Fact-checked by Grok 2 weeks ago

Launch window

A launch window is a specific time interval during which a spacecraft or rocket must be launched to meet mission objectives, such as achieving the desired orbit, trajectory, or rendezvous with a target, while adhering to safety and operational constraints.^[1]^[2] These windows arise primarily from orbital mechanics, where the relative positions of Earth, the launch site, and the mission target—such as another planet or spacecraft—must align to minimize energy requirements and ensure efficient travel paths, often using Hohmann transfer orbits that leverage Earth's orbital velocity of approximately 107,000 km/h.^[2] For interplanetary missions, launch periods can span weeks every 26 months (e.g., for Mars), allowing the spacecraft to arrive at the target just as it reaches the optimal position, while daily windows are typically limited to hours due to Earth's rotation and the need to launch eastward near the terminator for optimal velocity addition of about 1,670 km/h at the equator.^[3]^[2] Key factors influencing launch windows include planetary alignments, vehicle performance limits, weather conditions, and contingency requirements like emergency landing sites or rendezvous timing, which can narrow the window to as little as minutes for precise operations such as docking with the International Space Station.^[1]^[2] Delays beyond the window may require rescheduling for the next opportunity, potentially months or years later, as seen in the Mars Express mission, which launched on June 2, 2003, within a four-week window opening May 23, 2003, to align with Mars' orbit using a Soyuz-Fregat vehicle.^[1] For missions like NASA's MAVEN to Mars in 2013, the daily window was two hours, driven by Earth-Mars geometry to enable an approximately 10-month journey.^[4]^[5] Launch windows are categorized by duration and scope: instantaneous windows for exact alignments (e.g., certain rendezvous), daily windows accommodating countdown holds, and broader launch periods for flexible interplanetary transfers, all analyzed using tools like multiple-impulse trajectory modeling to balance fuel efficiency and mission risks.^[6]^[7] In crewed missions, such as the Space Shuttle era, windows overlapped "plane windows" (for orbital inclination) and "phase windows" (for target phasing), ensuring safe returns and precise insertions.^[2] Modern programs like Artemis continue this tradition, with SLS launches featuring variable periods of consecutive daily opportunities (up to about two weeks) separated by gaps to optimize lunar trajectories while mitigating delays from technical or environmental issues.^[8]^[9]

Core Concepts

Launch Period

The launch period represents the extended timeframe over multiple days, weeks, months, or years during which a space mission can initiate launches to achieve its objectives, encompassing numerous potential opportunities dictated by celestial mechanics and orbital constraints. This broader interval contrasts with shorter daily slots by focusing on recurring alignments that make missions feasible, such as synodic periods between planets. For interplanetary transfers, these periods arise from the relative orbital motions of Earth and target bodies, allowing planners to select optimal departure times for energy-efficient trajectories. A prominent example is the Earth-Mars Hohmann transfer, where the launch period recurs approximately every 26 months, aligned with the 780-day synodic period of the two planets. During each such interval, typically lasting several weeks, missions like NASA's Perseverance rover can be scheduled to minimize propellant use and travel time. Similarly, for geostationary orbits, launch periods span the full 365 days of the year, providing near-continuous opportunities to position satellites at equatorial longitudes with minimal adjustments, as the Earth's rotation enables daily access to the required inclination. For sun-synchronous orbits, used in Earth observation missions, launch periods offer flexibility with daily opportunities during suitable alignments, ensuring the satellite's orbital plane precesses at the same rate as Earth's orbit around the Sun for consistent lighting conditions. In contrast, irregular launch periods can span decades or centuries due to rare planetary configurations; the Voyager 2 mission exploited a 1977 alignment within a 175-year window for the outer solar system Grand Tour, enabling gravity assists across Jupiter, Saturn, Uranus, and Neptune with a single launch. These extended periods highlight how launch timing must synchronize with long-term astronomical events to enable ambitious trajectories. In mission planning, the launch period governs long-term scheduling by dictating when resources like launch vehicles, ground support, and international collaborations must be committed, often years in advance to align with budgetary cycles and technical readiness. This foresight allows for contingency planning, such as rescheduling within the period if weather or technical issues arise. Within these overarching periods, narrower daily launch windows define the precise intraday opportunities for liftoff.

