This chapter deals with Earth to Orbit (ETO) transportation and the infrastructures required in Low Earth Orbit (LEO) to support the selected space exploration missions.

Types of Launchers

Current expandable launchers are based on the same approach as those developed over half a century ago by space pioneers like Konstantin Tsiolkovsky, Robert Goddard, Hermann Oberth, and Wernher Von Braun. These operational launchers can be split into three categories:

• Small launchers that can put up to two tons into LEO. Athena, Rockot, and the future Vega are some representative examples of this category.
   
• Medium launchers that are adapted both to LEO and geostationary transfer orbit (GTO) services. Payload capacity ranges from two tons up to 10 tons into LEO, and from one ton up to five tons into GTO. Ariane 4, Delta, Soyuz, and H-2 are examples of medium launchers.
   
• Heavy launch vehicles with payload capacity ranging from 10 tons up to 30 tons into LEO and from 5 tons up to 10 tons into GTO. The Space Shuttle, Ariane 5, Titan IV, and the future Heavy EELV fall within this category.

Payload Capacity Needs

Human space exploration requires high performance launches into LEO, both in terms of payload mass and the available volume under the fairing. Several preliminary mission designs were performed over the last ten years, providing valuable data to assess the needs for ETO transportation systems. Demand in terms of single launches was shown to be outside of current capabilities as shown in Table 2-1 Within each of these projects, the demands result from a compromise between limiting ETO launcher performance and limiting rendezvous and assembling in orbit.

Project - Mission	Payload Mass Demand (tons)
90 day study - Moon mission	60-100 tons (A. Cohen, 1989)
90 day study - Mars mission	140 tons
Synthesis group on America's space exploration	150 - 250 tons (T.P. Stafford, 1991)
Alternative infrastructure study from General Dynamics	98 - 150 tons (General Dynamics, 1993)
NASA Mars reference human mission. Version 1.0	240 tons (S. Hoffman, 1997)
NASA Mars reference human mission. Version 3.0	80 tons

Heavy-Lift Launch Vehicles

Unfortunately, the most powerful launchers ever developed, the Saturn V and the Energia, are no longer operational. The Saturn V, used for the Apollo and Skylab missions, was able to put 120 tons into LEO (M. Wade, 1999). Energia, developed in the 1980s by the Soviet Union, only flew twice. Its maximum payload mass into LEO was 88 tons (M. Wade, 1999). NASA investigated several new versions of the Energia and the Saturn V, within the framework of the Mars reference mission, to meet the requirements of 240 tons into LEO. By using flight proven elements from these two launchers as well as the Space Shuttle system (such as external tank), launch configurations delivering from 180 tons up to 290 tons were proposed (Hoffman, 1997).

In the last version (3.0) of the NASA Mars reference mission (S. Hoffman, 1998), the ETO transportation system is composed of 4 Magnum launches for cargo delivery during the first opportunity and 2 Magnum launches in the 2014 opportunity with the piloted vehicle. The Magnum launch vehicle is designed for a 80 ton payload capability into LEO. The Magnum is an inline core vehicle (same diameter as the Shuttle External tank) with two attached Shuttle boosters (the aim is in particular to use the Shuttle launch facilities).

In the late 1980's, NASA engaged in studies--NLS for National Launch System--on heavy launch vehicles to meet the needs of the space station assembly. The most powerful version planned would have had the capacity of placing 45 tons into LEO (M. Wade, 1999).

In 1998, Aerospatiale considered the use of improved versions of Ariane 5 to perform Mars robotic and human missions (F. Bonnefond, 1998). A powerful version composed of an upgraded cryogenic core stage (250 tons of propellant and two Vulcains) and four solid rocket boosters--instead of two--was addressed.The LEO payload capacity was assessed at roughly 50 tons.

In the frame of his Mars direct proposal, R. Zubrin has suggested developing a new large booster of the Saturn V class, dubbed Ares, based on Space Shuttle main engines and two Shuttle solid rocket boosters (R. Zubrin, 1996).

