No abstract

The space propulsion industry and, indeed, the overall space transportation industry in the United States have been in decline since the first human landing on the moon in 1969. The hoped-for reversal to this decline through the space shuttle and space station programs never really materialized. From an 80% market share in the late 1970s, the U.S. share of the world launch market fell to 20% by 2002. During that period, only two new booster engines have been developed and flight certified in this country. Only limited progress has been made in reducing engine costs or increasing performance although these factors are not necessarily directly related. Upper-stage and in-space propulsion in the United States have not fared much better in the world market. On the other hand, space-faring nations in Europe, the Middle East, Asia, and the former Soviet Union are believed to have developed 40-50 new, high-performance engines over the same period. This trend will have to be reversed to enable future exploration missions. The intent of this paper is to summarize past propulsion-system development, assess the current status of U.S. space propulsion, survey future options, evaluate potential impact of ultra low-cost, small launch-vehicle programs, and discuss some future propulsion needs for space exploration.

The FALCON ((Force Application and Launch from CONUS) program is a technology demonstration effort with three major components: a Small Launch Vehicle (SLV), a Common Aero Vehicle (CAV), and a Hypersonic Cruise Vehicle (HCV). Sponsored by DARPA and executed jointly by the United States Air Force and DARPA with NASA participation, the objectives are to develop and demonstrate technologies that will enable both near-term and far-term capability to execute time-critical, global reach missions. The focus of this paper is on the SLV as it relates to small satellites and the implications of lower cost to orbit for small satellites. The target recurring cost for placing 1000 pounds payloads into a circular reference orbit of 28.5 degrees at 100 nautical miles is $5,000,000 per launch. This includes range costs but not the payload or payload integration costs. In addition to the nominal 1000 pounds to LEO, FALCON is seeking delivery of a range of orbital payloads from 220 pounds to 2200 pounds to the reference orbit. Once placed on 'alert' status, the SLV must be capable of launch within 24 hours.

A never-ending major goal for the Space Shuttle program is to continually improve flight safety, as long as this launch system remains in operational service. One of the options to improve system safety and to enhance vehicle performance as well, that has been seriously studied over the past several decades, is to replace the existing strap-on four segment solid rocket boosters (SRB's) with more capable units. A number of booster upgrade options have been studied in some detail, ranging from five segment solids through hybrids and a wide variety of liquid strap-ons (both pressure and pump fed with various propellants); all the way to a completely reusable liquid fly back booster (complete with air breathing engines for controlled landing and return). All of these possibilities appear to offer improvements in varying degrees; and each has their strengths and weaknesses from both programmatic and technical points of view. The most beneficial booster upgrade/design, if the shuttle program were to continue long enough to justify the required investment, would be an approach that greatly increased both vehicle and crew safety. This would be accomplished by increasing the minimum range/minimum altitude envelope that would readily allow abort to orbit (ATO), possibly even to zero/zero, and possibly reduce or eliminate the Return to Launch Site (RTLS) and even the Trans Atlantic Landing (TAL) abort mode requirements. This paper will briefly survey and discuss all of the various booster upgrade options studied previously, and compare their relative attributes. The survey will explicitly discuss, in summary comparative form, options that include: five segment solids; several hybrid possibilities; pressure and/or pump-fed liquids using either LO2/kerosene, H20/kerosene and LOz/Jz, any of which could be either fully expendable, partly or fully reusable; and finally a fully reusable liquid fly back booster system, with a number of propellant and propulsion system options. Performance and configuration comparison illustrations and tables will be included to provide a comprehensive survey for the paper.