Launch Window

A launch window refers to the specific time interval on a given day within the broader launch period during which a launch vehicle can be ignited to place a spacecraft on the required trajectory toward its destination.^[6] This interval typically spans from seconds to several hours, depending on the mission's orbital parameters and constraints.^[1] It is generally defined in Coordinated Universal Time (UTC) for precision and then converted to the local time zone of the launch site to coordinate ground operations.^[1] Launch windows exhibit distinct characteristics shaped by the geometry of the launch site and planetary motion. They may be continuous, permitting launches at any moment within the open interval, or discrete, comprising isolated instants separated by unusable gaps due to varying launch azimuths.^[6] The longitude of the launch site plays a key role, as Earth's rotation aligns the facility with the desired orbital plane only during specific alignments, limiting opportunities to brief periods each day.^[3] For missions tolerant of minor trajectory adjustments, flexibility can be introduced through the use of intermediate parking orbits, which temporarily hold the spacecraft in a low Earth orbit before the final burn to the target trajectory, thereby extending the viable launch window from minutes to hours.^[6] This approach acts as a temporal buffer, accommodating delays without fully missing the daily opportunity. In rendezvous missions, such as those targeting the International Space Station (ISS), adherence to the launch window is critical for synchronizing arrival with the station's orbital position. Precise timing ensures the incoming vehicle matches the ISS's plane, velocity, and location for safe docking, with windows often constrained to 2.5 to 10 minutes to conserve propellant for maneuvering.^[10] Deviations beyond this interval could necessitate excessive fuel use or abort the rendezvous entirely.^[1]

Instantaneous Launch Window

The instantaneous launch window refers to a precise, zero-duration moment in time during which a launch vehicle must ignite to achieve the exact orbital parameters required for a mission, such as the right ascension of the ascending node (RAAN) necessary for a specific orbital inclination without subsequent corrective maneuvers.^[11] This alignment ensures that the launch site's latitude and the Earth's rotation position the vehicle directly into the desired orbital plane, minimizing fuel expenditure for plane adjustments.^[12] As the tightest subset of a daily launch window, it demands exact timing to satisfy geometric constraints imposed by celestial mechanics.^[13] Such windows are particularly critical for missions requiring precise orbital plane matching, including rendezvous operations with targets like the International Space Station (ISS), where the launch must occur exactly when the ISS's orbital plane passes overhead the launch site to enable efficient docking without excessive propulsion.^[14] Missing an instantaneous launch window typically necessitates significant onboard fuel reserves for trajectory corrections, such as plane changes or powered rendezvous adjustments, which can reduce payload capacity or extend mission timelines; in severe cases, it may result in a full-day scrub and rescheduling.^[15] For interplanetary or Lagrange point missions, deviations often lead to inefficient paths requiring more propellant, potentially compromising overall mission viability.^[16] A notable example is the 2015 launch of the Deep Space Climate Observatory (DSCOVR) satellite toward the Sun-Earth L1 Lagrange point from Cape Canaveral, which featured instantaneous windows lasting just one second each day, dictated by the need for a precise Earth-relative trajectory to reach the halo orbit without mid-course corrections.^[16] Similarly, the Mars Global Surveyor mission in 1996 required launches within approximately one-second windows to align with the optimal interplanetary transfer orbit.^[13]

Influencing Factors

Orbital Mechanics Basics

A fundamental aspect of orbital mechanics relevant to launch timing is the rotational motion of Earth, which imparts an eastward velocity to launch sites. This rotation provides a tangential boost to rockets launched in the eastward direction, effectively reducing the delta-v required to achieve orbital velocity. At the equator, this boost equates to approximately 465 meters per second due to Earth's surface speed of about 1675 kilometers per hour. Launch sites are often selected at low latitudes, such as Cape Canaveral at 28.5° N, to maximize this advantage, as the rotational velocity decreases with increasing latitude according to the cosine of the latitude.^[17]^[18] The achievable orbital inclination is constrained by the latitude of the launch site and the chosen launch azimuth, which is the horizontal angle measured clockwise from north to the initial velocity vector. For a due-east launch (azimuth of 90°), the minimum inclination equals the site's latitude, as the initial velocity vector lies in the local horizontal plane tangent to Earth's surface. To reach lower inclinations, launches must occur at oblique azimuths, while higher inclinations up to 180° (retrograde) are possible but require more energetic maneuvers or specific site orientations. Polar orbits (inclination near 90°), for instance, demand launches toward the north or south, forgoing the rotational boost. These geometric constraints dictate daily launch opportunities, with windows opening when Earth's rotation aligns the site with the desired orbital plane.^[19]^[20] Key orbital elements further influence launch timing, particularly inclination (i), right ascension of the ascending node (RAAN, Ω), and argument of perigee (ω). Inclination defines the tilt of the orbital plane relative to Earth's equator, ranging from 0° for equatorial prograde orbits to 180° for equatorial retrograde. RAAN specifies the longitude in the equatorial plane where the orbit crosses from south to north, measured from the vernal equinox, and is directly tied to launch epoch because Earth's rotation shifts the site's position relative to the inertial frame over time. The argument of perigee measures the angle within the orbital plane from the ascending node to the perigee point, orienting the orbit's closest approach to Earth. While ω can be adjusted post-launch via maneuvers, its initial value is influenced by the timing and azimuth of launch, ensuring alignment with mission requirements such as apogee positioning.^[20]^[21] For interplanetary missions, the Hohmann transfer represents the minimum-energy trajectory between two circular, coplanar orbits, forming an elliptical path tangent to both at departure and arrival. This transfer requires two impulsive burns: one to enter the transfer ellipse from the departure body's orbit and another to circularize at the target. The duration of a Hohmann transfer is half the orbital period of the ellipse, governed by Kepler's third law, and opportunities arise periodically based on the synodic period—the time for two bodies to realign in their relative orbits around the Sun. For Earth-Mars transfers, this synodic period is approximately 780 days, or 26 months, dictating launch windows every two years.^[22] Planetary positions fundamentally dictate launch windows by requiring geometric alignment for efficient transfers, such as the Hohmann path where the target planet lies ahead in its orbit upon spacecraft arrival. Relative heliocentric longitudes must align so the transfer arc matches the angular separation covered during flight, minimizing propellant use. These configurations recur with the synodic period, constraining missions to brief windows—often hours long—when Earth and the target are optimally phased.^[3]^[22]

