The Worldwide
Space Shuttle
Landing Network

While a worldwide network of approved landing sites existed throughout the Space Shuttle Program, only a small subset were actively considered for a given mission phase. Landing site priority was determined by Flight Rules, vehicle performance, mission objectives, and real-time operational conditions.

End-of-Mission (EOM) Landings

For nominal mission completion, the preferred landing site was always Kennedy Space Center (KSC). Returning the Orbiter directly to Florida minimized turnaround time, reduced ferry flight requirements, and simplified post-landing processing.

If weather or other constraints prevented a landing at KSC, the next preferred option was Edwards Air Force Base (EDW) in California. Edwards offered excellent weather reliability and extensive runway infrastructure, making it the primary backup landing site throughout the program.

Northrup Strip (NOR) at White Sands Space Harbor in New Mexico served as a tertiary option. NOR was generally considered only after multiple landing opportunities at KSC and EDW had been waived due to weather or operational concerns. Flight Rules typically favored NOR when consumables and mission timelines no longer supported additional landing attempts at the primary sites.

Although White Sands successfully hosted the landing of STS-3 in 1982, the fine gypsum dust encountered during post-landing operations proved highly invasive to Orbiter systems and processing activities. As a result, NOR remained an approved landing site but was rarely selected when KSC or EDW remained viable alternatives.

Transoceanic Abort Landing (TAL) and East Coast Abort Landing (ECAL)

For ascent abort scenarios, landing site selection was driven by the Shuttle's trajectory, launch azimuth, lighting conditions, weather, runway status, and support readiness.

Transoceanic Abort Landing (TAL) sites in Europe and Africa, along with East Coast Abort Landing (ECAL) sites in the eastern United States, were evaluated continuously during launch preparations. Flight controllers monitored real-time weather observations, forecasts, navigation system status, runway conditions, emergency services readiness, and communications capability to determine which sites were available for launch support.

Unlike End-of-Mission planning, TAL and ECAL priorities could change significantly on launch day as conditions evolved.

Primary Landing Site (PLS) and Emergency Landing Site (ELS) Selection

During each mission, Flight Dynamics Officers maintained a daily assessment of available landing opportunities around the world. These evaluations supported deorbit planning as well as contingency scenarios requiring an earlier-than-planned landing.

Primary Landing Sites (PLS) generally followed a preference order of KSC, EDW, and NOR, provided acceptable weather and operational conditions existed. When multiple opportunities were available, preference was typically given to a daylight (lit) CONUS landing opportunity. If no daylight opportunity existed at the preferred site, the next available continental United States opportunity might be selected instead.

When orbital geometry, weather, or mission constraints prevented a suitable CONUS landing opportunity, Flight Dynamics Officers evaluated approved Emergency Landing Sites (ELS) around the world. These assessments considered runway suitability, weather constraints, support capability, and the vehicle's ability to safely reach the site from the current orbit.

The daily selection process relied heavily on the Deorbit Opportunities Planning System (DOPS), which provided mission planners and flight controllers with the information necessary to evaluate landing opportunities and maintain a prioritized set of options throughout the mission.

While runway length, navigation capability, and support infrastructure were important factors in landing site selection, weather was often the single most critical constraint. A landing site that appeared ideal on paper could be removed from consideration immediately if weather conditions violated Shuttle Flight Rules.

The Spaceflight Meteorology Group (SMG), located at Johnson Space Center, provided continuous weather support for Shuttle missions. SMG meteorologists delivered regular weather briefings throughout a mission, coordinated closely with Flight Dynamics Officers (FDOs), and monitored conditions at landing sites around the world. During launch and landing operations, weather updates could occur multiple times as forecasts evolved and operational decisions approached.

Based on these forecasts, FDOs evaluated landing opportunities against established weather constraints and maintained a prioritized list of available sites. Site status information was transmitted to the crew through daily updates, including notifications when a landing site became unavailable due to weather, maintenance activities, airfield restrictions, political considerations, or other operational concerns. In the event of a communications failure, the crew carried procedures that allowed them to perform an emergency deorbit and independently select an appropriate landing site, although Mission Control support was always preferred whenever available.

Precipitation, Thunderstorms, and Cloud Constraints

The Space Shuttle was prohibited from landing in weather conditions that posed unacceptable risks to the vehicle or crew. Flight Rules established minimum separation requirements from precipitation, thunderstorms, and lightning-producing weather. Convective activity near the runway represented a particular concern due to the potential for wind shear, turbulence, reduced visibility, and electrical activity.