All of these initiatives were not successful due to the large development schedule and predicted costs. Five to ten years, as well as a budget of ten billion dollars, are required to develop such systems. For instance, the NLS development was estimated at US $ 12 Billion and the recent Ariane 5 upper stage improvement program would cost about US $ 1.5 Billion. The revival of Saturn V is unanimously considered dead in the US. Nevertheless, as previously mentioned the Saturn V engines are often regarded as a good option to power new heavy lift launchers. In Russia, it is believed that Energia could be revived within the next 5 to 7 years for an estimated cost of between US $1.5 to 2 Billion. The cost of a Titan IV launch reaches more than US $ 200 Million whereas a Shuttle launch costs about US $ 450 Million. The recurrent cost of a renewed Energia was assessed to range from US $ 150 Million to US $240 Million (ESA, 1997).

For large-scale human exploration missions, heavy lift launchers remain mandatory. Considering past experience, the need for limiting both development and recurrent costs, the Energia option could be the most credible, provided that efforts will begin in no more than the next two years. Realistically, Russian skill and experience is waning far too quickly to expect a renewal of Energia after 2001. If this opportunity is missed, only American and/or European solutions can be considered for a development cost two or three times higher.

Expendable Launch Vehicles

The current expendable systems are expected to evolve significantly over the next decade. Main improvements will be mainly performance increases and a decrease of the specific cost, i.e. cost per kilogram into orbit. An average value of $ 6000 per kilogram into LEO can be considered for launchers such as Ariane 5 (Engstrom, 1998), the future US EELV, and HII-A.

A new approach is to move away from the performance-optimized high cost designs characteristic of many existing launch vehicles toward the use of a simple, robust design. This approach, advocated by programs such as Scorpius (J. Wertz, 1997), is based on low cost manufacturing processes by which one achieves low cost and high reliability at the expense of optimal performance. Reducing near term launch costs by a factor of 10 is presented as an acheivable objective (J. Wertz, 1997).

Reusable Launch Vehicles

For regular missions such as the regular supply of Moon settlements, systems other than heavy launchers have to be considered. For this purpose, reducing the cost of ETO transportation is essential to keeping the cost of human space exploration within acceptable limits.

Over the last twenty years, launch cost into low-Earth orbit (LEO) has remained relatively unchanged. The main reason is the technologies used to design and build the current launch systems are rather similar to those that were used thirty years ago. Currently one of the most promising vehicles for low cost launch is the reusable launch vehicle.

The strategy assumes that such a system will be available by the end of the next decade with a launch cost in the range of US $ 30-50 M (ref.: 20 tons into LEO). Several programs are underway:

• In the USA, Lockheed Martin, Boeing, OSC and NASA are regarding the technical and economical feasibility of various configurations
   
• In Europe, ESA has approved to undertaking of a new program devoted to reusable launchers. This program, so-called FLTP (Future Launcher Technology Program) will take place from late 1999 up to the end of 2002
   
• In Japan, current studies are underway to implement a Single-Stage-To-Orbit reusable launcher by the end of the next decade

All of these programs aim to develop cost effective launch systems that are much more cost-effective than today's, within a time frame of 10 to 15 years. The expected cost reduction ranges from one third to one tenth of present day budgets. Both public entities and private initiatives, and governmental agencies developing the needed technologies will likely finance these programs.

Transfer from LEO to Human Bases

Reusable systems pose a specific problem for human space exploration missions since current launch capabilities of payloads into LEO remain too small compared to what is required. Capabilities of no more than 20 or 25 tons to LEO can be expected over the next two decades. A dedicated system, which aims at performing multi-stage assembly, has to be developed. With the techniques of on-orbit rendezvous and docking being well mastered for several years, such an approach does not present significant risks, technologically and economically speaking.

Reusable transportation systems may also be used for LEO-planet transfer when regular missions are considered. For the purpose of our strategy, LEO-lunar transfer particularly has to be addressed. Multiple lunar settlements, both public and private, will require frequent and low-cost access to the Moon. In this case, we propose the use of a double reusable transportation system: from Earth to LEO and from LEO to lunar orbit and then to the Moon's surface. Figure 2-1 presents such scenarios as well as more common ones, i.e. when a single planetary mission is required.