Environmental and Operational Constraints

Environmental and operational constraints significantly narrow launch windows by introducing Earth-based and engineering limitations that must be satisfied alongside orbital requirements. These factors ensure vehicle integrity, crew safety, and mission success but often lead to delays or rescheduling when conditions are unfavorable. Weather represents a dominant environmental constraint, with launch commit criteria prohibiting ascent through adverse atmospheric conditions such as thick cloud cover, excessive wind shear, high surface winds, or lightning activity. For example, NASA guidelines stipulate no launch if lightning is observed within 10 nautical miles of the pad or initial flight path, as it poses risks to the vehicle from electrical discharge. Modern vehicles like the Falcon 9 adhere to similar rules, avoiding liftoff if sustained winds exceed 30 miles per hour at the 162-foot pad level or if upper-level wind shear could induce control issues. The Atlas V rocket follows comparable prohibitions against shear that might jeopardize stability. These criteria are evaluated via probability of violation forecasts, frequently resulting in weather-related countdown holds or scrubs that reduce overall window usability.^[23]^[24]^[25] Beta angle constraints stem from the geometric relationship between the Sun, the orbital plane, and the spacecraft, influencing thermal control and solar array efficiency. The beta angle measures the Sun's position relative to the orbit; values exceeding 60 degrees can cause uneven solar exposure, leading to overheating on the spacecraft's sunlit side and requiring fuel-intensive attitude adjustments like barrel rolls. In missions to the International Space Station, the Space Shuttle program imposed a beta angle limit of less than 60 degrees to maintain thermal balance during docking, though subsequent engineering assessments extended this to ±65 degrees for specific configurations. Such restrictions confine launches to time periods when the beta angle aligns with vehicle tolerances, further segmenting available opportunities.^[26]^[27] Operational factors encompass range safety protocols, airspace coordination, and payload-specific requirements that prioritize risk mitigation and system compatibility. Range safety analyses, as outlined in NASA Standard 8719.25, define hazard areas, impact limits, and flight termination criteria to protect public health and property, often necessitating pre-launch clearances for downrange regions. Airspace management under Federal Aviation Administration oversight requires temporary restrictions in the National Airspace System to prevent conflicts with commercial or military traffic. Payload sensitivities, particularly for those using cryogenic propellants, impose timing limits to control boil-off during extended countdowns; cooler dawn or dusk periods help preserve propellant integrity and enhance ground tracking visibility. These elements collectively overlay orbital windows, potentially closing portions deemed too hazardous or incompatible.^[28]^[29]^[30] Contemporary challenges include ionospheric disturbances and space debris avoidance, which introduce variability tied to space weather and orbital population density. Ionospheric scintillation, intensified by geomagnetic storms or solar activity, disrupts GPS signals essential for real-time navigation and telemetry during ascent, complicating separation and orbit insertion if severe irregularities are forecasted. For instance, in November 2025, a severe geomagnetic storm delayed the launch of Blue Origin's New Glenn rocket carrying NASA Mars probes.^[31] Space debris conjunction screening assesses collision risks with tracked objects; while overall per-launch probability remains low (around 4 × 10⁻⁸), applying a 10⁻⁷ risk threshold can reduce window availability by 65–70% in analyzed scenarios, though NASA recommends against routine checks in favor of higher thresholds like 10⁻⁴ to balance safety and scheduling. These modern constraints highlight the evolving demands of a congested orbital environment.^[32]^[33]

