under development is not tied too closely to a specific mission or destination. EDL technologies that enable the broadest spectrum of future missions by accommodating the widest range of variations in destination and timing would be of particular value. This is reflected in the broad set of six top technical challenges and the discussion of generic reference missions that follows. The top technical challenges defined by the panel are listed below in priority order. The first four challenges would make EDL systems more technically capable, the fifth challenge would make them safer and more reliable, and the sixth challenge would make them more affordable.

1. Mass to Surface: Develop the ability to deliver more payload to the destination.

NASA’s future missions will require ever greater mass delivery capability in order to place scientifically significant instrument packages on distant bodies of interest, to facilitate sample returns from bodies of interest, and to enable human exploration of Mars. For a given launch system and trajectory design, the maximum mass that can be delivered to an entry interface is fixed. Hence, increasing the mass delivered to the surface (or other destination, such as a planetary orbit or a mobile flight platform) will require reductions in spacecraft structural mass; more efficient, lighter thermal protection systems; more efficient, lighter propulsion systems; and/or lighter, more efficient deceleration systems. In a sense, increasing mass delivery to a planet surface is “the name of the game” for EDL technology because it may enable missions that are presently impossible (such as a human Mars landing) and/or provide enhancements such as more sophisticated science investigations and sample return capability for currently planned missions.

2. Surface Access: Increase the ability to land at a variety of planetary locales and at a variety of times.

Ideally, any exploration mission would have the ability to land at a variety of locales, including those at higher latitudes or elevations that may be difficult to access, at whatever time best satisfies other mission requirements and goals. Access to specific sites can be achieved by landing at one or more specific locations or by transiting (e.g., via a rover) from a single designated landing location to other locations of interest. However, it is not currently feasible to transit long distances and through extremely rugged terrain on Mars. In addition, improving the robustness of entry systems to better withstand a variety of environmental conditions (atmospheric winds, solar incident angle, etc.) could aid in reaching more varied landing sites. Alternatively, uncertainties in the entry environment could be better dealt with if the entry vehicle first went into orbit. Increased surface access could be achieved by tailoring the mission entry (i.e., the ability to control the inclination of entry and/or cross range capability during entry). Systems that have higher lift-to-drag ratios are an area for potential investigation in improving surface access on exploration destinations, such as Mars, that have a significant atmosphere.

3. Precision Landing: Increase the ability to land space vehicles more precisely.

A precision landing capability allows a vehicle to land closer to a specific, predetermined position in order to assure that the vehicle lands safely (without damage to itself or other personnel that may already be on the surface), or in order to meet other operational or science objectives. The level of precision (e.g., 1000 m, 100 m, etc.) that is achievable at touchdown is a function of the design of the guidance, navigation, and control (GN&C) system, the control authority of the vehicle, and the entry environment. Precision landings require accurate GN&C performance throughout the entire descent and landing phases. This requires accurate control of vehicle position, velocity, attitude, and other vehicle states (Paschall et al., 2008).

4. Surface Hazard Detection and Avoidance: Increase the robustness of landing systems to surface hazards.

The surface hazards associated with exploration destinations remain uncertain to some degree until the site has been visited. Relying on passive systems alone to characterize a landing site can be problematic, as was evident during the Apollo Program, where each of the six landing missions faced potentially mission-ending hazards at the



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