T he history of transportation teaches us that the country that excels in transportation does well economically, in national security and in exploration. So, h ow is leadership in Earth to low Earth orbit (LEO) transportation assured? What is necessary as the foundation to expand space frontier beyond LEO?

Humans could land again on the Moon before 2020. Space entrepreneurs could provide transportation capabilities to LEO and develop space tourism within the next 12-14 years.

Two-stage-to-orbit (TSTO) launch vehicles with rocket engines on both stages could provide by 2020 some degree of operationally responsive space lift. If it were developed, it would be without all-azimuth launch capability and with partial reusability.

Such space transportation systems developed with a combination of existing and evolved technologies will neither assure leadership in Earth-to-LEO transportation nor change the space-transportation paradigm.

In addition to evolved technologies, we need revolutionary technologies. Innovations, including revolutions in propulsion, are necessary to achieve and maintain the leadership. Revolutionary propulsion systems are necessary to provide a change in transportation paradigm.

Instead of the Earth-orbit rendezvous technique mode, the Moon-lunar-orbit rendezvous technique mode was chosen for Apollo missions to the Moon to reduce development time and program cost. Initially, the space shuttle was designed as a reusable system. However, a semi-reusable system was built to reduce development cost.

Time and money constraints are again in the works as we prepare to send humans back to the Moon.

The vision for space access should be to make most space launches almost as remarkable as an airplane taking off from a runway. Low-Earth orbits must be accessible, affordable, reliable, safe and on-demand because that capability is essential for leadership. “Accessible” (easy to enter or reach) space is also “assured” (guaranteed) space access.

A combination of evolved and revolutionary technologies would lead to Earth-to-LEO transportation systems that would be affordable and reliable for exploration, security and commerce; safe for humans and critical cargo; and operationally responsive for security and emergency human spaceflights.

The most pressing need is to reduce the cost by a factor of 10 to transport from Earth to LEO payloads, ranging in weight from a couple thousand to a few tens of thousands of pounds. Operationally responsive spacelift requires cost-effective, reliable, quick and assured access to space.

A revolutionary in-space propulsion system is a prime necessity to significantly reduce travel times achievable with chemical rocket propulsion for human missions to Mars.

A paradigm change in space transportation can be made only if existing chemical rocket engines are replaced by revolutionary modes of propulsion. Air-breathing propulsion and nuclear-thermal propulsion are revolutionary modes of propulsion for hypersonic flight in Earth’s atmosphere and for human missions to Mars, respectively.

The U.S. investments in Earth-to-orbit innovative launch technologies, including revolutionary propulsion technologies, and in in-space revolutionary propulsion technologies for human missions to Mars have decreased to the point of being irrelevant.

Space entrepreneurs cannot develop revolutionary propulsion systems and demonstrate them in space transportation systems without a substantial external assistance. Without substantial investments to develop innovative space access technologies, the U.S. launch technology base will eventually become obsolete. Sustained long-term investments in other countries will lead to foreign innovative space access technologies.

Konstantin Tsiolkovskiy, Hermann Oberth, Robert Goddard and Max Valier advocated the development of hypersonic vehicles before the arrival of the early modern airplane in the 1930s. Extraordinary accomplishments such as ICBM warheads, the X-15, Apollo spacecraft and the s pace shuttle were achieved since the early 1950s.

Hypersonic flight is still not exploited to the extent subsonic and supersonic flights are.

A reusable TSTO vehicle with air-breathing engines on the first stage and rocket engines on the second stage would be a revolutionary launch system. More than 40 years ago, this vehicle concept was the preferred first generation launch vehicle.

The key near-term goal should be to develop technologies leading to an experimental vehicle and test this vehicle across a wide flight envelope. A flight research program a la X-15 with air-breathing propulsion from Mach 0 to 7 should be conducted.

For leadership in Earth-to-LEO transportation, revolutionary propulsion systems and reusable launch vehicles for transportation to LEO are required. To make progress in space transportation, a change in transportation paradigm is required.

By 2025, low Earth orbits should be readily accessible. That is the necessary foundation for exploration beyond LEO. Revolutionary propulsion modes and reusable vehicles would open up space beyond imagination.

Will and leadership are required to achieve leadership in Earth-to-LEO transportation. It will take persons such as Gen. Bernard Shriever, Adm. Hyman Rickover, Wernher von Braun and Kelly Johnson to make space accessible and to expand space frontier beyond LEO.

B. Mehta is an associate fellow of the American Institute of Aeronautics and Astronautics.