Calculation and Planning

Porkchop Plots

Porkchop plots are contour maps used in interplanetary mission design to visualize the characteristic energy or delta-v requirements for spacecraft transfers as a function of departure and arrival dates. These plots derive their name from the bone-like shape of the low-energy contours, resembling a porkchop bone, and are constructed by solving Lambert's problem for a grid of launch and arrival times, assuming ballistic trajectories with impulsive maneuvers at departure and arrival. The contours represent iso-lines of total delta-v or C3 (characteristic energy, in km²/s²), with lower values indicating more fuel-efficient opportunities; for instance, they are generated using discretized time steps of 5 to 16 days via tools like NASA's Trajectory Browser, which pre-computes solutions for planetary targets.^[34]^[35] In practice, porkchop plots aid mission planners in identifying optimal launch windows by highlighting periods where energy costs are minimized, such as for Earth-to-Mars transfers where contours below 4 km/s delta-v reveal viable opportunities in the 2020s, including the 2020 and 2028 synodic periods. Generated by software like the Jet Propulsion Laboratory's Small-Body Mission-Design Tool or NASA's Program to Optimize Simulated Trajectories II (POST2), these plots allow rapid assessment of trade-offs, such as delaying launch for reduced fuel at the expense of longer travel time. For the Mars Science Laboratory mission, such plots mapped 14,488 launch-arrival combinations to constrain entry velocities below 7 km/s, informing feasible date ranges aligned with Mars solar longitudes of 70–210°.^[36]^[35]^[34] The primary advantages of porkchop plots lie in their visual simplicity, enabling quick identification of low-energy windows and parametric sensitivities without exhaustive simulations; they facilitate early-stage planning by revealing inaccessible regions due to high energy demands or planetary geometry. However, limitations include their reliance on simplified impulsive models, which overlook continuous thrusting or detailed atmospheric entries, and incomplete representation of gravity assists, necessitating follow-up with more comprehensive tools for refined trajectories.^[36]^[34]

Mathematical Formulations

The computation of launch windows relies on fundamental equations from orbital mechanics that account for Earth's rotation, planetary alignments, nodal timing, and energy requirements for transfers. These formulations enable precise determination of viable launch epochs by balancing geometric, temporal, and propulsive constraints. To incorporate Earth's rotation into launch window calculations, the launch azimuth θ, which is the initial heading angle from north, must align with the desired orbital plane defined relative to the launch site's position. For a launch site at latitude φ and a longitude difference λ between the site and the reference meridian corresponding to the desired ascending node, the azimuth is given by

\theta = \arctan\left( \frac{\sin \lambda}{\cos \lambda \cdot \cos i - \sin \lambda \cdot \tan \phi} \right),

where i is the target orbital inclination. This equation derives from spherical trigonometry applied to the great circle path in the orbital plane, ensuring the velocity vector lies within the plane at injection. The allowable range of θ is typically constrained by site safety and overflight limits, typically 45° to 135° east for many facilities, which bounds the daily launch window duration.^[37] For interplanetary missions, launch windows are governed by the synodic period S between Earth and the target planet, which dictates the recurrence of favorable alignments. The synodic period is calculated as

S = \frac{1}{\left| \frac{1}{P_e} - \frac{1}{P_t} \right|},

where P_e is Earth's orbital period (approximately 365.25 days) and P_t is the target's sidereal period. For Earth-Mars transfers, P_t ≈ 687 days, yielding S ≈ 780 days; opportunities thus recur roughly every 26 months. Within each window, the optimal launch epoch corresponds to the phase angle for a Hohmann transfer, where the target planet leads Earth by approximately 44° at departure to minimize energy, as Mars advances about 136° during the 259-day transfer while the spacecraft traverses 180° heliocentrically. This phase ensures rendezvous at arrival without excessive mid-course corrections.^[3]^[38] The right ascension of the ascending node (RAAN, Ω) further constrains Earth-orbit launch windows through coordination with Earth's rotation. The launch time t must satisfy Ω = θ_{LST}(t) + \Delta, where θ_{LST}(t) is the local sidereal time at the site (computed as Greenwich mean sidereal time plus site east longitude, modulo 24 hours), and Δ is the azimuth adjustment typically Δ = β - 90°, with β the launch azimuth in degrees. Equivalently, the launch epoch modulo one sidereal day (≈23h 56m) is ω = t \mod 86164 seconds, such that θ_{LST}(ω) = Ω - \Delta. This ties the daily window to the desired nodal precession or coverage requirements, with window width scaling inversely with inclination sensitivity to timing.^[39] Launch window bounds for transfers are ultimately set by delta-v (Δv) tolerances, using the Hohmann transfer as the baseline minimum-energy profile. The departure Δv_1 at heliocentric distance r_1 (e.g., 1 AU for Earth) to enter the elliptic transfer orbit with semi-major axis a = (r_1 + r_2)/2 is

\Delta v_1 = \sqrt{\frac{\mu}{r_1}} \left( \sqrt{\frac{2 r_2}{r_1 + r_2}} - 1 \right),

while the arrival Δv_2 at r_2 (e.g., 1.52 AU for Mars) to circularize is

\Delta v_2 = \sqrt{\frac{\mu}{r_2}} \left( 1 - \sqrt{\frac{2 r_1}{r_1 + r_2}} \right),

with μ the solar gravitational parameter (1.327 × 10^{20} m³/s²). The heliocentric total Δv ≈ 5.6 km/s for an Earth-Mars Hohmann transfer, but windows extend to epochs where excess Δv remains below vehicle capacity, often ±10-20 days around the optimum, trading energy for shorter/longer transfers. These integrate into window limits by varying departure hyperbolic excess velocity while maintaining arrival geometry.^[40]^[41]

