Further Reading

For a not-too-technical introduction to the interstellar ramjet concept and its derivatives, consult E.F. Mallove and G.L. Matloff, The Starflight Handbook (Wiley, New York, 1989). A more recent, and more technical, ramjet review is in G.L. Matloff, Deep-Space Probes (Springer—Praxis, Chichester, UK, 2000).

The above references also describe the early history and physics of beamed-propulsion concepts. For more recent work on the experimental levitation of small payloads by microwave (maser) and laser beams, consult J. Benford and J. Benford, "Flight of Microwave-Driven Sails: Experiments and Applications,'' and L.N. Myrabo, "Brief History of the Lightcraft Technology Demonstrator (LTD) Project,'' which are published in Beamed Energy Propulsion, First International Conference on Beamed Energy Propulsion, Huntsville, AL, 2002, ed. A.V. Pakhomov, AIP Conference Proceedings, vol. 664 (American Institute of Physics, Melville, New York, 2003).

Trailing Ballute B#ii Aerospace

Hypercone Vertigo, inc

Clamped Ballute

Ball Aerospace

L/D Aeroshell NASA

Blunt Body Aeroshell NASA

Aerocapture: A braking maneuver using atmospheric drag to slow an interplanetary spacecraft and capture it into final orbit - using the natural environment of the destination instead of an on-board propulsion system.

Key disciplines for Aerocapture:

* Aerothermodynamics

* Atmospheric modeling

* Guidance, Navigation & Control

* Trajectory design & performance

* Aeroshell structures & materials

* Thermal Protection System materials/models

* Instrumentation

* Systems Engineering & Integration

Materials technology requirements:

* High temperature operation

* Low mass, high tensile strength

* High ultraviolet reflectivity & visable/irifrared emissMty

* Resistance to reactive planetary atmospheres

* Appropriate bonding & insulation materials

* Capable of compact stowage & deployment in space

* Resistance to space environment effects

Inflatable Aeroshell

Lodcfteed Martin

Hypercone Vertigo, inc

L/D Aeroshell NASA

Clamped Ballute

Ball Aerospace

Trailing Ballute B#ii Aerospace

Atmospheric drag slows the spacecraft, which must be protected from the atmospheric entry environment. Types of Aerocapture systems include:

• Rigid aeroshell

• Inflatable aeroshell

• Thin-film baflutes—combination balloon & parachute

Aerocapture can:

* Reduce fuel requirements by 20-30%

* Achieve orbit much faster than aerobraking

* Reduce trip time from Earth

Potential destinations enabled or enhanced by Aerocapture include:

Blunt Body Aeroshell NASA

Titan

[See also Plate II in the color section]

f'UVWG HY US3M AT

E iRA^E

The upper air hurst into life! And a hundred fire-flags sheen, To and fro they were hurried ahout! And to and fro, and in and out, The wan stars danced hetween.

Samuel Taylor Coleridge, from The Rime of the Ancient Mariner

FUTURE space explorers should consider a planet's atmosphere as a natural resource to be exploited to allow more affordable and capable space exploration. Planetary atmospheres provide a tremendous resource for explorers who want to minimize the amount of propulsion they must carry from the home planet and, potentially, reduce interplanetary trip times. By allowing a spacecraft to have a controlled entry into the upper atmosphere of a planet, the resulting friction with that atmosphere may replace costly and heavy fuel that would otherwise be used to slow the spacecraft as a means to decelerate and enter into orbit.

There are three ways the atmosphere of a planet may be used to offload propellant and provide a new capability for orbit capture or descent to the surface: aeroentry, aeroassist, or aerocapture. A fourth, aerogravity assist, might use the planet's atmosphere to increase the performance of the gravity-assist maneuver described in Chapter 4. Each has its own challenges, but they all share a common physics and may use very similar technologies. Not discussed here is the notion that the gases within the atmosphere might be extracted and used as fuel for a conventional rocket engine.

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