Getting to Space Cheaply

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Getting to Space Cheaply

It costs a lot to get to space—in 2001 it cost as much to put something in low Earth orbit ($22,000 per kilogram [$10,000 per pound]) as it did in 1957. Anyone who wants to do things in space (e.g., such as experimenters and scientists) has a cost hurdle to overcome that is not encountered in any other area of human endeavor.

Low Earth orbit (LEO) is a few hundreds miles up. To get to LEO, it takes 30,000 feet per second of velocity change; the total energy needed to get to the Moon is about 45,000 feet per second. LEO is therefore two-thirds of the way to the Moon.

Two factors make the step from Earth to LEO hard. First is Earth's atmosphere, which causes drag and aerodynamic heating . Second is the gravity gradient, or the change in the force of gravity as one moves away from Earth. The force of gravity declines inversely as the square of the distance from Earth, meaning that the farther away one gets from Earth, the easier it is to overcome the force of gravity. As a result, it is harder to get from Earth to LEO than from LEO to almost anywhere else in the solar system.

Expendable Launch Vehicles and Single-Stage-to-Orbit Reusable Rockets

Throughout the twentieth century, getting to space was accomplished almost exclusively with expendable launch vehicles (ELVs)—rockets that are used once and then discarded in the process of putting their payloads into orbit. ELVs are inherently incapable of providing cheap access to space for the same rationale that throwing away an automobile after each use is also not economical. Nevertheless, ELVs are here for the foreseeable future (i.e., the early twenty-first century).

As of February 2002, every rocket used to place payloads into orbit has used multiple parts, or stages. Each stage is itself a working rocket. One or more stages are discarded and dropped off as the vehicle ascends, with each discard eliminating mass, enabling what is left over to make orbit.

However, a single-stage-to-orbit (SSTO) reusable rocket would probably be the best technical solution to inexpensively get to LEO. Even when all parts of a multistage rocket are reused, the rocket still needs to be put back together again. An SSTO rocket would not have to be reassembled, reducing the number of people required for operations.

Unfortunately, it is hard to get to LEO without staging. To get to LEO with a single stage, a rocket has to be 90 percent fuel, leaving only 10 percent for everything else. Such a rocket has proven difficult in practice to build, leading to the continued use of multistage rockets.

In 1994 the National Aeronautics and Space Administration (NASA) decided to develop technologies to lead to a reusable launch vehicle (RLV) with a single-stage rocket. Its major step toward this goal was the $1.4 billion X-33 program, which aimed to fly a vehicle to demonstrate some of these technologies. Like many X-vehicle programs before it, the X-33 encountered severe technical difficulties as well as budget overruns and schedule delays. As a result, NASA terminated the X-33 program in early 2001.

NASA is also planning to investigate technical paths to SSTO other than conventional rockets. All involve air-assisted propulsion, such as ramjets, supersonic combustion ramjets ("scramjets"), or liquid air cycle rockets, and all lie in the future.

The Marketplace

There is only one commercial space market: geostationary communications satellites, a market that has had dependable growth for decades. There are several possible new markets, such as remote sensing and space tourism. Remote sensing is the act of observing from orbit what may be seen or sensed below on Earth. But remote sensing requires only a few additional launches a year. Another possible new market, LEO communications satellite constellations, was halted by the business failure of Iridium, the first such system.^* Without new markets there are no business needs for anything but ELVs and no incentives to develop new launch systems to get payloads to space cheaply.

ELVs available at the beginning of the twenty-first century include the two EELV ("Evolved ELV") families paid for by the U.S. Air Force: the Atlas V and Delta IV. Still available for purchase are the Delta II and III, as well as the Atlas II and III ELVs, and the Boeing SeaLaunch ELV, a converted Zenit rocket launched from a ship at sea. There is also the market leader, the French Ariane 4 and 5 ELV family. The Russian Proton and Rokot ELVs are also available, as are the Chinese Long March families of throwaway boosters.

New Beginnings

Kistler Aerospace is designing and building a two-stage-to-orbit RLV. The company will need investments of $200 million to $400 million above the $500 million already spent to achieve a first flight in 2002 or 2003. There are also small company start-ups such as Kelly Space and Technology and Pioneer Rocketplane, which are involved in developing technologies to get to space cheaply. Kelly wants to develop the Astroliner, a winged rocket towed into the air by a 747 jet and released at altitude to soar on a suborbital trajectory under its own power. At the high point of its trajectory, an upper stage is released and injected into LEO. The Astroliner descends and then lands using onboard jet engines.

Pioneer Rocketplane also has an airplane-like RLV it wants to develop, the Pathfinder, which would take off using jet engines. Once at altitude the Pathfinder meets a tanker carrying liquid oxygen, which air-to-air refuels the Pathfinder's liquid oxygen tanks, which are empty at takeoff. After the Pathfinder and the tanker disconnect, the Pathfinder's rocket engines fire, putting it in a suborbital trajectory. At its high point, an upper stage is released and injected into LEO. The Pathfinder descends and then lands using its jet engines.

Space Access LLP will need $5 billion to get to first flight. The company's SA-1 winged vehicle is designed to take off using an ejector ramjet—a ramjet that can also convert to function as a "pure" rocket engine. Once at higher altitude and speed, the vehicle would switch to rocket propulsion and exit the atmosphere where, at the high point of its trajectory, an upper stage would be released and be injected into LEO. This particular upper stage would descend and land for reuse using rocket propulsion to de-orbit, space shuttle-style heat shield tiles, and a parachute. In the meantime, the main SA-1 vehicle would descend and land using its onboard ramjets.

Both the Astroliner and the Pathfinder will need about $300 million to get to first flight. But all of the small RLV companies have had incomes of only a few million dollars a year, and while most of them manage to stay in business, none have yet been able to obtain sufficient funding to begin full development. (A few have small NASA study contracts.) Several other RLV start-ups, such as Rotary Rocket, have failed to obtain sufficient funding and have been forced out of business. The problem is that as of the early twenty-first century, all of the RLV start-up firms have been able to obtain funding only from "angels"—investors who are personally interested in the project. It is only the large established aerospace companies (e.g., Boeing, Lockheed Martin, Orbital Sciences) that manage to secure significant amounts of funding.

see also Launch Industry (volume 1); Launch Vehicles, Expendable (volume 1); Launch Vehicles, Reusable (volume 1); Reusable Launch Vehicles (volume 4); Spaceports (volume 1).

Timothy B. Kyger