Applications and Examples

Earth Orbit Missions

For missions targeting low Earth orbit (LEO), such as rendezvous with the International Space Station (ISS), launch windows are primarily driven by the need to align the incoming vehicle's ground track with the target's orbital plane and phasing. These windows typically last 5 to 10 minutes and recur approximately every 90 minutes, corresponding to the ISS's orbital period, allowing for potential intercepts on early revolutions post-launch. However, daily opportunities are constrained by the beta angle—the angle between the orbital plane and the sun vector—which must remain within limits (often -20° to +20°) to ensure adequate lighting for visual docking and sensor operations, avoiding periods of deep eclipse that could complicate proximity maneuvers. For instance, Space Shuttle missions to the ISS, such as STS-130 in 2010, targeted beta angles around -23° for optimal illumination during terminal phase initiation.^[42] Sun-synchronous orbits (SSO), commonly used for Earth-observing satellites in LEO at altitudes of 600 to 800 km, require precise launch timing to achieve the desired local solar time at the ascending node, enabling the orbit to precess at 1° per day to match Earth's revolution around the sun. This results in narrow daily windows, typically 30 to 60 minutes long, often centered in the late afternoon or evening to maintain consistent lighting conditions for imaging. Site-specific geometry further restricts launches; polar SSO missions favor sites like Vandenberg Space Force Base due to its high latitude, which facilitates near-polar inclinations without excessive plane-change maneuvers. The NASA SPHEREx mission, for example, features a nearly instantaneous daily window around 7:10 p.m. PST to enter its SSO, ensuring perpetual dawn-dusk lighting for infrared observations.^[43]^[44] Geostationary Earth orbit (GEO) insertions, at approximately 35,800 km altitude, benefit from the orbit's equatorial alignment, providing broader launch windows compared to inclined LEO paths, as the launch site's latitude determines the initial inclination that can be corrected en route. From near-equatorial sites like ESA's Guiana Space Centre, windows can extend several hours daily, leveraging Earth's rotation to target various longitudes. However, for precise slot assignments without excessive station-keeping fuel consumption—typically limited to 50 m/s per year—insertions aim for instantaneous windows that deliver the satellite directly to the desired longitude, minimizing apogee kicks and drift adjustments.^[43]^[2] Modern LEO constellations, such as SpaceX's Starlink, exploit reusable launch vehicles like the Falcon 9 to enable frequent deployments, with windows accommodating multiple missions per day across pads to rapidly build out the network in multiple orbital shells. This operational flexibility, supported by instantaneous LEO insertion capabilities, allows for windows as short as 40 to 57 minutes while prioritizing rapid booster turnaround, as seen in rideshare missions like Transporter-15.^[45]^[46]

Interplanetary Missions

Interplanetary launch windows are characterized by infrequent planetary alignments that enable efficient transfers from Earth to other bodies in the solar system, often spanning years or decades due to orbital periods. These windows arise from the relative positions of planets around the Sun, allowing spacecraft to exploit gravitational dynamics for low-energy trajectories. Unlike near-Earth missions, interplanetary opportunities demand precise timing to minimize propellant use and maximize payload capacity, with planning tools like porkchop plots used to identify optimal departure and arrival dates.^[35] For missions to Mars, Hohmann transfer orbits form the basis of most launch windows, occurring approximately every 26 months when Earth and Mars align favorably for a minimum-energy elliptical path. These windows typically last 2 to 4 weeks, during which daily launch opportunities of 30 minutes to 2 hours allow for low-delta-v departures. The Perseverance rover mission exemplified this in 2020, launching on July 30 within a three-week window from July 22 to August 11 to reach Jezero Crater after a seven-month journey.^[47]^[48]^[49] Gravity assists extend these windows by leveraging planetary flybys to adjust trajectories, opening rare multi-planet opportunities. The Voyager program's 1977 launches capitalized on a once-every-176-years alignment of Jupiter, Saturn, Uranus, and Neptune, enabling the Grand Tour with Voyager 2 departing on August 20 and Voyager 1 on September 5 to sequentially encounter the outer giants.^[50]^[51] Ballistic capture techniques offer alternatives to traditional propulsive insertion, providing more flexible launch windows by allowing spacecraft to be passively captured into orbit around the target body through gravitational perturbations, thereby reducing fuel requirements for Mars cargo missions. Proposed in 2014, these transfers extend viable launch periods beyond standard Hohmann constraints while adding months to flight time, as detailed in analyses showing substantial savings in capture delta-v.^[52]^[53] Upcoming Mars windows in 2026 and 2028 are relevant for sample return efforts. While NASA and ESA are revising their Mars Sample Return plans for launches in the 2030s due to cost and technical challenges, China's Tianwen-3 mission targets a 2028 launch to collect and return samples by 2031.^[54]^[55]