These constraints were evaluated continuously using weather observations, radar data, forecasts, and pilot reports. Even when conditions directly over the runway appeared acceptable, nearby weather systems could render a landing site unavailable if required separation criteria could not be maintained.

Space Shuttle Flight Rules - Thunderstorms, Lighting, and Precipitation Proximity

Surface Winds and Turbulence

Wind conditions were among the most heavily scrutinized factors in Shuttle landing operations. Unlike conventional aircraft, the Orbiter was an unpowered glider during the final phases of flight. Once committed to landing, there was no possibility of executing a go-around or applying additional thrust to compensate for adverse conditions.

As a result, crosswinds, tailwinds, gusts, and turbulence were monitored closely and often became the determining factor in site selection. A landing site with clear skies and excellent visibility could still be declared "no-go" if forecast winds exceeded allowable limits.

Space Shuttle Flight Rules - Surface Wind and Turbulence Limits

To support these evaluations, FDOs used several specialized analysis tools that incorporated forecast weather information into landing assessments. QuAC (Quick Analysis of Crosswinds) provided rapid calculations of runway-relative headwind, tailwind, and crosswind components based on the forecast wind conditions and planned runway selection. For more detailed evaluations, the Approach and Landing Processor (ALP) simulated the Orbiter's final approach and landing environment, including trajectory performance, lighting conditions, and potential sun-glare impacts on the flight deck windows.

Together, these analyses allowed flight controllers to determine not only whether a site met published weather criteria, but also whether the anticipated landing conditions would support a safe and controllable Orbiter approach. In many cases, wind constraints, not precipitation or cloud cover, proved to be the factor that ultimately removed a landing site from consideration.

Weather and runway conditions determined whether a landing site was operationally acceptable, but vehicle performance ultimately determined whether the Orbiter could reach the site at all. One of the most important measures used by Flight Dynamics Officers during landing site selection was crossrange, the lateral distance between the Orbiter's ground track and the desired landing site.

Crossrange capability varied from mission to mission and depended on numerous factors, including the specific Orbiter being flown, vehicle weight, orbital inclination, altitude, season, atmospheric conditions, and mission objectives. As a result, crossrange limits were calculated individually for each mission and provided to flight controllers through mission planning products and the Deorbit Opportunities Planning System (DOPS).

Dispersed Crossrange Limit

The dispersed crossrange limit represented the maximum acceptable crossrange for a planned Shuttle landing opportunity. This value accounted for realistic operational uncertainties, including navigation errors, atmospheric variations, vehicle energy dispersions, and wind effects. Specifically, it assumed a three-sigma combination of navigation, atmosphere, energy, and wind uncertainties while still allowing the Orbiter to converge to nominal conditions by Terminal Area Energy Management (TAEM) interface at approximately Mach 2.5.

All planned landing opportunities were expected to remain within the dispersed crossrange limit. Landing sites with crossrange values between the dispersed and undispersed limits were considered increasingly risky because the vehicle might not possess sufficient performance margin to absorb the real-world dispersions encountered during entry.

Space Shuttle - sample Groundrules and Constraints for Crosswind Limits

Undispersed Crossrange Limit

The undispersed crossrange limit represented the theoretical maximum capability of the Orbiter. This value assumed perfect onboard navigation, design atmosphere, design winds, nominal vehicle energy, and ideal vehicle response throughout entry.

Landing sites beyond the undispersed limit were considered unreachable. Even under ideal conditions, the Orbiter could not reliably achieve the required trajectory. In practical terms, attempting to deorbit toward a site outside the undispersed limit offered little advantage over a bailout scenario because insufficient vehicle performance existed to reach the runway.

For this reason, DOPS did not generate landing opportunities beyond the undispersed crossrange limit. Such opportunities were considered operationally unachievable and were therefore excluded from planning products provided to flight controllers.

Operational Application

During daily landing site selection, DOPS provided Flight Dynamics Officers with candidate landing opportunities and their associated crossrange values. Under normal circumstances, FDOs selected sites that remained comfortably within the dispersed crossrange limit, ensuring adequate margin for navigation errors, atmospheric variations, winds, and vehicle performance uncertainties.

Opportunities that exceeded the dispersed limit but remained within the undispersed limit were generally avoided and considered only when no better alternatives existed. These cases represented situations where the Orbiter possessed sufficient theoretical capability to reach the site, but with significantly reduced operational margin.

The distinction between dispersed and undispersed crossrange limits served as an important safeguard throughout the Shuttle Program. The question was never simply whether the Orbiter could reach a runway. The question was whether the Orbiter could reach that runway safely while maintaining sufficient margin to accommodate the uncertainties of real-world flight.