Getting to space and back.

Overcoming gravity is the main challenge in getting to space.To go into orbit the craft has to reach a speed of 11 km per sec / 39600 km per hour / Mach 26 (!).

The fastest rocket aeroplane, the X-15 managed Mach 6.6.(This high speed got it to fly higher than 80 km,making it's pilots astronauts).The Concorde flies at Mach 2.0 .

While coming back,a spaceplane faces problems opposite to those of getting into space.It must lose speed instead of gaining it.

The U.S. Space Shuttle Orbiter enters the atmosphere at speeds greater than 25,800 km/h.The friction due to the air raises the temperature of the wings to 1500 degrees C.The shuttle finally touches down at speeds of 320 km/h.

Today, aerospace scientists even in NASA are looking to make space travel cheaper, safer and regular. Hence the push in development of SCRAMJETs, Pulse Detonation engines, Magnetic Levitation etc. Infact, there is a host of such research that is nearing completion or actual testing. Some already exist for even decades, only now are we putting them to actual use. Together their success will make routine access to space possible.

There many ways to reach and come back from space.Let's take each one of them separately:

Vertical Vs Horizontal Take-off ,single stage

Ever wondered why all present-day rockets take-off verticaly? It's because it is the easiest and cheapest way to do it with current technology. A vertical launch means that all energy is used to go in one direction : upwards while in a horizontal launch most energy is used to drive the craft forward . An aeroplane generates lift mostly by it's wings. It uses the power of the engines to go faster and thus generating more lift. But wings have no use in space where there is no air.

Thus we see that vertical launch has been prefered for space travel since it maximizes usage of rocket power available. Though horizontal launch can also be used,the technology needed to go in orbit has not been developed. Most of the current proposals can manage only sub-orbit. Also, wings increase the surface area dramaticaly but add very little to the volume and hence cannot store much fuel.

Another important concern is that the wings heat up excessively during launch and reentry. This is one of the more challenging problems facing designers.

Vertical Vs Horizontal Landing

During re-entry a spacecraft has to slow down considerably. A vertical landing will mean that it has to land under rocket power which needs fuel. This is a major shortcoming of vertical landing : it cannot use the the atmosphere alone to slow down. Parachutes and parasails can be used but they are good only for small capsules like those of Mercury, Apollo, future X-38 missions and X-Prize contestants. A large vehicle cannot do with them alone. Starchaser's Thunderbird hopes to solve this problem by splitting up into two parts, each brought down separately by parachutes.

Horizonatal landing means using wings(or lifting bodies) to land. This technique effectively utilises the atmosphere and has been in use in the U.S. Space Shuttle since 1981. But unpowered horizontal landing is also dangerous , but then they have been doing it for decades now.

So we see that in most respects horizonatal landing is better than a vertical one if one wants to use current technology. However,this is not to say vertical landing is not possible. Each technique has it's own set of problems.

The Roton is one gem of a solution to the problems of vertical landing. It lands verticaly,but it still has wings. But this case they are not fixed. This is the essence of a chopper concept : instead of moving the whole body to generate lift,just move the wings.

Vertical Take Off and Landing-Single Stage To Orbit (VTOL-SSTO)

One advantage of VTOL is it can be structurally simple(no wings and tails). Spherical and simple it can have a large volume. Such proposals have been their for decades,but have not been tried out untill recently.

One future problem may be that it may not be easy to transport large (more than 50) number of people as aerospace planes designed for superfast travel between continents. After all,people may have difficulty in adjusting to a flight which is more like a roller coaster!

PS : Remember that all manned space missions (except for Shuttle ones) have been VTOL. Hence the words "single stage to orbit" are significant.

Safety

This is an important issue a spacecraft has to address. Both VTOL and HTOL concepts have their own noisy supporters,each claiming to be safer than the other.But it is probably safe to say that a HTOL craft has an edge over VTOL in this respect. No pun intended!

Horizontal Take Off and Landing -2 Stage To Orbit ( HTOL-2STO )

Since current technology does not allow us to build HTOL-SSTO craft,many ideas have taken the 2STO route which is the most tried and thoroughly trusted way( the X-15 remember?).

Such an approach has been taken by Kelly Space Technology. Their winged spaceplane Eclipse will take off horizontally, fully fuelled but unpowered, being towed behind another aircraft. In this way they too can get to high altitude before they have to use any of their propellants.

1.5STO is the approach by the Pioneer Rocketplane team. A vehicle takes off from a runway with almost empty LOX propellant tanks. Then it refuels in mid-air, using technology that's been used for decades by Air Forces. It thereby gets to "launch" fully fuelled at high altitude, neatly getting round the impossibility of HTOL SSTO.

For further detail on this technique, see the HTOL-TSTO Technology page . It also has discussions on aircraft that would perform the crucial role as the first stage (An-225, Tu-160, B-52 and more).

Vertical Take Off Horizontal Landing(VTOHL)

One would like to combine best of both worlds by using a VTOHL design. But it is not so easy.The U.S.Space Shuttle uses this approach but it is not a single stage vehicle. In a VTOL vehicle the loads are basically along the vehicle from bottom to top. In a HTOL vehicle they are mainly across the vehicle like an aeroplane. But a VTOHL has to support stresses both along and across the vehicle - so it's heavier. Lockheed's Venture Star,the successor to the current shuttle will have a VTOHL-SSTO operation.

Why Superman has a flying body:

Lockheed Martin's Skunkworks hope to solve the problems associated with VTOHL by doing away with the wings. Instead of using only the wings to fly the Venture Star's main body itself will generate the lift. Somewhat opposite to the "Flying Wing" (as seen in B-2 Stealth Bomber and some old designs) the "Lifting Body" will replace the wings and also provide lots of storage space.

See the lifting body artitcle .