Historical and Modern Cases

The Apollo 11 mission in July 1969 exemplified early launch window constraints for lunar landings, with a daily window of approximately 4 hours and 24 minutes on July 16, driven by the need to align the trajectory with the Moon's phase for optimal landing illumination during the local dawn period.^[56] This timing ensured the Eagle lunar module could descend in sunlight while avoiding shadows that might obscure surface features, limiting viable launch opportunities to specific days within the month.^[57] In the Space Shuttle era, operational constraints like solar beta angles—measuring the angle between the orbiter's orbital plane and the Sun—could significantly influence mission scheduling to the International Space Station. The STS-133 mission aboard Discovery, originally targeted for September 2010, faced repeated postponements primarily due to cracks in the external tank, with beta angle constraints (up to approximately 60 degrees) also affecting available launch windows; it ultimately launched on February 24, 2011, after slipping past a restrictive period from January to February.^[27] Modern launch windows for developmental vehicles like SpaceX's Starship have typically ranged from 30 to 60 minutes for test flights in 2024 and 2025, accommodating suborbital trajectories and booster catches while factoring in weather and range safety.^[58] For crewed missions, NASA's Artemis II, set for no earlier than February 5, 2026, benefits from the Space Launch System's (SLS) high thrust and payload capacity, which enables a broader monthly window extending through April, allowing greater flexibility in trajectory options for the lunar flyby compared to earlier heavy-lift systems.^[59] Advancements in reusable rocket technology, particularly SpaceX's Falcon 9 and Starship, have increased global launch cadence to over 150 missions in 2025, providing backlog tolerance by enabling rapid turnaround and multiple daily opportunities from shared pads, a stark evolution from the single-launch-per-month norms of the Shuttle program.^[60] Launch window precision has led to notable scrubs, such as the 2015 Deep Space Climate Observatory (DSCOVR) mission, which required an instantaneous one-second window to position the satellite at the Sun-Earth L1 Lagrange point, resulting in two aborts before successful liftoff on February 11 due to minor anomalies outside that narrow timeframe.^[61] In contrast, interplanetary missions like Mars 2020 Perseverance offered more forgiving multi-week periods with daily two-hour slots in July-August 2020, highlighting how destination-specific geometry influences scrub risks.^[49]