Low-Earth Orbit Infrastructure

Considering availability of low-cost access to space, Low Earth Orbit will become a stepping stone for human exploration beyond the Earth since utilization of LEO will make it possible to prepare for long term space missions.

LEO Needs vs Strategy

Long term human exploration needs a tremendous amount of new technology, science, human adaptation and also public awareness. LEO can be used for each of these items. To prepare for future human exploration in space, it is proposed to build a permanent orbital fully autonomous facility in which necessary steps can be taken toward future missions.LEO can be used for:

• Storage and assembly

In order to minimize cost, assembly of large modules will be performed in LEO. This will require storage of large-scale modules for assembling elements of shuttle vehicles.

• Manufacturing

Manufacturing could be done in LEO. Plant modules will be installed in LEO to transform resources and produce materials. Here, not only large-scale elements but also specific space components like electronic chips, solar cells, plants, and medicine could be manufactured. In this way, private companies could invest in the plant module itself and its use. A new era for commercialization will start in LEO.

• Science and test laboratory

LEO is a unique place to perform scientific experiments. It is near the Earth, with microgravity and no atmosphere. Science in LEO will serve our strategy, as it will allow for the testing of new materials, to evaluate issues such as the effect of radiation, and impacting meteoroids.

Investigation of fundamental physics in areas such as astronomy and magnetospherical experiments is also foreseen. Biological experiments including, for example, effects to animals and plants based on exposure to radiation, can be used for preparing future human settlements on planets exposed to high radiation doses. Other experiments such as crystal growth studies, high purity materials production (vitrified ceramics, for example) are exclusively possible in space. High quality optical lenses can be easily realized in space. Applications of such could be for astronomical instruments in space and also on Earth. The effect of microgravity allows the manufacture of high stiffness materials. A challenge for future exploration will be to develop new materials which are able to protect against high and continuous radiation. In addition, private pharmaceutical companies have shown interest in producing medicine in space. This is consistent with our strategy, since long term human travel exploration or settlement will oblige the space colony to produce medicine self-sufficiently.

The high visibility of LEO programs will attract public interest by showing the direct application of new technology development. In this respect, science can be an important spin-off for private investment and application on Earth.

Means for Utilization in LEO

The cost effective way to perform all the LEO activities is to build a permanent unmanned orbital platform facility (OPF) which would be positioned at an orbit of 400 km like the current ISS but with a lower inclination between 18 to 28 degrees (to facilitate access to the Moon). This structure will be composed of a set of docking nodes where different modules can attach.

Extensive robotic technologies will have to be developed to deal with complex automatic functions and large scale elements of the structure. The technological challenges for building such a space facility are:

• Accurate orbital automatic procedures for large scale elements which can be fully autonomous or semi-autonomous
  
• Docking mechanisms
  
• Upgraded positioning systems for assembly of modules
  
• Sensors
  
• Robotic arms to manipulate and assemble large elements

Inspection of final assembly will require development of in-space survey equipment. As an example, the robotic camera developed for NASA, the AEROCAM camera, is intended for survey on the ISS.

In addition to heavy robotic tools for large-scale activities, small robotic functions will need to be developed for various tasks, e.g. experiment manipulation. Improvements to communications systems, such as larger bandwidth and extended capacity for data storage suggest that teleoperation will become more and more systematic. In this case, teleoperation, telepresence, and virtual reality systems will be used extensively. This would allow the scientists on the ground to follow in real-time the progress of their experiment and even to interact with it. Such interactive capability can be performed using master-slave robotic systems. As LEO is near the Earth, time delay is quite insignificant and such teleoperations can be done almost instantaneously.

During the ISU Summer Session Program '98 (SSP'98), a similar orbital facility was studied during the "Magic" design project. Although this project was different in focus, it confirms the convergence of ideas of the need for and interest in infrastructures in LEO.

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