science fiction. In April 2016, the first stage of a Falcon-9 spacecraft landed safely on an offshore barge. This was after one year of hard work and four other failed attempts. I put this video below, and I must admit, it is pretty darn cool. According to SpaceX lot of work still needs to be done to make this technology reliable, but there is no doubt that it is a game changer in the space industry.
Recently India has also been working on a RLV program. Earlier it was code named “AVATAR” which was a RLV concept that used scramjet propulsion. AVATAR stood for “Aerobic Vehicle for Transatmospheric Hypersonic Aerospace TrAnspoRtation”. Since then it has evolved into what is now called the RLV-TD project. ISRO has staged its RLV program in small steps. The first of this was the HEX or Hypersonic Flight Experiment was performed earlier this month in 2016. The experiement was designed to validate flight performance of the spaceplane at Mach 6. The plane itself was boosted into Mach 6 speed by a sounding rocket booster and had no propulsion. In the future flights, it will feature a scramjet engine. The hope is that ISRO’s RLV will be used to deploy small satellites into LEO and return back to earth