IS HORIZONTAL LAUNCH ONLY A FLIGHT OF FANTASY, OR WILL THIS BECOME A REALITY?
Leaving a runway with an aircraft seems to offer the basic machine of an inclined plane to raise a weight to a given height. But there is a lot more involved than that simple mechanism. Let’s look at the basic mission and let you consider some of the many proposals that keep being revived.
MANY PROPOSALS PAST AND PRESENT
There have been government and military budget studies, private proposals, concepts: art and sales, evaluation and evolution. Both sides of the Cold war produced concepts that are still being used today. Private ideas appear on the cover of Popular Science, which many consider to be their death sentence. They still keep coming back after all these decades..
REALITIES: PHYSICS AND FINANCES
Space access is hard. The journey is extremely long and violent, and the cost is still prohibitive. Space and military costs dragged both sides of the Cold War into crippling debt. Let’s look at a layman’s oversimplification of the issues.
As a draftsman I like to see scale. If the earth is the size of a basketball, the moon is the size of a tennis ball, and it is across the room from you. The space station only flies about one inch above the basketball. Now we can appreciate how far Apollo 13 was from the nearest gas station when they had a blowout!
The International Space Station is orbiting about 230 miles above the earth. Other satellites, their altitude and speed is shown on this chart. You can see that we need to reach about 15,000 miles per hour and reach 230 miles up to get a decent orbit. Aerodynamic lift begins to struggle at 60,000 feet, or about 11 miles. Air breathing jet engines are starving for oxygen about then too. And jet speeds of 1,000 miles per hour or less are far short of orbital velocity. So why would we bother to use an airplane to make the smallest part of the journey?
Consider the alternative presently being used to launch rockets to space. The most sophisticated materials are assembled to save weight and high tech rocket engines provide immense power. One capsule like the Soyuz is our only way to the space station now. That little capsule sits on a multi stage rocket about 150 feet tall. The Saturn 5 moon rocket was about 360 feet tall. That was equal to some Navy destroyers. And all that lifts three or five men to orbit.
If we consider the cost to design and build such a huge sophisticated machine we might expect to get some good use out of it right? A navy destroyer may be in service for 20 years or more. An airplane designed in the 1930s like the DC-3 is still being used today. So how long does a space launch vehicle last? It lasts for only one flight.
All that expensive equipment in the booster stages is burned up on reentry into the atmosphere. If it didn’t burn up, it would be crashing into cities or ships at sea. What goes up comes down…hard. The capsule usually returns safely, but always damaged and rarely re-usable. For the Saturn 5 that translated in today’s dollars to $1.18 billion per flight. The senate is forcing NASA to build a similar “Space Launch System” for our future space system today. It will probably cost a lot more.
The space shuttle attempted to be reusable and provided valuable lessons for future designs. It came back to be refurbished for each new mission, an expensive process. That design recovered the solid boosters, also for expensive refurbishing. So engines and the orbiter were partially re-usable. It still killed our national budget.
We were paying to lift a crew and a payload in one giant space truck. That meant that safety procedures for human flight had to be applied to cargo that could fly with less expensive procedures. Costs could not be kept down. We may benefit from vehicles devoted to specialized duty with either crew or cargo service.
So why does a space airplane offer any help? Vertical launchers carry oxygen on board to feed the engines. That is heavy, and jets can breathe oxygen from the air for part of the flight. Wings do provide aerodynamic lift and that ramp to space is some help for the mission. If the first stage is an airplane, it may have that long service life that salvages the airframe and engines for many missions. Unlike the shuttle, these flyback boosters do not reach the extreme speed that require elaborate thermal protection. Their flight is only suborbital and reentry is at lower speeds. Thus wings deliver lift on ascent, lift for reentry, runway landings, and long service life.
If saving the booster is good, saving the orbiter should also be good. The shuttle proved that winged vehicles can return safely to a runway…if they are protected from booster malfunctions. No shuttle failure occurred due to an orbiter failure. We are still flying a winged orbiter called the X-37 and the Air Force seems quite happy with it. It has made multiple flights for long periods of time doing…whatever the Air Force won’t tell us about.
Another X plane has been purchased from NASA by the Sierra Nevada Corporation. This will be launched by a conventional rocket but return to a runway on wings. So orbiters are still candidates for reusable service. The alternative for wingless recovery is vertical landing, a difficult and possibly dangerous technique. At least an airplane may still glide back from a propulsion failure.
What else does aerodynamic launch offer? Rocket engines must be designed differently for low altitude operations. If they are launched at high altitude they may have a more optimum design for the higher ranges of the flight. An aircraft booster can fly down range to a unique location for special mission needs. Certain orbits are hard to make, and fixed launch facilities can’t be moved to fit the mission.
Vertical launch facilities are limited and cause scheduling backups. They are also vulnerable to sabotage. Recently a sniper took out part of an electrical power grid. What could one 50 caliber tracer round do for a liquid fuel rocket? Air launchers can be hidden in bunkers on secluded air strips in time of war.
Horizontal launch systems may offer the comfort and familiarity of conventional airlines for passengers. There may not be long waits for launch holds while strapped into a seat. And individual pressurized passenger “pods” could replace space suits so one could scratch an itch, or enjoy a snack in flight.
These potential advantages are the “carrots” that motivate designers to keep the dream alive. Some builders are already on the path to flying hardware. Some designs are more conservative but they will help build the market. The real visionaries are looking ahead to provide the optimum systems for these new markets. There will be trade studies to evaluate what really does and does not work. Stay tuned for a look at the next generation of space access.