References

[1]
ESA - What is a 'launch window'? - European Space Agency
The launch window is a term used to describe a time period in which a particular mission must be launched. If the spacecraft intends to rendezvous with ...
[2]
Chapter 14: Launch - NASA Science
Nov 4, 2024 · A launch window is the span of time during which a launch may take place while satisfying the constraints imposed by safety and mission ...
[3]
Let's Go to Mars! Calculating Launch Windows – Math Lesson
Sep 25, 2025 · When launched within the proper launch window, the spacecraft will arrive in the planet's orbit just as the planet arrives at that same place.
[4]
2-Hour Launch Window for MAVEN - NASA Science
Nov 4, 2013 · The launch window is dictated by a number of factors, primarily the alignment of Earth and MAVEN's destination, Mars. The spacecraft will ...
[5]
Launch Windows Essay - NASA
The launch must occur at a certain time for each launch azimuth in order to intercept the moons antipode. This correct launch time was defined by the antipodes ...
[6]
[PDF] ANALYSIS OF LAUNCH WINDOWS FOR REPRESENTATIVE ...
This report analyzes launch windows for Mars missions, investigating one, two, and three-impulse transfers, and the influence of heliocentric trajectories on ...
[7]
[PDF] AAS 20-591 SPACE LAUNCH SYSTEM LAUNCH WINDOWS AND ...
The launch window is the span of time within a given day when the vehicle can launch and achieve its objective: reaching a target orbit within an acceptable ...<|control11|><|separator|>
[8]
How Things Work: Shuttle Launch Windows - Smithsonian Magazine
Basically, Jones explains, a launch window is the overlap of two time periods, known as the plane window and the phase window. ... “If it passes directly over ...
[9]
[PDF] AAS 12-255 LAUNCH WINDOW ANALYSIS FOR THE ...
The launch window problem can be stated as that of selecting values for the RAAN, Ω0 , and AOP, ω0 , for the MMS orbit such that the various MMS orbital ...
[10]
How do RAAN steering increase the launch window?
Oct 22, 2021 · RAAN steering helps calculate the best way to adjust trajectory in real-time, allowing for a 75-minute launch window, not just a 1-second ...Why would a mission to Sun-Earth L1 have an instantaneous launch ...What decides if a launch has to be done instantaneously or during a ...More results from space.stackexchange.com
[11]
MGS Mission Plan Section 3. Launch Phase
Instead, MGS must launch within a very small time period (about 1 second). These extremely short windows are referred to as "instantaneous launch windows.3.1. 1. First Stage · 3.3. Launch Strategy · 3.4. Boost Profile And...<|control11|><|separator|>
[12]
Explained: Why Atlas 5 will have longer windows for station flights
Nov 18, 2015 · “Instantaneous launch windows are the standard way to accomplish a rendezvous mission with a low-earth object like the ISS, and this ...Missing: definition | Show results with:definition
[13]
Do geosynchronous satellite launches require a tight launch window?
Jul 18, 2016 · Geosync launches tend to have a fairly small fixed time window due to the need to get the satellite into sunlight before too much time passes.What decides if a launch has to be done instantaneously or during a ...spacecraft - What is the rarest launch window?More results from space.stackexchange.com
[14]
Why would a mission to Sun-Earth L1 have an instantaneous launch ...
Feb 9, 2015 · There's no amount of thrust regulation that can solve that problem, it will simply take more fuel. And that's why the window is so short.
[15]
Technical Problems Postpone Falcon 9 Launch of DSCOVR
Feb 8, 2015 · 20. All the launch windows are considered “instantaneous,” lasting one second, so any issues that halt the countdown prevent the launch from ...
[16]
Launch a rocket from a spinning planet | NASA Space Place – NASA Science for Kids
### Summary: Earth's Rotation and Eastward Velocity Boost for Launches
[17]
24 Rotating Frames of Reference in Space and on Earth - PWG Home
Oct 24, 2004 · Launching in the direction of the Earth's rotation (namely, eastward) does provide an initial velocity equal to the surface velocity of rotation ...
[18]
Launch Windows and Time – Introduction to Orbital Mechanics
A launch window is a period of time that we have where we can directly send the object into the specific obit we want. It would be possible to simply shoot it ...
[19]
Basics of Space Flight: Orbital Mechanics
The time of the launch depends on the launch site's latitude and longitude and the satellite orbit's inclination and longitude of ascending node. Orbit ...
[20]
Chapter 3 – The Classical Orbital Elements (COEs)
The argument of perigee, ω indicates theorientation of the orbit, or where its perigee is located. It is the angle measured between the ascending node vector, ...
[21]
[PDF] Interplanetary Mission Design Handbook:
However, Earth and Mars nearly return to their original relative heliocentric positions every 7 to 8 synodic periods, or every 15 to 17 years (Ref. 3).
[22]
[PDF] Space Shuttle Weather Launch Commit Criteria and KSC End of ...
– Do not launch when lightning is observed and the cloud that produced the lightning is within 10 nautical miles of flight path. Launch may not occur until ...
[23]
[PDF] Falcon 9 Crew Dragon Launch Weather Criteria | NASA
Do not launch if the sustained wind at the 162-foot level of the launch pad exceeds 30 mph. Do not launch through upper-level conditions containing wind shear.
[24]
https://www.nasa.gov/wp-content/uploads/2021/07/falcon9_crewdragon_launch_weather_criteria_fact_sheet.pdf
[25]
Why do NASA launch times depend on lighting conditions?
Jul 13, 2009 · When the beta angle is greater than 60 degrees, however, the shuttle must do slow barrel rolls to keep the sun from overheating one side. This “ ...
[26]
NASA Reviews Beta Angle Constraints for STS-133 Launch Date ...
Nov 22, 2010 · The analysis that followed showed that the Shuttle orbiter and ISS could support a docked mission up to but not exceeding a +/-65 degree Beta Angle.
[27]
[PDF] Range Flight Safety Requirements - NASA Standards
Feb 5, 2018 · 9. A range safety analysis shall establish launch/flight commit criteria and operational constraints, such as hazard areas and impact limit ...
[28]
14 CFR Part 417 -- Launch Safety - eCFR
14 CFR Part 417 sets forth responsibilities of launch operators, requirements for maintaining a launch license, and safety requirements for licensed launches.
[29]
[PDF] CONCEPT OF OPERATIONS - for Commercial Space Transportation
May 11, 2001 · This document provides a conceptual overview of commercial space transportation (CST) operations in the National Airspace System (NAS) in 2005 ...
[30]
Launch Operation Services - ESA Space Weather
Adverse space environment conditions can further complicate critical operations such as separation and orbit insertion, and disrupt real-time communications ...
[31]
[PDF] Recommended Screening Practices for Launch Collision Aviodance
The objective of this document is to assess the value of launch collision avoidance. (COLA) practices and provide recommendations regarding its implementation ...Missing: constraints | Show results with:constraints
[32]
Trajectory Browser User Guide
Apr 12, 2023 · These solutions can be visualized on a plot of launch date vs. duration color-coded by ΔV, in what are colloquially known as 'porkchop plots' ( ...Missing: interplanetary | Show results with:interplanetary
[33]
Small-Body Mission-Design Tool - JPL Solar System Dynamics
Add new points: the tooltip and the table under the pork-chop plot will display information about any point, and clicking on feasible missions will add them to ...Missing: interplanetary | Show results with:interplanetary
[34]
https://trajbrowser.arc.nasa.gov/user_guide.php
[35]
[PDF] Orbit Selection and EKV Guidance for Space-Based ICBM Intercept
Sep 11, 2005 · ... azimuth launch angle to be a function of geodetic locations and the cosa term as given by. (. ) cos cos sin tan sin cos sin o o o. C a. µ. µ λ λ.
[36]
[PDF] A Simple Leapfrog Integration Scheme to Find Optimal ...
Mar 8, 2018 · 𝑎 = 𝑅𝐸𝑎𝑟𝑡ℎ + 𝑅𝑀𝑎𝑟𝑠 2 . To find the desired phase angle between Earth and Mars at launch, we first calculate the angular distance that Mars ...
[37]
[PDF] Lecture 9: Bi-elliptics and Out-of-Plane Maneuvers - Matthew M. Peet
Feb 27, 2025 · Launch Window determines RAAN (Ω) ... Launch Window (Time). Referring to the triangle, our desired launch time (in Local Sidereal Time) is.
[38]
[PDF] Hohmann Transfer Orbit - Physics Courses
Velocity equation where ... is the semi-major axis of the body's orbit. Therefore the delta-v required for the Hohmann transfer can be computed as follows,.
[39]
[PDF] History of Space Shuttle Rendezvous
This document covers the history of Space Shuttle rendezvous, including early studies, early shuttle rendezvous, and first proximity operations and rendezvous ...
[40]
ESA - Types of orbits - European Space Agency
A satellite in a Sun-synchronous orbit usually flies at an altitude of between 600 to 800 km. At 800 km, it will travel at a speed of approximately 7.5 km per ...Low Earth orbit (LEO) · Sun-synchronous orbit (SSO) · Medium Earth orbit (MEO)
[41]
Mission | NASA Jet Propulsion Laboratory (JPL)
27, 2025, and is targeted to lift off no later than April 2025. Each day within the launch period provides a single, nearly instantaneous launch window around 7 ...
[42]
[PDF] Falcon Payload User's Guide - SpaceX
Falcon 9 and Falcon Heavy can launch multiple satellites on a single mission. As a liquid-propellant launch vehicle with restart capability, Falcon launch ...
[43]
https://www.esa.int/Enabling_Support/Space_Transportation/Types_of_orbits
[44]
Mars Mission Timeline - NASA Science
Nov 15, 2024 · As Earth and Mars orbit the Sun at different speeds and distances, about once every 26 months they are aligned in a way that allows the most ...
[45]
What's the reasonable "window" in days for a Mars-Earth Hohmann ...
Feb 2, 2018 · There is usually a few weeks, each day of which during that period of time has a window of between 30 minutes- 2 hours where the launch can be performed.Determining the launch period for Hohmann transferWhat is the minimum transfer time for Earth/Mars cycler and still ...More results from space.stackexchange.com
[46]
Launch of NASA's Perseverance Mars rover delayed to July 22
Jun 24, 2020 · There is a two-hour launch window July 22 opening at 9:35 a.m. EDT (1335 GMT). NASA says the mission has until Aug. 11 to launch this year ...
[47]
Voyager: The Grand Tour of Big Science - NASA
Despite the limited aim of the Mariner Jupiter-Saturn, the mission had the Grand Tour launch window, that rare planetary alignment, and the engineers at JPL ...
[48]
There is a reason why Voyager missions were launched in 1977, not ...
Sep 4, 2025 · Approximately every 176 years, a Grand Tour alignment occurs in the outer solar system. This is when Jupiter, Saturn, Uranus, and Neptune come ...
[49]
[1410.8856] Earth--Mars Transfers with Ballistic Capture - arXiv
Oct 27, 2014 · We construct a new type of transfer from the Earth to Mars, which ends in ballistic capture. This results in a substantial savings in capture \Delta v.Missing: windows concepts
[50]
Researchers propose ballistic capture as cheaper path to Mars
Dec 24, 2014 · Ballistic capture would eliminate the need for retrorockets, making a mission to Mars much cheaper—but it would also add months to the trip, ...Missing: flexible concepts
[51]
NASA, ESA Officials Outline Latest Mars Sample Return Plans
Aug 13, 2019 · The surface retrieval lander will launch in July 2026. Those familiar with Mars exploration travel opportunities may realize July is well before ...<|separator|>
[52]
https://arxiv.org/abs/1410.8856
[53]
[PDF] Apollo 11 Flight Plan July 1 1969 - NASA
Translunar phase (through LOI-2). 204. Lunar oreit phase. _II. Transearth Phase (includes TEl). 75. Nominalremaining. 6,30ib. 5-2. Page 276. TABLE 5-2. TIME.
[54]
Apollo 11 Flight Journal - Day 1, part 1: Launch - NASA
Oct 3, 2022 · All is Go with Apollo 11 at this time. At 3 hours, 29 minutes, 27 seconds and counting; this is Kennedy Launch Control. This is Apollo ...<|separator|>
[55]
Ship 37 Completes the Redemption Arc and Lands in the Indian ...
Aug 26, 2025 · Starship Flight 10 lifted off from Pad 1 (A) at 6:30 pm Central Daylight Time on Aug 26, following a smooth countdown with no holds at T-40 ...
[56]
Orion Spacecraft Completes Major Stacking Milestone Ahead of ...
Oct 24, 2025 · The first crewed flight of the Artemis program is set to launch no earlier than February 2026, with potential launch windows extending through ...
[57]
https://www.nasa.gov/history/afj/ap11fj/01launch.html
[58]
Next Falcon 9 launch rescheduled for Feb. 8 - Spaceflight Now
Jan 21, 2015 · “DSCOVR is now expected to launch no earlier than February 8, 2015. ... 8 would occur in an instantaneous launch window at 6:10 p.m. EST ...